M. Dubar

Friction and Wear in Metal Forming: 25 Years at LAMIH UMR CNRS 8201

Since the beginning of the 90’s, research activities focused on friction and wear in metal forming have been developed at the LAMIH UMR CNRS 8201 in Valenciennes. Specific methodologies have been designed to optimize a given forming process (bulk forming process or sheet forming process). These methodologies involve prototype benches which have been built to reproduce contact conditions encountered in manufacturing plants by taking specimens and contactors from the real industrial workpieces and tools. The evaluation of the friction coefficient added to the fine analysis of the surfaces have helped us to better understand friction and wear during processes. These facilities have been settled by numerical simulation at meso and macro scales by means of finite element methods. So, this paper is the sum up of the output of these methodologies with a specific focus on wear and lubrication, at room and hot temperatures.

Towards a Fracture Energy Based Approach for Wear Prediction of WC-Co Tools in Industrial Cold Heading Process

Tools sustainability and reliability is a key axis for economic competitiveness of companies in the field of cold heading of steels. This durability is currently limited by the damage occurring at the contact surfaces.The main objective of this study is to propose an energy based approach to understand the mechanisms of deterioration of the WC-Co carbide tools.Firstly a finite element simulation of an industrial cold heading process is run in order to identify the contact condition at the tool workpiece interface. Main results are the stress, strain and temperature distributions in the near surface of the tools. A particular attention is paid to the location of critical areas that may limit the tool life.Jointly, characterizations of the morphology of the worn surfaces are performed. SEM observations added to EDS and roughness measurements are done from midlife to end of life of industrial tools. Friction tests are performed with the Upsetting-Sliding Test involving contactors extracted from real worn tools to identify friction coefficients in order to provide the evolution of the friction coefficient according to the wear state of the tools. Finally, the correlation between the numerical analysis and the experimental measurement is discussed to attest to the relevance of the energy fracture based model to explain the deterioration of the tribological conditions.

Toward Oxide Scale Behavior Management At High Temperature

Oxide scales grow freely on bare metallic surface under environmental conditions such as high temperature and oxygen. These act as thermal and mechanical shields, especially during high hot forming processes (>1000°u2009C). But product quality can be impacted by these oxide scales due to scale remaining on product or sticking on tools. Thus the TEMPO laboratory has created an original methodology in order to characterize oxide scale under high temperature, pressure and strain gradients. An experimental device has been developed. The final purpose of this work is to understand the scale behavior as a function of temperature, reduction ratio and steel composition.

Towards the Mastering of the Free Surface Position in Roll Coating

This paper deals with an industrial three rolls coater. The behaviour law of the elastomer roll cover in different environments is first established in order to be taken into account in the numerical simulation of the process. Cyclic compression tests are performed and compared to the corresponding numerical simulation to precisely determine the viscoelastic parameters. With the identified parameters, a finite element simulation of the process is then performed to evaluate the meniscus stability in real contact conditions. The influence of the determined elastomer behaviour laws on the free surface position is discussed.