Polycrystalline diamond tools

As a superhard diamond cutting tool materials have been used for hundreds of years of history. In the tool development process, from the nineteenth century to the mid

-twentieth century, high-speed steel tool material as the main representative; 1927 Germany developed the first carbide tool material and is widely available; nineteen

fifties, Sweden and USA were synthesized diamond cutting tool with superhard materials from entering the representative period. 1970s, people were synthesized using

high pressure synthesis of   polycrystalline diamond (PCD), to solve the natural diamond scarce and expensive problems, make the diamond tool applications extended to

aviation, aerospace, automotive, electronics, stone other fields.
Features
Diamond tool with high hardness, high compressive strength, thermal conductivity and good wear resistance and other characteristics, can be obtained in a high-speed

cutting machining accuracy and processing efficiency. Above characteristics of diamond tools is determined by the state of the diamond crystal. In the diamond crystal,

the carbon atoms of the four valence electrons enter the tetrahedral bond, each carbon atom with four adjacent atoms form a covalent bond, and then form a diamond

structure, the structure is very strong binding force and direction, so that the diamond has a very high hardness. As polycrystalline diamond (PCD) of varying

orientation of the structure of fine grain diamond sintered body, although the added binding agent, the hardness and wear resistance is still lower than the single

crystal diamond. However, due to the performance of polycrystalline diamond sintered body is isotropic, so easy to split along a single cleavage plane.
Application
Polycrystalline diamond tools for industrial countries study carried out earlier, its application has been more mature. The first time since 1953 in Sweden since the

synthetic diamond , polycrystalline diamond tools for cutting a lot of research to get results, polycrystalline diamond tool application and usage is expanding rapidly.

By turning around early to drilling, milling expansion. Organized by the Japanese conducted a survey of about superhard cutting tool: polycrystalline diamond tools

people use the key consideration is based on the polycrystalline diamond tool machined surface accuracy, dimensional accuracy and tool life and other advantages. PDC

synthesis technology has been greatly developed.
Domestic polycrystalline diamond tool market with the level of development of tool technology is also expanding. At present, China First Automobile Group has over one

hundred point of use polycrystalline diamond tools, and many companies are using wood-based panels polycrystalline diamond tools for wood processing. The application

of polycrystalline diamond tools for its further promote the design and manufacture technology. Domestic Tsinghua University, Dalian University of Technology, Huazhong

University of Science, Jilin University, Harbin Institute of Technology are on active research in this area. Engaged in research and development of polycrystalline

diamond tools, production of a Shanghai Shubohate, Zhengzhou New Asia, Nanjing, Leitz, Shenzhen Runxiang, Chengdu Tool Research Institute and dozens of units.

Currently, the processing of polycrystalline diamond tools range from traditional metal cutting extended to stone processing, wood processing, metal matrix composites,

glass, ceramics and other materials processing engineering. In recent years, through the analysis of the application of polycrystalline diamond tools visible,

polycrystalline diamond tools are mainly used in the following two aspects: ① difficult to machine non-ferrous materials processing: with ordinary non-ferrous

materials difficult to machine tooling, often generating tool easy to wear, processing efficiency and low defects, and polycrystalline diamond cutting tool can exhibit

good processability. Such as the use of polycrystalline diamond cutting tool can be effectively and processing of new materials, engine pistons - hypereutectic silicon

aluminum (mechanism of the materials processing has made breakthroughs). ② difficult to machine processing of non-metallic materials: polycrystalline diamond cutting

tool is very suitable for stone, hard carbon, carbon fiber reinforced plastics (CFRP), artificial board and other difficult to machine processing of non-metallic

materials. If Huazhong University in 1990 to achieve a glass with polycrystalline diamond cutting tools; currently laminate flooring and other wood-based panels (eg

MDF) is a widely used, with a polycrystalline diamond cutting tool machining these materials can effectively prevent the tool wear and other defects .
Manufacturing Process
PCD cutting tool manufacturing process consists of two stages: ① polycrystalline diamond compact manufacturing: Polycrystalline Diamond Compact is made from natural

or synthetic diamond powder and binder (which contains cobalt, nickel and other metals) by a certain percentage in high temperature (1000 ~ 2000 ℃), pressure (5 to

