Abrasive discs are carriers used to coat or embed abrasives so that the abrasive grains can perform cutting functions, and at the same time, they are also shaping tools for grinding surfaces. Rotating discs, cylinders, cones, flat plates, oil stones, thin plates, pipes, rings and special shaped abrasion disks can be used as grinding tools.
The material of the abrasion disk should be softer than that of the workpiece, so that the grinding powder can be embedded in the surface of the abrasion disk. The abrasion disk is made of pig iron, soft copper, red copper, brass, lead, and hard wood. Lead and hardwoods are used only for glossing after the workpiece has been ground to final size.
The hardest abrasive is diamond dust; grind hardened hardware with diamond dust. But diamond powder is very expensive, so it is rarely used. The second hardest is corundum. It is followed by corundum powder, silicon carbide and iron red powder. The most commonly used is emery.
With different abrasion disks, different types of lubricants are required. Pig iron abrasion disk needs kerosene or gasoline as lubricant. Mild Steel abrasion disk - Use engine oil. Copper abrasion disk - Use motor oil, alcohol, carbonated water. Where the quality requirements of the copper surface are particularly high, talcum powder diluted with alcohol or iron powder mixed with vaseline is used as a lubricant. When grinding aluminum, use diatomaceous earth diluted with toluene and stearic acid or diatomaceous earth diluted with wood oil as a lubricant. When grinding copper alloys, use machine oil and fat as lubricants, mix the selected lubricating fluid with grinding powder, and then rub the mixture carefully.
The abrasion disk itself and the workpiece are mutually trimmed during the grinding process, and the geometric accuracy of the abrasion disk itself is "transferred" to the workpiece to a certain extent, so the processing surface of the abrasion disk is required to have high geometric accuracy. The main requirements for abrasion disks are:
(1) The hardness of the material is generally lower than that of the workpiece material, the structure is uniform and dense, free of impurities, foreign matter, cracks and defects, and has certain abrasive embedding and impregnation properties.
(2) Reasonable structure, good rigidity, precision retention and wear resistance. Its working surface should have high geometric accuracy.
(3) Good chip removal and heat dissipation.
The control of the wafer grinding process is mainly to control the rotation speed of the abrasion disk and the applied load. Firstly, the grinding pressure should be increased slowly from low to allow the abrasive to spread evenly and remove the raised spots on the wafer. It is also necessary to slowly reduce the grinding pressure before the end of grinding. Wafer grinding rate generally increases with the following parameters:
(1) Increase in grinding pressure.
(2) An increase in the flow rate of the grinding slurry.
(3) The increase of abrasive powder in the abrasive slurry.
(4) Increase in the speed of the abrasion disk.
The completion of the grinding process is mainly based on timing or constant thickness (grinding amount). Among them, the thickness setting method is to use the thickness probe to sense the thickness of the wafer. Once the set thickness is reached, the machine will gradually depressurize and stop grinding.
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