Resistance welding
Welding with electricity is not limited to ARC WELDING methods. Heat can also be generated in a workpiece as a consequence of current flow. This approach is collectively called ____, but a number of specifically named techniques are used.
Spot welding
____ is arguably the most well-known of all the "Resistance Welding" methods, since it is universally employed on automotive production lines to weld car bodies together.
Spot welding
As the name implies, ____ does not create continuous beads, but instead fuses material together only at localized "Spots".
Spot welding
The equipment required for ____, which can be portable or static, has two rugged copper electrodes projecting forwards of the power supply, and is operated via a "Trigger" or "Foot Switch" respectively.
Spot welding
The power needed for ____ is of high current, not the high voltage required by arc welding.
Spot welding
The ____ technique is generally performed on two overlapping sheets of metal, and relies on there being resistance to current flow through the interface where the two sheets are in contact.
Spot welding
Of course, if two large oppositely-charged sheets were simply laid on top of one another, there would be ample contact area to allow current flow without significant heating. To ensure sufficient heat is generated when ____, the electrode tips are designed to encourage current flow through a very localized area.
Spot welding
When ____, first the electrodes apply a squeezing force to the sheets and then their tapered shape effectively "funnels" electricity through the small spot in hard contact between the tips. The copper metal used for the electrodes is an excellent conductor, and its ductile nature allows copper to conform to the surface. Very little resistance (and heating) occurs where the electrodes make contact, but the surface asperities between sheets (usually of steel) cause high resistance and rapid heating up to the melting point.
Spot welding
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Spot welding
____ occurs rapidly and in the small interfacial gap between the sheets.
FluxInert gas shielding
SPOT WELDING occurs rapidly and in the small interfacial gap between the sheets. These factors mean that there is very little oxygen available, and therefore NO need for ____ or ____.
Filler
SPOT WELDING occurs rapidly and in the small interfacial gap between the sheets. These factors mean that there is very little oxygen available, and therefore NO need for FLUX or INERT GAS shielding. Furthermore, there is no requirement to fill grooves or create a bead, and so NO ____ is needed either.
Spot welding
____ is very simple to perform, requires little operator skill, and minimal PPE (just safety glasses and perhaps light cloth gloves).
Spot weld(s)
The technique lends itself perfectly to automation, especially when combined with robot arms. Such systems allow repetitive SPOT WELDS to be performed in 3D space using relatively simple programming.
Spot welding
Robotic ____ systems can also be combined with laser rangefinders to correct for positioning inaccuracies on car body production lines.
Spot weld(s)
One problem with "____" is that they don't produce fluid tight joints. The area between the individual ____ is un-joined and effectively open. ____ed joints should always be caulked to prevent moisture intrusion and hidden corrosion, but sealants are not structural.
Seam welding
One way to use "Resistance Welding" to create structural fluid-tight joints is through the adoption of SEAM WELDING.
Seam welding
____ is essentially the same as "Spot Welding" except that the cylindrical electrodes are replaced by "Copper Disc Electrodes" that act as rollers.
Seam welding
The ____ technique can be used in an Intermittent Mode, with the power turned on and off at intervals. This creates a series of discrete spot welds, which offers the same result as with spot welding, but completes the task much faster if all that is needed is a long line of individual spots.
Seam welding
When ____ in Continuous Mode the power remains on as the workpiece is squeezed and fed through the disc electrodes. The result is a continuous fluid tight weld, which is actually a series of overlapping spot welds due to the motion and time involved for the metal to reach its melting point.
High frequency resistance welding
A similar fluid-tight resistance weld is performed in pipe manufacturing, when the pipe is to be constructed from folded sheet metal continuously welded along the seam. This method is called ____ (HFRW).
...
Power is delivered via an induction coil that doesn't physically contact the sheet metal. High frequency electromagnetic energy induces a current that flows around the sheet periphery. Squeeze rollers push the edges together creating a localized high-resistance gap where heating and welding occurs.
High frequency induction welding
The addition of an impeder (which changes the "high frequency resistance welding" process name to ____) increases the inductive reactance of the current path around the inside wall and thus makes the outside current larger. The impeder is usually made of ferrite laminations and is water cooled.
Ferrite laminationsWater cooled
What is the impeder made of and how is it cooled in high frequency induction welding?
Projection welding
____ is a "Resistance Welding" technique that makes it easier to confine the welding to specific locations, and which can perform multiple spot-type welds simultaneously.