100,000 atmospheres) for sintering. In the sintering process, due to binding agent is added, between the diamond crystals to form TiC, SiC, Fe, Co, Ni, etc. as a main

component with the bridge, the diamond crystals to form a covalent bond with the bridge mounted on the skeleton. The composite sheet is usually made from a fixed

diameter and the thickness of the disc, the need for sintering the composite sheet for grinding and polishing and other appropriate physical and chemical treatment. ②

polycrystalline diamond blade processing: the processing of polycrystalline diamond blade includes a composite sheet cutting, welding blade, blade sharpening and other

steps.
Cutting process
Since Polycrystalline Diamond has high hardness and wear resistance, it must use a special processing technology. Currently, the processing Polycrystalline Diamond

Compact mainly EDM wire cutting, laser processing, ultrasonic machining, high pressure water jet technology, such as several methods polycrystalline diamond compact

cutting process comparison
Process methods - Process Features
EDM - highly concentrated pulse discharge energy, a powerful explosive discharge of the polycrystalline diamond material of the metal melt, some diamond graphitization

and oxidation, and some diamond shedding, good technology, high efficiency
Ultrasonic machining - Machining efficiency is low, diamond powder consumption, dust pollution
Laser processing - non-contact processing, high efficiency machining deformation, poor process
In the processing method, EDM better results. Polycrystalline diamond composite bridges in the presence of EDM composite sheet becomes possible. In conditions of a

working fluid, a pulse voltage to the electrode near the metal working fluid is formed at the discharge channel, and the local produce sparks, polycrystalline diamond

instantaneous high temperature can melt off, thereby forming the desired triangular, rectangular or square head blank. EDM Polycrystalline Diamond efficiency and

surface quality by cutting, polycrystalline diamond size, thickness and electrode quality and other factors, including reasonable choice of cutting speed is critical

experiments show that increasing the cutting speed will be reduced surface quality, and cutting speed is too low will produce "arch wire" phenomenon and reduce cutting

efficiency. Increase will reduce the thickness of polycrystalline diamond blade cutting speed.
Welding
PCD composite sheet and the cutter body binding mode in addition to the use of mechanical clamping and bonding methods, mostly by brazing way Polycrystalline Diamond

Compact suppressed in the cemented carbide substrate. Welding methods include laser welding, vacuum diffusion welding, vacuum brazing, high frequency induction

brazing. Currently, less investment, low cost high frequency induction heating brazed polycrystalline diamond blade welding is widely used. The blade welding process,

the welding temperature, the choice of flux and solder alloy weld will directly affect the performance of the tool. During the welding process, the welding temperature

control is very important, such as welding temperature is too low, then the weld strength is not enough; such as welding temperature, polycrystalline diamond

graphitization easy and may lead to "over-burning" effect Polycrystalline Diamond Compact with the carbide substrate combination. In the actual process, according to

the holding time and the degree of difficulty of polycrystalline diamond red controlled soldering temperature (generally should be lower than 700 ℃). Use more foreign

high-frequency welding automatic welding process, welding, high efficiency, good quality, enabling continuous production; country is to use more manual welding,

production efficiency is low, the quality is not ideal.
Grinding process
The high hardness of polycrystalline diamond material removal rate so low (even only one ten thousandth of carbide removal). Currently, polycrystalline diamond tool

sharpening process is mainly made of resin bonded diamond grinding wheel. As polycrystalline diamond abrasive wheel and grinding are two hardness between similar

interaction between the materials, so the grinding more complicated laws. For high granularity, low-speed wheel, using a water-soluble coolant can improve the

efficiency of polycrystalline diamond grinding and grinding accuracy. Grinding binder type should be selected as the grinding and processing conditions. Since

discharge grinding (EDG) technology is almost free from hardness of workpiece to be ground, so the use of polycrystalline diamond grinding EDG technology has great

advantages. Some complex shapes polycrystalline diamond tools (such as woodworking tools) are also on this flexible grinding grinding process has a huge demand. As

