A New Method for Grinding Large Circular Raceway of Bearing Inner Rings

Abstract: The disadvantages of traditional infeed grinding method for large circular raceway of bearing inner rings are analyzed，and a compound dressing method is put forward for grinding grinding wheel． The dressing for grinding wheel is realized by using compound motion of grinding wheel and diamond pen． The mechanical structure is simplified，having convenient coarse and fine adjustment function. The grinding accuracy of large circular raceway of inner rings is improved by grinding out mesh texture. 

Key words: rolling bearing; large circular raceway; grinding; grinding wheel; compound dressing

The dressing of the grinding wheel is an important process in the grinding of the inner ring of the bearing, and the accuracy of the grinding wheel dressing directly affects the grinding quality of the workpiece.

1. Traditional grinding methods for inner ring grooves

In the grinding of the bearing inner ring groove, the traditional cutting method is generally used for grinding, as shown in Figure 1. The grinding wheel adopts diamond pen arc swing adjustment, and the quality of the repaired wheel arc directly affects the quality of the workpiece to be ground. The radius of the outer edge of the grinding wheel is the radius of the inner ring groove of the bearing. If the radius of the groove increases, when dressing the grinding wheel, the radius of the outer edge of the grinding wheel needs to be correspondingly increased. Therefore, the distance H0 between the rotation center of the bow frame of the dressing device (Figure 2) and the diamond pen also needs to be increased. When H0 exceeds a certain range, the structure of the trimmer will become very complex and sometimes even unusable. If dual servo CNC interpolation and repair are used, on the one hand, the cost is high and the operation is complex; On the other hand, the accuracy of interpolated and trimmed arcs is poor, making it difficult to meet high-precision production needs.

Figure 1 Traditional Cut in Grinding Method

1-Trimmer; 2- Bow frame; 3- Diamond pen; 4- Grinding wheel

Figure 2 Structural diagram of grinding wheel trimmer

2. Composite dressing method for large circular groove grinding wheel

In view of the problems existing in the traditional cutting and grinding wheel dressing of large circular arc grooves, the grinding wheel dressing method was changed and a composite dressing method was adopted, as shown in Figure 3.

Figure 3 Machining Principle of Grinding Wheel Composite Dressing Method

Replace traditional grinding wheel structures with cylindrical grinding wheels. As the cylindrical grinding wheel rotates, at the height of its rotation centerline, the diamond pen rotates and is tangent to one side of the outer end face of the cylindrical grinding wheel, forming a spherical ring surface. Use this spherical grinding wheel to grind the large circular groove of the bearing inner ring.

2.1 Rotary mechanism of cylindrical grinding wheel

The outer radius of the cylindrical grinding wheel is R1, the inner hole radius is R2, and the width is H (Figure 3a). Using traditional electric spindle (or belt shaft) to drive rotation.

2.2 Diamond Pen Rotating Mechanism

The diamond pen is placed at the front end of one side of the grinding wheel, aligned with the centerline of the grinding wheel rotation α  Rotate the tangent plane of the angle with a diameter of d. Trim the leading edge of the grinding wheel into a spherical torus with a radius of R. The center point of the spherical torus is at the intersection point O between the rotation centerline of the grinding wheel and the rotation centerline of the diamond pen.

3. Adjustment of parameters and accuracy

3.1 Roughly adjust the radius of the arc as shown in Figure 3b, and the intersection point of the diamond pen rotation centerline and the grinding wheel rotation centerline is O. For the convenience of calculation, the distance between the center of rotation of the diamond pen and point O is represented by RX; The distance between the diamond pen trimming point (contact point with the grinding wheel) and point O is R, which is the radius of the grinding wheel end face ball ring to be obtained. As shown in Figure 3

In the formula: L is the vertical distance between the center point of diamond pen rotation and the centerline of grinding wheel rotation, mm; α  The angle between the rotation centerline of the diamond pen and the rotation centerline of the grinding wheel, in degrees. Adjust L or α， The size of RX can be changed. Because α ＜  90 °, then sin α ＜  1, so adjust L (or α  The angle of RX can be greatly adjusted, and it can be set as coarse adjustment during actual operation.

