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A THESIS SUBMITTED IN PARTIAL FULFILLMENT FOR THE REQUIREMENT FOR THE DEGREE OF Master of Technology In Production Engineering By VIVEK SINGH
Department of Mechanical Engineering National Institute of Technology Rourkela 2011
A THESIS SUBMITTED IN PARTIAL FULFILLMENT FOR THE REQUIREMENT FOR THE DEGREE OF Master of Technology In Production Engineering By VIVEK SINGH 207ME209 Under the guidance of Dr. K P MAITY Professor, Department of Mechanical Engineering
Department of Mechanical Engineering National Institute of Technology Rourkela
National Institute of Technology Rourkela
This is to certify that the thesis entitled, "ANALYSIS OF PROCESS PARAMETERS OF PLASMA ARC CUTTING BY USING DESIGN OF EXPERIMENT " submitted by Vivek Singh (207ME209) in partial fulfilment of the requirements for the award of Master of Technology Degree in Mechanical Engineering with specialization in Production Engineering at the National Institute of Technology, Rourkela (deemed University) is an authentic work carried out by him under my guidance. To the best of my knowledge, the matter embodied in the thesis has not submitted to any other University/Institute for the award of any degree or diploma.
Dr. K P MAITY Date: Dept. of Mechanical Engineering National Institute of Technology Rourkela – 769008
GM. Bhopal for extending all possible help in carrying out the experimental and dissertation work directly or indirectly. VIVEK SINGH 207ME209 . Fabrication Division. I am especially indebted to my parents for their love. AGM. Project Division. I consider it my good fortune to have got an opportunity to work with such a wonderful person. I like to express my gratitude to Shri U C Srivastava. P. who not only guided the academic/industrial project work but also stood as a teacher and philosopher in realizing the imagination in pragmatic way. BHEL. study and work. BHEL. Fabrication for his valuable advice and permission for carrying out project work inside the plant premises. sacrifices and support. Bhopal .ACKNOWLEDGEMENT I would like to express my deep sense of respect and gratitude toward my supervisor Dr. K. They have been great source of inspiration to me and I thank them from bottom of my heart. I express my gratitude to my co-guide Shri Sachin Bhartiya. and staff of Department of Fabrication Division. Senior Engineer. Maity. I want to thank him for introducing me for the field of Optimization and giving the opportunity to work under him. BHEL. Bhopal and Shri R N Edikie. His optimism have provided an invaluable influence on my career and outlook for the future. They are my teachers after I came to this world and have set great example for me about how to live.
1.8 Significance of Findings 1.9 Summary 2 4 6 7 8 9 10 11 14 14 2.5 Scope 1.6 Introduction to PAC 1. LITERATURE REVIEW 2.1.3 Secondary Gas Selection for Plasma Cutting 2.1 Principle of Plasma Arc Cutting 2.1 Shielding & Cutting Gases for Plasma Cutting 2.2 Plasma Cutting Capability 2.2 Plasma Gas Selection 2.1.7 Design of Experiment (DOE) 1.4 Objectives 1.1 Problem Statement 1.3 Introduction to Problem 1. ABSTRACT LIST OF TABLES LIST OF FIGURES LIST OF GRAPHS 1.2 Process Description 1.1 Overview 1.3.CONTENTS TITLE PAGE NO.3 System 17 22 23 24 26 27 . INTRODUCTION 1.
5.5.5 Plasma Arc Cutting Response 3. DESIGN OF STUDY 4.5 Analysis of Variance (ANOVA) 4.5 Plasma Torch 126.96.36.199 Standard L 16 Array 4.2 Material 3.5.6 Taguchi Design Overview 2.2 Design of Experiment 4. PROJECT METHODOLOGY 3.7 What is Taguchi Design? 28 29 30 31 34 36 3.1 Torch Design 2.3 Equipments 3.2 Torch Consumables 2.4 Arc Starting Circuit 2.5.4 Signal to Noise (S/N) Ratio 4.3 Selection of Orthogonal Array & Parametric Assignment 4.1 Outline of Thesis Work 4.2 Surface Roughness (Ra) 38 38 40 43 44 45 45 4.1 Test Specimen Preparation 3.5.1 Material Removal Rate (MRR) 3.1 ANOVA Formulas 48 49 50 51 52 54 55 .4Design Factors 3.
1.2 Prediction of Optimum SR (Ra) 5.1.1 Prediction of Optimum MRR 5.1 Bivariate Regression 6.3 Summary 58 61 63 64 66 68 69 71 6.2 The Least Square Method 6.5.5. MATHEMATICAL MODELLING 126.96.36.199 Experimental Result for SR (Ra) 5.2 Experimental Result for MRR 5.3 First order Linear Model for SR (Ra) 73 73 74 75 75 76 76 77 79 .5 Coefficient of Determination (R2) 6.6 Multicollinearity 6.1. EXPERIMENTAL ANALYSIS 5.1 Introduction to Regression Analysis 6.5 Confirmation Test 5.3 Residual 6.1.1 Experiment Layout 5.2 First order Linear Model for MRR 6.4ANOVA Calculations 5.1.4 Sampling Error 6.5.
5 Scope of Future Work 82 83 84 85 86 BIBLIOGRAPHY Journal Reference Book Reference Web Reference 87 89 90 MINITAB 15 SOFTWARE ANALYSIS SHEETS Experimental Layout for MRR and SR Linear Model Analysis of MRR Main Effect Plot for MRR Regression Analysis for MRR Normal Probability Plot of MRR (Residuals) Linear Model Analysis for Surface Roughness (Ra) Main Effect Plot for Ra Regression Analysis for Ra Normal Probability plot for Ra .1 Summary 7.4 Conclusion 7.3 Discussions 7.7.2 Results 7. RESULT CONCLUSION & FUTURE SCOPE 7.
1 Composition Ranges for 316 grades of SS Table 3.3 Experimental Layout & S/N Ratios (In Actual Factor Levels) Table 5. Table 2.3 Experimental Layout in Coded Factor Levels Table 5.3 Technical Features of Plasma Machine Table 4.4 ANOVA Table for MRR Table 5.8 Confirmation Test Result for MRR Table 5.5 ANOVA Table for Surface Roughness (Ra) Table 5.1 Summary Table for Plasma Gas Selection Table 3.1 Fixed Machining Parameters Table 4.2 Calculation Sheet for MRR and Surface Roughness (Ra) Table 5.9 Confirmation Test Result for Surface Roughness (Ra) Table 5.10 Summary Table for Results Table 7.7 Response Table for S/N Ratio of SR (Ra) Table 5.6 Response Table for S/N Ratio of MRR Table 5.2 Parametric Level Assignment Table 4.2 Mechanical Properties of 316 Grade SS Table 3.LIST OF TABLES Page No.1 Result Before & After Optimisation 25 39 39 40 50 50 58 58 59 60 64 65 66 67 70 70 71 83 .1 Values of Variables at Different Level Table 5.
1 Test Specimen Figure 3.3 Plasma Arc Setup Figure 2.8 Swirl Ring Figure 2.1 PAC Arc Cut Away Figure 1.9 Tip Figure 3. Figure 1.4 Plasma Arc Cutter System Figure 2.7 Electrode Figure 2.2 Air Plasma Figure 2.1 Principle of Plasma Cutting Figure 2.2 TIG and Plasma Arc Figure 2.2 DC Power Supply 4 5 18 21 26 27 31 31 32 33 33 38 42 .5 Torch Stand Off Figure 2.LIST OF FIGURES Page No.6 Torch Break Down Figure 2.
Graph 5.2 Main Effect Plot for Mean of MRR Graph 5.2 Normal Probability Plot for Residuals of SR (Ra) 61 62 63 78 80 .1 Normal Probability Plot for Residuals of MRR Graph 6.LIST OF GRAPHS Page No.3 Main Effect Plot for S/N Ratio of SR (Ra) Graph 6.1 Main Effect Plot for S/N Ratio of MRR Graph 5.
In thesis work literature has been studied in context to parametric optimization of Plasma Arc Cutting Machine. 150 A (Current flow rate). Error within 10 % was allowed.635µm.0 bar (Gas pressure). Experimental results are provided to confirm the effectiveness of this approach. 400 mm/min (Cutting Speed) and 2 mm (Arc Gap). The optimum value has been determined with the help of main effect plot and ANOVA table. The work pieces of Stainless Steel (316 L) materials were used for experiment purpose. The optimum parameter level for Surface Roughness are 6.ABSTRACT In last forty years there is tremendous research in machining and development in technology. 150 A (Current). . The appropriate orthogonal array has been selected as per number of factors and there levels to perform minimum experimentation. Confirmation test have done to confirm the value estimated through the software. Its high accuracy.0 Bar (Gas Pressure). After the confirmation the MRR value was 0. With increase in competition in market and to attain high accuracy now a days the nonconventional machining are become lifeline of any industry. One of the most important non conventional machining methods is Plasma Arc Machining. 600 mm/min (cutting speed) and 4. ability of machining any hard materials and to produce intricate shape increases its demand in market. finishing.8331 g/sec and Ra 2. Taguchi method employed. The Regression equation for MRR and Surface Roughness (Ra) has been developed with the help of Minitab 15 Software. The Confirmation for MRR run was done by using the setting of 5. In order to attain target and optimum results.0 mm (arc gap).
plasma. There are four states in which physical matter may be found: solid. INTRODUCTION 1. steam. A person doesn't need to be a physicist or chemist to understand the Plasma Arc Cutting (PAC) and Gouging process. The plasma arc is the result of the electrical arcs heating of any gas to a very high temperature so that its atoms are ionized (an electrically charged gas due to an unequal number of electrons to protons) and enabling it to conduct electricity. looks and behaves like a high temperature gas. the liquid state. but with an important difference. it conducts electricity.1.) or hotter) converts this liquid to its gaseous state. (100 degrees C. gas or plasma. in the form of heat. The addition of more heat to temperatures of 212 degrees F. by either supplying or subtracting energy. With the addition of heat the ice melts and changes to water.1 OVERVIEW The topic for the thesis writing is the Analysis of Process Parameters of Plasma Arc Cutting Using Design of Experiment Techniques. Changes from one physical state to another occur. liquid. The fourth state of matter. In the solid state it is ice at temperatures of 0 degrees Celsius or colder. Water can be used as an example of these four states of matter. . The major difference between a neutral gas and plasma is that the particles in plasma can exert electromagnetic forces on one another. The focus on this project is to obtain an optimum condition (setting) to obtain maximum MRR and minimum the surface roughness (SR).
oxy-acetylene cutting was often the process of choice for quickly cutting through steel plate. for some very good reasons to perhaps most importantly. and can get cleaner cuts. That means that one unit will cut steel. It is ionized by a high voltage across electrodes at the ends of the tube and conducts an electric current which causes the plasma to radiate which in turn causes the phosphor coating on the inner surface of the tube to glow [19] . Over the past few years plasma cutting has pretty much taken over.If you happen to be reading this by the light emitted by a fluorescent lamp you see plasma in action. This makes plasma cutting particularly well-suited for cutting sheet metal. stainless steel. copper. . a task the oxy-acetylene cutting torch is not particularly well-suited for since it leaves a lot of slag on the edges. The plasma jet that does the cutting is hotter and narrower than an oxy-acetylene flame. and brass etc. as well. Within the glowing tube of the lamp is plasma consisting of low pressure mercury or sodium vapour. so the kerfs width is smaller. A plasma cutter will cut through any metal that is electrically conductive. For many years. The extremely tight focus of the plasma arc tends to minimize heat distortion in the cut parts. bronze. aluminium.
