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Polycrystalline diamond tools have become an indispensable tool in modern machining. This is mainly reflected in the following aspects:

 (1) High-speed cutting, high-stability processing

(2) Ultra-precision mirror processing

(3) Dry cutting and cleaning processing

Performance introduction

The characteristics of Polycrystalline diamond tools(1) High hardness and wear resistance

Polycrystalline diamond has a hardness of up to 10000 HV. It is the hardest material in the world. It is much harder than hard alloys and engineering ceramics. Because of its extremely high hardness and isotropic properties, polycrystalline diamond has extreme Good wear resistance.

 (2) Low friction coefficient

The coefficient of friction between polycrystalline diamond and some non-ferrous metals is lower than that of other materials, which is about 1/2 of that of cemented carbide. The low coefficient of friction not only reduces the deformation and cutting force, but also causes no built-up edge during cutting, thus reducing the surface roughness of the machined surface.

 (3) High thermal conductivity

Polycrystalline diamond has a high thermal conductivity, which is better than silver and copper. It is much higher than that of ordinary hard alloys. Therefore, the cutting heat is easily dissipated during the cutting process, so the cutting temperature is low.

(4) High processing accuracy

Because the polycrystalline diamond tool has a low coefficient of thermal expansion and a high modulus of elasticity, the tool is not easily deformed during the cutting process. Under the action of the cutting force, the tool can maintain its original parameters, maintain sharpness for a long time, and has high cutting precision. Therefore, when machining with a PCD tool, the cutting force can be reduced and the cutting temperature can be lowered, the tool durability and the cutting rate can be improved, and a good machined surface can be obtained.

The main problem: the high hardness and high wear resistance of PCD materials make molding and surface finishing very difficult, which seriously hinders its popularization and application.

Common processing methods: EDM, laser processing, chemical processing, ultrasonic processing.

 Ideal processing method: grinding or grinding.

Processing technology introduction

(1) Grinding

In view of the high hardness and wear resistance of polycrystalline diamond, the grinding process mainly includes diamond grinding wheel grinding, electric discharge grinding and electrolytic grinding. The simplest and most effective grinding method is diamond grinding wheel grinding. In the actual machining process, different grinding methods can also be combined according to the requirements.

(2) ELID mirror grinding of polycrystalline diamond

Online Electrolytic Dressing Wheel (ELID) Precision Mirror Surface Grinding Technology is a new ultra-precision machining technology developed by Dr. Daisuke, Institute of Physical Chemistry, Japan in the late 1980s. The basic principle is to use the non-linear electrolytic dressing and the dynamic balance of the metal oxide super-abrasive grinding wheel surface oxide insulating layer to suppress the electrolysis during the grinding process, and continuously trim the grinding wheel to obtain the grinding wheel abrasive grain. Constant amount of protrusion, so that the grinding wheel is continuously processed in the best grinding state, it is suitable for precision mirror grinding of hard and brittle materials.

The diamond grinding wheel with metal bond and ELID precision mirror grinding technology can obtain good effect. It is a new way of precision processing of polycrystalline diamond, which has great promotion value and application prospect.

(3) Electric spark grinding

The characteristics of the pulse generator during EDM are very important, especially for processing PCD materials. PCD has a certain conductivity, good thermal conductivity and high melting point, so the traditional EDM processing of polycrystalline diamond is very difficult.

The erosion mechanism of EDM grinding PCD includes: gasification of diamond, oxidation of diamond, conversion of diamond to graphite and amorphous carbon, throwing force by electric spark discharge, thermal stress to microcrack on diamond surface, and diamond The fracture of the crystal grains is broken and the like. Among them, the graphitization of diamond plays a key role in the process of electric spark polishing of diamond film. It not only acts as a conductive force, but also maintains the existence of the discharge channel, so that the top of the diamond film protrudes from the top of the peak, and the graphitization-oxidation process of diamond continuously Perform to remove the diamond.

EDM and EDM are the most efficient and cost-effective methods of processing polycrystalline diamonds, but they do not efficiently process large areas of polycrystalline diamond.

Grinding

There are three main methods for grinding polycrystalline diamond: one is to use a resin bond fine-grained diamond wheel for precision grinding; the other is to use a hardened high-hardness steel plate (or agate plate) without any abrasive. Direct grinding; another is the use of high-speed rotating cast iron discs, supplemented by diamond micro-powder grinding. Grinding can be used as a fine polishing process for polycrystalline diamond, which is an important part of the production of polycrystalline diamond tools.

(1) Grinding of diamond grinding wheel with polycrystalline diamond

Grinding of diamond grinding wheel Polycrystalline diamond is similar to grinding of grinding wheel, except that the model of grinding wheel is different. Grinding wheel with resin concentration of 50%-70% and particle size of W40-W7 is generally used for grinding. When grinding polycrystalline diamond with diamond grinding wheel, the grinding of PCD material by diamond abrasive grains in the grinding wheel is essentially a process of interaction between two objects with similar hardness and properties, which is essentially different from the traditional grinding process. The PCD grinding mechanism and grinding process have their own characteristics.

