OTHER PROCESSESProjection WeldingSeam WeldingButt WeldingFlash WeldingHigh FrequencyCapacitive DischargeElectro-Brazing
Other Resistance Welding ProcessessLesson ObjectivesWhen you finish this lesson you will understand: Projection Welding & Applications Seam Welding & Applications Butt Welding & Applications Flash Welding & Applications High Frequency Welding & Applications Capacitive Discharge Welding & Applications Electro Brazing & ApplicationsLearning ActivitiesView Slides; Read Notes, Listen to lectureDo on-line workbookKeywords: All Processes Above, Pulsing, Roll Spot Weld, Overlap Spot Weld, Continuous Seam Weld, Mash Seam Weld, Metal Finish Seam Weld, Percussion Welding
Principal Types of Resistance WeldsElectrodesor WeldingTipsElectrodesor WeldingWheelsElectrodesor DiesProjectionWeldsElectrodes or DiesSpot WeldSeam Weld Projection WeldUpset WeldFlash Weld
After WeldingAfter Welding[Reference: Resistance Welding Manual, RWMA, p.1-3]
Basic Single Impulse Welding CycleElectrode ForceWelding CurrentWelding CycleSqueeze TimeWeld TimeHoldTimeOffTime[Reference: Welding Handbook, Volume 2, AWS, p.538]
Enhanced Welding CycleSqueezeTimePreheatTimeUpslopeTimeCool TimeWeldTimeCool TimePreweldIntervalWelding CycleWeld IntervalPostweld IntervalDownslopeTimeQuenchTimeTemperTimeHoldTimePulseImpulseTemperingCurrentWelding CurrentElectrodeForceForge Delay TimeForge Force[Reference: Welding Handbook, Volume 2,AWS, p.539]
PulsingCool TimePulse 1Pulse 2Pulse 3PulseTime
Definition of Projection WeldingA resistance welding process that produces coalescence by the heat obtained from the resistance to the flow of the welding current. The resulting welds are localized at predetermined points by projections, embossments, or intersections.FixedMovingworkpiecestransformerProjection welding setup.Definition
Link to Projection Welding video
Process FundamentalsTwo parts, one projected, are placed upon one another between two electrodes.They make contact at the projected point.High current starts to flow through projection.Force is applied to cause the heated projection to collapse, and help fusion.A.B.Formation of a projection weld.Process Fundamentals
Introduction to Projection Welding(a)(b) (c) (d)[Reference: Welding Handbook, Volume 2, p.566, AWS]
Examples of Various Projection Designs(a)(b)(c) (d) (e)[Reference: Welding Handbook, Volume 2, p.562, AWS]
Examples of Various Projection Designs (CONT.)(f) (g) (h)(i)(j)[Reference: Welding Handbook, Volume 2, p.562, AWS]
Projection DesignProjection should besufficiently rigid to support the electrode force.have adequate mass to heat a spot.collapse without metal expulsion.be easy to form.cause little distortion to the part.Spherical radiusWall thicknessshould be at least70% of sheetthicknessDProjectionshould blendinto stocksurface withoutshoulderingGeneral design of a projection steel sheetProjection Design
Advantages of Projection WeldingA number of welds can be made simultaneously in one welding cycle of the machineLess overlap and closer weld spacings are possible1 < Thickness ratio < 6Smaller in size than spot weldingBetter appearance on the side without projectionLess electrode wear than spot weldingOil, rust, scale, and coatings are less of a problem than spot welding
Limitations of Projection WeldingRequire an additional operation to form projections
With multiple welds, require accurate control of projection height and precise alignment of the welding dies
Thickness limitation for sheet metals
Require higher capacity equipment than spot welding
Process AdvantagesMultiple welds can be made simultaneously.Can be located with greater accuracy than spot weld.Electrode wear is much lower because of flat faced electrode.Oil, rust, scale and coatings are less of a problem compared with spot welding.Advantages
Process LimitationsForming of projection may require an additional operation.With multiple welds, accurate control of projection height and precise alignment of welding dies are necessary.Higher capacity equipment requires to make multiple weld simultaneously.
Definition of Seam WeldingResistance Seam Welding (RSEW): A resistance welding process which produces coalescence at the faying surface by heat obtained from resistance to electric current through the work parts held together under pressure by electrodes. The resulting weld is a series of overlapping resistance spot welds made progressively along a joint by rotating the electrodes.
