What is a mirror? How is the mirror grinder processed? (under)
Fourth, the defects and measures that are easy to produce during mirror grinding
Mirror grinding on a surface grinder often produces some defects, such as surface ripples, burns, scratches, obvious patterns and wear marks (silk flow), etc. To address these problems, the following measures can be taken:
1) Surface ripples are mostly caused by the vibration of the grinding wheel, such as excessive bearing clearance, deviation of the spindle, poor dynamic balance of the motor rotor, uneven oil film between the spindle and the bearing, etc. In addition, the poor balance of the grinding wheel will also produce ripples. If the grinding wheel is well balanced and there are still ripples, then the grinding wheel and its mating parts must be repaired or adjusted to completely eliminate the ripples.
2) When processing materials with high hardness, the grinding efficiency of the grinding wheel is poor, and the grinding point will generate high temperature, which is easy to burn the workpiece (for example, when grinding W18Cr4V, it is more likely to produce burns). In order to prevent burns, there must be sufficient grinding fluid at the grinding point. In addition, the amount of knives on the back should also be appropriate, not too large. The best way is to reduce the linear speed of the grinding wheel, about 18m/s is appropriate. Using a low speed of 1440r/min on the M7120A grinder can basically eliminate burns. Another advantage of reducing the linear speed of the grinding wheel is to reduce the vibration of the grinding wheel holder, which can also reduce and eliminate the ripple phenomenon.
3) There are roughly two types of scratches in mirror grinding: one type of scratch is irregular, which is caused by impure grinding fluid, and the impurities and abrasive particles brought out are washed between the grinding wheel and the workpiece and scratched. The method to eliminate this kind of scratches requires the filtration of the grinding fluid, which generally uses three filtrations of magnetic and copper wire mesh; the other kind of scratches are like dotted lines, shallower, and the length is about the same. This is a grinding wheel. When the grain is about to fall off, it will be scratched as the grinding wheel rotates. At this time, the elimination method is to use sufficient grinding fluid when dressing the grinding wheel, and trim the two end faces of the grinding wheel into an oblique shape with an outer width and a narrow inner diameter. In addition, the selection of the grinding wheel should be appropriate, not too soft, and don't use a grinding wheel with too good self-sharpening properties.
4) When mirror grinding, there are many forms of patterns that are easy to appear. There are also many factors that produce patterns. The main reason is vibration. Among them, there are periodic vibration of the grinding wheel, external influences and vibration of adjacent machine tools, etc., and patterns will also appear when the grinding wheel is too blunt and the stroke is unstable. When grinding is performed when the adjacent machine tool is not running, the pattern is not easy to appear at this time.
5) When the wear scar (silk flow) in mirror grinding is more obvious, to remove this kind of wire flow, you must switch to a fine-grained grinding wheel. However, when using fine-grained grinding wheels, the following points must be considered:
①When finishing the grinding wheel, the diamond knife should be sharp, and the grinding fluid should be sufficient, and the debris should be washed away in time to avoid affecting the surface of the grinding wheel.
②The amount of grinding should be appropriate to prevent the occurrence of surface burns and other defects that affect the surface smoothness. Pay attention to leave an appropriate grinding allowance.
③The linear speed of the grinding wheel must be reduced to 15～18m/s.
④The grinding fluid is strictly filtered to prevent scratches.
⑤ When using the grinding stone to fine-tune the grinding wheel, the contact area between the grinding stone and the grinding wheel should not be too small, and the grinding stone used should not be too soft, otherwise it will not play the role of finishing the grinding wheel.