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Testing a closed loop forming algorithm on a part created by discrete die stretch forming

Sheet metal forming is a very old process and there is a significant amount of empirical data concerning the material properties, cost and quality. However, the process is still run very inefficiently and does not take advantage of the present technology. Currently, tooling is a trial and error science which takes months to build and thousands of dollars to finance. Forming over a reconfigurable, discrete die cuts down lead times to hours and reduces cost tremendously. Parts can now be formed, measured, and input to a controller which will change the shape accordingly to create the proper part. The closed loop shape control algorithm developed at MIT has been in use for many years in matched die forming. The discrete matched die press has been retrofitted to accomplish stretch forming. During the course of this thesis the stretch forming machine was built and a new control system was introduced. The new stretch forming machine had to be characterized to find out the repeatability of the process, as well as the machine capabilities when forming. Once characterized the closed loop shape control algorithm had to be tested on the stretch forming operation. A measurement technique which employs the use of a coordinate measurement machine (CMM) had to be developed. The raw data from the CMM was manipulated so the minimum number of data points necessary were taken to recreate the part shape. The actual algorithm was then tested and the part shape converged on the defined reference shape in two cycles of the controller. Thesis Supervisor: David E. Hardt Title: Professor of Mechanical Engineering