The cold forming process is a high speed process in which, at first, the wire rod is precisely cut at room temperature. After that is moved under a succession of dies and punches, which progressively conform the workpiece to the desired geometry.
The metal is hardened beyond the elastic limit and keeps the changed shape after its extraction from the die. The load does not exceed tensile strength, otherwise a fracture would occur (an exception when cutting).
Historically, the cold forming projects are based on empirical experience, but is changing by new computer-based analytical tools, which are in constant development.
This process is recommended when producing big quantities, as it is able to create complex shapes and tight tolerances. The raw material is wire rod and enters the high speed horizontal press. This material is fed by an automatic system, and cut into preforms by a shear process. A robot transfer with fingers, transports the blank to the first die. The punch pushes the blank into the die, as the fingers holding it and they open totally before the punch hits them; the first cycle is done, so it returns to the previous operation. All the blanks are thus pressed simultaneously. The blanks will be stuck fast in the die until they are released by an ejector and transported to the next work station. The process then begins again.
The technical required specifications and material properties of the end product, will influence the material chosen to become the cold formed part. The array of raw materials to be used is quite large, which enables to chose one that has a good response to the plastic deformation. Generally speaking, low alloyed materials (such as steel, copper, aluminum and titanium alloys) are used in cold forming, as these tend to respond better to plastic deformation. Many well-known steel alloys containing chromium, molybdenum and nickel are also highly suitable for cold forming. Thanks to their particular grain structure and high ductility, highly alloyed austenitic chrome-nickel steels are also suitable.
Fobric offers support to designers in the material select process.
There are several considerations to take into account in the components design for the cold forming process, in geometric terms. Minimal changes during design, which do not compromise functional integrity, can save stages or eliminate the second operations. An important fact is that the presses are mostly designed to work only in one axis.
Another one is the bigger or lesser conformability of the material we are working on, and also the cut that has a big influence on the tops of the part.
Below, we present some considerations that can help in the optimization of the design for the production by cold forming process.
Fobric has been developing innovating technical skills which have rendered many considerations obsolete, which means that they depend on how sophisticated is the technology used.
There are several advantages of this process, mechanical, economical and ecological ones:
– Conformation of the fibers without cutting them.
– By hardening, the metal becomes tougher and more resistant.
– Enables the reduction or elimination of second operations.
– Excellent surface roughness.
– Many of the components can be produced with Vi=Vf (Initial volume = Final volume). Material saving and scrap disposal.
– Speed; Currently there are projects producing 800 parts per minute.
This stage of the process is very specific and it’s where Fobric stands out. This is the biggest challenge, but it’s what we like the most.
The conversion of a part made by a chip forming process to cold forming is an exercise that has resulted on many components in the portfolio of our team. To develop a cold forming cycle, we have to make a journey that begins in the customer drawing and ends in the wire rod (raw material). There are several premises that have to be evaluated like:
– Geometric complexity of the part (number of stations)
– Number of stations (choice of press)
– Part dimensions(forming force and choice of the press)
– Intrinsic limits of material conformation(geometry of the phases)
– Transport (geometry of the phases)
– Speed (choice of the press and geometry of the phases)
Once all considerations are taken into account, the phases are projected with numerical calculation support. All development is supported too with simulation software.