Advanced friction modeling for sheet metal forming

Abstract

The Coulomb friction model is frequently used for sheet metal forming simulations. This model incorporates a constant coefficient of friction and does not take the influence of important parameters such as contact pressure or deformation of the sheet material into account. This article presents a more advanced friction model for large-scale forming simulations based on the surface changes on the micro-scale. When two surfaces are in contact, the surface texture of a material changes due to the combination of normal loading and stretching. Consequently, shear stresses between contacting surfaces, caused by the adhesion and ploughing effect between contacting asperities, will change when the surface texture changes. A friction model has been developed which accounts for these microscopic dependencies and its influence on the friction behavior on the macro-scale. The friction model has been validated by means of finite element simulations on the micro-scale and has been implemented in a finite element code to run large scale sheet metal forming simulations. Results showed a realistic distribution of the coefficient of friction depending on the local process conditions.

Multi-Scale Friction Modeling for Manufacturing Processes: The Boundary Layer Regime

“…A non-linear plastic load model has been developed inspired by the ideal-plastic load model proposed by Westeneng [4,15]. Besides, Westeneng proposed an ideal-plastic stretching model [4,15] which has been used in this research.…”

“…Westeneng [4] extended the model of Challen & Oxley to describe friction conditions between a flat workpiece material and multiple tool asperities. For this purpose, statistical parameters (asperity height distribution, asperity density and mean radii) have been used to make the translation from single asperity scale to multiple asperity scale [15]. However, statistically based contact models tends to lose its applicability under fully plastic contact conditions.…”

“…The height of the paraboloid is determined by equating the volume of the indented contact patch by the volume of the elliptical paraboloid. The geometrical characteristics of this equivalent contact patch are indicated in Figure 4c (15) in which a shape factor χ has been introduced [22]. Since the 3-D nature of the contact patch is captured by this expression, anisotropic surfaces can be handled as well.…”

Advanced Friction Modeling in Sheet Metal Forming

“…In this section a brief explanation of the theory will be provided. For a detailed derivation of the following equations, the reader is referred to [4]. The asperities of the rough surface are modeled by bars which can represent arbitrarily shaped asperities.…”

Experimental Evaluation of Draw Bead Coefficient of Friction

“…At the microscopic level, friction is due to adhesion between contacting asperities and the ploughing effects between asperities. The ploughing effects between asperities and adhesion DOI 10.12776 effects between boundary layers are the main factors causing friction in the boundary lubrication regime [12]. In the lubrication regime the contact pressure is carried by the lubricant flow and asperities.…”