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Metal Forming and Lubrication

Abstract : In metal forming (cold or hot), localized compressive force is applied on the workpiece through a forming tool. This force leads to generate high contact pressures at the workpiece/tool interface and as a result the workpiece is deformed to deliver a desired shape and surface of the product. In this deformation process, high shear stresses are developed with an increase in local temperature due to frictional effect and plastic strain. But for protection of tool geometry and product quality, lubricant is normally used to control friction at workpiece/tool interface and cool down the tool to avoid overheating and hardness drop. However, the load carried from one surface to another passes through several stages, the basic contact conditions of which are defined by lubrication regimes. With a general outline on the type and the chemical composition of lubricants applied in metal forming, this article addresses the relevant friction models and establishes links with the lubrication regimes. The incorporated models are related to friction stress under sticking and sliding conditions, shear stress to the sliding velocity as derived from the adhesion theory, crushing of surface asperities by flat and rough tool sliding against a flat workpiece, and load carrying ability of liquid lubricant. Based on friction reduction and control of final surface roughness and shape of workpiece, mixed and boundary lubrication regimes are considered for estimating the shear and friction stresses developed in metal forming processes. Guidelines for choice of appropriate models to calculate the stresses for the prevailing forming conditions are furnished. A combination of Coulomb’s and Constant Friction models is also suggested for incorporation into the finite element software solutions as a generalized friction model for reliable numerical simulation of forming operations. Thus the article is expected to be a useful source of comprehensive information and strategies for selection of appropriate lubricant and determination of the optimal values of parameters relevant to metal forming.
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Submitted on : Tuesday, April 26, 2022 - 9:54:43 AM
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André Dubois, Abu N.M. Karim. Metal Forming and Lubrication. Reference Module in Materials Science and Materials Engineering, Elsevier, 2019, 978-0-12-803581-8. ⟨10.1016/B978-0-12-803581-8.03565-7⟩. ⟨hal-03651843⟩



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