Tribology of Manufacturing Processes - Presses des Mines

4 th International Conference on Tribology in Manufacturing Processes - ICTMP 2010while the mineral oil does not [87]. Differential Thermal Analysis (DTA) proves that thechlorinated paraffin oil as well as P1 reacts chemically with the punch material, PMHSS, at elevated temperature implying that it is likely that a thin boundary film isestablished on the punch. The poor performance of the polymer coating is to beexpected due to the small punch clearance (10-15 μm) and the fact that this semi-solidfilm lubricant has difficult access to the clearance area between punch and die.Figure 16 : Maximum punch stem friction stress during backstroke as a function ofstroke number. Curve legends refer to lubricants listed in Table 3.7 CONCLUSIONSThe increased focus on environmental issues in industrial production as well as on externalenvironment has resulted in important developments of new, environmentally benignlubricants for metal forming. As regards cold forging new, single bath lubricant systemsdepositing a double layer of an inorganic salt and a wax on the slug surface have proven veryefficient in substituting phosphate coating and soap lubrication. In warm and hot forging theblack lubricants have been abandoned by many industries now using white lubricants oneither polymer base, carvone base or liquid glass base. The huge amount of lubricantconsumption in rolling has promoted the application of water based emulsions, whichlubricate almost as well as the oil based and have better cooling efficiency.In sheet metal forming pre-lubrication at the rolling mill with polymer coating is replacing inprocesslubrication with mineral oils. Regarding more severe sheet forming of materials26