In metal cutting, there will be different workpiece materials, and different materials have different cutting formation and removal characteristics. How can we master the characteristics of different materials? ISO standard metal materials are divided into 6 different type groups, each type has unique characteristics in terms of machinability, and they will be summarized separately in this article.Metal materials are divided into 6 categories:
- P-steel
- M-stainless steel
- K-cast iron
- N- non-ferrous metals
- S-heat-resistant alloy
- H-hardened steel
#1 P Steel
What Is Steel?
- Steel is the largest material group in the field of metal cutting.
- Steel can be non-hardened steel or quenched and tempered steel (hardness up to 400HB).
- Steel is an alloy whose main component is iron (Fe). It is manufactured through a smelting process.
- Unalloyed steels have less than 0.8% carbon and only Fe and no other alloying elements.
- The carbon content of alloy steel is less than 1.7%, and alloying elements such as Ni, Cr, Mo, V, W, etc. are added.
Within metal cutting, Group P is the largest material group as it covers several different industrial sectors.
The material is usually a long chipping material, capable of forming a continuous, relatively uniform chip. The specific chip form usually depends on the carbon content.
- – Low carbon content = tough sticky material.
- – High carbon content = brittle material.
The Characteristics Of Processing
- Long chipping material.
- Chip control is relatively easy and smooth.
- Mild steel is sticky and requires a sharp cutting edge.
- Unit cutting force kc: 1500–3100 N/mm2
- The cutting force and power required for machining ISO P materials are within the limited range.
#2 M Stainless Steel
1.What Is Stainless Steel?
- Stainless steel is an alloy material with a minimum of 11–12% chromium.
- Carbon content is usually very low (down to a maximum of 0.01%).
- The alloys are mainly Ni (nickel), Mo (molybdenum) and Ti (titanium).
- Forms a dense layer of Cr2O3 on the steel surface, making it corrosion resistant.
In Group M, the majority of applications are in the oil and gas, fittings, flanges, process industries, and pharmaceutical industries.
The material forms irregular flaky chips, and its cutting force is higher than that of ordinary steel. There are many different types of stainless steel. Chip breaking properties (from easy to almost impossible) vary with alloy properties and heat treatment.
2.The Characteristics Of Processing
- Long chipping material.
- Chip control is relatively smooth in ferritic and difficult in austenitic and duplex.
- Unit cutting force: 1800-2850 N/mm2
- Machining with high cutting forces, built-up edge, heat and work hardening.
#3 K Cast Iron
1.What is cast iron?
- There are 3 main types of cast iron: Gray Iron (GCI), Ductile Iron (NCI) and Compacted Graphite Iron (CGI).
- Cast irons are mainly composed of Fe-C with a relatively high silicon content (1–3%).
- The carbon content exceeds 2%, which is the maximum solubility of C in the austenitic phase.
- Cr (chromium), Mo (molybdenum) and V (vanadium) are added to form carbides which increase strength and hardness but reduce machinability.
Group K is mainly used in auto parts, machine building and iron making industries.
The chip formation of the material varies from nearly powdery chips to long chips. The power required to process this material group is generally small.
Note that there is a big difference between gray cast iron (which usually has chips that are close to powder) and ductile iron, where the chip breaking is often more similar to steel.
2.The Characteristics Of Processing
- Short chipping material.
- Good chip control in all conditions.
- Unit cutting force: 790-1350 N/mm2
- Machining at higher speeds produces abrasive wear.
- Moderate cutting forces.
#4 N Non-Ferrous Metals
1.What are non-ferrous metal materials?
- This category includes non-ferrous metals, soft metals with a hardness below 130 HB.
- Non-ferrous (Al) alloys containing almost 22% silicon (Si) make up the largest portion.
- Copper, bronze, brass.
The aircraft industry and aluminum alloy automotive wheel manufacturers dominate Group N.
Although the power required per mm3 (cubic inch) is low, it is still necessary to calculate the maximum power required to obtain a high metal removal rate.
2.The Characteristics Of Processing
- Long chipping material.
- Chip control is relatively easy if it is an alloy.
- Non-ferrous metals (Al) are sticky and require sharp cutting edges.
- Unit cutting force: 350-700 N/mm2
- The cutting force and power required to process ISO N materials are within the limited range.
#5 S Heat-Resistant Alloy
1.What are Heat Resistant Alloys?
- Heat Resistant Alloys (HRSA) include many high alloy iron, nickel, cobalt or titanium based materials.
Group: Iron-based, Nickel-based, Cobalt-based
Working conditions: annealing, solution heat treatment, aging treatment, rolling, forging, casting.
characteristic:
- Higher alloy content (cobalt higher than nickel) ensures better heat resistance, higher tensile strength and higher corrosion resistance.
- Difficult-to-process S-group materials are primarily used in the aerospace, gas turbine, and generator industries.
- Wide range, but usually high cutting forces.
2.The Characteristics Of Processing
- Long chipping material.
- Difficulty in chip control (jagged chips).
- A negative rake angle is required for ceramics and a positive rake angle is required for carbide.
- Unit cutting force:
For heat resistant alloys: 2400–3100 N/mm2
For titanium alloy: 1300-1400 N/mm2
High cutting forces and power required.
#6 H Hardened Steel
1.What is hardened steel?
- Hardened steels are the smallest grouping from a machining point of view.
- This group contains quenched and tempered steels with a hardness >45–65 HRC.
- Generally, the hardness range of hard parts being turned is generally between 55–68 HRC.
Hardened steels in Group H are used in various industries such as the automotive industry and its subcontractors, as well as machine building and tooling business.
Usually a continuous, red-hot chip. This high temperature helps lower the kc1 value, which is important to help solve application challenges.
2.The Characteristics Of Processing
- Long chipping material.
- Relatively good chip control.
- Negative rake angle is required.
- Unit cutting force: 2550-4870 N/mm2
- High cutting forces and power required.