The performance of various diamond grinding wheels and their advantages and disadvantages are introduced
Jul 30, 2020

1. the introduction

Super hard abrasive wheel made of diamond or cubic boron nitride (CBN) abrasive has been widely used in various grinding fields due to its excellent grinding performance.

Special effect tools for grinding hard and brittle materials such as hard alloy, glass, ceramics and precious stones with diamond grinding wheel.

In recent years, with the rapid development of ultra-precision grinding technology of high-speed grinding, higher requirements have been put forward for the grinding wheel. The ceramic resin bonded wheel can no longer meet the production needs, and the metal bonded wheel has been widely used due to its remarkable characteristics, such as high binding strength, good shaping and long service life.

There are two main types of metal-bonded diamond grinding wheels, sintering and electroplating, according to different manufacturing methods.

In order to give full play to the role of super hard abrasive, a new grinding wheel, namely single-layer high temperature brazing super hard abrasive grinding wheel, has been developed in foreign countries since the early 1990s by using high temperature brazing technology. At present, this grinding wheel is still in the development stage in China.

2. Sintered diamond grinding wheel

The sintered metal bonded grinding wheel is mostly made of bronze and other metals as the bonding agent by high temperature sintering method. It has high bonding strength, good molding property, high temperature resistance, good thermal conductivity and wear resistance, long service life and can bear a large load.

Due to the inevitable shrinkage and deformation in the sintering process of the grinding wheel, it is necessary to shape the grinding wheel before use, but it is difficult to dress the grinding wheel.

At present, the common method of grinding wheel to roll shaping is not only time-consuming and laborious in dressing, but also more diamond particles are shed during dressing, so the dressing grinding wheel itself consumes a lot and the shaping precision is low.

In recent years, scholars around the world have carried out researches on the application of special processing methods to dressing metal-bonded diamond grinding wheels, mainly including electrolytic dressing method and electrospark dressing composite dressing method.

The electrolytic dressing method has high speed but low shaping precision.

The edM shaping method has high precision and can be reshaped and sharpened, but the shaping speed is slow.

The composite dressing methods include electrochemical spark composite dressing method and mechanochemical composite dressing method, etc., with good dressing effect, but the system is more complex, so the dressing problem of sintered diamond grinding wheel has not been well solved.

In addition, due to the manufacturing process of the grinding wheel, its surface morphology is random, the geometric shape and distribution of each grinding grain and the height of the cutting edge are not consistent, so only a few high cutting edges cut into the workpiece during grinding, which limits the grinding quality and further improves the grinding efficiency.

3. Electroplated diamond grinding wheel

Advantages of electroplated diamond grinding wheel:

(1) Simple electroplating process, less investment, convenient manufacturing;

(2) No repair, easy to use;

Single-layer structure determines that it can reach a very high working speed, which is as high as 250 ~ 300m/s in foreign countries at present.

(4) Although only a single layer of diamond, but still have enough life;

(5) For wheels with high precision, electroplating is the only manufacturing method.

As a result of these advantages, high speed grinding and ultra-high speed grinding of electroplated grinding wheel occupy the undisputed dominant position.

Defects of electroplated diamond grinding wheel: there is no firm chemical-metallurgical bond between the coated metal and the matrix and the abrasive bonding surface. In fact, the abrasive is only mechanically embedded and embedded with the coated metal, so the control force is small and the diamond particle load is heavy. In efficient grinding, it is easy to fall off (or the coating flakes off), resulting in overall failure.

In order to increase the control force must increase the coating thickness, the result of the grinding grain exposed height chip space reduction, grinding wheel easy to jam, heat dissipation effect is poor, workpiece surface is easy to burn.

At present, the manufacturing of electroplated grinding wheel in China has not realized the optimum design of grinding wheel physiognomic according to the requirements of processing conditions. The inherent disadvantages of single-layer electroplated diamond grinding wheel are bound to greatly limit its efficient grinding application.

4. Single layer brazing diamond grinding wheel

In order to give full play to the role of diamond, we should try to increase the holding force of binder on diamond and improve the bonding strength of grinding wheel.