1.000 degrees F.000 ft/s). The plasma is sufficiently hot to melt the metal being cut and moves sufficiently fast to blow molten metal away from the cut.) and 6000 m/s (20. an inert gas (in some units.2 PROCESS DESCRIPTION Plasma cutting is a process that is used to cut steel and other metals (or sometimes other materials) using a plasma torch. It is in this chamber that the plasma gas is heated and ionized. The . between the inside circumference of the torch tip or nozzle.1 PAC Arc Cut-Away The plasma arc torch has a space or area surrounding the circumference of the electrode. In this process. (16. at the same time an electrical arc is formed through that gas from the nozzle to the surface being cut. The plasma gas exits from the constricting orifice of the torch nozzle or tip at very high speeds and temperatures. turning some of that gas to plasma.000 degrees C. up to 30.1. This heating causes the plasma gas to greatly expand in volume and pressure. FIG. compressed air) is blown at high speed out of a nozzle. Plasma can also be used for plasma arc welding and other applications [24].
its pressure & volume. The force of the arc pushes the molten metal through the work piece and severs the material. and the tip to work distance. there's very little warping. constricted.intensity and velocity of the plasma is determined by several variables including the type of gas. the flow pattern. PAC also offers quality gouging and piercing capabilities [17]. FIG. .2 TIG and Plasma Arcs The PAC process uses this high temperature. high velocity jet of ionized gas exiting from the constricting orifice of the torch tip to melt a much localized area and remove the molten material from the metal being cut by the force of the plasma jet. Because of the tightly focused heat energy. the size and shape of the constricting tip or nozzle orifice. the amount of electric current. 1. even when cutting thin gauge sheet metal thickness. Extremely clean and accurate cuts are possible with PAC.
advanced machining such as Plasma Arc Cutting is normally used. A clean cut with little or no dross means less time and money is required to finish the work piece. titanium alloys and stainless steel can be used as the work piece in this type of cutting. A torch in which temperatures as high as 30. spraying of molten metal.1. For applications where difficult shapes are being handled or cut. A plasma arc is hot enough to burn through most surface coatings such as paint and rust and still provides excellent cutting results.3 INTRODUCTION TO PROBLEM Advanced materials exhibit very excellent technical properties. to form a jet for welding. and cutting of hard rock or hard metals [25]. With plasma cutting. especially on thinner metals. tanks or vessels. Parts are virtually weld-ready. . plasma cutting offers considerable advantage since no fixturing is required [25]. the high cost of both raw materials and processing limit their use. there is minimal heat input and distortion of the metal as there is with jigsaws or cutting shears. With plasma cutting. with low or no heat affected zone. Alternatively. such as ventilation ductwork (HVAC). The plasma arc also cuts ferrous and non-ferrous metals much faster than an OxyFuel torch or abrasive saws. less preparation work is required.000°C are achieved by injecting a plasma gas tangentially into an electric arc formed between electrodes in a chamber. the resulting vortex of hot gases emerges at very high speed through a hole in the negative electrode. Advanced material such as nickel-base alloys. However.
What are the best conditions to achieve optimum performances? . forming the so-called dross and how to properly select a plasma cutting system. vaporizes and removes the metal from the region of impingement of the nozzle.1 Problem Statement Plasma arc cutting can be characterized in terms of two distinct speeds. the molten metal from the kerf sticks to the bottom of the plate. Traditional way of cutting takes a lot of time. e. f. What type of metal is to cutting? b. metal thicknesses and nozzle orifice diameters) for plasma arc cutting of stainless steel materials. the plasma jet does not cut through metal plate. What is primary input power when cutting process? c. How thick is the metal want to cut? d. Plasma can cut in a wide range of cutting parameters (currents. 1. The energy and momentum of the high-velocity plasma jet generated by the plasma torch melts. At cutting speeds above. The most important factors that influence the cutting process? g. Others problem is: a.The feasibility and effectiveness needs to be proven by experiment and by using Taguchi Method of the processing parameter to obtain the best factors combination (MRR and Surface Roughness). The plasma arc cutting process employs a plasma torch with a very narrow bore to produce a transferred arc to the work piece at an average current density of within the bore of the torch. At speeds below. The effective way to conduct the cutting process for Stainless Steel.3.
1. b) To design a series of experiment using the help of Design of Experiments (DOE) layout in order to study about Plasma Arc Cutting (PAC). The main purposes of this project are listed below: a) To study about the influence of Plasma Arc Cutting Parameters on Stainless Steel.4 OBJECTIVES This project was developed to study about the plasma arc cutting parameter in smooth cutting using straight polarity process. c) To study about the best combination of solution for maximizing the Material Removal Rate (MRR) and for minimizing the Surface Roughness (µm) with Taguchi Method . .
This project focuses on the optimization of cutting parameters of Plasma Arc Cutting (PAC). 2. The machine used will Silverin CNC Plasma Cutting Machine with Sharp line.1. . Bombay make Burney 10 LCD to perform the machining operation. All of data was analyzed by using Minitab 15 Software to produce the best combination setting in plasma cutting for Stainless Steel.5 SCOPE Generally these projects will be developing within the scopes below: 1. Design of Experiments (DOE) layout will be used for testing and analyzing with Taguchi Method . 5. 3. 4. The material used to cut was Stainless Steel of specification ASTM A240 TP316 L.
metal salvage (scrap and recycling). It can be used in many applications. all metals that conduct electricity. . whether they are common or exotic metals. maintenance. it's recommended to slightly tilt torch into the work piece. When cutting materials at the rated size and above. Pay close attention to the machine's capabilities. metal art and sculpting. The manner in cut the work piece will vary depending on the output of your plasma arc cutting machine and the thickness of material.1. With engineering advances in PAC equipment. automotive repair. When cutting metals at and below a machine's rated thickness. as that gives an idea of how fast to move across the cutting surface. bevelling.6 INTRODUCTION TO PAC Plasma arc cutting is not quite as involved as welding. can be cut economically with one process. When needing to make multiple passes on a work piece to properly cut it and simply need a more powerful plasma cutting machine. including stack cutting. fix the gun at a 90deg angle to the work piece. shape cutting. The PAC process is used in industries such as metal fabrication. construction. gouging. Make sure to take note of a machine's mm per minute capabilities on varying thicknesses. Since the plasma arc cutting process is capable of hand-held or machine torch cutting metals ranging from thin gauge aluminium to 5-60 mm carbon or stainless steel. and piercing in all positions.
and field performance. and Verification. Designed experiments are often carried out in four phases: a) b) c) d) Planning. . it is very important to get the most information from each experiment you perform. reliability. and which one has less. In addition.1. b). designed experiments can be used to systematically investigate the process or product variables that influence product quality. Optimization. . In industry. you can direct improvement efforts to enhance a product's manufacturability. quality. After you identify the process conditions and product components that influence product quality.7 DESIGN OF EXPERIMENTS (DOE) Design of Experiments (DOE) is a powerful statistical technique introduced by R. fisher in England in 1920s to study the effect of multiple variables simultaneously DOE can highly effective when: a). Because resources are limited. Well designed experiments can produce significantly more information and often require fewer runs than haphazard or unplanned experiments. Study the influence of individual factors on the performance and determine which factor has more influence. It can also find which factor should have higher tolerance and which tolerance should be relaxed. a well-designed experiment will ensure that you can evaluate the effects that you have identified as important [20]. Optimize product and process design . Screening (also called process characterization). study the effect of multiple factor on process.A.
2. Taguchi method systematically reveals the complex cause and effect relationship between design parameter and performance. The second point aims at quality engineering. . Society incurs a loss any time the performance of product is not on target.The foundation of quality depend upon two premises : 1. These lead to building quality performance into process and product before actual production begins . Product and process design require a systematic development. they lead to the major reductions into process and products before actual production begins .Taguchi method have rapidly attained prominence because wherever they have been applied. parametric design and finally tolerance design. a discipline that aims at engineering not only function but also quality performance into products and process . Such a loss has two components: The manufacture incurs a loss when he repairs or rectified return or rejected product. progressing stepwise through system design.Taguchi methods are most recent additions of tool kit design process for manufacturing engineers and quality assurance experts. society suffer loss. The significance of beginning quality assurance with an improved process or product design is not difficult to gauge. In contrast to stastical process control which attempt to control the factors that adversely affect the quality of production. The first point suggests that whenever the performance of a product deviates from its target performance.
According to him the quality of a manufactured product is the total loss generated by that product to the society from the time it is shipped. 3. Variation in the product depends primarily on the engineering design of the product and its manufacturing process. 7. In a competitive economy continuous improvement (CQI) and cost reduction are necessary. 4. Customer loss attribute to the product performance variation is often proportional to the square of the deviation performance characteristic from its target value. 6. 2. A CQI programmed include continuous reduction in the variation of product performance characteristic in their target values. The finally quality and cost of a product manufactured depends primarily on the engineering design of the product and its manufacturing process. 5. Taguchi defined the term quality as the deviation from on target performance which appears to be first paradox.The following seven points highlight the distinguish feature of Taguchi's approach which aimed at assuring quality: 1. . Statically planned experiments can efficiently and reliably identify the settings of the product and process parameters that reduce performance variations.
1. 1. and the conclusions for the works that have been carried out can be determined. From the result of the experiments using the Taguchi Method by Minitab 15 Software for Design of Experiments. the introduction to the problem has been specified. From the problem that arises. The objectives and the scopes have been determined in order to solve the problems . it is important to get the best setting of Plasma Arc Cutting machine to maximize the Metal Removal Rate (MRR) and minimize the Surface Roughness (Ra) response during the advance material cutting process.9 SUMMARY As a conclusion.8 SIGNIFICANCE OF FINDINGS From the thesis writing. the solution has to be carried out. the best combination of factors can be obtained.
