The following segments give an overview of the usually applied attachmenttechnologies for contact parts to carrier components. They include mechanicalas well as brazing and welding methods used for electrical contact assemblies.

the staking process is integrated into a progressive die for fully automated assembly. Rivets are fed in the correct orientation through special feeding tracks into the staking station of the tool. To ensure a mechanically secure attachment , the rivet shank must be dimensioned correctly. As a general rule , the shank length of the rivet should be about 1/3 longer than the thickness of the carrier material.

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 or are often offset by higher and more efficient manufacturing speeds. For the more brittle Ag/SnO₂ materials however , close attention must be paid to the danger of crack formation.

Fig. 3.7<figure id="fig: Direct press-insertion of wire segmentsDirect_press_insertion_of_wire_segments">[[File:Direct press-insertion of wire segments.jpg|right|thumb|Figure 1: Direct press-insertion of wire segments]]</figure>

materials in each other , diffusion processes are thermally activated by which elements of the base material diffuse into the brazing alloy and elements of the braze alloy diffuse into brazing alloy. This increases the bond strength and therefore the mechanical stability of the brazed joint.

For attachment of contact parts to carrier base materials , only brazing alloys (as opposed to solders) are used. The reason is the higher softening temperature and melting point as well as higher mechanical strength and electrical conductivity of these alloys. The brazing alloys and fluxes used for electrical contact attachment are listed in Chapter 4 [[Brazing Alloys and Fluxes|Brazing Alloys and Fluxes ]] in more detail. Following the most frequently used brazing methods are described.References to the bond quality are given according to the test methods described in Chapter 3.4.[[Evaluation_of_Braze_or_Weld_Joints|Evaluation of Braze or Weld Joints ]]

The simplest easiest way to produce braze joints , is the use of a gas torch fueled by a burning gas and air or oxygen containing gas mixes. For higher production volumes , partial automation is applied. The parts to be assembled are transported after adding the suitable amounts of brazing alloy and flux through a series of fixed gas burners on a turntable or belt driven brazing machine. To limit the amount of flux or gas inclusions , it is recommended to slightly move the contact tips back and forth and back (also known as puddeling) as soon as the brazing alloy is liquefied. The bonded area achieved in torch brazing is typically 65 – 90% of the contact foot print , depending on the size and geometry of the contact tip.

The protective atmosphere brazing is conducted in batch operation in either muffle or pot furnaces or as a continuous process in belt furnaces , using a reducing atmosphere of pure hydrogen (H₂) or dissociated ammonia (H₂,N₂).

Parts with oxygen containing copper supports should not be brazed in reducing atmosphere atmospheres because of their susceptibility to hydrogen embrittlement. Similarly contact tips containing silver–metal oxide should not be exposed to protective atmospheres because a reduction of the metal oxide , even in a thin contact surface layer changes the contact properties of these materialschange.

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>

[[File:Resistance brazing (schematic).jpg|right|thumb|Resistance brazing (schematic)]] During Direct Resistance Brazing the electric current flows straight through the joint area composed of the contact tip, brazing alloy, flux, and the contact carrier. These components are secured between the electrodes of a resistance brazing machine and heated by an electrical current until the brazing alloy liquefies.

process allows to move the contact tip (“puddeling”"puddeling") when the brazing alloy is in its liquid stage and this way 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 />

Graphite electrodes are mainly used for indirect resistance brazing and for joint area > 100 mm². For contacts contact tips with a bottom area < 100 mm² which are already coated with a phosphorous containing brazing alloy , the heating time can be reduced to a degree that the softening of the contact carrier occurs only very closely to the joint area. For this “short"short-time brazing” brazing" specially designed metal electrodes with compositions selected for the specific assembly component pairings are used.

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 generated 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 largercontact assemblies. The widely varying working times needed for the different brazing methods , are given in Table 3.1. Table 3.1<xr id="tab: Brazing Times for Different Brazing Methods"/><!--(Table 3.1)-->.

