What’s the Application Of CBN Wheel In Grinding ?

There are many cams on the camshaft of an auto engine, the rough and fine grinding of quenched cams are the key process of the cam quality. Usually, we adapt imitating shape grinding, the increasing of the workpiece speed is limited and easy to burn out. And the camber curve of cam surface is strongly affected by the diameter of grinding wheel. So it is hard to promise the accuracy of cam profile. The production practice proves that when the wheel diameter is large, the cam that ground is thin; and when the wheel diameter is small, the cam that ground is fat. Only when the wheel diameter is similar or equal to the roller diameter (usually φ570mm)of grinding cam, its profile tolerance is almost zero, which means the camber curve of cam surface is near imitated cam. In real production, the wheel diameter is generally from D600 to D500, while is far from the ideal grinding wheel diameter(φ570mm), so in production there always have most camshafts are out of standard line. In order to solve this problem, we use CBN wheel grinding on the imitated shaping cam grinding machine, we can make the diameter of CBN wheel D575mm, the thickness of CBN layer 4-5mm, while the smallest diameter of grinding wheel is D565 and the diameter range of grinding is only 10mm, meanwhile the numbers of grinding parts is equivalent to dozens of ordinary wheels. Through CBN wheel grinding , can not only promise the curve of camshaft but also won’t cause burns.

For example, Liton company uses CBN grinding wheel to grind camshaft, its cost decreased 50%, while the fatigue strength of the camshaft surface increased 30%; Dongfeng Motor Corporation Xiangfan Diesel Engine Works uses vitrified CBN grinding wheels to rough grind of Cold-shock cast iron camshaft, its grinding tolerance is t=4~5mm, v=60m/s(grinding wheel), the rotating speed of workpiece n=100r/min, vf=0.1mm/s. By using high speed grinding fluid, the life span of CBN wheel equals 20pcs Corundum abrasive wheels.

The efficiency of internal grinding is always low, its mail reason is the grinding speed, the rigidity of grinding wheel material and grinding rod. The time spent in dressing and changing grinding wheels during the production process accounted for almost 1/3~ 1/5 of the production time per piece. If grind inside circle or groove with electroplated CBN wheel,by increasing the wheel speed and grinding rod diameter, the rotate speed and feed speed can be appropriately increased. In this way not only can guaranteed hole(arc) diameter, groove width size ,geometric tolerance, surface roughness and not easy to burn, but also can greatly increased the working efficiency and decrease production cost.

For example: One factory processes an annual output of 600,000 spinning machine rolling bearing sleeve, they used to use GC grinding wheel to grind φ15.5+0.04 hole and adjacent arc slots, need to machining in two steps in two different M224 internal grinding machine. The groove (arc) diameter difference and size and hole coaxiality is difficult to ensure, and the efficiency is very low. After using CBN wheel, the grinding rod is thickened, the feed amount is improved and the time of dressing and changing grinding wheel is shortened, which completely solved the original issues. Afterwords,the machining way changed to grind hole and groove in the same time, which means install two grinding wheels on the grinding rod, increased one time grinding efficiency and saved one grinding machine. The processed surface roughness of workpiece is RA0.63um. The adopted grinding parameters are as follows: V=36m/s(grinding wheel), V2=19m/min, f=1um/r(rough machining),f=0.5um/r(fine machining).

Gear grinding usually adapt single tooth face grinding and multi-tooth surface grinding. Single tooth face grinding can achieve higher machining accuracy,but its efficiency is lower and cost is higher; While multi-tooth surface grinding can get higher production efficiency but its machining quality is worse than single tooth face grinding. If using CBN wheel grinding, no matter use single tooth face grinding or multi-tooth surface grinding, when using electroplated CBN wheel or vitrified CBN wheel , its performances are very amazing:

(1)CBN grinding wheel can be made into high precision tooth profile, without frequent dressing and adjusting machine,and because of high durablity, it can achieve steady tooth profile, lead and pitch accuracy.

(2)Can realize high speed grinding and high feed amount when grind gear face. It is not easy to burn and roughness is low, under the condition of improving grinding efficiency can achieve higher gear accurancy(level 6~7).

(3)Longer lifespan and better grinding efficiency, it saves the time of dressing and changing of grinding wheel, also shorten the time of adjusting machine and measurement of workpiece.

For honing holes of hardened steel or chilled cast iron, we can use CBN honing stones. For machining alloy steel, stainless steel, heat-resistant steel and alloy with high strength, high hardness and high heat sensitivity, it is better to choose high hardness and high strength CBN grinding wheel, meanwhile use extreme pressure emulsion or high speed grinding fluid for cooling. It is advisable to use CBN grinding wheel for long guide or complex surface and cam-grinding machine.

CBN material, whether it is used to make tools or abrasives, can be used in high speed cutting or grinding to improve product quality, improve processing efficiency, shorten the processing cycle and reduce the processing cost. Therefore, in the processing, vigorously promote CBN cutting (grinding) tools is a powerful measure to improve the manufacturing technology. However, if it is widely used, there are still exist .many problems.