Hard cutting (an application field of high-speed cutting technology) refers to a processing method for machining hardened materials (usually hardness between 54-63HRC) – hardened steel, gray cast iron, ductile iron, powder metallurgy and special materials parts using superhard cutting tools such as ceramics, superhard CBN, and superfine cemented carbide on lathes. This processing is usually used as final processing or finishing. It has the advantages of high efficiency, good flexibility, simple process and low investment compared to traditional grinding. It is increasingly used in time-consuming and high-cost grinding and polishing processing scenarios.
For example, in the automotive industry, CBN cubic boron nitride cutting tools are used to process the inner hole of 20CrMo5 hardened gears (60HRC) instead of grinding, and the surface roughness can reach 0.22μm. It has become a new process promoted by the automotive industry at home and abroad.
Hard Cutting Finishing PK Grinding Finishing
For high-hardness steel, the traditional processing method is mainly to rough-process the workpiece under annealing conditions, then heat treat it, and finally grind it to complete the workpiece processing. Hard cutting technology is different from traditional processing methods. It has fewer processing steps than traditional processing methods. By eliminating the second heat treatment to save processing time, hard processing technology provides higher flexibility, increases material removal rate, and can even achieve dry processing. Due to the emergence of superhard material tools and the improvement of the precision of processing equipment such as CNC machine tools, the use of hard cutting instead of grinding to complete the final processing of parts – turning instead of grinding has become a new and important finishing method.
Hard cutting can greatly shorten the process flow, increase the flexibility of the processing technology, reduce the investment in enterprise equipment, improve productivity, and has huge economic benefits. since hard cutting basically does not use cutting fluid, it is beneficial to environmental protection, so hard cutting is getting more and more attention. Of course, this superhard material tool is not cheap, but after practical application, you will definitely find which method is more suitable for your actual requirements, which one is more cost-effective to use, and can create more value for your product.
Hard Cutting Tool Materials
Hard Cutting Tool Material Types
High-speed hard cutting requires the use of hard and super-hard cutting tool materials. The super-hard tool materials that can be used for high-speed hard cutting mainly include diamond, polycrystalline cubic boron nitride (PCBN), ceramics, TiC (N)-based cemented carbide, etc. Among them, diamond is mainly used to process high-hard non-ferrous metals and non-metallic materials, while polycrystalline cubic boron nitride, ceramics and TiC (N)-based cemented carbide are mainly used to process high-hard steel, cast iron and super alloys.
New Cemented Carbide End Mill Tool Materials
Cemented carbide milling cutters have good tensile strength and fracture toughness, but their low hardness and poor high temperature stability limit their application in high-speed hard cutting. However, fine-grained and ultra-fine-grained cemented carbides have a smaller hard phase size after grain refinement, and the bonding phase is more evenly distributed around the hard phase, which improves the hardness and wear resistance of cemented carbides and is widely used in hard cutting.
Metal ceramic insert in cemented carbide industry generally refers to TiCN/TiC/TiC/TiC/S with Co or Ni as bonding phase. In many cases, one or more nitrides of VB, VB and VB group metals in the periodic table are added as additives to enhance the mechanical and high temperature properties of metal ceramics.
Ceramic Cutting Tools
Ceramic cutting tool materials include alumina (Al2O3), silicon nitride (Si3N4) and silicon aluminum oxynitride (SiAlON) ceramics. Because Si3N4 and SiAlON ceramics have relatively high toughness, especially their high-temperature toughness, tools made of this material are most suitable for cutting cast iron and heat-resistant superalloys. NTK’s five black ceramic materials are made by adding carbides to alumina to enhance toughness and hardness. They have high-temperature red hardness and low plasticity and can be used to turn alloy steel, cold-worked or ductile iron rolls, and powder metallurgy metals with a hardness of up to HRC62.
Since ceramic cutting tools are very brittle, in order to improve the edge strength of ceramic tools, negative chamfers must be used. Generally, T-shaped or double T-shaped edges are selected. Liquid cutting fluids cannot be used during the cutting process of ceramic tools. Therefore, ceramic tool materials generally develop in the direction of toughening and self-lubrication.
