ME 134 2SAY2324 Resistance and Solid State Welding Process PDF

University of the Philippines Diliman Department of Mechanical Engineering Resistance and Solid-State Welding Processes Introduction Resistance Welding Joints are formed using electrical resistance Solid-State Welding...

University of the Philippines Diliman Department of Mechanical Engineering Resistance and Solid-State Welding Processes Introduction Resistance Welding Joints are formed using electrical resistance Solid-State Welding Joints are formed without any melting of the workpiece or filler metal University of the Philippines Diliman – Department of Mechanical Engineering Theory of Resistance Welding ▪ Heat + Pressure = Coalescence Electrodes that supply current also apply pressure on the workpiece. Occurs at lower temperature compared to oxyfuel or arc welding. University of the Philippines Diliman – Department of Mechanical Engineering Resistive Welding Temperature Distribution Temperature is determined by the magnitude and duration of the welding current. ✓ High current and short time intervals Bulk resistance- increase as temperature rises Faying Surface Contact resistance- decrease as the metal softens and pressure improves the contact (not desirable) University of the Philippines Diliman – Department of Mechanical Engineering Current and Pressure for Resistive Welding Too little pressure – surface burning or pitting of electrodes Too much pressure – molten or softened metal may be expelled from between the faying surface – electrodes may indent the softened workpiece FIGURE 32-3 A typical current and pressure cycle for resistance welding. This cycle includes forging and postheating operations. University of the Philippines Diliman – Department of Mechanical Engineering Resistance Welding Processes Resistance Spot Welding Resistance Seam Welding Projection Welding University of the Philippines Diliman – Department of Mechanical Engineering Resistance Spot Welding University of the Philippines Diliman – Department of Mechanical Engineering Resistance Spot Welding ▪ Simplest and most widely used form of resistance welding ▪ Fast and economical means of joining overlapped materials electrodes University of the Philippines Diliman – Department of Mechanical Engineering Microstructure of a Resistance Weld A spot-weld nugget between two sheets of 1.3-mm (0.05-in.) aluminum alloy. The nugget is not symmetrical because the radius of the upper electrode is greater than that of the lower electrode. (Courtesy Lockheed Martin Corporation, Bethesda, MD.) University of the Philippines Diliman – Department of Mechanical Engineering Tear Test ▪ Weld should remain intact while failure occurs in the heat-affected zone surrounding the nugget University of the Philippines Diliman – Department of Mechanical Engineering Resistive Welder Single-phase, air-operated, press-type resistance welder with microprocessor control. (Courtesy Sciaky Inc., Chicago, IL.) University of the Philippines Diliman – Department of Mechanical Engineering Spot Welding Application University of the Philippines Diliman – Department of Mechanical Engineering Resistance seam welding University of the Philippines Diliman – Department of Mechanical Engineering Resistance Seam Welding ▪ Overlapping Welds ▪ Weld is made between overlapping sheets of metal and the seam is a series of overlapping spot welds ▪ Electrodes are in the form of rotating disks ▪ Applications: gas or liquid tight vessels (gas tanks, mufflers and simple heat exchangers) University of the Philippines Diliman – Department of Mechanical Engineering Resistance Seam Welding ▪ Resistance Butt Welding ▪ Produces butt welds between thicker metal plates ▪ Used in manufacture of pipes and tubes University of the Philippines Diliman – Department of Mechanical Engineering Projection Welding University of the Philippines Diliman – Department of Mechanical Engineering Resistance Welding Process ▪ Projection Welding ▪ Used to overcome limitations of spot welding ▪ Spot welding limitations ▪ Electrodes generally require frequent attention to maintain their geometry ▪ Produces only one spot weld at a time. University of the Philippines Diliman – Department of Mechanical Engineering Projection Welding ▪ Dimple is embossed into one of the workpieces at the location where a weld is desired. ▪ Two workpieces are then placed between large-area electrodes in a press machine, and pressure and current are applied as in spot welding ▪ As the metal heats and becomes plastic, the pressure causes the dimple to flatten and form a weld University of the Philippines Diliman – Department of Mechanical Engineering Advantages of Resistance Welding ▪ Rapid ▪ Can be fully automated ▪ Skilled operators not required ▪ No filler metal, shielding gas and flux required ▪ Minimal distortion of the parts being joined ▪ Dissimilar metal can be joined easily ▪ High degree of reliability and reproducibility can be achieved University of the Philippines Diliman – Department of Mechanical Engineering Limitations of Resistance Welding ▪ High initial cost ▪ There are limitations to the thickness of material that can be joined ▪ Lap joints tend to add weight and material ▪ Access to both