1. Preface

Polycrystalline diamond compact (PDC) refers to a super hard composite material composed of diamond powder layer with a thickness of 0.1 to several millimeters and cemented carbide substrate under high pressure and high temperature (5 ~ 7GPa, 1400~1700 ℃). It has high hardness, high wear resistance, high elastic modulus, isotropic and relatively high thermal conductivity and other significant advantages, in recent years has become a high-end machining tools, geological and petroleum drill bits, ceramic abrasive, stone processing tools, concrete tools and valve seat, valve core and other high wear-resistant equipment materials of choice, but also become one of the most vital pillar products in the field of high-tech new materials. At present, domestic and foreign composite sheet manufacturers mainly use diamond grinding wheels for cylindrical grinding of composite sheets to meet the required dimensional tolerance requirements. Resin diamond grinding wheel because of its processing efficiency and processing accuracy is much less than the ceramic bond diamond grinding wheel, so in the past few years, the cylindrical grinding of the composite basically began to use the ceramic bond diamond grinding wheel. At present, there are many domestic manufacturers of ceramic bond diamond grinding wheels, but few companies have real research and development strength, and the quality of products is also uneven. In order to meet the demand for ceramic diamond grinding wheels in the powerful composite cylindrical grinding market, Antai Steel Research Superhard Material Products Co., Ltd. has carried out research on ceramic bond diamond grinding wheels special for composite cylindrical grinding. Through cooperation with customers, the complete preparation and application technology of ceramic bond diamond grinding wheels for composite cylindrical grinding has been greatly improved. At present, the performance of the ceramic bond diamond grinding wheel produced by the company has reached the leading level in China. Based on the experience of grinding wheel preparation, this paper focuses on the analysis of the main factors affecting the performance of the grinding wheel, aiming to exchange experience with the majority of colleagues, make common progress, and jointly promote the complete set of preparation technology of ceramic bond grinding wheel in China.

2. Introduction to the experimental process

A certain wetting agent is added to the commercially available diamond abrasive and a self-made ceramic binder, and then the green ceramic block is formed by pressure molding, and the green ceramic block is fired into a semi-finished grinding wheel block by step heating and heat preservation. Finally, the grinding wheel block is bonded to the aluminum alloy substrate. Through the later dressing, balance and rotation tests, the qualified product is printed with labels and packaged as the finished product (1A1-400 × 50 × 10 × 203 D120). The prepared product was used to grind 1304PDC composite sheet on the cylindrical grinder, and the grinding experiment was compared with the commercially available resin and ceramic grinding wheel, and the influence factors of the grinding wheel performance were analyzed and discussed through a series of experiments.

3. Experimental results and analysis

Effect of 3.1 vitrified bond on grinding wheel

In this experiment, a self-made Al-Si-B-Li-O low-temperature ceramic bond is used. In the experiment, the wear ratio test of the grinding wheel segment and the grinding experiment in the PDC production plant are used to obtain the influence of the ceramic bond content in the grinding wheel on the grinding effect. During the experiment, it was found that the life of the grinding wheel was the highest when the ceramic bond content was 22wt%~ 26wt%. The content of binder in the grinding wheel has three main effects on the grinding wheel:

(1) the effect on the hardness of the grinding wheel. The hardness of the superhard material grinding wheel refers to the degree of difficulty of the superhard abrasive falling off from the grinding wheel, and the harder the abrasive particles fall off, the higher the hardness of the grinding wheel. Generally speaking, the more the combined dose, the stronger the abrasive grip, the more difficult it is for the abrasive to fall off, and the higher the hardness of the grinding wheel. When grinding, the grinding wheel blade is not good, easy to appear the phenomenon of grinding, the life of the grinding wheel will be increased, but the surface of the composite sheet is prone to chipping, it is necessary to properly cut the grinding wheel for a period of time to avoid waste in grinding.

(2) the effect of the bond content and the bond strength of diamond abrasive. The hardness of the composite sheet itself is very high. In the process of cylindrical grinding, the diamond on the surface of the grinding wheel is subjected to a lot of grinding force and impact force. If the amount of ceramic bond is too small, the ceramic bond is not enough to keep the diamond, resulting in some diamonds not fully play the role of grinding began to fall off, resulting in a shorter life of the grinding wheel. And when the binding agent is too much, the grinding wheel hardness is too large, the sharpness is not enough, easy to make the composite sheet to produce collapse, resulting in increased rejection rate.

