Crossed spiral traces appear on the surface The reason for this kind of mark is mainly due to the poor straightness of the busbar of the grinding wheel and the existence of concave and convex phenomena. During grinding, the grinding wheel and the workpiece are only partially in contact. When the workpiece or the grinding wheel moves back and forth several times, the intersection will appear on the surface of the workpiece. Spiral and visible to the naked eye. The pitch of these spirals is related to the speed of the workpiece table and the rotation speed of the workpiece, and is also related to the non-parallel axis of the grinding wheel and the guide rail of the worktable.

►Main causes of spiral formation

1. The grinding wheel is poorly dressed, the corners are not chamfered, and coolant is not used for dressing;

2. There is too much lubricating oil in the guide rail of the workbench, causing the workbench to float;

3. The accuracy of machine tools is not good;

4. The grinding pressure is too high, etc.

►The specific reasons for the formation of spirals

1. The V-shaped guide rail has poor rigidity. When grinding, the grinding wheel is offset, and only the edge of the grinding wheel is in contact with the working surface;

2. When dressing the grinding wheel, the reversing speed of the workbench is unstable and the accuracy is not high, causing a certain edge of the grinding wheel to be slightly less trimmed;

3. The workpiece itself has poor rigidity;

4. There are broken and flaky sand grains on the grinding wheel and iron filings from the grinding of the workpiece accumulated on the surface of the grinding wheel. For this reason, the trimmed grinding wheel should be rinsed or brushed with cooling water;

5. The grinding wheel is not well dressed, with local bulges, etc.

Fish scales appear on the surface The main reason why fish scale marks reappear on the surface is because the cutting edge of the grinding wheel is not sharp enough, and the “gnawing” phenomenon occurs during grinding. At this time, the vibration is large and the workpiece is caused.

►The specific reasons for the appearance of fish scale marks on the surface are:

1. There is garbage and oil on the surface of the grinding wheel;

2. The grinding wheel is not rounded;

3. The grinding wheel becomes dull. The trimming is not sharp enough;

4. The diamond fastening frame is not strong, the diamond shakes or the diamond quality is not good and sharp;

5. Uneven hardness of the grinding wheel, etc.

Working surface roughening The main reason for the recurrence of roughening marks on the surface is that after the coarse-grained abrasive grains fall off, the abrasive grains are sandwiched between the workpiece and the grinding wheel.

►The specific reasons why the workpiece surface is roughened during grinding are:

1. The traces left during rough grinding are not removed during fine grinding;

2. The coarse abrasive particles and fine abrasive particles in the coolant are not filtered cleanly;

3. When the coarse-grained grinding wheel is just dressed, the abrasive grains are easy to fall off;

4. The material toughness expires or the grinding wheel is too soft;

5. Improper matching of abrasive grain toughness and workpiece material toughness, etc.

There are straight wave traces on the surface of the workpiece When we take a cross-section of the vertical axis center line of the ground workpiece and enlarge it, we can see that its periphery is approximately a sine wave. Make its center move along the axis without rotation and translation, and the trajectory around the sine wave is the wave cylinder, which is also called a polygon.

The reason for the straight waveform is the vibration caused by the movement of the grinding wheel relative to the workpiece or the periodic changes in the pressure of the grinding wheel on the workpiece. This vibration may be forced vibration or self-excited vibration, so there is often more than one straight wave frequency on the workpiece.

►The specific reasons for producing straight wave traces are:

1. The clearance of the grinding wheel spindle is too large;

2. The hardness of the grinding wheel is too high;

3. The static balance of the grinding wheel is not good or the grinding wheel is dull;

4. The workpiece speed is too high;

5. The horizontal knife is too large

6. The grinding wheel spindle bearing is worn and the fitting clearance is too large, causing radial runout;

7. The grinding wheel pressing mechanism or workbench “crawls”, etc.

Reproduction of burn marks on the workpiece surface The surface of the workpiece is often burned during the grinding process. There are several types of burns. One is that the burns are in the form of dark black patches along the grinding direction of the grinding wheel; the other is that the burns are in the shape of lines or intermittent lines.

►The workpiece surface is burned during the grinding process for the following reasons:

1. The grinding wheel is too hard or the grain size is too fine and the structure is too dense;

2. The feed rate is too large, the cutting fluid supply is insufficient, and the heat dissipation conditions are poor;

3. The workpiece speed is too low and the grinding wheel speed is too fast;

4. The vibration of the grinding wheel is too large, causing burns due to constant changes in grinding depth;

5. The grinding wheel is not dressed in time or is not dressed well;

6. The diamond is sharp and the grinding wheel is not well dressed;

7. The workpiece was burned too deeply during rough grinding, and the amount left for fine grinding was too small and was not ground away;

8. The clamping force or suction force of the workpiece is insufficient, and the workpiece stalls under the action of grinding force.

So how do you know whether the workpiece surface is burned during the grinding process? This can be checked by regular pickling.

After the workpiece is pickled, when the surface is wet, it should be visually inspected under a scattered light immediately. The normal surface will be uniform dark gray. If it is a soft spot, there will be cloud-like dark black spots with an irregular perimeter; if it is decarburized, it will appear gray or dark black spots; if it is ground to crack, the crack will be cracked. If it is burnt, one is along the surface. There are dark black patches in the processing direction of the grinding wheel, and secondly, there are lines or intermittent lines.

If the above-mentioned burn phenomenon occurs during the grinding process, the cause must be analyzed in time and effective measures must be taken to solve it to prevent batch burns.

Surface roughness does not meet requirements The surface roughness of bearing parts has standards and process requirements, but during the grinding and super-finishing processes, due to various reasons, the specified requirements are often not met.

►The main reasons that cause the surface roughness of the workpiece to fail to meet the requirements are:

1. The grinding speed is too low, the feed speed is too fast, the feed amount is too large, and the no-feed grinding time is too short;

2. The workpiece speed is too high or the workpiece shaft and grinding wheel shaft vibrate too much;

3. The grinding wheel grit is too coarse or too soft;

4. The dressing speed of the grinding wheel is too fast or the clearance of the dressing mechanism is too large;

5. The diamond used for dressing the grinding wheel is not sharp or of poor quality;

6. The quality of the super fine oil stone is poor and the installation position is incorrect;

7. The quality of super-refined kerosene does not meet the requirements;

8. Super precision time is too short, etc.

 

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