Selection of Cold Forging Lubricants by Tip Test

Determination of reliable friction data associated with a given lubrication system is core to successful process design and simulation by FE analysis. The dependable performance evaluation of cold forging lubricants is largely dependent on the suitability of the test procedure to accurately model the severe deformation conditions that occur in actual cold forging operations. The tip test experiment emulates these practical conditions (severity of deformation and surface expansion) found in most cold forging operations better than the ring compression test. Also, the differential frictional condition at the punch/billet and billet/counter punch interfaces makes it more authentic for selection of cold forging lubricants than the double cup extrusion test. For the test, cylindrical specimens made of aluminium alloys of 6061-O, 1050-O and copper alloys and four lubricants such as grease, corn oil, VG100 and VG32 were used. Two different deformation speeds of 0.1 and 1mm/s were used for the test to evaluate the performance of each lubricant. It is seen that, using tip test, we can simultaneously know the interface frictional conditions (high or low) at the punch/billet and billet/counter punch interfaces without resulting into elaborate instrumentation. That is, the farther or closer the tip distance is from the die wall, the higher and or lower is, comparatively, the frictional stress at the punch/billet than at the billet/counter punch interface. It is found that in the choosing lubricant for cold forging operations the type of alloy and deformation speed should be properly considered. The present study shows that tip test can, however, be utilized not only to differentiate among lubricants performance but also select appropriate lubricant for a particular alloy under increasing speed magnitude. For increasing deformation speed, the best of the four lubricants investigated for annealed copper, AL6061-O and AL1050-O is corn oil.