Patrick Mattfeld

Influence of the dressing process on grinding wheel wear

The generation of the grinding wheel topography is described in many different models and approaches. These models do not consider the influence of the dressing process on the wear of the grinding wheel. In particular the prediction of this wear dependent on the dressing process parameters is not possible with the currently available models. This article describes a novel model for the initial wear of vitrified bonded grinding wheels on the basis of Linke’s dressing model. Therefore, the load of the grinding wheel in dressing process is depicted using the mean dressing chip cross section, which is then used to model the wear of the grinding wheel. An analytical-empirical model for the initial radial grinding wheel wear in dependence of the load in dressing process is presented. Furthermore, the influence of the load in the dressing process on the wear mechanisms of the grinding wheel, in particular on the relative frequency of the fracture phenomenon grain break-out, is shown. The new model allows the prediction of the wear of the grinding wheel as a function of the geometric-kinematic engagement in dressing processes using the mean dressing chip cross section.

Mathematical modeling of ceramic bond bridges in grinding wheels

Ceramic-bonded grinding wheels with cubic boron nitride (CBN) as grain material belong to the most efficient grinding tools available. They feature a high hardness combined with a high thermal stability and the applicability to grinding ferrous materials. However, the appropriate volumetric composition of grain and bonding material is an expensive and time-consuming process based on experience. Our objective is the mathematical modeling of grinding wheel structures for the prediction of compositions which fulfill given grinding requirements such that using trial and error methods can be avoided. For this purpose, we focus on a three-dimensional element of a grinding wheel which we call volumetric structure element. In this paper, we briefly describe our overall modeling approach and present in detail how we model the ceramic bond. For the latter, we combine analytical and discrete calculations, embedded into an iterative algorithm which ensures to meet bond volume fractions prescribed by grinding wheel specifications.

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.

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.

Contact Forces in Unguided Vibratory Finishing

In vibratory finishing the material removal rate is influenced by the contact forces between work piece and media. In this paper a measurement system is presented which is capable of measuring the contact forces between work piece and media in unguided vibratory finishing. The unique feature of the measurement system is its completely wireless construction. The measurement results are not influenced by wires of the force sensor system including the electrical power supply and the data logging. By means of this measurement system, contact forces can be measured in unguided vibratory finishing processes for the first time. Furthermore, the influence of media size and adjustment of the unbalance motor like revolution speed, phase angle and mass distribution between the upper and the lower eccentric weight was investigated.Copyright

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.

Time-Efficient and Precise FEM/BEM Simulation of a Cold Forging Process Verified by Tool Load Determination

Developing green processes establishes new possibilities for cold forging industry. Current technological developments require automotive parts with less mass, but higher material-efficiency. To achieve these goals, high-strength steels and complex geometries are used. The rising process forces lead to increased tool loads and subsequently elastic tool deformation resulting in early tool failure or dimensional deviations. A numerical determination of tool loads during process enables their reduction by a load-dependent design of the tool geometry. Aim of this work is a time-efficient and precise determination of tool loads considering the complete tool system using the example of a lateral extrusion process. By domain decomposition into Finite Element Method (FEM) and Boundary Element Method (BEM) domains and subsequently an integrated FEM/BEM simulation, a significant computation time reduction towards a conventional FEM model is achieved. Experiments of the examined lateral extrusion process provide data for the verification of the investigated process simulation models. In order to be able to validate the simulated elastic tool deformations, strain gauges are installed on the die insert and allow an experimental measurement of the elastic radial die strains. Additionally the simulated process force development and the final workpiece geometry of the simulation models are compared with experimental results.

Robust technology chain design: considering undesired interactions within the technology chain

Existing methodologies in technology chain design are used to plan the deployment of manufacturing technologies under consideration of interactions between these technologies and workpiece properties. Present methodologies focus on workpiece characteristics which the technologies are designated to change. However, workpiece properties can also be negatively affected because of interactions between the manufacturing technologies and features which the technologies are not supposed to change. These undesired interactions can cause a lower quality of the produced parts and an increased amount of defective parts. In this paper, a new methodology is presented which enables the user to identify undesired interactions during the technology chain design process. Firstly, the product to be manufactured is analyzed and described as a set of individual features. Secondly, feature-specific technology chains are designed under consideration of possible undesired interactions. Thirdly, the individual feature-specific technology chains are merged to generate a robust technology chain for the manufacturing of the analyzed product. Since undesired interactions usually occur during production ramp-ups for the first time, the methodology is applied to a case study concerning a ramp-up in the automotive industry. In this context, improving the process stability by preventing the occurrence of undesired interactions is of high economic importance.

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.

Zielsystem zur Berücksichtigung der Anlaufsituation

Kurzfassung Der Erfolg eines Produktionsanlaufs wird maßgeblich durch die eingesetzten Fertigungstechnologien beeinflusst. Gleichzeitig spielt der Produktionsanlauf in bestehenden Arbeiten zur Bewertung und Auswahl von Technologien nur eine untergeordnete Rolle. Aus diesem Grund wird in dem vorliegenden Beitrag ein Zielsystem entwickelt, das eine Bewertung von Fertigungstechnologien im Hinblick auf den Anlauf ermöglicht und somit die vorliegende Anlaufsituation bei der Technologieauswahl berücksichtigt.