Introduction to several commonly used polishing methods (3)

Diamond grinding and polishing should pay attention to the following points:

(1) This polishing must be carried out under light pressure as much as possible, especially when polishing pre-hardened steel parts and polishing with fine abrasive paste. When polishing with #8000 abrasive paste, the common load is 100-200g/cm2, but it is difficult to maintain the accuracy of this load. To make this easier, you can make a thin and narrow handle on the strip, such as adding a piece of copper; or cut a part of the strip to make it softer. This helps control the polishing pressure to ensure that the mold surface pressure is not too high.

(2) When using diamond grinding and polishing, not only the working surface is required to be clean, but also the hands of the worker must be carefully cleaned.

(3) The polishing time should not be too long, the shorter the time, the better the effect. If the polishing process is carried out too long, it will cause "orange peel" and "pitting".

(4) In order to obtain a high-quality polishing effect, polishing methods and tools that are prone to heat should be avoided. For example: polishing wheel polishing, the heat generated by the polishing wheel can easily cause "orange peel".

(5) When the polishing process is stopped, it is very important to ensure that the surface of the workpiece is clean and carefully remove all abrasives and lubricants. Then, a layer of mold anti-rust coating should be sprayed on the surface.

Since mechanical polishing is mainly done manually, polishing technology is still the main reason for the quality of polishing. In addition, it is related to the mold material, the surface condition before polishing, the heat treatment process, and the like. High-quality steel is a prerequisite for good polishing quality. If the surface hardness of the steel is uneven or the characteristics are different, it will often cause polishing difficulties. Various inclusions and pores in the steel are not conducive to polishing.

3.1 Influence of different hardness on polishing process

The increase in hardness increases the difficulty of grinding, but the roughness after polishing decreases. Due to the increased hardness, the polishing time required to achieve lower roughness is correspondingly increased. At the same time, the hardness is increased and the possibility of over-polishing is correspondingly reduced.

3.2 Influence of surface condition of the workpiece on the polishing process

During the crushing process of steel machining, the surface layer may be damaged by heat, internal stress or other factors, and improper cutting parameters may affect the polishing effect. The surface after EDM is more difficult to grind than the surface after ordinary machining or heat treatment. Therefore, the fine gauge quasi-electric spark should be used before the end of EDM, otherwise the surface will form a hardened thin layer. If the EDM is not properly selected, the depth of the heat affected layer can be up to 0.4mm. The hardness of the hardened layer is higher than the hardness of the substrate and must be removed. Therefore, it is better to add a rough grinding process to completely remove the damaged surface layer to form an average rough metal surface, which provides a good basis for polishing.

The difference between shot blasting and sand blasting

Shot blasting is the use of a high-speed rotating impeller to throw small steel shots or small iron shots out of the surface of the part at high speed, so the oxide layer on the surface of the part can be removed. At the same time, the steel shot or the iron shot hits the surface of the part at high speed, causing the lattice distortion of the surface of the part to make the surface hardness increase. It is a method for cleaning the surface of the part. The shot blasting is often used to clean the surface of the casting or to strengthen the surface of the part. deal with.

Generally, shot blasting is used for regular shapes, etc. Several heads are placed up and down together, with high efficiency and low pollution.

Repair, shipbuilding, shot blasting, sand blasting are commonly used. But whether it is shot blasting or sand blasting, it is in the form of compressed air. Of course, it is not the impeller that does not use high-speed rotation. In the repair and shipbuilding industry, shot blasting (small steel shot) is often used in steel plate pretreatment (pre-painting rust removal); sand blasting (repairing and shipbuilding is used in ore) is often used in forming ships or segments. The role is to remove the old paint and rust on the steel plate and repaint. In the repair and shipbuilding industry, the main role of shot blasting and sand blasting is to increase the adhesion of steel coating paint.

In fact, the cleaning of casting parts is not only the use of shot blasting. For large parts, the drum is first cleaned. The riser of the casting is cut off and placed in the drum. The parts collide with each other in the drum, and the sand of the surface is mostly Remove it and then perform shot blasting or shot peening.

The size of the shot blasting ball is 1.5mm.

Studies have shown that in terms of damage, the tensile stress on the surface of the metal material is much easier than the compressive stress. When the surface is under compressive stress, the fatigue life of the material is greatly improved. Therefore, it is usually sprayed on components such as shafts that are susceptible to fatigue fracture. The pellet forms surface compressive stress and improves product life. In addition, the metal metal material is very sensitive to stretching, which is why the tensile strength of the material is much lower than the compressive strength. This is also the tensile strength of the metal material (yield, anti-wear). Pull) indicates the reason for the material properties.

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