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Application of cubic boron nitride (CBN) in cutting
1. Hardened steel with PCBN blade finishing
Using PCBN tools to finish hardened steel, the hardness of the workpiece is higher than 45HRC, and the effect is best.
The cutting speed is generally 80-120 m/min. The higher the hardness of the workpiece, the lower the cutting speed. For example, the workpiece with a hardness of 70HRC should be 60-80m/min. The cutting depth of the finished car is 0.1-0.3mm, the feed rate is 0.05-0.025mm/r, the surface roughness of the workpiece after finishing the car is Ra0.3-0.6μm, and the dimensional accuracy can reach 0.013mm. If the standard CNC lathe machining with good rigidity can be used, the rigidity of the PCBN tool is good and the edge is sharp. The surface roughness of the workpiece after finishing the car can reach Ra0.3μm, the dimensional accuracy can reach 0.01mm, and it can be processed by CNC grinding machine. Level.
If the machine tool is rigid and the cutting speed is low, the PCBN compound blade can be used to finish the surface.
The finishing allowance of the finishing car is generally about 0.3mm, which can improve the dimensional accuracy and reduce the thermal deformation of the workpiece before quenching as much as possible to ensure uniform cutting allowance and prolong the service life of the PCBN tool.
The finishing car generally does not use cutting fluid, because at higher cutting speeds, a large amount of cutting heat is carried away by the chips, and rarely stays on the surface of the workpiece to affect the quality and precision of the machined surface.
The finishing blade should use a 80° diamond blade with high strength and toughness. The radius of the tool tip is between 0.8 and 1.2 mm. To protect the cutting edge of the tool, a fine stone chamfer is required before use.
Finished car hardened workpiece is a new process. It needs to be tested before implementation. It can be used for finishing or roughing test on the same machine tool with the same material, hardness and size. The key is to test the tool and cut. The choice of parameters and the process system are sufficiently rigid. The process has been adopted in China at present. For example, FAW Group uses PCBN tool to process 20CrMnTi gearbox fork groove of carburizing and quenching (58～63HRC). The process parameters are υc=150m/min, f=0.1mm/r, αp. = 0.2 ~ 0.3mm, the realization of the car to wear.
2. Processing hard cast iron and grey cast iron
(1) Processing hard cast iron
When turning hardened steel with PCBN tool, the hardness of the workpiece is required to be higher than 45-55HRC. When the hard cast iron is processed, as long as the hardness reaches the medium hardness level (45HRC), good processing results will be obtained. For example, the exhaust valve seat on the cylinder head of an automobile engine is made of high-chromium alloy cast iron material containing copper and molybdenum. Its hardness is generally about 44HRC, and the upper hole of the valve seat adopts two processes: 锪 (hinge) and car. Most of them are processed on a dedicated automatic line, along with the gun hinge hole. The cutting amount used is: υc=71.6m/min, υf=26.5mm/min, αp=1.0mm, BC broaching oil, after processing with PCBN tool, it is processed with various carbide blades used in the past. In comparison, the average durability of the tool is 1200 pieces, the surface roughness of the machined surface is Ra0.4μm, and the valve seat surface slip is ≤0.05mm. Since the engine factory of Dongfeng Motor Corporation used PCBN tools in 1988, its effect has remained stable, which has solved the problem of localization of tools imported equipment.
(2) High-speed milling gray cast iron
When milling gray cast iron at high speed, K-type cemented carbide can of course be used for roughing, and silicon carbide ceramic inserts can be used for finishing. For example, if you use a symmetrical two-piece PCBN insert on an end mill with 8 inserts and increase the cutting speed by 4 times, the result is the same metal removal rate and a 3/4 reduction in cutting force. Tool life and processing quality exceed the former.
For pearlite cast iron and chilled cast iron, PCBN tools should also be used for high-speed machining. Compared with other tool materials, it can improve cutting speed, extend tool life and reduce surface roughness.
3. High speed boring casting hole
Compared with the single-piece boring tool, the paired insert PCBN boring tool on the high-speed mast has a good balance, which increases the rigidity of the mast. At a given feed rate, the PCBN double-blade boring can be used. A high metal removal rate and surface quality are obtained.
