Bearing manufacturing technology – grinding

 

 

Abstract:

Bearing grinding includes grinding, superfinishing, lapping, etc. This article will focus on some technologies and characteristics of bearing grinding and superfinishing.

 

 

Key words:Bearing manufacturing technology, bearing grinding, bearing superfinishing.

 

 

 

Bearing grinding includes grinding, superfinishing, lapping, etc. This article will focus on some technologies and characteristics of bearing grinding and superfinishing.

 

1.Grinding and superfinishing process of bearings

After plastic processing and cutting, the workpiece is formed and heat treated. First, the reference end face is ground with a double-end grinder. Then the outer diameter surface of the outer ring is ground with a longitudinal feed through centerless grinder, which can be processed continuously. After that, the outer ring groove is ground and super-finished based on the outer diameter surface of the outer ring end face. Similarly, the inner ring is ground with inner groove, inner diameter surface ground, and inner groove super-finished. Then it is submitted to the assembly and inspection process.

1.1 Surface grinding

The inner and outer rings are ground with a double-end surface grinder. Double-end surface grinding is to align and assemble two grinding wheels at a specified interval, so that the ring passes between the two grinding wheels and grinds the two end surfaces with the specified size and parallelism, which can achieve continuous and efficient processing.

1.2 Longitudinal feed through centerless grinding

The outer diameter of the outer ring is ground using a longitudinal feed through centerless grinder. The method is as follows: the outer ring is supported at three points by the guide wheel, the support plate and the grinding wheel of the centerless grinder. The guide wheel rotates the outer ring and the grinding wheel rotates to grind. Because there is no workpiece rotation center like chuck processing, it is called centerless grinding. By correctly setting the angles of the grinding point, the support point of the pallet and the guide wheel support point, the grinding surface is supported for processing. At the beginning of processing, the rough grinding accuracy is formed, and the outer diameter roundness of the outer ring is gradually corrected to finally ensure sufficient roundness of the outer ring. In addition, by tilting the guide wheel and feeding along the axial direction of the workpiece, continuous and efficient processing can be achieved.

1.3 Support block centerless grinding

The outer diameter surface or inner groove being ground is supported by support blocks, and the end face is adsorbed to a fixture called a support plate by electromagnetic force. The outer groove or inner diameter surface is ground while the spindle is rotating. The spindle center and the workpiece (outer ring) supported by the support block are eccentric, and the workpiece rotates stably on the support block by using the thrust generated by the eccentricity and rotation. The outer diameter and outer groove can be processed with a constant wall thickness, and the specified concentricity and groove roundness of the groove and outer diameter can be obtained.

In order to realize the arc-shaped R-shaped groove, the grinding wheel is formed into an R shape (grinding wheel dressing), and the shape is copied and processed. There are two methods for R-shaped dressing: copying the shape of a formed rolling grinding wheel dresser that has been pre-made into its R shape; and dressing with a rotating single diamond dressing tool.

The inner groove is also centerless grinding with support blocks, and this process uses support blocks to support the groove to be ground. Because the grinding surface is supported by support blocks, it is not on the roundness reference surface as in the aforementioned outer groove grinding. This process produces a new roundness. It is a form-finishing process. The mechanism of this roundness is the same as the centerless grinding of the outer ring. The centerless front support block and rear support block are equivalent to the support plate and guide wheel of the centerless grinder.

1.4 Superfinishing

Superfinishing is to press a fine-grained oilstone onto a rotating workpiece (such as the inner and outer rings) and give it a small swing at right angles to the workpiece to finish the workpiece surface. As for the superfinishing of the ball bearing groove, the center of the groove R is used as the oilstone swing center for processing. Furthermore, at the beginning, an oilstone adapted to the shape of the workpiece is used, and since the oilstone is not trimmed, the self-sharpening effect of the oilstone due to the wear of the oilstone is utilized to continuously perform processing while maintaining the shape of the oilstone.

 

2.Bearing processing technology direction

2.1 Processing technology for difficult-to-cut materials

From the perspective of grinding characteristics, high-performance new materials are basically difficult-to-cut materials, resulting in poor processing efficiency and difficulty in maintaining the sharpness of the grinding wheel. As a grinding technology suitable for difficult-to-cut materials, the first thing to mention is to expand the application range of CBN grinding wheels. The abrasive hardness, sharpness and life of CBN grinding wheels are better than those of traditional alumina grinding wheels, and are suitable for difficult-to-cut materials.

2.2 Processing technology to deal with environmental issues

One of the grinding processing technologies that is in harmony with the environment is the development of processing cooling lubricants (coolants). Coolants are used for lubrication, cooling, and cleaning of processing parts. In most cases, grinding generates heat during processing, and a large amount of coolants is required to meet the requirements of surface accuracy and quality. The technology being developed is a processing technology that uses the smallest amount of coolant necessary for grinding, as well as a processing technology that uses droplet and oil mist cooling.

In order to reduce CO2 emissions, the first countermeasure is to improve the energy efficiency of grinding machines and super finishing machines. However, as a processing technology, grinding requires more energy than turning, such as removing the energy required for processing. Therefore, it is necessary to reduce the grinding load by reducing the grinding allowance or hard turning, and achieve energy saving in the entire process.

2.3 Processing technology for high precision

In order to improve the rotation accuracy of machine tool spindle bearings, the requirements for vibration and quietness of motor bearings are getting higher and higher.

In order to improve the rotation accuracy of bearings, the grinding conditions should be optimized and the interference of grinding state should be eliminated to improve the roundness through low vibration and high precision of grinding equipment. Spindle bearings with sub-micron roundness should be used.

In order to achieve low vibration and quietness of bearings, improve the superfinishing quality of rolling surface of rolling elements, which is beneficial to greatly improve surface roughness.

2.4 Processing technology to cope with low cost

The grinding technology of bearings is also asking for low cost. Therefore, it is necessary to increase the output of automatic production lines, develop low-cost production line equipment, and use labor-saving and unmanned production line operation technologies.

To increase production, it is necessary to compress cycle time and improve equipment operation rate. In order to shorten the operation cycle, it is necessary to develop equipment that can compress idle time such as loading and develop technology to improve grinding efficiency.

In order to improve grinding efficiency, the use of CBN grinding wheels and vitrified grinding wheels is increasing. These grinding wheels have abrasive strength and sharpness that exceed conventional alumina grinding wheels. Even in the super finishing process, the grinding allowance is reduced through the development of grinding wheels, and the processing time is shortened.

In addition, in order to achieve both improved grinding efficiency and high precision, it is necessary to achieve high rigidity, low vibration, and high precision of grinding equipment. By concentrating functions and re-evaluating the manufacturing process of equipment, we will develop equipment that can achieve both low cost and high efficiency and high precision.

In terms of labor-saving and unmanned operating systems, we are currently developing a system that can automatically handle the monitoring of processing status, diamond grinding wheel wear and thermal deformation of machinery without human intervention, such as size adjustment, grinding wheel replacement and handling of equipment abnormalities.

2.5 Processing technology suitable for high-variety and low-volume production

As a way to cope with the replacement of devices (equipment), we are developing processing equipment and production lines that have carefully considered the above aspects in order to facilitate the exchange of fixtures, tools and finishing devices including conveying on automated production lines and improve precision.

 

3. Summary

The environment of bearing grinding will also change greatly with the different processing requirements, but high function, high precision and low cost are the eternal topics of bearing grinding, and environmental protection is also a very important topic.