DROP FORGING: Fullering impression, Edging impression, Bending impression, Blocking impression, Finishing impression, Trimming

DROP FORGING

Drop forging utilizes a closed impression die to obtain the desired shape of the component. The shaping is done by the repeated hammering given to the material in the die cavity. The equipment used for delivering the blows are called drop hammers.

Drop forging die consists of two halves. The lower half of the die is fixed to the anvil of the machine while the upper half is fixed to the ram. The heated stock is kept in the lower die. While the ram delivers four to five blows on the metal, in quick succession so that the metal spread and completely fills the die cavity. When the two die halves closed the complete cavity is formed.

The die impressions are machined in the die cavity, because of more complex shapes can be obtained in drop forging, compared to smith forging. However too complex shape with internal cavities, deep pockets, cannot be obtained in drop forging. Due to limitation of withdrawal of finished forging from die. The final shape desired in drop forging cannot be obtained directly from the stock in the single pass. Depending upon the shape of the component, the desired grain flow direction and the material should be manipulated in a number of passes. Various passes are used are

Fullering impression: 

Since drop forging involves only a reduction in cross section with no upsetting, the very first step to reduce the stock is fullering.The impression machined in the die to achieve this is called fullering impression.

Edging impression: 

Also called as preform. This stage is used to gather the exact amount of material required at each cross-section of the finished component. This is the most important stage in drop forging.




Bending impression:

This is required for those parts which have a bend shape. The bend shape can also be obtained without the bending impressions. Then the grain flow direction will not follow the bend shape and thus the point of bend may become weak. To improve the grain flow, therefore a bending impression is incorporated after edging impression.

Blocking impression:

It is also called as semi finshing impression. Blocking is a step before finishing. In forging, it is difficult for the material to flow to deep pockets, sharp corners etc. Hence before the actual shape is obtained, the material is allowed to have one or more blocking impressions where it requires the shape very near to final one. The blocking impression is characterized by large corner radii and fillet but no flash.

Finishing impression:

This is the final impression where the actual shape required obtained. In order to ensure that the metal completely fills the die cavity, a little extra metal is added to the stock. The extra metal will form the flash and surround the forging in the parting plane.

Trimming:

In this stage the extra flash present around the forging is trimmed to get the forging in the usable form.

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