Besides the selection of the most suitable contact materials , the design and typeof attachment is critical for the reliability and electrical life of contactcomponents for electromechanical switching devices. The materials most important factors here are the material-saving useof high cost precious metals and the most economic economical manufacturing method forcontact parts are most important factors..

There are two basic manufacturing solutions available: One can start with singlecontact parts , such as contact rivets or tips , which then are attachedmechanically or by brazing or welding resp. to carrier parts. In the second case, a base material coated or clad with the precious contact metal - for specialapplications also clad with another non-precious material – in the form of stripsor profiles is manufactured as a semi-finished pre-material from which thecontact components are then stamped and formed. Besides mechanicalcladding other processes such as electroplating and deposition from the gasphase are utilized.Which of the following manufacturing processes is finally chosen , depends onthe final application of the contact components in their respective switchingdevices or electromechanical components. Other considerations , such as therequired number of electrical operations, the most economical use of preciousmetals and the anticipated volumes of parts are also important for the processselection.

===3.1 Manufacturing of Single Contact Parts===The group of single contacts includes contact rivets, contact tips, and formedparts such as weld buttons. Contact spheres (or balls) are today rarely usedbecause of economical considerations.<br>Main Articel: [[3.1 Manufacturing of Single Contact Parts| Manufacturing of Single Contact Parts]]===3.1.1 Contact Rivets===

==Manufacturing of Semi-Finished Materials=3.1.1=Semi-finished contact pre-materials can be manufactured from solid precious metals, precious metal alloys or precious metal containing composite materials.1 Solid Contact Rivets===<br>Main Articel: [[Manufacturing of Semi-Finished Materials | Manufacturing of Semi-Finished Materials]]

Solid contact rivets are ==Attachment of Single Contact Parts==The following segments give an overview of the oldest utilized usually applied attachment technologies for contact partsto carrier components. Their manufacturingrequires a ductile contact material and is done without scrap on fully automatedspecial cold heading machines. A wire slug is cut off and the rivet head isformed by pressing They include mechanical, as well as brazing and hammering. This way welding methods used for electrical contact rivets with various headconfigurations such as flat, domed, spherical, or pointed can be manufactureddepending on the final application and switch or relay designassemblies.

*Typical Main Articel: [[Attachment of Single Contact Shapes Parts | Attachment of Solid Contact RivetsBild*Single Contact MaterialsBild*Dimensional RangesBildThe respective parameters cannot be chosen independently of each other.They mainly depend on the ductility of the required contact material. Before afinal decision on the dimensions we recommend to consult with the contactmanufacturer.Parts]]

===3.1.1.2 Composite Contact Rivets===Clad rivets for which only a part Main Articel: [[Evaluation of the head (composite Braze or bimetal rivets) Weld Joints| Evaluation of Braze or alsothe shank end (tri-metal rivets) are composed of contact material – with thebalance of the body mostly being copper – have replaced for many applicationssolid rivet versions because of economical considerations. The cost savingsdepend on the contact material and its required volume for a specificapplication. These composite rivets are also produced scrap-less from wirematerial on special machinery with two process variations utilized.Weld Joints]]

During ''cold bonding'' and heading the bond between the ==Stamped Contact Parts==Stamped electrical contact parts typically consist of a base carrier material to which a contact material andthe copper is achieved without external heat energy attached by high plastic deformationat the face surfaces of the two wire segments ''various methods (<xr id="fig:Plated and contact containing pre-stamped strips and stamped parts"/><!--(Fig. 3.117)-->)''. The bonding pressuremust be high enough to move They serve as the lattice important functional components in many switching and electromechanical devices for a broad range of electrical and electronicapplications. On the one hand, they perform the mostly loss-free electrical current transfer and the two metals within afew atom radii so that closing and opening of electrical circuits, while on the adhesion forces between atoms become effective.Therefore other hand, the head contact carriers are important mechanical design components, selected to shank diameter ratio of 2:1 must be closely met for astrong bond between meet the two metalsrequirements on electrical, thermal, mechanical and magnetic properties.