Projection welding
Basically one sheet is provided with surface projections, usually via embossing, while the other sheet remains flat. A single pair of wide (non-tapered) copper electrodes apply pressure to all the projections together, and then deliver current that flows through each projection at one time. Simultaneously performing multiple welds can generate significant heat, such that the electrodes need to be water cooled.
Flash weldingStud welding
ARC and RESISTANCE welding both use electrical power, but the former demands high voltage while the latter requires high current. It is not possible to supply both at the same time without extreme power demand, but the two can be supplied sequentially, as in ____ and ____.
Flash welding
In ____, two parts are each connected to an electrode and high voltage is applied. As the parts are moved closer together an electrical arc will be struck between them. This softens up the entire cross-section before the two parts are pushed together. At that point the power is switched to high-current mode and the weld proceeds as in resistance welding.
Entire surface
The flash welding technique can look quite impressive when performed on large parts, and has the advantage of welding across an ____.
Stud welding
____ uses the same basic technique but is confined to welding fasteners to plate. A ceramic ferrule (broken away later) is used to confine the weld pool to the base of the stud fastener.
FlameElectricity
There are ways of fusing metal together without needing the direct application of a ____ or ____. Some of these methods are the oldest techniques known, while others are very modern.
Forge weldingCold welding
Arguably the crudest way of welding is to simply apply mechanical force, as is done with ____ and ____.
Forge welding
____ does require elevated temperatures, but this is obtained indirectly through the use of a furnace or blacksmith's forge. Once heated, the joint is subjected to high pressure through hammering or pressing. The method relies on impact or deformation to break up the oxide layer and allow the two parts to fuse together. The process is not very precise or controllable, and joint strength is low.
Cold welding
____ also uses hammering or pressing to fuse the parts together, but this time at room temperature. The low temperature limits the process to ductile metals only in order to achieve the necessary plastic flow required.
Cold welding
The parts first need cleaning with a wire brush to remove as many surface contaminants as possible, but some will always remain, along with an oxide layer. The mechanism of fusion is complex, but it is likely that passages open up between fragmented contaminants/oxide layer as the surfaces are squeezed together. Base metal is extruded through these pathways, bonding together as they meet. The contaminants and oxide remain at the interface, locked up in pockets surrounded by fused metal. The joint is unlikely to be very strong.
Ultrasonic welding
A much more modern approach to mechanically welding without any external heat source is known as ____. In this case two surfaces are "Rubbed" together, thereby generating frictional heat just as you might light a campfire from rubbing two sticks of wood together.
Ultrasonic welding
The process is used on small parts made of metals (often foils and those of different composition) or plastic, and it welds across the entire interface. The ultrasonic vibrations fragment and remove the oxide layers and plastically deform the interface surfaces, causing bonding. Temperatures don't reach melting levels, but materials will flow enough for significant mutual intrusion and mixing to occur.
Friction welding
Another welding process that also rubs surfaces together is called ____. In this case the friction is not caused by vibrations, but rather via relative rotation. It is generally performed when at least one of the parts can be rotated at high speed about a symmetrical axis without imbalance.
Friction welding
____ does get hot enough to cause melting, and will often exhibit upset (flash) which might require subsequent removal.
Friction welding
____ is used to attach the stems to valve heads for internal combustion engines. A weld is necessary since the slender tough stem material must be different to the hardened heat resistance head material.
Friction weld(s)
____ are very strong, and fuse across the entire interface area.
Friction welding
No fluxes are needed for ____ since the friction and rotation strips and slings the oxide respectively.
Friction stir welding
____ is one of the best new innovative welding methods to have come along in recent years (1991). It involves simply plunging (or feeding in from an edge) a stepped rotating tool.
Friction stir welding
The lower PROBE or PIN is forced along the interface and rotated. Metal from both parts are softened by friction, stirred together and deposited as a bead. The SHOULDER makes for a flush bead, and the process can weld dissimilar metals. No flux or shielding gas are required since there is no melting. It is easily automated, and even welds vertically.
Explosion welding
Another process that can weld dissimilar metals is ____. Unlike "Friction Stir Welding" it can weld over large plate areas, and is not restricted to butt welds.
