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.

Rivet staking and the insertion and forming of wire segments into pre-stampedcarrier parts or strips with punched holes are the most commonly used methodsfor the mechanical attachment of contact materials.

Riveting (or staking) for smaller volumes of assemblies is mostly done onmechanical, pneumatic or magnetically operated presses. For larger volumesthe staking process is integrated into a progressive die for fully automatedassembly. Rivets are fed in the correct orientation through special feedingtracks into the staking station of the tool. To ensure a mechanically secureattachment , the rivet shank must be dimensioned correctly. As a general rule , theshank length of the rivet should be about 1/3 longer than the thickness of thecarrier material.For switch-over contacts part of the rivet shank is formed into the secondaryrivet head. To minimize deformation of the contact blade carriers, especially thinones, this head forming is often performed by orbital riveting.

The insertion and forming of wire segments can be easily integrated into stampand bending multi-slide tooling ''(<xr id="fig:Direct_press_insertion_of_wire_segments"/><!--(Fig. 3.7)''-->). Compared to the use of compositerivets this process uses more precious contact material but for silver basedcontact materials these costs or are often offset by higher and more efficientmanufacturing speeds. For the more brittle Ag/SnO₂ materials however , closeattention must be paid to the danger of crack formation.

Fig. 3<figure id="fig:Direct_press_insertion_of_wire_segments">[[File:Direct press-insertion of wire segments.7jpg|right|thumb|Figure 1: Direct press-insertion of wire segments]]</figure>

Brazing is a thermal process for the metallurgical bonding of metallic materials inwhich a third metal component (brazing alloy or solder) is added. In addition aflux or processing in a protective atmosphere is applied to eliminate oxidation ofthe non-precious carrier. The melting range of the brazing alloy starts at thebeginning of the melting (solidus temperature) all the way to complete liquidphase (liquidus temperature). This range always is below the melting points ofthe two materials to be joined. During the brazing process with solubility of thematerials in each other , diffusion processes are thermally activated by whichelements of the base material diffuse into the brazing alloy and elements of thebraze alloy diffuse into brazing alloy. This increases the bond strength andtherefore the mechanical stability of the brazed joint.

For attachment of contact parts to carrier base materials , only brazing alloys (asopposed to solders) are used. The reason is the higher softening temperatureand melting point as well as higher mechanical strength and electricalconductivity of these alloys. The brazing alloys and fluxes used for electricalcontact attachment are listed in Chapter 4 [[Brazing Alloys and Fluxes|Brazing Alloys and Fluxes ]] in more detail. Following the mostfrequently used brazing methods are described.References to the bond quality are given according to the test methodsdescribed 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 aburning gas and air or oxygen containing gas mixes. For higher productionvolumes , partial automation is applied. The parts to be assembled aretransported after adding the suitable amounts of brazing alloy and flux through aseries 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 movethe contact tips back and forth and back (also known as puddeling) as soon as thebrazing alloy is liquefied. The bonded area achieved in torch brazing is typically65 – 90% of the contact foot print , depending on the size and geometry of thecontact tip.

Furnace brazing is usually defined as brazing in a protective atmosphere or invacuum. Both processes do not require the use of fluxes.

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

A vacuum is a very efficient protective environment for brazing but using vacuumfurnaces is more complicated and rather inefficient. Therefore this process isonly used for materials and assemblies that are sensitive to oxygen, nitrogen, orhydrogen impurities. Not suitable for vacuum brazing are materials whichcontain components with a high vapor pressure.

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

In this process , the resistive heating under electric currents is the source ofthermal energy. For contact applications two methods are used for resistancebrazing''(<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>

During Direct Resistance Brazing the electric current flows straight through thejoint area composed of the contact tip, brazing alloy, flux, and the contactcarrier. These components are secured between the electrodes of a resistancebrazing machine and heated by an electrical current until the brazing alloyliquefies.

In Indirect Resistance Brazing the current flows only through one of thecomponents to be joined (usually the non-precious contact carrier). Thisprocess allows to move the contact tip (“puddeling”"puddeling") when the brazing alloy is inits liquid stage and this way additionally remove residue bubbles from the heated and boilingflux 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 jointarea > 100 mm². For contacts contact tips with a bottom area < 100 mm² which arealready coated with a phosphorous containing brazing alloy , the heating time canbe reduced to a degree that the softening of the contact carrier occurs only veryclosely to the joint area. For this “short"short-time brazing” brazing" specially designed metalelectrodes with compositions selected for the specific assembly componentpairings are used.

The bond quality for normal resistance brazing with the application of flux rangesfrom 70 to 90% of contact size, for short-time welding these values can beexceeded significantly.

Fig====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. 3Typical bond qualities of > 80% can be reached with this method, also for larger contact assemblies.8The widely varying working times needed for the different brazing methods, are given in <xr id="tab: Resistance brazing Brazing Times for Different Brazing Methods"/><!--(schematicTable 3.1)-->.

