What is bearing superprecision?

Bearing superfinishing is a smoothing method that is a feed movement to achieve micro-grinding.

The surface before superfinishing is generally precision turned and ground. Specifically, it refers to a smoothing processing method that exerts little pressure on the workpiece with a fine-grained abrasive tool (oil stone) under good lubrication and cooling conditions, and makes a fast and short reciprocating oscillation motion on the workpiece rotating at a certain speed in the vertical dry workpiece rotation direction.

What is the role of bearing superfinishing?

In the manufacturing process of rolling bearings, superfinishing is the final process of bearing ring processing, which plays an important role in reducing or eliminating the circular deviation left by grinding processing, repairing the shape error of the trench, refining its surface roughness, improving the physical and mechanical properties of the surface, reducing the vibration and noise of the bearing, and improving the mission of the bearing.

It can be embodied in the following three aspects

1. It can effectively reduce the waviness. In the process of super-finishing, in order to ensure that the oil stone always acts on the crest of the wave and does not contact with the trough, the arc of the oil stone in contact with the workpiece ≥ the wavelength of the waviness on the surface of the workpiece, so that the contact pressure of the crest is larger, and the convex peak is removed, thereby reducing the waviness.

2. Improve the groove error of the ball bearing raceway. Super-finishing can effectively improve the groove error of about 30% of raceways.

3. It can produce compressive stress on the surface of the super-fine grinding. In the process of superfinishing, cold plastic deformation is mainly generated, so that after superfinishing, residual compressive stress is formed on the surface of the workpiece.

4. It can increase the contact area of the working surface of the ferrule. After super-finishing, the contact bearing area of the working surface of the ferrule can be increased from 15%~40% after grinding to 80%~95%.   

Bearing superfinishing process:

1. Cutting of bearings

 

When the surface of the grinding stone is in contact with the convex peak of the rough raceway surface, due to the small contact area and the large force on the unit area, under the action of a certain pressure, the grinding stone is first subjected to the "reverse cutting" action of the bearing workpiece, so that part of the abrasive particles on the surface of the grinding stone fall off and fragment, revealing some new sharp abrasive grains and cutting edges. At the same time, the surface bump of the bearing workpiece is rapidly cut, and the crest and grinding deterioration layer on the surface of the bearing workpiece are removed by cutting and reverse cutting. This stage is called the cutting phase, and it is in this stage where most of the metal allowance is removed.

2. Half-cutting of bearings

As the machining continues, the surface of the bearing workpiece is gradually smoothed. At this time, the contact area between the grinding stone and the surface of the workpiece increases, the pressure per unit area decreases, the cutting depth decreases, and the cutting capacity decreases. At the same time, the pores on the surface of the grinding stone are blocked, and the grinding stone is in a semi-cutting state. This stage is known as the half-cut stage of bearing finishing, in which the cutting marks on the surface of the bearing workpiece become lighter and have a darker gloss.

3. Finishing stage

This stage can be divided into two steps: one is the grinding transition stage, and the other is the grinding stage after the cutting is stopped

Grinding transition phase:

The abrasive grain is self-sharpened, the edge of the abrasive grain is smoothed, the chip oxide begins to be embedded in the void of the oil stone, the abrasive powder blocks the oil stone pores, so that the abrasive grain can only be cut weakly, accompanied by extrusion and grinding, then the surface roughness of the workpiece is quickly reduced, and the surface of the oil stone is attached with black chip oxide.

Stop the cutting grinding phase:

Oil stone and workpiece friction with each other has been very smooth, the contact area is greatly increased, the pressure drops, the abrasive grain has been able to penetrate the oil film and contact with the workpiece, when the oil film pressure of the bearing surface is balanced with the oil stone pressure, the oil stone is floated. During the formation of an oil film, there is no cutting effect. This stage is unique to superfinishing.