Tribological systems for cold forging of stainless steels

The aim of this project is the forming of stainless steels without conversion layers. This is realized by the adaptation and further development of single-layer lubricant systems. For this purpose, the tribological loads and temperatures during forming are determined and currently available lubricant systems are characterized.

Motivation

Stainless steels are characterized by excellent corrosion resistance and high strength and are therefore nowadays frequently used in screw production.However, products with complex geometries that require higher degrees of deformation due to more complex geometries are currently difficult to produce with cold forging processes. When forming stainless steels, in addition to the high mechanical tool loads, the tribological system in particular must be taken into account. Due to the higher strength of the material, the tribological loads (above all normal contact stresses and temperatures) increase in the contact zone [1]. On the other hand, the zinc phosphate coating commonly used in the processing of low-alloy steels cannot be used as a lubricant carrier layer for these materials. Alternatively, an oxalate layer in combination with chlorparaffin is typically used as lubricant. Both are regarded as critical due to the high environmental pollution of the coating. Alternative ecologically advantageous single-layer lubricant systems have not yet been sufficiently researched in the forming of stainless steels.

Temperature problems during cold forging of stainless steels

Approach

Based on a numerical process simulation, the tribological loads of three cold extrusion processes are determined. To increase the simulation quality, the heat transfer coefficient for the temperatures and contact normal stresses occurring in the forming process is determined experimentally in a test setup. Subsequent tribometer tests serve to characterize current lubricant systems under the previously determined loads and form the basis for the further development of single-layer lubricant systems. In addition to single-layer lubricants, lubricant systems with a conversion layer (oxalate) and lubricant as reference are used. In final validation tests, the further developed lubricants are examined in real cold extrusion processes. A tool temperature control allows the setting of temperature ranges close to those of the industry as well as optimized temperature ranges.

Acknowledgement

The IGF-Research Project 19803 N, supported by the GCFG, is funded in the scope of the “Progamm zur Förderung der Industriellen Gemeinschaftsforschung” (IGF) via the German Federation of Industrial Research Associations (AiF) by the German Ministry for Economy and Energy as decided by the German parliament.

Furthermore, we thank all involved companies for the support of the research project.

  • Arnold Umformtechnik GmbH & Co. KG
  • baier & michels GmbH & Co. KG
  • Carl Bechem GmbH
  • Chemetall GmbH
  • CPM GmbH
  • Eifeler Vacotec GmbH
  • fischerwerke GmbH & Co. KG
  • Hilti Corporation
  • KAMAX Holding GmbH & Co. KG
  • Räuchle GmbH + Co. KG
  • RIBE Verbindungstechnik GmbH & Co. KG
  • Schondelmaier Presswerk GmbH
  • SSF-Verbindungsteile GmbH
  • Wezel GmbH Kaltumform-Technik
  • ZWEZ-Chemie GmbH

 

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