Single high temperature brazing of superhard abrasive grinding wheel electroplated grinding wheel can be overcome shortcomings, can realize the diamond, binder, chemical metallurgical bonding between metal matrix, has high bonding strength, only will combine layer thickness highly 20% ~ 30% can maintain grits heavy load high speed high efficiency grinding firmly control grinding grain, make brazing grinding wheel abrasive naked height can reach 70% ~ 80%, thus increasing the capacity space, grinding wheel is not easy to jam, abrasive use more fully.

Under the same processing conditions as electroplating grinding wheel, the grinding force, power loss and grinding temperature of single-layer high-temperature brazing super-hard abrasive wheel are lower, which means that higher working speed can be achieved. The ultra-high speed grinding above 300 ~ 500m/s has special significance.

Single-layer high-temperature brazing non-plated diamond grinding wheel plus Cr silver base brazing wheel Adopts high-frequency induction brazing method, with crag-Cu alloy added as the filler metal, 780-℃ air brazing 35s, natural cooling, can realize the solid connection between diamond and steel matrix.

By X-ray energy spectrum and X-ray diffraction analysis found that Cr and Cr3C2, formed between diamond and the steel substrate formed between (FexCry) C, compared with and without Cr solder experiments show that this alloy layer and has high bonding strength between diamond and the steel substrate main factors, and through the grinding experiment confirmed that the diamond has higher holding strength.

The technology has the advantages of low brazing temperature and little damage to diamond.

Disadvantages: low melting point of silver base solder, poor resistance to high temperature grinding, high efficiency heavy load grinding application is limited.

Foreign diamond brazing technology of ni-CR alloy single layer brazing grinding wheel: firstly, a layer of NI-CR alloy layer is sprayed on the oxyacetylene welding torch steel substrate by flame spraying. This layer of active metal can be used as a filler metal to braze diamond grinding particles directly, and then argon induction brazing at 1080℃ for 30s.

Because the surface of steel matrix is easy to oxidize, it is difficult to control the uniformity of abrasivesetting uniformity of brazing binder layer thickness.

Wu Zhibin et al. directly arranged diamond abrasive particles on ni-CR alloy sheets or powders, pressed diamond abrasive particles with ceramic blocks, and then brazed them for 30s on vacuum high-frequency induction machine with the brazing temperature of 1080℃.

Or brazing in an argon shielding radiation heating furnace, appropriately controlling brazing temperature and cooling speed of holding time.

Using scanning electron microscopy, X-ray energy spectrum and X-ray diffraction structure analysis showed that the brazing process, Cr Ni - Cr alloy elements separated form rich Cr layer of diamond surface, and the surface of the diamond - elements generate Cr3C2Cr7C3 reaction, good infiltration with steel alloy layer and diamond substrate reaction (FexCry) C carbides, so the brazing process can ensure that alloy layer and the diamond and can get higher bonding strength between the steel substrate.

The heavy load grinding experiment proves that the diamond is normal wear without the whole diamond falling off.

The advantages of this process are as follows: ni-CR alloy has high strength, and the brazing strength can be higher than that of silver-based alloy.

Ni-cr alloy has high melting point and high grinding temperature resistance.

However, it still has some limitations. Due to high brazing temperature (1080℃), diamond strength is easy to be reduced due to thermal damage of diamond. Brazing under vacuum condition or argon gas protection can minimize diamond thermal damage oxidation.

Ma Chufan et al. used NiCr13P9 alloy as the active solder and added a small amount of Cr powder to braze the diamond wheel at 950℃ under pressure in a vacuum furnace, and developed a single-layer high-temperature brazing diamond wheel for dental use.

Scanning electron microscopy (SEM) was used to observe the silver-white alloy around the diamond, and X-ray diffraction analysis confirmed the formation of Cr3C2. The positive carbide layer realized the high bonding strength between the diamond and the steel matrix.

The grinding experiment also confirmed that diamond has high holding strength and the life and grinding efficiency of single layer brazed diamond grinding wheel are improved obviously compared with electroplated grinding wheel.