<figtable id====Induction "tab:Brazing Times for Different Brazing====During induction brazing the heat energy is produced by an induction coil fed bya medium or high frequency generator. This creates an electromagnetic alternatingfield in the braze joint components which in turn generated eddy currentsin the work piece. Because of the skin–effect these currents and their resultingheat are created mainly on the surface of the assembly components. Thedistance of the inductor must be chosen in a way that the working temperatureMethods">is generated almost simultaneously in the full joint area. For different contactshapes the geometry of the induction coil can be optimized to obtain shortworking cycles. One of the advantages of this method is the short heating timewhich limits the softening of the material components to be joined.Typical bond qualities of <caption> 80% can be reached with this method also for largercontact assemblies'''<!--Tab. The widely varying working times needed for the differentbrazing methods are given in Table 3.1.:-->Brazing Times for Different Brazing Methods'''</caption>

Table {| class="twocolortable" style="text-align: left; font-size: 12px"|-!Brazing method !Brazing time in s (seconds)|-|Torch brazing|3 - 100|-|Direct resistance brazing|1 - 3|-|Indirect resistance brazing|1 - 5|-|Short time brazing (weld-brazing)|0.1: Brazing Times for Different Brazing Methods- 1|-|Induction brazing|0.5 - 5|-|Furnace brazing|100 - 1000|}</figtable>

*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 hasgained some application more recently. Friction welding is mainly used forbonding (see Chapter 9)[[Applications for Bonding Technologies|Applications for Bonding Technologies. ]] Other welding methods such as ball (spheres) weldingand ultrasonic welding are today used in only limited volume and therefore notcovered in detail here.Special methods such as electron beam welding and cast-on attachment ofcontact materials to carrier components are mainly used for contact assembliesfor 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 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 formthrough a clamp , which at the same time acts as one of the weld electrodes''(<xr id="fig:Vertical wire welding (schematic)"/>)<!--(Fig. 3.9)''. With one or more weld pulses the roof shaped wire end – from theprevious cut-off operation – is welded to the base material strip while exertingpressure by the clamp-electrode>. Under optimum weld conditions the weldedarea can reach up to 120% of the original cross-sectional area of the contact<figure id="fig:Vertical wire welding (schematic)">[[File:Vertical wire. After welding the wire is cut off by wedge shaped knives forming again aroof shaped weld projection(schematic). The welded jpg|right|thumb|Figure 5: Vertical wire segment is subsequently formedinto the desired contact shape by stamping or orbital forming. This welding(schematic)]]process can easily be integrated into automated production lines. The contactmaterial must however be directly weldable, meaning that it cannot containgraphite or metal oxides.</figure>

FigWith 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. 3After welding the wire is cut off by wedge shaped knives, forming again a roof shaped weld projection.9: 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.

===== Horizontal Wire or Profile Welding=====During horizontal welding the wire or profile contact material is fed at a shallowangle to the carrier strip material ''(Fig. 3.10)''. The cut*Contact materials <br />Ag, Ag-Alloys, Au-off from the wire or profileis performed either directly by the electrode or in a separate cutting station. Thishorizontal feeding is suitable for welding single or multiple layer weld profiles.The profile construction allows to custom tailor the contact layer shape andthickness to the electrical load and required number of electrical switchingoperations. By choosing a twoPd-layer contact configuration multiple switchingduty ranges can be satisfied. The following triple-layer profile is a good examplefor such a development: The top 5.0 μm AuAg8 layer is suitable to switch drycircuit electronic signalsAlloys, the second or middle layer of 100 μm Ag/Ni 90<br /10 isused to switch relative high electrical loads and the bottom layer consists of aneasily weldable alloy such as CuNi44 or CuNi9Sn2. The configuration of thebottom weld projections, i.e. size, shape, and number of welding nibs or weldrails are critically important for the final weld quality.>

Because of high production speeds (approx*Carrier materials <br />Cu, Cu-Alloys, Cu clad Steel, et. 700 welds per min) and thepossibility to closely match the amount of precious contact material to therequired need for specific switching applications, this joining process hasgained great economical importanceal.<br />

Fig*Dimensions (<xr id="fig:Vertical Wire Welding Dimensions"/>)<figure id="fig:Vertical Wire Welding Dimensions"> [[File:Vertical Wire Welding Dimensions. 3jpg|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.10: Horizontal profile cut-off welding (schematic)

Tip ===== Horizontal Wire or Profile Welding=====During horizontal welding the wire or profile contact material is also used for fed at a shallow angle to the attachment of weld buttons carrier strip material (<xr id="fig:Horizontal profile cut-off welding (schematic)"/>)<!--(see chapter Fig. 3.110)-->.3<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 welding cut-off from the wire or profile is performed mostly semi either directly by the electrode or fully automated with 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 buttonsoriented 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 specific way 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 fed into a number of welding station by suitably designedfeeding mechanismsnibs or weld rails are critically important for the final weld quality.

