Investigations on belt polishing of heat-resistant titanium alloys

Abstract

The majority of aero-engine components are designed and manufactured with high surface quality/integrity in mind. Repeatable and productive finishing processes are needed to support this. There is little information available in the literature related to finishing processes of aero-engine components. Up to now limited research has been reported in the use of belt polishing for finishing aero-engine components made of thermally sensitive alloys. The paper aims to investigate the possibility of using belt polishing as a final finishing operation for components made of Ti-6-4 heat-resistant alloy. The challenge of this attempt resides in achieving a required workpiece surface quality/integrity that ensures high fatigue performances of the polished components. The capability to remove the machining marks and to establish a required workpiece surface quality was optimised on three different milled surface textures by changing cutting parameters (cutting speed, depth of cut, feed rate, and belt stepover) as well as the finishing strategy (e.g. succession of polishing stages/type of belts). For the ‘optimised’ cutting conditions, the belt lives were evaluated relative to the following output measures: surface roughness, belt material removal, and machining time. Additional polishing trials, directed to reduce the thermal effect on the polished surfaces, were carried out using chilled air (−10 °C) supplied close to the machining zone. Workpiece surface integrity inspections (e.g. microhardness measurements, optical analysis) revealed that no major microstructural changes occurred on or under the polished surfaces. Taking into account the capacity to remove machining marks and the satisfactory results of the workpiece surface analysis, it could be concluded that belt polishing might be considered as a viable process for finishing aero-engine components.