Oxy fuel cuts by burning. an inert gas (Argon) is blown at high speed out of a nozzle and at the same time an electrical arc is formed through that gas from the nozzle to the surface being cut. apart from gases. which are not bound to an atom or molecule. thereby generating a small pocket of plasma gas. It is therefore limited to steel and other ferrous metals which support the oxidizing process. In this process. because of its unique properties. LITERATURE REVIEW Plasma cutting is a process that is used to cut steel and other metals (or sometimes other materials) using a plasma torch. Ionized refers to presence of one or more free electrons. The Arc type uses a two cycle approach to producing plasma. a high-voltage. Plasma can also be used for plasma arc welding and other applications [24]. turning some of that gas to plasma. Plasma arcs are extremely hot and are in the range of 15. . low current circuit is used to initialize a very small high intensity spark within the torch body. or oxidizing. The pilot arc will maintain until it is brought into proximity of the work piece where it ignites the main plasma cutting arc.2. First. The free electric charges make the plasma electrically conductive so that it responds strongly to electromagnetic fields [27]. The plasma is sufficiently hot to melt the metal being cut and moves sufficiently fast to blow molten metal away from the cut. The pilot arc has a return electrical path built into the torch head. the metal it is severing. Plasma is typically an ionized gas. This is referred to as the pilot arc.000 degrees Celsius. Plasma is considered to be a distinct state of matter.
oxyfuel is still preferred since oxyfuel is typically faster and. While different gasses can be used for plasma cutting. does not rely on oxidation to work. Plasma cutting. 5 to 160 mm thicknesses.Metals like aluminium and stainless steel form an oxide that inhibits further oxidization.1 PRINCIPLE OF PLASMA ARC CUTTING This process uses a concentrated electrical arc which melts the material through a high-temperature plasma beam. very high capacity power supplies are required for plasma cutting applications [28] . oxygen or argon/ hydrogen to cut mild and high alloy steels. The plasma arc process has always been seen as an alternative to the oxy-fuel process. However. and on thinner materials. compressed air is readily available. most people today use compressed air for the plasma gas. aluminium. In most shops. and thus it can cut aluminium. for heavy sections of steel (1inch and greater). . nitrogen. Plasma cutting units with cutting currents from 20 to 1000 amperes to cut plates with inert gas. Plasma gases are compressed air. In this part of the series the process fundamentals are described with emphasis being placed on the operating features and the advantages of the many process variants. however. stainless and any other conductive material. All conductive materials can be cut. copper and other metals and alloys [4]. making conventional oxyfuel cutting impossible. plasma cutting is much faster than oxyfuel cutting. for heavier plate applications. Plasma cutting is typically easier for the novice to master. 2. and thus plasma does not require fuel gas and compressed oxygen for operation.
Inside the plasma arc temperatures of 30 000oC can arise. Because of the high temperature the plasma expands and flows with supersonic velocity speed to the work piece (anode).Fig 2. c) Water. The term for advisable state of plasma arc is called stability of arc too. The stability of arc is keeping the plasma jet in desired form. that realize in connection with the high kinetic energy of the plasma beam and depending on the material thickness very high cutting speeds on all electrically conductive materials. . It is possible to be provided by [4]: a) Shape of Plasma Torch. With this energy densities up to 2x106 W/cm2 inside of the plasma beam can be achieved. b) Streaming Jet.1 The principle of the plasma cutting The plasma is additionally tied up by a water-cooled nozzle.
the open circuit voltage needed to initiate the arc can . Density of plasma jet. Thus. This low. The temperature of the plasma is in excess of 20 000°C and the velocity can approach the speed of sound. aluminium. Diameter of plasma beam. the plasma process can be applied to cutting metals which form refractory oxides such as stainless steel. unlike the oxy-fuel process. Although the operating voltage to sustain the plasma is typically 100 to 160V.energy pilot arc prepares by ionization in parts the way between plasma torch and work piece. The power source required for the plasma arc process must have a drooping characteristic and a high voltage. The process differs from the oxy-fuel process in that the plasma process operates by using the arc to melt the metal whereas in the oxy-fuel process. flying piercing). When used for cutting. the plasma gas flow is increased so that the deeply penetrating plasma jet cuts through the material and molten material is removed in the efflux plasma. the main arc will start by an automatic increase in power The basic principle is that the arc formed between the electrode and the work piece is constricted by a fine bore. For the cutting process first of all a pilot arc ignition by high voltage between nozzle and cathode takes place.We must monitor these parameters: Temperature and electrical conducting. Degree of the plasma beam focusing in output from nozzle. This increases the temperature and velocity of the plasma emanating from the nozzle. cast iron and non-ferrous alloys. When the pilot arc touches the work piece (flying cutting. copper nozzle. the oxygen oxidizes the metal and the heat from the exothermic reaction melts the metal.
The inert or uncreative plasma forming gas (argon or nitrogen) can be replaced with air but this requires a special electrode of hafnium or zirconium mounted in a copper holder. as described in Process variants. The plasma gas flow is critical and must be set according to the current level and the nozzle bore diameter. poor edge squareness or a bevel on the cut edge. The process variants have principally been designed to improve cut quality and arc stability. If the gas flow is too low for the current level. electrode to nozzle and nozzle to work piece. reduce the noise and fume or to increase cutting speed. such as air or oxygen can be used but the electrode must be copper with hafnium. However. the plasma is inert. by shearing . The electrode has a negative polarity and the work piece a positive polarity so that the majority of the arc energy (approximately two thirds) is used for cutting. formed using either argon. the arc must be transferred to the work piece in the so-called 'transferred' arc mode. The advantage of an air plasma torch is that it uses air instead of expensive gases. or the current level too high for the nozzle bore diameter. On initiation. The air can also replace water for cooling the torch. For cutting. oxidizing gases. as the plasma process cuts by melting. argon-H2 or nitrogen. As these limitations are associated with the degree of constriction of the arc. It should be noted that . the pilot arc is formed within the body of the torch between the electrode and the nozzle. In the conventional system using a tungsten electrode. a characteristic feature is the greater degree of melting towards the top of the metal resulting in top edge rounding. The effect of 'double arcing' is usually catastrophic with the nozzle melting. However.be up to 400V DC. The quality of the plasma cut edge is similar to that achieved with the oxy fuel process. several torch designs are available to improve arc constriction to produce more uniform heating at the top and bottom of the cut. the arc will break down forming two arcs in series.
hafnium tipped electrodes can be expensive compared with tungsten electrodes. such as multiple torches cutting of mild steel. The net result is greatly improved cut quality on virtually all metals. are becoming common place [31]. previously unheard of applications. dry plasma cutting in that water is injected around the arc.2: Air Plasma This relatively new process differs from conventional. Figure 2. .although the electrode and nozzle are the only consumables. because of advances in equipment design and improvement in cut quality. including mild steel. Today.
For base metal over 3 inches thick. is a problem with the argon blend.1. Air may be used for the cutting gas when special electrodes made from water-cooled copper with inserts of metals such as hafnium are used. more tenacious dross formed with argon is the greater surface tension of the molten metal. Recently. Argon-hydrogen and nitrogen-hydrogen mixtures The first two have become standard for high-speed mechanized applications. helium. . This results in nonparallel cut surfaces that are generally wider at the top than at the bottom. A possible explanation for the heavier. The surface tension of liquid steel is 30 percent higher in an argon atmosphere than in one of nitrogen. Air cutting gives a dross similar to that formed in a nitrogen atmosphere. Almost all plasma cutting of mild steel is done with one of three gas types: 1. but the formation of dross.2. can produce cuts that are square on one side and bevelled on the other side. and nitrogen (except at elevated temperatures) are used with tungsten electrodes. PAC units shielded by compressed air have been developed to cut thin-gauge materials. Nitrogen-oxygen or air 3. because of its uniform heat pattern or the injection of water into the torch nozzle (mechanized only). argon-hydrogen is frequently used without water injection [17]. The plasma jet tends to remove more metal from the upper part of the work piece than from the lower part.1 Shielding and Cutting Gases for Plasma Cutting Inert gases such as argon. The use of argon-hydrogen. Nitrogen with carbon dioxide shielding or water injection (mechanized) 2. Argonhydrogen and nitrogen-hydrogen (20 to 35 percent hydrogen) are occasionally used for manual cutting. a tenacious deposit of resolidified metal attached at the bottom of the cut.
Any oil or moisture in the air supply will substantially reduce torch parts life. 3. Air Plasma is normally used with air secondary. 2. dry air is recommended to use as plasma gas.1. . Mostly used on ferrous or carbon based materials to obtain good quality a faster cutting speeds. 4. A good clean welding grade nitrogen should be used.2 Plasma Gas Selection Air Plasma 1. Provides faster cutting speeds and high cut quality on thicker material to offset the higher cost of the gas. Nitrogen Plasma 1.2. Argon/Hydrogen Plasma 1. Provides much better parts life than air Provides better cut quality on non-ferrous materials such as stainless steel and aluminium. 3. 2. 3. A 65% argon/35% hydrogen mixture should be used. Only clan. 2. Recommended for 12mm and thicker non-ferrous material. Ar/H2 is not normally used for thinner non-ferrous material because less expensive gases can achieve similar cut quality. Can be used in place of air plasma with air secondary. Recommended use on 19mm and thicker stainless steel.
2. 2. 3. 4. Provides faster cutting speeds. Usable on any ferrous or non-ferrous material May reduce smoke when used with Ar/H2 plasma. . CO2 secondary is used with nitrogen or Ar/H2 plasma. 2. Poor quality on ferrous materials.3 Secondary Gas Selection for Plasma Cutting Air Secondary 1.4. 3. Oxygen is recommended for cutting ferrous metals.reduces operating costs Improves cut quality on some ferrous materials CO2 Secondary 1. 3. 2. Air secondary is normally used when operating with air plasma and occasionally with nitrogen plasma. Oxygen Plasma 1. Provides very smooth finishes and minimizes nitride build-up on cut surface (nitride build-up can cause difficulties in producing high quality welds if not removed). Inexpensive . Provides good cooling and maximizes torch parts life.1.
1 SUMMARY TABLE FOR GASE SELECTION Material Gas Material Thickness Gage to Carbon Steel Good Excellent Excellent Stainless Steel Aluminium / Good Excellent Good Fair / Good Excellent / Good Excellent / Good Excellent NR Excellent / Excellent / / / / Air Plasma Air Secondary Gage 12mm / Good Excellent Good Fair / Good Excellent / Good Excellent / Good Excellent NR Good Good Excellent 12mm and Up Excellent Nitrogen Plasma Gage to Good Excellent Good Excellent Gage Air Secondary 12mm Or CO2 12mm and Up Secondary Good Excellent Ar/H2 Plasma Gage to 6mm N2 or CO2 Secondary 6mm 30mm NR to NR NR 12mm and Up .Table 2.
