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Numerical simulation of lubricated wire rolling and drawing

A numerical framework for simulation of lubricated contact between two rough surfaces in metal forming simulations is presented in this work. The framework is implemented as a contact condition for the hyperelastoplastic finite volume deformation solver within the foam–extend software package, a community driven fork of the open source OpenFOAM software. The main features of the model are: calculation of film thickness, hydrodynamic pressure and shear stress of the lubricant, estimation of asperity contact pressure and contact area ratio for a realistic rough surface, solution of the heat transfer problem considering the liquid film shear stress and asperity contact, and calculation of pressure– and temperature–dependent transport properties of the lubricant. The lubricant pressure is calculated by solving the Reynolds equation, using the Finite Area Method of discretisation. A mass–conserving cavitation algorithm is implemented for the liquid lubricant in the finite area formulation. Contact between the asperities is calculated with a deterministic elastic–perfectly plastic contact model using a measured surface roughness profile or a three–dimensional surface scan as an input. Temperature increase of the lubricant is calculated using a two– dimensional thin film energy equation, discretised with the Finite Area Method. Each model is verified and validated against available analytical, other numerical or experimental results. Very good agreement is achieved between the calculated values and results from the literature. In order to assess the accuracy of the complete numerical framework, extensive verification and validation is performed on point contact test cases, where film thickness and friction coefficients are compared to experimental results of ball–on–disc tribometer tests. The study shows that acceptable accuracy can be achieved using the implemented numerical framework, provided that complete information regarding lubricant transport properties is available and surface roughness has been measured. Finally, the numerical framework is tested on industrial–grade wire drawing and wire rolling simulations. The framework is capable of calculating hydrodynamic pressure, film thickness, asperity contact pressure, contact area ratio, and other fields useful for designing a metal forming process. The increase of computational time when using the lubricated contact model is around 40%, compared to the non–lubricated penalty contact model. The increase is acceptable considering the complexity of the implemented model. Stability of the lubricated contact model is shown to be similar to the stability of the penalty contact.

Numerical analysis, Metal forming, Lubrication, Reynolds equation, Finite Area Method, wire rolling, wire drawing, OpenFOAM, Finite Volume Method

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