Other Welding Processes - Home - SCCPSSinternet.savannah.chatham.k12.ga.us/schools/wts/staff...Other Welding Processes 587 The welding current required to make a resistance weld must

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Chapter 24Other Welding Processes

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OBJECTIVESAfter completing this chapter, the student should be able to:

• Describe how resistance, ultrasonic, inertia, laser beam, plasma arc, and stud welding processes work.

• Describe the different applications of hardfacing.• List some of the applications or uses for resistance, ultrasonic, inertia,

laser beam, plasma arc, and stud welding processes.

KEY TERMSelectron beam welding

(EBW)

hardfacing

inertia welding

laser beam welding (LBW)

plasma arc welding (PAW)

resistance welding (RW)

resistance spot welding (RSW)

stud welding (SW)

thermal spraying (THSP)

ultrasonic welding (USW)

INTRODUCTIONThere are some 67 welding and joining processes listed by the American Weld-ing Society (AWS). Most of the welding and joining processes are very unique, but some are slight variations of other processes. Of the seven processes briefly covered in this chapter, resistance welding and hardfacing are the ones you are most likely to see in a welding shop. You might have an opportunity to observe or use the five other processes only in a large production-type welding shop because of the high cost of the equipment.

RESISTANCE WELDING RWIn the resistance welding (RW) process the weld is made by clamping the parts together between the welding machine’s electrodes. Then an electric current is passed through the parts to heat up the surfaces so they will fuse together.

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Other Welding Processes 587

The welding current required to make a resistance weld must be at a very low voltage but high amperage, Figure 24-1. The pressure is applied to ensure a contin-uous electrical circuit and to force the heated parts together. The parts are usually joined as a result of heat and pressure and are not simply melted together. Fluxes or filler metals are not needed for this welding process.

The current for resistance welding is usually supplied by either a transformer or a transformer/capacitor arrangement. The transformer, in both power supplies, is used to convert the high line voltage (low-amperage) power to the welding high-amperage current at a low voltage. A capacitor, when used, stores the welding current until it is used. This storage capacity allows such machines to use a smaller size transformer. The required pressure, or electrode force, is applied to the workpiece by pneumatic, hydraulic, or mechanical means. The pressure applied may be as little as a few ounces for very small welders to tens of thousands of pounds for large spot welders.

Most resistance welding machines consist of the following three components:

The mechanical system to hold the workpiece and •to apply the electrode forceThe electrical circuit made up of a transformer and, •if needed, a capacitor, a current regulator, and a secondary circuit to conduct the welding current to the workpieceThe control system to regulate the time of the weld- •ing cycle

There are several basic resistance welding pro-cesses. These processes include spot (RSW), seam (RSEW), high-frequency seam (RSEW-HF), projection (PW), flash (FW), upset (UW), and percussion (PEW).

Resistance welding is one of the most useful and practical methods of joining metal. This process is ideally suited to high-production methods.

Resistance Spot Welding (RSW)Resistance spot welding (RSW) is the most common of the various resistance welding processes. In this process, the weld is produced by the heat obtained at the interface between the workpieces. This heat is due to the resistance to the flow of electric current through the workpieces, which are held together by pressure from the electrode, Figure 24-2. The size and shape of the formed welds are controlled somewhat by the size and contour of the electrodes.

ELECTRODESWORK

PRESSURECYLINDER

FORCETRANSFORMER TIMER

AC SUPPLY

FIGURE 24-1 Fundamental resistance welding machine circuit. American Welding Society

PRESSURE

PRESSURE

ELECTRODES

FIGURE 24-2 Heat resulting from resistance of the current through the metal held under pressure by the electrodes creates fusion of the two workpieces during spot welding. © Cengage Learning 2012


588 CHAPTER 24

The welding time is controlled by a timer built into the machine. The timer controls four different steps, Figure 24-3. The steps are as follows:

Squeeze time, or the time between the first applica- •tion of electrode force and the first application of welding currentWeld time, or the actual time the current flows •Hold time, or the period during which the electrode •force is applied and the welding current is shut offOff period, or the time during which the electrodes •are not contacting the workpieces

Tables supplied by the machine manufacturer provide information for the exact time for each stage for different types and thicknesses of metal.

Material from 0.001 in. (0.0254 mm) to 1 in. (25 mm) thick may be joined by spot welding.

