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#025 Basics of Blanking Work (15) Blanking Work without Burrs on Both Surfaces

Category : Shearing work
January22, 2010

Blanking operations always result in generation of burrs. Because of that, burrs are very frequently removed by flattening the burrs. However, there are problems about Product Liability laws, and recently there is an increasing trend of removing burrs. One of the methods of eliminating burrs is given here. This method is generally called the flash pressing method.

In this method, to begin with partial blanking is done as shown in Fig. 1. Usually the punch is slightly larger than the die. This condition is called "negative clearance". By pushing the punch inside the material, the material is pushed inside the die and single sided shear droop is formed. The amount of pushing in by the punch at this time is very important, and should be 75% or more of the material plate thickness.

[Fig. 1] Partial blanking process

The next process is the flash pressing process. In the flash pressing processing although the operation is very simple, it content is unique. This is explained in Fig. 2. The material is in the partially blanked condition. This condition is considered dividing it into three parts, namely, the virtual punch part, the virtual die part, and the part that is gripped between the virtual punch and the virtual die. The material in this part is blanked using the virtual punch and the die. In this process the material blanks itself the forms the die roll (shear droop) part.

[Fig. 2] Principle of flash pressing process

The condition after flash pressing is shown in Fig. 3. The amount of pushing in the partial blanking process is the one that makes the flash pressing process successful. If this is shallow, the virtual punch and die are not effective. If this is too deep, the material gets cut before flash pressing. The reason for having this negative clearance is to make sure that the material does not get fused during the flash pressing process.

[Fig. 3] Flash pressing process

The shape after separation is shown in Fig. 4. Compare this shape carefully with that in Fig. 1. The finished dimensions, in terms of the external dimensions of the blanked product, will be almost the same as the punch dimensions in the partial blanking process. This is slightly different from the ordinary blanking process.

[Fig. 4] Separation process

This method has not been tried for large products. Try out this process for small products.

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