1 An example of the tooling and the die cavity into which the metal is placed.

2 Semifinished hydroformed components.

–  Strong, often complex, single components due to the elimination of joints.

–  Potential for parts with lower weight but with high strength.

–  Ability to reduce multiple components and joins into one complex part.

–  High tooling investment needed.

–  Limited number of companies offering the process.

Volumes of production

High production volumes.

Unit price vs. capital investment

Considerable investment in tooling required, but being able to produce components as single parts, rather than as multiple parts joined together, should help to reduce the price per unit.

Speed

In a highly automated factory setting, it is possible to achieve production cycle times of 20–30 seconds for a small part, even in a workflow setup where parts are positioned and connected inside the die.

Surface

In general, hydroforming does not have much of an effect on the surfaces of materials. It does, however, leave small scratches and marks at the ends of a work piece from the clamps that seal the ends, but these are normally trimmed off.

Types/complexity of shape

Tubular materials can be made to bulge into quite elaborate forms. Examples of this include T-sections, which would otherwise need to be made by joining multiple components.

Scale

The bigger the part, the more pressure is needed for forming, which in turn requires a heavier mold to contain the powerful forces involved in this process. Some large car parts, including hoods, can be made with hydroforming, although it would be difficult to manage pieces that were much larger than this.

Tolerances

Because of the die, the process allows the part to be controlled during forming to prevent wrinkling or tearing.

Relevant materials

Any metal with reasonably elastic properties that can take the high levels of tension involved, including high-grade steel and heat-treatable aluminum.

Typical products

Bicycle frames, bellows, T-sections, and a variety of structural automobile components, including floor pans, van body sides, and roof panels.

Similar methods

Inflating metal (p.76) and superforming aluminum (p.70).

Sustainability issues

The hydroforming technique can allow for thinner-walled parts and eliminate the need for complex joins, which can substantially reduce material consumption and weight without compromising strength and rigidity. As the metal flows instead of stretching during forming, it is less likely to work-harden, which eliminates the need for further processing such as annealing, which would require additional resources and energy.

Further information

www.hydroforming.net

http://salzgitter.westsachsen.de

Backward Impact Extrusion

AKA Indirect Extrusion

Product	Sigg drinks bottle
Materials	aluminum
Manufacturer	Sigg
Country	Switzerland
Date	range brought to market 1998

This cutaway of the famous Sigg container shows the thin walls and the typical shapes that are a feature of impact extrusion.

Impact extrusion is a cold process for forming metals that marries forging (see p.187) with extrusion (see p.96). In a nutshell, backward impact extrusion is a method of forming hollow metal parts by striking a metal billet (or disk), which is confined within a cylindrical or square die, so hard that the metal is forced upward into the space between the “hammer” (or punch) and the die. The gap between the punch and the inside of the die determines the wall thickness of the final component.

There are in fact two types of impact extrusion, forward extrusion and backward extrusion. Backward (or indirect) extrusion is used to make hollow shapes, because the punch is solid and thrusts the material around itself into the space between itself and the die.

The other sort of impact extrusion, forward (or direct) extrusion, can only produce solid sections. In this instance the space between the punch and the die is too small to allow metal to wrap itself around the punch. Instead, the metal is hammered downward into a die forming a straightforward solid shape. Nevertheless, these processes can also be combined in a single operation, where the repeated action of the punch pushes material both upward (in order to form a hollow top) and downward (to make a solid, shaped base).

Designs that require outward tapering may need some post forming after extrusion, and any threaded sections, such as the bottle neck, are also added after forming.

1 The aluminum billet, which is placed on the die.

2 The cylinder created by the action of the punch using backward extrusion.

3 Tapering is added by a secondary process.

4 With the threading at the neck added, this is now recognizable as a Sigg bottle.

–  Produces cost-effective shells in a variety of square and cylindrical cross-sectional shapes.

–  Removes the issue of joints by producing components with a uniform, seamless wall.

–  Inexpensive tooling compared with other high-volume processes.

–  The final component is limited in length to the length of the punch needed to strike the billet.

–  Only suited to parts where the length of the part is greater than four times the diameter.

–  Post forming is required to add tapers or threads.

–  Subject to the limitations of the die.