Materials • Processes • Finishes
the forming process. These enable high-quality stainless steel parts to be produced while retaining all of the traditional benefits associated with conventional cold forming. Dawson Shanahan says it has carried out extensive
prototype tests, with components being tested for material and part integrity by an independent laboratory. Stainless steel parts produced with the new cold forming
process can be used in applications where machined parts would otherwise be unsuitable due to cost or quality concerns. In some applications, such as engine components, cold formed stainless steel parts can provide performance advantages over machined parts. Other industries that can benefit from cold formed stainless steel parts include the medical and aerospace sectors.
Precision flowforming
Precision flowforming is another advanced, cold forming process that is suitable for producing precise, round, seamless, hollow components. There are three variants of flowforming: forward flowforming, reverse flowforming and shearforming, all of which can usually be performed on the same machine by changing the tooling. Typically, cylinders with one closed or partially-closed end are forward flowformed, whereas cylinders with two open ends are reverse flowformed. Conical or ogivial components are produced by shearforming, which can be thought of as a combination of metal spinning and forward flowforming. Sometimes a combination of forward and reverse flowforming is required to achieve the necessary part geometry. In simple terms, flowforming is similar to metal spinning, with one or more rollers forcing a blank - which may be a disc or tube - over a mandrel. Dynamic Flowform, which is based in the USA, says it has flowformed a myriad of thin-walled net- or near-net-shape components in more than 50 different metals, ranging from aluminium to zirconium, for customers in the defence, nuclear, aerospace and industrial markets. The company’s capabilities cover component diameters from 22 to 650mm, wall thicknesses from 0.15 to 15mm and lengths up to 8m. One project in which Dynamic Flowform was recently
involved was the development of a lighter, more portable 60 mm mortar for the USA Marines. The company is now manufacturing lightweight components for this weapon, which
Cold forming explained C
old forming produces metal components at low temperatures – usually ambient temperature –
without removing any material. A simple blank, sawn or cropped from round bar or wire, or a cold headed pre-form, is placed within a die and a punch is applied, forcing the blank to take the form of the punch and die. There are a number of types of cold
forming, ranging from forward and backward extrusion through to freeflow, with the type of component and its finished geometry determining the most appropriate method.
Cold forming offers many advantages in
the manufacture of metal components over and above cost savings. As it is performed without heating, cold forming is a far quicker process than more conventional processes, so production times and lead times can be reduced. Production cycle times can be cut still further by using multi-station machines for large production runs. In cold forming, the grain structure of
the material is forced to follow the geometry of the component, unlike in machining. As a result, the strength of the part is
enhanced along its axis. Additionally, parts undergo work hardening during the cold forming process, thereby improving their machinability and durability. As this increase in strength is comparable to that available from heat treatments, it can be more cost- effective to cold work a lower-cost and weaker metal than to hot work a more expensive metal, particularly when tighter dimensional tolerances are required. The cold forming process also makes it possible to produce component parts with a superior finish, both internally and externally. l
www.engineerlive.com 27
Fig. 2. Dynamic Flowform has supplied flowformed lightweight inconel alloy parts for a portable 60mm mortar used by the USA Marines.
weighs 4 kg less than the World War II era M2 Mortar and M119 mortar that it replaces (Fig. 2). The lighter mortar means that the Marines can move faster from one location to another, and with less fatigue. In the battlefield, the Marines will be able to carry more ammunition. While precision cold forming is attractive for many
applications, it will not be suitable for all components that are currently manufactured by machining; in many cases, components will also need to be redesigned to some degree if this alternative production process is to be adopted. l
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