Yoshinari Tsuchiya

Damage behavior and tribo-characteristics of DLC-SI coating for forming die

Improvement of not only lubricity but also the quality of die materials is desired in the fields where the difficult-to-form materials such as aluminum, stainless steel and high tensile steel sheets are formed. Aluminum is also difficult-to-form material because of its seizure property. Recently DLC (Diamond Like Carbon) which has quite low friction is used and VC coating by TRD (Thermo-reactive Deposition and Diffusion) process is reevaluate in forming high intensity materials. But it is entirely inadequate to adopt the evaluating methods for characteristics of exfoliation resistance. The method used most widely is the scratch test. However, practical limit is not clear to use for judging method of selecting coatings. Therefore the damage behavior accompanies the scratch of various coatings is observed and evaluated in conditions of some kinds of base metal, difference of hardness, the coating thickness and lubricating. Through these observations the DLC-Si coating, which Toyota Central R and D Labs., Inc. developed, is evaluated to have superior adhesion performance. And the ironing type tribo-test and the ball penetration test are conducted. The results of these tests are as follows; 1) DLC-Si coating shows low friction under dry lubricating condition ironed high-tensile strength steel sheets. 2) It shows low forming load in the case of using mineral oil without additives. There are less gallings on tool and work metal.Copyright