Improvement of seizure resistance in ironing of stainless steel cup with cermet die having fine lubricant pockets

摘要

Seizure resistance was improved by using a TiCN-based cermet die having fine lubricant pockets by polishing a shot-peened surface. ATiCN-based cermet die having a fine polished surface without lubricant pockets was applied to ironing of stainless steel and aluminium alloy drawn cups to investigate the ironing limit. In the TiCN-based cermet die, additional surface coating is not required because of making of hard TiCN having low friction. For a comparison, TiC-coated WC-Co, non-coated WC-Co and tool steel dies were employed. With both stainless steel and aluminium alloy drawn cups, the cermet die exhibited the highest seizure resistance due to low friction. Then, the seizure resistance was accelerated using a TiCN-based cermet die having fine lubricant pockets by polishing a shot-peened surface. The shape of the lubricant pockets was controlled to improve seizure resistance. The seizure resistance for the die having fine lubricant pockets was higher than that for a polished surface having very fine roughness, because friction reduces by squeezing liquid lubricant from the pockets during ironing. The mechanism of the superior seizure resistance of the die having lubricant pockets was examined from the remaining amount of the lubricant on the surface of the ironed cups. It was found that the TiCN-based cermet die having fine lubricant pockets is effective in preventing the seizure in the ironing of stainless steel drawn cups. (C) 2016 Elsevier B.V. All rights reserved.