Bearing ring processing technology level analysis and solutions

1. Foreword As a mechanical manufacturing industry based on the entire industry, it is developing in the direction of high precision, high efficiency, intelligence and flexibility. Grinding and super-finishing processing (referred to as “grinding and super-processing”) are often the ultimate processing links of mechanical products, and the quality of their machining directly affects the quality and performance of the products. In the production of bearings as one of the basic components of the mechanical industry, the grinding and over-machining of the ferrule is the main link that determines the precision of the ferrule parts and even the entire bearing. The grinding super-machining of the rolling surface affects the bearing life and the bearing vibration reduction. The main link of noise. Therefore, grinding and over-machining has always been a key technology and core technology in the field of bearing manufacturing technology.
In the foreign bearing industry, in the 1960s, a stable ferrule grinding super-processing process and basic method have been formed, namely: double-face grinding - centerless external grinding - raceway cutting into centerless grinding - raceway super-finishing Processing. In addition to the special structure of the bearing, a number of additional processes are required, and the mass produced ferrules are processed according to this process. There have been no fundamental changes in the process flow for decades, but this does not mean that bearing manufacturing technology has not developed. Briefly speaking, in the 1960s, it was only the process of establishing and developing the "double end - unintentional outer circle - cutting into the grinding - super fine grinding" process, and correspondingly produced a series of cutting centerless grinding machines and super precision grinding machines, parts The machining accuracy is 3~5um, and the single machining time is 13~18s (small and medium size). In the 1970s, the application of 60m/s high-speed grinding, control grinding technology and control grinding machine was widely adopted. The digital control technology of electronic control technology featuring integrated circuits was widely used, which improved the grinding machine and the process. Stability, part processing accuracy of 1 ~ 3um, parts processing time 10 ~ 12s. Since the 1980s, the processing precision of process and equipment has not been a problem. The main development direction is to pursue higher efficiency under the premise of stable quality. {TodayHot} adjustment is more convenient and the numerical control and automation of the manufacturing system.

2. Grinding of bearing rings In the production of bearings, the grinding labor accounts for about 60% of the total labor, and the number of grinding machines used accounts for about 60% of all metal cutting machines. The cost of grinding accounts for the entire bearing cost. More than 15%. For high-precision bearings, these proportions of grinding are larger. In addition, the grinding process is the most complicated in the whole process, and it is still the most incomplete one. This complexity is manifested in: the required performance indicators are more, the precision is higher; the processing and forming mechanism is more complicated, and there are many factors affecting the processing accuracy; the processing parameters are difficult to detect online. Therefore, for the grinding process of one of the key processes in bearing production, how to adopt the new technology and new technology to complete the grinding process with high precision, high efficiency and low cost is the main task of the grinding process.
2.1 High-speed grinding technology High-speed grinding can achieve the two goals pursued by modern manufacturing technology to improve product quality and labor efficiency. Practice has proved that if the grinding speed is increased from 35m/s to 50-60m/s, the general production efficiency can be increased by 30% to 60%, the durability of the grinding wheel is increased by about 0.7 to 1 times, and the surface roughness parameter value of the workpiece is increased. Reduce it by about 50%.
Generally, the grinding speed of 45 m/s or more is called high speed grinding. The domestic ZYS-811 automatic bearing internal grinding machine developed by our company in the 1980s is the first to apply high-speed grinding technology in the domestic bearing industry ferrule grinding process. It has successfully developed high rigidity, high speed and high power. Electric spindle and high speed grinding wheel. At home and abroad, high-speed grinding has been widely used, and with the wide use of high grinding ratio, high durability super-hard abrasive such as CBN, grinding wheel grinding speed has reached 80 ~ 120m / s, or even higher. Such as: Germany Mikrosa, Japan KOYO company centerless grinding machine, Japan TOYO company's bearing internal grinding machine, etc., the outer surface grinding wheel line speed of 120m / s, the internal surface grinding line speed of 60m / s ~ 80m / s. Bearing Master WeChat Increasing the power of the grinding wheel drive (drive) system and increasing the rigidity of the machine tool is an important measure to achieve high-speed grinding, and the high-speed spindle unit is the most critical part of the high-speed grinding machine. In high-speed grinding, in addition to having sufficient strength, the grinding wheel needs to ensure good grinding performance in order to obtain high grinding effect. In addition, the cooling device is also one of the {HotTag} devices that are indispensable for high-speed grinding.