ULTRASONIC WELDING USWUltrasonic welding (USW) is a process for joining similar and dissimilar metals by introducing high-frequency vibrations into the overlapping metals in the area to be joined. Fluxes and filler metals are not required, electrical current does not pass through the weld metal, and only localized heating is generated. The temperature produced is below the melting point of the materials being joined. Thus, no melting occurs during the welding cycle.

Ultrasonic welding has many applications in the assembly of electrical products. Typical applications include the following:

Attaching oxide-resistant contact surface buttons •to switchesAttaching leads to coils of foil, sheet, or wire made •of aluminumAttaching very fine wire leads and elements to other •components

Figure 24-4 shows an ultrasonic spot welder used to perform the types of welds just listed.

SQUEEZE TIME,APPLICATION OF

ELECTRODE FORCE

WELD TIME,CURRENT FLOWS

HOLD TIME,FORGING OCCURS

OFF TIME,RELEASE OFELECTRODE

FIGURE 24-3 Basic periods of spot welding. © Cengage Learning 2012

AIR PRESSUREADJUSTMENT

HEIGHTADJUSTMENT

CONVERTER

BOOSTER

HORN

ANVIL

FIGURE 24-4 Ultrasonic spot welder. © Cengage Learning 2012



INERTIA WELDING PROCESSInertia welding is a form of friction welding. In inertia welding, one workpiece is fixed in a stationary holding device, Figure 24-5. The other is clamped in a spindle chuck, which is accelerated rapidly. At a predetermined

speed, power is cut, as shown in Figure 24-6A. As a result, one part is then thrust against the other piece. Friction between the parts causes the spindle to deceler-ate, converting stored energy to frictional heat. Enough heat is formed to soften, but not melt, the faces of the part, Figure 24-6B.

Some of the advantages of the inertia welding process are as follows:

Superior weld •A very narrow heat-affected zone adjacent to the weld •Uniform production welds •Fast production welds •Clean operation •Lowest cost of energy •Minimum skill required to operate the welder •The amount of upset of parts can be controlled to •close tolerancesA complete interface weld can be obtained •Safe to operate •

LASER BEAM WELDING LBWIn laser beam welding (LBW) fusion is obtained by directing a highly concentrated beam of coherent light to a very small spot, Figure 24-7. Laser beams combine

ROTATING CHUCK

STATIONARY CHUCK

WELDSTOCK BEING WELDED

DRIVE MOTOR AND FLYWHEEL

SPEED, TIME, ANDSPEED, TIME, ANDFORCE CONTROLSFORCE CONTROLS

FIGURE 24-5 Inertia welder. © Cengage Learning 2012

(A)

(C)

(B)

(D)

FORCE

WORKPIECES

FORCE

STA

RT R

OTA

TIN

G

ROTATINGSPINDLE

STATIONARYCHUCK

CO

NTI

NU

E R

OTA

TIN

G

STO

P R

OTA

TIN

G

WELD

FIGURE 24-6 Inertia welding process. American Welding Society


590 CHAPTER 24

low-heat input (0.1 to 10 joules) with high-power intensity of more than 10,000 watts per square cen-timeter (considerably more than the electron beam). Because the heat is provided by a beam of light, there is no physical contact between the workpiece and the welding equipment. It is possible to make welds through transparent materials.

The ease with which the beam can be directed to any area of the work makes laser welding very flexible. In the manufacture of complex forms, for example, it is possible to move the focused laser beam under digital control to seam weld any desired shape. The proven high-quality laser welds, along with the flex-ibility and the comparatively moderate cost of laser welding equipment, indicate that laser welding plays an increasing role in microelectronics and other light-gauge metal welding applications.

Laser welding of materials with high thermal con-ductivity, such as copper, is not difficult to do. The extremely concentrated laser heat will melt the metal locally to make a weld or will vaporize the metal to drill a hole before it can be conducted away by the copper, which happens in most other forms of welding.

Advantages and Disadvantages of Laser Welding Laser welding has some distinct advantages and disad-vantages when compared to other welding processes. Electron beam welding (EBW) is the only method that rivals the heat output of a laser. Generally, however, electron beam welding must operate in a vacuum. Since the laser beam is a light beam, it can operate in air or any transparent material, and the source of the

beam need not even be close to the work. The mate-rial being welded need not be an electrical conductor that limits most other processes or even part of an electrical or a mechanical circuit. However, the light may be diffused by the welding vapors, so techniques to bypass the vapors have been developed.

