Experimental study on the effect of deforming material and speed on friction and lubrication by tip test

Abstract

Choosing the proper metal forming lubricant for nonferrous metals such as aluminum, copper, and brass has become a difficult and complicated decision. The effects of deformation velocity and the influence of deforming material were determined in the two sets of experiments carried out using a single punch with a roughness magnitude Ra of 0.17 lm and four lubricants such as grease, corn oil, VG100, and VG32. In the first set, two different deformation speeds of 0.1 and 1mm/s were used for cylindrical specimens made of aluminum alloys of 6061-O, 1050-O, and copper alloys tests using a counterpunch die of roughness magnitude Ra of 0.08 lm. In the second set of experiments, cylindrical specimens made of aluminum alloys of AA2024-O and AA6061-O and three deformation speeds of 0.1, 1, and 5mm/s were used to evaluate the performance of each lubricant under increasing ram speed, but with a roughness magnitude Ra of 0.63 lm. All the lubricants show reduction in maximum load with increasing deformation speed except grease which shows a rise in the maximum load from zero to a maximum at a deformation speed of 1mm/s and then descends gradually to a minimum load at a speed of 5mm/s for AA2024-O and AA6061-O. This load reduction seen with grease as lubricant is probably due to thermal softening; therefore grease will not be considered a desirable lubricant under increasing deformation speed because of the adverse effects on the tooling. The present findings show that tip test can be utilized to select an appropriate lubricant for a particular alloy. It reveals that none of the tested lubricants can be used for copper alloy as all the lubricants show increasing measured load for increasing speed magnitude. However, of the liquid lubricants (corn oil, VG100, and VG32) considered, corn oil shows as the best lubricant for cold forging operations of aluminium 6061-O, 1050-O, and 2024-0 under increasing speed magnitude. Also, the tip test has been able to differentiate among materials.