2.2 CBN grinding wheel grinding technology Cubic boron nitride abrasive material is referred to as CBN abrasive material. The grinding wheel manufactured by it is called CBN grinding wheel. It has the following characteristics: (1) High hardness, high thermal conductivity, good thermal stability and can withstand 1300~ 1500 ° C high temperature. (2) High durability, low wear, grinding ratio up to 4000 ~ 10000 (grinding ratio refers to the ratio of the amount of workpiece material removed to the grinding wheel wear during grinding) and the ordinary corundum grinding wheel is only 50 ~ 80. (3) The grinding force is small, the grinding heat is small, the stress on the workpiece is small, and the surface stress is thin or not. (4) Auxiliary time (dressing wheel, replacing grinding wheel) is greatly reduced.
For China's bearing industry, the use of CBN for ferrule grinding is a new processing technology, and the application prospect is very broad, but it is necessary to study and solve the following technologies: CBN grinding wheel manufacturing technology, dressing technology, special bearing grinding machine and grinding cooling Liquid, etc.
Due to the good processing characteristics of CBN grinding wheel, the use of CBN grinding wheel for bearing ring grinding has been developed and applied in production abroad, and it is called "a revolution in production and processing technology". Since 1982, CBN grinding wheels have been widely used in Japan and are growing at a high speed.
2.3 External surface grinding wheel automatic dynamic balance technology For external surface grinding, because the grinding wheel is large and non-homogeneous structure, the center of gravity of the grinding wheel system always deviates from the center of the spindle, and the grinding wheel system and its entire machine tool are inevitably caused by high-speed rotation. The vibration directly affects the service life of the machine. In this case, it is difficult to achieve high precision in the grinding process, which tends to cause grinding and vibration on the surface of the workpiece, and the waviness is increased.
The mechanical or other automatic balancing device is directly installed on the grinding wheel of the machine tool. After starting the machine, it can quickly approach the most balanced position. The automatic balance is perfect and the static balance of the grinding wheel can be omitted. The breakthrough of this technology promotes the development of grinding technology, and can greatly extend the life of grinding wheel, dressing diamond and spindle bearing, reduce machine vibration, and maintain the original precision of the machine tool for a long time.
2.4 Techniques for quickly eliminating internal surface grinding and emptying The level of the internal surface grinding machine is symbolic in all bearing grinding equipment. This is mainly because the grinding aperture limits the size of the grinding wheel and the corresponding system mechanism set parameters, which fundamentally limits the rigidity of the process system, and at the same time requires high processing precision. All of these require us to carry out in-depth research on the internal surface grinding process. In addition to maximally limiting the cutting ability of the machine tool and the grinding wheel, reducing the auxiliary grinding time is the key to improving the grinding efficiency, because the grinding is empty. It accounts for about 10% of the entire grinding time.
At present, there are several techniques for rapidly eliminating the grinding of the lost motion at home and abroad: control grinding technology, constant power grinding technology, active measuring instrument technology and measuring electric spindle current technology.
2.5 CNC technology and AC servo technology AC servo motor and PLC programmable controller positioning module, servo amplifier connected to form a servo system, the servo motor itself with optical rotary encoder, the output of its signal is fed back The servo amplifier can form a semi-closed loop control system. At high speed (3000 rpm) and low speed operation, the positioning accuracy can be ensured. The servo system can be used to complete fast jump, fast trend, trimming compensation and rough grinding, which greatly simplifies the machine feed mechanism and greatly improves the performance reliability.
2.6 AC variable frequency speed control technology In the grinding, the linear speed of the grinding wheel gradually decreases with the consumption of the grinding wheel, and the ratio of the starting line speed to the end line speed is about 3:2. At present, high-speed grinding has been used in the grinding wheel grinding field. In order to improve the grinding efficiency and ensure the consistency of the grinding quality, the programmable controller calculation function is used to calculate the grinding wheel radius after each grinding wheel, and then calculate the retention. The input frequency of the inverter of the constant speed of the grinding wheel is transmitted to the AC drive to ensure the linear speed of the grinding wheel.

3. The super-finishing processing of the bearing ring has been developed since the mid-1930s. It was created for the rolling surface of bearings. It is a precise and economical machining process, with machined parts. With ever-increasing precision and surface quality requirements, ultra-finishing processing is becoming more and more widely used. It plays an important role in the finishing of our bearings (polishing, abrasive belt grinding, super finishing and super finishing).
Super-finishing processing, referred to as “super-finishing”, generally means that under good lubrication conditions, the workpiece to be processed rotates at a certain speed, and the oil stone elastically presses the surface of the workpiece to a certain pressure and rotates perpendicular to the workpiece. A method of smoothing and finishing that can be automatically completed in a reciprocating oscillation motion according to a certain rule.
