Rebound of stamping parts

There is springback after sheet metal forming, and rebound is one of the main defects in stamping production. Proper design of the mold is an effective way to reduce springback. The formation of any conventional three-dimensional profile generally uses the trial-and-errox method to compensate for springback deformation. This method requires the operator to have high skill and rich experience, and the success or failure is accompanied by certain contingency. For the complex aluminum body cover, it takes more than half a year to compensate for the rebound time in the mold trial stage. Therefore, the traditional "trial and error method" consumes a lot of money and time. With the improvement of computer hardware and software technology, the finite element numerical simulation technology has been successfully applied to the field of thin plate forming, which can accurately predict various defects in the forming of stamping parts. If the sheet metal forming springback prediction is accurate and the numerical iterative method is used to complete the compensation process less than the "trial and error method" used in actual production, then the numerical simulation method will be used to save the mold development capital and shorten the new product development. cycle. This paper proposes a "cycle displacement compensation" design die method based on numerical simulation iterative process, and applies it to the mold compensation process of a small aluminum alloy three-dimensional sheet metal forming; a reasonable mold shape is obtained through multiple cycles calculation, and finally the shape is obtained. High precision workpiece.

The mold design force method based on the numerical simulation to compensate the rebound of the cyclic displacement compensation method "circular displacement compensation" is to use the finite element numerical simulation to calculate the springback amount to correct the mold profile. The steps are: the knot from the initial mold profile The point displacement is reversed by subtracting the corresponding node rebound amount from the simulation calculation, and the mold profile for compensating for the rebound is obtained. The metal sheet is first formed by using a tentative mold (for the first cycle, the shape of the test mold is the same as the workpiece), and the shape of the workpiece after the springback is formed. This workpiece is compared with the target workpiece. If the existing shape error exceeds the allowable value, the shape error is subtracted from the mold shape to obtain a new mold profile. In the next cycle, the sheet metal will be formed from this new trial mold profile. If the shape of the shaped workpiece and the target workpiece error still exceed the allowable value, the shape error of the cycle will be subtracted again from the test mold profile, and the updated mold profile will be obtained, and the next cycle will be entered until the shape of the formed workpiece fulfil requirements. The specific calculation process is as follows: firstly, the convex and concave model surface is established according to the shape of the target workpiece, and the application software ANSYS/LS-DYNA is used to dynamically simulate the forming of the book; the unit node coordinates of the forming front sheet and the formed stamping parts are formed. The node displacements are respectively stored in the data file, heel.dat and form.dal, and the data file Loan.dat and the data file sheet.dal are added to obtain the node coordinate data file part.dal of the target workpiece; dynamic explicit simulation is performed The obtained shaped workpiece with preserved shape and stress is simulated by static implicit unloading process, and the obtained rebound displacement of the node is stored in the data file springback. dat, and the corresponding nodes of part.dat and springback.dal are displaced. The coordinate data is added to obtain the shape coordinate of the workpiece shape after the shape rebound, and the data file newpart.dal is stored; comparing the files part.dat and newpart.dat, the profile error of the test workpiece and the target workpiece can be obtained; If the profile error between the test piece and the target workpiece is large, the springback.dat will be subtracted from the new part. dat by a certain ratio, and the workpiece shape file newform.dat which should be formed after the rebound is obtained. In order to establish a new stamping die shape, in the 3D CAD software UG, the workpiece coordinate point cloud in newform.dat is used to generate a sheet having an actual thickness, and part of the surface of the picking sheet is offset to generate a mold profile. The obtained new mold profile data file was transferred to the analysis software ANSYS/LS-DYNA in IGES format for a new forming-rebound-error analysis process. The following is an example of the process and effect of this type of mold surface design based on springback prediction.