What is Cold Forming?
Cold forming is a high speed manufacturing process whereby metal
is shaped at room temperature often without the need for the removal
of material. A simple blank is placed within a die and a punch is
pressed into the blank. The blank then takes on the form of the punch
and the die. By utilising multiple dies and punches in succession
very complex shapes can be achieved. Metal is forced beyond its yield
(elastic) limit and retains its altered shape upon removal from the die.
The metal is not forced beyond its tensile strength, otherwise fracturing
would occur (the exception is when trimming or piercing). Historically cold
forming has been an experienced based technology, but this is changing as
new computer based analytical tools are constantly being developed.
The benefits of cold forming over machining from solid
Many machined components can be re-designed as cold formed components
resulting in significant cost savings.
Material cost savings:- up of to 70% can be achieved by the
cold forming process when compared to a traditional machining process.
Enhanced product characteristics:- can be achieved by
coldforming, due to the metal deformation resulting in improved grain
structure, while work hardening can yield significantly improved product
Higher quality surface finish:-
can result from the Cold forming processes compared to conventional machined
surfaces. With careful product and process design, the cold forming process
can eliminate the need for costly secondary operations, such as welding,
Reduced Production costs:- will be result from this high speed
manufacturing process. Speeds range from around 10 pieces per minute for low
volume large press work to to 450 pieces per minute on the cold heading process.
Consistent and improved tolerance control:- can be achieved throughout
the production process by coldforming compared to more expensive machining
The 3 Basic Techniques of Coldforming.
A method to reduce diameter where the material is forced to flow into a cavity of
Method to make holes, where material flows backward around a penetrating punch.
Method to form heads on fasteners, where material is upset at the face of
dies and can be open or trapped to upset a particular shape
The Main Coldforming Processes
This process is typically used for the production of simple fasteners and
works by using the force of a punch to strike/ forge the end of a metal blank
in a die. This process uses force rather than heat to achieve its goal.
Single Die, Two-Blow Process:-
During the single die, two-blow process, extrusions and upsets can be carried
out in the same die. Pre-form shapes are provided by the first blow and the
final shape is completed by the second blow.
Two Die, Three-Blow Process:-
Two die, three-blow offers added extrusion and heading as well as the upsetting
of lengths equal to up to 4 X diameters of the bar stock. This process allows
more variety in shapes and increased head up-set ratios compared to processes
that use a single die.
In this process the final shape is accomplished in various stages using multiple
punches and dies with the finished component being completed in less than one
second. This can eliminate the need for expensive secondary post forming machining
operations. Where it is not possible to produce a fully finished part by
coldforming due to tight tolerances (+/- 0.05mm on diameters +/- 0.1mm
on length.), the process can produce a near net shape blank for
subsequent finishing with significantly reduced secondary process times.