Lukas Seeholzer

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Seeholzer

First Name

Lukas

ORCID

0000-0003-4492-5219

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Publications 1 - 10 of 15

Analytical force model for drilling out unidirectional Carbon Fibre Reinforced Polymers (CFRP)
Seeholzer, Lukas; Scheuner, Daniel; Wegener, Konrad (2019)
Journal of Materials Processing Technology
Carbon fibre reinforced polymers (CFRP) are characterised by a high potential for lightweight constructions due to their high specific strength and stiffness properties. Especially applications in aerospace industries necessitate numerous drilling operations in CFRP with high tolerance requirement for subsequent riveting. The bore quality in drilling CFRP is the result of complex interactions of various geometry parameters of the drilling tool, the process parameters and the material properties. Due to a strong correlation between the process forces and the resulting bore quality, analytical force models are valuable to optimise tool geometries and process strategies. Furthermore, analytical force models enable single parameter variation, which would be feasible in experiments only with excessive effort and costs. This research aims to develop an analytical force model for drilling out predrilled UD CFRP material. Based on detailed chip formation analysis by means of high-speed recordings and scanning electron microscopy (SEM), four intervals with similar chip formation mechanisms and two fundamental failure mechanisms are identified. In the modelling approach, a coordinated structural failure of entire fibre regions by axial compression is considered by micro-buckling. For fibre loading situations dominated by lateral bending deformations, fibre failure by exceeding tensile strength in the contact region is considered. Therefore, the tool-fibre contact situation is simplified as the Hertzian contact between two cylinders. In addition to force components due to an initial fibre separation in front of the cutting edge, additional force components due to elastic spring back effects of the CFRP material on the flank face are taken into account. Combined with the drilling kinematics and under consideration of oblique cutting conditions, the thrust force and the torque values are analytically determined for the entire range of fibre cutting angles during one half tool rotation. Subsequent validation shows a good agreement of simulated and experimental data.
Efficient method for quality assessment in drilling CFRP based on digital images
Seeholzer, Lukas; Kneubühler, Fabian; Meier, Christopher; et al. (2022)
SAMPE Europe Conference 2021 Baden/Zurich: Innovating Towards Perfection
In this study, an efficient quality assessment method based on digital 2D image post-processing via segmentation and feature recognition is presented to quantify bore entry damages in drilling CFRP. Drilling experiments in CFRP are conducted to validate the proposed method and to evaluate its robustness in terms of the important camera parameters contrast and gain. Furthermore, a comparison based evaluation between the results of the presented method and those of a commercial 3D microscope is conducted. The evaluation duration can be reduced by a factor of 60 while at least 67% of the accuracy of a 3D measuring device is achieved.
Tool wear and spring back analysis in orthogonal machining unidirectional CFRP with respect to tool geometry and fibre orientation
Seeholzer, Lukas; Kneubühler, Fabian; Grossenbacher, Frank; et al. (2021)
The International Journal of Advanced Manufacturing Technology
Machining abrasive carbon fibre reinforced polymers (CFRP) is characterised by extensive mechanical wear. In consequence, the cutting edge micro-geometry and thus the tool/material contact situation are continuously changing, which affects process forces and machining quality. As a conclusion, a fundamental understanding of the tool wear behaviour and its influencing factors is crucial in order to improve performance and lifetime of cutting tools. This paper focuses on a fundamental tool wear analysis of uncoated tungsten carbide cutting inserts with different combinations of fibre cutting angles and tool geometries. For this purpose, orthogonal machining experiments with unidirectional CFRP material are conducted, where the wear progression of the micro-geometry is investigated by means of five wear parameterslα, lγ, γ*, α*, and bc. For detecting the actual contact zone of the cutting edge and to measure the elastic spring back of the material, the flank face is marked via short pulsed laser processing. Furthermore, the process forces and the wear rate are measured. It is shown that the material loss due to wear clearly varies along the tool’s contact region and is highly dependent on the clearance angle and the fibre cutting angle Φ, while the influence of the tested rake angles is mostly negligible. Especially in machining Φ=30° and Φ=60°, a strong elastic spring back is identified, which is more intense for smaller clearance angles. For all tested configurations, the material’s elastic spring back increases in intensity as wear progresses which, in combination with the decreasing clearance angle, is the main reason for high thrust forces.
Fundamental analysis of the cutting edge micro-geometry in orthogonal machining of unidirectional Carbon Fibre Reinforced Plastics (CFRP)
Seeholzer, Lukas; Voss, Robert; Grossenbacher, Frank; et al. (2018)
Procedia CIRP ~ 8th CIRP Conference on High Performance Cutting (HPC 2018)
Machining of carbon fibre reinforced plastics (CFRP) is closely related to strong abrasive tool wear and represents a significant process challenge due to its anisotropic material structure and brittle fracture behavior. Furthermore, machining of unidirectional CFRP material shows a significant increase in process forces due to tool wear effects, resulting in a changing micro-geometry of the cutting edge. This research work aims to give a detailed analysis of the tool wear behavior with respect to the five micro-geometry parameters based on an approach of “straight line–ellipse–straight line”, capable also to describe the developing asymmetric cutting edge. Therefore, fundamental orthogonal machining experiments with varying fibre orientations and tool geometries are conducted. It can be shown that the micro-geometry changes with increasing cutting length, whereby an increase of the resulting friction length and spring back height can be detected, having a significant influence on the process forces.
Experimental investigation of the machining characteristics in diamond wire sawing of unidirectional CFRP
Seeholzer, Lukas; Süssmaier, Stefan; Kneubühler, Fabian; et al. (2021)