The entire process of the superfinishing machine consists of three distinct stages: independent dressing, constant cutting, and polishing (also divided into: cutting stage or self-sharp stage, half-cutting stage, and finishing stage). And the whole process is automatically completed under the condition that the basic process parameters (such as cutting speed, oil pressure and hardness, oscillation frequency, abrasive type, workpiece material and lubricating coolant) are constant.
3.1 Advantages of ultra-finishing processing 3.1.1 It can effectively reduce the circular deviation (mainly waviness).
3.1.2 It can effectively improve the linearity of the raceway busbar or process it into the required crown shape.
3.1.3 It can remove the grinding and deterioration layer and reduce the surface roughness value.
3.1.4 The surface can have residual compressive stress.
3.1.5 It is able to form a uniform and delicate texture and ideal cross-grain on the machined surface.
3.1.6 The working contact area can be increased.
3.2 Influence of super-precision on the working performance of rolling bearings 3.2.1 Improve the rotation precision of bearings and reduce the vibration and noise of bearings.
3.2.2 Improve the bearing capacity of the bearing.
3.2.3 Improve the lubrication effect of the bearing and reduce wear.
3.2.4 Reduce the heat generated during bearing operation.
3.3 Super-finishing processing technology 3.3.1 Whetstone manufacturing technology It determines the use performance of oil stone, which is the premise of super-finishing technology. The requirements of use: the cutting performance of oil stone is good, the loss is slow, and it has sufficient strength.
Among them, ceramic combined with CBN super essential oil stone, can maintain a constant high cutting rate, while the wear amount is very small, the critical pressure is high, which can greatly improve the overall quality and uniformity of workpiece processing. Diamond super essential oil stone, which can achieve the highest cutting rate, the smallest wear rate and the best surface finishing effect. Cubic silicon carbide whetstone, similar to diamond cubic boron nitride, is second only to the former two in terms of cutting force and processing quality, and is higher than ordinary silicon carbide.
3.3.2 Super-precision process technology The super-finishing process divides the whole super-finishing process into two stages: coarse super and fine super. In the coarse super stage, the oil stone abrasive is relatively sharp, the oil stone pressure is high, the workpiece rotation speed is low, and the swing frequency is high, so the cutting ability is strong, which is the main stage for removing the workpiece processing amount. In the fine super stage, the oil stone abrasive is relatively passivated, the oil stone pressure is low, the workpiece rotation speed is high, and the swing frequency is low, so the cutting ability is weakened, the polishing effect on the workpiece surface is strengthened, and the surface roughness value is greatly reduced.
Among them, the first-order two-stage method, the first-order two-step method, the oil stone automatic compensation technology, the oil stone automatic supply technology, the coarse and fine super-oil stone automatic conversion technology and the high-frequency small oscillation plus low-frequency large reciprocating technology are all on domestic or foreign equipment. Some application.
3.3.3 Workpiece positioning technology At present, the workpiece positioning methods commonly used in the raceway superfinishing machine are as follows: the end roller mechanical pressing type centerless clamping, the hydraulic centering end roller mechanical pressing clamping, the double roller driving end pressure Tight and unintentional clamping.
3.3.4 Lubrication and Cooling Technology The main three functions of lubricating fluid during super finishing are: flushing and cooling, and forming an oil film for adsorption.
Ultra-finishing requirements for lubrication and cooling: proper viscosity, anti-rust function, low volatility, repeated use.
Ultra-precision has strict requirements on the filtration accuracy of lubricating coolants, so it must be ensured by high-precision filtration devices.
In summary, the Process Tooling Professional Committee has built a fine roller bearing around the requirements of the “10th Five-Year” project of the Central Axis Technical Committee. The key research is as follows:
1. Bearing roller grinding, super problem. Among them, the roller crown logarithmic curve super-precision technology has been successful in the “Eighth Five-Year Plan”. At present, it is mainly to promote the application and improve the reliability and stability of the ultra-precision system.
2. Developed and perfected the ferrule raceway crown super precision machine. Although this technology research has achieved certain results, it is still a certain distance away from the advanced physical level of SKF.
3. The development of the technology and equipment for the convexity of the flange.
4. Roller end face ultra-fine technology research and equipment development.
5. Promote the industrialization project and popularization and application of new oilstone.
6. Apply the above advanced and latest patented technology to the technical transformation of grinding equipment and the development of new generation equipment for roller bearings. At the same time, vigorously promote the development of automatic production assembly line for roller bearings.

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