The system and the process are the important elements when utilizing plasma arc cutting. and stronger computercontrolled torches can pierce and cut steel up to 12 inches (300 mm) thick.2 PLASMA CUTTING CAPABILITY Plasma is an effective means of cutting thin and thick materials alike. however new technologies allow the plasma ignition arc to be enclosed within the nozzle thus allowing the cutter to be used for non-conductive work pieces. Formerly. Plasma Arc Cutter was utilized to perform Stainless Steel (316 L) material cutting.3Plasma Arc Setup .2. plasma cutters could only work on conductive materials. In this work. Fig 2. Hand held torches can usually cut up to 2 in (48 mm) thick steel plate. It is important to know current plasma arc cutting research areas to plan the direction of this work so that this work would contribute information that will be useful in future. Since plasma cutters produce a very hot and much localized cone to cut with they are extremely useful for cutting sheet metal in curved or angled shapes.
Manufacturers of transportation and agricultural equipment.2. power supply. ground clamp. heavy machinery. Figure 2. AC plug.3 SYSTEM Plasma arc cutting can increase the speed and efficiency of both sheet and plate metal cutting operations.4 : Plasma Arc Cutter System . air handling equipment. Basically Plasma Arc Cutter comprises of 8 major parts such as air compressor. plasma torch. aircraft components. electrode. and many other products have discovered its benefits. nozzle and workpiece [17].
thereby producing the plasma. The power supply is a constant current DC power source.4 ARC STARTING CIRCUIT The arc starting circuit is a high frequency generator circuit that produces an AC voltage of 5. .000 to 10. thereby producing the plasma [35]. This voltage is used to create a high intensity arc inside the torch to ionize the gas.000 volts at approximately 2 megahertz. The output current (amperage) of the power supply determines the speed and cut thickness capability of the system. The arc starting circuit is a high frequency generator circuit that produces an AC voltage of 5. 2. The nozzle and electrode constrict and maintain the plasma jet [35]. The Torch serves as the holder for the consumable nozzle and electrode. The main function of the power supply is to provide the correct energy to maintain the plasma arc after ionization. This voltage is used to create a high intensity arc inside the torch to ionize the gas.2. an arc starting circuit and a torch. and provides cooling (either gas or water) to these parts. highly productive cuts on a variety of different materials.000 to 10.000 volts at approximately 2 megahertz.5 PROCESS The basic plasma arc cutting system consists of a power supply. ionization capability and process control that is necessary to produce high quality. The open circuit voltage is typically in the range of 240 to 400 VDC. These system components provide the electrical energy.
depending on the thickness of metal to be cut.2. Modern plasma torches have self-aligning and self-adjusting consumable parts. PAC torches operate at extremely high temperatures. Mechanized torches can be mounted either on a tractor or a on a computer-controlled cutting machine or robot. The standoff distance must be maintained with fairly close tolerances to achieve uniform results. Some mechanised torches are equipped with an automatic standoff controlling device to maintain a fixed distance between the torch and work piece. In other cases mechanical followers are used to accomplish this. As long as they are assembled in accordance with the manufacturer's instructions.5 PLASMA TORCH The Plasma cutting process is used with either a handheld torch or a mechanically mounted torch. Some torches can be dragged along in direct contact with the work piece. while others require that a standoff be maintained between the tip of the torch and work piece. The timely replacement of consumable parts is required to achieve good quality cuts. the torch should require no further adjustment for proper operation [19]. The tip and electrode are the most vulnerable to wear during cutting. Usually a standoff is maintained between the torch tip and work piece for best-cut quality. and various parts of the torch must be considered to be consumable. . and cutting performance usually deteriorates as they wear. There are several types and sizes of each.
a standoff distance of 1/16" to 1/8" will be required. Low heat build-up while cutting with less than 40 amperes may allow dragging the torch tip on the material. The Dual Flow Torch has a flow of gas or air for the cutting plasma and shielding gas flow for the torch cooling. This is easily accomplished with a Miller ICE torch with a "Drag Shield". 2. This is because its use is limited to lower amperage. It does not need a shielding gas flow to cool the torch because of the low amperage output required for cutting thin gauge sheet metal. The "Drag Shield" works with the flow dynamics of the torch to provide better cooling of the consumable parts for longer parts life. seals etc may also require periodic inspection and replacement if they are worn or damaged. 2. This permits the operator to drag the torch on the work piece while cutting at full output. thin gauge sheet metal cutting applications.1 Torch Designs The Single Flow Torch has only a flow of air for cutting. .5. If a high build-up of heat is expected. This is used for cutting thicker materials.5. insulators. This standoff distance will be determined by the thickness of material being cut and the amperage required. which increases operator comfort and makes template cutting easier [19].Other torch parts such as shield cups. which require higher amperages.2 Torch Stand Off "Torch stand-off" is the distance the outer face of the torch tip or constricting orifice nozzle is to the base metal surface.
the same parts are used: an electrode to carry the current form the power source. 2. and a shield and retaining ring to protect the torch.3 Torch Consumables The plasma torch is designed to generate and focus the plasma cutting arc. a swirl ring to spin the compressed air.Fig 2.5 Torch Stand Off 2.6 Torch Breakdown . Fig. a tip that constricts and focuses the cutting arc. In either hand held or machine torches.5.
The electrode is typically made of copper with an insert made of hafnium. The purpose of the electrode is to provide a path for the electricity from the power source and generate the cutting arc. The swirl ring on Miller plasma cutting equipment causes the gas to swirl in a clockwise direction. dry compressed air or nitrogen is used (although. Fig 2. The swirl ring is made of a high temperature plastic with angled holes that cause the gas to spin. The Hafnium alloyed electrodes have good wear life when clean.ELECTRODE. Spinning the gas centres the arc on the electrode and helps to control and constrict the arc as it passes through the tip.7 Electrode SWIRL RING. The swirl ring is designed to spin the cutting gas in a vortex. electrode consumption may be greater with air plasma than with nitrogen). .
with a specifically sized hole or orifice in the centre of the tip. Constricting the arc increases the energy density and velocity. The purpose of the torch tip is to constrict and focus the plasma arc. 2.Fig. Tips are sized according to the amperage rating of the torch that they are to be used in [19]. The tips are made of copper.8 Swirl Ring TIP. Fig. 2.9 Tip .
no factor is weighted more or less in an experiment. which allow us to analyze many factors with few runs. Robust parameter design uses Taguchi designs (orthogonal arrays). The noise levels selected should reflect the range of conditions under which the response variable should remain robust. we should choose a design that is capable of estimating those interactions. while adjusting (or keeping) the process on target. make the product insensitive to changes in uncontrollable (noise) factors. After we determine which factors affect variation. or both. A product designed with this goal will deliver more consistent performance regardless of the environment in which it is used. we can try to find settings for controllable factors that will either reduce the variation. Minitab can help us to select a Taguchi design that does not confound interactions of interest with each other or with main effects. Engineering knowledge should guide the selection of factors and responses. Genichi Taguchi is regarded as the foremost proponent of robust parameter design. In robust parameter design. thus allowing factors to be analyzed independently of each other [18]. Noise factors for the outer array should also be carefully selected and may require preliminary experimentation. the primary goal is to find factor settings that minimize response variation. Taguchi designs provide a powerful and efficient method for designing products that operate consistently and optimally over a variety of conditions.2. A process designed with this goal will produce more consistent output.6 TAGUCHI DESIGN OVERVIEW Dr. . When used properly. When interactions among control factors are likely or not well understood. that is. which is an engineering method for product or process design that focuses on minimizing variation and/or sensitivity to noise. Taguchi designs are balanced.
• In a static response experiment. Minitab calculates response tables. slopes (dynamic design). the control factors • natural log of the standard deviations vs. the quality characteristic of interest has a fixed level. The goal of robust experimentation is to find an optimal combination of control factor settings that achieve robustness against (insensitivity to) noise factors. We can create a dynamic response experiment by adding a signal factor to a design − see Creating a dynamic response experiment. and standard deviations [18]. the control factors • means (static design) or slopes (dynamic design) vs. the control factors • standard deviations vs. • In a dynamic response experiment. . An example of a dynamic response experiment is an automotive acceleration experiment where the input signal is the amount of pressure on the gas pedal and the output response is vehicle speed. To get a complete understanding of factor effects it is advisable to evaluate S/N ratios.Minitab provides both static and dynamic response experiments. the quality characteristic operates over a range of values and the goal is to improve the relationship between an input signal and an output response. linear model results. means (static design). the control factors Use the results and plots to determine what factors and interactions are important and evaluate how they affect responses. which provide a measure of robustness) vs. and generates main effects and interaction plots for: • signal-to-noise ratios (S/N ratios.
along with an experimental design for this set of factors. next to the factors settings for that run of the control factors in the inner array Each column in the orthogonal array represents a specific factor with two or more levels. By default.7 WHAT IS TAGUCHI DESIGN? A Taguchi design.. .2. Each row represents a run. the integers 1. is a method of designing experiments that usually requires only a fraction of the full factorial combinations. In robust parameter design. will be the coded levels for the design [18]. An orthogonal array means the design is balanced so that factor levels are weighted equally. 3.. 3. The response data from each run of the noise factors in the outer array are usually aligned in a row. The experiment is carried out by running the complete set of noise factor settings at each combination of control factor settings (at each run). . the cell values indicate the factor settings for the run. At the same time. 2. The control factors comprise the inner array. we first choose control factors and their levels and choose an orthogonal array appropriate for these control factors. If we enter factor levels.. or an orthogonal array. to represent factor levels.. 2. Because of this. The noise factors comprise the outer array.. so the effect of one factor does not influence the estimation of another factor. Minitab's orthogonal array designs use the integers 1. we determine a set of noise factors. each factor can be evaluated independently of all the other factors.
corrosion resisting chromium oxide film on the steel surface.1 Test Specimen 3. It is this addition of chromium that gives steel its unique stainless. Fig.2 MATERIAL Stainless Steel is essentially a low carbon steel which contains chromium at 10% or more by weight.3. invisible. The material for test specimen was Stainless Steel ASTM A 240 TP 316 L. Here L stands for Low Carbon Content. Here L stands for Low Carbon Content [37]. Generally pipe flanges are manufactured from the Stainless Steel of grade 316 L. . The chromium content allows the formation of a tough. 3. corrosion resisting properties.1 SPECIMEN PREPARATION 16 test specimens having dimension 30mm x 30mm x 12 mm were prepared for the experimental work. adherent.
