Lehrstuhl für Fertigungstechnologie, Universität Erlangen-Nürnberg

Basic investigations on the measurement of the real prestressing conditions of cold forging tools by ultrasonics

Datum: 01.03.2006



  • Prof. Dr.-Ing. Dr.-Ing. E.h. mult. Dr.h.c. M. Geiger
  • Prof. Dr.-Ing. habil. K. Steinhoff, Universität Kassel

In cold forging the load on the die significantly depends among others on the quality of the prestressing conditions that counteract the process load. Mainly due to manufacturing tolerances the prestressing conditions can be inhomogeneous or insufficient. This leads to a prestressing situation that deviates from the ideal supposed one, which can have early tool failure as a consequence. Aim of this work therefore was the development of an ultrasonic measurement system for the non destructive determination of the real prestressing conditions in cold forging tools with high sensitivity and resolution. The measurement principle is based on the amount of reflection of ultrasonic waves at the interface, which consists of the real contact area (RCA) and remaining gaps. The intensity of the reflection reveals information about the contact status between die and prestressing ring that is a result of the contact pressure as well as the usually not totally completed flattening of the surface asperities of both metallic contact partners. In this work, the basics for the non destructive measurement of the real prestressing conditions of cold forging tools were developed. This enables the securing of prestressing conditions that have a significant influence on tool life already before the usage in the press. These results have a significant meaning for the process stability and therefore for the production planning.