[[File<figtable id="tab:Brazing Times for Different Brazing Methods"><caption>'''<!--Tab.jpg|right|thumb|3.1:-->Brazing Times for Different Brazing Methods]]'''</caption>

*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/SnO₂ (SISTADOX), Ag/ZnO (DODURIT ZnO) and Ag/C (GRAPHOR D) with brazable backing, refractory materials on W -, WC- and Mo-basis<br />

Welding of contact assemblies has both technological and economicimportance. Because of the short heating times during welding , the carriermaterials retain their hardness except for a very small heat affected area. Of themethods described below, resistance welding is the most widely utilizedprocess. 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.processSpecial 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.

Because *Examples of miniaturization Wire Welding (<xr id="fig:Examples of electromechanical components laser welding hasgained some application more recently. Friction welding is mainly used forbonding (see Chapter 9Wire Welding"/>). Other welding methods such as ball (spheres) weldingand ultrasonic welding are today used in only limited volume and therefore not<figure id="fig:Examples of Wire Welding">covered in detail here[[File:Examples of Wire Welding.Special methods such as electron beam welding and cast-on attachment jpg|right|thumb|Figure 4: Examples ofWire Welding]]contact materials to carrier components are mainly used for contact assembliesfor medium and high voltage switchgear.</figure>

Resistance welding is the process of electrically joining work pieces by creatingthe required welding energy through current flow directly through thecomponents without additional intermediate materials. For contact applicationsthe most frequently used method is that of projection welding. Differentlyshaped weld projections are used on one of the two components to be joined(usually the contact). They reduce the area in which the two touch , creating ahigh electrical resistance and high current density which heats the constrictionarea to the melting point of the projections. Simultaneously exerted pressurefrom the electrodes further spreads out the liquefied metal over the weld jointsarea. The welding current and electrode force are controlling parameters for theresulting weld joint quality. The electrodes themselves are carefully designedand selected for material composition to best suit the weld requirements.

The waveform of the weld current has a significant influence on the weld quality.Besides 50 or 60 Hz AC current with phase angle control, also DC (6-phasefrom 3-phase rectified AC) and medium frequency (MF) weld generators areused for contact welding. In the latter the regular AC supply voltage is firstrectified and then supplied back through a controlled DC/AC inverter as pulsedDC fed to a weld transformer. Medium frequency welding equipment usuallyworks at frequencies between 1kHz to 10kHz. The critical parameters ofcurrent, voltage, and weld energy are electronically monitored and allow , throughclosed loop controls , to monitor and adjust the weld quality continuously. Thevery short welding times needed with these MF welding machines , result in verylimited thermal stresses on the base material and also allow the reliable joiningof otherwise difficult material combinations.

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>

[[File:Vertical 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 (schematic)the wire is cut off by wedge shaped knives, forming again a roof shaped weld projection.jpg|right|thumb|Vertical The welded wire segment is subsequently formed into the desired contact shape by stamping or orbital forming. This welding (schematic)]]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.

With one or more weld pulses the roof shaped wire end – from the previous cut*Contact materials <br />Ag, Ag-off operation – is welded to the base material strip while exerting pressure by the clampAlloys, Au-electrode. Under optimum weld conditions the welded area can reach up to 120% of the original crossand Pd-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 weldableAlloys, meaning that it cannot contain graphite or metal oxides.Ag/Ni <br />

Fig*Carrier materials <br />Cu, Cu-Alloys, Cu clad Steel, et. 3al.9: Vertical wire welding (schematic)<br />

*Dimensions (<xr id="fig:Vertical Wire Welding Dimensions"/>)<figure id==== Horizontal "fig:Vertical Wire Welding Dimensions"> [[File:Vertical Wire Welding Dimensions.jpg|right|thumb|Figure 6: Vertical Wire or Profile Welding=====Dimensions]]</figure>During horizontal welding the wire Functional quality criteria such as bonded area percentage or profile contact material is fed at a shallow angle to shear force are usually agreed upon between the carrier strip material ''(Fig. 3.10)''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 speeds speed (approx. 700 welds per min) and the possibility to closely match the amount of precious contact material to the

Fig. 3.10: Horizontal profile cut*Contact materials <br />Au-off welding (schematic)Alloys, Pd-Alloys, Ag-Alloys, Ag/Ni, Ag/CdO, Ag/SnO₂, Ag/ZnO, and Ag/C<br />