technology continues to evolve EDG, EDG polycrystalline diamond grinding technology will become one of the main development direction.
Polycrystalline diamond size
Polycrystalline diamond size selection and tool processing conditions, such as design for finishing or super-finishing tool should be used in high strength, good

toughness, good impact resistance, fine-grained polycrystalline diamond. Coarse grain polycrystalline diamond tools can be used for general roughing. Polycrystalline

diamond material particle size for tool wear and breakage significantly influence the performance. Studies show that: the greater the number of polycrystalline diamond

size, tool wear resistance is stronger.
Blade thickness
Typically, polycrystalline diamond composite sheet thickness is about 0.3 ~ 1.0mm, carbide layer with a total thickness of about 2 ~ 8mm. Thin polycrystalline diamond

blade thickness is conducive to EDM. Polycrystalline Diamond Compact welding and cutting material, carbide layer thickness can not be too small, the combination of the

two materials in order to avoid stress difference between the surface and cause delamination.
Structural Design
Polycrystalline diamond tool geometry parameters depend on the workpiece position, tool materials and structures and other specific processing conditions. As

polycrystalline diamond tools commonly used in finishing a workpiece, the cutting thickness is small (and sometimes equal to the radius of the tool cutting edge), are

micro-cutting, so after the cutting angle and the subsequent processing quality has significant effect on the face of the smaller rear angle, the higher the quality of

the flank polycrystalline diamond tools for improving the processing quality can play an important role.
Polycrystalline Diamond Compact connection with Arbor methods include mechanical clamping, welding, indexable variety of ways, their characteristics and applications

are shown in Table 2.
Polycrystalline Diamond Arbor connection with the characteristics and applications
Connection - Features - Applications
Mechanical clamping - from standard cutter body and can be made into various collections consisting blade angle can be changed with a quick and easy regrinding

advantages - small machine tools
Welded - compact, easy to make, can be made small tools - special tools or difficult to machine clip tool for small machine tools
Machine folder Welding - Welding in knife blade head, you can use standard shank for easy sharpening and adjusting head position - automatic machine tools, CNC machine

tools
Indexable - compact, reliable clamping, without re-grinding and welding, can save auxiliary time, improve tool life - ordinary general machine
Cutting parameters
Polycrystalline diamond cutting tool cutting parameters on the impact of
Cutting speed
Polycrystalline diamond tools in high spindle speed for cutting, but cutting speed changes on processing quality can not be ignored. Although high-speed cutting can

improve processing efficiency, but in high-speed cutting conditions, cutting temperature and cutting force increases can tip breakage, and make the machine vibrate.

Processing of different workpiece materials, polycrystalline diamond cutting tool is reasonable also different, such as Al2O3 laminate flooring milling reasonable

cutting speed 110 ~ 120m/min; turning SiC particle reinforced aluminum matrix composites and ceramic works reasonably silicon oxide cutting speed is 30 ~ 40m/min.
Feed
Polycrystalline diamond tools such as the feed is too large, the workpiece residual geometric area will increase, resulting in increase of surface roughness; if the

feed is too small, the temperature rise will cause the cutting, the cutting life is reduced.
Cutting depth
Increased PCD tool cutting force will increase the depth of cut, cutting heat increased, thereby increasing tool wear, impact tool life. In addition, the cutting depth

increases likely to cause PCD tool chipping.
Different levels of granularity of polycrystalline diamond tools in different processing conditions processing of different workpiece materials, the performance of the

cutting are not the same, it should be determined according to the specific processing conditions of the actual cutting parameters PCD tool.
Failure Mechanism
Mainly in the form of tool wear abrasive wear, adhesive wear (cold welding wear), diffusion wear, oxidation wear, thermal wear. Polycrystalline diamond tool failure

modes differ with traditional tools, mainly for the polycrystalline layer is damaged, adhesive wear and diffusion wear. Studies have shown that using polycrystalline

diamond tools when machining metal matrix composites, mainly in the form of its failure to adhesive wear and defects caused by a microscopic diamond grain

intergranular cracks. In the processing of high hardness, high brittle material, bonded polycrystalline diamond tool wear is not obvious; contrast, in the processing

of low brittle materials (such as carbon fiber reinforced material), the increase in tool wear, adhesive wear dominant time effect.