Introduction to Resistance Seam WeldingUpper Electrode WheelWorkpieceLower Electrode WheelThroatKnurl or FrictionDrive WheelRoll Spot WeldOverlapping SeamWeldContinuous SeamWeld[Reference: Welding Handbook, Volume 2, p.553, AWS]
Lap Seam WeldElectrodesOverlappingWeldNuggetsTravelFront viewSide View[Reference: Welding Handbook, Volume 2, p.554, AWS]
Mash Seam WeldSlightly LappedSheetsWide, FlatElectrodesWeld NuggetsBefore weldingAfter Welding[Reference: Welding Handbook, Volume 2, p.554, AWS]
Metal Finish Seam WeldChamferedElectrodeBroad, FlatElectrodeFlashFinishSideBefore WeldingAfter Welding[Reference: Welding Handbook, Volume 2, p.554, AWS]
Definition of Flash Welding A resistance welding process in which coalescence is produced simultaneously over the entire abutting surfaces.
Flash Welding Process
Two parts to be joined are clamped in dies.The dies are connected to a transformer.A voltage is applied as one part approaches other.A. Position and clamp the parts.B. Apply flashing voltage
Flash Welding ProcessUpon contact, resistive heating occurs.High amperage causes rapid melting and explosion of the metal known as flashing.Finally an upsetting force is applied to forge the parts together.
Link to Flash Weld Video
Common Types Of Flash Welds
MeterweldAxially aligned weld. Flash Welding
Common Types of Flash WeldsRing weldFixed platenMovableplatenTransformerX-sectionafter welding
Flash Welding ApplicationsWheel rims in the automotive industry Motor and generator frames in the electrical industry.Landing gear, control assemblies and hollow propeller blades in the aircraft industry.Typical metals used are stainless steel, aluminum, copper, and nickel alloys.
Introduction to Upset WeldingFinished Upset WeldHeated ZoneTo Welding TransformerClamping DieUpsettingForceMovable PartClamping DieStationary Part[Reference: Welding Handbook, Volume 2, p.598, AWS]
Resistance Butt Welded Spike for a Baseball ShoeOgawa, M et al, Spike For Baseball Shoe US Patent 6,041,461 Mar 28, 2000Abrasion-Resistant Cemented Tungsten Carbide Tip Resistance Butt Welded to Carbon Steel Sole Attachment
High Frequency Welding Applications [Reference: Welding Handbook, Volume 2, p.653, AWS]Tube Butt SeamTube Butt SeamTube Mash SeamHFHFHFInduction Coil
High Frequency Welding Applications (CONT.)Strip ButtT-JointSpiral TubeSpiral Tube FinHFHFHFHF[Reference: Welding Handbook, Volume 2, p.653, AWS]
High Frequency Welding Applications (CONT.)Projection SeamPipe ButtBar ButtHFHFHFInductionCoil[Reference: Welding Handbook, Volume 2, p.653, AWS]
Advantages of High-Frequency WeldingProduce welds with very narrow heat-affected zonesHigh welding speed and low-power consumptionAble to weld very thin wall tubesAdaptable to many metalsMinimize oxidation and discoloration as well as distortionHigh efficiency
Limitations of High-Frequency WeldingSpecial care must be taken to avoid radiation interference in the plants vicinityUneconomical for products required in small quantitiesNeed the proper fit-upHazards of high-frequency current
Some Products of High-Frequency Welding[Reference: Welding Handbook, Volume 2, p.665, AWS]
Percussion Welding (PEW): A resistance welding process which produces coalescence of the abutting members using heat from an arc produced by a rapid discharge of electrical energy. Pressure is applied percussively during or immediately following the electrical discharge.
