CNC Knowledge: How to do the “crushing of the mirror”?

01
What is the grinding of the mirror

After grinding, the surface roughness of the part is Ra <0.01 µm. Surface treatment of high precision and large added parts generally requires mirror grinding.

02
Mirror grinding machines must meet the following conditions

1) have high precision and rigidity and take measures to reduce vibrations;
2) The rotation accuracy of the grinding wheel pin is greater than 1 µm;
3) the amplitude of the grinding wheel frame compared to the workbench is less than 1 µm;
4) The transverse power supply mechanism can move with precision;
5) The establishment does not crawl when it moves at low speed.

03
Mirror grinding methods

1 and 1 balance and cutting wheels of cutting

(1) balanced grinding wheel. Once the grinding wheel is equipped with a flange, it is first carried out to perform a thick static balance, then install it on the grinding wheel to cut the two end sides and the exterior circles, and finally carry out a precise static balance.

(2) Cut the grinding wheel. The good or bad grinding wheel grinding directly affects the softness of the grinding surface. The following things should be paid to the attention of the grinding wheel:

1) The general grinding margin is 0.015 ~ 0.02 mm. And easy to grind steel must be kept at a weak grinding allowance), so the grinding wheel must be repaired.

2) When you refine the grinding wheel, first remove the thickness of about 0.1 mm, then use twice 0.02 mm deep, then use a depth cut of 0.01 mm three times, And finally repeat twice without cutting the depth space. During refining, the lateral power speeds are all 20 to 30 mm / min. For gentle steel parts, the side supply is better when repairing the grinding wheel, but the reverse is true when treatment of high speed at high speed.

3) When reducing the grinding wheel, you need to use enough grinding liquid or other cooling liquid to wash the contact point between the grinding wheel and the diamond knife, and wash the shouting wheel debris in time to avoid assigning the quality of grinding.

4) The diamond knife used during refining does not need to be very clear, because the grinding wheel has a relatively thick particle size. The diameter of the tip of the diamond knife is less than 0.8 mm. During the cut with a pointed diamond knife, the processing speed must be slowed down.

5) When the newly cut grinding wheel begins to be used, surface roughness is slightly worse and it will stabilize after use for a while.

2 quantity of grinding

1) The back of the grinding wheel is approximately 0.005 mm. Increase and decrease appropriately depending on the properties and hardness of the room steel.

2) The only race for the transverse supply volume is 0.2 to 0.4 mm. The lateral power supply speed has a greater impact on the roughness of the surface, because the cutting capacity of the grinding wheels of the grinding of the mirror is very mediocre. got.

3) Longitudinal power supply is 12 ~ 15 m / min. Longitudinal food has a relatively low impact on the roughness of the surface, but if it is too slow, a ripple or a pattern will occur on the surface of the room.

4) Souion of deep light without cutting. Due to the bad cutting capacity of the grinding wheel during the grinding of the mirror, the cuts often appear on the surface of the room (the round room is in the form of the moon and the rectangular room is in the shape of a belt) , which reflects this the surface of the room is not straight, so it is also necessary to crush light without food for about two minutes.

04
Defects and measurements subject to mirror grinding

Mirror grinding on a flat grinder often produces defects, such as surface corruption, burns, scratches, patterns and obvious wear marks (cable flows) in response to these problems, the following measures can be taken:

1) Most surface undulations are caused by vibrations of the grinding wheel, such as excessive clearance of the bearings, the deviation of the spindle, a poor dynamic balance of the engine rotor, a film of unequal oil between the spindle and rolling, etc. In addition, a bad balance of the grinding wheel will also cause undulations. If the grinding wheel is well balanced and there are still undulations, the grinding wheel and its matching parts must be inspected or adjusted to completely eliminate the ripple phenomenon.

2) When you work with high hardness materials, the grinding efficiency of the grinding wheel is bad and the grinding point will produce high temperatures, which will easily burn the room (for example, during the W18CR4V grinding, it is more likely to cause burns). To avoid burns, a sufficient grinding liquid must be present at the grinding point. In addition, the knife must be measured appropriately and should not be too large. The best way is to reduce the linear speed of the grinding wheel, which is suitable for around 18 m / s. The M7120A mill uses a low speed of 1440R / min, which can mainly eliminate burns. Another advantage of reducing the linear speed of the grinding wheel is to reduce the vibration of the grinding wheel, which can also reduce and eliminate corruption.

3) There are about two types of scratches in the grinding of the meal: the first is that the scratches are irregular, which is unclean in the grinding liquid, and the impurities and the abrasive particles highlighted are striped between the wheel of grinding and room. The method to eliminate this scratch requires grinding fluid to filter, which generally uses three lines of filtration of magnetic mesh and copper; Like length and short distance. The elimination method at this time is to use enough grinding liquid when reducing the grinding wheel and making both ends of the grinding wheel in an inclined shape with a large exterior and narrow inside. In addition, the grinding wheel must be selected appropriately, not too gentle and do not use grinding wheels with too good self-drunk properties.

4) When the grinding of the mirror, there are many forms of patterns which are inclined to appear. There are many factors that produce models, and the main reason is vibration, including periodic vibrations of the grinding wheel, external influences and vibrations of adjacent machine tools, etc. . When the adjacent machine tool does not start, the pattern will not appear very easily.

5) When the wear marks (flow of wire) in the grinding of the mirror are more obvious, to eliminate this flow rate, a fine grain grinding wheel must be used instead. However, when using fine grinding wheels, the following points must be taken into account:

① When repairing the grinding wheel, the diamond knife must be sharp, the grinding liquid must be sufficient and the debris must be carried in time to avoid affecting the surface of the grinding wheel.

② The amount of grinding should be appropriate to prevent surface burns and other problems that affect the softness of the surface. Be sure to leave an appropriate grinding margin.

③The linear speed of the grinding wheel must be reduced to 15 ~ 18 m / s.

④The grinding liquid is strictly filtered to avoid scratches.

⑤ When using grinding stone to repair grinding wheels, the contact zone between grinding stone and grinding wheels should not be too small, and the grinding stone used should not be too Soft, otherwise it will not work like a grinding wheel.