FigThe increasing miniaturization of electromechanical components requires ever smaller stamped parts with low dimensional tolerances. Such precisionstamped parts are needed in the automotive technology for highly reliable switching and connector performance. In the information and data processingtechnology, they transfer signals and control impulses with high reliability and serve as the interface between electronic and electrical components. 3<figure id="fig:Plated and contact containing pre-stamped strips and stamped parts">[[File:Plated and contact containing pre-stamped strips and stamped parts.jpg|left|thumb|Figure 1: Cold bonding of bimetall rivets (schematic)Plated and contact containing pre-stamped strips and stamped parts for different applications]]</figure><br style="clear:both;"/>Main Articel: [[Stamped Contact Parts| Stamped Contact Parts]]

During ''hot bonding'' the required heat energy is applied by a short term electricalcurrent pulse ''(Fig. 3.2)''. In the case of Ag and Cu a molten eutectic alloy ofsilver and copper is formed in the constriction area between the two wire ends.When using metal oxide containing contact materials the non-soluble oxideparticles tend to coagulate and the bonding strength between the componentmaterials is greatly reduced. Therefore the cold bonding technology is preferredfor these contact materials. The during cold bonding required high surfacedeformation ratio can be reduced for the hot bonding process which allows thehead to shank diameter ratio to be reduced below 2:1. For composite rivets with AgPd alloys as well as alloys on the basis of Au, Pd,and Pt the above methods cannot be used because of the very different workhardening of these materials compared to the base material copper. Thestarting material for such composite rivets is clad strip material from which thecontact rivets are formed in multiple steps of press-forming and stamping.Similar processes are used for larger contact rivets with head diameters > 8 mmand Ag-based contact materials. Fig 3.2. Hot bonding of bimetal rivets (schematic) *Typical contact shapes for composite rivetsbild *Contact materialsbild *Base materialsbild *Dimensional rangesbildThese parameters cannot be chosen independently of each other. They dependmainly on the mechanical properties of the contact material. Before specifyingthe final dimensions we recommend to consult with the contact manufacturer. *Quality criteria and tolerancesbild *Typical contact shapes of tri-metal rivetsbild *Contact materialsbild *Base materialsbild *Dimensional rangesbild *Standard values for rivet dimensionbild ===3.1.1.3 Braze Alloy Clad Contact Rivets===For special cases, especially high surrounding temperatures with high thermaland mechanical stresses during switching operations, a full metallurgical bondbetween the contact rivet and the contact carrier may be required to prevent aloosening of the connection and early failures of the device. To accomplish thissuperior bond a thin layer of brazing alloy is added to the underside of the headand the rivet shank. During assembly a thermal treatment is added after themechanical staking. ===3.1.1.4 Contact Rivets with Brazed Contact Material Layers===For certain applications contact rivets with non-ductile or brittle materials suchas tungsten, silver–tungsten, or silver–graphite are required. Rivets with thesecontact materials can only be fabricated by brazing. Small round tips are brazedto pre-fabricated copper or steel bases using special brazing alloys in areducing atmosphere. ===3.1.2 Contact Tips===Flat or formed contact tips, welded or brazed to contact carriers, are frequentlyused in switching devices for higher power technology. Depending on thecontact material and specified shapes these tips are produced by variousmanufacturing processes. The most frequently used ones are: *Stamping from strips and profiles*Cutting from extruded rods*Pressing, Sintering, and Infiltrating*Pressing, Sintering, and Re-Pressing*Pressing and Sintering For stamping sufficiently ductile semi-finished materials are needed. These aremainly silver, silver–alloys, silver–nickel, silver–metal oxide, and silver–graphite(with graphite particle orientation parallel to the switching surface). silver–metaloxides and silver–graphite need an additional well brazable or weldable silverlayer on the underside which can be bonded to the bulk of the contact materialby various processes. To further facilitate the final attachment process strips andprofiles are often coated on the brazing underside with an additional thin layer ofbrazing alloy such as L-Ag 15P (CP 102 or BCuP-5).For Ag/C with the graphite orientation perpendicular to the switching surface thebrazable underside is produced by cutting tips from extruded rods and burningout graphite in a defined thickness. The press-sinter-infiltrate process (PSI) is used mainly for Ag/W and Cu/Wmaterial tips with tungsten contents of > 50 wt%. A silver or copper surplus onthe underside of the tip later facilitates the brazing or welding during finalassembly. The press–sinter–re-press method (PSR) allows the economic manufacturing ofshaped contact parts with silver or copper contents > 70 wt%. This process alsoalloys parts pressed in two