1. The grinding of auto parts--camshaft and crankshaft
Camshaft in the automobile engine has multiple cams. The coarse and fine grinding of quenched cam are the key factors affecting the quality of cam process. The imitating grinding is commonly used in the cam processing, as a result, the speed increase of workpiece is restricted and workpiece is easy to generate burn and crack. By imitating grinding, the cam contour curve on wheel surface will be affected by the diameter of grinding wheels. So it is difficult to ensure the correctness of cam contour curve. Production practice has proved that when the diameter of grinding wheel is large, the cam is thinner. When the grinding wheel diameter is small, the cam is fatter. Only when the grinding wheel diameter is close or equal to the diameter of roller wheel to grind cam (generallyφ570 mm), and the contouring grinding error is close to zero, namely the the cam contour curve on surface is close to the profiling cam. In actual production, the grinding wheel diameter generally ranges from 600 ( or 610)mm to 500mm, and there is a large gap from the ideal grinding wheel diameter (570). So there will always be that in the production of cam, a large part of the cam curve over the standard. To solve this problem, we use the CBN grinding wheel in the profile modelling cam grinding machine. CBN grinding wheel diameter can be manufactured to 575mm, and the thickness of CBN layer to 4 ~ 5 mm. The minimum diameter of the grinding wheel is 565mm, and the grinding diameter range is only 10 mm, but the processed parts quantity is equivalent to dozens of universal grinding wheels. It not only can ensure the cam curve correct, but also won't generate burn.
For example, the Liton industrial automation company uses the CBN grinding wheel to grind camshaft, the cost reduces by 50% and the fatigue strength of cam increases by 30%; Xiangfan diesel engine factory of DongFeng Automobile Company uses the vitrified CBN grinding wheel to coarse grind camshaft made of chilled cast iron. The cam grinding allowance t = 4 ~ 5 mm, υ = 60 m/s, the workpiece speed n = 100 r/min, υf = 0.1 mm/s. Application of the high speed grinding fluid, CBN grinding wheel’s life span is basically equivalent to that of 20 pieces corundum abrasive grinding wheels.
2. The application of CBN grinding wheel in inner hole grinding
The internal grinding efficiency has always been very low. The main reasons include grinding speed, grinding wheel material and grinding rod rigidity. The time taken to dress and change grinding wheels, accounts for almost one-third to one-fifth of the total working hours. If the inner or groove grinding adopt the CBN electroplated grinding wheel, increase the grinding wheel speed and increase the rod diameter, we can improve the speed and feed rate. This appropriately can not only ensure hole diameter, groove width, size, shape accuracy, surface roughness and avoid burns, but also can improve the machining efficiency multiply, and reduce the processing cost.
For example, a Chinese factory who processes textile machinery rolling bearings cover with an annual output of 600000 pieces, grind the φ 15.5 + 0.04 hole and the adjacent arc slot. In the past, they processed them with chromium corundum grinding wheel (GG). It need two process steps respectively on two M224 internal grinders. The variation in groove (arc) diameter and the alignment of size and hole are very difficult to guarantee, and the efficiency is low. After using CBN grinding wheel, the grinding rod is larger in diameter, the feeding is improved, which saves dressing and replacement time of wheels and completely solves the original problems. Then it is changed to grind the hole and groove at the same time, namely mount two grinding wheels on the grinding rod, which improves the grinding efficiency by 1 times and saves a grinding machine. The processing surface roughness υwheel= 36 m/s, υ2 = 19 m/min, coarse cutting f = 1 μm/r, fine cutting f = 0.5 μ m/r, finishing time t = bs and 10% concentration of emulsified value.
3. Using CBN grinding wheel to process gears
Gear in the past is grinded by single surface or multi surface grinding, although the single surface grinding can gain higher machining precision, but it is of low efficiency and high cost. Although the multi-surface grinding is of high production efficiency, but its processing quality is worse than single surface grinding. If using the CBN grinding wheel, whether the single surface grinding or multi surface grinding, the electroplating CBN grinding wheel or ceramic bonded grinding wheel, the effect of grinding is very significant:
(1) The CBN grinding wheel can be made into tooth profile of high precision, due to their high durability, infrequent dressing, no need to adjust the grinding machine, it often obtains stable tooth profile, lead and pitch accuracy.
(2) We can realize high speed and high feed rate tooth surface grinding, lower roughness and no burn. Besides, we can improve the gear accuracy under the condition of improving the efficiency(6 ~ 7 grade).
(3) The CBN grinding wheel is of long service life and good grinding performance, which saves the replacement, dressing auxiliary machine adjustment and workpiece inspection time.
4. The application of CBN abrasive tools to machine difficult-to-machine materials
For the hole honing of hardened steel or chilled cast iron, CBN honing stone can be used for alloy steel, stainless steel, heat-resistant steel and alloy of high strength, high hardness and high heat sensitive. It is suitable to adopt the CBN grinding wheel of high hardness and high strength. The use of extreme pressure emulsion or high speed grinding fluid for cooling is also needed. For the longer guideway, complex planes or modeling of cam grinding machine are all appropriate to match with CBN grinding wheels.
Vigorously promote the CBN material in mechanical processing and the application in the critical working procedure. CBN material either in the production of cutting tools or production of abrasive tools or high speed cutting and grinding can receive high product quality, improve the machining efficiency, shorten the cycle and reduce processing costs and other significant effects. In the processing, therefore, our vigorous promotion of the CBN cutter (grinding) tools is an effective measure to improve manufacturing technology. But if populate it, there are still many problems.