=====Tip Welding=====Contact tips or formed contact parts produced by processes as described inchapter 3.1.2 are mainly attached by tip welding to their respective contactsupports. In this process smaller contact parts such as Ag*Carrier materials <br /C or Ag/W tips withgood >(weldable backings are welded directly to the carrier parts. To improve thewelding process and quality the bottom side backing of these tips may have serrations(Ag/Cmulti-layer profiles) or shaped projections (AgNi, CuNi, CuNiFe, CuNiZn, CuSn, CuNiSn, and others.<br /W). These welding aids can also be formed onthe carrier parts. Larger contact tips usually have an additional brazing alloylayer bonded to the bottom weld surface.>

Tip welding is also used for the attachment of weld buttons *Braze alloy layer <br />L-Ag 15P (see chapter 3.1.3CP 102 or BCUP-5).The welding is performed mostly semi or fully automated with the buttonsoriented a specific way and fed into a welding station by suitably designedfeeding mechanisms.<br />

*Dimensions (<xr id==== Percussion "fig:Horizontal Wire Welding====This process of high current arc discharge welding required the contact materialand carrier to have two flat surfaces with one having a protruding nib. This nibacts as the igniter point for the high current arc ''(Fig. 3.11Dimensions"/>)''. The electric arcproduces a molten layer of metallic material in the interface zone of the contact<figure id="fig:Horizontal Wire Welding Dimensions"> tip and carrier. Immediately afterwards the two components are pushed togetherwith substantial impact and speed causing the liquid metal to form a strong jointacross the whole interface area[[File:Horizontal Wire Welding Dimensions.jpg|right|thumb|Figure 8: Dimensions]]Because of the very short duration of the whole melt and bonding process thetwo components, contact tip and carrier, retain their mechanical hardness andstrength almost completely except for the immediate thin joint area. Theunavoidable weld splatter around the periphery of the joint must bemechanically removed in a secondary operation.The percussion welding process is mainly applied in the production of rodassemblies for high voltage switchgear.</figure>

Fig*Quality criteriaFunctional quality criteria such as bonded area percentage or shear force are usually agreed upon between the supplier and user and defined in delivery specifications. 3.11: Percussion welding (schematic)

====Laser =Tip Welding=====This Contact tips or formed contact attachment process is also one parts produced by processes as described in [[Manufacturing of the liquid phase Single Contact Parts#Contact Tips|Contact Tips ]] are mainly attached by tip weldingmethodsto their respective contact supports. Solid phase lasers In this process smaller contact parts such as Ag/C or Ag/W tips with good weldable backings are predominantly used for welding and brazing.The exact guiding and focusing of the laser beam from the source welded directly to the jointlocation is most important to ensure the most efficient energy absorption in thejoint where the light energy is converted to heatcarrier parts. Advantages of To improve the method arethe touch-less energy transport which avoids any possible contamination ofcontact surfaces, the very well defined weld effected zonewelding process and quality, the exactpositioning bottom side of these tips may have serrations (Ag/C) or shaped projections (Ag/W). These welding aids can also be formed on the weld spot and carrier parts. Larger contact tips usually have an additional brazing alloy layer bonded to the precise control of bottom weld energysurface.

Laser Tip welding is mostly applied also used for rather small contact parts to thin carriermaterialsthe attachment of weld buttons (see [[Manufacturing of Single Contact Parts#Weld Buttons|Weld Buttons]]). To avoid any defects in the contact portion, the The welding is usuallyperformed through mostly semi or fully automated with the carrier material. Using buttons oriented a higher power laser specific way and beamsplitting allows high production speeds with weld joints created at multiplespots at the same timefed into a welding station by suitably designed feeding mechanisms.

==== Special Percussion Welding and Attachment Processes====In This process of high voltage switchgear current arc discharge welding requires the contact parts are exposed material and carrier to have two flat surfaces with one having a protruding nib. This nib acts as the ignition point for the high mechanicalcurrent 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 thermal stressescarrier. This requires mechanically 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 100%metallurgically bonded joints between bonding process, the contacts two components, contact tip and carrier, retain their carrier supportswhich cannot be achieved by mechanical hardness and strength almost completely, except for the traditional attachment methodsimmediate thin joint area. The twoprocesses unavoidable weld splatter around the periphery of electron beam the joint must be mechanically removed in a secondary operation. The percussion welding and process is mainly applied in the cast-on with copper can howeverused to solve this problemproduction of rod assemblies for high voltage switchgear.