At present, there are many engine manufacturers in China, and PCBN tools have been used for finishing the cylinder bore (or cylinder liner) of the cylinder block. As the engine manufacturers of Shanghai Volkswagen and FAW Group, the cylinder bores are all made of PCBN inserts and can be automatically compensated (υc=500m/min, f=0.2mm/r, αp=0.1mm). Therefore, the processed cylinder bore has high precision and dimensional stability, and has high production efficiency and long tool life.
For small hole boring, ceramic or coated blades can be used, but the blade should have a negative rake angle, which will increase the resistance to cutting and chip removal, and easily cause the slender mast to vibrate. If the PCBN tool is used for high-speed boring, the surface quality of the hole is good and the production efficiency is high.
4. Reaming hardened steel or hard casting small holes
CBN electroplated reamer should be used for the hole machining of such workpieces. This kind of reamer is made of 45# steel or 9CrSi steel with a hardness of 42HRC. It has front and rear guiding and cutting parts. The base manufacturing precision is high and the design should be reasonable. If the diameter of the front guiding portion of the reamer is smaller than the diameter of the cutting edge portion by 0.04 mm, the length of the cutting zone is larger than the depth of the workpiece hole, and the length of the rear guiding is greater than the length of the cutting zone, and the diameter should be smaller than the diameter of the cutting edge of 0.02 mm. In order to flush the chips with the cutting fluid and to cool the lubricated surface in the reaming, the reamer base has two deep spiral grooves.
For example, a factory processing hardened steel workpiece hole φ12.06±0.05mm, hardness is 45HRC, bottom hole size is φ12±0.01mm, the cylindricity of the hole is required to be 0.005mm, and the surface roughness is Ra0.2μm. After processing with a set of five electroplated CBN reamers, good economic results are achieved. Some engine manufacturers use diamond or CBN electroplating reamer to knead the main bearing hole of the cylinder block instead of the original honing process, which improves the processing efficiency several times and the quality is stable.
5. For the machining of difficult materials
Use PCBN tool with positive rake angle, select appropriate cutting parameters, ie υc=100m/min, f=0.05～0.2mm, αp=0.1～0.2mm, use extreme pressure type emulsion or oil coolant, can process Materials such as stainless steel (45HRC), high-temperature alloy steel, high-manganese steel, high-strength steel and high-nickel alloy steel can obtain high processing efficiency and surface quality.
Application of CBN grinding wheel in grinding
In addition to the tools used to make the CBN material, the largest application area is the CBN grinding tool, which is used for high-speed and high-efficiency grinding and honing, which can greatly improve the grinding efficiency and improve the grinding precision and quality.
1. Grinding automotive parts - camshafts and crankshafts
The camshaft on the automobile engine has a plurality of cams, and the coarse grinding and fine grinding of the cam after quenching are the key processes that affect the quality of the cam. Generally, the grinding is simulated, the speed of the workpiece is limited, and the workpiece is prone to wear and burn cracks. The shape of the cam surface of the cam surface is affected by the diameter of the grinding wheel. Ensure that the curve of the cam wheel is correct. Production practice proves that when the diameter of the grinding wheel is large, the grinding cam is thin. When the diameter of the grinding wheel is small, the grinding cam is fat, only when the diameter of the grinding wheel is close to or equal to the diameter of the roller for grinding the cam (generally φ570 mm), The profiling error is close to zero, ie the curved cam surface vertex curve is close to the cam. In actual production, the diameter of the grinding wheel used is generally from D600 (or 610) to D500, which is much different from the ideal grinding wheel diameter (570). Therefore, the cam curve of most camshafts exceeds the standard in production. In order to solve this problem, we use CBN grinding wheel grinding on the analog cam grinding machine. The diameter of CBN grinding wheel can be made into D575, the thickness of CBN abrasive layer is 4~5mm, the grinding diameter of grinding wheel is D565, grinding diameter Although the range is only 10mm, the number of grinding parts is equivalent to dozens of ordinary grinding wheels, which not only ensures the correct cam curve, but also does not cause grinding burns.
