Multi-scale friction modeling for manufacturing processes: The boundary layer regime

This paper presents a multi-scale friction model for largescale forming simulations. A friction framework has been developed including the effect of surface changes due to normal loading and straining the underlying bulk material. A fast and efficient translation from micro to macro modeling, based on stochastic methods, is incorporated to reduce the computational effort. Adhesion and ploughing effects have been accounted for to characterize friction conditions on the micro scale. A discrete model has been adopted which accounts for the formation of contact patches ploughing through the contacting material. To simulate metal forming processes a coupling has been made with an implicit Finite Element code. Simulations on a typical metal formed product shows a distribution of friction values. The modest increase in simulation time, compared to a standard Coulomb-based FE simulation, proves the numerical feasibility of the proposed method

Multi-scale friction modelling for rough contacts under sliding conditions

In Finite Element (FE) simulations of sheet metal forming (SMF), the coefficient of friction is generally expressed as a constant Coulomb friction. However in reality, the coefficient of friction at the local contact spot varies with the varying operational, deformation and contact conditions. Therefore, it is important to calculate the coefficient of friction under local contact conditions to better evaluate the formability of the sheet metal product. Friction at the local contact spot is largely influenced by the micro-mechanisms occurring at asperity level like shearing in the boundary layer, ploughing, surface deformation of the sheet metal surface and hydrodynamic lubrication. In this paper, a multi-scale contact model is developed for predicting the friction occurring in the SMF processes. The model describes the asperity flattening and ploughing phenomenon between the sheet metal and the tool which is predominant amongst the other friction mechanisms. The change occurring in the surface topography of the sheet metal during the deep drawing processes influences the ploughing process. An asperity flattening model for pure plastic conditions is used to describe this phenomenon. The developed model is analyzed with various sheet metal and tool surfaces. The result shows that the coefficient of friction is very much dependent on the surface topography of the interacting surfaces at low nominal contact pressures. At high nominal contact pressures, the surface topography influences less the friction. The coefficient of friction is also compared with tool surfaces of different roughness, bandwidth and surface lay. The coefficient of friction is found to be high for rough, low bandwidth and transversal anisotropic tool surface

Investigations on the tribological behaviour, toxicity, and biodegradability of kapok oil bio-lubricant blended with (SAE20W40) mineral oil

Published online: 4 March 2021Vegetable oil becomes a viable alternative to mineral or synthetic oils due to its biodegradable nature. In this work, one such vegetable-based non-edible oil (kapok oil) is blended with a mineral-based oil (SAE20W40) at 15 and 30% ratio (by volume), and its changes in thermal, tribological, and corrosive properties were evaluated. Four-ball tribometer is utilized to assess its dynamic friction coefficient and the wear scar diameter of the worn out area on the ball. Biodegradability and toxicity test of kapok oil were examined and compared with the palm and mineral oil through bacterial growth and brine shrimp assay methods, respectively. The results showed that the dynamic friction coefficient and specific wear rate of the blended oil were lesser than the mineral oil. The mineral oil produced a higher roughness average (Ra) value than that of the blended oil. Kapok oil shows an adequate tribological properties (anti-friction and anti-wear) in contrast to the other vegetable oils. Overall, kapok oil had a high biodegradability nature and lower toxicity than the mineral oil.S. Shankar, M. Manikandan, D. K. Karupannasamy, C. Jagadeesh, Alokesh Pramanik, Animesh Kumar Basa

A friction model for loading and reloading effects in deep drawing process

Deep drawing is one of the most widely-used forming processes to manufacture automotive bodyparts from sheetmetal. In order to simulate deepdrawing processes,a finite element(FE) method was used to predict formability. The accuracy of the FEsimulation depends on the material models,numerical techniques, and contact algorithms. Despite the fact that the contact conditions between the tool and sheet material influences the coefficient of friction in forming processes, the coefficient of friction is often treated as a constant Coulomb friction coefficient in FE simulations. However, a friction model based on local contact conditions and surface topography is required to improve forming predictability. There is growing interest in developing contact models to predict the nature of friction conditions for use in FE calculations.In deepdrawing processes, the sliding contact predominantly occurs in the blankholder region between the tool and sheet material. The contact pressure in the blankholder is non-uniform due to bending and material compression which vary depending on tool geometry.The sheet metal surface is subjected to repeated contact during sliding, which in turn affects the local friction conditions. The objective of this paper is to develop a sliding friction model for mixed modes of surface deformation. The deterministic approach used in the current model includes the roughness of both the sheet material and the tool.The sheet material is subject to an asperity flattening process. Further, the tool surface indents into the sheet material under normal loading.The geometry of the asperities is characterized by an elliptical paraboloid shape to better calculate the load-dependence of friction.The model has been compared with data from experiments using a rotational friction tester under multiple loading conditions