Anton Shirobokov

Analysis of friction between stainless steel sheets and machine hammer peened structured tool surfaces: experimental and numerical investigation of the lubricated interaction gap

Forming of stainless steel with stringent requirements on surface integrity is currently realized using protective foils as a separating agent between tools and workpiece. The protective foils are applied with special machines and need to be removed after the forming process or at the end customer. This approach has pronounced economic and ecological disadvantages. Alternative tribological systems for a foil free forming are insufficiently researched and not yet reliably applicable in a production process. Recent developments in the field of machine hammer peening motivate the investigation of surface modifications for foil free sheet metal forming. The research question of this paper is: under which tribological boundary conditions do structured tool surfaces provide a total separation of tools and workpiece? The performed research work is based on experimental analyses investigating the friction behavior of surface structured tools. Numerical simulations of normal and sliding contact using finite element method enable the investigation of the lubricated interaction gap in order to identify significant tribological process parameters.

Analysis of the fluid pressure, load capacity, and coefficient of friction of an elliptic machine hammer peened surface structure in hydrodynamic lubrication

Recently, the velocity distribution within an elliptical machine hammer peened (MHP) surface structure was discussed by solving analytically the Reynolds equation using Full-Sommerfeld boundary condition (Trauth et al. in Tribol Lett 60(19):1–13, 2015). However, in order to design the MHP process to obtain defined friction characteristics and load capacities of a fluid film, the pressure distribution has to be analyzed as well. Thus, in this contribution, the fluid pressure is discussed using Full-Sommerfeld first, then the previous work is extended by the Swift–Stieber boundary condition to account for cavitation effects. Thereby, the influence of geometry and process parameters on the fluid pressure, load capacity and coefficient of friction will be analyzed both using an approach based on absolute and dimensionless numbers. To asses the influence of lateral effects, the semi-analytic 1D results are compared to numerical 2D results based on the Raimondi approach. Thereby, a recommendation for a surface design manufactured by machine hammer peening is formulated.

Blanking of Unidirectional Carbon Fibre Reinforced Plastics

Fibre reinforced plastics (FRP) are being increasingly used for advanced applications where an appropriate mechanical performance should be achieved at minimum weight. A substantial increase of the FRP usage is expected across various industries e.g. in automotive sector in the nearest future. This leads to the mass manufacturing of FRP components. Reduction of manufacturing costs of FRP components is regarded as the main enabler for the usage of this material in mass production. Although FRP components are manufactured near-net-shape, they often have to be pierced or trimmed in one of the last manufacturing steps. With rising production numbers blanking is a potentially more cost efficient technology for trimming and piercing of FRP components compared to the conventionally performed abrasive water jet cutting or machining. The mechanisms of FRP separation in blanking have not yet been researched. In particular, the influence of the fibre orientation relative to the cutting line on the cutting force is not known. In the scope of this work an experimental study of blanking of a unidirectional carbon fibre reinforced plastic with a thermoset resin at different fibre orientations to the cutting line was performed. It was shown that the cutting force decreases from the perpendicular to the parallel fibre orientation to the cutting line. A possible mechanical explanation of this dependency was formulated.

Friction and Wear Analysis of Deep Rolled and Vibrorolled Specimens in Lubricated Contact

Deep rolling is an established mechanical surface treatment technology based on local plastic deformation of the surface layer. By these means, residual stresses, and strain hardening are induced into the surface layer as well as its surface structure is smoothed. Vibrorolling is a derivate technology of deep rolling characterized by sinusoidal rolling lanes. Due to process kinematics of vibrorolling the surface layer is incrementally deformed multiple times in different directions. As a result, a more intensive plastic deformation of the surface layer is achieved and potentially tribologically active surface structures are produced. To investigate and compare the effects of both surface treatment technologies on the tribological behavior of a processed component, a friction and wear analysis under lubricated conditions was conducted in this work. Friction and wear behavior of untreated, deep rolled, and vibrorolled specimens using a pin-on-cylinder tribometer was conducted. Hardness, roughness, and geometrical measurements of the wear traces were used to characterize the specimens. Additionally, qualitative assessments of the wear traces using scanning electron microscopy imaging were made. The measurements were performed before, during, and after the friction and wear analysis. Furthermore, contact forces between a tribometer pin and the workpiece were determined to analyze the development of contact shear stresses. Based on the conducted investigations, the effects of deep rolling and vibrorolling on the friction and wear behavior of the treated specimens are discussed and explanations for the observed phenomena are formulated in this work.

Finite element modelling of cutting force in shearing of multidirectional carbon fibre reinforced plastic laminates

Lightweight structural components made of carbon fibre reinforced plastics are manufactured near-net-shape. However, in order to fulfil geometrical or functional requirements, carbon fibre reinforced plastic components have to be trimmed and pierced in a finish processing step. Shearing is a highly productive technology that is potentially suitable for cost-effective finishing of carbon fibre reinforced plastic components in high-volume series production. Shearing of carbon fibre reinforced plastic has not yet been sufficiently researched. Cutting force is an important characteristic of the shearing process. Up to now, there exists limited knowledge on numerical modelling of the cutting forces in carbon fibre reinforced plastic shearing. In order to address this, a finite element process model of carbon fibre reinforced plastic trimming was developed in this work. The process modelling included a formulation of continuum mechanical material model for a unidirectional ply as well as a development of a kinematic model of the trimming process. The developed finite element process model was validated by means of experimental data. The simulated and experimentally determined maximum specific cutting forces demonstrated a very good qualitative and quantitative agreement.