COMPARISON OF WELDING/BONDING METHODS

Transcription

1 TYPE OF WELDING/BONDING Adhesive Bonding Diffusion Welding Electron Beam Welding Explosive Welding SUMMARY ADVANTAGES DISADVANTAGES Bond is established through use of an intermediate adhesive layer applied to one or both of the substrates. Uses differential atomic concentration gradients to bond metals under high temperature and pressure. The kinetic energy of a focused beam of electrons is converted to heat upon contact, melting two metals together. Uses explosives to impact flyer metal to bonding surface at velocities high enough to remove oxide coatings; solid state impact welding. Relatively low bonding temperature No dangerous voltages Produces leak-tight welds Materials of different thicknesses can be welded One can localize heating to a precise point during welding One can control the exact amount of energy needed for a welding operation Large areas can be bonded very quickly (except for preparation and clean up time) Creates a relatively clean weld Page 1 of 7 Possible lack of hermetically sealed encapsulation Thermal instability Allows moisture penetration Bonding surfaces must be mated in size to within a few angstroms of each other before bonding takes place Requires a long thermal cycle Only penetrates the surface of the outer rim of parts being joined, not all the way through Requires extensive safety procedures Excessive material waste for small to medium size parts Chemical pollution WHY NEXW IS SUPERIOR Hermetically sealed Is thermally stable in accordance with the thermal stability of each material being bonded AHPT can produce the same or better weld quality instantaneously without thermal or surface material preparation NEXW can form a welded joint over entire surfaces Environmentally benign Little to no material waste which can then be recycled No explosives

2 Handling of explosives Noise pollution Acres of space required Fabrication takes months Large, specialized workforce required handled Requires no extensive amounts of knowledge for operation Can be done in-house in small areas Fabrication takes seconds No noise pollution Mostly imported parts Long clean up time Unidirectional wave morphology More cost effective Circumferential wave morphology for stronger joints Flash Welding A type of electric resistance welding that involves welding butt joints with sudden applied pressure and flashing heat with no filler metal. Expulsion of flash (molten metal) removes impurities and creates a sound solid-state joint Certain non-circular cross sections can be welded Expelled flash material is hazardous to the surrounding environment and humans Work pieces often require similar or identical cross sections Cartridges don t expel debris or hazardous Work pieces don t need identical cross sections or be butt joints Page 2 of 7

3 Friction Stir Welding A rapidly rotating tool heats and plastically displaces to weld them at the seam. No toxic fumes No consumables Good weld appearance thus reducing postweld machining When tool is withdrawn, an exit hole remains Heavy-duty clamping required to hold plates together Leaves no exit hole Doesn t require heavy-duty clamping Can weld non-linear configurations Great difficulty with non-linear welds Friction Welding Rotating or moving workpieces are contacted under pressure to forge a non-melted weld. No filler metal is required Defects and porosity aren t a problem Minimizes sparks, smoke, and fumes Operators aren t required to have manual welding skills Easily automated At least one workpiece must be capable of rotation Interface geometry must be prepared to achieve proper heat balance Capital equipment and tooling costs are very high Pieces don t need an axis of rotation or any rotation capabilities Takes up little plant space Gas Metal Arc Welding A shielding gas is fed through the welding gun during an arc welding process. Can somewhat easily be adapted to automated use Relatively quick process Unsuitable penetration for welding thick metals Can both bond thin and thick metals Less skill is required Page 3 of 7

4 Magnetic Pulse Welding Electromagnetic force accelerates a flyer into a bonding surface; very similar to explosive welding. Creates a relatively clean weld Can only be used for conductive Equipment would result in strong magnetic fields and thus requires extensive safety procedures Can be used to bond nonconductive No extensive safety measures Efficient for both mass production and one-offs Coils have to be custom made to suit the parts being fabricated, thus requiring mass production and eliminating one-offs Projection Welding A type of electric resistance welding that involves the positioning of welds by raised embossments. A number of welds can be made simultaneously in one welding cycle Projection electrodes see less wear and tear than spot electrodes The formation of projections may require additional work Projections limit sheet metal thicknesses NEXW cartridges could form all of the projections without additional machining Can bond diverse thicknesses Resistance Seam Welding Like resistance spot welding, except electrodes are in the form of wheels that progressively move to form a continuous, leaktight seam. Same as Resistance Spot Welding (below) Can produce a leaktight seam Same as Resistance Spot Welding (below) NEXW technology can instantly produce a large spot weld that would eliminate the Page 4 of 7

5 need for a progressive seam weld and save time in the process Resistance Spot Welding Resistance to electric current is used to generate heat to join contacting metal surfaces. Electrodes weld metals at discrete points. High speed and adaptability Can be done in house Requires less skill than arc welding or brazing Disassembly for maintenance or repair is difficult Equipment costs are generally higher than arc welding NEXW can spot weld dissimilar metals Equipment and maintenance is One cartridge shot can power large numbers of spot welds Roll Bonding Sheets are cut, aligned prewelded at the edges, evacuated of gas, and then rolled together as a cladding process. Less costly and safer than explosive welding Requires extensive preparation in alignment, surface preparation, prewelding, and gas evacuation Requires no prewelding, gas evacuation, and only minimal alignment and surface preparation Shielded Metal Arc Welding A consumable electrode coated in flux is manually applied to the metals intended to be joined. During welding, the flux electrode coating disintegrates and forms shielding gases and slag. relatively in Versatile for field work Operator skill level greatly determines amount of common defects Generally limits welding to ferrous Weld times can be slow Requires little to no training and no technique mastery Materials to be joined are essentially not restricted Weld times are instantaneous Page 5 of 7

6 Submerged Arc Welding Weld and arc zone are protected from contamination by submersion in a blanket of granular fusible flux. High deposition rates Deep, sound welds Requires little edge preparation Minimal welding fumes and arc light Due to flux blanket, there is no weld splatter Limited to ferrous and nickel-based alloys Limited to long, straight seams or rotated pipes or vessels Flux and slag residue present health concerns Requires troublesome flux handling systems Not limited to ferrous and nickel-based alloys There is no flux and slag residue to present health concerns There is no limitation to long, straight seams System is straightforward and easy to operate Thermite Welding An aluminothermic reaction between aluminum powder and a metal oxide heats and welds metals. No overly complex equipment is required Can weld relatively difficult shapes Can t weld low melting point or reactive metals (Pb, Sn, Zn, Ti) Low deposition rate Can weld low melting point and reactive metals Doesn t require skilled workers Requires skilled workers Welds are essentially instantaneous Ultrasonic Welding Solid-state welding process that applies high-frequency vibratory energy to workpieces held together under pressure. A solid-state process that welds with minimum impact Relatively quick process (welds within fractions of a second) Easily automated High-powered electrical equipment and thus high voltages create safety problems Ultrasonic welding machines can cost around three times more than resistance welding machines Can weld thick metals as well as thin metals No dangerous voltages Page 6 of 7

7 Cannot weld relatively thick metals Upset Welding A similar process to flash welding without the flashing. Faster than flash welding Typically uses DC power source Can only be used when parts are equal in cross-sectional area Work pieces do not need identical cross sections or butt joints No material ejected and thus process is inherently clean Page 7 of 7