Search Results

Deep drawing with hydraulic counter pressure has numerous advantages compared to conventional deep drawing. Hydromechanical deep drawing is a capable process for producing complex and tapered-shaped stamping parts as well as parts with excellent surface quality, i.e., outer body panels. Due to the low costs of dies, compared to the conventional deep drawing dies, hydromechanical deep drawing has to be considered especially for low volume production. This paper deals with press- and die concepts for hydromechanical deep drawing. The die concepts can be equipped with an integrated multi-point cushion system. It is also possible to build a press with a multipoint cushion system integrated into the press. In this case, the die is less expensive but the press is more complex. The counter pressure pot can be product specific as a part of the die or as a part of the press investment.

The costs for development and production of draw dies for car outer panels are extremely high and should be reduced. Furthermore it is necessary to reduce the time for developing, designing and producing the dies for the production of parts. This paper discusses new press techniques, die designs and an adjustment program for press operators. The trend goes to single action presses with CNC-controlled multipoint cushion systems in the press table and to special designed dies. These systems lead to a more robust and reproducible forming process with improved product quality. This paper deals with: Cushion Systems, New Binder Designs for Draw Dies for Sheet Metal Automotive Parts, New Computer Program to Adjust the Blankholder Forces of Modern Hydraulic Cushion Systems of Single Action Presses and Pressure Measurement for Detecting the Pressure between the Blank and the Binders of Draw Dies for Sheet Metal Automotive Parts.

In sheet metal stamping some industrial applications have shown that it is possible to achieve larger drawn depth by using a pulsating blankholder force. In deep drawing, areas with and without tangential stresses have to be distinguished. Areas without tangential stresses can be described by the strip drawing test. Areas with tangential stresses are described by using a deep drawing die for the production of cups which are axisymmetric. With the strip drawing test it could be shown that it is possible to reduce the increase of the friction force, caused by adhesion. Another effect is the reduction of the peak of the transition of static to dynamic friction. It was shown by experimental research, that the wrinkle height of parts, produced with pulsating blankholder force is in the range of the wrinkle height of parts produced with a constant blankholder force which is equal to the maximum force of the pulsation.

In deep drawing and drawing of car-body parts the friction conditions have a great influence on process limits, on the robustness of the production process and on the quality of the produced parts. Beside the used lubricant, the friction conditions are influenced by the topography of the sheet metal surface and of the tool surface. Therefore the roughness of these surfaces has to be measured. It is well established to measure the roughness of sheet metal surfaces with a stylus device. But more and more optical measurement techniques are upcomming. There are for example instruments on the market which can characterize the roughness profile along a line with an infra-red laser beam. Doing this for parallel lines the topography can be plotted in three dimensions. The disadvantage of all those systems is that the samples to be measured have to be cut from the sheet or from the coil and that is not possible to measure directly the surface of heavy forming tools.