Laser welds are small, sometimes less than 0.001 in.(0.0254 mm). Laser welding is used to connect leads to elements in integrated circuitry for electronics. Lead wires insulated with polyurethane can be welded without removing the insulation.

Using the laser welding process, it is possible to weld heat-treated alloys without undoing the heat treatment.

This method of welding can be used to join dis-similar metals. Metals that are difficult to weld, such as tungsten, stainless steels, titanium alloys, Kovar, nickel alloy, aluminum, and tin-plated steels, can also be successfully welded by this process.

An optical system is used to focus the beam on the workpiece. A switch controls the welding energy.

PLASMA ARC WELDING PAW PROCESS The term plasma should be defined in its electrical sense. A gas, or plasma, is present in any electrical discharge if sufficient energy is present. The plasma consists of charged particles that transport the charge across the gap.

The two outstanding advantages of plasmas are higher temperature and better heat transfer to other objects. The higher the temperature differential between the heating fluid and the object to be heated, the faster the object can be heated.

In plasma arc welding (PAW), a plasma jet is produced by forcing gas to flow along an arc restricted electromagnetically as it passes through a nozzle, Figure 24-8. The stiffness of the arc is increased by its decreased cross-sectional area. As a result, you have better control of the weld pool. By forcing the gas into the arc stream, it is heated to its ionization tem-perature, where it forms free electrons and positively charged ions. The plasma jet produced resembles a brilliant flame. The tip of the electrode is situated above the opening in the torch nozzle, which con-stricts the arc. A plasma welding installation is shown in Figure 24-9. The plasma jet passing through the restraining orifice has an accelerated velocity.

FIGURE 24-7 Gas filter, laser welded. Preco, Inc.



When this intense arc is directed on the work-piece, it is possible to make a welded butt joint in metal having a thickness of up to 1/2 in. (13 mm) in a single pass. No edge preparation or filler metal is required.

Any known metal can be melted, even vaporized, by the plasma jet process, making it useful for many welding operations. This process can be used to weld carbon steels, stainless steels, Monel, Inconel, alumi-num, copper, and brass alloys.

STUD WELDING SWStud welding (SW) is a semiautomatic or automatic arc welding process. An arc is drawn between a metal stud and the surface to which it is to be joined. When

the end of the stud and the underlying spot on the surface of the work have been properly heated, they are brought together under pressure.

The process uses a pistol-shaped welding gun, which holds the stud or fastener to be welded. When the trigger of the gun is pressed, the stud is lifted to create an arc and is then forced against the molten pool by a backing spring. The operation is controlled by a timer. The arc is shielded by surrounding it with a ceramic ferrule, which confines the metal to the weld area.

In the welding operation, a stud is loaded in the chuck of the gun, and the ferrule is fastened over the stud. The gun is then placed on the workpiece. The action of the gun when the trigger is squeezed causes the stud to pull away from the workpiece, resulting in an arc. The arc melts the end of the stud and an area on the workpiece. At the correct moment, a timing device shuts off the current and causes the spring to plunge the stud into the molten pool, which freezes instantly. The gun is then released from the stud and the ferrule knocked off.

HARDFACINGHardfacing is defined as the process of obtaining desired properties or dimensions by applying, using oxyfuel or arc welding, an integral layer of metal of one composition onto a surface, an edge, or the point of a base metal of another composition. The hard-facing operation makes the surface highly resistant to abrasion.

There are various techniques of hardfacing. Some apply a hard surface coating by fusion welding. In other techniques, no material is added but the surface metal is changed by heat treatment or by contact with other materials.

Several properties are required of surfaces that will be subjected to severe wearing conditions, includ-ing hardness, abrasion resistance, impact resistance, and corrosion resistance.

Hardfacing may involve building up surfaces that have become worn. Therefore, it is necessary to know how the part will be used and the kind of wear to expect. In this way, the proper type of wear-resistant material can be selected for the hardfacing operation.

When a part is subjected to rubbing or continu-ous grinding, it undergoes abrasion wear. When metal is deformed or lost by chipping, crushing, or cracking, impact wear results.

