Abstract
Deep hole drilling processes for high-alloyed materials are characterised by worn guide pads and chatter vibrations. In order to increase feed rates, process stability and bore quality in STS deep hole drilling, various investigations were carried out with adjustments to the tool. First, a new process chain for the production of tribologically optimised guide pads and their effects on the guide pad shape is described in detail. The results of these studies show that the shape change in the area of the axial run-in chamfer through a micro finishing process leads to a better bore hole quality. Furthermore, the influence of guide pad coating and cooling lubricant on the deep hole drilling process was investigated. In addition, the machining of the austenitic steel AISI 304 is analysed by using a conventional steel boring bar and an innovative carbon fibre reinforced plastic (CFRP)-boring bar. While the conventional drill tube oscillates with different eigenfrequencies, the CFRP-boring bar damps chatter vibrations of the drill head and stabilises the process. Even at higher feed rates up to f = 0.3 mm, it is possible to machine austenitic, difficult-to-cut-materials with significantly reduced vibrations.
Highlights
Modern machining technology aspires the combination of economical productivity and increased quality
The high tendency of the austenitic steel to strain harden leads to significant material adhesion to the guide pad and has a significant influence on the bore hole surface quality
The single tube system (STS) deep hole drilling is not accompanied by vibrations of the boring bar when choosing low cutting parameters
Summary
Modern machining technology aspires the combination of economical productivity and increased quality. Single-lip drills are used in industrial applications as tools for deep hole drilling austenitic steel. The implementations of these drilling processes are performed on deep hole drilling machines as well as on machining centres, which both use emulsions as coolants [10]. Biermann et al have studied the effects of microfinished guide pads on bore surface quality in SLS drilling. They found out that a friction reducing coating (e.g. ta-C) is appropriate to reduce abrasive wear effects [4, 6]. The tribological qualities were determined in the form of tool wear, workpiece surface roughness and mechanical loading [13]
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