Daniel Trauth

Analysis of the Velocity Distribution of an Elliptic Surface Structure Manufactured by Machine Hammer Peening

Machine hammer peening (MHP) is an incremental forming process for surface structuring of technical workpieces or tools. Currently, MHP strongly attracts the attention of automotive and toolmaking industry. Recently performed research showed improved tribological characteristics in lubricated deep drawing in terms of a reduced friction coefficient due to a lubricant pocket effect and a reduced contact area. In order to design the MHP process to obtain an optimized load capacity of the fluid film, the velocity distribution has to be analyzed. Thus, an analytic approach for solving the Reynolds equation as a valid simplification of the Navier–Stokes equations for an elliptic geometry of a MHP structure is proposed in this work. The research assumes stationary hydrodynamic lubrication and is restricted to the longitudinal properties. Thereby, the influence of the structure geometry, the fluid film thickness, the sliding velocity and the dynamic viscosity on the fluid velocity distribution is researched by means of an analytic solution of the Reynolds equation. The derived formula is applied to contribute to the understanding in lubricated deep drawing with MHP structures, but is also transferable on further sliding contacts, e.g. bearing lubrication.

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.

Fine Blanking of Helical Gears

Fine blanking is a well-established process for the production of near net shape components with high quality. The produced parts are characterized by a smooth sheared edge up to 100 %, excellent surface properties with good flatness and little burr as well as close tolerances for near net shape manufacturing. These process characteristics are suitable for the efficient production of spur gears with large batch size. In this work, the application of fine blanking was extended for the production of helical gears. Therefore, the fine blanking process was modified with an additional rotary movement of the dies to realize the manufacturing of helical gears. In this contribution the process idea, experimental and numerical work as well as the potential of fine blanked helical gears is presented.

Friction analysis of alternative tribosystems for a foil free forming of stainless steel using strip drawing test: analysis of physicochemical interactions between coatings and lubricants

Abstract Forming of stainless steel sheets with stringent requirements on surface quality is currently realized using protective foils as a separating agent between the tools and the sheet metal. The protective foils are applied with special machines and need to be removed after the forming process or at the end customer. This approach goes along with economic disadvantages. Alternative tribological systems for foil free forming are insufficiently researched and not yet reliably applicable in a production process. The performed research work is based on experimental analyses investigating the physicochemical properties of selected lubricants with regard to the contact angle, the wetting characteristic, the cohesion strength, and intermolecular forces. Additionally, the surface free energy and the wetting envelope of selected coatings and the sheet metal are investigated. The interactions between the tribological properties of the lubricants and the coatings are evaluated performing a strip drawing test. Finally, the performed work discusses and derives basic mechanisms enabling a foil free forming based on friction coefficients from strip drawing.

Influence of the cemented carbide specification on the process force and the process temperature in grinding

Cemented carbides are hard and brittle materials. Their material properties are adjusted by their chemical composition, in particular their average hard phase grain size and their binder fraction. The research paper focusses on grinding of cemented carbides with cobalt (Co) as binder and tungsten carbide (WC) as hard phase material. Within the research paper, it is discussed if and to what extent the cemented carbide composition affects the occurring thermo-mechanical load collective in the grinding process. In particular, the influence of the average WC grain size and the cobalt fraction on the thermo-mechanical load collective is investigated and explained by the cemented carbide material properties. The results of the publication contribute to a knowledge-based design of cemented carbide grinding processes.

Setup of a Parameterized FE Model for the Die Roll Prediction in Fine Blanking using Artificial Neural Networks

Die roll is a morphological feature of fine blanked sheared edges. The die roll reduces the functional part of the sheared edge. To compensate for the die roll thicker sheet metal strips and secondary machining must be used. However, in order to avoid this, the influence of various fine blanking process parameters on the die roll has been experimentally and numerically studied, but there is still a lack of knowledge on the effects of some factors and especially factor interactions on the die roll. Recent changes in the field of artificial intelligence motivate the hybrid use of the finite element method and artificial neural networks to account for these non-considered parameters. Therefore, a set of simulations using a validated finite element model of fine blanking is firstly used to train an artificial neural network. Then the artificial neural network is trained with thousands of experimental trials. Thus, the objective of this contribution is to develop an artificial neural network that reliably predicts the die roll. Therefore, in this contribution, the setup of a fully parameterized 2D FE model is presented that will be used for batch training of an artificial neural network. The FE model enables an automatic variation of the edge radii of blank punch and die plate, the counter and blank holder force, the sheet metal thickness and part diameter, V-ring height and position, cutting velocity as well as material parameters covered by the Hensel-Spittel model for 16MnCr5 (1.7131, AISI/SAE 5115). The FE model is validated using experimental trails. The results of this contribution is a FE model suitable to perform 9.623 simulations and to pass the simulated die roll width and height automatically to an artificial neural network.

Influence of different grinding wheel and dressing roller specifications on grinding wheel wear

A targeted adjustment of the dressing results and the methodological influence of the dressing process on the non-stationary wear of a grinding wheel after dressing increases the productivity and the reproducibility of grinding processes. Despite the great economic importance of grinding processes with vitrified corundum grinding wheels and the great relevance of the dressing process for the application behavior of these grinding wheels, quantitative models are missing for the purposeful design of the dressing process. In previous studies, a dressing model was successfully developed which predicts the dressing force in the dressing process as well as the workpiece roughness and the grinding wheel wear behavior in a grinding process for a specific grinding wheel and form roller specification. However, a transferability of this model to other grinding wheel and form roller specifications is not possible because the influence of the grain size and the hardness of the grinding wheel as well as the dressing tool topography on the grinding wheel wear and thus on parameters of the dressing model are not known. The objective of this work was to extend the model to additional grinding wheel and form roller specifications to ensure a broad applicability of the model.

A predictive model for die roll height in fine blanking using machine learning methods

Abstract A method for the development of a predictive model for the die roll height in fine blanking using artificial neural networks and support vector machines is presented. Since artificial neural networks require big amounts of training data and generation using experiments is very time consuming and cost intensive, a validated FE model is used instead. The required training data will be determined using learning curves. The optimal architecture and hyperparameter of the artificial neural network will be derived. Additionally, the die roll height is modelled using support vector machines and also conventional statistical regression models. Finally the accuracy of the methods is compared.

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.