EuroWire January 2015

News Technology

Effective welding with cold pressure

The design of the dies is crucial – they must hold the material firmly to avoid slippage. To improve the grip, the inside of the cavity is either etched with an electric pencil, or, when the die is to be used for joining large pieces of aluminium, grip marks are put in the cavity before the die is heat treated. The gap between the two faces or noses of the die is particularly important. If it is too large, the material will just collapse or bend away. This dimension is carefully calculated during die manufacture and cannot be changed. Lastly, there is the offset of the die noses. This has the effect of making the weld look out of line around the circumference of the material. The purpose of the offset is to break the weld flash or burr (spare material containing impurities which is pushed out from the core of the weld) into two halves to allow it to be removed easily. PWM (PressureWelding Machines) Ltd – UK Website : www.pwmltd.co.uk

Cold pressure welding offers wire and cable manufacturers a quick and cost-effective method of permanently joining non-ferrous materials and their alloys without heat, flux or fillers. The process offers many benefits: it produces permanent welds stronger than the parent material, while the electrical integrity of the material is not affected. It can be used to join strip and profile as well as round wire; even dissimilar materials and materials of two different sizes can be cold-welded. Because cold welding takes place at ambient temperatures, no thermal changes occur in the material being welded, so there is no splattering or waste, and no risk of the operator being burned. Welding with cold pressure is also simple and inexpensive. Fine wire can be joined in seconds using small, manually operated cold welders. Powered machines are required to weld larger wire and rod sizes, but use considerably less power and take much less time than electrical butt welders.

▲ ▲ The EP500 rod welder from PWM

The cold weld process employs a ‘multi-upset’ technique, whereby the two ends of the material are gripped and forced together under high pressure. Each time the cold welding machine is activated, the material is gripped by the die and fed forward. As the two ends of the material are pushed against each other, they are stretched and enlarged over their entire surface area. Oxides and other surface impurities are forced out and a bond is formed. A minimum of four upsets is recommended to ensure all impurities are squeezed out of the interfaces.

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January 2015