045 - S 0.1.0 18.08 0. Continuous use of 316 in the 425-860°C range is not recommended if subsequent aqueous corrosion resistance is important.045 0.0 14. Grade 316 316L 316H Min Max Min Max Min max C 0.00 Ni 10.0 14.75 P 0 0.00 3.0 18.2 Mechanical properties of 316 grade stainless steels Grade Tensile Strength (MPa) Yield Str Elongation Rockwell B Brinell (HB) in (HR B) max max 0.0 Mo 2.04 0.0 16. Grade 316L is more resistant to carbide precipitation and can be used in the above temperature range.0 0. .75 0 0.10 Mn 2.03 0.Table 3.0 N 0.10 0.0 16.00 2.0 2.0 14.0 18.03 Table 3.75 0.03 - Cr 16. Grade 316H has higher strength at elevated temperatures and is sometimes used for structural and pressure-containing applications at temperatures above about 500°C.00 2.00 3.0 10.04 0.00 3. Composition ranges for 316 grades of stainless steels.10 - 0.10 Si 0.2% Proof (% (MPa) 50mm) 316 316L 316H 515 485 515 205 170 205 40 40 40 95 95 95 217 217 217 Good oxidation resistance in intermittent service to 870°C and in continuous service to 925°C.03 0.045 0.0 10.
1 Plasma Arc Cutting System Plasma Arc Cutter used in this work is Silverin Make with Sharpline Bombay make Burny 10 LCD. worker always know plasma arc cuts all electrically conductive metals (Ox fuel is usually limited to steel). Table 3. the process produces a small heat-affected zone.3. turnaround time is fast.3. Plasma arc cutting system Silverin Make with Sharpline Bombay make Burny 10 LCD 2. Digital weight balancer equipment 3. The surface roughness tester (FORM TALY SURF) Taylor Hobson Make (U. plasma arc cutting requires no preheating.) 3. Before cutting.3 Technical Features Technical Features Supply voltage Rated power Operating pressure Primary fuse Open circuit voltage Pilot arc current Machine 3x400V .50Hz 30 kW 5 bar 16 A 260 V 50 A .K.3EQUIPMENTS Equipment for the experiment use is: 1.
Stylus: Diamond 2µm tip radius. Force: 4mN.3. clamp the work piece of project use a clamping in the machine.2 Digital Weight Balancer The weight of the work pieces (specimens) before and after the cutting process need to be measuredin order to obtain the amount of Material Removal Rate (MRR). Travelling length: 01mm-50mm. Power ratings are commonly between 20 and 200 kW. Software: Form ultra software 3. . a data value for roughness can print out after finish measured. And then. The surface roughness tester (FORM TALY SURF) used in this work. with the following specifications: Manufacturer: Taylor Hobson. Lastly.3. U. can start measured a work piece. Firstly.3 Surface Roughness Tester There are five steps to measure the surface roughness of specimens. right or left direction.K. After finish setting. 3. Resolution: 16nm/1. setting a prop of axis likes up and down.0mm.3. Increasing the power increases the cutting speed or enables thicker metals to be cut without slow down.3.4 Power Supply The power supply required depends on the material thickness and cutting speeds desired.
Fig3.2 DC Power Supply Source .
4 DESIGN FACTORS Design of Experiments technique has been utilized to obtain the best combination of design factors to achieve optimum performance measures. When the cutting current increases or the cutting speed decreases. It is important to have the correct gas flow rate for the size tip. These factors are the most important to have the best value for Material Removal Rate (MRR) and Surface Roughness (Ra) when cutting material like Stainless Steel or Nickel Base Alloy etc. Plasma Arc Cutting involves several input parameters to be considered during machining process. Current Flow Rate Current flow rate is the value of current given during cutting process. metal type and thickness. Normally Nitrogen or Argon with 0-35% Hydrogen is used for cutting Stainless Steel material. the combination factors such as Gas Pressure [bar]. Cutting Speed [mm/min] and Arc Gap [mm] are considered. Too high a gas flow will produce a poor cut because of turbulence in the plasma stream and waste gas. The cause of the burn-through was the increase in the cutting current or the decrease in the cutting speed. If the cutting current and the flow rate of .3. Controlling the pressure is one way of controlling gas flow [23]. Too low a gas flow will result in a cut having excessive dross and sharply bevelled sides. In this thesis. the stable state of the keyhole changes accordingly. Gas Pressure According to Larry Jeffus. Current Flow Rate [A]. We used Argon with 0-35% Hydrogen for our experiment purpose. almost any gas or gas mixture can be used today for the PAC process. "Principle and Application of Welding" Sixth Addition.
the process will withstand larger variations in the cutting parameters . Surface Roughness (Ra) . dross free cuts. Material Removal Rate (MRR) ii. known as: i.the plasma gas are increased and/or the cutting speed is decreased. or zero degrees as it exits the bottom side of the cut. an exit arc that is opposite to the direction of torch travel). In most metals there is a window between these two extremes that will give straight. If cutting with nitrogen or argon/hydrogen. then the correct cutting speed will produce a trailing arc (that is. Observe the angle of the cutting arc through the proper welding lens. Cutting Speed The best way to judge cutting speed is to look at the arc as it exits the bottom of the work piece. A cutting speed that is too slow or too fast will cause cut quality problems. the arc should be vertical straight down. Arc Gap Arc gap is the gap between the plasma arc cutter torch and welding electrodes with the work piece [23] .5 PLASMA ARC CUTTING RESPONSE There are two Plasma Arc Cutting responses measured in this study. clean. 3. If cutting with air. The torch speed needs to be adjusted to get a good-quality cut.
if they are small the surface is smooth.5.2 SURFACE ROUGHNESS Roughness is a measure of the texture of a surface. the surface is rough.008g/mm3. can be defined as the volume of material removed divided by the machining time. short wavelength component of a measured surface. Roughness is typically considered to be the high frequency. If these deviations are large. WRW: workpiece removal weight (g) T: cutting time(s) WRW is the weight different between before and after work piece cutting.5. The relation between WRW and WRV is given as follow: WRV = WRW/ρ Where. Material Removal Rate (MRR) is defined by: MRR = WRW/T [g/min] Where.1 MATERIAL REMOVAL RATE The material removal rate. 3. It is quantified by the vertical deviations of a real surface from its ideal form. Surface roughness normally measured. . ρ : Work piece density (g/ mm3) The density of the Nickel-Base Alloys is 8 g/cm3 or 0.3. The volume different can be calculated when information regarding material density available. MRR.
Where L is the length taken for observation. Rough surfaces usually wear more quickly and have higher friction coefficients than smooth surfaces (see tribology). since irregularities in the surface may form nucleation sites for cracks or corrosion. Roughness is often a good predictor of the performance of a mechanical component. the average surface roughness is measured and calculated. and Y is the ordinate of the profile curve [9]. The average surface roughness is the integral of the absolute value of the roughness profile height over the evaluation length and is denoted by the following equation. In this thesis. .Roughness plays an important role in determining how a real object will interact with its environment.
Here in my thesis work I will try to find out optimal value of MRR and SURFACE ROUGHNESS (Ra). Various Input parameters Voltage Current Flow Rate Arc Gap Kerf (width of cut) Cutting Speed Material Type and Thickness Cutting gas Pressure After extensive brain storming with the experts of Fabrication Division of BHEL Bhopal. they suggested that Stainless Steel (316L) materials are cheaply available and widely used in Plasma Cutting Machine . The results obtain will be analyzed and the models will be produced by using MINITAB software. This will help in improving the effective and efficient working of the PAC process. As I am going to perform my work on Silverin make Plasma . it has been found that above are important input parameters for studying material remove rate.4. For this I consult to Fabrication Division of BHEL.1 OUTLINE OF THESIS WORK It is found already many work has been done in MRR and Surface finish but very little work has been done on optimization of Plasma Arc Cutting.O. Bhopal.Taguchi method using design of experiments approach can be used to optimize a process Here we will to apply D.E approach for modelling of MRR in PAC process and the various input parameters will be taken under experimental investigation and then model will be prepared then again experimentation work will be performed.
the orthogonal array was to be selected for four design variables (namely Gas Pressure. . Out of the above listed design variables. 4. Cutting Speed and Arc gap) which would constitute the L16 orthogonal array.2 DESIGN OF EXPERIMENT The objective of this research work is to study MRR and Surface roughness. Current. The two most important outputs are Material Removal Rate and Surface Roughness the same have been selected as response parameters for this research work also. The following machining parameters were kept fixed.Arc Cutting Machine No. d) Two levels of Arc Gap (2mm and 4mm) For conducting the experiments. B/0/2163 and after literature review four main input parameters selected are Gas Pressure. Current. b) Two levels of Current Flow Rate (150A and 200A). Cutting Speed. the design variables can be summarized as follows: a) Two levels of the Gas Pressure (6Bar and 7Bar). and Arc Gap. The material used is Stainless Steel ASTM A240TP316L in the overall experiment. The other two parameters kerf (5mm) and Material Thickness (12mm) is kept fixed for the whole experiment. it has been decided to follow the Taguchi method of experimental design and an appropriate orthogonal array is to be selected after taking into consideration the above design variables. The effect of the variation in input process parameter will be studied on these two response parameters and the experimental data will be analyzed as per Taguchi method to find out the optimum machining condition and percentage contribution of each factor. c) Two levels of Cutting Speed (400mm/min and 600mm/min).
there are four parameters at two levels each. The degree of freedom (DOF) of a two level parameter is 2 (Number of Levels minus 1).3 SELECTION OF ORTHOGONAL ARRAY AND PARAMETER ASSIGNMENT In this experiment. No.2 Parametric Level Assignment Parameter Gas Pressure Current Flow Rate Cutting Speed Arc Gap Unit bar ampere mm/min mm Level 1 5 150 400 2 Level 2 6 200 600 4 DOF 1 1 1 1 .Table 4. hence total DOF for the experiment is 4. Table 4. Machining Parameters 1 2 3 4 Material Type Material Thickness Kerf Operating Voltage Fixed Value Stainless Steel (316 L) 12 mm 5mm 200 V 4. The DOF of the orthogonal array selected should have higher than that of total DOF of the experiment.1 Fixed Machining Parameters S.
1 Standard L16 Array with (2*4) :. and each table cell represents the factor level for that run.3.3 Experimental Layout in Coded Factor Levels Runs 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Gas Pressure 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 Current 1 1 1 1 2 2 2 2 1 1 1 1 2 2 2 2 Cutting Speed 1 1 2 2 1 1 2 2 1 1 2 2 1 1 2 2 Arc Gap 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 The above table displays the L16 (2*4) Taguchi design (orthogonal array). The table columns represent the control factors. This array is orthogonal. 2*4 means 4 factors with 2 levels each. .4.Column number 1 2 4 and 8 of L16(2**15) Array is used for this experiment:- Table 4. the table rows represent the runs (combination of factor levels). factor levels are weighted equally across the entire design. L16 means 16 runs.
