Abstract
The combined Coulomb constant shear friction law is widely used in commercial and research software for the finite-element analysis (FEA) of metalworking and is naturally more flexible and hence, more relevant to real-life manufacturing than the individual Coulomb and constant shear friction laws. In this work, a new mathematical model of coefficients in the Coulomb constant shear friction law for extruding a metal through narrow V-shaped channels with small convergence angles has been developed and evaluated and compared with laboratory measurements. The extrusion of the model material (lead) through narrow V-shaped channels with small convergence angles varying from 0 to 3.5 degrees has been studied. The Coulomb friction coefficient µ and the constant friction factor m appear to be independent of the dimension ratio and are influenced mostly by roughness and range from µ = 0.363 (with lubricant) to µ = 0.488 (without lubricant) and from m = 0.726 (with lubricant) to 0.99 (without lubricant). The relative length dominated by the Coulomb friction law is less than 1%, and the Coulomb’s coefficient of friction can be approximated as ½ the constant shear friction factor for all tested cases. The developed method and algorithm can be used in both FEA of manufacturing processes and efficiency tests for lubricants used in metalworking.
Highlights
Introduction iationsThe critical importance of friction for metal-forming processes and its adverse impacts on wear resistance of dies are well-established
Since friction in the large contact area may differ greatly depending on the conditions of the die surface and changes in the contact pressure, the Coulomb constant shear friction law is better suited for the description of friction than either the Coulomb friction law or the constant shear friction law, and the friction coefficients derived from analysis of the occupancy of narrow V-shaped channels in the present study are more relevant to the real-life manufacturing than those obtained using other methods
The accurate description of friction laws and their coefficients is key for the accurate assignment of the friction boundary conditions
Summary
Introduction iationsThe critical importance of friction for metal-forming processes and its adverse impacts on wear resistance of dies are well-established. Non-linear FEM simulations employ phenomenological friction models [13,14], allowing us to uniquely set the boundary conditions for stresses at the workpiece–tool interface via the friction coefficients that greatly improve the convergence of numerical solutions for strongly deformed parts of complex geometries at reasonable computational costs. In view of these circumstances, the correct choice of the friction model and accurately determining the corresponding friction coefficients are a must in the case when a real-life manufacturing process is being simulated
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