Abstract The machine tool itself is not the only secret to high-precision grinding. Diamond grinding wheel and particle size, diamond wheel dressing system, software system, operator intelligence and other factors play a key role in the processing and production of high-precision products. Grinding has become more and more enjoyable for people...
The machine tool itself is not the only secret to high-precision grinding. Diamond grinding wheel and particle size, diamond wheel dressing system, software system, operator intelligence and other factors 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 become the only way to machine. With the continuous decline in the price of CBN diamond grinding wheels, grinding machines have become a more commoditized product. The grinding and grinding processes have been further improved and improved by fully utilizing the newer abrasive grain size. Now, the entire market is basically monopolized by more sophisticated grinding machines. However, the machine tool itself is not the only secret to high-precision grinding. Diamond grinding wheel and particle size, diamond wheel dressing system, software system, operator intelligence and other factors play a key role in the processing and production of high-precision products. Below we will introduce the above factors affecting the processing quality of the grinding machine.
Grinding wheel and grain size
The National Institute of Standards and Technology (NIST) is dedicated to the research of high performance grinding processes. Recently, NIST researchers are looking for a high-speed grinding process using a single-layer abrasive (SLA) diamond wheel. In one machining case, they used a 254 mm diameter SLA diamond wheel to study when operating at 14,000 r/min and a surface speed of 186 m/s. It is found that as the grinding time increases, the exposed abrasive grains on the diamond grinding wheel increase, the wear surface expands, and the continuous particle blunt phenomenon occurs, and the grinding temperature and the grinding force also increase, but there is no abrasive particle fragmentation. Or shedding occurs. Mechanical engineers attempt to understand how feed and speed affect the wear of SLA diamond wheels in order to find patterns of latent heat damage due to increased wear in the planar area, predicting variables that can effectively regulate the production process.
To this end, the researchers plotted the microstructure of the surface of the diamond wheel. As the degree of wear of the diamond wheel operating at different feed rates and at different speeds increases, it shows changes in the size, shape and distribution of the abrasive particles. The graph shows that the number of abrasive grains in some diamond wheels exceeds the actual required amount, and the abrasive particles should spread out rather than “crust†on the surface of the diamond wheel. NIST has confirmed by research that when using SLA diamond grinding wheels, each part should not be ground at the same feed rate and speed, because the ideal cutting parameters will change with the degree of wear of the diamond 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 number of unused diamond wheel abrasive grains are not wasted.
In order to obtain sufficient information to predict the cutting parameters of the diamond wheel, this requires that the shape and size of the SLA diamond wheel abrasive particles must be regular. If the user knows the microstructure of the diamond wheel and the surface of the diamond wheel is uniform, the cutting variable can be programmed to compensate for the wear parameters of the diamond wheel.
Diamond wheel dressing system
Studies have shown that the use of CNC numerical control dressing devices and sound sensors reduces the grinding cycle time. The latest finishing technology has been applied to relatively special machine tools, diamond wheel design or production applications. For example, ELID grinding is a novel grinding method that combines electrolytically trimmed diamond wheels with conventional mechanical grinding during processing. Efficient grinding and mirror grinding can be achieved on the basis of selective use of bonding agents. Similarly, new glass-like adhesives for diamond diamond wheels and CBN superabrasives place new demands on diamond wheel dressing systems used in special applications.
Customers have very specific requirements for diamond wheels, such as better dimensional tolerances, taper and roundness, especially in the automotive industry and bearing applications. Therefore, it is desirable to increase the grinding rate of the material to 16.39 cm 3 /min while keeping the Cpk value at 1.33 or better. Ensuring better roundness and surface finish of bearing parts is important to help reduce friction, reduce noise and hum, and extend service life.
Saint-Gobain has focused on the improvement of the porous diamond wheel.