..... Let desired performance be µ1 . robust design seeks optimum settings of parameters to achieve a particular target performance value under the most noise condition...4. Maximizing become equivalent to minimizing the loss after adjustment.... If Y is the performance characteristic measured on a continuous scale when ideal or target performance is T then according to Taguchi the loss caused L(Y) can be modeled by a quadratic function as shown in equation (1) L(Y) = K (Y-T2). and the target lies under acceptable range of product quality are often inadequate.4 SIGNAL TO NOISE (S/N) RATIO Noise factors are those that are either too hard or uneconomical to control even though they may cause unwanted variation in performance.. Since on target is goal the loss after adjustment is due to variability remaining from the new standard deviation. It is observed that on target performance usually satisfies the user best.. ....Then one make adjustment in design to get performance on target by adjusting value of control factor by multiplying it by the factor .. Suppose that in a set of statistical experiment one finds a average quality characteristic to be µ and standard deviation to be σ.. Loss after adjustment shown in equation (2): The factor reflects the ratio of average performance µ^2(which is the signal) and or S/N ratio therefore σ^2(the variance of performance) the noise. Finding a correct objective function to maximize in an engineering design problem is very important...... (1) The objective of robust design is specific..
The formula for the smaller-is-better S/N ratio using base 10 log is: S/N = -10*log(Sum of(Y2)/n) Where Y = responses for the given factor level combination and n = number of responses in the factor level combination. the following three types of S/N ratios are employed in practice: Larger is Better The signal-to-noise (S/N) ratio is calculated for each factor level combination. The formula for the larger-is-better S/N ratio using base 10 log is: S/N = -10*log(Sum of (1/Y2)/n) Where Y = responses for the given factor level combination and. In my thesis work MRR is considered larger is better. n = number of responses in the factor level combination. .Depending upon the type of response. Smaller is Better The signal-to-noise (S/N) ratio is calculated for each factor level combination. Value of MRR is measured by difference between initial and final weight after machining Surface roughness of specimen is considered as smaller is better. Surface roughness is measured by Taylor Hobson Make Talysurf Instrument.
and are sometimes known as Fisher's ANOVA or Fisher's analysis of variance. Based on the ANOVA. Two types of variations are present in experimental data: 1. The average loss is proportional to the mean squared error of Y about its target T. Observation to observation variability So ANOVA helps us to compare variabilities within experimental data. In my thesis ANOVA table is made with help of MINITAB 15 software. due to the use of Fisher's Fdistribution as part of the test of statistical significance. When performance varies one determines theaverage loss by statistically averaging the quadratic loss. the relative importance of the machining parameters with respect to material removal rate and surface roughness is investigated to determine more accurately the optimum combination of the machining parameters. Fisher in the 1920s and 1930s. .5 ANOVA (Analysis of Variance) The purpose of the statistical analysis of variance (ANOVA) is to investigate which design parameter significantly affects the material removal rate and surface roughness.4. The initial techniques of the analysis of variance were developed by the statistician and geneticist R. A. Within treatment variability 2.
. It is also known as the sum of squares between treatments..= mean of the observations at the ith factor level.y.. .)2 SS Error SS Total = Si Sj (yij .1 Various formulas for ANOVA: Degrees of freedom (DF) Indicates the number of independent elements in the sum of squares. The calculations are: SS (Factor) = S ni (yi. )2 Where yi. = mean of all observations and yij = value of the jth observation at the ith factor level. SS Error is the deviation of an observation from its corresponding factor level mean. The degrees of freedom for each component of the model are: DF (Factor) = r-1 DF (Error) = nt – r Total = nt – 1 Where nT = the total number of observations and r = the number of factor levels.y. SS (Factor) is the deviation of the estimated factor level mean around the overall mean.yi. . It is also known as error within treatments.4. SS Total is the total variation in the data.5. y. Sum of squares (SS) The sum of squared distances. )2 = Si Sj (yij .
r.1 and for the denominator are nT . Larger values of F support rejecting the null hypothesis that the means are equal.Pure sum of square SS' (Factor) = SS (Factor) – DF (Factor) * MS (Error) Mean square (MS) The calculations for the mean square for the factor and error are: MS (Factor) = SS (Factor)/ DF (Factor) MS (Error) = SS (Error)/ DF (Error) F Value A test to determine whether the factor means are equal or not. The formula is: F = MS (Factor)/ MS (Error) The degrees of freedom for the numerator are r . .
Since in my thesis work there are four factors and two levels for each which are shown below:
Table 5.1 Values of variables at different level
Control Factors Gas Pressure Current Flow Rate Cutting Speed Arc Gap Unit bar ampere mm/min mm Level 1 5 150 400 2 Level 2 6 200 600 4 DOF 1 1 1 1
After deciding parameters and levels as shown above orthogonal array L16 decided as per degree of freedom of each factor and dof of interaction among the parameters. Data of parameter was collected in such a way that it shouldn't damage or cause any accident to operator and as per literature review. Now perform experiment as per orthogonal array (L16) on Plasma Arc Cutting Machine Number B/0/2163, output like MRR and surface roughness is being given in tabulated form. After the experimental results have been obtained, analysis of the results was carried out analytically as well as graphically. Graphical analysis is done by MINITAB, shows interactions of all parameters. Then ANOVA of the experimental data has been done to calculate the contribution of each factor in each response. Then we calculated S/N ratio for MRR and surface roughness of specimens.
Then we obtain optimal conditions has been calculated for MRR and surface roughness of specimen. The following table shows readings of MRR and surface roughness at each experiment, it also shows S/N ratio for MRR and surface roughness at each experiments.
Table 5.2 Calculation Sheet for MRR and Surface Roughness
Exp No.
Mass (Before
1 Mass 2 Mass (After Loss (g)
Surface roughness (µm)
Taken (g/Sec) (Sec)
Cutting) Cutting) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 90 87 85.4 79.05 98.54 79.69 102.77 99.48 82.63 82.67 72.4 73 93.45 89.1 86.75 93.27 61.2 58.6 56.4 49.65 69.74 52.69 73.87 70.68 56.23 53.77 43 43.2 64.65 60.9 58.55 64.77 28.8 28.4 29 29.4 28.8 27 28.9 28.8 26.4 28.9 29.4 29.8 28.8 28.2 28.2 28.5
45 45 40 36 40 36 36 35 40 39 38 37 49 47 37 35
0.640000 3.834 0.631111 3.688 0.725000 4.393 0.816667 4.679 0.720000 3.180 0.750000 3.458 0.802778 4.571 0.822857 3.568 0.660000 3.255 0.741026 3.688 0.773684 3.951 0.805405 3.958 0.587755 2.352 0.60000 2.636
0.762162 3.969 0.814286 4.123
750000 0.636 3.60334 -2.805405 0.660000 0.762162 0. ure (Bar) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 5 5 5 5 5 5 5 5 6 6 6 6 6 6 6 6 Current (A) Speed Arc MRR (g/Sec) S/N ratio SR for MRR Ra (µm) S/N ratio for SR 11.958 2.9495 7.8552 13.79324 -1.7765 13.3358 12.180 3.99788 -2.3358 11.688 3.2510 11.6730 11.814286 -3.60000 0.9341 11.90809 -1.458 4.22873 -1.4031 10.49877 -1.69351 -3.4287 8.741026 0.571 3.631111 0.587755 0.802778 0.725000 0.3 Experimental Layout and S/N ratios for MRR and Surface Roughness (Actual Factor Levels) Exp Press No.352 2.4189 11.87640 -3.969 4.87971 -4.3043 (mm/min) Gap (mm) 150 150 150 150 200 200 200 200 150 150 150 150 200 200 200 200 400 400 600 600 400 400 600 600 400 400 600 600 400 400 600 600 2 4 2 4 2 4 2 4 2 4 2 4 2 4 2 4 0.60912 -2.773684 0.393 4.Table 5.43697 -2.0485 10.816667 0.688 4.720000 0.0485 10.255 3.75910 -2.9736 12.2002 11.951 3.568 3.78446 3.123 .61607 -4.679 3.35905 -1.640000 0.822857 0.834 3.85335 -2.
Main Effects Plot for SN ratios
Data Means
-2.0 -2.4 -2.8 pressure current
Mean of SN ratios
-3.2 -3.6 5 -2.0 -2.4 -2.8 -3.2 -3.6 400 600 2 4 cutting speed 6 100 arc gap 150
Signal-to-noise: Larger is better
Graph 5.1 Effects of various factors on S/N Ratio of MRR
By using MINITAB software we obtain some interactions if we look at the graph we will observe that with increase in Gas Pressure MRR S/N ratio is decreasing. Material removal rate increases with increase in Current, Cutting Speed and Arc gap.
Main Effect Plot for Mean of MRR
Main Effects Plot for Means
Data Means
0.80 0.75 0.70 0.65 5 0.80 0.75 0.70 0.65 400 600 2 4 cutting speed 6 100 arc gap 150 Gas Pressure current
Mean of Means
Graph 5.2 Effects of various factors on Mean of MRR
With the above graph of mean of MRR and various factors, we can observe that MRR is decreasing with increase in Gas Pressure and MRR is increasing with increase in Current, Cutting Speed and Arc Gap.
Main Effects Plot for SN ratios
Data Means
-10.0 -10.5 -11.0 Gas Pressure current
Mean of SN ratios
-11.5 -12.0 5 -10.0 -10.5 -11.0 -11.5 -12.0 400 600 2 4 cutting speed 6 100 arc gap 150
Signal-to-noise: Smaller is better
Graph 5.3 Effects of various factors on S/N Ratio of SR
Above graph represent the effect of parameters on Surface Roughness. It can be seen that as value of Gas Pressure and Current increases, S/N ratio of Surface roughness also increases. However S/N ratio of Surface roughness decreases with increase in the Cutting Speed and Arc Gap.
05 21.44 5.0223 9. P value less than 0.0500 indicate model terms are significant.0223 9.2854 0. In this case Cutting Speed is significant model term.822 0.8056 0. shows the Analysis of Variance (ANOVA) for MRR response.8601 0.42 31. Values greater than 0.1295 0.8056 4. The percentage contribution by each of the process parameter in the total sum of squared deviation SSt can be used to evaluate the importance of the process parameter change on the quality characteristic.6172 14.427 0.41975 0. The important information can be obtained here is the percentage influence of all factors over responses.2854 0.5 61.07 100 TablE 5.92 1.4 ANOVA Table for MRR Parameters DOF SS MS F P Contribution (%) Gas Pressure Current Cutting Speed Arc Gap Residual Error Total 1 1 1 1 11 15 0.1000 indicate the model terms are not significant.75 1.68 0.5.Minitab 15 software is used for statistical calculation purpose.92 0.4 ANALYSIS OF VARIANCE (ANOVA) Since as already stated ANOVA help us to identify which parameter is important for us after literature review following ANOVA table is obtained for MRR and Surface roughness .1295 0.4. .193 1.001 0. Table 5.
