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[[File:Examples of brazed contact assemblies.jpg|right|thumb|Figure 3: Examples of brazed contact assemblies]]
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*Contact materials <br />Ag, Ag-Alloys., Ag/Ni (SINIDUR), Ag/CdO (DODURIT CdO), Ag/SnO<sub>2</sub> (SISTADOX), Ag/ZnO (DODURIT ZnO) and Ag/C (GRAPHOR D) with brazable backing, refractory materials on W -, WC- and Mo-basis<br />
*Brazing alloys <br />L-Ag 15P, L-Ag 55Sn et.al.<br />
With one or more weld pulses the roof shaped wire end – from the previous cut-off operation – is welded to the base material strip while exerting pressure by the clamp-electrode. Under optimum weld conditions the welded area can reach up to 120% of the original cross-sectional area of the contact wire. After welding the wire is cut off by wedge shaped knives, forming again a roof shaped weld projection. The welded wire segment is subsequently formed into the desired contact shape by stamping or orbital forming. This welding process can easily be integrated into automated production lines. The contact material must however be directly weldable, meaning that it cannot contain graphite or metal oxides.
*Contact materials <br />Ag, Ag-Alloys, Au- and Pd-Alloys, Ag/Ni (SINIDUR)<br />
*Carrier materials <br />Cu, Cu-Alloys, Cu clad Steel, et.al.<br />
required need for specific switching applications, this joining process has gained great economical importance.
*Contact materials <br />Au-Alloys, Pd-Alloys, Ag-Alloys, Ag/Ni (SINIDUR), Ag/CdO (DODURIT CdO), Ag/SnO<sub>2</sub> (SISTADOX), Ag/ZnO (DODURIT ZnO), and Ag/C (GRAPHOR D)<br />
*Carrier materials <br />(weldable backing of multi-layer profiles) Ni, CuNi, CuNiFe, CuNiZn, CuSn, CuNiSn, and others.<br />
The exact guiding and focusing of the laser beam from the source to the joint location is highly important to ensure the most efficient energy absorption in the joint, where the light energy is converted to heat. Advantages of this method are the touch-less energy transport, which avoids any possible contamination of contact surfaces, the very well defined weld effected zone, the exact positioning of the weld spot and the precise control of weld energy.
Laser welding is mostly applied for rather small contact parts to thin carrier materials. To avoid any defects in the contact portion, the welding is usually performed through the carrier material. Using a higher powered laser and beam splitting, allows a high production speed with weld joints created at multiple spots at the same time.
==== Special Welding and Attachment Processes====
In high voltage switchgear, the contact parts are exposed to high mechanical and thermal stresses. This requires mechanically strong and 100% metallurgically bonded joints between the contacts and their carrier supports, which cannot be achieved by the traditional attachment methods. The two processes of electron beam welding and the cast-on with coppercan, can however , be used to solve this problem.
===== Electron Beam Welding=====
The electron beam welding is a joining process which has shown its suitability for high voltage contact assemblies. A sharply focused electron beam has sufficient energy to penetrate the mostly thicker parts and generate a locally defined molten area so that the carrier component is only softened in a narrow zone (1 – 4 mm). This allows the attachment of Cu/W contacts and also hard and thermally stable copper alloys as for example CuCrZr for spring hard contact tulips (<xr id="fig:Contact tulips with CuW welded to CuCrZr carriers"/><!--(Fig. 3.12)-->).
<figure id="fig:Contact tulips with CuW welded to CuCrZr carriers">
[[File:Contact tulips with CuW welded to CuCrZr carriers.jpg|right|thumb|Figure 11: Contact tulips with CuW welded to CuCrZr carriers]]
===== Cast-On of Copper=====
The cast-on of liquid copper to pre-fabricated W/Cu contact parts is performed in special casting molds. This results in a seamless joint between the W/Cu and the copper carrier. The hardness of the copper is then increased by a secondary forming or deep-drawing operation.
==References==
