Volumes of production

From simple hand forgings up to about 10,000 units.

Unit price vs. capital investment

In hot open-die forging, done by hand, the cost is based on the skilled manual labor. In automated methods, tooling costs can be very high.

Speed

Quite slow, which is partly due to the fact that 90 percent of all forging processes are hot processes, so that the work pieces need to be heated before forming.

Surface

Forged parts will generally need to be machined in order to achieve a good, smooth surface and to remove flash, which is the result of metal being squeezed out into a flat web around the outside of the part.

Types/complexity of shape

The type of forging process will dictate the complexity and type of shape that is possible. In drop forging, draft angles are generally required, and parting lines need to be designed in order for complex shapes to be formed. Draft angles vary and are dependent on the type of metal used.

Scale

Forging can be used for parts that weigh from just an ounce or so to those reaching half a ton.

Tolerances

High tolerances are difficult to achieve, partly due to the wearing of the die. Different metals offer a range of tolerances.

Relevant materials

With hot forging, most metal and alloys can be formed. However, the ease with which they can be forged varies enormously.

Typical products

Because of the increased strength of forged components (compared with cast metals), a large number are used in aircraft engines and structures. Other applications include hand tools such as hammers, wrenches and spanners, and swords—notably Samurai swords.

Similar methods

Powder forging (p.190). Impact extrusion (p.146) and rotary swaging (p.106) are both forms of forging.

Sustainability issues

The increased strength the material acquires during forging can increase the durability and lifespan of the final product. However, the heated forging techniques consume high amounts of energy, which increases emissions and subsequent effects on the environment. In addition, a significant amount of excess metal is produced, and secondary machining and further energy use is required to trim it. Fortunately this excess can be recycled.

Further information

www.forging.org

www.iiftec.co.uk

www.key-to-steel.com

www.kingdicktools.co.uk

www.britishmetalforming.com

Powder Forging

AKA Sinter Forging

Powder metal forging is a process that sits within the realm of powder metallurgy. It combines sintering (see p.168) and forging (see p.187) to produce finished parts. As in other forms of powder metallurgy, the process begins with the forming of the metal powder into a “green” state in a die. At this stage, the component is known as a “pre-form,” and is slightly different in shape from the final component. The pre-form is sintered to obtain a solid component, which is removed from the furnace, coated with a lubricant such as graphite, and transferred to a forging press. Here, the final component is formed in a closed-die forge, which forces the metal particles to interlock and become a solid, dense mass. The extra compaction provided by this process gives a highly dense, nonporous component.

–  No gaps or voids in the metal, which can occur in, for example, sand casting (see p.228).

–  Compared with other powder metallurgy processes, powder forging provides parts with greater ductility and strength.

–  Efficient use of material, with less wastage than in other forms of forging (see p.187).

–  Requires far fewer post-forming operations than other forging methods.

–  Expensive tooling that requires large volumes of production.