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<figure id="fig:Direct_press_insertion_of_wire_segments">
[[File:Direct press-insertion of wire segments.jpg|right|thumb|Figure 1: Direct press-insertion of wire segments]]
</figure>
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)]]
</figure>
process allows to move the contact tip ("puddeling") when the brazing alloy is in its liquid stage and additionally remove residue bubbles from the heated and boiling flux and increase the percentage of the bonded area. Two different kinds of electrodes are used for resistance brazing:
*Electrodes from poorly conducting carbon containing materials (graphite)<br />The heat is created in the electrodes and thermally conducted into the joint area<br />
*Electrodes from higher conductive and thermally stable metallic materials<br />The heat is created by the higher resistance in the joint area which, through selected designs, creates a constriction area for the electrical current in addition to the resistance of the components to be joined.<br />
*Examples of brazed contact assemblies <xr id="fig:Examples of brazed contact assemblies"/>
<figure id="fig:Examples of brazed contact assemblies">
[[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 />
Because of miniaturization of electromechanical components laser welding has gained some application more recently. Friction welding is mainly used for bonding see [[Applications for Bonding Technologies|Applications for Bonding Technologies.]] Other welding methods such as ball (spheres) welding and ultrasonic welding are today used in only limited volume and therefore not covered in detail here.
Special methods such as electron beam welding and cast-on attachment of contact materials to carrier components are mainly used for contact assemblies for medium and high voltage switchgear.
*Examples of Wire Welding (<xr id="fig:Examples of Wire Welding"/>)
<figure id="fig:Examples of Wire Welding">
[[File:Examples of Wire Welding.jpg|right|thumb|Figure 4: Examples of Wire Welding]]
</figure>
====Resistance Welding====
===== Vertical Wire Welding=====
During vertical wire welding the contact material is vertically fed in wire form through a clamp, which at the same time acts as one of the weld electrodes (<xr id="fig:Vertical wire welding (schematic)"/>)<!--(Fig. 3.9)-->.
<figure id="fig:Vertical wire welding (schematic)">
[[File:Vertical wire welding (schematic).jpg|right|thumb|Figure 5: Vertical wire welding (schematic)]]
</figure>
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 />
*Dimensions (<xr id="fig:Vertical Wire Welding Dimensions"/>)
<figure id="fig:Vertical Wire Welding Dimensions">
[[File:Vertical Wire Welding Dimensions.jpg|right|thumb|Figure 6: Vertical Wire Welding Dimensions]]
</figure>
Functional quality criteria such as bonded area percentage or shear force are usually agreed upon between the supplier and user and defined in delivery specifications.
===== Horizontal Wire or Profile Welding=====
During horizontal welding the wire or profile contact material is fed at a shallow angle to the carrier strip material (<xr id="fig:Horizontal profile cut-off welding (schematic)"/>)<!--(Fig. 3.10)-->.
<figure id="fig:Horizontal profile cut-off welding (schematic)">
[[File:Horizontal profile cut-off welding (schematic).jpg|right|thumb|Figure 7: Horizontal profile cut-off welding (schematic)]]
</figure>
The cut-off from the wire or profile is performed either directly by the electrode or in a separate cutting station. This horizontal feeding is suitable for welding single or multiple layer weld profiles. The profile construction allows to custom tailor the contact layer shape and thickness to the electrical load and required number of electrical switching operations. By choosing a two-layer contact configuration, multiple switching duty ranges can be satisfied. The following triple-layer profile is a good example for such a development: The top 5.0 μm AuAg8 layer is suitable to switch dry circuit electronic signals, the second or middle layer of 100 μm Ag/Ni 90/10 is used to switch relative high electrical loads and the bottom layer consists of an easily weldable alloy such as CuNi44 or CuNi9Sn2. The configuration of the bottom weld projections, i.e. size, shape, and number of welding nibs or weld rails are critically important for the final weld quality.
Because of the high production speed (approx. 700 welds per min) and the possibility to closely match the amount of precious contact material to the
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 />
*Braze alloy layer <br />L-Ag 15P (CP 102 or BCUP-5)<br />
*Dimensions (<xr id="fig:Horizontal Wire Welding Dimensions"/>)
<figure id="fig:Horizontal Wire Welding Dimensions">
[[File:Horizontal Wire Welding Dimensions.jpg|right|thumb|Figure 8: Dimensions]]
</figure>
*Quality criteria
Functional quality criteria such as bonded area percentage or shear force are usually agreed upon between the supplier and user and defined in delivery specifications.
=====Tip 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)]]
</figure>
The electric arc produces a molten layer of metallic material in the interface zone of the contact tip and carrier. Immediately afterwards, the two components are pushed together with substantial impact and speed, causing the liquid metal to form a strong joint across the whole interface area.
Because of the very short duration of the whole melt and bonding process, the two components, contact tip and carrier, retain their mechanical hardness and strength almost completely, except for the immediate thin joint area. The unavoidable weld splatter around the periphery of the joint must be mechanically removed in a secondary operation. The percussion welding process is mainly applied in the production of rod assemblies for high voltage switchgear.
*Contact materials <br />W/Cu, W/Ag, others<br />
*Carrier materials <br />Cu, Cu-Alloys, others<br />
*Dimensions <br />Weld surface area (flat) 6.0 to 25 mm diameter <br />Rectangular areas with up to 25 mm diagonals<br />
*Quality criteria <br />Test methods for bond quality are agreed upon between supplier and user<br /> (<xr id="fig:Examples for percussion welded contact parts"/>)<!--(Fig. 3.13)-->
<figure id="fig:Examples for percussion welded contact parts">
[[File:Examples for percussion welded contact parts.jpg|right|thumb|Figure 10: Examples for percussion welded contact parts]]
</figure>
====Laser 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]]
</figure>
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==
