Grinding with the highest precision tolerance

2022-08-02
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Grinding with high precision tolerance

machine tool itself is not the only secret recipe to achieve high precision grinding. Factors such as grinding wheel and grain size, grinding wheel dressing system, software system and operator intelligence all play a key role in the processing and production of high-precision products

grinding has become a processing method that people are more and more willing to use. In order to meet today's high-precision machining standards, grinding has sometimes even become the only machining method. With the continuous decline of CBN grinding wheel price, grinding machine has become a more commercialized product after instrument reset. The grinding machine and grinding process have been further improved and improved by making full use of updated abrasive grains to improve the degree of advanced textile materials. Now, the whole market is basically monopolized by more sophisticated grinding machines. However, the machine tool itself is not the only secret recipe to achieve high-precision grinding. Factors such as grinding wheel and grain size, grinding wheel dressing system, software system, operator intelligence and so on all play a key role in the processing and production of high-precision products. Below we will introduce the above factors that affect the machining quality of grinding machines

grinding wheel and grain size

the National Institute of standards and Technology (NIST) is mainly committed to the research of high-performance grinding process. Recently, NIST researchers are seeking a high-speed grinding process using single-layer abrasive (SLA) wheels. In a machining case, they used a 254MM diameter SLA grinding wheel to study its operation at 14000 r/min speed and 186m/s surface linear speed. The results show that with the increase of grinding time, the exposed abrasive grains on the grinding wheel increase, the wear surface expands, and the continuous particle dulling phenomenon occurs. The grinding temperature and grinding force also increase, but there is no breakage or falling off of abrasive grains. Mechanical engineers try to understand how the feed rate and speed affect the wear of SLA grinding wheel, so as to find out the mode of latent heat damage caused by the increase of wear in the plane area, and predict the variables that can effectively adjust the production process

for this reason, the researchers drew the microstructure of the grinding wheel surface. With the increase of the wear degree caused by the grinding wheel running at different feed rates and speeds, the changes of the size, shape and distribution of the abrasive particles are shown. The chart shows that the number of abrasive grains of some grinding wheels exceeds the actual required number, and the abrasive grains should be diffused and distributed rather than "crusting" on the surface of the grinding wheel. NIST research has proved that when SLA grinding wheel is used, each part should not be ground at the same feed rate and speed, because the ideal cutting parameters will change with the wear degree of the grinding wheel. Different processed parts should be treated differently and the variables should be adjusted appropriately, so that the processing cost of each part can be greatly reduced and a large amount of unused grinding wheel abrasive particles will not be wasted

in order to obtain enough information to predict the cutting parameters of the grinding wheel, it is required that the shape and size of SLA grinding wheel must be regular. If the user knows the microstructure of the grinding wheel and the surface of the grinding wheel is consistent, the cutting variables can be programmed to compensate the wear parameters of the grinding wheel

grinding wheel dressing system

the research shows that the use of CNC dressing device and sound sensor reduces the grinding cycle time. The latest dressing technology has been applied to the design or production of relatively special machine tools and grinding wheels. For example, ELID grinding is a novel grinding method that combines electrolytic dressing wheel with conventional mechanical grinding in the machining process. On the basis of selective use of binders, efficient grinding and mirror grinding can be achieved. Similarly, the new glassy binder used for diamond wheels and CBN Super Abrasives puts forward new requirements for wheel dressing systems used in those special applications

customers have very clear requirements for grinding wheels, such as better dimensional tolerance, taper and roundness, especially in the automotive industry and bearing applications. Therefore, it is hoped that the grinding rate of the material can be increased to 16.39cm3/min and the CPK value can be maintained at 1.33 or better. It is very important to ensure better roundness and surface finish of bearing parts, which will help reduce friction, reduce noise and clicking, and prolong service life

Saint Gobain focused on the research on the improved porous grinding wheel

no matter whether ordinary abrasive or CBN material is used, in the application field of precision automobile grinding, the grinding wheel should be made of glass binder, which can make the abrasive have better adhesion and obtain higher grinding ratio. The porosity of the grinding wheel can make the grinding wheel bring more grinding coolant to the chip arc area, and can also reserve more space for grinding chips, which can reduce the friction between parts and chips in the grinding area. The volume of abrasive in the grinding wheel is usually described by the structure (ordinary abrasive) or concentration (carborundum or CBN material). Generally speaking, in the application fields with large contact area and high sensitivity to metallographic structure damage, such as creep feed grinding, double disc or high alloy steel, the grinding wheel with loose structure or low concentration (small abrasive volume) should be used. Saint Gobain's new common abrasive technology can obtain loose grinding wheel structure without artificial porosity

