Increasing Productivity and Process Stability in Turning of Aerospace Materials with High Pressure Lubricoolant Supply

Abstract:

In the field of machining difficult-to-cut materials like titanium or nickel-based alloys, the use of a high-pressure lubricoolant supply may result in a significant increase of productivity and process stability. Due to enhanced cooling and lubrication of the cutting zone and thus reduced thermal tool load, tool wear can be decreased which allows higher applicable cutting speeds. Furthermore, the process stability can be increased as a result of effective chip breaking and chip evacuation. Since energy efficiency is very crucial, pressure and flow rate have to be adjusted carefully and in accordance with the cutting parameters to guarantee best results with less energy. For this purpose, experimental investigations were carried out under variation of the flow rate in order to find the minimum required value for a certain machining task with the overall aim to prevent waste of the media used. To maximize the positive effect of high pressure lubricoolant supply strategy on productivity and process stability, specially designed lubricoolant jet guidance geometry on the rake face was also investigated and compared to conventional turning inserts. To study the effect of high-pressure lubricoolant supply on tool temperature, reference tests also carried out using conventional overflood cooling (CoC). The results suggest that the tool temperature can be significantly decreased compared to CoC by applying the high pressure lubricoolant supply and using specially designed jet guidance geometry in turning the investigated aerospace materials TiAl6V4 and Inconel 718.

• Periodical: Materials Science Forum (Volumes 836-837)
• Pages: 48-55
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.836-837.48
• Online since: January 2016
• Authors: Fritz Klocke, Tolga Cayli*, Dražen Veselovac
• Keywords: Aerospace, High-Pressure Lubricoolant Supply, Jet Assisted Cutting, Tool Temperature, Turning

References

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[3] A liquid wedge is formed which effectively cools and lubricates the cutting zone, leading to reduced tool wear, which is an optimum prerequisite to increase the cutting speed. Sharman has shown that the conventional flood cooling is effective to extend tool life when cutting at low speed and cutting easy to machine materials. In machining difficult-to-cut materials with increased cutting speed, higher cutting temperatures are generated.

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[4] Some researchers report that the high temperatures at the cutting zone cause the lubricoolant to vaporise and to generate a vapour barrier which, during conventional lubricoolant supply, prevents effective cooling of the tool in the region of the cutting edge.

[5] By using high-pressure lubricoolant supply, the vapour barrier may be displaced, enabling the lubricoolant to get closer to the cutting edge, thus leading to enhanced cooling of the tool [5, 6]. Furthermore, the mechanical jet force acting on the chip's underside acts as a liquid chip former reducing the upward bending radius of the chip. As a result, the tool-chip contact zone is reduced by up to 50% in comparison to the conventional flood cooling [3, 7, 9]. The chip bending can be influenced by the hydraulic jet force, which mainly depends on the lubricoolant supply pressure and flow rate [3, 10, 11]. In dependence of the predominant conditions it must be prevented that the flowing chip respectively chip fragments captured by the high-pressure jet do not collide with the newly generated workpiece surface that may be damaged in this way. This undesirable effect can be influenced by the geometrical jet alignment and the jet force point of impact [5, 12]. However, it has to be taken into consideration that the tool-chip contact length decreases when using the rake face sided supply variant. If the tool-chip contact area is reduced too much, the generated temperature and mechanical load will act on a small area close to the cutting edge and lead to an increased specific tool load that may result in cutting edge break-outs [7, 8]. Dahlman and Kaminski have shown, that it is possible to achieve a 40% reduction in tool temperature by the use of HP-lubricoolant supply compared to conventional flood cooling [5, 13]. The shorter contact length and reduced friction in this area also result in a larger shear plane angle and reduced chip compression, proving that chip formation is significantly influenced by the high-pressure lubricoolant supply.

[18] Moreover, Palanisamy et al. detected that the application of lubricoolant below a pressure of 90 bar in turning titanium alloys results in increased frequency of chip serration, shear-band thickness and average chip thickness compared to a pressure of 6 bar.