DK_Einfluss von Werkzeugspannmitteln auf die Werkstückqualität bei Stanz- und Tiefziehprozessen

Influence of tool clamping devices on the workpiece quality in shear cutting and deep drawing processes (EFB 15/114; IGF 18602N)

 

Motivation

The variation of the type and number of clamping devices changes certain properties of the tool such as the rigidity and vibration behaviour. Based on scientific investigations it is known that tool vibrations increase the punch wear. Nevertheless, neither tool manufacturers nor providers of clamping devices offer technically specific and clear instructions for the design of the tool clamping situation. From a scientific point of view the effects of the tool clamping situation on the forming process has not yet been investigated and at the same time offers great potential for process optimization.

Figure 1: Schematic representation of the tool deflection (l.) and tool vibration
Figure 1: Schematic representation of the tool deflection (l.) and tool vibration
 

Aim

The aim of the research project was to measure and evaluate the influences of tool clamping systems on process variables in deep drawing and shear cutting processes. The analysis of this influence was used for the systematic selection of suitable clamping devices. In addition, the possibilities and limitations of an innovative, magnetic tool clamping system – to influence the tool bahaviour and to optimize the process quality – were shown. Concerning conventional clamping devices, possibilities for influencing the tool properties were shown in order to determine their optimum use.

Figure 2: Classification of clamping devices depending on the type of the force application
Figure 2: Classification of clamping devices depending on the type of the force application
 

Methodical approach

To achieve the desired research results, the tool geometry and tool vibration were determined by measurements during the forming process. By varying the tool clamping situation and by the comparison with a reference state, the context of the clamping situation and the impact on the process could be indicated. Parallel to the experimental analysis a numerical model of the experimental tools and processes was built in order to be able to investigate tool areas, which were inaccessible for the application of measuring technology.

Significant results

It turned out that a stiffer tool clamping situation leads to smaller tool vibration movement. High stiffness is achieved by the use of conventional clamping systems, such as clamping bolts and quick-release fasteners, by increasing the number of clamping points as well as by shortening the lever arm between the process force and the clamping point. The size of the biasing force, on the other hand, has a subordinate influence, as long as the required minimum clamping force is not undershot. The stiffest connection between the tool and the press and thus the smallest tool vibration movement was achieved by the use of magnetic clamping plates.

With regard to the wear of the cutting punch, it was found that, that the use of conventional clamping systems leads to an abrasive wear, while using the magnetic clamping plates solely adhesive wear was observed.

Measurements of the flux density showed that, when using the magnetic clamping plates, there are no magnetic fields in the working space of the press that are harmful to human health. Moreover, the flow densities measured at the stamping scrap were too low to cause mutual clogging or clumping. With regard to these two aspects, the use of magnetic clamping plates is suitable.

Acknowledgment

PtU would like to thank the German Federation of Industrial Research Associations (Arbeitsgemeinschaft industrieller Forschungsvereinigungen “Otto von Guericke” e.V. AiF), the European Research Association for Sheet Metal Working and the following companies for their support.

  • BMW AG (München)
  • GOM GmbH (Braunschweig)
  • Heitkamp & Thumann Group (Crimmitschau)
  • Hilma-Römheld GmbH (Hilchenbach)
  • Hubert Stüken GmbH & Co. KG (Rinteln)
  • Lenzkes Spanntechnik GmbH (Lüdenscheid)
  • Scheuermann und Heilig GmbH (Buchen)
  • Siebenwurst Werkzeugbau GmbH (Zwickau)
  • Systeme + Steuerungen GmbH (Grafenau)

In addition, the company Bruderer is committed to providing the press BSTA 810.