A Study of Evaluating Methods on Lubricants for Cold/Warm Forging of Steels

The tribological conditions between tools and work pieces on cold/warm forging of steels are very severe because of high contacting pressure, high temperature, and large surface extension of work pieces. Therefore, many lubricants and estimating methods have been developed. But even using these methods, it's difficult to estimate that lubricants have a good effect on production or not. We have estimated many lubricants by ring compression and spike forging test to find new coating which is substitutes for conventional one such as Zn-phosphate and Na-stearate coating or oxalate and resin coating on cold/warm forging of steels. We selected some lubricants by spike forging test which gave large extension to work pieces and agreed with the result of backward extrusion qualitativly, and further evaluated the lubricants by heading test and mass production test of bolts by multi stage cold bolts former. As a result of tests, we found the new coating method which was over coated by Ca-stearate with MoS2 or Ca-hydroxide with PTFE on the inorganic salts precoating such as K2SO4 or Na2B4O7·5H2O.