Application of Cubic Boron Trioxide (CBN) in Machining

Cubic deuterated boron (CBN) is a new type of superhard cutting material artificially synthesized after synthetic diamond. Its hardness is second only to diamond, and it has been widely used in cutting and grinding processing.

Application of Cubic Boron Trioxide (CBN) in Machining

1. Use PCBN blade precision car hardened steel using PCBN tool precision car hardened steel, the workpiece hardness is higher than 45HRC, the best effect.
The cutting speed is generally 80 ~ 120m/min, the higher the workpiece hardness, cutting speed should be taken to a low value, such as car hardness 70HRC workpiece, the cutting speed should choose 60 ~ 80m/min. The depth of cut of the finishing car is 0.1-0.3mm, the feeding amount is 0.05-0.025mm/r, and the surface roughness of the workpiece after finishing the car is Ra0.3-0.6μm, and the dimensional accuracy can reach 0.013mm. If rigid standard CNC lathes are used for processing, PCBN tools have good rigidity and sharp edges, then the surface roughness of finished workpieces can reach Ra 0.3μm, and the dimensional accuracy can reach 0.01mm, which can be achieved with CNC grinding machines. Level.

If the machine tool is rigid and the cutting speed chosen is low, the PCBN composite blade can be used to finish the discontinuity of the surface.

The finishing allowance is generally about 0.3mm, so as to improve the dimensional accuracy of the workpiece before quenching and reduce the thermal deformation, so as to ensure that the cutting allowance is uniform and the service life of the PCBN tool is prolonged.

Generally, no cutting fluid is used for the finishing car, because at high cutting speeds, a large amount of cutting heat is carried away by the chips and rarely stays on the surface of the workpiece, which affects the quality and accuracy of the machined surface.

Fine turning inserts should be made of 80° diamond blades with high strength and toughness. The radius of the tool nose should be between 0.8 mm and 1.2 mm. To protect the tool edge, chamfering must be done with a fine whetstone before use.

Quenching a hard workpiece is a new process. Before the implementation, a process test is required. The same material as the workpiece material, hardness and size can be used to perform the finishing or roughing test on the same machine. The key is to test the tool and cutting. The choice of parameters and whether the process system has sufficient rigidity. This process is currently used in China, such as FAW Group's PCBN tool processing carburizing quenching (58 ~ 63HRC) 20CrMnTi transmission gear fork groove, using the process parameters υc = 150m/min, f = 0.1mm/r, αp = 0.2 ~ 0.3mm, to achieve a car on behalf of the mill.

2. Processing of hard cast iron and gray cast iron (1) When processing hard cast iron with a PCBN tool to turn hardened steel, the quenched hardness of the workpiece is required to be higher than 45 to 55HRC. When processing hard cast iron, as long as the hardness reaches a medium hardness level (45HRC), Will achieve good processing results. Such as automotive engine cylinder head exhaust valve seat, the valve seat is the use of copper, molybdenum high chromium alloy cast iron material, the hardness is generally about 44HRC, the valve seat hole using 锪 (hinge), car two processes Mostly, it is processed on a dedicated automatic line, and is carried out along with the gun hinge duct hole. The cutting amount used is: υc = 71.6m/min, υf = 26.5mm/min, αp = 1.0mm, using BC broaching oil, since the use of PCBN tool processing, and the previous use of various carbide blade processing In comparison, the average tool life is 1,200 pieces, the surface roughness is Ra0.4μm, and the valve seat surface swing is ≤0.05mm. Dongfeng Motor Company's engine plant has been using PCBN tools since 1988, its effect has remained stable, and it has solved the problem of the localization of imported tools.

(2) High-speed milling of gray cast iron When high-speed milling of gray cast iron, general rough machining can of course use K-type hard alloy, and silicon carbide ceramic inserts can be used for finishing. For example, when using a symmetric two-piece PCBN insert on an end mill equipped with eight inserts and increasing the cutting speed by four times, the result is that the metal removal rate is the same and the cutting force is reduced by 3/4. Tool life and processing quality exceed the former.

