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For switch-over contacts part of the rivet shank is formed into the secondary rivet head. To minimize deformation of the contact blade carriers, especially thin ones, this head forming is often performed by orbital riveting.
The insertion and forming of wire segments can be easily integrated into stamp and bending multi-slide tooling (<xr id="fig:Direct_press_insertion_of_wire_segments"/><!--(Fig. 3.7)-->). Compared to the use of composite rivets this process uses more precious contact material but for silver based contact materials these costs are often offset by higher and more efficient manufacturing speeds. For the more brittle Ag/SnO<sub>2</sub> materials however, close attention must be paid to the danger of crack formation.
<figure id="fig:Direct_press_insertion_of_wire_segments">
==== Resistance Brazing====
In this process, the resistive heating under electric currents is the source of thermal energy. For contact applications two methods are used for resistance brazing (<xr id="fig:Resistance brazing (schematic)"/><!--(Fig. 3.8)-->).
<figure id="fig:Resistance brazing (schematic)">
[[File:Resistance brazing (schematic).jpg|right|thumb|Figure 2: Resistance brazing (schematic)]]
====Induction Brazing====
During induction brazing the heat energy is produced by an induction coil fed by a medium or high frequency generator. This creates an electromagnetic alternating field in the braze joint components which in turn generate eddy currents in the work piece. Because of the skin–effect, these currents and their resulting heat are created mainly on the surface of the assembly components. The distance of the inductor must be chosen in a way, that the working temperature is generated almost simultaneously in the full joint area. For different contact shapes, the geometry of the induction coil can be optimized to obtain short working cycles. One of the advantages of this method, is the short heating time which limits the softening of the material components to be joined. Typical bond qualities of > 80% can be reached with this method, also for larger contact assemblies. The widely varying working times needed for the different brazing methods, are given in <xr id="tab:Brazing Times for Different Brazing Methods"/><!--(Table 3.1)-->.
<figtable id="tab:Brazing Times for Different Brazing Methods">
[[File:Examples of brazed contact assemblies.jpg|right|thumb|Figure 3: Examples of brazed contact assemblies]]
</figure>
*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 />
=====Tip Welding=====
Contact tips or formed contact parts produced by processes as described in [[Manufacturing of Single Contact Parts#Contact Tips|Contact Tips ]] are mainly attached by tip welding to their respective contact supports. In this process smaller contact parts such as Ag/C or Ag/W tips with good weldable backings are welded directly to the carrier parts. To improve the welding process and quality , the bottom side of these tips may have serrations (Ag/C) or shaped projections (Ag/W). These welding aids can also be formed on the carrier parts. Larger contact tips usually have an additional brazing alloy layer bonded to the bottom weld surface.
Tip welding is also used for the attachment of weld buttons (see [[Manufacturing of Single Contact Parts#Weld Buttons|Weld Buttons]]). The welding is performed mostly semi or fully automated with the buttons oriented a specific way and fed into a welding station by suitably designed feeding mechanisms.
==== Percussion Welding====
This process of high current arc discharge welding requires the contact material and carrier to have two flat surfaces with one having a protruding nib. This nib acts as the ignition point for the high current arc (<xr id="fig:Percussion welding (schematic)"/><!--(Fig. 3.11)-->).
<figure id="fig:Percussion welding (schematic)">
[[File:Percussion welding (schematic).jpg|right|thumb|Figure 9: Percussion welding (schematic)]]
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==