Spring 2016 (Issue No. 30) Contents:

1. Welding of Ni Plated Components

2.Upset Welding

3. Breaking In

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Welding of Ni Plated Components

Ni plated components are commonly used in industry and often have to be welded as part of the assembly process. Challenges associated with welding are discussed in the pdf document which can be downloaded by clicking on the link below.

Welding Ni Plated Components (pdf)

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Upset Welding

Upset welding is one of those processes whose name can adequately describe the process as well the emotional state of the user under vexing circumstances. Upset welding a variant of resistance welding which is used to make a butt joint. Parts to be welded are held in grippers and pushed against each other while the required welding current flows through the parts and the weld interface. Resistive heating softens a narrow region of metal volume on either side of the interface. At the appropriate time, the force is increased to upset the joint which pushes the softened material out of the joint; this action helps to push out any oxides and impurities at the weld and allows clean parent metal on both sides to come in intimate contact. After the required upset action has taken place, the welding current is turned off and the weld is allowed to cool under action of the upset force.

Upset welding is commonly used in wire and bar mills to joint wire coils and bars to facilitate continuous processing. The upsetting action does pushout some of the metal which is then removed by grinding and leaves a joint that is often indistinguishable from the original parts. The welds can be made strong and ductile enough to pass through subsequent rolling and forming operations. One of the most challenging applications of upset welding, and possibly all of resistance welding, is upset welding of metallic tubes to form hermetic seals for aerospace o-rings. In this application a tube of suitable alloy is cut to length, and rolled to form a ring; tube diameters are of the order of 1/8 inch (3 mm). The two ends of the ring are held in grippers and upset welded to form a ring; excess flash is removed by grinding. A common method for testing upset welds is the bend test where the sample is bent at the weld and the weld joint is expected to withstand a full bend without failure.

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Breaking In

Resistance welding is one of the few material joining processes where the welding tip comes in direct contact with the work piece. Consequently, tip shape, surface smoothness, and cleanliness are important factors that can affect weld quality. Even with a carefully machined tip, a brand new tip can take a few welds to break-in where the tip conforms to the parts being welded. Breaking in a tip is difficult to do offline and is best done on the machine with actual parts or simulated parts that are practically identical. During the break-in process, the tip conforms to the part surface, smoothens tip surface asperities, and in some cases also transfers a small amount of material from the part being welding to the tip surface. After break-in, the tip can produce consistent weld quality over its lifetime, after which it has to be redressed or replaced. Break-in can be a couple of welds when using copper electrodes or can be up to 100 welds with tungsten electrodes. Life of the tip after break-in depends on the application (materials, welding frequency, and tip cooling) and has to be established by testing.

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