Improving Machinability of Difficult-to-Cut Advanced Aerospace Materials Through High-Speed End-Milling

Student: Emenike Chukwuma (M.Sc candidate), Mechanical and Aerospace Engineering Faculty Advisor: Dr. A.C. Okafor, Mechanical and Aerospace Engineering

Objectives•To improve the machinability and productivity of end milling of difficult-to-cut advanced aerospace materials through high speed machining and application of different cooling and lubrication strategies. • To investigate the effects of cooling and lubrication strategy on tool wear, surface integrity and temperature

BackgroundTitanium alloy, Nickel-based alloy, and Inconel 718 are attractive materials in various key industries due to their excellent combination of strength to weight ratio maintained at high temperature, and resistance to corrosion and fracture but they are classified as difficult-to-cut materials due to their low thermal conductivity, low modulus of elasticity and high chemical reactivityEnd-milling is a type of milling process most commonly used for metal removal in aerospace and automotive industries for making prismatic and monolithic parts. Cutter breakage, high cutting forces, high cutting temperature, and rapid tool wear , and accuracy of machined parts , vibration and chatter are the major problems experienced with end milling process. Application of lubricants and coolants in cutting processes play very important roles including increase in tool life and dimensional accuracy, decrease in cutting temperatures, surface quality improvement and reduction in cutting force/power consumed during machining . Conventional coolants are more costly, ineffective and create some techno-environmental problems such as, environmental pollution due to chemical dissociation or break up due to high cutting temperature. So, it is absolutely necessary to use an environmentally acceptable cooling and lubrication strategies in manufacturing industry.

DiscussionHigh Speed Machining (HSM) is defined as machining process using spindle speeds greater than 7,000rpm and feedrates greater than 100 meters per minute for aluminum. The current industrial standard for machining titanium, here after referred to as baseline parameters, are spindle speed of 153 rpm (50 fpm) for roughing with HSS-Co and spindle speed of 2037 rpm (400 fpm) for finishing using solid carbide end-mill. Therefore any speed above this baseline parameter for titanium is regarded as High Speed Machining. HSM is an emerging technology that offers significant potential for fabricating large intricate and delicate structural components and hardened materials faster and accurately, especially for the aerospace industry. It results in greater material removal rates, lower cutting force, especially when enhanced with an effective cooling and lubrication strategy, thus improvement in productivity. However a lot of HSM issues are not well understood by airframe and automotive manufacturers.

Concluding RemarksThis research work hopes to improve the structure and properties of machined difficult-to-cut metals and alloys, thereby increasing tool life while maintaining an industrially acceptable surface finish and surface integrity.

Future WorkOur current approach to end milling of difficult-to-cut aerospace materials may be extended to machining of advanced composite materials used for the same industrial applications.

AcknowledgementsSupport from Dr. Okafor’s National Science Foundation grant and that from Intelligent Systems Center is greatly acknowledged.

ApproachAll machining experiments will be conducted on Cincinnati Milacron, Sabre 750 vertical machining center equipped with Acramatic 2100 controller, using a five-flute solid carbide end-mill tool sized 0.5inch diameter. Surface roughness will be measured with profilometer, tool wear will be measured with tool maker’s microscope, temperature of the workpiece will be measured with an embedded thermocouple probe in the workpiece and cutting force will be acquired with a 4-component Kystler dynamometer model.

Chips from end-milling Titanium Alloy

Machining set-up after end-milling Titanium alloy