Regardless of whether ordinary abrasives or CBN materials are used, in precision automotive grinding applications, diamond grinding wheels should be made of glass-like adhesives, which can make the abrasives have better adhesion and higher. Grinding ratio. The porosity of the diamond wheel allows the diamond wheel to bring more grinding coolant to the chip arc and also retains more space for grinding chips, which reduces the mutual interaction between the parts and the chips in the grinding zone. friction. The volume of abrasive in a diamond wheel is typically described by tissue (ordinary abrasive) or concentration (silicon carbide or CBN material). In general, in applications where the contact area is large and the sensitivity to metallographic structure damage is high, such as peristaltic feed grinding, double-disc or high-alloy steel, materials should be loose or have a low concentration ( Diamond grinding wheel with smaller abrasive volume. Saint-Gobain's new common abrasive technology enables the looser diamond wheel organization without the need for artificial porosity.
Truing Systems of the United States produces dressings for diamond wheels and diamond wheels for dressing diamond wheels. The tolerances of the products are 0.5 mm, with a very high-precision spherical size. The standard of use has also been improved from the past Ra16 to the current Ra4. In the 1990s, turning of hard materials once occupied the market for grinding, but the opposite is true. We can attribute this change to the price reduction of CBN materials, and the grinding process is more suitable for the processing of harder materials.
Truing Systems reduces the grinding cycle time by reducing the dressing cycle and improves the consistency of the diamond wheel. In addition, rough materials can exacerbate the wear of the diamond wheel, requiring a rougher finishing system.
Truing Systems' diamond disks are designed for specific projects, including the type, size, concentration, binder and amount of sand. There may be up to 6 different types of corundum and concentration on a roller. The positioning of the roller and diamond wheel depends on the accuracy of the machine.
Tru Tech of Michigan has developed a very strict set of standards for high precision CNC CNC grinding machines designed to grind cylindrical parts. Its characteristics are as follows:
The spindle speed is adjustable, the speed range is 2000~5000 r/min, and it can be used for finishing various surfaces;
The machine is positioned using a stepper motor instead of a servo motor. The motor encoder has a high resolution and the machine can be edited in 0.00003 mm increments.
Online diamond wheel dressing allows the diamond wheel to be shaped and trimmed on the spindle. The diamond wheel has a better surface finish and a longer service life.
The company uses a 3-axis grinding machine with a diamond wheel that grinds a variety of shapes on one part. With just one program and one commissioning setup, the grinder can grind multiple steps, radii, angles, anti-cone bevels and drill points with a 1A1 diamond wheel.
The above characteristics of the Tru Tech grinding machine allow the grinding to have a roundness accuracy of 0.0004 mm. The eccentricity between the diameters of all standard parts is kept within the tolerance of 0.0008 mm, and the eccentricity tolerance of high-precision parts is within 0.00003 mm.
Tru Tech's 3-axis diamond wheel dressing system guarantees high-precision grinding performance of the grinding machine.
Software system
The software can help new operators with little operational experience work on the machine, and most of the workpiece machining procedures can be programmed in less than 5 minutes. Tru Tech's software features self-training and built-in “help†recordings that guide the operator through programming, commissioning, setup, and preventive maintenance without leaving the machine. This software has greatly increased the flexibility of the company in the process of cross-training employees and reduced training costs. In the grinding industry, it is difficult to find a skilled operator. Tru Tech manufactures high-precision grinding machines with good user interface software, and anyone can quickly learn to operate and solve the problems that skilled operators lack.
Dynamic stiffness and thermal stability
Dynamic stiffness and thermal stability are two key issues affecting the accuracy of UGT's Studer grinder. UGT replaces cast iron with artificial granite (this material is mainly made of granite blocks bonded with epoxy resin), which reduces the vibration of the machine and improves the thermal stability inside the machine. Studer grinding machines have been used for higher precision bearing grinding. In the past, UGT used fluid-dynamic bearings, but now it uses high-precision, angular contact ball bearings. Provides high precision and flexibility when speed changes. However, hydrodynamic bearings are used on some special machine tools, such as special machine tools for machining injectors. When grinding the chuck, the roundness tolerance is between 0.2 and 0.4 mm. The Studer machine is equipped with a specially designed linear motor drive, which can achieve a machining accuracy of 10 nm. The advantage of using a linear motor is that the cutting time is short, saving positioning time, and the linear motor can move at a high speed of 30 m/min and 3 m/s2 acceleration.
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