For pearlite cast iron and chilled cast iron, PCBN tools are also suitable for high-speed machining. Compared with other tool materials, cutting speed can be increased, tool life can be extended, and surface roughness can be reduced.

3.High-speed boring of casting holes The use of paired insert PCBN boring tool on high-speed boring bar compared to single boring knife has good balance, thus increasing the rigidity of the boring bar, at a given feed rate, High metal removal rates and surface quality can be achieved with PCBN dual-blade boring.

At present, there are many engine manufacturers in China. PCBN tools have been used for the machining of the cylinder bore (or liner) of the cylinder block. Such as Shanghai Volkswagen and FAW Group's engine plant, cylinder hole precision boring are used PCBN blade and can automatically compensate (υc=500m/min, f=0.2mm/r, αp=0.1mm). Therefore, the processed cylinder hole has high precision and dimensional stability, and has high production efficiency and long tool life.

For small hole boring, although ceramic or coated inserts may be used, the insert should have a negative rake angle, which will increase the resistance to cutting and chip removal and tends to cause vibration in the elongated boring bar. If the PCBN tool is used for high-speed boring, the hole surface quality is good and the production efficiency is high.

4. Reaming Hardened Steel or Hard Casting Holes CBN plated reamers are preferred for hole machining of these types of workpieces. The reamer is a 45-gauge steel or 9CrSi steel with a hardness of 42 HRC. The reamer has a front-rear guide and a cutting part, and the base body has a high manufacturing precision and the design must be reasonable. If the diameter of the leading part of the reamer is smaller than the diameter of the cutting edge part by 0.04mm, the length of the cutting zone should be greater than the depth of the workpiece hole. The length of the rear guide should be greater than the length of the cutting zone, and its diameter should be smaller than the diameter of the cutting edge part by 0.02mm. In order to use the cutting fluid to flush the chips and cool and lubricate the machined surface during reaming, the reamer base has two deeper spiral grooves.

Such as a factory processing quenched steel workpiece hole φ12.06 ± 0.05mm, hardness 45HRC, bottom hole size φ12 ± 0.01mm, the required cylinder cylindricity 0.005mm, surface roughness Ra0.2μm. A group of five electroplated CBN reamers are used to achieve better economic results. Some engine manufacturers use a diamond or CBN plated reamer to twist the main bearing bore of the cylinder block, instead of the original honing process, the machining efficiency is improved several times, and the quality is stable.

5. For the machining of difficult-to-machine materials, use a PCBN tool with a positive rake angle, select the 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 austenitic stainless steel (45HRC), high temperature alloy steel, high manganese steel, high strength steel and high nickel alloy steel and other materials, and can obtain higher processing efficiency and surface quality.

Application of CBN Grinding Wheel in Grinding

In addition to CBN materials used to make tools, the largest application area is to make CBN grinding tools for high-speed and high-efficiency grinding and honing process, which can greatly increase the grinding efficiency, and improve the grinding accuracy and quality by one grade.

1. Grinding automotive parts - camshafts and crankshafts The camshafts on automotive engines have multiple cams. After quenching, rough grinding and fine grinding of cams are key processes that affect cam quality. Generally rely on imitation grinding, the workpiece speed is limited, the workpiece is prone to grinding burn cracks, using imitation grinding, the cam surface curve of the wheel to be affected by the size of the diameter of the wheel, so it is difficult Ensure that the cam profile curve is correct. Production practice has proved that when the grinding wheel diameter is large, the worn out cam is thin. When the grinding wheel diameter is small, the cam worn out is fat. Only when the grinding wheel diameter is close to or equal to the grinding wheel diameter of the grinding cam (generally φ570 mm), The profiling error is close to zero, that is, the worn-out cam surface curve is close to the cam cam. In actual production, the diameter of the grinding wheel used is generally from D600 (or 610) to D500, which is quite 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 the CBN grinding wheel on the imitating cam grinder. The diameter of the CBN grinding wheel can be made into D575, the thickness of the CBN abrasive layer is 4~5mm, and the minimum grinding diameter of the grinding wheel is D565. Although the range is only 10mm, but the number of grinding parts is equivalent to several dozen ordinary grinding wheels, not only to ensure that the cam curve is correct, but also does not produce grinding burns.

