Abstract
Microstructure and chip formation were evaluated during the step shoulder down-milling of Ti-6Al-4V using a water-miscible vegetable oil-based cutting fluid. Experiments were conducted using the Cut-list fluid supply system previous developed by the authors and a conventional cutting fluid supply system. A thin plastically deformed layer below the machined surface was observed during the metallurgical investigation of the surfaces produced using both systems. Despite noticeable reductions in cutting fluid consumption achieved by Cut-list, no significant disparity was found in microstructural damage. The microstructure of the machined surfaces was strongly affected by cutting speed and fluid flow rate with a discontinuous serrated chip being the principal type. However, increases in cutting fluid flow rate associated with increased cutting speed significantly changed chip morphology where average distance between chip segments increased with cutting speed. Cut-list produced smaller saw-tooth height and larger segmented width, while the transition from aperiodic to periodic serrated chip formation was governed by cutting speed and feed rate. Chip segmentation frequency and shear angle were also sensitive to cutting speed.
Highlights
The application of cutting fluid plays a vital role in metal cutting processes
A typical microstructure of an undeformed Ti-6Al-4V alloy, pre-machined, as-received material, is shown in Figure 7, whilst Figure 8 shows the microstructure of post-machining samples
Results related to microstructural alterations and chip formation using two cutting fluid supply systems have been presented, and the main conclusions are as follows:
Summary
Most machining processes cannot be performed effectively without cutting fluids, when cutting refractory materials such as titanium and nickel-based alloys. Cutting fluids contribute to reducing the contact pressure between the cutting tool and workpiece material and dissipate heat from the machining zone, resulting in extended tool life and reduced power consumption [1]. More details of the benefits, types of cutting fluid, their environmental impacts and supply systems, problems and requirements when machining titanium alloys, as well as the detailed design and fabrication of the new cutting fluid supply system known as Cut-List developed by the authors are available in previous publications [2,3]. The following discussion considers the relevant literature on these two crucial measures in the machining of titanium alloys
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