Influence of Die Machining Operation on the Friction Condition in the Cold Forming Process

The texture of a die surface plays an important role in the tribology of metal forming processes. The surface texture is defined by surface roughness and its orientation, which is influenced by the manufacturing process. In this research, the effects of various die machining operations on the friction condition in the forming process of CK45 steel are investigated using ring compression tests. The dies are fabricated through six machining operations, including horizontal and vertical milling, electrical discharge machining, grinding, polishing, and turning. The ring specimens are compressed by parallel die plates. The effects of different parameters such as machining method, lubrication condition, and deformation percentage on the friction coefficient are investigated using design of experiments and analysis of the results. Finite element simulation is also used to obtain the calibration curves in the ring compression test. The obtained results reveal the significant effect of the die machining process on friction coefficient. In addition, the maximum and minimum friction coefficient values are associated with electrical discharge machining and grinding with polishing, respectively. Furthermore, it is found that despite the approximately same values of mean roughness (R-a ) in vertical milling, electrical discharge machining, and turning, different friction coefficients are obtained due to the dissimilar mean roughness depth (R-z ), surface hardness, and surface texture of the inserts.