For example, Liton Industrial Automation used CBN grinding wheels to reduce the cost of camshafts by 50% and the cam surface's fatigue strength increased by 30%. The Dongfeng Motor Company's Xiangfan diesel engine plant used CBN grinding wheels to grind chilled cast iron camshafts. , The cam grinding allowance t = 4 ~ 5mm, sand = 60m / s, workpiece speed n = 100r/min, Ï… f = 0.1mm / s, using high-speed grinding fluid, CBN grinding wheel life is basically equivalent to 20 Corundum abrasive wheel.

2. CBN Grinding Wheels for Internal Hole Grinding The efficiency of internal grinding is always low. The main reasons are the grinding speed, the material of the grinding wheel and the rigidity of the grinding rod. In the production process, the grinding wheels and grinding wheels are used for almost 1/3 to 1/5 of the individual work hours. If the inner circle or groove grinding uses CBN electroplating grinding wheel, and the speed of the grinding wheel is increased to increase the diameter of the grinding rod, the workpiece rotation speed and feed speed can be properly increased, not only the hole (arc) diameter and the groove width dimension and shape can be guaranteed. Bit accuracy, surface roughness and avoidance of burns, but also can double the processing efficiency and reduce processing costs.

For example, a factory in China processes an annual output of 600,000 spinning bearings for rolling machines, grinding φ15.5+0.04 holes and adjacent arc slots, and in the past using chrome corundum (GG) grinding wheels, two processes were required in two separate machines. It is difficult to guarantee the groove (arc) diameter difference and size and the coaxiality of the hole in the M224 internal grinding machine, and the efficiency is low. After the CBN grinding wheel is used, the grinding rod is thickened, the feed amount is increased, and the dressing is saved. And the time to replace the wheel completely solved the original problem. Afterwards, it changed to the simultaneous grinding of holes and grooves, that is, two grinding wheels were mounted on the grinding rod, which increased the grinding efficiency by a factor of two and saved one grinding machine. The surface roughness of the machined workpiece is Ra0.63μm. The grinding process parameters are: sand = 36m/s, υ2 = 19m/min, f rough = 1μm/r, f = 0.5μm/r, light grinder Time t = bs, using a 10% concentration of emulsification.

3. Grinding with CBN Grinding Wheels Grinding gears Grinding gears previously used single-flank and multi-flank grinding. Although single-flank grinding can obtain high machining accuracy, it has low efficiency and high cost. Multi-tooth surface grinding Although the production efficiency is high, the processing quality is worse than that of single tooth grinding. If grinding with CBN grinding wheel, whether using single-tooth grinding or multi-tooth grinding, grinding with electroplated CBN grinding wheel or ceramic bonding agent wheel is very effective:

(1) The CBN grinding wheel can be made into a high-precision tooth profile. Due to its high durability, it is not frequently trimmed and does not require frequent adjustment of the machine tool to obtain a stable tooth gallery, lead, and pitch accuracy.

(2) It can realize high-speed grinding and high feed rate grinding of tooth surface, low roughness and no burn, and can achieve higher gear precision (levels 6 to 7) under the condition of improving grinding efficiency.

(3) CBN grinding wheel has a long life, good grinding performance, and saves a lot of auxiliary time such as grinding wheel replacement dressing, machine tool adjustment and workpiece detection.

4. Application of CBN Grinding Tools Difficult-to-machine materials and difficult-to-machine face CBN honing stone can be used to face the honing of hardened steel or chilled cast iron parts, for high strength, high hardness and high heat-sensitive alloy steel, stainless steel, and resistant For hot steels and alloys, high-hardness, high-strength CBN wheels should be used for cooling with extreme pressure emulsions or high-speed grinding fluids. CBN grinding wheels are recommended for long guideways or complex surfaces, camshafts for cam grinders, etc.