==== Percussion Welding====This process Because 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 ''production speed (Fig. 3approx.11700 welds per min)''. The electric arcproduces a molten layer of metallic material in the interface zone of the contacttip and carrier. Immediately afterwards the two components are pushed togetherwith substantial impact and speed causing the liquid metal possibility to form a strong jointacross closely match the whole interface area.Because amount of the very short duration of the whole melt and bonding process precious contact material to thetwo components, contact tip and carrierrequired need for specific switching applications, 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 this joining process is mainly applied in the production of rodassemblies for high voltage switchgearhas gained great economical importance.

====Laser Welding====This contact attachment process is also one *Carrier materials <br />(weldable backing of the liquid phase weldingmethods. Solid phase lasers are predominantly used for welding and brazing.The exact guiding and focusing of the laser beam from the source to the jointlocation is most important to ensure the most efficient energy absorption in thejoint where the light energy is converted to heat. Advantages of the method arethe touchmulti-less energy transport which avoids any possible contamination ofcontact surfaceslayer profiles) Ni, CuNi, CuNiFe, CuNiZn, CuSn, the very well defined weld effected zoneCuNiSn, the exactpositioning of the weld spot and the precise control of weld energyothers.<br />

*Dimensions (<xr id="fig:Horizontal Wire Welding Dimensions"/>)<figure id=== Special "fig:Horizontal Wire Welding and Attachment Processes====Dimensions"> In high voltage switchgear the contact parts are exposed to high mechanicaland thermal stresses[[File:Horizontal Wire Welding Dimensions. This requires mechanically strong and 100%metallurgically bonded joints between the contacts and their carrier supportsjpg|right|thumb|Figure 8: Dimensions]]which cannot be achieved by the traditional attachment methods. The twoprocesses of electron beam welding and the cast-on with copper can howeverused to solve this problem.</figure>

===== Electron Beam Welding=====*Quality criteriaThe 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 Functional quality criteria such as bonded area percentage or shear force are usually agreed upon between the mostly thicker parts supplier and user 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 Cu/W contacts to hardand thermally stable copper alloys as for example CuCrZr for spring hardcontact tulips ''(Fig. 3.12)''delivery specifications.

Fig. 3.12:=====Tip Welding=====Examples 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 tulips parts such as Ag/C or Ag/W tips with Cugood 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/Wcontacts electron beam welded). These welding aids can also be formed on the carrier parts. Larger contact tips usually have an additional brazing alloy layer bonded to CuCrZr carriersthe bottom weld surface.

===== Cast-On Tip welding is also used for the attachment of Copper=====weld buttons (see [[Manufacturing of Single Contact Parts#Weld Buttons|Weld Buttons]]). The cast-on of liquid copper to pre-fabricated W/Cu contact parts welding is performedin special casting molds. This results in mostly semi or fully automated with the buttons oriented a seamless joint between the W/Cu specific way andthe copper carrier. The hardness of the copper is then increased fed into a welding station by asecondary forming or deep-drawing operationsuitably designed feeding mechanisms.

*Examples ==== Percussion Welding====This process of Wire Weldinghigh 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.bildBecause 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 Carrier materials <br />AgCu, AgCu-Alloys, Au- and Pd-Alloys, Ag/Ni (SINIDUR)others<br />

*Carrier materials Dimensions <br />Cu, Cu-Alloys, Cu clad Steel, et.alWeld surface area (flat) 6.0 to 25 mm diameter <br />Rectangular areas with up to 25 mm diagonals<br />

*DimensionsbildFunctional Quality criteria <br />Test methods for bond quality criteria such as bonded area percentage or shear force areusually agreed upon between the supplier and user and defined in delivery<br /> (<xr id="fig:Examples for percussion welded contact parts"/>)<!--(Fig. 3.13)--><figure id="fig:Examples for percussion welded contact parts">specifications[[File:Examples for percussion welded contact parts.jpg|right|thumb|Figure 10: Examples for percussion welded contact parts]]</figure>

===Horizontal 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 />Au-Alloys, Pd-Alloys, Ag-Alloys, Ag/Ni (SINIDUR), Ag/CdO (DODURIT CdO), Ag/SnO₂ (SISTADOX), Ag/ZnO (DODURIT ZnO). To avoid any defects in the contact portion, the welding is usually performed through the carrier material. Using a higher powered laser and Ag/C (GRAPHOR D)<br />beam splitting allows a high production speed with weld joints created at multiple spots at the same time.

*Carrier materials <br />(weldable backing ==== 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 multielectron beam welding and the cast-layer profiles) Ni, CuNion with copper can, CuNiFehowever, CuNiZn, CuSn, CuNiSn, and othersbe used to solve this problem.<br />

*Braze alloy layer ===== 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 (<br xr id="fig:Contact tulips with CuW welded to CuCrZr carriers"/>L<!--Ag 15P (CP 102 or BCUPFig. 3.12)-5->).<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]]<br /figure>

*Dimensionsbild *Quality criteriaFunctional quality criteria such as bonded area percentage or shear force areusually agreed upon between the supplier and user and defined in deliveryspecifications. ===Percussion Welding== Cast-On of Copper===== *Contact materials <br />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/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]]