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Principles, characteristics and solutions for cracks generated by grinding workpieces by grinding wheels
When grinding wheels operate at high speeds, the grinding heat produced can lead not only to grinding burns but also to a significant number of relatively regular cracks—commonly referred to as grinding cracks—on the workpiece surface. These cracks don’t just mar the appearance of the components; they also directly impact the quality of the finished product.
Characteristics of Grinding Cracks: Grinding cracks differ significantly from quenching cracks that occur during conventional heat treatment. Unlike quenching cracks, which can extend deep into the material, grinding cracks are confined to the grinding surface, with a relatively shallow depth and consistent width throughout. Mild grinding cracks often appear as perpendicular or nearly parallel lines to the grinding direction, arranged in a regular pattern. This is classified as the first type of crack. More severe cases present as tortoise-shell-like patterns (closed networks). When these cracks are subjected to acid etching, they become clearly visible, which defines the second type of crack.
Prevention of Grinding Cracks: Since grinding cracks are primarily caused by excessive grinding heat, minimizing this heat is crucial for addressing the issue.
Grinding Process Improvements:
- **Cooling**: In dry grinding operations, it’s advisable to reduce the amount of stock removed per pass to limit heat buildup. For wet grinding, the choice of grinding fluid matters. Water-based fluids typically offer better cooling than oil-based ones.
- **Grinding Wheel Selection**: Opting for grinding wheels with appropriate properties can help mitigate the risk of cracks.
- **Hardness**: Using softer grinding wheels reduces the pressure on the workpiece, thus lowering the heat generated.
- **Abrasive Type**: Sharper abrasives can minimize the grinding heat produced.
- **Grinding Margin Distribution**: Implementing a coarse-to-fine grinding strategy—starting with coarse grinding using softer wheels and progressing to fine grinding with finer wheels—can help. This approach allows for larger initial cuts, improving efficiency, while subsequent finer cuts reduce the risk of cracks.
- **Feed Speed**: Slowing down the grinding wheel's feed rate is another effective method to prevent cracks.
All these techniques contribute to reducing the amount of heat generated during the grinding process, consequently minimizing the incidence of cracks on the workpiece. By carefully managing these factors, manufacturers can achieve higher-quality parts while maintaining productivity.