Freely expand sections of a hydroformed part has gained a great deal of prominence in the burgeoning hydroforming industry. A number of misconceptions have arisen concerning what can be achieved in various forming situations and the cost of accomplishing them.
This paper focuses on part cross section expansion and objectively discusses 5 different techniques. These are hydroexpansion without end feeding, hydroexpansion with end feeding, mechanical preforming, hydraulic preforming and elastomeric bulge forming. The 1st two happen in the hydroforming die while the 3rd, 4th and 5th occur prior to placement in this die.
Careful analysis of the following factors can lead to choosing the ‘best’ option. Those that require consideration are demands on the material, material type, expansion size and position relative to any bends, amount of wall thinning and process robustness.
It all distills down to judging which is the simplest, cheapest and most flexible for any changes that may come, or the best combination of all 3. Once a path is chosen it gets succeedingly more difficult to change direction with each passing step, so the most knowledgeable initial decisions are essential.