Adjusting the Contact Surface of Forming Tools in Order to Compensate for Elastic Deformations during the Process

Nowadays, despite powerful simulation programs, the tool design process still contains manual and not reproducible work. In specific, the manual die spotting is mostly dependent on the workers experience and consumes a lot of time. A large potential to reduce time and costs is seen by decreasing the die maturing. The paper introduces an approach to obtain deep drawing tools from FE simulation with LS-DYNA, which need less additional manual maturing until good parts can be manufactured. Therefore, the current tool design process was analyzed and it was found out, that not properly assessing elastic tool and press properties in FE simulations in one of a the causes that lead to additional die spotting effort. Hence, a methodology was developed to compensate for the effects of those elastic properties. Depending on their intensity, afore mentioned machine and tool properties are included in the FE model. Based on former research work at the IWM the effects of elastic deformations and dislocations of the die surface on the final shape of the part are calculated. Derived from the calculated deformations, a transformations matrix is calculated and a new die surface is obtained after a few iterations. The new die surface has the same shape under load like the initial die surface without load. The new method was tested through an experimental set-up, which allowed an excessive deformation of the die under load. This experiment does not reflect the reality but serves for general demonstration purposes of the compensation approach. As expected the simulation and experiment show a massive impact of the die deflection on the draw-in of the manufactured part. The die deformation affects the distribution of the blankholderforce on the part. It was found a higher pressure on the die corners and lower pressure in the centre. By means of the compensation method, the die surface was adjusted to achieve that the die surface under load is the same as the initial surface without deformations. The experiments show that the final shape of the part, which was drawn with the compensated die, is very close to the shape, which was predicted without calculating the die deformation.

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