Explosion welding
When ____ one plate on top of another, called CLADDING, one plates is placed above the other perched on "stand-off" props. The upper plate is then covered in an explosive layer. The explosives are detonated at one end, thereby forcing the explosion to progress across the top of the stack. The upper plate is progressively slammed down onto the lower plate, blowing out the props and brittle oxides as contact proceeds from one end to the other.
Cladding
Welding one plate on top of another is called ____
Explosion welding
The rapidly evolving high temperatures and pressures turn the interface into a plastic state, which not only fuses them together, but also "Rings" them like a bell. The surfaces are set into a wave motion, resulting in a mechanical "Interlock" of ripples between the two metals.
Explosion forming
Some might consider this the perfect weld, since it: welds dissimilar metals, welds over the entire interface area, requires no flux or shielding gas, and creates a mechanical interlock. Unfortunately its noisy, dangerous, and heavily regulated.
Magnetic pulse welding
The explosion welding process is slowly being phased out following the introduction of ____ (MPW), which achieves the same result (albeit on a much smaller scale) by using a powerful magnetic pulse, and thereby avoids many of the hazards.
Thermit welding
____ (aka THERMITE WELDING, EXOTHERMIC WELDING) uses a non-explosive, but rapidly burning mixture of powdered ingredients similar to that used in the solid rocket boosters of the "Space Shuttle". The actual mixture is called Thermite and involves the blending of Iron oxide and aluminum:
...
The actual mixture for ____ is called Thermite and involves the blending of Iron oxide and aluminum:2(Al)(solid) + (Fe2)(O3)(solid) --> (Al2)(O3)(solid) + 2(Fe)(liquid)The reaction generates a lot of heat and results in pourable liquid iron (or steel) within seconds.
Thermit welding
The ____ process has many uses, but is best known for welding lengths of railroad track together to create "Continuous Rail". Welded track provides a smoother ride, but also avoids the buckling of individual segments due to expansion during hot weather, which previously led to derailments. Welding rail needs to be performed in the field and be completed quickly. Each rail segment must be welded to its neighbor across the entire interface area, and be strong enough to resist the flexing and bending stress when the wheels of a heavy locomotive pass between ties.
Thermit welding
When welding rail in place, a ceramic mold is created out of clay and formed around the joint. Two crude channels act as sprue and riser, and a catchment area serves to capture the buoyant slag as it rises to the top. The superheated liquid steel is able to run into the gap between adjacent rails, softening the surfaces, fusing them together and fully filling all voids. The mold is then broken up and removed. The process from start to finish typically takes 45 minutes, although extra time may be needed for complete cooling and for grinding off excess from the upper surfaces where the flanged wheels run.
Electron beamsLasers
____ and ____ were already discussed in the section on "Non Traditional Machining". These same methods can also be used for welding simply by turning down the beam intensity to permit melting, but not vaporization.
Laser beam welding
____ (LBW) produces extremely fine welds on both metals and plastics, and can even weld dissimilar metals due to very focused intense heating.
Laser beam welding
It also has the advantage of being able to project the beam into otherwise inaccessible places, such as in-bore welding of tube.
Titanium
____ has always been a challenge when it comes to welding because of its reactivity when molten.
Titanium
FRICTION STIR WELDING can be used for ____ because no melting occurs, as is the case with ULTRASONIC WELDING. EXPLOSION WELDING is another option, albeit a rather aggressive one, with no melting involved.
Titanium
____ can, of course, be welded by processes that do involve melting, such as TIG under copious pure 99.999% Argon (Ar) with special precautions to remove moisture and all contaminants.
Diffusion bondingDiffusion welding
For cases where large interface areas of Titanium need to be welded, on precision parts, the answer is ____.
Diffusion bondingDiffusion welding
This process is akin to "Sintering" in PM processing, in that the parts are assembled and placed in an oven under vacuum or special atmospheric conditions. By applying pressure and raising the temperature to about 50% of the melting point, the voids between part surfaces will slowly disappear, just as green-state porosity does during PM sintering.
Diffusion bondingDiffusion welding
The process is slow, but the final assembly is indistinguishable from a single solid partDissimilar metals can also be joined
Brazing
Conventional welding techniques, such as OXY-FUEL, MIG and TIG, leave a Heat Affected Zone (HAZ) flanking the bead. This can negatively impact the material properties of the base metal. Also, for some, the appearance of a weld bead can seem rather ugly. For no HAZ and a clean look it is always possible to use an adhesive, but these can't resist the kind of temperatures that metals can easily endure. The solution is to use what is effectively a "Metal Adhesive", such as ____.