3.2 Fine tune the arc radius

In ensuring L, α  Under unchanged conditions, RX is a constant value. At this point, the relationship between the radius R of the ball ring, the rotation diameter d of the diamond pen, and RX is

If the rotation diameter d of the diamond pen is adjusted, R will change accordingly, but the change in R is very small and can be set as a fine adjustment in actual operation.

3.3 Machine Tool Layout

The layout of the machine tool is shown in Figure 4. The workpiece and the trimmer are installed on the same drag plate (workpiece drag plate) and driven by a servo motor in the direction shown in Figure 4. The cylindrical grinding wheel is installed on the grinding wheel drag plate and is also driven by a servo motor. Two drag boards are arranged in a T-shape.

Figure 4 Machine Tool Layout Diagram

During operation, driven by a servo motor, the cylindrical grinding wheel moves to the left, the workpiece drag plate moves upwards, and the dressing device rotates to complete the dressing of the grinding wheel. Then, the workpiece drag plate moves downwards, and the other side of the grinding wheel contacts the workpiece groove for grinding. The grinding of workpieces relies on the feeding and compensation of grinding wheels.

4. Advantages and disadvantages of composite dressing method

4.1 Advantages

1) The structure of the dressing device is simple. Compared with the traditional 1:1 grinding wheel dressing method, this scheme uses a smaller diamond pen rotation radius to control the grinding wheel ball ring radius several times that of the diamond pen rotation radius. 2) The radius of the grinding wheel ball ring can be adjusted and controlled through two stages of coarse adjustment and fine adjustment in practical operation, with higher accuracy and easier operation. 3) Compared with traditional interpolation and trimming, this is a geometric forming method with higher accuracy and lower cost. 4) The leading edge ball ring of the grinding wheel is ground by the rotation of the diamond pen and the grinding wheel, which can produce cross mesh patterns. The geometric accuracy of the ball ring is higher, avoiding the traditional cutting in grinding where the workpiece grinding marks are always on the same trajectory, which affects the surface roughness of the workpiece, thus improving the grinding accuracy. 5) The compensation and feed of the grinding wheel are in the same direction, and no other auxiliary structures are required. 6) The grinding wheel uses a ball ring on the front end face for grinding, and the grinding speed will not change with the dressing of the grinding wheel.

4.2 Disadvantages

1) When grinding with a grinding wheel, the speed of each grinding point is inconsistent, resulting in slight differences in the surface roughness of each point of the ring after grinding.

2) When grinding different rings, the shape of the grinding wheel will be limited to a certain extent. If the model difference is too large, different models of grinding wheels need to be used.

5. Conclusion

The composite dressing method provides a simple, practical, efficient, and easy to operate method for grinding large circular grooves on the inner ring of bearings for small and medium-sized bearing manufacturing enterprises. When the radius of the channel is greater than 100mm, this scheme has the best effect. In practice, when grinding inner circle large arc grooves with a diameter of 90 mm, a height of 46 mm, and an inner circle groove radius of 180 mm, a grinding wheel diameter of 180 mm is selected, and the angle between the rotation centerline of the diamond pen and the rotation centerline of the grinding wheel is included α at 21 ° 46 ", the rotation radius of the diamond pen is 25.75 mm, which is only 1/7 of the groove radius. After grinding, the surface roughness of the groove can reach 0.15 Ra μ M.

2024 April 2nd Week KYOCM Product Recommendation:

Spherical Roller Bearing：

A spherical roller bearing is a rolling-element bearing that permits rotation with low friction, and permits angular misalignment. Typically these bearings support a rotating shaft in the bore of the inner ring that may be misaligned in respect to the outer ring. The misalignment is possible due to the spherical internal shape of the outer ring and spherical rollers.[1] Despite what their name may imply, spherical roller bearings are not truly spherical in shape. The rolling elements of spherical roller bearings are mainly cylindrical in shape, but have a (barrel like) profile that makes them appear like cylinders that have been slightly over-inflated.