ARC CORE

ELECTRODE ORIFICE

SHIELDINGGAS

GAS LENS

OUTER COOLSHEATH

WORKPIECE

FIGURE 24-8 Schematic diagram of plasma welding process. American Welding Society

+

––

CONSTRICTING NOZZLE

ORIFICE GAS

SHIELDINGGAS

WORK

TRANSFERRED NONTRANSFERRED

+

FIGURE 24-9 Transferred and nontransferred plasma arc modes. American Welding Society


592 CHAPTER 24

Selection of Hardfacing Metals Many different types of metals and alloys are avail-able for hardfacing applications. Most of these mate-rials can be deposited by any conventional manual or automatic arc or oxyfuel welding method. Deposited layers may be as thin as 1/32 in. (0.794 mm) or as thick as necessary. The proper selection of hardfacing materials will yield a wide range of characteristics.

Steel or special hardfacing alloys should be used where the surface must resist hard or abrasive wear. Where surfacing is intended to withstand corrosion-type or friction-type wear, bronze or other suitable corrosion-resistant alloys may be used.

Most hardfacing metals have a base of iron, nickel, copper, or cobalt. Other elements that can be added include carbon, chromium, manganese, nitro-gen, silicon, titanium, and vanadium. The alloying elements have a tendency to form carbides. Hardfac-ing metals are provided in the form of rods for oxy-acetylene welding, electrodes for shielded metal arc welding, or in hard wire form for automatic welding. Tubular rods containing a powdered metal mixture, powdered alloys, and fluxing ingredients can be pur-chased from various manufacturers.

Many hardfacing materials are designated by manufacturers’ trade names. Some of the materials have AWS designations. AWS materials are classified into the following designations:

High-speed steel •Austenitic manganese steel •Austenitic high chromium iron •Cobalt-base metals •Copper-base alloy metals •Nickel-chromium boron metals •Tungsten carbides •

The coding system identifies the important ele-ments of the hardfacing metal. The prefix R is used to designate a welding rod, and the prefix E indicates an electrode. Certain materials are further identified by the addition of digits after a suffix.

Hardfacing Welding ProcessesOxyfuel WeldingIn hardfacing operations, oxyfuel welding permits the surfacing layer to be deposited by flowing molten filler metal into the underlying surface. This method of sur-facing is called sweating or tinning, Figure 24-10.

With the oxyacetylene flame, small areas can be hardfaced by applying thin layers of material. In addi-tion, the alloy can be easily flowed to the corners and edges of the workpiece without overheating or build-ing up deposits that are too thick. Placement of the metal can be controlled accurately.

The size of the weld is affected by many factors. These factors include the rate of travel, degree of preheat, type of metal being deposited, and thickness of the work.

Figure 24-11 shows the approximate relationship of the tip, rod, molten pool, and base metal during the hard-facing operation for both backhand and forehand travel.

Iron, nickel, and cobalt-base alloys require a car-burizing flame. Copper alloys and bronze call for a neutral or slightly oxidizing flame. Laps, blowholes, and poor adhesion of deposits can be prevented by a flame characteristic that is soft and quiet.

In all types of surfacing operations, the metal should be cleaned of all loose scale, rust, dirt, and other foreign substances before the alloy is applied. The best method of removing these impurities is by grinding or machining the surface. Fluxes may be used to maintain a clean surface. They also help to overcome oxidation that may develop during the operation.

OUTER ENVELOPEFLAME

EXCESS ACETYLENEFEATHER

INNER CONE

TIP

SWEATING SURFACE

STEEL

FIGURE 24-10 An example of how to produce sweating.American Welding Society

STEELMOLTEN POOLOF ALLOY

ALLOYDEPOSIT

OUTER ENVELOPEFLAME


WELDING ROD

INNER CONE

TIP

FOREHANDDIRECTION OF TRAVEL

FIGURE 24-11 Approximate relationship of the tip, rod, and molten weld pool for forehand hardfacing.American Welding Society



Conventional methods may be used in holding the torch and rod. Figure 24-12 shows the backhand method of hardfacing.

If the base metal is cast iron, it will not “sweat” like steel. Therefore, slightly less acetylene should be used. Alloys do not flow as readily on cast iron as they do on steel. Usually, it is necessary to break the surface crust on the metal with the end of the rod. A cast-iron welding flux is generally necessary. The best method is to apply a thin layer of the alloy and then build on top of it.

The oxyacetylene process is preferred for small parts. Cracking can be minimized by using adequate preheat, postheat, and slow cooling. Shielded metal arc welding is preferred for large parts.

