52 Modern Welding 3.3.1 Preparation The edges of thick metal are prepared for welding by fl ame cutting, gouging, or machining. Preparation allows the weld to penetrate as deep as required by the engineer or weld designer. A groove joint allows the welder to reach the bottom of the weld joint. The groove angle must be large enough to allow the torch tip or electrode to reach near the bottom of the joint. However, if the groove angle is too large, fi ller metal and the welder’s time are wasted. This increases the cost of making a weld. See Figure 3-12A. A properly designed J-groove or U-groove joint also decreases the groove dimensions while allowing adequate space for welding. See Figure 3-12B. 3.3.2 Joint Alignment The alignment of a joint before welding is very important. In the shop, the alignment of the weld joint is often referred to as “fi t-up.” A ragged edge or an edge that is not cut straight is hard to weld. See Figure 3-13. Edges to be welded must be straight and cut to exact size. Parts of a weldment should be properly aligned and held in position during the welding operation. Tack welding is usually adequate to hold parts during welding. A tack weld is a small weld used to hold pieces in alignment. Parts may also be held mechani- cally during the welding operation because the metal expands, bends, and changes shape when heated. Clamps or other devices, such as jigs and fi xtures, are used to hold weldments during welding. See Figure 3-14. Figure 3-12. Compare the 70° and 90° groove angles. A—A 70° groove angle is cheaper to weld than a 90° groove angle. The shaded area represents an unnecessary cost in fi ller metal and welder time. B—Look at the U-groove joint. The root of the weld can be reached easily. Little fi ller metal and welder time are wasted. 90° 70° A B Figure 3-13. Poorly prepared base metal edges. The edges in A are ragged. One edge in B is not cut straight, which changes the width of the joint. Both joints would be diffi cult to weld. A B Figure 3-14. These various clamps are used to position and hold parts to be welded. (Bessey Tools North America)
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