For example, Liton Industrial Automation Company uses CBN grinding wheels to grind camshafts, which reduces the cost by 50% and the fatigue strength of the cam surface by 30%. Dongfeng Motor Corporation's Xiangfan diesel engine plant uses ceramic bond CBN grinding wheels to grind cold-casting cast iron camshafts. The cam grinding allowance t=4～5mm, υ sand=60m/s, workpiece rotation speed n=100r/min, υf=0.1mm/s, using high-speed grinding fluid, the life of CBN grinding wheel is basically equivalent to 20 pieces. Corundum abrasive wheel.
2.Application of CBN grinding wheel in internal hole grinding
The efficiency of internal grinding has been low, mainly due to the grinding speed, the material of the grinding wheel and the rigidity of the grinding rod. In the production process, it takes almost 1/3 to 1/5 of the time for dressing the grinding wheel and replacing the grinding wheel. If the inner circle or groove grinding adopts the CBN electroplating grinding wheel, and the grinding wheel speed is increased, and the diameter of the grinding rod is increased, the workpiece rotation speed and the feed speed can be appropriately increased, and the hole (arc) diameter and the groove width size and shape can be ensured. Position accuracy, surface roughness and avoidance of burns, but also can double the processing efficiency and reduce processing costs.
For example, a domestic factory processing a spinning bearing sleeve with an annual output of 600,000 pieces, grinding holes of φ15.5+0.04 and adjacent arc grooves. In the past, chrome corundum (GG) grinding wheels were used in two processes. M224 internal circular grinding machine processing, the groove (arc) diameter difference and the coaxiality of the size and the hole is difficult to guarantee, and the efficiency is low. After the CBN grinding wheel is used, the grinding rod is thickened, the feed rate is increased, and the trimming is saved. And the time to replace the grinding wheel completely solved the original problem. Later, it was changed to hole and groove at the same time, that is, two grinding wheels were installed on the grinding rod, which improved the grinding efficiency by one time and saved one grinding machine. The surface roughness of the machined workpiece is Ra0.63μm. The grinding process parameters are: υ sand = 36m / s, υ 2 = 19m / min, f rough cut = 1μm / r, f fine cut = 0.5μm / r, light grinding Time t = bs, using an emulsification value of 10% concentration.
3. Grinding gears with CBN grinding wheel
In the past, gear grinding used single-tooth surface and multi-tooth surface grinding. Although single-tooth surface grinding can obtain high machining accuracy, it has low efficiency and high cost. Although multi-tooth surface grinding has high production efficiency, its processing is high. The quality is worse than single tooth grinding. If CBN grinding is used, whether it is single-tooth grinding or multi-tooth grinding, grinding with CBN grinding wheel or ceramic bond grinding wheel is very effective:
(1) CBN grinding wheel can be made into a highly accurate tooth shape. Due to its high durability and infrequent trimming, it is not necessary to adjust the machine frequently, and stable tooth guide, lead and pitch accuracy can be obtained.
(2) It can realize high-speed grinding and high feed rate grinding tooth surface, low roughness and no burn, and can obtain high gear precision (6-7 grade) under the condition of improving grinding efficiency.
(3) CBN grinding wheel has long service life and good grinding performance, which saves many auxiliary time such as grinding wheel replacement and trimming, machine adjustment and workpiece inspection.
4. Application of CBN abrasive tools to process difficult-to-machine materials and difficult-to-machined surfaces
For the honing of hardened steel parts or chilled iron parts, CBN honing oil stone can be used. For high strength, high hardness and high heat sensitivity alloy steel, stainless steel, heat resistant steel and alloy, high hardness and high strength CBN should be adopted. The grinding wheel is cooled by an extreme pressure emulsion or a high speed grinding fluid. CBN grinding wheels are suitable for longer rail faces or complex profiles, camshafts for cam grinders, etc.
Promote the application of CBN materials in key machining processes
CBN materials can be used for high-speed cutting or grinding, regardless of the tool or the grinding tool, to achieve significant results such as improved product quality, improved machining efficiency, shorter cycle times and lower processing costs. Therefore, in the processing, the promotion of CBN knives (grinding) is a powerful measure to improve manufacturing technology. However, if it is widely used, there are still many problems.
