Abstract
Because of its superior friction and abrasion properties, DLC films are anticipated for application to components of various kinds as a sliding mechanism. In the field of plastic working, the currently used lubricant shall be replaced from a high-viscosity one to a lowviscosity one to simplify washing and cleaning of the products. The ultimate goal in plastic working is to establish a lubricant-free or dry processing technique to meet ecological goals. One steel pipe joining technique is slip-joint technique, which can join two pipes by insertion of a pipe end having a smaller diameter into one with a larger diameter. However, this technique requires a high-viscosity lubricant to form the pipe ends, thereby necessitating washing of the ends before joining. This study addresses the possibility of applying a DLC coated die on the dry forming of the ends of zinc plated steel pipe. Heat-treated SKD11 of HRC60-HRC62 hardness was used as the die material. To ascertain the die surface influence on coating, surfaces of two kinds were prepared: one turned and one sandblasted using greencarborundum grains. Then 3-5 um thick DLC films were synthesized on the die surfaces using an RF plasma CVD system with CH4 gas as the precursor. A dry forming experiment was conducted using a zinc-plated steel pipe to increase the 70 mm inner diameter. Results show no defect such as adhesion of zinc on the die or fracture of the DLC film after forming of 200 pipes.