layers, with the upper being the contact material andthe bottom side consisting of pure Ag or Cu to support easy attachment. Press–sinter processes are limited to smaller Ag/W contact tips with a Agcontent of approximately 65 wt%. *Contact materialsbild *Typical contact shapes of tips and formed contact partsbild *Dimensional rangesbildBecause of the wide variety of shapes of contact tips and formed contact partsthe user and manufacturer usually develop special parts specific agreementson quality and tolerances. ===3.1.3 Weld Buttons=== For contacts used at higher temperatures, such as for example in controls forstove tops, the use of contact rivets or the direct welding of silver based contactmaterials on steel or thermo-bimetal carriers is usually not feasible. For suchapplications weld buttons are suitable contact components. Weld buttons are round or rectangular tips manufactured from clad contact bimetalor in some cases tri-metal semi-finished materials. The surface layer isproduced from the specified contact material, the bottom weldable layer from amaterial with higher electrical resistivity such as steel, nickel, or for example acopper-nickel alloy. For precious metal savings a third high conductive layer ofcopper may be inserted between the contact material and weld backing. Toimprove the welding process the underside often has an embossed pattern withone or more weld projections. The manufacturing of weld buttons from bi– or tri–metal strip requires a ductilecontact material. Weld buttons with tungsten contact layers are thereforeproduced by brazing of tungsten discs to a weldable pre-formed base. *Typical contact forms of weld buttonsbild *Contact materialsbild *Carrier materialsbild *Dimensional Rangesbild Equipment for the Production of Wires, Rivets and Miniature - Profilesbild *Quality criteria of standard weld buttonsbilder ===3.2 Manufacturing of Semi-Finished Materials===Semi-finished contact pre-materials can be manufactured from solid preciousmetals, precious metal alloys, or precious metal containing composite materials.They are made in wire, strip, and profile form by known processing technologiessuch as extrusion and subsequent annealing and drawing or roll-forming. Theyare supplied following the manufacturer's internal standards usually related toDIN EN specifications for copper based materials. The most important materialsare two – or multiple material layered semi-finished materials with the contactmaterial bonded in its solid phase to non-precious carriers by cladding, brazing,or welding. The contact material can also be deposited on the carrier from theliquid or vapor phase. ===3.2.1 Clad Semi-Finished Pre-Materials (Contact-Bimetals)===Clad materials consist of two or more layers of different materials, the contactmaterial and the carrier, which are firmly bonded to each other. Depending onthe electrical requirements the contact material is mainly an alloy of gold,palladium, or silver based while the carrier material are mainly copper alloys. Tobond these materials various technologies are utilized, the two most importantones being described in more detail below. During ''hot cladding'', the classic process, the materials to be clad areassembled into a cladding package in block or plate form, heated to about800°C and clad (or “welded”) together under high pressure ''(Fig. 3.3)''. At theinterface between the two materials a non-separable bond is formed by eitherdiffusion of the reaction partners or in liquid phase by forming a AgCu eutecticalloy when an additional brazing alloy foil is placed between the two materials.Further processing is done by rolling with required annealing steps betweensubsequent thickness reductions. The disadvantage of this process is theusually limited short length of final material strips. Fig. 3.3: Hot cladding of pre-materials (schematic) In the ''Cold Roll-Cladding'' process the bond between the contact and carriermaterial is achieved by cold deformation of > 50% in one rolling pass ''(Fig. 3.4)''.The high plastic deformation causes cold welding in the boundary layer betweenthe two materials. To increase the quality and strength of the bond a subsequentdiffusion annealing is performed in most cases. This process is most suitable forclad semi-finished strips with thin contact material layers (> 2 μm) and large striplength (> 100 m). Fig. 3.4: Cold roll-cladding of semi-finished strips (schematic) *Typical configurations of clad contact stripsbild *Contact materialsbild *Carrier materialsbild? *DimensionsbildWhen specifying the contact material layer thickness it is recommended to use theminimum required thickness. *Quality criteria and tolerancesStrength properties and dimensional tolerances of clad contact bi-metals arederived from the standards DIN EN 1652 and DIN EN 1654 for Cu alloys. Whenspecifying the width of the contact material layer it is recommended to use theminimum required value. All dimensions should be specified originating from onestrip edge. ===3.2.2 Brazed Semi-Finished Contact Materials (Toplay–Profiles)===The toplay process starts with a flat or profile – shaped contact material stripwhich is fed together with the wider non-precious carrier material and in mostcases an intermediate