In metal cutting processing, there will be different workpiece materials, different materials its cutting formation and removal characteristics are different, how do we master the characteristics of different materials? ISO standard metal materials are divided into 6 different type groups, each of which has unique properties in terms of machinability and will be summarized separately in this article.
Metal materials are divided into 6 categories:
(1) P-steel
(2) M-stainless steel
(3) K-cast iron
(4) N- non-ferrous metal
(5) S- Heat resistant alloy
(6) H-hardened steel
What is steel?
- Steel is the largest material group in the field of metal cutting.
- Steel can be unhardened or tempered steel (hardness up to 400HB).
- Steel is an alloy with iron (Fe) as its main component. It is made through the smelting process.
- Unalloyed steel has a carbon content of less than 0.8%, only Fe and no other alloying elements.
- The carbon content of alloy steel is less than 1.7%, and alloying elements are added, such as Ni, Cr, Mo, V, W, etc.
- Low carbon content = tough viscous material.
- High carbon content = brittle material.
Processing characteristics:
- Long chip 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 to process ISO P materials are within a limited range of values.
What is stainless steel?
- Stainless steel is an alloy material with at least 11%~12% chromium.
- The carbon content is usually very low (as low as 0.01% Max).
- The alloys are mainly Ni (nickel), Mo (molybdenum) and Ti (titanium).
- Forms a dense layer of Cr2O3 on the surface of the steel, making it resistant to corrosion.
In Group M, the majority of applications are in the oil and gas, pipe fitting, flanges, processing and pharmaceutical industries.
The material forms irregular, flaky chips and has a higher cutting force than ordinary steel. There are many different types of stainless steel. Chip breaking performance (from easy to almost impossible to break chips) varies depending on alloy characteristics and heat treatment.
Processing characteristics:
- Long chip material.
Chip control is relatively smooth in ferrite and more difficult in austenite and biphase.
- Unit cutting force: 1800~2850 N/mm².
- High cutting force, chip buildup, heat and work hardening during machining.
What is cast iron?
There are three main types of cast iron: gray cast iron (GCI), nodular cast iron (NCI) and vermicular cast iron (CGI).
- Cast iron is mainly composed of Fe-C, with a relatively high silicon content (1%~3%).
- Carbon content of more than 2%, which is the largest solubility of C in the austenite phase.
- Cr (chromium), Mo (molybdenum) and V (vanadium) are added to form carbides, increasing strength and hardness but reducing machinability.
Group K is mainly used in automotive parts, machine manufacturing and ironmaking.
The chip forming of the material varies, from nearly powdered chips to long chips. The power required to process this material group is usually small.
Note that there is a big difference between gray cast iron (which usually has chips that are approximately powdered) and ductile cast iron, whose chip breaking is in many cases more similar to steel.
Processing characteristics:
- Short chip material.
- Good chip control in all operating conditions.
- Unit cutting force: 790~1350 N/mm².
- Abrasive wear occurs when machining at higher speeds.
- Medium cutting force.
What are non-ferrous materials?
- This category contains non-ferrous metals, soft metals with hardness less than 130HB.
Nonferrous metal (Al) alloys with nearly 22% silicon (Si) make up the largest portion.
- Copper, bronze, brass.
Aircraft manufacturers and manufacturers of aluminium alloy car wheels 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.
Processing characteristics:
- Long chip material.
- If it is alloy, chip control is relatively easy.
- Non-ferrous metals (Al) are sticky and require the use of sharp cutting edges.
- Unit cutting force: 350~700 N/mm².
- The cutting force and power required to process ISO N materials are within a limited range of values.
What is heat resistant alloy?
Heat-resistant alloys (HRSA) include many highly alloyed iron, nickel, cobalt or titanium-based materials.
- Group: Iron, nickel, cobalt.
- Working conditions: annealing, solution heat treatment, aging treatment, rolling, forging, casting.
Features:
Higher alloy content (cobalt is higher than nickel) ensures better heat resistance, higher tensile strength and higher corrosion resistance.
S-group materials, which are difficult to process, are mainly used in the aerospace, gas turbine and generator industries.
The range is wide, but high cutting forces are usually present.
Processing characteristics:
- Long chip material.
- Chip control is difficult (jagged chips).
- A negative front Angle is required for ceramics and a positive front Angle is required for cemented carbide.
- Unit cutting force:
For heat-resistant alloys: 2400~3100 N/mm².
For titanium alloy: 1300~1400 N/mm².
- High cutting force and power required.
What is hardened steel?
- From a processing point of view, hardened steel is one of the smallest subgroups.
- This group contains tempered steels with hardness >45 to 65HRC.
- In general, the hardness range of the hard parts being turned is generally between 55 and 68HRC.
The hardened steels in Group H are used in a variety of industries, such as the automotive industry and its subcontractors, as well as in machine building and mold operations.
Usually continuous, red-hot chips. This high temperature helps to reduce the kc1 value, which is important to help solve application challenges.
Processing characteristics:
- Long chip material.
- Relatively good chip control.
- Require negative front Angle.
- Unit cutting force: 2550~4870 N/mm².
- High cutting force and power required.
Post time: Jul-24-2023