In high-performance grinding or high-efficiency deep grinding, due to the use of extremely high grinding wheel linear speed (about 100m/s ~ 250m/s) for deep grinding (depth of cut 5mm ~ 20mm), the workpiece feed The speed is also quite high, which places high demands on both the machine tool and the grinding wheel. For grinding wheels, they must have high crushing resistance, good shape accuracy retention, and the highest possible durability to reduce the impact of centrifugal force during rotation and shorten the time required to replace the grinding wheel. Traditional ceramic and resin bonded grinding wheels can no longer meet the needs of high-performance grinding, and new grinding wheels must be used to adapt to high speeds and large depths of cut. At present, single-layer electroplated CBN grinding wheels are mainly used in high-performance grinding of metal materials at home and abroad. In addition, in order to solve the problem of small chip space of single-layer electroplated grinding wheels, a metal single-layer CBN grinding wheel has also been developed. The following briefly discusses the basic characteristics of high-performance grinding wheels and the performance characteristics of two different bond types of grinding wheels.
2 Basic characteristics of high-performance grinding wheels
The effect of high-performance grinding is closely related to the reasonable design and use of the grinding wheel, and the grinding wheel used for high-performance grinding is closely related to There is a big difference between ordinary grinding wheels.
Under correct usage conditions, the wear of the grinding wheel during high-performance grinding is very small. Even under the conditions of high-efficiency deep grinding, the grinding ratio can reach 20,000 or even higher, and this phenomenon increases with time. The increase in grinding wheel speed is becoming more and more obvious, and the increase in speed places extremely high requirements on the strength of the grinding wheel. High strength and semi-permanence are two basic characteristics of high-performance grinding wheels. The design of high-performance grinding wheels should follow three principles: (1) good safety; (2) high processing accuracy; (3) good grinding performance. Safety is the most important. The safety of high-performance grinding wheels depends largely on the strength of the matrix, which also has high requirements on the strength of the abrasive layer and the bonding strength between the matrix and the abrasive layer. Since the thickness of the abrasive layer is relatively small, the safety design of the grinding wheel is mainly the comprehensive design of the matrix, which is also an important difference from the design of ordinary grinding wheels. According to the relevant principles (maximum tangential stress, fatigue strength, full plastic deformation of the grinding wheel), the critical failure speed of the grinding wheel can be determined. In addition, the reasonable matching of the grinding wheel diameter and the spindle speed must be considered, and the base body cross-section should be optimized and designed by considering multiple factors.
The combination of extremely high grinding wheel linear speed and high workpiece feed speed in high-performance grinding may cause vibration of the grinding system. Therefore, the grinding wheel should have certain damping and vibration reduction characteristics. Generally, The grinding wheel disc can be made by adding a damping pad between the grinding wheel and the spindle or using polymer or composite materials with good damping properties. Since the grinding wheel removal rate is large, the grinding wheel disc should be rigid enough to withstand large normal and tangential grinding forces. In addition, the grinding wheel disc should also have good thermal conductivity. Steel and aluminum-based grinding discs have high strength and good thermal conductivity, but have poor damping properties. In actual systems, steel and aluminum-based grinding discs are more common, and grinding discs made of other composite materials have also been reported.
3 Characteristics of single-layer electroplated and metal single-layer CBN grinding wheels
Single-layer electroplated CBN or diamond abrasive grinding wheels are generally used for form grinding of difficult-to-grind materials and have been developed in recent years. It has also been widely used in high-performance grinding or high-efficiency grinding. The metal single-layer CBN grinding wheel is a new type of grinding wheel that has only been developed recently to meet the needs of high-performance grinding. The most common feature of these two types of grinding wheels is that the shape accuracy of the grinding wheel is maintained well. The base body is generally made of steel or aluminum alloy, so it has high strength and is suitable for situations where the linear speed of the grinding wheel is extremely high.
A single-layer electroplated grinding wheel is a nickel-based bonding layer obtained by electroplating or electrodeposition of abrasives and fixed on a steel substrate. The grinding wheel has good shape retention and low cost. As a semi-permanent grinding wheel, it is The best choice for automated grinding. However, the manufacturing cycle of electroplated grinding wheels is long, the efficiency is low, and the electroplating process specifications are strict. The manufacturing process of electroplated grinding wheels is divided into external plating method and internal plating method. The internally plated grinding wheel has good cutting edge properties, high surface precision, and a large number of effective abrasive grains, so it has high grinding efficiency and is especially suitable for high-performance grinding of large depths of cut. However, the manufacturing process is complex, the cost is high, and the manufacturing efficiency is particularly low. Therefore, external plating is generally used to manufacture electroplated grinding wheels. The external plating method has a simple manufacturing process and low cost, but the exposed cutting edges are uneven, and the initial effective number of abrasive grains is only 5% to 10%; the grinding efficiency is low, the initial profile accuracy is difficult to improve, and the durability of the grinding wheel is low, and the abrasives The losses were serious. Improving the manufacturing process of coated grinding wheels, improving the manufacturing accuracy of grinding wheels and improving the properties of abrasive grains are currently the main research issues in the manufacturing of electroplated grinding wheels.
When the electroplated grinding wheel is in use, it generally does not need to be trimmed like the resin or ceramic bonded grinding wheel, and can be put into use directly. In addition, since there is no chemical bonding between the base bonding base of the single-layer electroplated CBN grinding wheel and the abrasive grains and the matrix, most of the volume (60%) of a single grinding wheel is wrapped by the electroplated base bonding base, so the chip space between the abrasive grains is limited. Restrictions have affected the further improvement of the removal rate.
Metal single-layer CBN sand theory fixes a layer of abrasive on the steel substrate through the same welding process. The bond, the substrate and the abrasive are mainly bonded together by chemical bonding force. In some aspects, it shows advantages over single-layer electroplated grinding wheels. The metal single-layer grinding wheel bond is a highly active metal alloy, so the abrasive grains are wrapped in a smaller volume, and 80% of the abrasive grain size is exposed at the bond interface without falling off.
Due to its corresponding larger chip space, a higher grinding removal rate can be obtained, and the grinding force is relatively small. The picture below shows a comparison of the combination of abrasive grains between the two grinding wheels.
Simple diagram of the combination of two grinding wheels
The main advantage of the single-layer electroplated grinding wheel is that it does not need to be trimmed before grinding and can be put into use directly after installation; its main The disadvantage is that when the abrasive grains gradually become passivated during use, the grinding force gradually increases, further aggravating the abrasive wear and possibly causing thermal damage to the workpiece surface.
In addition, since after installation...More↓↓↓