===== Electron Beam Welding=====The electron beam welding is a joining process which has shown its suitabilityfor high voltage contact assemblies. A sharply focused electron beam hassufficient energy to penetrate the mostly thicker parts and generate a locallydefined molten area so that the carrier component is only softened in a narrowzone (1 – 4 mm). This allows the attachment of *Contact materials <br />W/Cu, W/W contacts to hardand thermally stable copper alloys as for example CuCrZr for spring hardcontact tulips ''(Fig. 3.12)''.Ag, others<br />

Fig. 3.12:Examples of contact tulips with *Carrier materials <br />Cu, Cu-Alloys, others<br /Wcontacts electron beam weldedto CuCrZr carriers.>

===== Cast-On of Copper=====The cast-on of liquid copper *Dimensions <br />Weld surface area (flat) 6.0 to pre-fabricated W25 mm diameter <br /Cu contact parts is performedin special casting molds. This results in a seamless joint between the W>Rectangular areas with up to 25 mm diagonals<br /Cu andthe copper carrier. The hardness of the copper is then increased by asecondary forming or deep-drawing operation.>

*Quality criteria <br />Test methods for bond quality are agreed upon between supplier and user<br /> (<xr id="fig:Examples of Wire Weldingfor percussion welded contact parts"/>)<!--(Fig. 3.13)-->bild<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>

'''Vertical Wire ====Laser Welding'''====This contact attachment process is also one of the liquid phase welding methods. Solid phase lasers are predominantly used for welding and brazing.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.

*Contact Laser welding is mostly applied for rather small contact parts to thin carrier materials <br />Ag. To avoid any defects in the contact portion, Ag-Alloys, Au- the welding is usually performed through the carrier material. Using a higher powered laser and Pd-Alloys, Ag/Ni (SINIDUR)<br />beam splitting allows a high production speed with weld joints created at multiple spots at the same time.

*Carrier materials <br />Cu==== Special Welding and Attachment Processes====In high voltage switchgear, Cuthe 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-Alloyson with copper can, Cu clad Steelhowever, et.albe used to solve this problem.<br />

*Dimensions===== Electron Beam Welding=====bildFunctional quality criteria such as bonded 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 percentage or shear force areusually agreed upon between so that the carrier component is only softened in a narrow zone (1 – 4 mm). This allows the supplier attachment of Cu/W contacts and user also hard and defined in deliverythermally 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">specifications[[File:Contact tulips with CuW welded to CuCrZr carriers.jpg|right|thumb|Figure 11: Contact tulips with CuW welded to CuCrZr carriers]]</figure>

'''Horizontal Wire Welding''' *Contact materials <br />Au-Alloys, Pd===== Cast-Alloys, Ag-Alloys, Ag/Ni (SINIDUR), Ag/CdO (DODURIT CdO), Ag/SnO₂ (SISTADOX), Ag/ZnO (DODURIT ZnO), and Ag/C (GRAPHOR D)<br /> *Carrier materials <br />(weldable backing On of multi-layer profiles) Ni, CuNi, CuNiFe, CuNiZn, CuSn, CuNiSn, and others.<br />Copper===== *Braze alloy layer <br />LThe cast-Ag 15P (CP 102 or BCUPon of liquid copper to pre-5)<br fabricated W/> *Dimensionsbild *Quality criteriaFunctional quality criteria such as bonded area percentage or shear force areusually agreed upon Cu contact parts is performed in special casting molds. This results in a seamless joint between the supplier and user and defined in deliveryspecifications. '''Percussion Welding''' *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 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 /> Figthe copper carrier. 3The hardness of the copper is then increased by a secondary forming or deep-drawing operation.13: Examples for percussion welded contact parts[[Category:Manufacturing Technologies for Contact Parts|Category]]