Methodology for service life increase of hot forging tools
Résumé
Hot forging is widely used in the manufacturing of automotive components. The high production rate induces severe thermomechanical stresses in the tools. The lifetime of dies is commonly driven either by wear or thermal cracking. This paper describes the methodology that has been applied to gain understanding of the thermomechanical stress field in a cemented carbide punch used for the manufacture of airbag container type parts. The stresses are the result of a combination of purely mechanical stresses due to the forging process, and thermomechanical stresses induced by the thermal cycling of the punch surface during successive hot forging and waiting periods. Simulation results have been validated as a result of experimental investigations. The results show that in the critical area subjected to thermal cracking, the thermomechanical stress contribution is as high as 75% of the total stress field. As a consequence, it has been determined that an increased tool life could be expected by a global modification of the nominal hot-forging process parameters, i.e. by the modification of biller temperature and forging rate.
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