05.040 0.5 ANOVA Table for Surface Roughness (Ra) Parameters DOF SS MS F P Contribution (%) Gas Pressure Current Cutting Speed Arc Gap Residual Error Total 1 1 1 1 11 15 4.22 14.23 24.027 0.10 0. .6862 18. The percentage contribution by each of the process parameter in the total sum of squared deviation SSt can be used to evaluate the importance of the process parameter change on the quality characteristic.36 0.1250 4.53 48. P values greater than 0.7795 5.0912 9. The P value for the factor Arc Gap is 0. There is 75.753 which is not significant.7795 5.001 0.9228 0.6862 18.01 indicates that model terms are not significant.753 12.3% chance that a this large could occur due to noise. Current and Cutting Speed are significant terms because their P values are less than 0.6452 39.58 0.8768 5.48 21.45 6.65 100 From table 5.9228 0.0912 0.5 we can conclude that Gas Pressure.Table 5.
769 0.6 Response table for S/N ratio of MRR Level 1 2 Effect (∆) Rank Gas Pressure -2.561 -2. Gas Pressure: 5 Bar Current: 150 A Cutting Speed: 600 mm/min Arc Gap: 4mm .511 1 -3.843 -2.673 -2.5 CONFIRMATION TEST From S/N ratio and mean of each level of every factor we will construct response table for MRR and Surface Roughness which are given below: Table 5.449 2 From above response table and main effect plot of MRR we can conclude that the optimum condition for MRR is.267 3 Current -2.5. A1B2 C2 D2 i.031 -2.582 0.075 4 Cutting Speed Arc Gap -3.051 1. e.940 0.
Table 5.32 0.7 Response table for S/N ratio of Surface Roughness Level 1 2 Effect (∆) Rank Gas Pressure -11. the next step of the Taguchi approach is to predict and verify the enhancement of quality characteristics using the optimal parametric combination.09 3 Current -11.19 2 Cutting Speed Arc Gap -10.17 -11.70 01. is the mean of the multi-response signal-to noise ratio at the optimal level.79 -10.33 2.18 1 -11. The estimated Optimum S/N ratio using the optimal level of the design parameters can be calculated: where .84 -10. e.Similarly we can create the response table for S/N ratio of Surface Roughness.15 4 From the above table and main effect graph of Surface Roughness we can say that optimal levels of parameters for SR are A2B2C1D1 i. is the total mean of the multi response signal-to-noise ratio.16 -12.65 1. and . Gas Pressure: 6 Bar Current: 150 A Cutting Speed: 400 mm/min Arc Gap: 2 mm After evaluating the optimal parameter settings.
80625) = .673 + 2. Yopt = 0.80625) + (-2.80625) + (-2. Based on the above equation the estimated multi response signal to noise ratio can be obtained.6525 And the corresponding value of MRR = Yopt = 2 = 0.q is the number of the process parameters that significantly affect the multiple quality characteristics.1.769 + 2.5.80625 + (-2.051 + 2.1Prediction of Optimum Value of MRR: Here = -2.582 + 2.80625 Optimum S/N Ratio for MRR = -2. 5.6829202 Predicted Optimum Value of MRR.2.8264 g/sec .80625) + (.
70 + 11.245) + (-11.245 + (-10.8006 µm .8433 Predicted Optimum Value of SR Yopt = 2.5.65 + 11.11.245) = .10.245) + (.945 And the corresponding value of SR = Yopt = 2 = 7.17 + 11.245 Optimum S/N Ratio for SR = -11.5.2Prediction of Optimum Value of SR : Here = .8.245) + (-10.16 + 11.
8331 Table 5.452 2.8 Confirmation Test Result for MRR Number Pressure (Bar) Current (A) Cutting Speed Gap (mm) (mm/min) MRR (g/sec) 1 2 3 5 5 5 150 150 150 600 600 600 4 4 4 Average 0.Once the optimal value of MRR and SR is predicted.635 .8254 0. Table 5.8345 0.8393 0. the final step is to verify the improvement of the quality characteristic using the optimal level of the process parameters.672 2.780 2.9 Confirmation Test Result for SR (Ra) Number Pressure (Bar) Current (A) Cutting Speed Gap (mm) (mm/min) SR (µm) 1 2 3 6 6 6 150 150 150 400 400 400 2 2 2 Average 2.
81% Percentage = 5. .81% improvement in MRR and also Surface Roughness reduce with 5.91% So we can say that there is 0.After performing experiment as per given optimum levels for MRR and SR following results obtained: Table 5.8331 Surface Roughness (µm) Optimum value of Experimental result of A2B2C1D1 = 2. This finding indicated that the experiments in this study possess excellent repetitiveness and great potential for future reference.91%.8264 A1B2C2D2= 0.8006 A2B2C1D1= 2.10 Summary Table for Results MRR (g/sec) Optimum value of Experimental result of A1B2C2D2 = 0.635 Percentage = 0.
1. In contrast. a and b. and coefficient b referred to as the slope.1 INTRODUCTION TO REGRESSION ANALYSIS The term multiple regression literally means stepping back toward the average. Bivariate regression Multiple regression 6. It was use by British mathematician Sir Francis Galton . The equation for a linear relationship between two social science variables would be written as: Y=a+bX+e Where e represents the presence of error . relationship between variables in social sciences is almost always inexact. The value whose value is influenced or is to be predicted is called dependent variable and the variable which influences the values or is to be used for prediction is called independent variable. determine respectively the precise height and steepness of the line. In regression analysis there are two types of variables.1 Bivariate Regression: Two variables X and Y may be related to each other or inexactly.Regression analysis is a mathematical measure of the average relationship between two or more variables in terms of the original units of the data. Thus coefficient a represent to as the intercept or constant. variables frequently have an exact relationship to each other. In physical sciences. The simplest relationship can be expressed by Y=a+bX Where the values of the coefficient. Regression analysis can be done in two ways.6.
Of course this assumption is not always correct. we commonly assume linearity.predicted Summing the prediction error for all observation would yield a total prediction error (TPE). The question arises out of all possible line we should choose. As we know Multiple Regression Analysis is use when more than two parameters are used .2 The least Squares Principle In postulating relationship among social science variables. From the scatter plot we will calculated prediction error is calculated as: Prediction error = observed error .in my thesis there are 4 parameters so I will consider multiple regression analysis. These values of a and b are our least square estimates.1. In multiple regressions analysis linear equation is given by: Where b.Some terms which are considered in multiple regressions are discussed below: . c etc are called partial slope .6. Least square principle tells us or identified best line which can fit the model for example.
3 Residual The difference between an observed value (y) and its corresponding fitted value (ŷ) is called residual. . This could be easily understood as the distribution of estimates of the regression coefficient that would be result if sample of given size were drawn repeatedly from the population and coefficient calculated from each sample . Residual values are especially useful in regression and ANOVA procedures because they indicate the extent to which a model accounts for the variation in the observed data.4 Sampling Error When estimating a population parameter from a sample it is important not only to derive a specific value but also estimate the effect of the sampling error on the estimate. the estimates of the coefficient from a series of random samples of population will not be identical but instead will distribute themselves around a mean .6. the estimated standard deviation of the sampling distribution of a regression coefficients is known as a standard error and is denoted by 's'.1. the estimates . 6. To accomplish this it is necessary to consider the concept of a sampling distribution for a regression coefficient.1.Because coefficient estimated from random samples will deviate from populations values by varying amounts.
1. 6. It can also been shown that R –sq is the correlation between actual and predicted value.1.In multiple regression if there is collinearity among variables .6. Its value lies between +1 and 0.6 Multicollinearity Multicollinearity means that none of that independent variable or linear variable is perfectly correlated with another independent variable or linear combination of other independent variable . It will reach maximum value when dependent variable is perfectly predicted by regression equation. then regression surface not even define (because in multiple regression instead of two plane we will consider multiple plain) as there are infinite number of surface that fit the observation equally well and there fore it is impossible to drive unique estimates of the intercepts and partial slope coefficient for the regression .5 Coefficient of Determination R2 This is called coefficient of determination indicates explanatory power of any regression model.
097676 F 6.017397 0. .097676 MS 0.2 FIRST ORDER LINEAR MODEL FOR MRR With the help of Minitab 15 Software.028086 0.050) indicates that the regression model is significant.000621 cutting speed (mm/min) + 0.2% which indicate the high significance of the model.000167 current (A) + 0.6.0.value of Regression equation (0.452 .2% R-Sq(adj) = 60.0205 Gas Pressure (Bar) + 0. The regression equation for MRR is MRR (g/sec) = 0. I developed first order linear model and ANOVA Table.069590 0.005 Model Adequacy Check: The P.0505298 R-Sq = 71. The coefficient of determination (R2) which indicates the goodness of fit for the model so the value of R2 =71.0194 arc gap (mm) S = 0.002553 0.81 P 0.8% Analysis of Variance Source Regression Residual Error Total DF 4 11 15 SS 0.
10 -0. the assumptions regarding the residual were not violated and the residuals are normally distributed.10 This graph indicates that the residual follows a straight line and there are no unusual patterns or outliers. .05 0. As a result.05 0.1 Normal Probability Plot for Residuals of MRR Normal Probability Plot (response is MRR (g/sec)) 99 95 90 80 Percent 70 60 50 40 30 20 10 5 1 -0.00 Residual 0.Graph 6.
.0.6.001 Model Adequacy Check: The P.91 .00897 current (A) + 0.3 FIRST ORDER LINEAR MODEL FOR SURFACE ROUGHNESS The regression equation for SR (Ra) is: SR (Ra) = 4.0.5% R-Sq(adj) = 69.value of Regression equation (0.3% Analysis of Variance Source Regression Residual Error Total DF 4 11 15 SS 4.00445 cutting speed (mm/min) + 0.0894 MS 1.001) indicates that the regression model is significant.0183 arc gap (mm) S = 0.47 P 0.430 Gas Pressure (Bar) .1797 0.352974 R-Sq = 77.3705 6.7189 1.5% which indicate the high significance of the model.1246 F 9. The coefficient of determination (R2) which indicates the goodness of fit for the model so the value of R2 =77.
6 0.8 -0.8 This graph indicates that the residual follows a straight line and there are no unusual patterns or outliers.6 -0.2 0.2Normal Probability Plot for Residuals of Surface Roughness (Ra) Normal Probability Plot (response is SR (micro m)) 99 95 90 80 Percent 70 60 50 40 30 20 10 5 1 -0.4 -0. As a result.0 Residual 0. .4 0.Graph 6. the assumptions regarding the residual were not violated and the residuals are normally distributed.2 0.