Due to poor thermal stability of diamond, graphitization transformation will occur at 800℃ for single-layer high-temperature brazing coated diamond grinding wheel. Therefore, higher brazing temperature is bound to cause thermal damage of diamond and decrease the strength of diamond.

At the same time, the harmful elements of the binder will make the diamond corrode graphitization, so the diamond surface can be coated with a layer of active metal and its alloy before brazing.

Superhard abrasive plating technology mainly includes chemical vapor deposition, ion plating, hot evaporation plating, vacuum micro-evaporation plating and so on.

Chemical vapor deposition (Cr) and vacuum micro-evaporation deposition (Ti) can effectively improve diamond surface properties.

Brazing process, with the coating interface function, in addition to more powerful metallurgy chemical combination between diamond and bond, due to the coating of hot air oxygen barrier and make the diamond surface carbon atoms and oxygen reaction rate greatly reduced, at the same time, the coating of strong carbide forming elements carbon atoms and diamond surface reaction carbide, closed hanging key diamond surface, increase the oxidation resistance, inhibiting settlement agent Fe, Co, Ni elements such as graphitization of diamond corrosion itself process, make the abrasive can still maintain the original strength after brazing crystal shape.

During brazing, a layer of NI-P alloy (melting point 880℃) was precoated on the steel substrate, and then the coated diamond alloy layer was brazed with argon gas at 1050℃ for 5min, and then cooled to room temperature.

The grinding test shows that the coated diamond and the binder have good wettability, which can effectively avoid the particle falling off, greatly improve the grinding performance of the grinding wheel, and greatly increase the grinding efficiency of the grinding wheel.

However, it should be pointed out that due to the adaptability problem between the coated diamond and the binder, only the appropriate binder process can achieve the best physical and mechanical properties of the coated diamond.

The problem of single-layer high temperature brazing wheel and its Countermeasures Although good experimental results have been obtained at home and abroad, the manufacturing technology of single-layer high temperature brazing wheel still needs to be further improved.

At present, the main problems are as follows: (1) which brazing technology can be used to produce chemical metallurgical bonding with high bonding strength at the diamond bonding interface;

Control of appropriate thickness and uniformity of binder layer;

Reasonable and orderly arrangement of tri-abrasive.

For improve the diamond and solder bonding strength, the key process of brazing diamond, solder, can produce between chemical metallurgy combined with matrix, and therefore alloy solder should contain strong carbide forming elements, such as Ti, Cr, V, etc.), and under the low temperature brazing, minimize damage to diamond.

To develop a reasonable brazing alloy formula to develop a single layer brazing wheel should be solved first.

It is necessary to strictly control the thickness and uniformity of binder layer during industrial production of brazing grinding wheel.

Before brazing, the metal substrate surface should be treated with oxide film and the oil and dirt should be removed for the diamond filler metal.

The strong carbide forming element and BSi can reduce the melting point of the solder and improve the wetting property of the solder.

Brazing using a powder filler metal under vacuum conditions (or inert gas protection).

The thickness consistency of the brazing filler material before brazing is also very important to improve the thickness uniformity of the binder layer after brazing.

Reasonable and orderly arrangement of abrasive on grinding wheel working surface has been pursued by the abrasive industry, which is expected to be realized on single layer super hard abrasive wheel.

In the process of brazing grinding wheel development, the best physiognomorphism of the grinding wheel is optimized according to the requirements of the processing conditions, and then the grinding performance of brazing grinding wheel can reach a higher level by arranging abrasive according to the optimized results.

On the template, the holes with diameters similar to diamond abrasive particles and a depth of 70% diamond height are arranged regularly. The diamonds are arranged according to the holes, and the thickness of the alloy filler is about 30% diamond height after melting.

This brazing process using hole formwork can not only ensure the orderly arrangement of abrasive particles (good contour), but also guarantee the 70% diamond exposure height.

But its industrial production popularization application still needs further study.

PRCTOOLS is an experienced suppliers of diamond and CBN grinding tools,Our product is certified by MPA,Quality assurance!!!

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