Content Introduction
Grinding cracks are common defects in grinding process, which are caused by improper cutting parameters or system misalignment. Generally, tool wear, improper cutting parameters and out-of-balance forces during grinding are mainly responsible for grinding crack occurrence. When the grinding cracks are found, the grinding process has to be stopped immediately and the machined surface has to be inspected thoroughly. It is important to identify the mechanism of grinding crack and prevent it in order to avoid major problems such as scrap, rework and machining time delay.
Crack Formation Mechanism of Grinding Process
When performing grinding operation with abrasive grinding wheel, several types of forces will be generated and will be transmitted through the workpiece. These forces include cutting edge friction force, specimen surface pressure, thermal stress and tensile stress in addition to the normal compressive stress. As abrasion continues, the grinding force will gradually increase and if it exceeds the predetermined limit it will cause the crack formation in the material. An in-depth understanding of the grinding crack formation mechanism is beneficial in order to prevent the grinding cracks formation.
A typical grinding crack formation mechanism is the application of excessive cutting force which in turn causes high cutting temperature and the material will be heated beyond its limits. Too much cutting force can also cause plastic deformation of the workpiece and this plastic deformation will be discharged in the form of stress and thermal energy. This heat can cause grain slippage, resulting in workpiece material being pulled and stretched beyond its ultimate strength, causing cracks to appear.
Preventive Measures for Grinding Cracks
In order to prevent grinding crack occurrence, there are several prevention methods available.
1. Use Better Grinding Wheel: The grinding wheel is an essential element of the grinding process and if chosen appropriately, it can be used to reduce the risk of grinding cracks. The hardness of the grinding wheel should match the hardness of the workpiece. If the grinding wheel is too hard, it will generate more stresses during grinding process resulting in cracking.
2. Proper Cutting Parameters: Proper adjustment of cutting parameters such as the depth of cut, cutting speed and feed rate can help reduce the risk of grinding crack formation. Generally, high cutting speed will reduce the cutting force and lower the grinding temperature.
3. Heat Treatment: Heat treatment is a process that can help improve the mechanical properties of the workpiece. Heat treatment can relax the internal tension, relieve the built-up stress and redistribute the grain structure.
4. Balance System: Out-of-balance forces in the grinding process will cause vibration and this in turn might cause cracks. Therefore, it is important to keep the system balanced and properly aligned.
Conclusion
Grinding cracks are common defect in grinding process and improper understanding and selection of cutting parameters, quality of grinding wheel and system misalignment can increase the risk of grinding cracks formation. In order to prevent grinding cracking it is essential to understand the formation mechanisms of grinding cracks such as excessive cutting force, material softening and excessive plastic deformation. Therefore, it is important to take preventive measures such as proper selection of grinding wheel, use of proper cutting parameters, heat treatment and proper system alignment.
