Friction modelling in sheet metal forming simulations: application and validation on an U-Bend product
The accuracy of sheet metal forming simulations strongly depends on, amongst others, friction modelling. The industrial standard is to use the Coulomb friction model with a constant coefficient of friction. However, it is known that the true friction conditions are dependent on the tribology system, i.e. the applied sheet material, coating and tooling material, the lubrication and process conditions. In this paper, an approach is presented for friction modelling in sheet metal forming simulations. The approach is applied to the forming of U-bend test parts for varying tribology systems as commonly used in the automotive indus-try. The friction conditions per system are described using a physically-based friction model included in the Triboform Software. Friction in the U-bend simulations are described as a function of local contact pressure, relative sliding velocity and straining in the sheet material. The simulation results are validated using U-bend forming experiments. It is concluded that the numerical prediction of the punch force magnitude is highly sensitive to friction. In addition to an overall improvement of the prediction accuracy of stamping simulations by including friction modelling, this approach enables to model friction and the effect of varying tribology systems on the final stamped part quality.
Multi-scale friction modeling for sheet metal forming
The most often used friction model for sheet metal forming simulations is the relative simple Coulomb friction model. This paper presents a more advanced friction model for large scale forming simulations based on the surface change on the micro-scale. The surface texture of a material changes when two surfaces are in contact under a normal load. This is caused by flattening due to combined normal loading and stretching. The consequence of this is that shear stresses between the contacting surfaces, developed by adhesion and ploughing effects between contacting asperities, will change when the surface texture changes. A numerical procedure has been developed which accounts for the change of the surface texture on the micro-scale and its influence on the friction behavior on the macro-scale. The numerical procedure is implemented in a finite element code and applied to a full scale sheet metal forming simulation.
Characterization of ceramic composite membrane filters for hot gas cleaning
Abstract Novel composite ceramic membrane filters suitable for hot gas cleaning operations have been prepared from fly ash and titania particles on stainless steel woven mesh substrates. Both membranes had a structure like a solid packed bed with a thickness of less than 100 μm. In the domain of laminar flow, significant differences in the pressure drop between experimental results and those predicted from the Kozeny-Carman relationship were found, particularly for flow through the titania membrane. Membrane filters with extremely small pores such as the titania membrane are greatly affected by slip up to 80% in permeability at elevated temperatures. Efficiencies of filtration of typical coal fired power station exhaust fly ashes were found to be greater than 909% for both titania and ash membranes, whilst there was greater variation in the pressure drops in the ash membrane than in the titania at typical gas flows.