PCBN Tool Material
Cubic boron nitride (CBN) is a new type of inorganic superhard material synthesized by ultra-high temperature and high pressure technology using hexagonal boron nitride (commonly known as white graphite) as raw material. It is a synthetic material with hardness second only to diamond. It has the characteristics of high strength and hardness, good wear resistance and heat resistance. PCBN material is an ideal tool material for hard cutting. It has stable chemical properties, good thermal conductivity, and heat resistance of 1400-1500℃. The CBN content in PCBN cutting tool materials and the type of metal binder are the main factors affecting the performance of PCBN materials. It can be used for semi-finishing and finishing of high-temperature alloys, hardened steel, chilled cast iron and other materials.
Diamond Cutting Tools
Diamond is an allotrope of carbon and the hardest material in nature. Diamond tools have high hardness, high wear resistance and high thermal conductivity, and are widely used in the processing of non-ferrous metals and non-metallic materials. Especially in the high-speed cutting of aluminum and silicon-aluminum alloys, diamond tools are the main cutting tool variety that is difficult to replace. However, the disadvantage of diamond tools is that they have poor thermal stability.
When the cutting temperature exceeds 700℃~800℃, they will completely lose their hardness; in addition, they are not suitable for cutting ferrous metals, because diamond (carbon) easily reacts with iron atoms at high temperatures, converting carbon atoms into graphite structures, and the tools are easily damaged. According to different sources and process routes, diamond tools can be divided into the following three categories.
Natural diamond tools. Natural diamond has been used as a cutting tool for hundreds of years. After fine grinding, the natural single crystal diamond tool can be extremely sharp, with a cutting edge radius of up to 0.002μm, which can achieve ultra-thin cutting, and can process extremely high workpiece precision and extremely low surface roughness. It is a recognized, ideal and irreplaceable ultra-precision machining tool.
PCD diamond tool. Natural diamond is expensive, and the diamond widely used in cutting is polycrystalline diamond (PCD). Since the early 1970s, polycrystalline diamond (Polycrystauinediamond, referred to as PCD insert) prepared by high temperature and high pressure synthesis technology has been successfully developed. Artificial polycrystalline diamonds have replaced natural diamond tools on many occasions. PCD raw materials are abundant, and its price is only a few tenths to a dozen of natural diamonds. PCD tools cannot grind extremely sharp edges, and the surface quality of the processed workpiece is not as good as natural diamonds. At present, it is not easy to manufacture PCD with chip breakers in industry. insert. Therefore, PCD can only be used for precision cutting of non-ferrous metals and non-metals, and it is difficult to achieve ultra-precision mirror cutting.
CVD diamond tools. From the late 1970s to the early 1980s, CVD diamond technology appeared in Japan. CVD diamond refers to the synthesis of diamond film on a heterogeneous substrate (such as cemented carbide, ceramics, etc.) by chemical vapor deposition (CVD). CVD diamond has the same structure and characteristics as natural diamond.
The performance of CVD diamonds is very close to that of natural diamonds. It has the advantages of natural single-crystal diamond and polycrystalline diamond (PCD), and overcomes their shortcomings to a certain extent.
Coated End Mills
Coating the tool is one of the important ways to improve tool performance. The emergence of coated cutting tools has made a major breakthrough in tool cutting performance. Coated tools are coated with one or more layers of refractory compounds with good wear resistance on the tough tool body. It combines the tool base with the hard coating, thereby greatly improving the tool performance. Coated tools can improve processing efficiency, improve processing accuracy, extend tool life, and reduce processing costs.
Hard Cutting Tool Characteristics
The workpieces cut by hard cutting technology are mainly high-hardness workpieces. During the cutting process, the cutting force is large, and coolant is generally not used in the cutting process. The temperature can reach 900°C, and the tool is easy to wear. This requires hard cutting tools to have the characteristics of high strength, high temperature resistance, stable chemical properties, good thermal conductivity, and good wear resistance.
