Abstract
The galling process remains one of the least understood phenomena in metal forming. The transfer of material from a work-piece onto the tool surface can cause an evolutionary increase in friction coefficient (COF) and thus the use of a constant COF in finite element (FE) simulations leads to progressively inaccurate results. For an aluminium work-piece, material transfer, which has history and pressure dependency, is determined by a dynamic balance between the generation and ejection of wear particles acting as a ‘third body’ abrasive element at the contact interface. To address this dynamic interactive phenomenon, pin-on-disc tests between AA6082 and G3500 were performed under step load change conditions. The COF evolutions, morphologies of the transfer layer and its cross-section were studied. It has been found that contact load change will disequilibrate and rebuild the dynamic balance and high load will increase the generation and ejection rate of third body and vice versa. Moreover, based on the experimental results, an interactive model was developed and presented to simulate the dynamic formation process of the aluminium third body layer under load change conditions, enabling multi-cycle simulations to model the galling distribution and friction variation.
Highlights
Galling is a form of surface damage due to adhesive wear between two or more sliding solids and is commonly found in metal forming operations resulting in work-piece material adhering to the tool surface [1, 2]
After the contact load decreased to 2 N, the increasing rate of COF had reduced between 100 laps to approximately 570 laps
Experiments with a step change of contact load were conducted between AA6082 and G3500
Summary
Galling is a form of surface damage due to adhesive wear between two or more sliding solids and is commonly found in metal forming operations resulting in work-piece material adhering to the tool surface [1, 2] This phenomenon occurs frequently in the forming of ‘soft’ materials such as aluminium sheet metal against steel tooling material, where after repeated operations, a transfer layer originating from the work-piece forms on the tool surfaces [3,4,5,6,7]. This transfer layer may lead to products with low surface quality and damage functional surfaces on the tools. These transferred tribo-materials known as ‘third bodies’, to distinguish
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