Bhopal. The mechanical properties of Stainless Steel (316L) are given in appendix B .For this I consider regression analysis . For this L16 orthogonal array is considered . Current Flow Rate. In order to perform minimum experiments Taguchi method has been employed.Machining process is carried out on Plasma Arc Cutting Machine number B/0/2163 which is available in the Fabrication Division of BHEL.Experiment results and various response graph for MRR and SR (Ra) were obtained and there optimum value were also considered. As per literature review Gas Pressure. . Cutting Speed and Arc Gap were considered as most important parameters. In chapter 6 mathematical modeling were done . For this 16 specimens of Stainless Steel material were prepared which were easily and cheaply available in the scrap yard of Fabrication Division of BHEL.1 SUMMARY Objective of this study is to find out optimal condition of Plasma Arc Cutting Machine for maximizing MRR and minimizing Surface Roughness (Ra).7. I considered MRR and Surface Roughness (Ra) as two most important outputs. Mathematical equation both for MRR and SR (Ra)were obtained by regression analysis. Bhopal.
.91%.635 = 5.8006 A2B2C1D1=2.81% improvement in MRR and also Surface Roughness reduce with 5. Gas Pressure: 5 Bar Current: 150 A Cutting Speed: 600 mm/min Arc Gap: 4mm The optimum levels of parameters for minimizing Surface Roughness (Ra) are A2 B2 C1 D1 i.2 RESULTS The Optimum levels of parameters for maximizing MRR are A1 B2 C2 D2 i. e.8331 = 0.8264 A1B2C2D2=0.7. Gas Pressure: 6 Bar Current: 150 A Cutting Speed: 400 mm/min Arc Gap: 2 mm After performing experiment as per given optimum levels for MRR and SR following results obtained: Table 7.91% So we can say that there is 0. e.81% Surface Roughness (µm) Predicted value of Experimental result of Percentage A2B2C1D1 = 2.1 Results Before and After Optimisation MRR (g/sec) Predicted value of Experimental result of Percentage A1B2C2D2 = 0. This finding indicated that the experiments in this study possess excellent repetitiveness and great potential for future reference.
P values less than 0. Current and Cutting Speed are significant terms. The equipment systems. In this case speed is significant model term. Another factors influence for MRR is equipment system and environments. the MRR response also increase significantly. . the significant parameter for optimum MRR calculation is Cutting Speed and the significant parameters for Surface Roughness calculation are Gas Pressure. . Values greater than 0.2 shows the analysis result for MRR. Table 4.1000 indicate the model terms are not significant. Although some parameters are not significant but we able to improve MRR and Surface Roughness. In the main effect term graph for pressure and current are increased for minimizing Ra.7 shows the ANOVA result for Ra. torch vibration. nozzle gag (blocking air). In the model term graph for speed is increase for MRR. As per regression analysis the mathematical models of first order for MRR and SR (Ra) are showing significant results.0500 indicate model terms are significant.7. It can determined that when the level of the factor increased. In this case there are Gas Pressure. Table 4. and the speed is decreased for minimizing Ra. Current and Cutting Speed. Speed factor are most important to measured maximize Metal Removal Rate (MRR) for Stainless Steel (316L) Material. and working table area are each factors influence MRR.3 DISCUSSION As per analysis.
This is the basis work where Plasma Arc Cutting was utilized to perform the material removal process at finishing stage. the Taguchi method provides a systematic and efficient methodology for determining optimal parameters with far less work than would be required for most optimization techniques.2% and for Surface Roughness (Ra) is of R-sq 77. Bhopal to cut materials such as Stainless Steel and Nickel-Base Alloys. Mathematical equation for MRR of first order is of R-sq of 71.5% which is acceptable. Plasma Arc Cutting Machine is widely utilized in BHEL.This is because we must take large number of observations either by considering L27 0r L32 orthogonal array with 3 level designs. Current flow. The confirmation experiments were conducted to verify the optimal parameters. Cutting Speed and Arc gap of machine. As shown in this study. . From ANOVA of MRR we can say that some parameters are not making any significant effect .7. The Plasma Arc Cutting (PAC) machining of Stainless Steel (316L) has been performed with the application of combination with design of experiment (DOE). It has been shown that Material Removal Rate (MRR) and Surface Roughness (Ra) can be significantly improved in the Plasma Arc Cutting process using the optimum level of parameters.4 CONCLUSION This thesis has presented an application of the Taguchi method to the optimization of the machining parameters of Plasma Arc Cutting Machine.The PAC parameters studied were how to have setting for the parameter such as Gas Pressure.
5 SCOPE OF FUTURE WORK Based on result and discussion summary. and change advance material such as brass and bronze then compare the result obtained. Voltage. Using other methodology in the same material of study to compare the results obtained such as Response Surface Methodology. angle. . this project had archive it main objective but an improvement still can done to improve more on the Metal Removal Rate (MRR) and Surface Roughness (Ra) of parts by features. and Genetic Algorithm etc. Based on this work many improvements can be made and the scope can also be widened. Study for manual calculation for other method in DOE to improve knowledge and skills. Some of the suggestions to improve the result include the replication of the model which can reduce the variations of the data and increase the reliability of the data. Grey Relational Analysis. material dimension. No interaction is considered so we can consider interaction by applying L27 or L32 with 3-level design this will improve optimum condition as compare to L16 considered in this work. add the parameter such as Kerf. Following are suggestion for future work: Using Plasma Arc Cutting system.7. Also side clearance and thermal effect on material and work piece like Heat Affected Zone (HAZ) can also be considered to study the effect on properties of work piece.
Int. Ye Li (2009) Taguchi Based Six Sigma Approach to Optimize Plasma Arc Cutting Process: an Industrial Case Study.3. 2009. 1.K. Chen. J. Mahapatra S S (2007) An evolutionary approach to parameter optimisation of submerged arc welding in the hard facing process 462 Int. Hatala Michal Faculty of Manufacturing Technologies of the Technical University of Košice Štúrova The Principle of Plasma Cutting Technology and Six Fold Plasma Cutting. July 1 . European Journal of Scientific Research . Uttarwar S S. Vol. 6. Asiabanpour Bahram (2009) Optimising the automated plasma cutting process by design of experiments. J. No. No. Hussain Altaf (2010) Surface Roughness Analysis in Machining of GFRP Composites by Carbide Tool (K20). Vol. International Journal of Advanced Manufacturing Technology 41: 760-769. 1. Rapid Manufacturing. 5. Mahapatra S S. 4. Chopade I K. Patnaik Amar (2006) Optimization of wire electrical discharge machining (WEDM) process parameters using Taguchi method. Joseph C. 2009. Manufacturing Research. London. 2007 . Effect Of Voltage Variation On MRR For Stainless Steel EN Series 58A (AISI 302B) In Electrochemical Machining: A Practical Approach. U. 2. 2.BIBLIOGRAPHY Journals Referred 1. International Journal of Advanced Manufacturing Technology. 7. 2OHProceedings of the World Congress on Engineering 2009 Vol II WCE 2009. 4. 3. 5th International Multidisciplinary Conference.
Ding Yeng Chen (2006). 8. Lajis Mohammd Amri (2009) The Implementation of Taguchi Method on EDM Process of Tungsten Carbide.ISSN 1450-216X Vol.2 (2009). O. Yang W.609-617. pp. European Journal of Scientific Research ISSN 1450-216X Vol. pp. Tarng Y S. Uey-Jiuh Tzou.33 No.26 No. Umut Atici (2006) Investigation of the Effects of Plasma Arc Parameters on the Structure Variation of AISI 304 and St 52 Steels. and Strip for Pressure Vessels and for General Application.(1993).4 (2009). Journal of Material and Manufacturing Processes. Martikainen. J.. Abdul Kadir Gullu.455-467 13. ASTM Standard Designation: A 240/A 240M-09a.Invetigation of the effect of welding parameters on weld quality of plasma arc keyhole welding of structural . 9.330-337 10.and Moisio. H.41 No. Sheet. Taiwan (R. Standard Specification for Chromium and Chromium-Nickel Stainless Steel Plate.) 14. C. pp.T.I. 12. International Journal of Material and Design 27: 1157-1162 11. European Journal of Scientific Research ISSN 1450-216X Vol.84-98.K.J. Kandananond Karin (2009) Characterization of FDB Sleeve Surface Roughness Using the Taguchi Approach. 13:3. (1998) Application of the Taguchi Method to the Optimization of the Submerged Arc Welding Process.1 (2010). " Application of Taguchi Method in the Optimization of Cutting Parameters for Turning Operation" Lunghwa niversity of Science and Technology.
Books Referred 16. Inc. Plasma Arc Cutting Theory. Welding Principles and Applications: Sixth Edition: Inc. Design of Experiment Manual.(2000). and Lin. 20. 182-203. . J.Inc. R. p. Miller Electric Mfg. (2001). Montgomery C. Inc. Roy. 17. Jeffus Larry (2003). S & R Schmid. S. Ross J. Philip (2008) Taguchi Techniques for Quality Engineering 4th Edition Tata Mcgraw Hill Publication.steels. 19.Welding Journal 72(7): 329-340 15. Douglas (2007) Design and Analysis of Experiments 5th Edition: John Wiley & Sons.L. 21. The Use of the Orthogonal Array with Grey Relational Analysis to Optimize the Electrical Discharge Machining Process with Multiple Performance Characteristics. Lin.K. Minitab 15 Statistical Software. p. Kalpakjian. Journal of Machine Tools Manufacture. Co. Parweld Plasma Process Synopsis September 2001 Release 18.L. 164-165 23. Publication.Design of Experiment Canada: John Wiley & Sons.Manufacturing Engineering and Technology:4th Edition UK: Prentice-Hall. (2001). p. C. 76-86 22.
PlasmaEquipment. Technical System Consideration.com/knowledge/articles/content/plasma. http://www. Plasma Cutting.wikipedia.com/topic/plasma-torch?cattechnology 26.http://www. Plasma Cutting. Cutting Process.com/technology.hypertherm.wikipedia.com/global/en/education/processes- plasmacutting.4 April 2008 34.Websites 24.answers. Cutting Torch.centricut. 31.asp 35.esab.airgas.uk/j32k/protected/band_3/jk51. Quality.lincolnelectric. Plasma http://www.welding-advisers. Benefits Of Plasma Arc Cutting.apogee.htm .http://www.net/et/eftcpat.co.com/Cutting-torch. Plasma(Physics).twi. http://www.com 27. http://www.aws.org/wj/2003/02/024/#A. 28.asp Cutting.org/wiki/Plasma_(physics)#History 29. http://en. http://www.org/wiki/Plasma_cutting 25.html 33. http://www. 30.html 32.htm. http://www. Plasma Cutting.com/TA_CutQualityProblems. http://tristate. http://en.
http://en. Roughness.htm 37.co.howstuffworks.za/tech/tech_grade_316. Stainless Steel Properties. http://www.fanagalo.htm .36.org/wiki/Roughnesshttp://home.com/plasma -cutter1.wikipedia.


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