Brazing
____ uses a filler metal to join the parts together, but one with a lower melting point than the base metal of the parts.
Brazing
The base metal is never raised to a temperature hot enough to cause local melting during ____, and so there is no significant HAZ. Without melting, the parts retain their original dimensions and prejoined crisp/sharp edges, without warping, sagging or puddling.
Brazing
____ is most often performed on STEEL, with the lower melting point filler metal being a COPPER ALLOY. Mainly done on ferrous materials.It is also possible to braze many other materials provided the proper filler metal is chosen.
Flux
All brazing requires the use of a ____ (typically BORAX) to remove oxides. Unlike "Stick Welding" the ____ is not coated on a filler rod, but is applied to surfaces first, before any assembly or heating. The ____ comes as a paste and can be painted on with a brush. The brazing filler metal will flow across and adhere to surfaces only where the ____ has been applied. It is important to cover all faying surfaces with ____, but not to let it drip or splash onto areas that need to remain free of braze.
Faying surface
The surfaces of materials in contact with each other and joined or about to be joined together
Brazing
Once the faying surfaces have been coated with flux, the parts can be assembled together and heat applied. There are many ways of heating up the joint, but the simplest approach is to use MAPP gas (acetylene and propane mix) through a portable torch. It is not necessary to stab the filler rod into the joint until the correct temperature has been attained, which for STEEL is indicated by it glowing with a CHERRY RED color.
Brazing
The ____ filler is not as strong as the base metal, but just like with adhesives the overall strength of the joint can be elevated (perhaps to that of a welded bead) if sufficient overlap area is utilized. Brazed joints are designed specifically to maximize overlap area, and rely on the flux to enable the filler to be drawn into tight clearances through capillary action.
Soldering
____ is a similar process to "Brazing" but it is usually performed on non-ferrous materials (especially copper) and uses a very low melting point filler metal such as TIN (Sn) (and possibly, lead, silver, bismuth and cadmium).
Soldering
The joints are mechanically quite weak, but find widespread use in plumbing and electrical applications.
Sweat joint
PLUMBERS use solder to create leak-proof joints when dealing with copper pipe and fittings. The process steps are very similar to "Brazing", and usually require some scuffing (with emory cloth), followed by painting on flux, assembling the joint, applying heat and feeding in the filler metal (solder). There are just two differences, firstly a less expensive PROPANE gas flame is all that is required, and secondly the acceptance temperature for the solder is indicated by the flux beginning to hiss, bubble and ooze from the joint. Plumbers often refer to this joining method as a ____.
Soldering ironSoldering gun
For ELECTRICAL SOLDER JOINTS it would be inappropriate to use a gas torch, and impractical to apply flux paste to every contact point on a circuit board. For this application the heat is applied via a ____ or ____.
Flux-cored
Both the soldering iron and soldering gun are electrically powered and develop heat at their tip. Once at working temperature, the tip is then laid alongside the component requiring soldering and the filler (solder) fed in from the side. Without flux the joint wouldn't properly take, resulting in a bad electrical connection. So the solder wire used is always of ____ construction - meaning that the flux is already inside the wire.
Wave soldering
When mass producing computer circuit boards involving thousands of individual solder connections, it is not practical to make these joins one at a time manually. A process was therefore developed that could automatically solder an entire circuit board in one-fell-swoop. This is known as ____.
Wave soldering
The fundamental concept for ____ is fairly simple - create a wave of molten solder and pass the circuit board through the peak. For surface soldered boards the components will require temporary protection from the molten metal using a glue barrier, but this is not necessary for soldering pins projecting out the underside.
Flux
It is possible to set up a wave of solder that travels from one end of a bath to the other, and thereby sweeps across the surface of a stationary board. However, for higher volume product throughput it is better to create a stationary wave, and convey boards through it on a continuous basis. This approach also means the ____ can be applied separately rather than mixing it in with the molten solder, which affords more control and economy.
Standing waves
The stationary wave (for both the flux and solder) can be created by pumping up through baffles to induce a central upwelling and double cascade recirculation. Alternatively the flux can be sprayed on, but this method usually results in aerosolization and poor air quality. ____ can also be created acoustically using computer controlled sonic transducers, which is more energy efficient than pumping molten metal.