(2) High-speed steel disc grinding of polycrystalline diamond

High-speed steel disc grinding polycrystalline diamond, the basic principle is that the PCD workpiece is rubbed under a certain pressure and high-speed rotating high-speed steel disc, generating frictional heat, increasing the temperature of the sliding interface, sliding interface (grinding surface) The high temperature generated on the surface is beneficial to the oxidation, graphitization, diffusion, bonding and thermal stress cracking of the diamond grains in the sliding interface of the PCD, thereby achieving the purpose of grinding.

From the chemical properties of diamond, some metal elements can react with them to cause their disintegration. If the material of the grinding disc itself contains the above-mentioned metal element component, it will promote the diffusion, adhesion and thermal erosion of the diamond at the sliding sliding interface, which helps to improve the efficiency of the grinding process. However, the temperature of the grinding sliding interface should not be too high, otherwise it will affect the quality of the grinding surface.

(3) Abrasive grinding of polycrystalline diamond

Abrasive grinding of polycrystalline diamond is one of the traditional processing methods. During the abrasive grinding process, the cleavage of the crystal grains is one of the main removal methods in the process of grinding PCD; the sharp abrasive grains are at a high speed. With proper pressure across the PCD, a large number of damaging scratches are produced on the surface of the diamond grains. These scratches can be divided into plastic scratches and brittle scratches, which is also an important mechanical removal method for PCD materials. In addition to this, there are various thermochemical removal methods such as graphitization removal, thermal erosion removal, diffusion removal, and oxidation removal. However, the thermal chemical removal method does not occupy a major position in the removal of the polished PCD material. Abrasive grinding has high precision, but the efficiency is extremely low. However, when assisted in ultrasonic grinding, the efficiency is greatly improved.

Other processing methods

(1) Wire EDM

Wire EDM machine

The electric discharge wire cutting process realizes the cutting processing of the workpiece material by the pulse discharge of the local region between the electrode wire and the workpiece, and it is one of the commonly used methods for PCD cutting processing. Most of the wire-cut polycrystalline diamonds are used to make machining tools, geological drills and wire-drawing abrasives. The shape of these workpieces is complex and variable. It is economically feasible to form and process with EDM.

(2) Laser processing

The mechanism of laser processing polycrystalline diamond is: a laser beam with extremely high energy density is irradiated onto the surface of polycrystalline diamond, part of the light energy is absorbed by the surface and converted into heat energy, and the temperature of the local area of the irradiated spot rapidly rises to tens of thousands of degrees. The polycrystalline diamond material is partially melted or even vaporized and forms a pit. At the same time, thermal diffusion started, and as a result, the material around the spots melted. As the laser energy continues to be absorbed, the steam in the trap expands, the pressure increases, and the melt is ejected at high speed in an explosive form. The recoil pressure generated by the jet forms a strong shock wave inside the workpiece. Thus, the polycrystalline diamond etches part of the substance under the action of high temperature melt vaporization and shock waves to form a laser etch pit.

Laser processing is non-contact processing. It has excellent characteristics in PCD material processing. It can process high-purity PCD materials (such as polycrystalline diamond film), processing distortion and thermal deformation are small, and laser processing speed is fast and efficient. It is a more effective processing method. Especially in microporous processing and non-conductive superhard material processing, it shows its superiority. However, there are problems such as difficulty in controlling dimensional accuracy and repeatability, and micro-graphitization on the machined surface, which requires further finishing. Currently only used for roughing or semi-finishing. The laser parameters that determine the function of the laser processing material are pulse width, maximum pulse power, and average pulse power.

(3) Chemical processing

The chemical processing of polycrystalline diamond is based on the characteristics that diamond is soluble in molten potassium nitrate, sodium nitrate and sodium phosphate, and the polycrystalline diamond is dissolved by molten nitrate. In view of the surface free energy distribution state and the principle of free enthalpy reduction, The surface of the polycrystalline diamond is gradually smoothed from rough to smooth. At the same time, an oxidation film can be formed on the surface of the diamond due to the oxidation reaction, which can be removed by grinding and then continue to dissolve.

(4) Ultrasonic machining

Ultrasonic processing of polycrystalline diamond is processed by using diamond micropowder (1-50um) as free abrasive. The factors affecting ultrasonic processing of PCD are vibration frequency, amplitude, diamond powder size, PCD material, unit pressure and processing area. At present, polycrystalline diamond ultrasonic processing includes ultrasonic grinding and ultrasonic grinding, etc., and is mostly used for processing PCD bores and PCD drawing dies and sand blasting dies. The core component of the ultrasonic grinding method is an ultrasonic grinding device that performs ultrasonic vibration on one side and high-speed rotation on one side.