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LAP JOINT. A joint between two overlapping members.
LASER BEAM CUTTING. Laser beam cutting uses the intense heat from a laser beam to melt and/or evaporate the material being cut. Any known material can be cut by this process. For some nonmetallic materials the mechanism is purely evaporation, but for many metals a gas may be supplied, either inert to blow away the molten metal and provide a smooth, clean kerf, or oxygen to speed the process through oxidation. The temperature achieved may be in excess of 11,093°C (20,000°F), and cutting speeds of the order of 25.4 meters (1,000 inches) per minute are not uncommon in nonmetals and 508 mm (20 inches) per minute in tough steels.
LASER BEAM WELDING. The heat source in laser beam welding is a focused laser beam, usually providing power intensities in excess of 10 kilowatts per square centimeter, but with low heat input -0.1 to 10 joules. The high-intensity beam produces a very thin column of vaporized metal, extending into the base metal. The column of vaporized metal is surrounded by a liquid pool, which moves along as welding progresses, resulting in welds having depth-to-width ratios greater than 4:1. Laser beam welds are most effective for simple fusion welds without filler metal, but filler metal can be added.
LAYER. A stratum of weld metal, consisting of one or more weld beads.
LEAD ANGLE. The angle that the electrode makes in advance of a line perpendicular to the weld axis at the point of welding, taken in longitudinal plane.
LEG OF A FILLET WELD. The distance from the root of the joint to the toe of the fillet weld.
LOCAL PREHEATING. Preheating a specific portion of a structure.
LONGITUDINAL RESISTANCE-SEAM WELDING. The making of a resistance-seam weld in a direction essentially parallel to the throat depth of a resistance-welding machine.
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