thin foil of brazing alloy into a induction brazing machine''(Fig. 3.5)''. An evenly distributed and reliable braze joint can be achieved this waybetween contact and carrier materials. The combined material strip is rather softafter the brazing process and re-hardened during a subsequent profile rollingstep. In this way different shapes and configurations can easily be achieved. Fig. 3.5: Toplay brazing with an inductive heating inline equipment (schematic) *Typical configurations of toplay contact profilesbild *Contact materialsbild *Carrier materialsbild *Quality criteria, dimensions and tolerancesbild Strength properties and dimensional tolerances of toplay profiles are derivedfrom the standards DIN EN 1652 and DIN EN 1654 for Cu alloys. ===3.2.3 Seam–Welded Contact Strip Materials (FDR–Profiles)===Seam–welding is the process by which the contact material in the form of a solidwire, narrow clad strip, or profile is attached to the carrier strip by overlapping orcontinuous weld pulses between rolling electrodes ''(Fig. 3.6)''. The weld joint iscreated by simultaneous effects of heat and pressure. Except for the very smallactual weld joint area the original hardness of the carrier strip is maintainedbecause of the limited short time of the heat supply. Therefore also spring-hardbase materials can be used without loss of their mechanical strength. The use ofclad contact pre-materials and profiles allows to minimize the use of the costlyprecious metal component tailored to the need for optimum reliability over theexpected electrical life of the contact components. *Typical configurations of seam–welded contact stripsand stamped partsbildFig. 3.6: Seam-welding process (schematic) *Contact materialsbild *Carrier materialsbild *Dimensionsbild *Quality criteria and tolerancesStrength properties and dimensional tolerances of toplay profiles are derived from thestandards DIN EN 1652 and DIN EN 1654 for Cu alloys.. ===3.2.4 Contact Profiles (Contact Weld Tapes)===Contact profiles span a broad range of dimensions. Width and thickness are typicallybetween 0.8 – 8.0 mm and 0.2 – 3.0 mm resp. Special configurations, often definedas miniature-profiles or even micro–profiles can have awidth < 2.0 mm. Miniature–profiles are mostly composed of a contact-bimetal material with the contactmaterial being a precious metal alloy or composite material clad, welded or coated byelectroplating or vacuum-deposition (sputtered) onto a weldable base material. Sincethese profiles are attached to carrier strip materials usually by segment– or seam–welding to the base materials, materials with good welding properties such as nickel,copper-nickel, copper-tin, as well as copper-nickel-zinc alloys are used. The bottomsurface of the profiles usually has formed weld rails or similar patterns to ensure asolid continuous metallurgical weld joint between the profile and the contact carrier. Contact profiles in larger sizes are often used for switching devices in the low voltagetechnology. For these the contact layer mostly consists of arc erosion resistantmaterials such as silver–nickel, silver–metal oxides or the weld resistant silver–graphite. The brazable or weldable underside of the metal oxide or silver–graphitematerials is usually pure silver with also quite often a thin layer of a phosphorouscontaining brazing alloy applied to aid the welding process. *Typical configurations of multi-layer contact profilesbild *Contact materialsbild *Carrier materialsbild *Brazing alloybild *Quality criteriaBeause of the variety of configurations of contact profiles usually the qualityissues are separately agreed upon between the manufacturer and the user. *Dimensions and tolerancesbildThe thickness of the Au top-layer, which is sputtered for example, is between 0.2and 5 μm, depending on the requirements. Tolerance of thickness is about + 10%. ===3.3 Attachment of Single Contact Parts===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. ===3.3.1 Mechanical Attachment Processes===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 ''(Fig. 3.7)''. Compared to the use of compositerivets this process uses more precious contact material but for silver basedcontact materials these costs or 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. 3.7: Direct press-insertion of wire segments ===3.3.2 Brazing Processes===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 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. ===3.3.2.1 Flame (or Torch) Brazing===The simplest 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 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. ===3.3.2.2 Furnace Brazing===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 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 materials. ===3.3.2.3 Resistance Brazing===In this process the resistive heating under electric currents is the source ofthermal energy. For contact applications two methods are used for resistancebrazing''(Fig. 3.8)''. 