truing systems of the United States produces emery rollers and wheel truing blocks for dressing grinding wheels. The tolerance of its products reaches 0.5 mm, with high-precision spherical dimensions. The use standard has also been raised from ra16 to RA4. In the 1990s, turning of hard materials once occupied the grinding market, but now the situation is just the opposite. We can attribute this change to the lower price of CBN materials and the fact that grinding is more suitable for processing harder materials

truing systems reduces the grinding cycle time and improves the consistency of the grinding wheel by reducing the dressing cycle. In addition, rough material will aggravate the wear of grinding wheel, so a rougher dressing system is required

truing systems' emery rollers are designed for specific projects, including the type, size, concentration, bonding material and quantity of oilstone. There may be up to 6 different types of emery and concentrations on a roller. The positioning of rollers and grinding wheels depends on the accuracy of machine tools

tru tech of Michigan has developed a set of very strict standards for high-precision CNC grinding machines, which are designed for grinding cylindrical parts. Its features are as follows:

□ the spindle speed is adjustable, and the speed range is 2000 ~ 5000 r/min, which can be used for finishing of various surfaces

□ the positioning of the machine tool adopts stepping motor instead of servo motor. The resolution of this motor encoder is very high, and the machine tool can be operated in 0.00003 mm increments

□ grinding wheel dressing allows the grinding wheel to be reshaped on the spindle, and the grinding wheel has better surface finish and longer service life

the company adopts a 3-axis grinder equipped with a grinding wheel, which can grind and process multiple shapes on one part. With only one program and one commissioning fixture, the grinder can grind and process multiple steps, radii, angles, anti taper angles and drill points with one 1A1 grinding wheel

tru Tech's grinding machine has the above-mentioned characteristics, so that its grinding roundness accuracy can reach 0.0004 mm. The eccentricity between the diameters of all standard parts shall be kept within the tolerance range of 0.00008 mm, and the eccentricity tolerance of high-precision parts shall be within 0.00003 mm

tru Tech's 3-axis grinding wheel dressing system can ensure the high-precision grinding performance of the grinder

software system

software can help new operators with almost no operating experience to work on the machine tool, and the processing program of most workpieces can be completed within 5min. Tru Tech's software has the function of self-training and built-in "help" video, which guides the operator to carry out programming, debugging, setting and preventive maintenance without leaving the machine tool. This software greatly improves the flexibility of the company in the process of cross training employees and reduces the training costs. In the grinding industry, it is difficult to find a skilled operator. Tru tech has manufactured high-precision grinding machines equipped with good user interface software. Anyone can quickly learn to operate them and solve the problem of lack of skilled operators

dynamic rigidity and thermal stability

dynamic rigidity and thermal stability are two key issues affecting the accuracy of UGT's student grinder. UGT company uses artificial granite (this material is mainly made of granite bonded with epoxy resin) instead of cast iron, which reduces the vibration of the machine tool and improves the internal thermal stability of the machine tool. The student grinder has been used for high-precision bearing grinding. In the past, UGT company used hydrodynamic bearings without any chemical additives, but now it uses high-precision, angular contact ball bearings. When the speed changes, it can provide high accuracy and greater flexibility. However, hydrodynamic bearings are used in some special machine tools, such as those for machining fuel injection nozzles. When grinding the chuck, its roundness tolerance is between 0.2 ~ 0.4mm. The Studer machine tool is equipped with a specially designed linear motor drive, which can make the machining accuracy reach 10nm. The advantage of using linear motor is that the cutting time is short, and the positioning time is saved. The linear motor can move at a high speed of 30m/min and 3m/s2 acceleration

automobile and truck manufacturers in the United States tend to adopt grinding process in the processing of bevel gear components. The old method is machining, heat treatment and then grinding, while the new method is machining, heat treatment and grinding. When grinding a set of gear assemblies with the old method, the fit between the pinion and the big gear can not be separated, and any gear can not be replaced arbitrarily. If the grinding method is adopted, the pinion and big gear can be interchanged, and it is easy to mix and assemble together, because the tooth side geometry and backlash error of grinding are very small, and the interchangeability between parts is very good

bevel gear technology found that the scrap rate of grinding method was very high. When grinding is used, the positive tolerance on the gear can be easily corrected, and the scrap rate can approach zero. In the final automobile components of front wheel drive, the finishing of spiral bevel gear and spur gear also tends to adopt grinding. This is due to the increased torque transmitted through these gears, especially in the higher transmission speed range to achieve the need to reduce noise

thermal problem is also a major problem that should be considered. The design idea of Gleason company in New York state is to prevent the thermal effect by automatically eliminating the dimensional change, or prevent the dimensional change caused by the thermal effect from reaching the work area. In addition, common coolant temperature control method and complex temperature compensation method for main mechanical parts can also be used. (end)

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