1.6 HYDROFORMING
• Basic process,
- A metal sheet is placed over a male punch.
- Fluid is on the other side of the metal sheet.
- The punch advances and the metal sheet is forced into the shape of the punch. The hydraulic chamber acts as a mate for the punch.
• The basic operation is,
1. The metal is placed between the fluid chamber and the punch bed.
2. The fluid is encased behind a wear pad, and this wear pad is brought into contact with the sheet with pressures up to 5 Kpsi.
3. The punch is advanced with pressures up to 15 Kpsi causing the metal to take the shape of the punch.
4. The pressures are released, the punch withdrawn, the fluid chamber pulled back to remove the metal part.
• Compared to conventional forming,
- higher drawing ratios
- reduced tool costs
- less scarring of parts
- asymmetrical parts made in on pass
- many high strength alloys can be formed, for example stainless steel
• Compared to spinning,
- faster forming speeds
- fewer anneals required
- only rotational parts possible with spinning
• Methods permissible,
- punch forming - for large drawing depths
- negative punch forming - allows recessed features
- cavity die forming
- male die forming
- expansion forming
• Advantages,
- any type of sheet material can be used
- thicknesses of 0.1 to 16mm
- tools can be used for more than 1 metal thickness
- flexible and easy to operate
- less expensive tooling
- tolerances down to 0.002”
- reduced setup times
- less thinning
- reduced die wear
• Disadvantages,
- sharp corners difficult to control
- high equipment cost
- no holes in surface
- incorrectly set pressures may lead to buckling and tearing for high pressures
• Design points
- the metal springback should be considered in design, or the size of the punch/die changed through trial and error experiments.
- a draft (taper) of 1-2° will prolong tool life.
- the minimum part radius should be 2-3 times the sheet thickness.
• Applications,
- cups/kitchenware
- autobody panels
- covers