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”) when the brazing alloy is inits liquid stage and this way 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)The heat is created in the electrodes and thermally conducted into thejoint area *Electrodes from higher conductive and thermally stable metallic materialsThe heat is created by the higher resistance in the joint area which,through selected designs, creates a constriction area for the electricalcurrent in addition to the resistance of the components to be joined. Graphite electrodes are mainly used for indirect resistance brazing and for joint2 2 area > 100 mm . For contacts tips with a bottom area < 100 mm 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-time 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. 3.8: Resistance brazing (schematic) ===3.3.2.4 Induction 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 temperatureis 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 > 80% can be reached with this method also for largercontact assemblies. The widely varying working times needed for the differentbrazing methods are given in Table 3.1. Table 3.1: Brazing Times for Different Brazing Methods *Examples of brazed contact assembliesbild *Contact materialsals bild?Ag, Ag-Alloys., Ag/Ni (SINIDUR), Ag/CdO (DODURIT CdO),Ag/SnO (SISTADOX), Ag/ZnO (DODURIT ZnO) and Ag/C (GRAPHOR D) with 2brazable backing, refractory materials on W -, WC- and Mo-basis *Brazing alloysL-Ag 15P, L-Ag 55Sn et.al. als Bild? *Carrier materialsCu, Cu-Alloys. et al. als Bild? *DimensionsBrazing area > 10 mm² *Quality criteriaThe testing of the braze joint quality is specified in agreements between themanufacturer and the user. ===3.3.3 Welding Processes===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). 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. ===3.3.3.1 Resistance Welding===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. ===3.3.3.1.1 Vertical Wire Welding===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''(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 contactwire. After welding the wire is cut off by wedge shaped knives forming again aroof shaped weld projection. The welded wire segment is subsequently formedinto the desired contact shape by stamping or orbital forming. This weldingprocess can easily be integrated into automated production lines. The contactmaterial must however be directly weldable, meaning that it cannot containgraphite or metal oxides. Fig. 3.9: Vertical wire welding (schematic) ===3.3.3.1.2 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-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 two-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 signals, the second or middle layer of 100 μm Ag/Ni 90/10 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. 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 importance. Fig. 3.10: Horizontal profile cut-off welding (schematic) ===3.3.3.1.3 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/C or Ag/W tips withgood weldable backings are welded directly to the carrier parts. To improve thewelding 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 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 (see chapter 3.1.3).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. ===3.3.3.2 Percussion 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. 3.11)''. 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 to form a strong jointacross the whole interface area.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. Fig. 3.11: Percussion welding (schematic) ===3.3.3.3 Laser Welding===This contact attachment process is also one 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 touch-less energy transport which avoids any possible contamination ofcontact surfaces, the very well defined weld effected zone, the exactpositioning of the weld spot and the precise control of weld energy. Laser welding is mostly applied for rather small contact parts to thin carriermaterials. To avoid any defects in the contact portion, the welding is usuallyperformed through the carrier material. Using a higher power laser and beamsplitting allows high production speeds with weld joints created at multiplespots at the same time. ===3.3.3.4 Special Welding and Attachment Processes===In high voltage switchgear the contact parts are exposed to high mechanicaland thermal stresses. This requires mechanically strong and 100%metallurgically bonded joints between the contacts and their carrier supportswhich 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. ===3.3.3.4.1 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 Cu/W contacts to hardand thermally stable copper alloys as for example CuCrZr for spring hardcontact tulips ''(Fig. 3.12)''. Fig. 3.12:Examples of contact tulips with Cu/Wcontacts electron beam weldedto CuCrZr carriers. ===3.3.3.4.2 Cast-On of Copper===The cast-on of liquid copper to pre-fabricated W/Cu contact parts is performedin special casting molds. This results in a seamless joint between the W/Cu andthe copper carrier. The hardness of the copper is then increased by asecondary forming or deep-drawing operation. *Examples of Wire Weldingbild ===Vertical Wire Welding=== *Contact materialsAg, Ag-Alloys, Au- and Pd-Alloys, Ag/Ni (SINIDUR) als bild? *Carrier materialsCu, Cu-Alloys, Cu clad Steel, et.al. als bild? *DimensionsbildFunctional quality criteria such as bonded area percentage or shear force areusually agreed upon between the supplier and user and defined in