Designing for hydroforming
Hydroforming presents different opportunities to those available through stamping, but also has different manufacturing constraints.
It is important, even during the conceptual design phase, that the designer has a good understanding of the hydroforming process and accounts for the specific requirements to achieve an optimised design.
Tube diameter should be calculated based on the length of the shortest section perimeter and reduced by between 1-5% to ensure the tube does not get trapped during die closure. Check that the percentage increase of tube perimeter compared to the maximum section perimeter does not exceed the maximum elongation property of the selected material.
To extract the formed part from the die, draft is required on the component. In some cases the orientation of the part in the tool may provide sufficient draft. Where this is not possible and the product has deep vertical walls draft of 2-5 degrees should be included in the product design.
The finished part must be extracted from the die so it important to ensure that undercuts are minimised. This will often mean that even at a conceptual design phase, the designer must have an idea of where the dies split line is likely to be and design the component accordingly.
If undercuts cannot be avoided, sliding inserts may be used to ensure that the component can be extracted from the tool but this will add additional cost to the tooling and will increase process time.
Ideally all holes should be in a position and of a size that will enable them to be pierce in the hydroform tool. Some basic rules are:
- Minimum diameter 6mm
- Minimum ratio of diameter to thickness 3
- Minimum hole pitch – 2.5 x hole diameter
- Minimum distance to split line - 2 x hole diameter
The size of the filet radii have a significant effect on the overall feasibility of forming and the pressure that is required to for the part. In general the ratio of fillet radius to thickness should not be lower than 3 and will ideally be 5 or greater.
