CBN (Cubic Boron Nitride) is the second after the advent of synthetic diamond, in 1957 by the American GE company first synthesized yet another superhard materials. In 1966 our successful trial CBN.
Just below the diamond hardness of CBN, it has superior heat resistance than diamond and iron group metal chemically inert material. The use of its excellent properties as the abrasive CBN abrasive made of, is particularly suitable for all kinds of iron group metal material grinding. This diamond is mainly used for machining of hard and brittle materials complement each other, so that superhard materials greatly broaden the range of applications. And compared with ordinary abrasive abrasive, CBN abrasive with high-speed, high efficiency, high processing quality, long life, low cost, and can be used as high-speed CNC grinding efficiency, high precision grinding tool of choice. In the automotive, machine tools, tools, bearings and other industrial fields have a wide range of applications.
One, CBN nature
Cubic boron nitride is a high temperature and pressure synthesis, crystal structure consists of layered into cubic structure, density from 2.25g/cm3 to 3.48g/cm3, various properties have undergone a mutation.
In the CBN for abrasive materials used, we study its hardness, wear resistance, strength and thermal conductivity, etc.
CBN hardness much higher than other ordinary abrasive. High hardness means cutting ability stronger, sharper; CBN has a high abrasion resistance, which means it harder than ordinary abrasive wear; ability to maintain the shape of abrasive CBN as one of the main characteristics of high-performance abrasive; CBN's high compressive strength, which means that in the harsh conditions of use it can remain intact and not broken particles; CBN has good thermal conductivity, the grinding can be achieved when cold cutting.
CBN and diamond because some properties different from the scope of the work material are also different. CBN materials suitable for processing tool steel, bearing steel, alloy steel, super alloys, cast iron. The materials suitable for processing diamond carbide, glass, ceramics, metal ceramics.
Two, CBN grinding system
CBN abrasive is a different type of binding agent is bonded to the CBN abrasive and a tool made of a certain shape. Only through rational grinding process, relying on the superiority of grinding, in order to maximize its effect. In the study and application of CBN grinding technology, we must consider CBN abrasives, grinding, the workpiece, trimming, cooling, grinding and other factors into a system to be optimized in order to obtain the best technical and economic results.
CBN grinding technology are briefly described below dozens of important factors.
1. CBN abrasive
2 Grinder
3 dressing
4 Cooling
5 grinding process parameter optimization
CBN abrasive is characterized by its shape, size, CBN abrasive particle size, concentration, bond type and speed parameters to describe. In the manufacture of grinding is a major consideration and selection of the following four factors.
The shape, dimensions and marking CBN abrasive shapes can be divided into parallel, cup, bowl, dish, grinding, Whetstone. The shape, dimensions and marking according to GB/T6409.2-1996 and GB/T6409.1-1994 standard requirements.
Binding agent binding the four CBN abrasive agent (see Table 1), with the fastest growing vitrified. Worldwide, the proportion of ceramic CBN grinding tools has risen to more than 50%, showed a rapid growth trend. This is due to the ceramic CBN abrasive grinding efficiency, maintain good shape, high durability, easy trimming, grinding wheel, long life, and thus become efficient, high-precision grinding preferred abrasive.
According to regulations milling concentration, the concentration of abrasive in the abrasive is 100%, the per cm3 containing 4.4 kt (0.38g) of the abrasive, this value corresponds to 25% volume. Concentration Code is now scheduled in Table 2.
Concentration Code provisions
Abrasive content (ct / cm3)
Concentration
1.1
25%
2.2
50%
3.3
75%
4.4
100%
6.6
150%
8.8
200%
Indicates the level of concentration of abrasive grinding wheel in the working area of the grinding grains in the number of how many. High concentrations can bring high grinding ratio and a low surface roughness. The concentration ratio 100% 200% concentration extended wheel life 4-5 times.
Hardness of abrasive hardness rating represents binders on the size of the abrasive gripping force, which is an important manufacturer of process control indicators, but also the user to select the main parameters of the performance abrasive grinding wheel hardness uniformity and stability and hardness of the rational choice is to ensure that the level of an important prerequisite for the grinding quality.
Grinding is grinding system centers, grinding machines grinding effect on the performance of the most important influence is especially true of the CBN grinding. Improve grinding wheel working speed, can significantly improve the grinding efficiency and the grinding ratio, improved durability wheel and the workpiece surface quality. 80 ~ 125m / s the use of speed has become the domestic import basic characteristics of CBN camshaft grinding machines. In the conditions allow, as far as the use of high speed CBN grinding is to improve the technical and economic important prerequisite. High-speed grinding and CBN grinding wheel characteristics, requirements and machine to machine spindle with high rigidity and excellent vibration resistance, thus ensuring the accuracy of the workpiece and the grinding surface quality, which is CBN high-speed grinding technology for grinder basic requirements.
Table 1 Bond type
Grinding Performance
Abrasive binder type
Resin (B)
Metal (M)
Ceramic (V)
Plating (E)
Wheel life
In
High
High
Low
Metal removal rate
High / Medium
In
High / Medium
High
Shape retention
In
High
High
High
Power Requirements
In
Medium / High
In
Low / medium
Difficulty dressing
In
Difficult
Easy
Generally do not repair
Surface roughness
Good
Good / Medium
The best
Change
Recommended Applications
Tools, tool grinding surface grinding, cylindrical grinding, hob grinding, polishing, creep feed grinding, double face grinding profile grinding, internal grinding, honing form grinding, Cylindrical grinding, cam grinding, crankshaft grinding , creep feed grinding, polishing, ultra-fine grinding
Sample grinding, forming grinding, cylindrical internal and external cylindrical grinding, creep feed grinding, grinding gears or splines
Using a diamond wheel dresser, dressing can not only improve the efficiency, and more importantly, can achieve better wheel topography. Using other dressing tools, it is difficult to complete the dressing wheel surface with high hardness. Trimming device feeding accuracy is higher, the amount of each feed should be able to achieve micron level. Excessive trim only affects the quality will greatly reduce the grinding wheel life.
Grinding, 90% of the energy is converted into heat, which heat must be absorbed and to maximize the coolant away. Select the correct type of coolant and cooling process parameters, tend to have a multiplier effect. The use of different cooling fluid, causes the grinding wheel several times higher than difference.
Fully optimize the efficiency of the grinding process parameter enables grinding, grinding and grinding quality costs and other technical and economic indicators at a higher level to reach equilibrium.
Three, CBN abrasive applications
Speed, high efficiency, high precision grinding technology has become the mainstream of the development work Mogadishu. CBN grinding as an advanced processing technology flourish. High quality, low cost is to promote its rapid development.
CBN abrasive applications continue to expand, from the tool industry for hard grind metal materials processing, marketing to the bearing, automotive, machine tools, compressors and other industries in general ferrous metal materials processing, grinding ways from the general tool grinding, internal grinding, the development of creep feed grinding, precision grinding, high speed grinding, cam grinding, crankshaft grinding, abrasive corundum replace a great trend. CBN grinding with high speed, high efficiency, high quality, low cost. Widespread use of speed reaches 80 ~ 125m / s, large margin coarse grinding at once, because the grinding surface was compressive stress can make working life increased by 20% to 30%, the consolidated grinding costs can be reduced by 10% or more. In recent years, domestic and imported complete sets of CBN grinding technology showed a rapid growth trend. CBN abrasive domestic manufacturing and application technology into high-level and a new stage of rapid development, and has entered the mainstream automotive manufacturing market. Part CBN abrasive performance close to the level of similar foreign products, can replace imported. Domestic high-speed CNC CBN special grinder has been successfully developed.
