Investigation of the influence of reversing stroke patterns on workpiece properties during deep drawing with servo-press technology (ServoDrawing)

 

Deep drawing is a forming manufacturing process in which a three-dimensional workpiece is produced from a sheet metal. The sheet is drawn into a die using a punch. The edge of the sheet is pressed against by a blank holder. Deep drawing is used to produce simple geometries such as sinks and bathtubs as well as complex geometries such as body parts and powertrain parts in the automotive industry.

The process limits of deep drawing are limited by material and process properties. During the forming process, the material is exposed to a variety of stress conditions which determine the success of the manufacturing process. Typical defects in deep drawing are wrinkling in the area of the hold-down and tearing of the sheet metal. The use of servomechanical presses allows the use of any ram path in the forming process, which in previous investigations has been able to reduce the formation of wrinkles in deep drawing.

In the ServoDrawing project, the cause-effect relationships between the process parameters (hold-down force, lubricant quantity, punch speed, number of reversals, amplitude of reversals) and the workpiece quality (wrinkle formation, tear) in deep drawing with intermittent strokes are investigated. The investigations are carried out on a common deep drawing steel (DC04), a fine grain structural steel (S420MC) and a dual phase steel (DP800).

First, the friction between tool and workpiece at different relative speeds, contact normal stresses and lubricant quantities is analyzed using strip drawing tests. Rotationally symmetrical cups are then deep-drawn on a servomechanical press, varying the process parameters. With the aid of a friction model calibrated on the basis of the strip drawing tests and resolved in time and space, the deep-drawing tests are also mapped in a finite element (FE) model within the Abaqus simulation software. The results of the experiments and the FE analyses are synthesized into an explanatory model for the cause-effect relationships.