A Process-Centered Approach of lubrication and wear in cold and hot metal forming
Résumé
Cold and hot metal forming processes are families of manufacturing processes where tools apply compressive forces to shape a workpiece to a given geometry. These compressive forces generate high contact pressures and high plastic strains near the workpiece surface. They lead to shear stresses due to friction, and an increase of local temperature due to plastic stain and friction sliding. Consequently, specific lubricants are required to control friction at the workpiece/tool interface, to cool down tool surfaces to avoid overheating and a drop of tool hardness, and to protect workpiece and tool surfaces. Numerous lubricants have been developed to fulfill these requirements: liquid lubricant based mineral or vegetal oils, most of them containing chlorine, phosphorus, or sulphur additives, solid lubricant such as complex conversion coatings or polymers, etc. Tendencies are to limit the use forming lubricants containing hazardous compounds or based on non-renewable resources, such as mineral oil, and to turn to new environmentally friendly lubricants. Nonetheless, selecting a new lubricant remains a challenge for the manufacturer. Choosing a lubricant not adapted to the forming process may have dramatic consequences, untimely wear of tools, surface defects on the workpiece, resulting in an increase of the production cost.
The keynote focuses on liquid lubrication and how lubricant may affect the quality of the final workpiece.
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