Arc WeldingHardfacing by arc welding may be accomplished by shielded metal arc, gas metal arc, gas tungsten arc, submerged arc, plasma arc, or other processes.

The techniques employed for any one of these processes are similar to those used in welding for joining. The factor of dilution must be carefully con-sidered because the composition of the added metal will differ from the base metal. The least amount of dilution of filler metal with base metal is an important goal, especially where the two metals differ greatly. Little dilution means that the deposited metal main-tains its desired characteristics. When using alloys with high melting points, dilution of the weld metal is usually kept well below 15%.

Hardfacing by the arc welding method has many advantages, including high rates of deposition, flex-ibility of operation, and ease of mechanization.

Hardfacing may be applied to many types of met-als, including low and medium carbon steels, stainless

steels, manganese steels, high-speed steels, nickel alloys, white cast iron, malleable cast iron, gray and alloy cast iron, brass, bronze, and copper.

Quality of Surfacing Deposit The type of service to which a part is to be exposed governs the degree of quality required of the surfacing deposit. Some applications require that the deposited metal contain no pinholes or cracks. For other appli-cations, these requirements are of little importance. In most cases, the quality of the deposited metals can be very high. Steel-base alloys do not tend to crack, while other materials, such as high-alloy cast steels, are subject to cracking and porosity.

Hardfacing ElectrodesThe proper type of surfacing electrode must be selected, as one type of electrode will not meet all requirements. Most electrodes are sold under manu-facturers’ trade names.

Electrodes may be classified into the following three general groups:

Resistance to severe abrasion •Resistance to both impact and moderate abrasion •Resistance to severe impact and moderately severe •abrasion

Tungsten carbide and chromium electrodes are included in the first group. The material deposited is very hard and abrasive resistant. These elec-trodes can be one of two types, either coated tubu-lar or regular coated cast alloy. The tubular types contain a mixture of powdered metal, powdered ferroalloys, and fluxing materials. The tubes are the coated type. These electrodes are used with the electric arc.

Electrodes contain small tungsten carbide crys-tals embedded in the steel alloy. After this mate-rial is applied to a surface, the steel wears away with use, leaving the very hard tungsten carbide particles exposed. This wearing away of steel results in a self-sharpening ability of the surfacing material. Cultiva-tor sweeps and scraping tools are among parts that are surfaced with this material, Figure 24-13.

Chromium carbide electrodes are tougher than tungsten carbide–type electrodes. However, chromium carbide electrodes are not as hard and are less abrasion resistant. This material is too hard to be machined, but it has good corrosion-resistant qualities.

DIRECTION OF TRAVEL

INNER CONE

TIP


OUTER ENVELOPE FLAME

STEELMOLTEN POOLOF ALLOY

ALLOYDEPOSIT

WELDINGROD

BACKHAND

FIGURE 24-12 Backhand method of hardfacing.American Welding Society


594 CHAPTER 24

The electrodes in the second group are the high carbon type. When used for surfacing, these elec-trodes leave a tough and very hard deposit. Examples of hardfaced products in this group include gears, tractor lugs, and scraper blades.

The third group of electrodes is used for sur-facing rock-crusher parts, links, pins, railroad trackcomponents, and parts where severe abrasion resistance is a requirement, Figure 24-14. Depositsfrom these electrodes are very tough but not hard. The surface toughness protects the softer base metal below from damage, and the soft base metal seems to prevent the surfacing material fromcracking.

Shielded Metal Arc MethodStart the process by cleaning the surface. •

Since most hardfacing electrodes are too fluid •for out-of-position welding, the work should be arranged in the flat position.Set the amperage so that just enough heat is pro- •vided to maintain the arc. Too much heat will cause excessive dilution.Hold a medium-long arc, using either a straight or •weaving pattern. When a thin bead is required, use the weave pattern and keep the weave to a width of 3/4 in. (19 mm).If more than one layer is required, remove all slag •before placing other layers.

Hardfacing with gas tungsten arc (GTA), gas metal arc (GMA), and flux core arc (FCA) welding processes may be used in hardfacing operations. These three processes, in many instances, are better methods of hardfacing because of the ease with which the metal can be deposited. In addition, the hardfacing materials may be deposited to form a porosity-free, smooth, and uniform surface.

Where the job calls for cobalt-base alloys, the GTA method does an effective job. Very little pre-heating of the base is required. The GMA and FCA welding processes are somewhat faster than surfacing by GTA due to the fact that continuous wire is used.

