PCD cutting tools, as an advanced cutting tool, are made by tightly combining the superhard material polycrystalline diamond (PCD) with the cutting tool matrix and using exquisite craftsmanship. PCD material is known for its unparalleled hardness and wear resistance, making it ideal for processing a variety of materials. Compared with traditional cutting tools, PCD cutting tools show excellent performance during the cutting process, including higher cutting speed, lower cutting force, better surface quality, and longer tool life.
Characteristics of PCD Cutting Tools
Ultra-high hardness and wear resistance are the hallmark features of PCD cutting tools. The hardness of PCD material is second only to natural diamond and much higher than other traditional tool materials. This ultra-high hardness gives PCD tools extremely strong wear resistance, allowing them to maintain a sharp edge when processing hard materials and significantly extend tool life. At the same time, PCD cutting tools remain stable under harsh working conditions of high temperature and high pressure, effectively reducing tool wear.
Excellent compressive strength allows PCD cutting tools to remain stable under high load conditions. During the cutting process, the tool will be subjected to huge cutting forces, especially when processing hard materials, the tool will bear greater pressure.
Excellent thermal conductivity is a major advantage of PCD tools in high-speed cutting. PCD material has good thermal conductivity, which helps to dissipate heat quickly and reduce the temperature of the tool, thereby reducing thermal deformation and improving machining accuracy.
Main Indicators of PCD Tools
- The hardness of PCD can reach 8000HV, which is 8 to 12 times that of cemented carbide.
- The thermal conductivity of PCD is 700W/mK, which is 1.5 to 9 times that of cemented carbide, and even higher than PCBN and copper, so PCD tools transfer heat quickly.
- The friction coefficient of PCD is generally only 0.1 to 0.3 (the friction coefficient of cemented carbide is 0.4 to 1), so PCD tools can significantly reduce cutting forces.
- The thermal expansion coefficient of PCD is only 0.9×10^-6~1.18×10^-6, which is only equivalent to 1/5 of cemented carbide. Therefore, PCD tools have small thermal deformation and high processing accuracy.
- The affinity between PCD cutting tools and non-ferrous metals and non-metallic materials is very small. During the machining process, chips are not easily bonded to the tool tip to form built-up edge.
PCD Tool Manufacturing Technology
Manufacturing Process
- Manufacturing of PCD composite inserts: PCD composite inserts are made of natural or synthetic diamond powder and binders (containing cobalt, nickel and other metals) in a certain proportion at high temperatures (1000 to 2000°C) and high pressures (50,000 to 100,000 atmospheres). ) and sintered under During the sintering process, due to the addition of binding agents, bonding bridges with TiC, SiC, Fe, Co, Ni, etc. as the main components are formed between diamond crystals. The diamond crystals are embedded in the skeleton of the bonding bridge in the form of covalent bonds. The composite sheet is usually made into a disc with a fixed diameter and thickness, and the sintered composite sheet needs to be ground, polished and subjected to other corresponding physical and chemical treatments.
- Processing of PCD insert: The processing of PCD insert mainly includes steps such as cutting of composite sheets, welding of blades, and sharpening of blades.
Cutting Process
Because PCD cutting tools have high hardness and wear resistance, special processing techniques must be used. At present, several process methods such as wire EDM, laser processing, ultrasonic processing, and high-pressure water jet are mainly used to process PCD composite inserts.
- Wire EDM uses electrical energy to discharge in tiny gaps to remove material layer by layer, and is suitable for precision machining.
- Laser processing uses high-energy laser beams to precisely cut and engrave materials, and is characterized by high efficiency and high precision.
- Ultrasonic machining uses ultrasonic vibration combined with abrasives to perform micro-cutting of materials, and is suitable for processing complex shapes.
- High-pressure water jet uses abrasives added to the high-pressure water flow to cut materials, and is suitable for cold processing to avoid the thermal impact of the material.
Among the above processing methods, EDM has the best effect. The presence of bonding bridges in PCD makes it possible to machine composite sheets by EDM. In the presence of working fluid, the pulse voltage is used to form a discharge channel in the working fluid close to the electrode metal, and locally generate discharge sparks. The instantaneous high temperature can cause the polycrystalline diamond to melt and fall off, thereby forming the required triangle, rectangle or Square cutter head blank. The efficiency and surface quality of EDM PCD composite insert are affected by factors such as cutting speed, PCD particle size, layer thickness and electrode quality. The reasonable selection of cutting speed is very critical. Experiments show that increasing the cutting speed will reduce the processed surface quality. If the cutting speed is too low, the phenomenon of “overshooting” will occur and the cutting efficiency will be reduced. Increasing PCD insert thickness will also reduce cutting speed.
Welding Process
In addition to mechanical clamping and bonding methods, the PCD composite insert is mostly pressed onto the cemented carbide substrate through brazing. Welding methods mainly include laser welding, vacuum diffusion welding, vacuum brazing, high-frequency induction brazing, etc. At present, high-frequency induction heating brazing with low investment and low cost is widely used in PCD insert welding. During the blade welding process, the selection of welding temperature, flux and welding alloy will directly affect the performance of the tool after welding. During the welding process, the control of the welding temperature is very important.
