Factors to be considered in the choice of cutting tools
Choosing a cut machine tool based on price and expected monetary savings is not usually the best decision. In the choice for cutting tools, what should always be considered by machinists is productivity and extended tool life. Different machining operations have different requirements according to the cut machine material which should have the following characteristics:
- It must be harder than the work material being cut
- It must have high temperature stability
- It must have resistance to wear and thermal shock
- It must be impact resistant
- It must be chemically inert to the work material and cutting fluid
No single cut machine possesses all these properties but there are some cutting tool materials that provide more superior performance than others. For example, ceramic cutting tool material has high heat resistance but it has low resistance to shock and impact. Due to the demands of production, rates of material removal have increased which requires heat resistant cutting holes. This has resulted into a progression from high-speed steel to carbide and eventually to ceramic and other materials.
Why carbide has replaced the traditional high speed steel
High speed steel can cut 4 times faster than carbon steel. The use of titanium nitride coatings has provided high speed steel tools with high surface hardness, corrosion resistance and minimal friction. However, carbide and carbide coated tools have now replaced high speed steel because they can cut 3 to 5 times faster than the latter. Each type of carbide affects the characteristics of the cut machine differently. For example, higher tungsten carbide content can improve wear resistance but tend to reduce tool strength. A cutting tool that has a higher percentage of cobalt binder has increased strength but lower wear resistance. This is the reason why manufacturers of carbide cut machines offer a variety of tools for different applications.
Factors in the choice of carbide cutting tools
There are no specific standards in the choice of carbide cutting tools and the machinist has to rely on the specifications provided by manufacturers on the grades for certain applications. About 2/3 of carbide tools are coated and they are considered for many applications due to longer life and faster machining. On the other hand, there is another option with ceramic cut machine that is harder and more heat resistant than carbide although it is more brittle. These ceramic cutting tools are more suitable for machining cast iron, hard steel and super alloys. Ceramic cut machines are available in two types, the alumina-based ceramic that is used for semi-finishing of ferrous and some non-ferrous materials and the silicon nitride-based ceramic used for rough and heavy machining of cast iron and super alloys.