Contact simulation for predicting surface topography in metal forming

Abstract

A surface contact model that takes account of flattening, roughening and tool elastic microwedge effects on workpiece surface is developed. The model can be implemented in FEM codes to predict the final surface qualities of the products in metal forming. As an example, the proposed model has been combined with a membrane finite element code of sheet metal forming process to predict the contact area ratio, surface roughness and mean asperity spacing. Numerical results showed good agreement with the experiments. KEY WORDS: contact model, asperity flattening, roughening, microwedge, metal forming Nomenclatures A contact area ratio (fractional contact area) @A increasing rate of contact area ratio; dA/dt @A S component of @A induced by smoothing effect @A M component of @A induced by microwedge effect @A R component of @A induced by roughening effect B geometric matrix c adhesion coefficient C coefficient of microwedge model C R coefficient of surface roughening model d distance between original surface centerline of workpiece and tool surface dA 0 differential undeformed area D nondimensional distance between original surface centerline of workpiece and tool surface; nondimensional gap D m material matrix D p AKDP E Young's modulus of tool material E t tangent modulus of workpiece E w

Prediction of surface topography in lubricated sheet metal forming

“…Due to the nature of plastic deformation, it is quite possible that there is a complex interaction among these mechanisms; and secondly, such a relationship must be represented in an incremental form. However, Yang and Lo [12] and Lo and Yang [15] already validated that the simplest form of linear, superposition type is able to capture the characteristics of lubricant flow, variation of contact area, and friction coefficient in their experiments. Therefore, we adopt their model and decompose the increasing rate of the contact area ratio into:…”

“…After the increasing rate of the contact area ratio is known by substituting Eqs. (12) and (13), and Eq. (14) into Eq.…”

“…(11), the contact area at next step will be obtained. For more detailed description of the asperity deformation theory used in this paper, please refer to the paper of Yang and Lo [12] and Lo and Yang [15].…”

“…Though their output is in good agreement with the experiment, however, to date the mechanism of reducing the contact area is still not thoroughly understood. Yang and Lo [12] boundary of G C non-dimensional asperity height distribution function C 0 new C after asperity deformation c asperity height distribution function codes to predict the final surface qualities of the products in metal forming. Numerical results agree well with the experiments for the surface roughness of workpiece by the proposed model.…”

A Refined Friction Modeling for Lubricated Metal Forming Process

“…However, Lo and Yang [23] already validated that the simplest form of linear, superposition type is able to capture the characteristics of lubricant flow, variation of contact area, and friction coefficient in their experiments. Moreover, Yang and Lo [28] developed a surface contact model that takes account of flattening, roughening and tool elastic microwedge effects on workpiece surface. Yang and Lo also showed that the linear relationship is able to predict contact area ratio, surface roughness and mean asperity spacing of the products in metal forming and the numerical results showed good agreement with the experiments.…”