Application technology of the hottest cubic boron

2022-08-01
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The application technology of cubic boron nitride (CBN) abrasive tools

- high speed, high efficiency, high precision and low cost grinding technology

cbn (cubic boron nitride) is another superhard material first synthesized by American GE company in 1957 after the advent of artificial diamond. CBN was successfully developed in 1966 in China, which has a history of nearly 40 years

The hardness of

cbn is only lower than that of diamond, but it has superior heat resistance and chemical inertness to ferrous metals. CBN abrasive tools made of these excellent properties as abrasive materials are especially suitable for the grinding of various iron group metal materials. It and diamond are mainly used to process hard and brittle materials, which complement each other and greatly expand the application range of superhard materials. Compared with ordinary abrasive tools, CBN abrasive tools have the characteristics of high speed, high efficiency, high machining quality, long service life and low cost, and can be used as the preferred tool for high-speed CNC grinding machines with high efficiency and high precision. It is widely used in automobile, machine tool, tool, bearing and other industrial fields

1. Properties of CBN

when CBN is used as abrasive material, we mainly study its hardness, wear resistance, strength and thermal conductivity

◆ the hardness of CBN is much higher than that of other common abrasives. High hardness means stronger and sharper cutting ability

◆ CBN has high wear resistance, which means it is more difficult to wear than ordinary abrasive. The ability to maintain the shape of abrasive particles is one of the main characteristics of CBN as a high-performance abrasive

◆ CBN has a high compressive strength, which means that it can keep the particles intact and not easy to break when used under adverse conditions

◆ CBN has good thermal conductivity and can realize cold cutting during grinding

due to the different properties of CBN and diamond, the range of their processing materials is also different. CBN is suitable for processing tool steel, bearing steel, alloy steel, super alloy and cast iron. The suitable materials for diamond processing are cemented carbide, glass, ceramics, cermet and cast iron

2. CBN grinding system

cbn abrasive is a tool that uses different types of binders to bond CBN Abrasives together and make them into a certain shape. Only through reasonable grinding technology and relying on the superior performance of the grinder, can it play its role to the greatest extent. In the research and application of CBN grinding technology, CBN grinding tools, grinding machines, workpiece, dressing, cooling, grinding process and other factors must be incorporated into a system for optimization, so as to obtain the best technical and economic results

Several important factors to be considered in CBN grinding technology are as follows

2.1 CBN abrasives

the shape, size, CBN abrasive particle size, concentration, bond type, service speed and other parameters are mainly considered when manufacturing and selecting abrasives

◆ the shape, size and mark of CBN abrasive tools shall be in accordance with gb/t6409 And gb/t6409 Standard provisions of

◆ among the four binders (resin, metal, ceramic and electroplating) of CBN abrasive tools (Table 1), ceramic binders have the fastest development. This is because the ceramic CBN grinding tool has high grinding efficiency, good shape retention, high durability, easy dressing, and long service life of the grinding wheel, so it has become the preferred grinding tool for high-efficiency and high-precision grinding. Table 1 bond type

grinding performance bond type of abrasive tools resin (b) metal (m) ceramic (V) electroplating (E) grinding wheel life medium high high high high high high high metal removal rate/medium high high/medium high shape retention medium high high high high high high power demand medium/medium low/medium hard to finish medium hard hard easy generally no surface roughness good/medium best change recommended application tools, tool grinding

surface grinding, external

circular grinding, hob grinding,

polishing Creep feed

grinding, double face grinding, internal

circular grinding, honing forming grinding, internal

cylindrical grinding, convex

wheel grinding, crankshaft grinding,

creep feed grinding, polishing, superfinishing template grinding, forming

grinding, cylindrical internal

cylindrical grinding, creep feed

gear or

spline grinding

◆ grinding powder concentration according to the regulations, when the concentration of abrasive in the abrasive tool is 100%, 4.4 carats (0.38g) of abrasive per cm3, equivalent to 25% by volume

the concentration of grinding wheel indicates the number of grinding particles on the working surface of grinding wheel during grinding. High concentration can lead to high grinding ratio and low workpiece surface roughness. For example, the service life of the grinding wheel with 200% concentration is times longer than that with 100% concentration. See Table 2 for the concentration code. Concentration code specification

code abrasive content (carat/cm3) concentration 251.125%502.250%753.375%1004.4100%1506.6150%2008.8200%

