A guide to workpiece materials and chip formation
In the complex world of metal cutting, selecting the correct cutting tool and process is essential to achieve optimal results. One of the key factors to consider is the workpiece material being cut, as different materials have different characteristics for chip formation and removal.
Six main groups of workpiece materials are classified based on their properties and characteristics. These include steel, stainless steel, cast iron, non-ferrous materials, heat-resistant super alloys, and hardened steel. To ensure the proper cutting tool and process is selected for a given material, it is important to understand the specific characteristics of each group.
Steel is a widely used material in the manufacturing industry and is classified as ISO-P. This group includes low, medium, and high carbon steels, as well as alloy steels. The machinability of steel varies based on its carbon content, with low carbon steel being more easily machinable than high-carbon steel.
Steel is a long chipping material with relatively easy, smooth chip control. Low-carbon steel can be sticky and requires sharp cutting edges. The specific cutting force (kc) for steel is between 1500-2000 N/mm2. Cutting forces and the power required to machine steel stay within a limited range.
It is commonly used in the automotive, aerospace, and construction industries, as well as in the production of consumer goods such as appliances, machinery, and tools.
Stainless steel (ISO-M)
Stainless steel is a group of materials that are highly resistant to corrosion and staining, making them ideal for use in environments where hygiene and cleanliness are critical. They are classified as ISO-M and include austenitic, ferritic, and duplex stainless steels.
Stainless steel is also a long chipping material, but the chip control can be difficult in austenitic and duplex varieties. The specific cutting force for stainless steel ranges between 2100-3550 N/mm2. Machining stainless steel can create high cutting forces, built-up edges, heat, and deformation hardening.
Materials within this group are commonly used in the production of medical equipment, and chemical processing equipment, as well as in the automotive and aerospace industries.
Cast iron (ISO-K)
Cast iron is a group of materials composed primarily of iron, carbon, and silicon. They are classified as ISO-K and include grey iron, ductile iron, and malleable iron. Cast iron is known for its excellent wear resistance and damping properties.
Cast iron is a short-chipping material with good chip control in all conditions. The specific cutting force for cast iron is between 940-2700 N/mm2. Machining cast iron at higher speeds can create abrasive wear, but cutting forces are moderate.
It is commonly used in producing automotive parts, machine tool components, and pipe and fitting applications.
Non-ferrous materials (ISO-N)
Non-ferrous materials are metals that do not contain iron, such as aluminium, copper, brass, and HRSA. They are classified as ISO-N and are known for their excellent electrical and thermal conductivity, as well as their corrosion resistance.
Non-ferrous materials are long chipping materials with relatively easy chip control if alloyed. Aluminium is sticky and requires sharp cutting edges. The specific cutting force for non-ferrous materials is between 500-1750 N/mm2, and cutting forces and the power required to machine them are within a limited range.
This group of materials are commonly used in the aerospace, automotive, and construction industries, as well as in the production of consumer goods such as electronics.
Heat resistant super alloys (ISO-S)
Heat resistant super alloys are a group of materials that are designed to withstand high temperatures and extreme environments. They are classified as ISO-S and include nickel-based alloys such as Inconel and Hastelloy, as well as titanium alloys.
Heat-resistant super alloys are long chipping materials with difficult chip control (segmented chips). A negative rake angle is required with ceramics, while a positive rake angle is required with carbide. The specific cutting force for heat-resistant super alloys ranges between 3000-3800 N/mm2 for HRSA and 1550-1700 N/mm2 for titanium, and the cutting forces and power required are quite high.
Heat-resistant super alloys are commonly used in the aerospace, automotive, and energy industries, as well as in the production of gas turbines and jet engines.
Hardened steel (ISO-H)
Hardened steel is a group of materials that have been heat-treated to increase their hardness between 45-65HRc. They are classified as ISO-H and include tool steels, high-speed steels, and bearing steels.
Hardened steel, categorised as ISO-H, is a long chipping material with fair chip control. A negative rake is required, and the specific cutting force for hardened steel ranges between 2800-5550 N/mm2. Cutting forces and power required are quite high.
Hardened steel is commonly used in the production of cutting tools, dies, and moulds, as well as in the automotive and aerospace industries.
It is important to note that the specific cutting force (kc) varies for each material, and the material constant kc1 (N/mm2) must be carefully considered and adapted for each machining operation.
In summary, understanding the different workpiece materials and their characteristics for chip formation and removal is essential in selecting the appropriate cutting tool and process. In summary, understanding the classification and characteristics of workpiece materials is essential in selecting the appropriate cutting tool and process for a given application. Each material has its unique properties and challenges when it comes to machining. By selecting the correct geometry and grade of cutting tool, engineers can optimise the cutting process and achieve optimal results in metal cutting.