Abstract: This paper analyzes the reasons why the common grinding method of thin-walled ferrules easily causes the deformation of the ferrule and the low processing efficiency, and introduces the working principle and improvement effect of the escape grinding method for machining the inner ring groove.
Key words: thin-wall bearing; escape grinding method; deformation; machining efficiency
There are many methods for grinding bearing rings, but no effective solution has been found for thin-walled rings. This is because the stiffness of the thin-walled ferrule is too low, and a slight application of load will easily lead to deformation regardless of clamping or processing, and it is difficult to ensure the dimensional and geometric accuracy required by the process. Therefore, the grinding of thin-walled ferrules is always a bearing manufacturing process. a difficulty.
1 Common grinding methods
For the thin-walled inner ring groove, the commonly used grinding methods are “branch diameter grinding groove” (supporting the inner diameter grinding groove), “branch groove grinding groove” (supporting the inner groove grinding inner groove) and “support edge grinding groove” ( Grinding inner groove of supporting ribs) and so on. Taking “branch diameter grinding groove” as an example, its grinding principle is shown in Figure 1. The machining error of the inner diameter during grinding will be reflected on the inner groove; the front and rear supports make the center of the workpiece and the center of the grinding wheel basically on the same level, and the workpiece directly bears the cutting force fed by the grinding wheel. When the feed rate is too large and exceeds the deformation resistance of the workpiece, the workpiece will be deformed, and the accuracy of the workpiece size and roundness will be difficult to control. In actual processing, the operating tools are required to have a high level of skill and rich practical experience. Generally, it is necessary to repeatedly feed and grind with a micro-feed of 1 μm. If the one-time feed is too large, it may cause waste, and The processing efficiency is very low. For example, the inner ring with an inner diameter of about 100 mm is only about 10 pieces per shift.
2 Escape grinding method
After many tests, a “escape grinding method” that is especially suitable for the processing of thin-walled inner ring grooves has been found-that is, when the feed of the grinding wheel is large, the workpiece can automatically “escape” when it is squeezed and deformed. Not only can ensure the machining accuracy, but also can significantly improve the machining efficiency.
The key to the escape grinding method is to set the workpiece support as a combined angular support with an inner support and an outer support, as shown in Figure 2. The front support is an inner support, the eccentricity is in the first quadrant, the support angle α = 15° ~ 20°, and the eccentricity e = 0. 15 to 0. 30 mm (when this range is taken, the wall thickness difference of the workpiece is more accurate). (2) The rear support is an external support, the eccentricity is in the fourth quadrant, and the included angle between the two supports is β = 30° ~ 45°.
The working principle of the escape grinding method: When the grinding wheel feeds and grinds the workpiece, if the cutting force exceeds the clamping force of the electromagnetic centerless clamp, the workpiece will be separated from the outer support of the fourth quadrant, avoiding the deformation caused by the extrusion of the grinding wheel, and maintaining the original shape . After grinding to a certain size, the workpiece falls back to the outer support for normal grinding. This is repeated until the desired size is reached.
Using the escape grinding method, since the workpiece can automatically “escape” during grinding to avoid the influence of deformation, it can achieve a high degree of
The machining accuracy and yield are greatly reduced. And because there is no need to consider the problem of excessive grinding wheel feed, not only ordinary operators can complete it, but also the shift production of the same workpiece is increased from the past 10 pieces to about 50 pieces, and the processing efficiency is increased by about 5 times. At present, this grinding method has been verified and promoted in 2 kinds of materials (stainless bearing steel 9Cr18 and high carbon chromium bearing steel GCr15) and many products (including “branch groove grinding diameter” of thin-walled bearing outer ring), The effect is very obvious, which solves the problem that the thin-walled bearing ring is difficult to process.