PEO coating as lubrication means for SPIF of titanium sheet: characteristics and performance

Abstract

Single point incremental forming (SPIF) is a cost effective alternative of conventional sheet forming processes. In the current study, a lubrication method for SPIF of a pure Ti sheet was proposed. The plasma electrolytic oxidation (PEO) process was employed to deposit a porous coating on the Ti sheet to carry the particles of MoS2 powder (a solid lubricant). First, a coating with the pore size of the order of lubricant particles (i. e, 6-8 mu m) was developed by varying the PEO parameters. Second, a variety of tests were conducted to characterise the coating. The results revealed that the coating was mainly composed of titanium oxide with the average thickness of 24 mu m, the average coating-substrate bonding strength of 12 N and the maximum compact hardness of 0.86 GPa. Further, the coating offered the least friction (0.2) when it was lubricated with the paste of MoS2 and grease with the proportion of 4 : 1. Last, the on-job performance of coating by lubricating with the said paste was examined by forming Ti components. It was found that the proposed lubricant and its application method were effective for a wide range of forming conditions.