◆ the hardness grade of the abrasive tool indicates the holding force of the binder on the abrasive. The uniformity and stability of the grinding wheel hardness and the more patient and reasonable selection of the hardness are the important prerequisites to ensure the grinding quality

2.2 grinder

the grinder is the center of the grinding system. The performance of the grinder has the most important impact on the grinding effect, especially for CBN grinding

◆ increasing the working linear speed of the grinding wheel can significantly improve the grinding efficiency, grinding ratio and workpiece surface quality. The service speed of 80~125m/s has become one of the basic features of CBN special camshaft grinder imported from China. Using high speed as much as possible is an important prerequisite to improve the technicality and economy of CBN grinding

◆ the characteristics of high-speed grinding and CBN wheel grinding require that the spindle and the whole machine tool should have high rigidity and good vibration resistance, which is the basic requirement for the grinder in CBN high-speed grinding technology. Without such conditions, the geometric accuracy and surface quality of the workpiece will become worse in order to obtain higher metal removal when using CBN grinding wheel. Ripple is a common surface quality defect, which is caused by vibration. The reason that may cause vibration is that the grinding force is too large due to the low rigidity of the machine tool, the poor vibration resistance or the unreasonable design of the grinding wheel parameters

dressing

dressing with diamond rollers can not only improve dressing efficiency, but also obtain better grinding wheel morphology. The feed accuracy of the dressing device shall be high, and each feed rate shall reach the micron level. Excessive dressing will not only affect the grinding quality, but also greatly reduce the service life of the grinding wheel

cooling

correct selection of coolant type and cooling process parameters will often achieve twice the result with half the effort

optimization of grinding process parameters

full optimization of grinding process parameters can balance the technical and economic indicators such as grinding efficiency, grinding quality and grinding cost at a higher level

3. Application of CBN abrasive tools

overview of technology development at home and abroad

with the progress of industrial technology, high-energy automatic measurement of bolt total elongation and residual deformation speed, high-efficiency and high-precision grinding has become the mainstream of the development of grinding technology. CBN grinding, as an advanced machining technology, plays its role here. The development of CBN abrasive tool manufacturing and application technology has the following characteristics:

① the application field has been expanding. It has been extended from the processing of difficult to grind metal materials in the tool industry to the processing of common ferrous materials in the bearing, automobile, machine tool, compressor and other industries. The grinding methods have also developed from general tool grinding and internal grinding to creep feed grinding, high-precision grinding, high-speed grinding, cam grinding, crankshaft grinding It has the potential to replace corundum abrasive tools

② its main characteristics are high speed, high efficiency, high quality and low cost. The service speed generally reaches 80~125m/s; Large amount of rough and fine grinding is completed at one time; Because the surface of the ground workpiece is in the state of compressive stress, the service life of the workpiece can be increased by 20~30%; The comprehensive grinding cost can be reduced by more than 10%

③ the whole set of CBN grinding technology imported from China is growing rapidly

④ the manufacturing and application technology of domestic CBN abrasive tools has entered a new stage of high level and rapid development, and has entered the mainstream market of automobile manufacturing industry. The performance of some CBN abrasives is close to the level of similar foreign products and can replace imports

⑤ domestic high-speed CNC CBN special grinding machine has been successfully developed

