Design and application of resin bonded Diamond wheel
1.Introduction to resin bonded diamond grinding wheel
Compared with ceramic binder or metal binder, it has the characteristics of simple manufacturing process, easy access to raw materials, low cost, and can be applied to a large number of low quality super hard abrasive, processing objects are wide, such as all kinds of difficult to process steel, hard alloy, glass, ceramics, stone, etc.
Resin superhard abrasive tools are widely used because they have good self-sharpness and are not easy to plug in the grinding process, and the workpiece has good surface quality and the grinding wheel is easy to dress.
Resin binder used in resin diamond tools can be divided into two categories: phenolic resin and polyimide resin. The actual working temperature of the phenolic resin diamond tools is not more than 120℃. Polyimide resin has better heat resistance and can be used for a long time at 260℃.
With relatively expensive polyimide Resins, phenolic Resins were increasingly used, especially in recent years with scientists modifying phenolic Resins to produce an actual working temperature of more than 200 ° C, such as 939P from Advanced Mixed Limited of the UK.
This paper mainly introduces the design idea and influence factors of resin diamond tools.
2. Design of resin bonded diamond tools
The design of resin-bonded diamond tools is mainly based on the following five aspects :
(1) Adhesion must be good.
The binder can be evenly distributed on the abrasive surface, the abrasive particles can be firmly controlled in the abrasive tool, and can be firmly bonded to the matrix, which not only makes the abrasive not easy to fall off prematurely, but also prevents the binder from separating from the matrix, ensuring production safety.
(2) High grinding efficiency, good wear resistance, good finish (or surface roughness) processing.
Resin bond because of elasticity and brittleness, so in grinding self-sharpening, not easy to plug, but poor wear resistance.
Therefore, when we study and design the binder formula, we must consider under the premise of ensuring the smoothness requirements, not only to have high grinding efficiency, but also to have as high wear resistance as possible.
The preparation of binder is very important. The best ratio of binder should be selected to meet both high grinding efficiency and good wear resistance, so as to ensure the requirements of grinding and reduce the cost.
(3) Good heat resistance.
If the heat resistance of the binder is poor, so that the abrasive in the process of use is not resistant to high temperature, fast consumption, and even because the grinding heat is too high, so that the abrasive burn, crack, ring, etc., so choose good heat resistance binder and add the appropriate filler, in order to improve its heat resistance;
(2) Use coolant for wet grinding as far as possible to improve the durability of the grinding tools;
(3) If dry grinding is used, make the feed as small as possible to improve the durability of the grinding tool.
(4) Binder strength must be high.
The strength of the binder directly affects the grinding efficiency, the size of the abrasion, the quality of the workpiece and the safety performance of the grinding tool in the process of use, so it is necessary to understand the factors that affect the binder strength.
The main factors affecting the strength of the binder are :
(1) the addition of fillers will increase or decrease the strength of the binder. Most of the fillers will increase the mechanical strength and increase with the increase of the amount of filler within a certain range, but the wear ratio will decrease.
Some filler, such as graphite and solid molybdenum disulfide, after adding the strength is reduced, so according to the requirements of reasonable selection of filler;
(2) The forming density of the abrasive (or the porosity of the abrasive) will affect the strength of the binder.
The forming density of the abrasive is low, the porosity is high, and the strength of the binder is low, whereas the strength of the binder is high.
Therefore, it is necessary to rationally design the parameters of the porosity of the abrasive tool.
(3) The hardening temperature, secondary hardening temperature and temperature rise curve of the abrasive molding will affect the strength of the binder.
Binder hardness must be appropriate, good wear resistance.
The strength of the binder must match the wear speed of the diamond (or cBN) abrasive particles. The abrasive particles should not fall off prematurely due to the fast wear of the binder. In that case, the abrasive will not be fully used, resulting in waste.
3. Influencing factors of resin bonded diamond tools
Resin diamond tools are made of resin binder, filler and diamond abrasive after being mixed and cured by hot pressing.
Its properties are also directly affected by resin binder, filler and diamond abrasive.
3.1 The influence of binder mainly includes the influence of binder type and content, etc
(1) the common characteristics of all kinds of resin bond diamond tools is a poor heat resistance, in the process of machining, the diamond tool and the workpiece between the heat generated by the local high temperature easily, once reached the critical value, the holding of the resin binder of diamond, diamond under the condition of not completely dull will fall off, so that the machining cost increase greatly.
At present, the resin binder is modified to improve its heat resistance.
Gao Liangchang modified phenolic resin with square alkyl ether, and its heat resistance can reach above 180℃.
Du Yang et al. synthesized borosilicone prepolymer, boric acid, phenol and formaldehyde as raw materials of the new borosilicone phenolic resin BSP, due to the introduction of B-O bond and organic silicon chain in the phenolic resin structure, BSP resin has excellent heat resistance and toughness, but also improved the water resistance and storage stability of the resin.
Xiao Dongzheng et al. [5] used BMI(bismaleimide) to modify phenolic resin, and obtained bismaleimide modified phenolic resin with good heat resistance.
(2) The influence of resin binder content.
The resin binder content has a great influence on the machining performance of diamond tools.
Monocrystalline silicon slice were introduced in literature thinning grinding wheel, resin binder content increased, the hardness of grinding wheel, the compressive strength increases gradually, when the resin binder content increased to a certain degree, higher than that of the grinding wheel wear tend to be slow, the grinding wheel surface prone to blocking phenomenon at the same time, the content is higher at the same time, the more serious the blocking phenomenon.
(3) The influence of resin binder size.
The particle size of resin powder used in the production of diamond abrasives in China is mostly between 80 ~ 180 mesh. There are two defects in this size range, one is that it affects the forming properties of abrasives, the other is that it may affect the properties of binder.
In the process of suppression, tree powder can be heated to soften, and have certain liquidity, achieve the goal of coated abrasive, but in the process of suppression, binder materials is the pressure in the mould, space is limited, the resin flow range is limited, when the tree thick powder particle size, there will be a part of the abrasive binder is not strong, which fall off too fast.
3.3 The influence of abrasive diamond mainly includes the influence of diamond coating, type and particle size, etc.
(1) After the diamond surface is coated with metal, the compressive strength of single particles is improved, and the wear ratio is decreased, which extends the service life.
Compared with no plating diamond, specific function includes the following aspects: (1) coating slow heat pulse of resin bond diamond coating thermal conductivity is smaller than the diamond, so contact tools, diamond grits of instantaneous high temperature after plating to the resin, thus protecting immediately abrasive parts of the resin is not affected by high temperature damage;
(2) the coating to improve the bonding strength of diamond and binder, metal coating with diamond inside, external and resin binder can be good bond;
(3) the coating to improve the diamond particle crushing strength, plated metal after the diamond particle defects are made up, played a reinforcing role, and the coating contains ductile metal, is conducive to improve the particle crushing strength;
(4) The coating on the abrasive particles play an isolation protection role, isolation of oxygen and other harmful media role, at the same time in grinding high temperature, the coating on the graphitization of diamond crystal can play an inhibition effect.
(2) Domestic and foreign superhard material manufacturers have made a relatively detailed classification of superhard abrasive, among which low-quality diamond abrasive or diamond abrasive with high self-sharpness and micro-crushing property treated by special technology is mainly used in the preparation of resin-bonded diamond tools.
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