Abstract
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 parameters lα, 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.
Highlights
Carbon fibre reinforced polymers (CFRP) are characterised by outstanding specific strength and stiffness properties that make them suitable for light weight constructions in aerospace industries [1, 2]
The interrelation between the wear-related change of the active micro-geometry and the measured process forces is discussed under consideration of the fibre cutting angle and the initial tool geometry
Each subsection contains two main plots, where the first one shows a summary of the evaluated wear parameters and the friction length lfr as functions of the cutting length for all tested combinations of rake and clearance angles according to Table 2
Summary
Carbon fibre reinforced polymers (CFRP) are characterised by outstanding specific strength and stiffness properties that make them suitable for light weight constructions in aerospace industries [1, 2]. The authors analysed the influence of the depth of cut on tool wear progression and found that the flank wear and the process forces increase for higher depth of cut which is explained by the larger engagement of the cutting edge. Numerous researchers have analysed the influence of progressive tool wear in machining of CFRP on changes in the chip formation mechanisms [22, 30, 31], the process forces [8, 11, 32], and the resulting workpiece quality [8, 32]. While the advancing bluntness of the tool has an influence on the chip formation mechanisms in front of the cutting edge, a decreasing clearance angle generally results in higher thrust forces as experimentally shown by Voss et al [22].
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