3.2 application examples of CBN abrasive tools

◆ engine camshaft grinding

example 1: fine grinding of automobile camshaft

grinding wheel: 1a1180mm V 125m/s Zhengzhou abrasive grinding Research Institute

machine tool: Schott cf41 CBN

workpiece: cast iron, 8 cams, allowance d1.0mm, rmax3.2

dressing: diamond roller, d180mm, dressing interval 200 pieces (800 cams), dressing amount 5% above the diameter μ m × 3+3 μ M2/time

cooling: synthetic liquid, pressure 23bar

effect: reach the level of imported grinding wheel, and reduce the comprehensive cost by more than 30%

example 2: fine grinding motorcycle camshaft

grinding wheel: 1a1350mm V 80m/s Zhengzhou abrasive grinding tool grinding Research Institute

machine tool: Toyota cams grinder

workpiece: 45# steel, 2 cams, HRC60, allowance 0.2~0.3mm, rz3.2, grinding efficiency 30s/piece

dressing: diamond roller, dressing interval 240 pieces, dressing amount 0.002mm/time

effect: the service life can reach 80~90% of that of imported grinding wheel, and the cost can be reduced by more than 30%

example 3: rough grinding of automobile camshaft

grinding wheel: 1a1660mm V 60m/s Zhengzhou abrasive grinding tool grinding Research Institute

machine tool: domestic mks8312 cam grinder

workpiece: alloy chilled cast iron, 13 cams, hrc45, allowance φ 4mm, ra2.5, grinding efficiency 12min/piece

dressing: Diamond cup-shaped roller, dressing interval 8~10 pieces/time, dressing amount φ 0.01x2;

cooling: high efficiency grinding fluid, pressure 4kg, flow 120l/min

wheel replacement cycle: 5000 pieces/piece

effect: instead of white corundum grinding wheel, the durability is increased by 100 times, the service life is increased by 50 times, the production efficiency is increased by 10%, and the cost of direct tools is reduced by 10%

◆ grinding example of automobile bearing inner diameter

grinding wheel: 1a810 × fifteen × 3.5V Zhengzhou abrasive grinding Research Institute

machine tool: domestic MZ204 automatic internal grinder 24000rpm

the smoke density produced by ADK stab FP ⑵ 000 series of workpiece decreased by 99%:6201/02, GCr15, hrc61~65, allowance 0.3~0.35mm, Ra0.8, grinding efficiency 25s/piece, feed rate 0.24mm/min (coarse) and 0.17mm/min (fine)

trimming: diamond pen, manual, trimming interval 200 pieces, trimming amount 0.02mm

cooling: emulsion, centralized supply

service life of grinding wheel: 2500 pieces (30 pieces/piece of corundum grinding wheel)

effect: compared with white corundum grinding wheel, the durability is increased by 200 times, the single piece production efficiency is increased by about 40%, and the grinding wheel cost consumption is reduced by 14%

◆ example of grinding inner diameter of refrigerator (air conditioner) compressor core assembly

grinding wheel: 1a812 × thirty × 6,1A1 25 × twenty × thirteen × 3 v50m/s Zhengzhou abrasive grinding Research Institute

machine tool: Germany Overbeck 400j-elc-va internal grinder, with a maximum speed of 60000rpm

workpiece: base, cylinder block (cover), ht20~40, ft20, hb170~223, hb70~90, machining allowance 0.2mm, ra0.2~0.25, machining cycle: 90~120 pieces/h.

dressing: diamond roller, dressing interval 200~300 pieces, dressing amount 0.002mm/time

cooling: cooling oil containing extreme pressure additives

service life of grinding wheel: 20000~2500 pieces/piece

in addition, there are other application examples for thread grinding, such as high-speed deformation of elastomer and change of resistance value of strain gauge pasted on it, grinding of tooth shape and inner diameter of steel cutter, double face grinding of compressor core components, honing of motorcycle cylinder and connecting rod, titanium alloy grinding, grinding of inner diameter of automobile inserting rod, grinding of inner diameter of automobile steering gear, etc. I will not list them here. (end)

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