Metals Handbook, ASM, 1983
Metals Handbook, ASM, 1983
Resistance Brazing/Soldering (RB): A brazing/soldering process in which the heat required is obtained from the resistance to electric current in a circuit of which the work is a part.Resistance Brazing
Electro-brazingW. Stanley, Resistance WeldingMcGraw-Hill, 1950
Resistance Soldering Flexible Braided Buss to Automotive Rear WindowRear Window with Silver Ceramic Material Silk Screened onto SurfaceFlat Braided Wire with Contact Pad AttachedGlassSilver CeramicBraidedWireContact PadWith Ball of SolderCurrent Passed, Melts Solder, Bond MadeIngles, G et al Braided Buss Bar with Selectively Clad Solder Pad Attachments US Patent 6,042,932 Mar 28, 2000
Spot, seam, and projection welding operations involve a coordinated application of electric current and mechanical pressure of the proper magnitudes and durations. The welding current must pass from the electrodes through the work. Its continuity is assured by forces applied to the electrodes, or by projections which are shaped to provide the necessary current density and pressure. The sequence of operation must first develop sufficient heat to raise a confined volume of metal to the molten state. This metal is then allowed to cool while under pressure until it has adequate strength to hold the parts together. The current density and pressure must be such that a nugget is formed, but not so high that molten metal is expelled from the weld zone. The duration of weld current must be sufficiently short to prevent excessive heating of the electrode faces. Such heating may bond the electrodes to the work and greatly reduce their life.The heat required for these resistance welding processes is produced by the resistance of the workpiece to an electric current passing through the material. Due to the short electric current path in the work and limited weld time, relatively high welding currents are required to develop the necessary welding heat.The four phases welding cycle for spot, seam, and projection welding are: (1) Squeeze time - the time interval between timer initiation and the first application of current. The time interval is to assure that the electrodes contact the work and establish the full electrode force before welding current is applied. (2) Weld time - the time that welding current is applied to the work in making a weld in single-impulse welding. (3) Hold time - the time during which force is maintained to the work after the last impulse of current ends. During this time, the weld nugget solidifies and is cooled until it has adequate strength. (4) Off time - the time during which the electrodes are off the work and the work is moved to the next weld location. The term is generally applied where the welding cycle is repetitive.The above slide shows a basic welding cycle. The use of one continuous application of current to make an individual weld is called single impulse welding. One or more of the following features may be added to this basic cycle to improve the physical and mechanical properties of the weld zone: (1) Precompression force to seat the electrodes and workpieces together. (2) Preheat to reduce the thermal gradient in the metal at the start of weld time. (3) Forging force to consolidate the weld nugget. (4) Quench and temper times to produce the desired weld strength properties in hardenable alloy steels. (5) Postheat to refine the weld grain size in steels. (6) Current decay to retard cooling on aluminum.In some applications, the welding current is supplied intermittently during a weld interval time. The next slide shows the sequence of operation in a more complex welding cycle.With direct energy machines, the rate of current rise and fall can be programmed. The current rise period is commonly called upslope time, and the current fall period is called downslope time (see the above slide). These features are available on machines equipped with electronic control system.Upslope is used to avoid overheating and expulsion of metal at the beginning of weld time, when the base metal interface resistance is high. Downslope is used to control weld nugget solidification to avoid cracking in metals that are quench-hardenable or subject to hot tearing.Prior to welding, the base metal can be preheated by using a low current. Following the formation of the weld nugget, the current can be reduced to some lower value for postheating of the weld zone. This may be part of the weld interval, as shown in the above slide, or a separate application of current following a quench time period.Multiple impulse welding consists of two or more pulses of current separated by a preset cool time. This sequence is used to control the rate of heating at the interface while spot welding a relatively thick steel sheet.Pulsing is employed primarily when resistance welding heavier gauge materials. Pulsing has two functions: preventing overheating of the electrode faces, and locating the weld nugget. Pulsing is particularly effective for preventing overheating of the electrode faces. Under continuous heating, the electrode-sheet contact resistance will promote considerable heat generation in that area. Where long weld times or high power levels are required, the steel will often soften or melt at the electrode face. This condition promotes electrode skidding, loss of weld quality and accelerated electrode wear. Pulsing, however, allows the electrode face to cool. Since the thermal conductivity of the copper electrode is considerably greater than the steel being welded, heat will be retained in the weld during the cool portion of the cycle, while the electrode will cool appreciably. As such, pulsing allows spot welding of heavier gauge materials without electrode face overheating.In a similar fashion, pulsing allows the weld nugget to be properly located between the sheets to be jointed. During the cool cycle, the electrodes will preferentially cool the surfaces of the weld in contact with the electrodes. This effectively concentrates the heating at the proper location between the sheets.The beneficial effects of pulsing vary with gauge. When there is sufficient steel thickness for heavier gauge materials pulsing is often beneficial, if not required. For lighter gauge materials, the temperature of the entire weld can fluctuate with even the fastest pulsing. Therefore, for light gauge materials pulsing is generally not considered beneficial.In projection welding, two parts - one of them have projections - are placed between two electrodes, which are connected through a transformer. The parts make contact at the projected point. When current starts flowing through the electrodes, it passes through the projected point. A tremendous amount of heat is produced at the projected end, and it gets melted. Now, a forging force is applied to make the projected part to weld with the other one. Resistance projection welding is a variation on resistance spot welding. Basically, a protrusion is placed on one of the two...