Research status of metal-bonded diamond grinding wheel

Diamond grinding wheel is the most widely used processing tool in grinding technology. According to different kinds of bond, diamond grinding wheel can generally be divided into resin-bonded diamond grinding wheel, ceramic-bonded diamond grinding wheel and metal-bonded diamond grinding wheel. The metal-bonded diamond grinding wheel has strong binding force and abrasive grain, good toughness, and can withstand large loads. It has been applied in the fields of forming grinding, precision and ultra-precision grinding of complex surfaces of brittle and hard materials.

 

The holding power of metal bond to diamond abrasive is the key factor that affects the life of metal bond diamond grinding wheel. Therefore, researchers at home and abroad mainly focus on the following aspects:

(1) Substitute Fe base for Co base as the bond of metal-bonded diamond grinding wheel to reduce production cost. For example, Han Juan and others investigated the effect of carbon content on the properties of ferrite-based matrix materials. When the carbon content is 1%, the matrix material density reaches the minimum value of 7.47g/cm3; When the carbon content is 0.4%, the matrix material density reaches the maximum value of 7.65g/cm3. Chen Xia et al. reduced the erosion of the binder on the diamond surface by adding a small amount of Co to the iron-based binder, and because of the addition of Co, a layer of dense matrix material was attached to the diamond surface, which made the matrix material and diamond more closely combined.

 

Dai Qiulian et al. found that the mechanical properties of iron-based matrix materials can be improved by properly increasing the content of C, Cu and Ni. The sintering temperature of grinding wheel has a significant impact on the hardness and bending strength of iron-based matrix materials. The appropriate amount of Zn and Sn is conducive to liquid phase sintering;

(2) Take technological measures to realize the holding ability of metal bond to abrasive. First, it is achieved by adding active Ti (TiN2), Cr, rare earth elements, etc. to the sintering raw materials; Second, the active metal or alloy coatings such as Ti and Cr are plated on the surface of diamond abrasive particles to improve the holding ability of the bond to the abrasive;

(3) Improve the dressing ability of metal-bonded diamond wheel. T Tanaka et al. tried to develop a kind of porous diamond metal grinding wheel with cast iron as the bond, and introduced the void structure of the porous ceramic diamond grinding wheel into the metal diamond grinding wheel, in order to obtain better cutting ability and self-sharpening of the diamond abrasive particles. Later, H.Tomino and S.H.Truong of Japan developed various preparation methods such as hot isostatic pressing sintering, electrifying sintering and vacuum sintering.

 

Through the comparative study of the preparation process, porosity and various grinding properties, we have a further understanding of the new type of porous metal-bonded diamond wheel. Domestic researchers propose to improve the self-sharpening ability of metal-bonded diamond grinding wheels by changing the formula of metal-bonded diamond to match its wear rate with the wear rate of diamond abrasive. However, this method is limited by the properties of the processed materials, different diamond grades and the limited range of adjustable formula composition of metal-bonded diamond. Liao Cuijiao et al. added a certain amount of pore-forming agent to the metal bond to obtain a porous metal bond diamond segment sample with a certain porosity.

At present, metal-bonded diamond wheels are divided into three types: electroplated diamond wheels, sintered diamond wheels and single-layer brazed diamond wheels. Electroplated diamond grinding wheel can only be used in the occasions with small grinding load, and sintered diamond grinding wheel is widely used, while single-layer brazed diamond grinding wheel is still in the development stage in China.

Electroplated diamond grinding wheel is made by electrochemical method. Electroplated diamond grinding wheel has many advantages, such as simple electroplating process, low investment, convenient manufacturing, no need to repair, high working efficiency, long service life, etc. At present, electroplated diamond grinding wheel plays an undisputed leading role in high-precision, high-speed and ultra-high-speed grinding. The defects of the electroplated diamond grinding wheel are as follows: the diamond abrasive grains in the electroplated diamond grinding wheel are only mechanically embedded with the coated metal and the substrate, and the joint surface does not form a solid chemical metallurgical bond, so its holding force is small. The working surface of grinding wheel is easily blocked, with poor heat dissipation, high grinding temperature and easy to burn the workpiece surface.

In order to solve the problems such as insufficient holding force of the abrasive grains of the electroplated diamond grinding wheel and easy blockage of the tools, and to give full play to the advantages of the superhard abrasive, the foreign countries began to develop the single-layer brazed diamond grinding wheel with the high-temperature brazing process in the early 1990s. In particular, certain progress has been made in high-temperature brazing of diamond grinding wheels.

 

For single-layer brazed diamond grinding wheel, the bonding strength at the interface provided by high-temperature brazing is high; At the same time, because the thickness of the bonding layer is very thin, the chip space between the abrasive grains is greatly expanded, and it is not easy to block. The effective abrasive cutting edge is more and sharper, and the grinding temperature is greatly reduced, which can effectively prevent grinding burns, especially in efficient grinding, which can show its incomparable advantages. At present, it has been used in the preparation of diamond wire saw, single-layer brazed diamond grinding wheel and various grinding heads and discs. However, there are few single-layer brazed superabrasive abrasives on the market at this stage.

The sintered diamond grinding wheel is formed by mixing superhard abrasive and bonding powder and sintering by powder metallurgy, forming a multilayer structure sintered body. The sintered diamond grinding wheel has the advantages of high bonding strength, good formability, high temperature resistance, good thermal conductivity and wear resistance, long service life, and can bear large loads. For sintered diamond wheel, some scholars have carried out research on dressing sintered diamond wheel with special machining methods in recent years, mainly including electrolytic dressing method, electric spark dressing method and composite dressing method.