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Seven suggestions for reducing defects during mould processing

Update:29-05-2020
Summary:

As an important tool for the manufacture of workpieces, […]

As an important tool for the manufacture of workpieces, Disposable medical device moulds will inevitably have some defects during the processing process, which will cause the workpieces to be unable to be used normally or even to be used after manufacturing.

 

1. Reasonably select and trim the grinding wheel. The white corundum grinding wheel is better.Its performance is hard and brittle, and it is easy to produce new cutting edges.Therefore, the cutting force is small, the grinding heat is small, and the medium particle size is used for the particle size, such as 46 to 60 mesh is better. Medium and soft (ZR1, ZR2 and R1, R2) are used for the hardness of the grinding wheel, that is, coarse-grained, low-hardness grinding wheel, good self-excitation can reduce cutting heat. It is very important to select the appropriate grinding wheel for fine grinding.For the high vanadium and high molybdenum condition of the disposable medical device mould steel, it is more suitable to use GD single crystal corundum grinding wheel. Grinding wheels, organic binder grinding wheels have good self-grinding, and the roughness of the workpieces can reach Ra0.2μm.In recent years, with the application of new materials, CBN (cubic boron nitride) grinding wheels have shown very good processing results. Finishing on CNC forming grinding machine, coordinate grinding machine, CNC internal and external cylindrical grinding machine, the effect is better than other types of grinding wheels. In the grinding process, pay attention to dressing the grinding wheel in time to maintain the sharpness of the grinding wheel. When the grinding wheel is passivated, it will slip and squeeze on the workpiece surface, causing burns on the workpiece surface and reduced strength.

 

2. Reasonable use of cooling lubricant, play the three major roles of cooling, washing and lubrication, keep cooling lubrication clean, so as to control the grinding heat within the allowable range to prevent the workpiece from thermal deformation. Improve the cooling conditions during grinding, such as the use of oil-immersed grinding wheels or internal cooling grinding wheels. The cutting fluid is introduced into the center of the grinding wheel, and the cutting fluid can directly enter the grinding area, which plays an effective cooling role and prevents burns on the surface of the workpiece.

 

3. The quenching stress after heat treatment is reduced to the limit, because the quenching stress and the network carbonized structure are subject to the grinding force, and the phase change of the structure is very easy to crack the workpiece. For the high-precision disposable medical device moulds, in order to eliminate the residual stress of grinding, low-temperature aging treatment should be carried out after grinding to improve the toughness.

 

4. To eliminate grinding stress, the mould can also be immersed in a salt bath at 260 ~ 315 ℃ for 1.5min, and then cooled in oil at 30 ℃, so that the hardness can be reduced by 1HRC and the residual stress can be reduced by 40% ~ 65%.

 

5. For precision grinding of precision moulds with dimensional tolerance within 0.01mm, attention should be paid to the influence of ambient temperature, and constant temperature grinding is required. It can be seen from the calculation that 300mm long steel parts have a change of about 10.8μm when the temperature difference is 3 ℃, (10.8 = 1.2 × 3 × 3, deformation per 100mm 1.2μm / ℃), each finishing process needs to be fully considered The influence of this factor.

 

6. Electrolytic grinding is used to improve the precision and surface quality of mould manufacturing. During electrolytic grinding, the grinding wheel scrapes off the oxide film: instead of grinding the metal, the grinding force is small and the grinding heat is also small, and there will be no grinding burrs, cracks, burns, etc., and the general surface roughness can be better than Ra0 .16μm; In addition, the wear of the grinding wheel is small, such as grinding cemented carbide, the wear amount of the silicon carbide grinding wheel is about 400% to 600% of the weight of the cemented carbide.When using electrolytic grinding, the wear of the grinding wheel The amount is only 50% of the amount of carbide removal ~ *.

 

7. Choose the amount of grinding reasonably, and use the fine grinding method with even smaller radial feed or even fine grinding. If the radial feed rate and the grinding wheel speed are appropriately reduced, the axial feed rate is increased, so that the contact area between the grinding wheel and the workpiece is reduced, and the heat dissipation conditions are improved, thereby effectively controlling the increase in the surface temperature.

 

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