Michael Terhorst

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 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.

Energy-Efficient Solid Forward Extrusion through Hybridization Based on Process-Integrated Resistance Heating

In this paper a hybridized solid forward extrusion process is proposed that uses a process-integrated resistance heating for the energy-efficient heating of the workpiece material in order to avoid the occurrence of chevron cracks. As for the process-integration of the resistance heating two variations are regarded: the preheating of the wrought material prior to the forming process as well as a resistance heating concurrent with the extrusion process. Based on a three-shouldered solid forward extrusion of Cf53 with emerging chevron cracks the broad temperature interval for crack elimination is derived from experiments where the wrought material is preheated in a furnace. With this derived temperature a numerical approach for the dimensioning of a resistance heating of both prior to the forming process and during extrusion is shown. The approach is based on solving the Fourier heat transfer equation using both numerical algorithms in MATLAB and finite element method (FEM) in Deform-2D. In a final step the two scenarios heating prior to and during the extrusion process are evaluated in terms of their energy-efficiency using FEM.

Riblet Rolling on Ti6Al4V Compressor Blades

Riblet structures on surfaces can reduce friction drag in turbulent flow. The optimal riblet geometry depends on the fluidic application. Fluid dynamic analyses have revealed that the application of riblets on compressor blades of jet engines promises to reduce fuel consumption and, thus, CO2 as well as nitrogen oxide emissions. Due to high operating temperatures the application of riblet films on compressor blades is not feasible. Alternatively, riblet structures can be manufactured directly on a metallic blade. Incremental riblet rolling is among possible manufacturing processes. This forming process has been designed at the Laboratory for Machine Tools and Production Engineering (WZL) of RWTH Aachen University. It goes along with a major advantage compared to riblet manufacturing by machining or laser structuring: Riblet rolling induces strain hardening and compressive residual stresses. These properties can almost fully compensate the reduced load capacity resulting from the notch effect which accompanies riblet structures.

2D-CFD Analysis of the Fluid Pressure and Velocity Distribution of Experimentally Machine Hammer Peened Surface Structures in Hydrodynamic Applications

Machine hammer peening is an incremental forming process for high frequency surface finishing of technical components. Recently, machine hammer peening has attracted automotive industry’s attention for the surface finishing and structuring of deep drawing tools. Deep drawing tools surface structured by machine hammer peening are characterized by beneficial friction and wear characteristics in lubricated sliding contacts. However, the physics of hydrodynamic effects in machine hammer peened structures is yet insufficiently researched. Therefore, this work investigates the hydrodynamic effects in surface structures generated by machine hammer peening using a two-dimensional computational fluid dynamic analysis. The effects of structure geometry, structure arrangement and selected sliding parameters on the hydrodynamic fluid pressure and velocity distribution within the structures are analysed. It was observed, that the sliding direction and the structure arrangement have a significant influence on the hydrodynamic fluid pressure maximum.

Riblet Application in Compressors: Towards Efficient Blade Design?

Nowadays, modern axial compressors have already reached a very high level of development. The current study is focused on the question, if the application of riblets on the surfaces of a highly efficient modern compressor blade can be a further step towards more efficient blade design. Therefore, a highly loaded compressor cascade has been designed and optimized specifically for low Reynolds number conditions, as encountered at high altitudes and under consideration of the application of riblets. The optimization was performed at a Mach number of 0.6 and a Reynolds number of 1.5×105. Two objective functions were used. The aim of the first objective function was to minimize the cascade losses at the design point and at incidence angles of +5 and −5 degrees. The intention of the second objective function was to achieve a smooth distribution of the skin friction coefficient on the suction side of the blade by influencing the blade curvature in order to apply riblets. The MISES flow solver as well as the DLR optimizer “AutoOpti” were used for the optimization process.The developed compressor cascade was investigated in the transonic cascade wind tunnel of DLR in Cologne, where the Reynolds number was varied in the range of 1.5×105 to 9.0×105. Furthermore, the measurements were carried out at a low turbulence level of 0.8 percent and at a high turbulence level of 4 percent, representative for high pressure compressor stages. The measurement program was divided into two parts. The first part consisted of the investigation of the reference cascade. In the second part of the study riblets were applied on suction and pressure side of the cascade blades; two different manufacturing techniques, a rolling and a coating technique were applied. The rolling technique provides riblets with a width of 70 μm and the coated riblets have a width of 50 μm.The wake measurements were performed using a 3-hole probe at midspan of the cascade in order to determine the resulting losses of the reference blade and the blades with applied riblets. The detailed analysis of the measurements shows, that the riblets have only a slight influence on the viscous losses in the case of the compressor application in this study. Finally, these results are discussed and assessed against the background of feasibility and effort of riblet applications within the industrial design and manufacturing process.© 2014 ASME