3D Printing: Controlling the Quality, Strength, Amount of Material Used and the Cost of 3D Prints

22 Aug

Do You Need to Get Better Quality or Have Faster 3D Printing Speed
3D printing is often a process where you may need to choose if you either need something printed fast or with higher quality. The larger the object you want to 3D print and the higher the quality you want, the more time it will take for the 3D printer to finish the job. Larger maximum quality prints can easily take from a few hours to even a day, though most of the time you will most likely be printing smaller objects and with not so high quality, so that they will need from a couple of minutes to an hour or two.

In-house 3D printing is often also used for the so called process “rapid prototyping” as it allows a product design to be printed in relatively short time, and then have it inspected and maybe tested. If there are some corrections required they can be done to the model and then have a new print with the applied change and so on. With a 3D printer available at your disposal corrections can be made and applied much faster than having to send the 3D model somewhere to be made physically and sent back to you.

Because rapid prototyping (as the name implies) and because it actually makes for a much faster prototyping of something with help of a 3D printer, while you are designing it, than it would take otherwise, some people believe that 3D printers are very fast. Yes, they can be fast for small objects, but still printing larger and more complex designs with higher quality does take quite a lot of time. So be prepared to wait and it is not a wise idea to just leave your 3D printer unattended while it is printing something for hours, especially when you are just starting. When you get more experience and you are sure there should be no potential problems you might be more confident, though still it is wise not to leave the printer do something while there is nobody around for long periods of time.

There are three general levels of detail when talking about the most common FDM/FFF consumer 3D printers, these depend on the thickness of the layers that will be used to build the physical object from the 3D model you have. These are with a thickness of 0.1mm, 0.2mm and 0.3mm (other values might also be available) and the thicker each layer is, the faster the 3D print will be ready as you will need less layers of thermoplastic material to make it. However the thinker the layer height you use, the lower the resolution and the detail level of the final object will be. As I’ve already told you – faster speed or higher quality, you can’t have both at the same time.

To get an idea on how the final 3D printed object will look like with the settings you have chosen in the 3D printing software (the slicer) you can just hit the Preview button and the program will try to estimate how long it will take to print it as well as will provide you with good estimate how the resulting object will look like. The numbers you get are a rough estimate of course, thought they are usually close to the actual ones, so you can use them as a pretty accurate reference. If you need something printed faster, you can just change the settings and Preview again to see if your changes were enough to speed up the process. Even though the resolution is pretty much the most influential parameter that can result in faster or slower printing time, other parameters such as the use of raft or support material as well as the infill percentage can also affect the time needed.

Different 3D printer software may give you different previews of how the 3D printed object will look like, but these usually don’t look as good as the final object will, mostly because you often zoom while in Preview mode. They can still be useful for inspecting how the resulting physical model should look like and if there might be some issues printing it as the preview very closely represents how and where the printing head of the device will move to create the 3D print.

This is the step where you can also find if there are some potential issues with the 3D model you have, it has some problems such as non-manifold edges or flipped surfaces these will cause problems in the print preview even though everything might seem fine on the initial 3D model preview in the software. I’ll be talking about the issues in the 3D models you use as a source for 3D printing an object in some of the next part of the series as well as provide some useful tips on how to avoid and fix these.

A useful tip for new users in getting to know what their 3D printer is capable of is to choose a relatively simple 3D model of something and print three copies from it, each with a different layer height or resolution/quality. This will give you a very good idea on what to expect from the device when used with different layer height both in terms of quality and in terms of time required for the print. Again the finer the resolution, the more time it takes as the 3D Printer needs to lay double or triple the number of layers it would usually need for the lowest level. Higher resolution makes for better print quality as the lines of each layer are thinner and not as noticeable as when using thicker layers.

When you learn what to expect from your device in terms of printing quality and speed with different settings after you use it for a bit, then it will be easier to select the right level of detail you may need. For the moment however going for the medium level is usually a good starting point for novice users as you get a good balance between speed and quality. Though often you might need to use a lower quality initially just to get more things printed in less time as you are experimenting with different things learning about your 3D printer, this is also fine.

How to Define or Change the Strength of a 3D Printed Object
If you remember in one of the earlier posts of the series I have explained the basic parameters you set for the printing of the model, one of these is the so called Number of Shells, or Outline/Perimeter Shells or just Shells or something along the lines. So I’ll just quote myself on that first and then continue to actually show you what it actually means and how you can control the process.

