- Good bonding strength
- Good formability
- Long service life
- Strong shock resistance
The metal bond diamond grinding wheel is made of diamond powder, and metal or alloy powder as bonding material by mixing, hot pressed or cold pressed sintering.
Metal bond diamond grinding wheels are usually manufactured by powder metallurgy. The manufacturing technology includes mixing, pressing, sintering. There are 3 kinds of main production methods of metal bond diamond grinding wheel blank: cold pressed sintered, hot pressed sintered, semi-hot pressed sintered.
Cold pressed sintered method: Press the molding materials into the blanks by certain pressure in the steel mold, and sintered in the furnace without pressure after removing the mold.
This sintered method features high forming pressure, long sintering time, high energy consumption, poor mechanical performance, and service performance. Especially need to supply much energy to make the blanks body sintered in the sintering process without press, and the sintering holding time is 1-2 hours. The production cycle is long, so this method is seldom used now. But mounted points and diamond finish pellets are mostly applied to this method.
Hot pressed sintered method: There are usually medium frequency induction hot pressed and high current resistance heating. This method usually is that heat and hot press the molding materials in the graphite mold at the same time(i.e. direct hot pressed sintered). Or the molding materials are cold pressed into the blanks with a certain density and strength in the steel mold, and then sintered by hot pressing in the graphite mold.
The specification of the abrasives is limited by the graphite mold, and the diameter of the abrasives is usually less than 300mm. It will consume a lot of energy in the heating process with medium frequency induction and high current resistance.
Semi-hot pressed sintered method: First, press the molding material into the blanks with a certain density and strength in the steel mold, and then sintered without pressure. After sintering, the blanks are pressed to the design density. This method is usually suitable for the production of large size grinding wheels.
It can keep heat for 30 minutes in the sintered. 1-10 pieces can be sintered once.
The main factors affecting the sintering process of metal bond diamond grinding wheels:
1.Effect of sintering temperature on the process of metal bond diamond grinding wheel:
The sintering temperature is the most important factor affecting sintering. With the increase of sintering temperature, the viscosity of powder materials decreases the vapor pressure increases, and the diffusion coefficient increases, and which promote the material flow process. On the other hand, with the increase of sintering temperature, and the factors affecting sintering decreases.
Effect of sintering time on the process of metal bond diamond grinding wheel:
The initial sintering temperature has a great influence on the sintered body performance. When the density of the sintered body reaches a certain value, if prolong the sintering time, the improvement of density is not obvious. On the contrary, it exacerbates the grain growth and secondary crystallization and causes the strength of the grinding wheel to decrease and forms the waste products.
Effect of sintering atmosphere on the process of metal bond diamond grinding wheel:
Sintering atmosphere is very important to ensure the sintering process. The influence of the atmosphere on sintering is complex. It not only affects the sintering of the powder grains but also affects the effect of additives. The same atmosphere often shows different or even opposite effects on the sintering of different powder materials.
Selection of the abrasives for metal bond diamond grinding wheel:
Abrasive grain selection:
Metal bond diamond grinding wheels are mostly applied to the synthetic diamond with MBD brand( Chinese standard).
Grain size selection:
Usually, the grain size is fine, and the surface finish is good, but the grinding efficiency is low. The grain size is rough, and the surface finish is low, but the grinding efficiency is high. When choosing the grain size, the influence of the metal bond to the grain size should be considered. Another, choose the roughest grain size of diamond to improve the grinding efficiency and reduce the grinding ratio under the requirement of surface finish.
The concentration of diamond abrasives:
When the diamond concentration is too high, the diamond grains increase, and the amount of the bond decreases, which reduces the holding force of the bond to diamond. When the diamond concentration is too low, the diamond grains decreases, the pressure acting on each abrasive grain increases, which makes the abrasive tools wear too early.
The dressing of metal bond diamond grinding wheel
In order to pursue the high holding force to the abrasives, the density of metal bond diamond grinding wheel is usually used as an important index to measure the quality of grinding wheels. Owing to the high densification of the metal bond diamond grinding wheel, the dressing and sharpening of diamond grinding wheel at the beginning of using and after wearing become more important. At present, there are mainly ELID( Electrolytic In-process Dressing), EDM dressing and compound dressing. The ELID is fast but the dressing precision is not high. The EDM dressing has high dressing precision, which can both be dressing and sharpening, but the dressing speed is low. The compound dressing includes ELID compound dressing, mechanochemical compound dressing, and etc. and the dressing effect is good, but the system is complex. Therefore, the pressing problem of the metal bond diamond grinding wheel is still not solved well.