Mechanism of Cracking in Grinding and Effective Preventive Measures
Abstract: Grinding is one of the most important metal working processes. It is widely used to make automotive parts, machine tools, aerospace components and other precision parts. It is an energy-intensive process and can cause damage or cracks to the workpiece during grinding. The mechanism of cracking in grinding is discussed in this paper, with a special focus on the stress fields generated during the grinding process. The stress fields are caused by the different grinding parameters and grinding conditions, such as cutting speed, cutting depth and grain size. Based on the understanding of the cracking mechanism, preventive measures for cracking in grinding are presented. These include methods for controlling the cutting parameters, cooling and lubrication, grinding wheel type and design, and temperature control.
1 Introduction
Grinding is a metalworking process where a hard material such as ceramics, metal, and polymers is cut with an abrasive wheel to produce the desired shape and dimensions. Grinding is widely used in manufacturing due to its high precision and improved surface finish at low costs. However, the process may lead to cracking in grinding due to the extreme stresses generated during the process. Cracks can severely reduce the fatigue strength and fatigue life of a component and drastically reduce its lifetime. Therefore, understanding the mechanism of cracking in grinding and effective prevention strategies are necessary for improving the service life of metal components.
2 Grinding Stress Fields
When grinding a metal workpiece, grinding stresses are generated due to the contact between the grinding wheel and the workpiece. These stresses are the result of cutting forces, frictional forces, damage forces, wear forces and thermal forces. During grinding, the grinding wheel acts as a hardliner, which applies a high normal stress and a large tangential stress to the workpiece surface. The cutting forces also give rise to a large sliding motion between the grinding wheel and the workpiece. The rotating grinding wheel causes a centrifugal force to be exerted onto the workpiece, and the large cutting forces created during grinding increase the potential for cracking. The stress fields generated during grinding are further complicated by the grain size and structure of the grinding wheel and the cutting parameters. These include cutting speed, depth of cut and feed rates.
3 Cracking Mechanism in Grinding
When there is a high normal stress, tangential stress and a sliding motion between the grinding wheel and the workpiece, cracks can easily be generated in grinding. The cracking can take place at the asperities of the grinding wheel or the cutting edges of the workpiece. The local stress field in the workpiece is further affected by the grinding parameters and the grain size of the grinding wheel. The grain size of the grinding wheel affects the size and shape of the grinding chip, which in turn affects the distribution of stresses. Furthermore, the cutting speed and depth of cut also affect the distribution of stresses. When the cutting speed is too high and the depth of cut is too deep, the resulting high normal and tangential stresses can exceed the material strength of the workpiece, resulting in cracking. Moreover, the grinding temperature also plays an important role in the cracking process and can further aggravate the severity of the process. Therefore, it is important to understand the mechanism of cracking in grinding and to control the grinding parameters and the grinding temperature in order to minimize the risk of cracking.
4 Prevention Measures for Cracking in Grinding
4.1 Control of Cutting Parameters To control the stresses generated during grinding, it is important to select the proper cutting parameters like cutting speed, feed rate and depth of cut. Generally, the cutting speed should not be too high and the depth of cut should not be too deep. This will reduce the normal and tangential stresses and minimize the risk of cracking. However, the selection of optimal cutting parameters depends on the machinability of the material, the grain size of the grinding wheel and the properties of the grinding fluid.
4.2 Cooling and Lubrication The use of coolants and lubricants during grinding can reduce the generated heat and reduce the risk of cracking. The coolant must be able to effectively cool the surface of the workpiece during grinding and control the grinding temperature. Generally, a coolant with high dielectric strength and good lubricity should be selected. Moreover, the lubricant should be able to lubricate and reduce the surface contact of the grinding wheel to the workpiece.
4.3 Grinding Wheel Type and Design The type and design of the grinding wheel also play an important role in controlling the cracking in grinding. Generally, a softer grinding wheel should be used to reduce the stress intensity and minimize the risk of cracking. The grinding wheel should also be designed with a large number of cutting edges and with closely spaced contact points to reduce the normal and tangential forces.
4.4 Temperature Control The grinding temperature is an important factor in the cracking process. The temperature should be closely monitored during grinding and kept at a safe value to minimize the risk of cracking. To control the temperature, the use of coolants and lubricants is essential. Additionally, the use of cooling systems can further reduce the temperature.
5 Conclusion
In conclusion, the mechanism of cracking in grinding is mainly due to the high normal and tangential stresses generated during the process. The stresses are caused by the grinding parameters and grinding conditions. By understanding the cracking mechanism, effective preventive measures can be implemented to reduce the risk of cracking. These include the selection of proper cutting parameters, the use of coolants and lubricants, the selection of proper grinding wheel type and design, and the proper control of temperature.