The International Journal of Advanced Manufacturing Technology
Especially for slicing hard and brittle materials, wire sawing with electroplated diamond wires is widely used since it combines a high surface quality with a minimum kerf loss. Furthermore, it allows a high productivity by machining multiple workpieces simultaneously. During the machining operation, the wire/workpiece interaction and thus the material removal conditions with the resulting workpiece quality are determined by the material properties and the process and tool parameters. However, applied to machining of carbon fibre reinforced polymers (CFRP), the process complexity potentially increases due to the anisotropic material properties, the elastic spring back potential of the material, and the distinct mechanical wear due to the highly abrasive carbon fibres. Therefore, this experimental study analyses different combinations of influencing factors with respect to process forces, workpiece surface temperatures at the wire entrance, and the surface quality in wire sawing unidirectional CFRP material. As main influencing factors, the cutting and feed speeds, the density of diamond grains on the wire, the workpiece thickness, and the fibre orientation of the CFRP material are analysed and discussed. For the tested parameter settings, it is found that while the influence of the grain density is negligible, workpiece thickness, cutting and feed speeds affect the process substantially. In addition, higher process forces and workpiece surface temperatures do not necessarily deteriorate the surface quality.
Method for evaluating cooling strategies in terms of chip formation/transport in drilling CFRP/Al-stacks
Kneubühler, Fabian; Seeholzer, Lukas; Spahni, Martina; et al. (2021)
Experimental study: comparison of conventional and low-frequency vibration-assisted drilling (LF-VAD) of CFRP/aluminium stacks
Seeholzer, Lukas; Voss, Robert; Marchetti, Luca; et al. (2019)
The International Journal of Advanced Manufacturing Technology
The increasing substitution of metallic structural components by carbon fibre reinforced polymers (CFRP) in aerospace applications results in a growing need for drilling metal and CFRP in one operation, the so-called stack machining. The different material properties of the stack components in combination with high geometrical tolerance requirements result in large challenges for the drilling tool and the process strategy. Focussing on the process strategy, this paper deals with an extensive comparison of conventional and low-frequency vibration-assisted drilling (LF-VAD) of CFRP/aluminium stacks. The influence of the cutting speed, the feed rate and the amplitude of the superimposed oscillation in LF-VAD on the resulting bore quality is analysed. For the bore quality, three separate aspects are considered, namely, damages at the CFRP entrance, burr formation at the aluminium exit and deviations from the nominal diameter in both materials. Online temperature and force measurements enable interpretation of the influence on the bore quality. Based on experimental data, a clear dependency of the bore quality and the chip transport on both, the process parameters and the drilling strategy are identified. Based on high-speed recordings, the dynamic loading situation due to the superimposed oscillation in LF-VAD is found to be crucial for the formation of peel-up delaminations.
Influence of different cooling strategies on the process temperatures and chip transport quality in one-shot drilling CFRP/Al-stacks
Seeholzer, Lukas; Spahni, Martina; Wegener, Konrad (2021)
Procedia CIRP ~ 9th CIRP Conference on High Performance Cutting
This study focusses on the influence of different cooling strategies on process temperatures and chip transport quality in one-shot drilling CFRP/Al-stacks. In addition to the maximum temperatures in both individual stack components, temperature changes in the CFRP material due to hot aluminium chip interactions are analysed. The following cooling strategies are compared: compressed air through the drilling tool, cryogenic CO2 cooling at the aluminium bore exit as well as the combination of both. It is shown that process temperatures and chip transport quality significantly differ for the tested cooling strategies. Whereas CO2-cooling of the Al-plate results in overall smaller chips, the use of compressed air mainly improves chip evacuation. The combination of both cooling strategies shows high potential to prevent clogging in the chip flute as well as its negative impacts on workpiece quality
Method for evaluating cooling strategies in terms of chip formation/transport in drilling CFRP/Al-stacks
Kneubühler, Fabian; Seeholzer, Lukas; Spahni, Martina; et al. (2021)
SAMPE EUROPE Conference and Exhibition 2021
Analytical model for predicting tool wear in orthogonal machining of unidirectional carbon fibre reinforced polymer (CFRP)
Seeholzer, Lukas; Krammer, Thomas; Saeedi, Parvaneh; et al. (2022)
The International Journal of Advanced Manufacturing Technology
Progressive tool wear due to abrasive carbon fibres is one of the main issues in machining of CFRP and responsible for the short tool life. Because of occurring wear during machining, the tool's micro-geometry changes continuously resulting in higher process forces and an increasing risk for workpiece damages. In this paper, a novel analytical model is presented in order to predict the wear-related change of the micro-geometry in orthogonal machining of CFRP depending on the fibre orientation and the initial tool geometry. For this purpose, a concept called the wear rate distribution is introduced which represents a measure to quantify the wear rate along the active micro-geometry. Based on experimental investigation, it is shown that the shape of an arbitrary wear rate distribution between two closely spaced wear states can be approximated and parameterised with a "line - curve - line" approach. Using the authors' previously published analytical force model, the wear rate distribution can be calculated as function of five wear parameters that are used to parameterise the active micro-geometry of an arbitrary wear state. Based on an iterative solver, this is used to simulate the tool wear progression during machining. For model validation, the simulation is compared to experimental data in terms of the cutting edge profiles, the amount of worn tool material and the process forces. Accordingly, the wear model is capable to reproduce the most important wear characteristics, e.g. the cutting edge rounding, the decreasing clearance angle and the increasing contact length at the flank face.

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Lukas Seeholzer

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