Precision cold forming receives a warm reception

Paul Boughton

Jon Severn investigates how precision cold forming has the potential to help manufacturers reduce component costs by up to 70 per cent, shorten lead times and, at the same time, improve mechanical properties and surface finish.

Competition from developing economies such as China, India and Brazil presents a threat to European manufacturers, especially as these countries are now capable of producing high-quality goods. At the same time, raw material prices have increased significantly in recent years, largely due to the demand from China, yet the global economy makes it very difficult for manufacturers to increase their prices to compensate for higher costs. Two engineering materials that have been the subject of sharp price rises are copper and stainless steel, though the latter appears to have peaked and returned to levels more commensurate with the long-term trend.

Copper is used extensively in many different sectors, from power generation and distribution, through to automotive and electronics. The recent rises in copper prices - and predicted long-term rises - are a significant problem for manufacturers using this metal, and the situation could well be compounded by copper inventories falling to their lowest levels on record. Users are therefore seeking ways to remain productive, competitive and profitable in such difficult times (Fig.1).

Cold forming can deliver significant benefits to manufacturers using high volumes of copper for precision parts, especially when mill-supplied tellurium copper (CuTe) rods or bars are specified. Although this alloy machines well, the processes that have traditionally been used to create finished parts - such as turning, milling, drilling and grinding - usually generate substantial amounts of waste material with a scrap value substantially lower than the stock price.[Page Break]

Less waste

For example, machining a typical 36g tellurium copper nozzle for plasma or laser welding applications generates 177g of swarf, representing over 80 per cent of the total starting weight. Depending on the prevailing copper price, this could easily equate to well over EUR1 of waste per component.

In contrast, precision cold forming produces minimal waste, often uses oxygen-free copper, and can therefore be much more commercially viable than machining tellurium copper. Indeed, oxygen-free copper is readily available, so prices are extremely competitive - and generally far lower than that of tellurium copper. Moreover, in many applications the components precision cold formed from oxygen-free copper can be superior to machined components thanks to the metal's better electrical and thermal properties. Cold formed components can also benefit from superior mechanical characteristics and a better surface finish. Other valued characteristics of copper, such as its antimicrobial properties and the ease with which it can be recycled, remain unaffected by cold forming.[Page Break]

New process

Dawson Shanahan is a specialist in precision cold forming parts from copper, aluminium and ferrous metals. Recently the company reported that it developed an innovative production process that could revolutionise the way stainless steel parts are made. The process enables high-precision stainless steel parts to be produced quickly, efficiently and with minimal waste.

Until the development of this new process, cold forming was generally restricted to ductile materials such as aluminium, copper and brasses. Cold forming tougher and more brittle alloys such as stainless steel has only been achieved using extremely expensive and often hazardous and/or environmentally unfriendly techniques.

The Dawson Shanahan process for cold forming stainless steel features specialised lubrication and protective coatings, together with enhancements in 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.[Page Break]

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 weighs 4kg 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.

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