Promote the application of CBN materials in the key processes of machining. CBN materials can be used to improve the quality of products, improve the processing efficiency, shorten the processing cycle and reduce the processing cost, such as the production of tools or grinding tools for high-speed cutting or grinding. Significant effect. Therefore, in the processing, vigorously promoting CBN knives (grinding tools) 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 tools) in production, the following aspects should be done:

1. Play the leading role of the CBN Knife (grinding) Research Institute (the institute) Currently, there are many domestic CBN material manufacturers and the output is not small, but there are not many high quality products, and there are fewer stable users of CBN knives (grinding tools). The main reasons for this are the lack of knowledge of the selection and use of expensive CBN knives by the machining department. The CBN tools purchased are not very effective, and they are afraid to invest in process tests under the conditions of economic tightening. In order to solve this problem, only the CBN Knife Institute's (institute's) active production units that are deeply involved in machinery manufacturing, choose weak points in production efficiency and quality, and have or can easily create CBN processing conditions, and negotiate with customers. Signed a joint development CBN application contract. The tool development unit is responsible for the free supply of CBN knives (grinding tools) for testing. The user is responsible for providing production tests under the conditions required for the tests. This has exerted a variety of enthusiasm. From the CBN quality selection to the tool manufacturing, it will be carried out at the optimal and fastest speed. From the preparation of the test conditions to the use, the user sees the achievement of the target value of the contract, and solves it without spending the test fee. Production problems are easily promoted. The tool institute (the institute) can also gradually recover profits in the future supply. As long as the two sides maintain reciprocity and mutual benefit, the collaboration relationship will be further consolidated. Our factory is using this method to develop many new technologies with a number of research institutes (schools).

2. Realize the joint development of three points and one line, namely CBN - tool manufacturing - users or CBN and tool manufacturing - machine tools - users to jointly develop CBN applications

The reasons are various, such as whether the CBN quality, content, brand specifications and binders are suitable for the processing of boron cast iron. As for the grinding effect of CBN grinding tools, there are more factors, in addition to the quality of their own raw materials, ratio and abrasive manufacturing technology, as well as the use of conditions and technology. Such as grinding speed (application of high-speed grinding speed), good rigidity of the grinding machine, no vibration, automatic fine feed and trim compensation mechanism, proper grinding parameters and coolant, etc. These are important factors that complement each other and rely on Work together to improve the quality of their own products and promote each other, so that CBN tools and special equipment can be successfully used for production.

3. Actively carry out research on the manufacture and use of CBN knives (grinding tools). Users want to use effective CBN tools. For this purpose, tool manufacturers are required to establish a clear definition of the quality of products, in addition to improving the manufacturing technology of CBN tools as soon as possible. The identification criteria and methods for the distribution of certain performance parameters, such as the CBN content of the tool and the brand, the hardness of the grinding tool and the CBN precision, and the concentration, are based on the production and use tests so as to give full play to the user's production experience. The comparison between the cutting parameters and the machining results obtained by the coolant results in a qualitative improvement of the CBN tool. The scope of application of CBN tools, the use of conditions and the application of technical support (such as equipment, coolant, etc.), users can correctly select and use CBN tools.

4. Users need to raise awareness of product quality and have the courage to improve manufacturing technology. The 21st century is a high-tech era. Products must have high-performance, high-quality and only have markets, and companies have vitality. Therefore, 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. This not only requires the strong support and support of the competent authorities, but also gradually and systematically promotes the technical support of CBN tools. Use, but also requires users to be brave to accept new materials, new technologies, change the old production concepts and management methods, that is, the cost of the knife (wear) equipment is very low, only about 1/100 of the cost of the product, not To improve production efficiency and ensure product quality, this will limit the application of high-quality and efficient knife (grinding) tools and the production of advanced equipment. Practice has proved that the effectiveness of CBN knives (grinding tools) can not only improve the processing quality of products, but also increase economic efficiency.