Drs Leung Soo and Richard Hood gave a comprehensive report on the Birmingham research group’s current program of Research and development in advanced machining processes for aerospace materials. Key challenges were identified and recent advances shown for HS machining/micro-milling of nickel-based aerospace engine superalloys, titanium alloys and composites. Applications and non-traditional processes were covered including EDM/wire, ultrasonic and abrasive machining/grinding. There was particular interest in ɣTiAl high-temperature/high-stiffness/low-density intermetallics for gas turbine application and CFRP carbon reinforced plastic composites for automotive, with new manufacturing technologies and processes needed. Comparative results for ball-nose end-milling were shown for ɣTiAl surface/sub-surface integrity and fatigue performance with improved tool life/cutting temperature and machining time vs cutting speed. Results for different processes, tooling and other parameters were shown for a range of superalloys, coatings and composites, including creep-feed/profiled point grinding, turning, wire EDM, drilling and edge-milling. The potential productivity benefits of different processes were illustrated, e.g. the point grinding of fir-tree root slots in compressor/turbine discs giving faster cutting rates and low set-up times when compared with current broaching process. Wire EDM advantages for slot forming were described in detail.
Professor I. S. Jawahir, University of Kentucky, USA presented the topic Cryogenically-assisted machining of difficult-to cut materials: Recent findings and potential for industrial applications. He noted that Cryogenic Machining was recognised in terms of its suitability for difficult-to-machine materials that typically involve long process times due to slow cutting speeds and poor tool life. Focusing on automotive, aerospace and biomedical applications he underlined that its use was also important in terms of sustainable manufacturing, especially energy efficiency, waste recyclability and operational safety and health. He noted that environmentally sustainable machining operations are moving away from the indiscriminate use of cutting fluids with negative impacts on surface integrity, product life, machining cost, energy consumption and chip recyclability. These issues added to the machinability issues of aerospace materials such as Ti and Ni-Ti alloys, Stainless steel grades, Inconel 718 and Co-Cr-Mo alloys, which were increasingly being used for volume applications such as automotive engine components and medical implants.
He explained that the material surface/sub-surface grain structures become altered during cryo-machining/burnishing with -196ᴼC liquid nitrogen coolant, affecting micro-hardness and improving surface integrity. Comparative machining test results were shown, demonstrating the significantly higher surface finish quality achievable together with enhanced component surface strength, toughness, corrosion/wear performance and reduced toxicity for medical implants.
The environmental benefits include longer component life, clean/sterile workpieces and uncontaminated chips favourable for recycling. The disposal of used coolants is eliminated. A patented Cryo liquid nitrogen delivery system through the insert direct to the cutting edge reduces tool wear with up to 10X life compared to conventional cooling, allowing substantially faster processing speeds and less downtime for maintenance.