sides is usually required ▪ For some materials, surfaces need special preparation prior to welding University of the Philippines Diliman – Department of Mechanical Engineering Solid State Welding University of the Philippines Diliman – Department of Mechanical Engineering  Solid-State Welding Processes ▪ Forge welding ▪ Forge-seam welding ▪ Cold welding ▪ Roll welding/ roll bonding ▪ Friction welding ▪ Inertia welding ▪ Friction Stir-Welding ▪ Ultrasonic Welding ▪ Diffusion Welding ▪ Explosive Welding University of the Philippines Diliman – Department of Mechanical Engineering Forge Welding (FOW) ▪ Most ancient of welding processes ▪ Utilized by blacksmiths ▪ Equipment needed: ▪ Charcoal forge ▪ Hammer ▪ Anvil ▪ Borax flux ▪ Procedure: ▪ Joint preparation → Flux application → Welding ▪ Pieces to be joined are heated then hammered together until coalescence is achieved ▪ Results are highly variable University of the Philippines Diliman – Department of Mechanical Engineering Forge Seam Welding ▪ Commonly used for pipes ▪ Uses conical welding bell or welding rolls ▪ Edges are joined in a lap or butt configuration University of the Philippines Diliman – Department of Mechanical Engineering Cold Welding ▪ Variation of forge welding ▪ Done at room temperature ▪ Coalescence is achieved by the application of high localized pressure ▪ Used for soft, ductile materials University of the Philippines Diliman – Department of Mechanical Engineering Roll Welding/ Roll Bonding (ROW) ▪ Sheets or plates of metal are passed through a rolling mill ▪ Can be done hot or cold ▪ Can be used to join similar or dissimilar metals University of the Philippines Diliman – Department of Mechanical Engineering Roll Welding Examples of roll-bonded refrigerator freezer evaporators. Note the raised channels that have been formed between the roll-bonded sheets. (Courtesy Olin Brass, East Alton, IL.) University of the Philippines Diliman – Department of Mechanical Engineering Friction Welding (FRW) ▪ Utilizes friction generated heat ▪ Surfaces to be joined must have square-cut, smooth surface ▪ Can be used for steel bars up to 8 inches in diameter or dissimilar metals University of the Philippines Diliman – Department of Mechanical Engineering Schematic for Friction Welding University of the Philippines Diliman – Department of Mechanical Engineering (Courtesy of Materials Engineering.) Friction Welding University of the Philippines Diliman – Department of Mechanical Engineering Inertia Welding ▪ Modification of friction welding ▪ Utilizes a flywheel ▪ Consistent weld quality since energy stored by the flywheel can be directly controlled for subsequent operations ▪ Fast and efficient University of the Philippines Diliman – Department of Mechanical Engineering Inertia Welding Schematic representation of the various steps in inertia welding. The rotating part is now attached to a large flywheel. University of the Philippines Diliman – Department of Mechanical Engineering Friction-stir Welding ▪ Uses a rotating probe to generate frictional heat ▪ Material is softened without melting and stirred ▪ Softened material coalesces and swept to the back University of the Philippines Diliman – Department of Mechanical Engineering Stir Welding Generates frictional heat Provides additional friction heating and prevents expulsion of softened material from the joint University of the Philippines Diliman – Department of Mechanical Engineering Features of Stir Welding University of the Philippines Diliman – Department of Mechanical Engineering Stir Welding University of the Philippines Diliman – Department of Mechanical Engineering Example of Stir Welding FIGURE 32-19 (a) Top surface of a friction-stir weld joining 1.5- mm- and 1.65-mm-thick aluminum sheets with 1500-rpm pin rotation. The welding tool has traversed left-to-right and has retracted at the right of the photo. (b) Metallurgical cross section through an alloy 356 aluminum casting that has been modified by friction-stir processing. University of the Philippines Diliman – Department of Mechanical Engineering Disadvantages of Friction-stir Welding ▪ Large downward force required ▪ Low flexibility ▪ Slow traverse rate University of the Philippines Diliman – Department of Mechanical Engineering Ultrasonic Welding ▪ Uses high frequency ( 10khz-200khz) ▪ Temperature rarely exceeds half of melting point ▪ Restricted to welding thin sheets University of the Philippines Diliman – Department of Mechanical Engineering Schematic of Ultrasonic Welding University of the Philippines Diliman – Department of Mechanical Engineering Advantages and Disadvantages ▪ Advantages ▪ Very fast ▪ Clean surface ▪ Equipment is simple to use ▪ Disadvantage ▪ Limited to welding thin sheets University of the Philippines Diliman – Department of Mechanical Engineering Application of Ultrasonic Welding University of the Philippines Diliman – Department of Mechanical Engineering Diffusion Welding www.sensorprod.com University of the Philippines Diliman – Department of Mechanical Engineering Explosive Welding Accelerates one of the components through the use of explosives Limited geometry University of the Philippines Diliman – Department of Mechanical Engineering