Application of CBN grinding wheel in grinding process

1. Grinding of automotive parts-camshafts and crankshafts 

The camshaft on the automobile engine has multiple cams, and the rough grinding and fine grinding of the cam after quenching are the key processes that affect the quality of the cam. In general, imitative grinding is used, and the speed of the workpiece is limited, and the workpiece is prone to grinding burn cracks. When the imitative grinding is used, the contour curve of the cam surface is affected by the diameter of the grinding wheel , so it is difficult Ensure that the cam contour curve is correct. Production practice has proved that when the diameter of the grinding wheel is large, the ground cam is thin, and when the diameter of the grinding wheel is small, the ground cam is fat. Only when the diameter of the grinding wheel is close to or equal to the roller diameter of the grinding master cam (usually φ570mm), its The profiling error is close to zero, that is, the contour curve of the ground cam surface is close to the master cam. In actual production, the diameter of the grinding wheel used is generally from D600 (or 610) to D500, which is very different from the ideal wheel diameter (570), so the cam curve of most camshafts always exceeds the standard in production. In order to solve this problem, we use CBN grinding wheel grinding on the imitated cam grinder. The diameter of the CBN grinding wheel can be made D575. The thickness of the CBN abrasive layer is 4～5mm. The minimum grinding diameter of the grinding wheel is D565. Although the range is only 10mm, the number of grinding parts is equivalent to dozens of ordinary grinding wheels, which not only guarantees 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 increases the fatigue strength of the cam surface by 30%; Dongfeng Motor Company Xiangfan Diesel Engine Plant uses ceramic bond CBN grinding wheels for rough grinding of chilled cast iron camshafts , Its cam grinding allowance t=4～5mm, υ sand=60m/s, workpiece 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 grinding wheel.

2. Application of CBN grinding wheel in inner hole grinding

The efficiency of internal grinding has been very low. The main reasons are the grinding speed, the material of the grinding wheel and the rigidity of the grinding rod. The time spent on dressing and replacing the grinding wheel in the production process accounts for almost 1/3 to 1/5 of the single-piece working hours. If CBN electroplated grinding wheel is used for inner circle or groove grinding, and the speed of the grinding wheel is increased, and the diameter of the grinding rod is increased, the rotation speed and feed speed of the workpiece can be appropriately increased. Not only can the hole (arc) diameter, groove width and shape be guaranteed Position accuracy, surface roughness and avoid burns, but also can double the processing efficiency and reduce processing costs.

For example, a domestic factory processes a textile machine rolling bearing sleeve with an annual output of 600,000 pieces, and grinds φ15.5+0.04 holes and adjacent arc grooves. In the past, chromium corundum (GG) grinding wheels were used, and two processes were used in two sets. For processing on M224 internal grinder, the groove (arc) diameter difference and the coaxiality between the size and the hole are difficult to guarantee, and the efficiency is low. After using CBN grinding wheel, the grinding rod is thickened, the feed rate is increased, and the dressing is saved. And the time to replace the grinding wheel, completely solved the original problem. Later, it was changed to simultaneous hole and groove grinding, that is, two grinding wheels were installed on the grinding rod, which doubled the grinding efficiency and saved a grinding machine. The surface roughness of the processed workpiece is Ra0.63μm. The grinding process parameters used: υ sand=36m/s, υ2=19m/min, f rough cutting=1μm/r, f fine cutting=0.5μm/r, smooth grinding Time t=bs, using 10% concentration emulsification value.

3. Grinding gears with CBN wheels

In the past, gear grinding used single-tooth surface and multiple-tooth surface grinding. Although single-tooth surface grinding can obtain higher machining accuracy, it has low efficiency and high cost. Although multi-tooth surface grinding has high production efficiency, its processing The quality is worse than single tooth grinding. If CBN grinding wheel is used for grinding, whether single-tooth surface grinding or multi-tooth surface grinding, electroplated CBN grinding wheel or ceramic bond grinding wheel is used for grinding, the effect is extremely significant:

(1) CBN grinding wheel can be made into high-precision tooth profile. Due to its high durability and infrequent dressing, there is no need to frequently adjust the machine tool, and stable tooth profile, lead and pitch accuracy can be obtained.

(2) It can achieve high-speed grinding and high-feed rate grinding of the tooth surface, with low roughness and no burns, and high gear accuracy (level 6 to 7) can be obtained under the condition of improving grinding efficiency.

(3) CBN long wheel life, grinding performance is good, the section about the replacement of many of the auxiliary wheel dressing time, adjust the machine and workpiece detection.