deliveryspecifications. ===Horizontal Wire Welding=== *Contact materialsAu-Alloys, Pd-Alloys, Ag-Alloys, Ag/Ni (SINIDUR), Ag/CdO (DODURIT CdO),Ag/SnO (SISTADOX), Ag/ZnO (DODURIT ZnO), and Ag/C (GRAPHOR D) *Carrier materials(weldable backing of multi-layer profiles)Ni, CuNi, CuNiFe, CuNiZn, CuSn, CuNiSn, and others. *Braze alloy layerL-Ag 15P (CP 102 or BCUP-5) *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=== *Contact materialsW/Cu, W/Ag, others *Carrier materialsCu, Cu-Alloys, others *DimensionsWeld surface area (flat) 6.0 to 25 mm diameterRectangular areas with up to 25 mm diagonals *Quality criteriaTest methods for bond quality are agreed upon between supplier and user Fig. 3.13: Examples for percussion welded contact parts  ===3.4 Evaluation of Braze or Weld Joints===The switching properties of brazed and welded contact assemblies is stronglydependent on the quality of the joint between the contact and the carrier. Therequired high quality is evaluated through optical methods, continuous controlof relevant process parameters and by sampling of finished products. ===3.4.1 Brazed Joints===Despite optimized brazing parameters non-wetted defect areas in the brazejoint cannot be avoided completely. These wetting defects can mostly be tracedto voids caused by flux inclusions in the braze joint area. Depending on theshape and size of the joint areas, the portion of the fully wetted joint is between65% and 90%. In its final use in switching devices a joint area of 80% isconsidered good or excellent if the individual void size does not exceed 5% ofthe joint area. Frequently wetted joint areas >90% with voids <3% can beobtained. Evaluation of the quality of the joint can be performed either by destructive ornon-destructive methods. ===3.4.1.1 Destructive Testing===Destructive tests can be performed on a sampling basis in rather simple ways: *De-brazingThe contact tip is being removed by slow heating and simultaneous applicationof force perpendicular to the contact surface area. Visual inspection of theseparated components reveals the non-wetted defect areas as discolorationfrom either flux remnants or oxidation of the carrier material. *Milling SampleThe contact tip is milled off in layers to a depth that makes the joint area visiblefor optical evaluation. *Saw-CuttingA crossing pattern is cut with a fine saw into the contact tip. Areas that are notbonded fall off in pieces. *Metallographic Micro-sectionIn a metallographic micro-section perpendicular to the contact surface wettingdefects can also be made visible ''(Fig. 3.14)'' which however are only indicativeof the brazing temperature and brazing time. Fig. 3.14:Braze joint with voids.Ag/CdO tip on Cu carrier. *Shear testThe contact tip is sheared off from the carrier with the required shear force beinga measure for the bond quality. This method is especially suitable for hard andbrittle contact tip materials such as for example tungsten. ===3.4.1.2 Non-Destructive Test Methods===Typically the non-destructive testing of braze joints requires more elaborate testequipment. Besides this such test methods have limitations regarding theshape of the contact tips and/or carriers. The prevalent methods are ultrasoundtesting and X-ray analysis. *Ultrasonic testing This method is based on the disruption of the propagation of sound waves indifferent media. High resolution modern test systems with graphic print-outcapabilities and analytical software are capable to detect even small (<0.5 mmdiameter) voids in the braze joint. The portion of the wetted areas is calculatedas a percentage of the whole joint area. Fig. 3.15 shows an example of differentbraze qualities for a Ag/SnO₂ contact tip brazed to a copper carrier andillustrates the position and size of void areas as well as the final joint quality. Fig. 3.15: Ultrasound print-out of braze joints between Ag/SnO 88/12 tips and Cu carrier with 2different degree of wetting (dark areas = voids) *X-Ray testing X-ray testing is an additional method for evaluating brazed joints. Using finefocusX-ray beams it is possible to achieve a sufficient picture resolution. Thereare however limitations about the thickness of the contact tip compared to thesize of the void area. This expensive test method is rarely used for contactassemblies. ===3.4.2 Welded Joints===Since welded contact assemblies are usually produced in rather high quantitiesthe quality of the weld joints is monitored closely. This is especially true becauseof the high mechanical and thermal stresses quite often exerted on the jointareas during switching operations. The quality of the joints is dependent on theprocess control during welding and on the materials used to manufacture thewelded assemblies. Despite the ability to closely monitor the relevant welding parameters such asweld current, voltage and energy, simultaneous testing during and aftermanufacturing are necessary. A simple and easy to perform quality test is based on the shear force.Evaluations of welding assemblies in electrical performance tests have shownhowever that the shear force is only a valid measure if combined with the size of2 the welded area. As rule of thumb the shear force should be > 100 N/mm withthe welded area > 60% of the original wire or