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Roll-weldingto weld a stack of sheets.SOLUTIONS with Effective, Practical Advice
Roll-welding, also called Roll Bonding, is a process that joins together a stack of sheets or plates. The stack is fed through a cold rolling mill under sufficient pressure to produce significant deformation and solid state welding. Metals should be ductile, like copper, aluminum, low carbon steel, nickel. These can just be stacked, possibly tack welded at certain locations, and then rolled. Thickness reduction is generally more than 60% for the first pass. To lessen the reduction required and still get solid state welding, one can preheat the stack and perform hot rolling, provided that the metals will not undergo excessive oxidation.
For processing reactive metals there is a version of the process called pack Roll welding. It entails the complete enclosure of the starting sheets in a pack sealed by fusion welding of the edges after removing all air. This permits processing of reactive metals or of multi-layer stacks. Titanium alloys are more difficult to Roll-weld because of narrow range of possible working parameters. They are enclosed under vacuum in a steel envelope or can.
One important application of Roll-welding is the production of heat exchanger panels with integral flow tubes embedded. Such elements are used for refrigerator evaporators, for radiators, for solar water heater panels and for industrial thermal controllers. These are produced by first thoroughly cleaning the surfaces, then by applying stop-off ink to define the pattern of the flow channels. After Roll welding and possibly annealing by a suitable post weld heat treatment, the fluid passages that were left not welded (by the presence of stop off material) are opened by inflating them with compressed air, while the panel is held between platens. Mild or low-alloy steel can be clad with a high-alloy material such as stainless steel. Strip cladding of copper with cupro-nickel by Roll-welding is used for making the composite material needed for minting certain coins. Roll-welding is also used for making bimetallic strips for thermostat actuators used by the instrument industry. A modification of the process called Laser Roll-welding, was explored by Japanese scientists in 2002 in research studies and developed for joining dissimilar metals. "Steel sheet was heated with CO2 laser beam, immediately followed by pressing it against the underlying aluminum sheet by means of a roll. Joints were made by inserting aluminum-brazing flux and shielding with argon gas to avoid surface oxidation. Temperature profiles across the section were simulated to identify suitable laser power and travel speed." An Article on Laser Roll Welding was published (2) in Issue 117 of Practical Welding Letter for May 2013.
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