4. Use CBN abrasives to process difficult-to-machine materials and surfaces

For the honing of hardened steel or chilled cast iron holes, CBN honing oilstone can be used. For alloy steel, stainless steel, heat-resistant steel and alloys with high strength, high hardness and high heat sensitivity, high hardness and high strength CBN should be used. The grinding wheel is cooled by extreme pressure emulsion or high-speed grinding fluid. CBN grinding wheels should be used for long guide rail surfaces or complex profiles, and the profile axis of cam grinders.

Vigorously promote the application of CBN materials in key processes of machining

Regardless of whether the CBN material is used to make tools or make abrasive tools, it can be used in high-speed cutting or grinding, and it can receive significant effects such as improving product quality, improving processing efficiency, shortening processing cycles and reducing processing costs. Therefore, in processing, vigorously promote CBN knife (grinding) is a powerful measure to improve manufacturing technology. But if it is widely used, there are still many problems.

In order to better promote the use of CBN knife (grinding) tools in production, the following tasks should be done:

(1) Give full play to the leading role of the CBN knife (abrasive) research institute (institute)

At present, there are many domestic CBN material manufacturers with a lot of output, but there are not many high-quality ones, and there are fewer stable users of CBN knife (grinding) tools. The main reason is that the machining department lacks knowledge about the selection and use of expensive CBN knives (grinding tools). The purchased CBN tools are not very effective. Under the conditions of economic contraction, they dare not easily invest in process experiments. To solve this problem, only the CBN knife (abrasive) tool research institute (institute) takes the initiative to go deep into the production units of machinery manufacturing, select the weak links of production efficiency and quality, and have or are easy to create CBN processing conditions, and negotiate with users Signed a contract for joint development of CBN applications. The tool development unit is responsible for providing the CBN knife (grinding) for the test free of charge, and the user is responsible for organizing the production test under the conditions required for the test. This gives full play to the enthusiasm of many parties. From CBN quality selection to tool manufacturing, it will be carried out at the best and fastest speed. From preparing test conditions to use, users can see the results of reaching the contract target value and solve it without spending test fees. Production problems are easy to promote. The tool institute (institute) can also gradually recover profits in future supplies. As long as the two parties maintain mutual benefit and mutual benefit, the cooperative relationship will be more consolidated. Our factory has developed many new technologies with many research institutes (schools) in this way.

(2) Realize the three-point and one-line joint development, namely CBN-tool manufacturing-user or CBN and tool manufacturing-machine tool-user to jointly develop the application of CBN

Many processing difficulties in mechanical processing can be solved with CBN tools, but under the current conditions, no one in China can do it alone, because CBN tools have unique and versatile processing capabilities. We have also used CBN inserts for fine boring boron cylinder liners, and the effect is not better than the new ceramic inserts. There are many reasons for this, such as whether CBN quality, content, brand specifications and bonding agent are suitable for the processing of boron cast iron. As for the grinding effect of CBN abrasive tools, there are more factors, in addition to the quality of the raw materials, the ratio of the abrasive tools and the manufacturing technology of the abrasive tools, there are also the conditions and technology of use. Such as the grinding speed (application of high-speed grinding speed), the grinding machine has good rigidity, no vibration, automatic fine feed and dressing compensation mechanism, appropriate grinding parameters and coolant, etc., these are all important factors that complement each other and rely on relevant aspects. Working together, improving the quality of their own products and promoting each other, can CBN tools and special equipment be successfully used in production.

(3) Actively carry out the research of CBN knife (abrasive) manufacturing and using technology

Users want to use effective CBN tools. For this reason, tool manufacturers are required to not only improve the manufacturing technology of CBN tools as soon as possible, but also establish clear identification standards and methods for product quality, and distribute certain performance parameters, such as the CBN of the tool. The content and brand, the hardness of abrasive tools and the accuracy of CBN, concentration, etc., are used in production and use tests on this basis, so as to give full play to the user’s production experience and compare and analyze the processing results obtained by different cutting parameters and coolants. CBN tools have been qualitatively improved. The scope of application, conditions of use, and technical support (such as equipment and coolant, etc.) of CBN tools allow users to select and use CBN tools correctly.

(4) Users need to improve product quality awareness and be brave 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 a company can have vitality. For this reason, 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 strong funding and support from relevant authorities, but also gradually promotes the technical support and support of CBN tools in an organized and planned manner. At the same time, users are required to be brave enough to accept new materials and new technologies, and to change the old production concepts and management methods in the past. That is, the cost index of knife (grinding) consumption is very low, which can only account for about 1/100 of the product cost. To improve production efficiency and ensure product quality shall prevail, which will limit the application of high-quality and efficient knife (grinding) tools and the production capacity of advanced equipment. Practice has proved that the effectiveness of CBN knife (abrasive) tools can not only improve the processing quality of the product, but also increase economic benefits.