(3) the influence on the organizational structure of the grinding wheel. Since the particle size of the binder used is finer than the diamond particle size, and during the firing process, the binder will densify. The content of binding agent in the grinding wheel increases, the denser the grinding wheel organization, the grinding wheel is prone to blockage and immobility. It is often necessary to use ordinary grinding wheel to cut the grinding wheel of superhard material to remove excess binding agent, so that the new diamond blade can participate in the next grinding, thus reducing the working efficiency of the grinding wheel.

Effect of 3.2 Sintering Temperature on Performance of Grinding Wheel

The control of the firing temperature of the vitrified bond directly affects the performance of the grinding wheel, which is mainly related to the nature of the superabrasive and the vitrified bond itself. In the air, CBN can withstand 1400 ℃ ~ 1600 ℃ high temperature, can withstand high toughness difficult to process the material grinding heat; and the poor thermal stability of diamond, at 800 ℃ that began to oxidation wear, even in the inert gas, 1100 ℃ also began to graphite. In this paper, the company's own development of the Li-Al-B-Si-O system of low-temperature ceramic bond, DSC curve analysis of the ceramic bond sintering temperature in the range of 660 degrees C to 800 degrees C can meet the ceramic grinding wheel block firing. From the analysis of this paper, it is concluded that within the firing temperature range of the ceramic bond, the superhard abrasive will not be burned. Thus, reference herein to a low temperature vitrified bond means that the firing temperature is less than the lowest temperature at which the superabrasive is burned.

From the company's current production of ceramic tool products, it is found that in the sintering range, the sintering temperature of the grinding wheel block is increased, and the strength of the grinding wheel block is also increased accordingly. At present, the company's low-temperature ceramic bond diamond grinding wheel used in the firing temperature of 680 ℃ ~ 760 ℃, according to the specific requirements of the use of diamond grinding wheel to determine the grinding wheel firing temperature. During the firing process of the low-temperature ceramic bond CBN grinding wheel block, it should also be noted that the heating and cooling rate should not be too high. If the rate is greater than 6 ℃/min, the grinding wheel is prone to micro-cracks and surface cracks. The company's project team used a heating rate of 2 ℃/min and a cooling rate of 3 ℃/min for the preparation of low-temperature vitrified bond diamond grinding wheels.

Effect of 3.3 diamond concentration on grinding wheel performance

The concentration of superhard abrasive is defined as 100% with 4.4ct in 1cm?, and the experiments were carried out with 100%, 150%, 200% and 210% ceramic bond diamond grinding wheels, respectively. The experiments of cylindrical grinding of 1304 composite discs were carried out. The experimental results are shown in Table 3.

From the experimental data, it is not difficult to find that the higher the concentration, the longer its life, and the life of the high concentration grinding wheel is more cost-effective than the life of the low concentration grinding wheel. With the increase of diamond concentration, the amplitude of the service life of the grinding wheel increases more. We believe that for the cylindrical grinding of composite discs, the diamond abrasive particles involved in the grinding of high-concentration ceramic diamond grinding wheels increase, and the bond strength can meet the requirements of the conditions can play a role in the force.

Comparison of 3.4 developed grinding wheel with domestic commercially available ceramic grinding wheel and resin grinding wheel

In this paper, the self-made ceramic bond grinding wheel and the domestic market of ceramic diamond grinding wheel and resin diamond grinding 1304 composite disc, among them, the grinding wheel produced by our company in the grinding process, obviously feel the noise is small (the higher the sharpness, the smaller the grinding force, the less noise), and the grinding time is short. The experiment shows that the service life of ceramic grinding wheel can be increased by 2~3 times compared with resin grinding wheel, and the grinding efficiency of single-piece composite sheet can also be increased by about 30%. The sharpness, service life and grinding efficiency of the developed grinding wheel are slightly higher than those of the commercially available ceramic grinding wheel, and the comprehensive performance of the grinding wheel under the same conditions is about 10% higher than that of the commercially available ceramic grinding wheel. It can be seen that the developed ceramic diamond grinding wheel has reached the leading level in the same category.

4. Conclusions

Through the study of the ceramic bond diamond grinding wheel for the outer circle grinding of the composite sheet (1304), the conclusions are as follows:(1) the self-made Li-Al-B-Si-O system low-temperature ceramic bond is suitable for the ceramic bond diamond grinding wheel for the outer circle grinding of the composite sheet; when the concentration reaches 210%, the life of the grinding wheel reaches the highest;(3) The life of the ceramic grinding wheel is 2 to 3 times higher than that of the resin grinding wheel, and the grinding efficiency of a single piece of composite sheet is increased by about 30%. The comprehensive performance of the low-temperature ceramic diamond grinding wheel has reached the domestic leading level, and has a high cost performance.