Work Piece

Characteristics: The P class material group includes carbon steels as well as alloy steels, the major component of which is iron(Fe). Carbon steels consist of iron-carbon alloys and are classified by carbon(C) content as low-C steel (<0.25%), medium-C steel (0.25%-0.60%) and high-C steel (0.60%-1.70%). Low-C steels have good toughness and weldability, and are most used for forming and welding applications. Medium-C steels have high strength and hardness and are suitable for mechanical components that require wear resistance and some strength. High-C steels are used in extreme environments where very high hardness and wear resistance are required. The alloying elements in the alloy steels are mainly Ni、Cr、Mo、V、W and etc, which can improve the hardness, corrosion resistance, high temperature resistance and wear resistance. According to the alloying element content, the alloy steels can be classified as low-alloyed steel (<5%), medium-alloyed steel (5% -10%) and high-alloyed steel (>10%).

Difficulties in machining: The P class material usually has good machinability, but the carbon concentration, hardness and etc. would make a big difference. Low-C steel has larger viscidity, which make it to be difficult to break the chip, increased adhesive wear, which will lead to built-up edge. Alloy steel machinability depends on the alloying elemens content and hardness, the higher the alloy content and hardness, the lower the machinability Carbide and some of the alloying elements will aggravate the abrasive wear, which makes the failure forms are mainly the flank wear and crater wear.

Characteristics: The hardness of this type material is between 45 and 65 HRC. Common materials include carburising steels, bearing steels and tool steels. Due to their high hardness, all materials in this group are difficult to machine. martensitic substrate, as an example, have dense stucture with excellent wear resistance but low ductiliy. Its thermal conductivity is as low as 15-25 W/m-K, which makes them susceptible to thermal shock during machining. Typical parts made by this kind of mateials include: drive shafts, gears, steering gears, and punching dies.

Difficulties in machining: Usually, the main machining process to this kind of materials is finishing. During the cutting process, a lot of heat is generated and the cutting edge is suffered significant abrasive wear. The high hardness leads to micro-chipping of the edge of cutting tools. To avoid this problem, the use of ultra-fine grain carbide (K10-K20) or CBN tools is required, since those cutting tools have good red hardness, chemical stability, mechanical strength and resistance to abrasive wear. Turning this materials are mainly using CBN tools, while carbide is mainly used for milling and drilling.

Characteristics: M class stainless steels are mainly composed of iron(Fe), and the chromium(Cr) content is larger than 12%, with other alloying elements, like Ni, Mo, Nb, Ti, etc.. These materials have excellent corrosion resistance and high temperature strength. Based on the content of Cr and nickel(Ni) in the material is classified as ferritic, martensitic, austenitic and austenitic - ferritic (duplex) stainless steel. Ferritic and martensitic stainless steels’ chromium content are usually in the range of 12-18%, with a little other alloying elements. They are easy to machining and hardening, and has low weldability and medium corrosion resistance. Austenitic stainless steels’ Cr content and Ni content are usually 18% and 8%, separatly (such as 304 stainless steel). Adding 2-3% of molybdenum(Mo) can improve corrosion resistance (such as 316 stainless steel). Duplex stainless steels’ Cr content and Ni content are usually 18-28% and 4-7%, separatly, These stainless steel high tensile strength and high corrosion resistance.

Difficulties in machining: The wear of cutting tools to machining these materials are mainly flank wear, crater wear and build-up edge A large amount of heat is geneated at the cutting edge during the cutting process, which may lead to plastic deformation and severe crater wear, meanwhile cutting processing is prone to harden the surfaces and creates hard chips, which in turn lead to notch wear. Hardened surface can cause the coating and base material to detach from the cutting edge, leading to chipping and poor surface quality. Machining austenite would produce long continuous chips with high strength, which make it difficult to break the chip.

Characteristics: K class materials-cast irons are alloys mainly composed of iron(Fe), carbon(C) and silicon(Si), where C content is generally greater than 2.11% or Fe-C alloy with eutectic organisation. The presence of C in cast iron is mainly in the form of graphite As a result, cast irons have a high vibration dissipation, low notch sensitivity, excellent wear resistance and has good machinability. They are classified as grey cast iron (HT250), malleable cast iron (KTH300-06), nodular iron (QT400-18), compacted cast iron (RuT400). Cast irons have a high carbon content of 2.5%-4.0%, with silicon content of 1.0%-3.0%, hardness of HB 150-300, thermal conductivity of 50-80 W/m-K and low coefficient of thermal expansion These properties make cast ions are suitable for high-speed machining. Due to its excellent casting performance and low price, it is applied to various machine tool bases, iron pipes and auto parts.

Difficulties in machining: The graphite morphology in cast iron determines the cutting characteristics, flake graphite is prone to produce ultrashort chips, and spherical graphite will increase the cutting resistance. All cast irons contain a silicon carbide (SiC) graphite phase, which severely abrades the cutting edge and causes abrasive wear. In addition, the brittleness of cast iron can cause edge chipping. grey cast iron and malleable cast iron are very easy to machine, but nodular cast irons, compacted cast irons and isothermal quenched nodula cast irons are more difficult to machine, mainly due to the higher C and Si content.

Characteristics: S class materials includes titanium-based materials and many high-alloyed materials with iron(Fe), cobalt(Co) and nickel(Ni), which are classified into iron-, nickel- and cobalt-based high-temperature alloys. This type of material has high strength, good corrosion resistance and high heat resistance, it can work stably for a long time at a high temperature of over 600℃ and under certain stress. For materials like Ti-6Al-4V, TC4 and other α + β titanium alloys, Their strength-to-weight ratios are up to 110 kN-m/kg with thermal conductivity of only 7 W/m-K, and temperature at cutting zone up to 1000 ° C. While β-phase content larger than 20%, there is a significant increase in plasticity, which leads to serious chip adhesion For high-temperature alloys, such as GH4169 containing γ ‘strengthened phase, its heat resistance can be maintained upto 650 ℃, which makes it to be difficult to machine  High-temperature alloys are mainly used in aerospace, gas turbines and power generation industries. Titanium alloys are more common in electronic product structures such as mobile phone frame knots.

Difficulties in machining: High-temperature alloys belong to the materials that is hard to machine, due to thei high machining stickness, relatively large elastic modulus and poor, thermal conductivity, which lead to generate lots heat and produce build-up-edge.. Therefore, the processing of the coated knife has higher requirements, so that the tool is prone to abrasive wear, diffusion wear and bonded wear and other forms of failure wear.

Characteristics: N class non-ferrous metals are defined as all metals other than iron(Fe), manganese(Mn) and chromium(Cr). For examples, aluminium alloys (6061, 7075), copper alloys (H62, C1100), magnesium alloys (AZ91D, AM60), etc. are all belong to this class. They have a hardness of HB 50-150 and a thermal conductivity of >120 W/m-K. Non-ferrous metals are usually softer with unique advantages, such as aluminium alloys with better strength and excellent corrosion resistance, and copper alloys with excellent electrical conductivity. Non-ferrous metals have a wide range of applications in machinery manufacturing, electric power, communications, home appliances, etc, industries.

Difficulties in machining: Using a cutting tool with relatively sharp cutting edge to machine the non-ferrous metals can achieve higher cutting speeds and longer cutting life. However, non-ferrous metals have small modulus of elasticity, low plastic deformation capacity and relatively large viscosity Fo Aluminium alloys, when Si content is larger than 12% (such as AlSi10Mg), the formation of hard SiC phase leads a increasing requirement of the tools’ abrasion resistance and toughness. Copper alloys are prone to produce long rolls of chips when cutting, which has a negative impact on the cutting.