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2 Journal of Machine Engineering

2 2015

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Modelling the Effects of Residual Stresses on Electro-Magnetic Properties of Super Alloys

Goetz S., Chandra D., Veselova D., Klocke F.

Journal of Machine Engineering

2015

Vol. 15, No. 3

33--40

Super Alloys, commonly used in safety-critical aerospace components, regularly impose problems when machined in drilling or milling processes, resulting in surface damages that facilitate cracks. Residual stresses are often induced to prevent crack mitigation, but national aviation agencies set high quality standards on them. Current methods are either destructive or impose safety risks for the employees. Eddy current methods, however, are fast and cheap non-destructive methods to receive information on metallic surfaces. They rely on electro-magnetic properties of the material. The influence of residual stresses on both permeability and conductivity are not yet fully understood. This article presents a simple model that describes the correlation between residual stresses and those aspects. At first, the dependency of permeability and conductivity on various metallurgical properties, such as grain size or orientation, is deduced. In a second step, the influence of residual stresses on these properties is shown. A third step combines both steps into a coherent and holistic model to describe the influence of residual stresses on the electro-magnetic properties of Super Alloys. This model will help establishing Eddy Current Testing in the product monitoring in the aerospace industry.

Cutting Force Reduction in The Milling of Aluminum Alloys with Serrated Cutting Tool Edges

Rekers S., Auerbach T., Veselovac D., Klocke F.

Journal of Machine Engineering

2015

Vol. 15, No. 4

27--36

Structural components for aerospace industry are in most cases milled from solid. Usually more than 80 % of the bulk material is removed by milling processes in order to obtain the parts final shape. Due to economic aspects, high material removal rates are desired to reduce cost intensive machine cycle times. In order to meet high process design demands, optimized cutting forces at maximized material removal rates are of crucial interest. These are especially depending on the work piece material to be machined, the cutter work piece engagement conditions as well as the milling cutters geometry. The usage of milling tools with serrated cutting edge geometries enables a significant reduction of cutting forces. In this article, cutting forces during milling aluminum alloys using different serration geometries and engagement conditions are investigated. At first, a generic cutting force model is introduced. The required model parameters are approximated for the machined material by subsequent milling tests employing non-serrated cutters. In a second step, a model is presented allowing a time-domain simulation to obtain cutting force variations for cutters with serrated cutting edges. Finally, experimental data for different serrated cutters are compared with the simulated predictions.