Care must be exercised when using the GMA, FCA, and GTA welding processes for hardfacing in order to avoid dilution of the weld. Helium or a mixture of helium-argon normally produces a higher arc voltage than pure argon. For this reason, the dilution of the weld metal increases. An argon and oxygen mixture should be used for surfacing with the gas metal arc processes and argon used with gas tungsten arc processes. When using FCAW, shielding may be provided as either shielding gas or self-shielding. The self-shielding hardsurfacing process is used when working outdoors because of its ability to better resist the effect of light winds.

THERMAL SPRAYING THSPThermal spraying (THSP) is the process of spraying molten metal onto a surface to form a coating. Pure or alloyed metal is melted in a flame or an electric arc

SILAGE KNIFECHURN DRILL

SCOOP LIFT BUCKET

FIGURE 24-13 Farm tools that can be hardfaced with tungsten carbide electrodes to increase the life of the tools. © Cengage Learning 2012

SILAGE KNIFECHURN DRILL

SCOOP LIFT BUCKET

FIGURE 24-14 Products that are hardfaced to produce moderate impact resistance and severe abrasion resistance. © Cengage Learning 2012



and atomized by a blast of compressed air. The result-ing fine spray builds up on a previously prepared sur-face to form a solid metal coating. Because the molten metal is accompanied by a blast of air, the object being sprayed does not heat up very much. Therefore, ther-mal spraying is known as a “cold” method of building up metal, Figure 24-15.

Thermal Spraying Equipment A thermal spraying installation requires, at a mini-mum, the following equipment: air compressor, air control unit, air flowmeter, oxyfuel gas or arc equip-ment, and exhaust equipment, Figure 24-16.

FIGURE 24-15 Rebuilding a worn crankshaft bearing with a Mogul Turbo-jet thermal spraying gun. Eutectic Corporation

TO AIR SUPPLY

ooooooooooo

ooooooooooo

GAS CONTROLUNIT

OXYGEN

FUELGAS

GASFLOWMETER

TO FLOWMETER

HEATING TORCH FOR PREHEATINGWORK AND FUSING COATINGS

AIR CONTROL UNIT(OPTIONAL)

REGULATOR

THERMOSPRAY GUN

VIBRATOR

TRANSFORMER

FILTER

FIGURE 24-16 Complete thermal spray installation. American Welding Society

SUMMARY

Of the nearly 70 welding processes in use today, only a few are commonly used. Often there are processes, not commonly used, that if applied to a weldment could increase productivity and reduce cost on a specific job. Having studied this chapter, you are in a better position to select the most cost-effective process. Understanding the opportunities that are afforded by these various processes will make you far more competitive in the labor market and business world. For example, a company may be using a torch brazing process, when a furnace

braze may be more effective. Sometimes we become comfortable with our knowledge and abilities with a single process and fail to look at all of the emerging technology’s opportunities.

Good sources of current knowledge are welding applications, manufacturers’ literature, and the Inter-net. You should become a member of a professional organization, such as the American Welding Society; this will provide you with up-to-date process infor-mation. Being a top-notch professional welder is a lifelong learning activity.


596 CHAPTER 24

REVIEW QUESTIONS

What two forces cause parts to be joined together 1. in resistance welding?What is the function of a transformer in resis-2. tance welding? What three components do most resistance weld-3. ing machines have?How is the weld produced in spot welding?4. What are some applications of ultrasonic welding 5. in the assembly of electrical products?How is heat generated in the inertia welding 6. process?List advantages of the inertia welding process.7. How is heat generated in laser beam welding? 8. How is the plasma jet produced in the plasma arc 9. welding process?What metals can be melted by the plasma jet 10. process?

Describe the stud welding process.11. Why is hardfacing used?12. What should be considered when selecting hard-13. facing metals?Describe the sweating or tinning method of 14. surfacing.Why must the factor of dilution be carefully con-15. sidered when hardfacing by arc welding? In what three general groups can electrodes be 16. classified?Why should the work be arranged in the flat posi-17. tion for the shielded metal arc method?Why can GTA, GMA, and FCA be better meth-18. ods of hardfacing?What is thermal spraying?19.


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Other Welding Processes - Home - SCCPSSinternet.savannah.chatham.k12.ga.us/schools/wts/staff...Other Welding Processes 587 The welding current required to make a resistance weld must