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Avoidance of drill cap formation in CFRP-titanium stack materials by using vibration assisted drilling with defined coupling of the oscillation

Krall Stephan, Prießnitz Markus, Baumann Christian, Brandt Peter, Bleicher Friedrich

Journal of Machine Engineering

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2023

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Vol. 23, No. 2

77--99

EN

Drilling of rivet holes in stacked materials consisting of CFRP and Ti-6Al-4V still represents unique challenges. It is common practice to drill the material layers using one single tool. When exiting the final metallic layer, formation of a drill cap usually leads to undesirable burrs and debris, requiring manual post-processing. In this work, a drilling process to avoid drill caps is presented. This is realized using low frequency high amplitude vibration assisted drilling with defined coupling of the rotational speed and the axial oscillations. Drilling parameters and their impact on the quality of the drilled hole in the metallic layer are also investigated. It is found that drill tip geometries and process parameters need to be tuned together to achieve a stable and repeatable process for drill cap avoidance. A highly sensorized experimental setup with multi-sensor systems including high-speed and thermal imaging was used for process evaluation.

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Investigation of multilayer coating of EN AW 6060 – T66 using friction surfacing

Krall Stephan, Baumann Christian, Agiwal Hemant, Bleicher Friedrich, Pfefferkorn Frank

Journal of Machine Engineering

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2022

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Vol. 22, No. 3

44--58

EN

The objective of this research is to investigate observable process changes during multi-layer friction surfacing of EN AW 6060 aluminum, whether for repair, remanufacturing, or new part manufacturing. In this study, friction surfacing was performed with a 10-mm-diameter rod of EN AW 6060 aluminum at spindle speeds ranging from 1000 to 7000 rpm to create up to three layers of 40-mm-long deposits on a substrate of the same alloy. The process forces and layer temperatures were observed. Post-process measurement of flash geometry, layer geometry and microhardness were conducted with the motivation to understand the impact of multi-layer depositions on performance and identifying acceptable conditions required to achieve acceptable build quality. The thickness, deposition and joining efficiency of layers in the multilayer configuration remained consistent. Friction surfacing of EN AW 6060 aluminum allowed for high deposition rates of 9 kg/hr, when compared to other metal additive technologies.

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Investigation of noise transmission of a machine tool enclosure

Bleicher Friedrich, Reichl Christoph, Linhardt Felix, Wimberger Peter, Habersohn Christoph, Krall Stephan

Journal of Machine Engineering

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2019

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Vol. 19, No. 3

5--16

EN

Machine tools are highly integrated mechatronic systems consisting of dedicated mechanic design and integrated electrical equipment – in particular drive systems and the CNC-control – to realize the complex relative motion of tool towards work piece. Beside the process related capabilities, like static and dynamic stiffness as well as accuracy behavior and deviation resistance against thermal influence, safety aspects are of major interest. The machine tool enclosure must fulfill multiple requirements like retention capabilities against the moving parts of broken tools, lose work pieces or clamping components. In regular use, the noise emission have to be inhibited at the greatest possible extent by the machine tool enclosure. Nevertheless, the loading door and the moving parts of the workspace envelope are interfaces where noise transmission is harder to be avoided and therefore local noise emissions increase. The aim of the objective investigation is to analyse the noise emission of machine tools to determine the local noise transmission of a machine tool enclosure by using arrays of microphones. By the use of this measuring method, outer surfaces at the front, the side and on the top of the enclosure have been scanned. The local transient acoustic pressures have been recorded using a standard noise source placed on the machine table. In addition, an exemplary manufacturing process has been performed to analyse the frequency dependent location resolved sound emissions.