Abstract
In the present research, the friction and wear behaviour of a hard coating were studied by using ball-on-disc tests to simulate the wear process of the coated tools for sheet metal forming process. The evolution of the friction coefficient followed a typical dual-plateau pattern, i.e. at the initial stage of sliding, the friction coefficient was relatively low, followed by a sharp increase due to the breakdown of the coatings after a certain number of cyclic dynamic loadings. This phenomenon was caused by the interactive response between the friction and wear from a coating tribo-system, which is often neglected by metal forming researchers, and constant friction coefficient values are normally used in the finite element (FE) simulations to represent the complex tribological nature at the contact interfaces. Meanwhile, most of the current FE simulations consider single-cycle loading processes, whereas many metal-forming operations are conducted in a form of multi-cycle loading. Therefore, a novel friction/wear interactive friction model was developed to, simultaneously, characterise the evolutions of friction coefficient and the remaining thickness of the coating layer, to enable the wear life of coated tooling to be predicted. The friction model was then implemented into the FE simulation of a sheet metal forming process for feasibility study.
Highlights
In the metal forming industry, finite element (FE) simulations are widely used for process analysis and parameter optimisations
As the current FE simulations are mostly performed in single cycles only, this differs from the cycles experienced by industrial metal forming tools, which are normally operated for a large number of cycles
The friction model constants of the hard coating used in the interactive friction model are determined from experimental results by using a numerical integration code
Summary
In the metal forming industry, finite element (FE) simulations are widely used for process analysis and parameter optimisations. After a certain number of cyclic loadings, the tools can be damaged due to wear It is of vital importance for engineers to understand the tribological behaviour in metal forming processes to enable tooling wear life prediction after cyclic loadings. It is of great importance to carry out FE simulations for multi-cycle loading to predict the tool life in metal forming processes. Previous tribological tests as well as models reviewed have focused on the wear and changes of the friction coefficient with both internal and external variables such as contact pressure, sliding speed etc. Most of these models can only model the constant friction coefficient at the steady-state period. In this paper, the friction coefficient and wear mechanism of a hard coating are modelled by a novel friction/wear interactive model developed in [17] to characterise the evolution of the friction and predict the coated tool life
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