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16 Cards in this Set
- Front
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Welding processes can be broadly defined by three distinct types of metallurgical bonds formed between the two parts being welded. What are the three types of welding? |
1. Fusion welding 2. Solid-state welding 3. Soldering/brazing |
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One of the three broad types of welding is fusion welding. Explain how fusion welding works. |
Fusion/melting of materials at the part/welding gun interface results in mixing of atoms. Results in very strong bond when molten weld cools. |
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One of the three broad types of welding is solid-state welding. Explain how solid-state welding works. |
Adhesion is produced by a metallic bonding of energised crystals (metals do not melt). Size of the fragments transferred between the parts grows until they become a continuous layer of plasticised metal. |
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One of the three broad types of welding is soldering/brazing. Explain how soldering/brazing works, and distinguish between soldering and brazing. |
Filler metal bonds to both components and is subsequently melted by a source of heat, joining the components. Solder: lower melting point, can be used near electronic components Braze: higher melting point, can be used to join ceramics to metals |
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Name three types of fusion welding processes |
1. Manual Metal Arc (MMA) welding with shielded electrode 2. Metal Inert Gas (MIG) welding 3. Tungsten Inert Gas (TIG) welding |
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Manual Metal Arc (MMA) welding with a shielded electrode is a type of fusion welding process (most flexible and widely used arc welding process). Describe how MMA welding works. |
Involves striking an arc between a covered metal electrode and a workpiece (arc produced by flow of current from workpiece to electrode). The heat of this arc melts the parent metal and electrode, which mix together to form, on cooling, a continuous solid mass. |
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Metal Inert Gas (MIG) welding is a type of fusion welding process. Describe how MIG welding works. |
MIG welding is an arc welding process where a continuous solid wire is fed through a welding gun and into the weld pool, joining the two metals. A shielding gas is also used to protect the welding pool from contaminants. |
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Tungsten Inert Gas (TIG) welding is a fusion welding process. Explain how TIG welding works. |
TIG welding is an arc welding process that uses a non-consumable tungsten electrode and filler wire. The weld zone is shielded by an Inert Gas to prevent contamination. |
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How does explosion welding work? |
Two metal surfaces are joined with sufficient impact and pressure to bond. Pressure is developed by a high-explosive shot placed in contact with (or in close proximity to) the metals. |
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How does stir friction welding work? |
Welding coalescence produced from heat generated by rotating one piece against another under controlled axial pressure. Two surfaces reach melting pressure, then relative motion is stopped and a forging pressure is applied. |
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Explain how thermite welding works, and what it is typically used for. |
Typically used for welding continuous rails (eg train track). Individual rail pieces are spaced apart ~25mm, then a mould is clamped around the rail ends. Molten steel is poured into mould, fusing with rail ends and forming the weld. |
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How does spot (resistance) welding work? |
The metal surfaces to be joined are placed between two electrodes. The heat obtained by the resistance to electric current flow between the two electrodes causes the metals to join (also requires pressure). |
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Explain how continuous seam welding works. |
Two pieces of sheet metal are in contact while two copper wheels roll along either side of the metal and act as electrodes. High current flows between the two wheel electrodes and forms a welded joint. |
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Explain how laser welding works |
Laser is focussed as a coherent beam of photons, allowing deep-penetration welds without affecting the base metal. |
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The rapid heating and cooling of metals can cause thermal stresses which are detrimental to the strength of the joint. List seven way that these stresses can be prevented/reduced. |
1. Edge preparation/alignment 2. Control of heat input 3. Preheating: reduces expansion/contraction forces 4. Peening: help metal stretch as it cools by hitting it with a hammer 5. Heat treatment: soak metal at high temperature to remove stresses 6. Jigs and fixtures: prevent distortion by holding metal fixed 7. Number of passes: fewer the better |
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What is the Heat-affected Zone? |
The area of base material which is not melted and has had its microstructure /properties altered by welding. |