profile cross-sectional area. Forcritical applications in power engineering, for example for high currents and/orhigh switching frequency, a higher percentage of the joint area is necessary. During series production every weld is usually probed in a testing stationintegrated in the manufacturing line with a defined shear force – mostly 20% ofthe maximum achievable force. In this way defective welds and missingcontacts can be found and sorted out. The monitoring of the actual shear forceand size is performed during production runs based on a sampling plan. Fig. 3.16: Ultrasonic picture of a weldjoint, Ag/C tip on Cu carrier(ABB-STOTZ-KONTAKT) Besides destructive testing for shear force and weld area the non-destructiveultrasound testing of the joint quality is also utilized for welded contactassemblies ''(Fig. 3.16)''. ===3.4.3 Selection of Attachment Methods===In the preceding sections a multitude of possibilities for the attachment ofcontact materials to their carriers was described. A correlation of thesemethods to the switching current of electromechanical devices is illustrated inTable 3.2. it shows that for the same switching load multiple attachmentmethods can be applied. Which method to chose depends on a variety ofparameters such as contact material, material combination of contact andcarrier, shape of the contact, required number of switching operations and lastbut not least the required volume of parts to be manufactured. Based on the end application the following can be stated as general rules:Electroplated contact surfaces are limited to switching without or underextremely low electrical loads. In the lower and medium load range contactrivets and welded contacts are used. For high switching loads brazing,especially resistance and induction methods, are utilized. For extremely highloads, for example in high voltage switchgear, percussion welding, electronbeam welding, and copper cast-on processes are preferred. Table 3.2: Correlation between Contact Joining Methods and Switching Currents  ===3.5 Stamped Contact Parts===Stamped electrical contact parts typically consist of a base carrier material towhich a contact material is attached by various methods ''(Fig. 3.17)''. They serveas the important functional components in many switching andelectromechanical devices for a broad range of electrical and electronicapplications. On the one hand they perform the mostly loss-free electricalcurrent transfer and the closing and opening of electrical circuits. In addition thecontact carriers are important mechanical design components selected to meetthe requirements on electrical, thermal, mechanical and magnetic properties. The increasing miniaturization of electromechanical components requires eversmaller stamped parts with low dimensional tolerances. Such precisionstamped parts are needed in the automotive technology for highly reliableswitching and connector performance. In the information and data processingtechnology they transfer signals and control impulses with high reliability andserve as the interface between electronic and electrical components. Fig. 3.17:Plated and contactcontaining pre-stamped strips andstamped parts for differentapplications ===3.5.1 Types of Stamped Parts===Stamped parts are produced as single pieces, in pre-stamped strip and combconfigurations. Depending on the requirements and application the contact andbase material as well as the coating and attachment technology is carefullyselected. *Coated stamped partsStamped parts can be selectively or completely coated with precious metalcontaining materials based on gold, palladium, and silver as well asnon-precious materials such as tin, nickel and copper ''(Fig. 3.17)''. For stampedparts in high volumes like those used as electrical components in automobilesthe carrier material is mostly coated in a reel-to-reel process starting with eithersolid or pre-stamped strips (see also chapter 7.1.1.3). Frequently the prestampedstrip will be used directly in further automated assembly of the finishedfunctional component. As an alternative finished stamped parts can beelectroplated using barrel and rack plating methods. Very thin coating layers with tight tolerances are deposited by electroplating. Formany applications the high mechanical wear resistance is advantageous. Sinceeven very thin layers are mostly pore-free, these coatings also act as aneffective corrosion inhibitor. The type of coatings, the sequence of multiplelayers, and the coating thickness, for example for connectors, are chosenaccording to the requirements for the end application. *Clad stamped parts For many applications thicker precious metal surfaces or AlSi layers arenecessary. These cannot be deposited by electroplating. Besides meltmetallurgicallyproduced materials on the basis of gold, palladium and silver,also powder-metallurgical materials are required frequently. The metallurgicalbond between these contact materials and the mostly copper based substratesis achieved through various mechanical cladding methods (see also chapter3.2.1). In this way also aluminum clad strips are manufactured in which thealuminum layer serves as the bondable surface in the interface betweenelectromechanical connections and electronic