engleski

Friction in metal forming – the coefficient of friction μ and the factor of friction m

Abstract Friction is sometimes helpful. For example, high friction on the punch surface helps increase reductions in deep drawing and ironing. In a few instances it has to have at least some small value, as in rolling where it assures entry of the workpiece into the roll gap and helps maintain rolling without skidding of the workpiece. However, in most instances friction is preferably reduced to zero by the introduction of a lubricant. In the vast majority of metalworking processes the workpiece is deformed by means of a contacting die. The pressure required for deformation generates a normal stress to the die surface, and movement of the workpiece relative to the die surface generates a shear stress at the interface. Thus a classical tribological situation arises, with friction at the die-workpiece interface, and with potential for wear of both die and workpiece materials. Mitigation of these effects then calls for the introduction of a lubricant. In contrast to nonmetalworking situations, deformation of theworkpiece results in a sometimes very substantial enlargement of surface areas. Thus new, fresh metal surfaces are exposed, and the lubricant must protect not only the old but also the new surfaces. The success or failure of such lubrication has important consequences on the quality of the issuing product, and also on pressures, forces, energy requirements, and often the very possibility of plastic deformation itself. For these reasons, the field of friction, lubrication, and wear (tribology) in metalworking has been the subject of many investigations.

friction; the coefficient of friction; the factor of friction

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