An Investigation into the Phenomenon of ‘Partially Restrained Injection’ during Kinetic Heading

Summary

Kinetic heading is a term used to describe the process of upsetting the end of a billet by virtue of inertia forces generated upon its high speed discharge into, and subsequent arrest within, a closed die-set.

The object of the present investigation is to determine the mechanism responsible for the occurrence of a tensile neck in the shank — immediately adjacent to the head — during the kinetic heading of bar stock. Tests were carried out in which aluminium billets were arrested in a hexagon-head die-form under various conditions, with a view to identifying the factors contributing to the phenomenon.

It has been established that the necking is due to the restrained component being partially ejected from the die by the release of elastic strain energy which had been transferred to the die-set during the closing stages of the forming process.

Evidence is presented in photographic and photomacrographic form, while attempts are made to graphically display the parameters affecting the necking phenomenon. In addition comparisons are drawn with the static tensile test.

The mechanism responsible for various component features is discussed, together with pointers to further investigation.