If the welding temperature is too low, the welding strength will be insufficient; if the welding temperature is too high, PCD will easily graphitize and may lead to “overburning”, affecting the PCD composite insert and cemented carbide. The combination of the matrix. In the actual processing process, the welding temperature can be controlled according to the holding time and the degree of redness of PCD (generally should be lower than 700°C). High-frequency welding abroad mostly uses automatic welding technology, which has high welding efficiency, good quality, and can achieve continuous production; domestically, manual welding is mostly used, with low production efficiency and unsatisfactory quality.
Sharpening Process
The high hardness of PCD makes its material removal rate extremely low (even only one ten thousandth of the removal rate of cemented carbide). At present, the PCD tool sharpening process mainly uses ceramic bond diamond grinding wheels for grinding. Since the grinding between the grinding wheel abrasive and PCD is the interaction between two materials with similar hardness, the grinding law is relatively complex. For high-grained, low-speed grinding wheels, the use of water-soluble coolant can improve the grinding efficiency and grinding accuracy of PCD.
The choice of grinding wheel bond should depend on the grinder type and processing conditions. Since electric discharge grinding (EDG) technology is almost unaffected by the hardness of the workpiece to be ground, using EDG technology to grind PCD has great advantages. The grinding of certain complex-shaped PCD tools (such as woodworking tools) also has a huge demand for this flexible grinding process. With the continuous development of electric discharge grinding technology, EDG technology will become a main development direction of PCD grinding.
Classification of PCD Tools
PCD Tools for Metal Cutting
PCD tools for metal cutting are mainly divided into welded PCD tools and indexable PCD inserts. In recent years, welded shank PCD tools have developed rapidly in the automobile and parts industry. There are mainly PCD milling cutters, PCD boring cutters, PCD reamers or a combination of two or even more than three of the above tools. PCD tools are mainly in the form of cylindrical shank, BT shank (BT40 and BT50), SK shank (SK40 and SKS0). , HSK handle (HSK63 and HSK100), etc.
PCD Cutting Tools for Wood Processing
PCD cutting tools are also widely used in the wood processing industry. PCD woodworking tools can be mainly divided into two categories: PCD saw blades and PCD formed woodworking milling cutters.
PCD Tool Design Principles
PCD Particle Size
The choice of PCD particle size is related to the tool processing conditions. For example, when designing tools for finishing or super-finishing, PCD with high strength, good toughness, good impact resistance, and fine grain should be selected. Coarse-grain PCD tools can be used for general roughing. The particle size of PCD material has a significant impact on the wear and breakage properties of tools. Research shows that the larger the PCD particle size number, the stronger the wear resistance of the tool.
Insert Thickness
Normally, the layer thickness of PCD composite insert is about 0.3~1.0mm, and the total thickness after adding the cemented carbide layer is about 2~8mm. The thinner PCD layer thickness is beneficial to the electric discharge machining of insert. When the PCD composite insert is welded to the cutter body material, the thickness of the cemented carbide layer cannot be too small to avoid delamination caused by the stress difference between the bonding surfaces of the two materials.
Structural Design
The geometric parameters of PCD tools depend on specific processing conditions such as workpiece conditions, tool materials and structures. Since PCD tools are often used for finishing machining of workpieces, the cutting thickness is small (sometimes even equal to the cutting edge radius of the tool), which is a micro-cutting. Therefore, its relief angle and flank surface have a significant impact on the processing quality. Small relief angle, Higher flank surface quality can play an important role in improving the processing quality of PCD tools.
- There are various ways to connect the PCD composite insert to the tool holder, including mechanical clamping, integral welding, machine clamp welding and indexability.
- Mechanical clamping is a method of fixing the PCD composite insert on the tool holder through a clamp, which facilitates quick replacement and adjustment.
- Integral welding is to directly weld the PCD composite insert and the tool holder together to form an overall structure to ensure the stability and rigidity of the connection.
- Machine clamp welding combines the advantages of mechanical clamping and welding, which can provide strong fixing force and a certain degree of flexibility.
- The indexable method allows continued use by rotating or replacing the insert after the cutting edge is worn, extending the service life of the tool.
PCD Tool Cutting Parameters
PCD Tool Cutting Speed
PCD tools can perform cutting operations at extremely high spindle speeds, but the impact of changes in cutting speed on processing quality cannot be ignored. Although high-speed cutting can improve processing efficiency, under high-speed cutting conditions, the increase in cutting temperature and cutting force can cause damage to the tool tip and cause vibration in the machine tool. When processing different workpiece materials, the reasonable cutting speed of PCD tools is also different. For example, the reasonable cutting speed for milling Al2O3 laminate flooring is 110~120m/min; the reasonable cutting speed for turning SiC particle reinforced aluminum-based composite materials and silicon oxide-based engineering ceramics It is 30~40m/min.
PCD Tool Cutting Feed
If the feed amount of the PCD tool is too large, the residual geometric area on the workpiece will increase, resulting in an increase in surface roughness; if the feed amount is too small, the cutting temperature will rise and the cutting life will be reduced.
PCD Tool Cutting Depth of Cut
Increasing the cutting depth of PCD tools will increase the cutting force and cutting heat, thereby aggravating tool wear and affecting tool life. In addition, the increase in cutting depth can easily cause PCD tool edge chipping.
PCD tools with different particle size levels exhibit different cutting performance when processing different workpiece materials under different processing conditions. Therefore, the actual cutting parameters of PCD tools should be determined according to specific processing conditions.