circuits. These clad semifinishedmaterials can be further fabricated into pre-stamped strips, in combform, or single stamped parts ''(Fig. 3.18)''. Fig. 3.18:Examples of clad stamped parts *Welded stamped parts Welded stamped parts can be fabricated by various methods (see also Chapter3.3.3). Single contact pieces can be attached to pre-stamped or finishedstamped strips as weld buttons and wire or profile segments by electricalresistance welding. Contact parts can also be stamped from seam-weldedsemi-finished strip. Fitting the end application contact materials based on gold,palladium and silver. Depending on the contact material and the design of thefinished contact component the contact bottom surface may be consist of aweldable backing material. *Brazed stamped parts Brazed stamped contact assemblies are manufactured by two joining methods(see also chapter 3.3.2). The contact material is either attached by resistanceor induction brazing to base metal carriers as prefabricated contact tip or theyare stamped from brazed semi-finished toplay strip. It is typical for brazedcontact parts that the contact material consists of silver based contact materialand a good conducting copper base material with larger cross-sectional areafor the usually higher current carrying capacity. *Stamped contact parts with rivets Riveted stamped contact parts are manufactured with the use of contact rivetswhich are transferred over suitable feed mechanisms correctly oriented intoholes punched into the carrier ''(Fig. 3.19)''. Frequently also wire or wire segmentsresp. are used which are subsequently coined and formed into the desiredcontact shape (see also chapter 3.3.1). Both attachment methods have theirdistinct advantages. Using composite or tri-metal rivets allows limiting the useof precious metal custom tailored to the volume needed for specific switchingrequirements. For wire staking the precious metal usage is usually higher butthe staking can be performed at significantly higher production ratesand the additional rivet making step is eliminated. Fig. 3.19:Examples of riveted stamped parts *Pre-mounted component stamped parts Components stamped parts consist of a minimum of two carrier parts whichdiffer in their material composition and geometrical form and the contactmaterial''(Fig. 3.21)''. The assembly of these components as single pieces or stampingprogressions is performed in a stamping die by riveting or coining. To increasethe current carrying capacity at the joining area an additional welding step canbe added. Depending on the requirements the different properties of the twocarrier components can be combined. As an example: the high electricalconductivity of a contact carrier blade is joined with the thermal or mechanicalspring properties of a second material to form a functional component. For thisprocess both carrier base materials can also be coated with additionallayers of other functional materials. Fig. 3.20:Examples of pre-mounted stampedcomponent parts Stamped parts which are insert molded into or combined with plastic parts areused in electromechanical components (see Chapter 10). ===3.5.2 Stamping Tools===For the design of stamping tools the latest CAD software systems are used.Modern stamping tools usually employ a modular design with integrateddimensional and functional controls ''(Fig. 3.21)''. Depending on the requirementson the parts and the volumes they are built with steel or carbide (-steel) insertswhich are coated with a wear resistant material such as for example TiN forlonger life. A special stamping process is precision stamping for contact parts made fromthin strip materials with thicknesses in the range of 0.05 – 2.5 mm. With highcapacity stamping technology up to 1400 strokes/min can be reached for highvolume parts. During the actual stamping operation frequently other processessuch as thread-forming, welding of contact segments and insertion and formingof contacts from wire segments are integrated. Depending on the productionvolumes these operations can also be performed in multiples. The quality of the tools used for stamping, like progressive dies and stamp-formingtools is important for the final precision and consistency of the parts. During highspeed stamping the tools are exposed to extreme mechanical stresses which mustbe compensated for to ensure the highest precision over long production runs. Withsuch high quality progressive dies parts of high precision with a cutting width of lessthan the material thickness and with strict quality requirements for the cutting surfacescan be manufactured.To ensure the highest demands on the surface quality of precision contact parts quiteoften vanishing oils are used as tool lubricants. Cleaning and degreasing operationscan also be integrated into the stamping process. Additionally most stamping linesare also equipped with test stations for a 100% dimensional and surface qualitycontrol.During the design of stamping tools for electrical contacts minimizing of processscrap and the possibility to separate the precious metal containing scrap must beconsidered. Fig. 3.21:Progressive die for stamped contact parts  ===References===

th Proc. 24 ^th Int. Conf.on Electr. Contacts, Saint Malo, France 2008, 206-209