Number of Shells represents the number of outer shells or walls that you are going to have on a 3D printed object before the inside part starts. The outer shells are fully solid while the inside part can be solid or semi-hollow based on the Infill percentage you have set. Normally the default value of 2 or 3 should be enough and you won’t have to change it.

Here you can see a print preview of an example object that is set to print with 10 Number of Shells. This is pretty much pointless and way too overkill, but just as an example on how this setting affects the actual object that you are going to get 3D printed. As you can see there are 10 solid layers on the outside wall of the object and after them starts the infill material structure that is semi solid. This way you are going to get a very thick wall making the 3D printed object very strong and tough on the outside.

This is a bit overkill as using just two or three layers as an outside wall should be enough in pretty much most of the cases. If you go for a thicker outside wall you are going to use more filament material and the printing time required will be increased, so you should do that only when you really need much stronger outside walls. The infill structure inside should be more than enough to provide additional strength and help with the support of the top layers instead of having a hollow insides of the object.

How Much Filament to Use When 3D Printing Something
There are multiple factors in play that ultimately decide how much material is needed for the priming of a 3D model and you have control over these with the settings you can change for the printing process itself. Normally the larger the 3D print is going to be, the more material will need to be used, but that may not always be the case. The main factor that can influence that is the Infill parameter, again going to quote myself here.

Infill is a percentage value that represents how solid a 3D printed model should be. Going for 100% means that the inside of the 3D printed object will be completely solid, going for 20% for example will result in having a semi-hollow structure inside that will be reinforced with hexagonal or square patterns. Most 3D prints are just fine with between 10% and 20% percent infill as it is enough to provide good strength while also reducing the needed material and the extra print time that a fully solid insides will require.

The Infill material or the internal structure of a 3D printed object has two main roles – to provide additional structural strength and to act as an inside support material. Because of these two important roles you cannot just go with a hollow insides of a model, or to be more precise you should not do it unless for a specific reason. You can remove all of the infill material by just setting a 0% Infill or if you want completely solid model inside you can just go for 100%. Either of the two extremes is rarely used as they can cause some issues, or it will take too much time and extra material, so most of the time you will be just fine with a small percentage of infill like 10% to 20%.

On the comparison image above we have a Preview of how the same simple object will look inside if printed with just 10% or with 50%. Using just 10% should still be able to provide decent additional strength while still acting as a decent support material for the upper layers and it would take just about 16 minutes (at maximum quality) to print with about 3.7 grams of material used. Using 50% is already going a bit overkill, unless you really need it, and will require 21 minutes for printing (5 more) as well as more than double the amount of filament with about 7.7 grams needed. It is up to you do change the Infill setting as you like or need, just don’t go too high or too low without a reasons and most of the time you will be just fine with the recommended small range for that parameter.

How to Calculate the Filament Cost of a 3D Print
Ok, so you have just 3D printed something cool, but how much in materials did it cost you? You can easily do the calculation of the cost for the material used thanks to the 3D printing software telling you an estimate on how much filament it will need when in the Preview mode (you probably noticed that on one of the above images). Again it might not be 100% accurate, but should be very close to the actual amount used. For better accuracy you can just measure the weight of the 3D printed object yourself using digital scales for example. You would also need to know the cost of the filament material you have used for the print, so it is a good idea to remember how much you paid and what was the weight of the spool you bought. Below you can see an example calculation:

Price of 1 kg spool of filament – 30 USD or EUR
1 kg = 1000 grams, so 1 gram costs 0.03 cents
Filament used for the 3D print 7 grams
Total cost in filament 7 grams times 0.03 cents equals 21 cents cost

Of course this is a simple calculation of the cost of the filament you need for a specific 3D print, smaller things are actually quite cheap to print, though larger builds may end up much more expensive. For the total cost of the print you need to also take into account the electricity used for the time it took printing and also the amortization cost of the 3D printer itself. To the total cost will be a bit higher than what you have spent for the filament along, but again it will not be that much especially for smaller 3D prints that do not require a lot of time to print and don’t use a lot of filament.

Since you already know how to calculate the cost of the filament needed for a 3D print before you actually even started printing the 3d model you have prepared and you know how to vary the amount of the filament needed via the different printing parameters you should be able to also influence the final cost. This is important if you actually want to start a small business for printing some 3D stuff for example, or just to properly manage your cost and plan when to stock on more filament spools.

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