Superalloys are known to be hard to process materials by reason of their elevated temperature resistance, fast strain hardening, minimal thermal conductivity, and the existence of abrasive deposits in the structure. At this point, it required the advancement of tools (carbides, ceramics and CBN) with superior thermal and chemical constancy for improving the machinability of aerospace alloys. Poor machinability of aircraft engine alloys exposes the tool cutting edge to extreme thermal and mechanical pressures and these frequently cause rapid tool wear
Nickel based super alloys display rather difficult machinability characteristics owing to their high temperature strength, work hardening tendency and low thermal diffusivity. Like stainless steels, their austenitic matrix is responsible for work hardening during machining. Besides, during high machining temperatures, these alloys have affinity to weld with the tool material. The strong tendency to form built up edge (BUE) and the presence of hard intermetallic compounds and abrasive carbides in their microstructure further exacerbate cutting difficulties. Excessive tool wear is one of the major problems in machining of nickel-based superalloys. Because of the low thermal conductivity, most of the heat produced during machining is transferred to the tool. Subsequently, high tool tip temperatures cause excessive tool wear, which can limit cutting speeds and reduce productivity. Another factor negatively affecting the machinability is the continuous and tough chips produced during machining. Although there are significant improvements in cutting tools, machine control systems, cooling and lubrication technology, machining of superalloys is still leading to problems in terms of cutting tool wear and surface integrity.
Being a major cause of the poor machinability of the superalloys, tool wear is an inevitable process during machining and it progresses until tool life ends. However, should the precaution be taken by knowing the type, rate and timing of the wear, the negativity of the tool wear can be minimized.
Cutting speed stands as the major factor of tool wear in machining of Ni-based superalloys. Tool wear rate is higher in areas in which concentrated force and temperature is present. This increased temperature negatively affects carbide tools, as they are composed of cobalt binders. While in ceramic tools, feed rate increase, which causes excessive flank wear, is the limiting factor. Feed rate is another limiting factor of tool wear. For carbide tools, average to higher feed rate values is recommended. For ceramic tools, lower feed rate values are preferable
Advances in the cutting tool industry are becoming more and more promising to machine difficult-to-machine parts with ease and precision. Advanced cutting tools help optimize machinability. Because hard-to-machine materials need an advanced insert to endure high heat creation, toughness and impact resistance in machining. Cutting tools utilized in the machining of superalloys have properties such as wear strength, excellent thermal shock, chemical consistency, high strength and toughness, efficient hot hardness at high temperatures at the cutting edge and workpiece. In the machining of nickel-based superalloys and titanium alloys, uncoated and coated sintered carbide tools and ceramic and CBN tools are generally used in continuous cutting applications at high speeds.
Article contributed
by Rajesh Gupta
Designation : VP – Sales & Marketing
Company :Â Rudrali Hitech Tools Pvt Ltd
Experience : 30 Years
Education : B-Tech in Mechanical, MBA in Marketi