In order to better promote the use of CBN knives (grinding) in production, the following aspects should be done:
1. Play the leading role of CBN knife (grinding) research institute
At present, there are many domestic CBN material manufacturers, and the output is also quite a lot, but the quality is not much, and the CBN knife (grinding) has fewer stable users. The main reason is that the mechanical processing department lacks the knowledge of the selection and use of expensive CBN knives. The purchased CBN tools are not effective, and under the conditions of economic contraction, they are not easy to invest in process testing. In order to solve this problem, only the CBN Knife Institute has taken the initiative to go deep into the manufacturing unit of mechanical manufacturing, select the weak link of production efficiency and quality, and has the point of having or easy to create CBN processing conditions, and negotiate with the user. Signed a joint development CBN application contract. The tool development unit is responsible for providing the CBN knife (grinding) for testing free of charge. The user is responsible for providing the tissue production test under the conditions required for the test. This has exerted a lot of enthusiasm. From CBN quality selection to tool manufacturing, it will be carried out at the optimal and fastest speed. From the preparation of test conditions to the use of the user, the user can see the achievement of the target value of the contract and solve it without spending the test fee. Production problems are easy to promote. The tool institutes can also gradually recover profits in future supply. As long as the two sides maintain mutual benefit and mutual benefit, the cooperative relationship will be further consolidated. Our factory has developed many new technologies with many research institutes (schools) in this way.
2. Realize the joint development of three points and one line, that is, CBN--tool manufacturing--user or CBN and tool manufacturing--machine tool--users jointly develop CBN application
The reasons are manifold, such as CBN quality, content, brand specifications and bonding agents are suitable for the processing of boron cast iron. As for the grinding effect of the CBN abrasives, there are more factors. In addition to the quality, proportion and abrasive manufacturing technology of the raw materials, there are conditions and techniques for use. Such as grinding speed (application of high-speed grinding speed), good rigidity of the grinding machine, no vibration, automatic fine feed and dressing compensation mechanism, appropriate grinding parameters and coolant, etc. These are all important factors that complement each other. Working together to improve the quality of their own products and promote each other, CBN tools and special equipment can be successfully used in production.
3. Actively carry out research on manufacturing and using technology of CBN knife (grinding)
Users want to use effective CBN tools. To this end, tool manufacturing units are required. In addition to improving the manufacturing technology of CBN tools as soon as possible, they should also establish clear identification standards and methods for product quality, and distribute certain performance parameters, such as tool CBN. The content and the brand, the hardness of the abrasive tool and the CBN precision and concentration, etc., on the basis of the production and use test, in order to give full play to the user's production experience, compare the different cutting parameters and the processing results obtained by the coolant, so that CBN tools have been improved in quality. The scope of CBN tools, the conditions of use and the technical support of the application (such as equipment and coolant), users can correctly select and use CBN tools.
4. Users need to improve product quality awareness and courage to improve manufacturing technology
The 21st century is a high-tech era. Products must have high performance and high quality to have a market, and enterprises can have vitality. To this end, the level of manufacturing technology should be improved as soon as possible, and the promotion of the use of CBN tools to improve manufacturing technology is a powerful measure, which not only requires strong funding and support from relevant authorities, but also systematically and systematically promotes the technical support of CBN tools. Use, but also requires users to accept new materials, new technologies, change the old obsolete production concepts and management methods, that is, the knife (grinding) has a low cost index, which only accounts for about 1/100 of the cost of the product, instead of In order to improve production efficiency and ensure product quality, this will limit the use of high-quality and efficient knife (grinding) tools and advanced equipment production capacity. Practice has proved that the effectiveness of CBN knives can not only improve the processing quality of products, but also improve economic efficiency.
Application of cubic boron nitride (CBN) in cutting
Cubic boron nitride (CBN) is a new type of superhard tool cutting material synthesized after synthetic diamond. Its hardness is second only to diamond, and it is widely used in cutting and grinding processing.