Welding Design and Process Selection

材料科学与工程学院College of Materials Science & Engineering Page 1

Fundamental of Materials Forming

-The Metallurgy of Welding;

Welding Design and Process Selection


Fusion Weld Zone

Figure 29.1 Characteristics of a typical fusion weld zone in oxyfuel gas and arc welding. See also Figs. 27.16 and 28.14.


Grain Structure in Shallow and Deep Welds

(a) (b)

Figure 29.2 Grain structure in (a) a deep weld (b) a shallow weld. Note that the grains in the solidified weld metal are perpendicular to the surface of the base metal. In a good weld, the solidification line at the center in the deep weld shown in (a) has grain migration, which develops uniform strength in the weld bead.


Weld Beads

Figure 29.3 (a) Weld bead (on a cold-rolled nickel strip) produced by a laser beam. (b) Microhardness profile across the weld bead. Note the lower hardness of the weld bead compared to the base metal. Source: IIT Research Institute.

(a)(b)


Regions in a Fusion Weld Zone

Figure 29.4 Schematic illustration of various regions in a fusion weld zone (and the corresponding phase diagram) for 0.30% carbon steel. Source: American Welding Society.


Corrosion

Figure 29.5 Intergranular corrosion of a 310-stainless-steel welded tube after exposure to a caustic solution. The weld line is at the center of the photograph. Scanning electron micrograph at 20 X. Source: Courtesy of B. R. Jack, Allegheny Ludlum Steel Corp.


Incomplete Fusion

Figure 29.6 Low-quality weld beads, the result of incomplete fusion. Source: American Welding Society.


Discontinuities in Fusion WeldsFigure 29.7 Schematic illustration of various discontinuities in fusion welds. Source: American Welding Society.


Cracks in Welded Joints

Figure 29.8 Types of cracks (in welded joints) caused by thermal stresses that develop during solidification and contraction of the weld bead and the surrounding structure. (a) Crater cracks. (b) Various types of cracks in butt and T joints.


Crack in a Weld Bead

Figure 29.9 Crack in a weld bead, due to the fact that the two components were not allowed to contract after the weld was completed. Source: S. L. Meiley, Packer Engineering Associates, Inc.


Distortion After Welding

Figure 29.10 Distortion of parts after welding: (a) butt joints; (b) fillet welds. Distortion is caused by differential thermal expansion and contraction of different parts of the welded assembly.


Residual Stresses Developed During Welding

Figure 29.11 Residual stresses developed during welding of a butt joint. Source: American Welding Society.


Destructive Techniques

Figure 29.12 Two types of specimens for tension-shear testing of welded joints.

Figure 29.13 (a) Wrap-around bend test method. (b) Three-point bending of welded specimens--see also Fig. 2.11.


Testing of Spot Welds

Figure 29.14 (a) Tension-shear test for spot welds. (b) Cross-tension test. (c) Twist test. (d) Peel test; see also Fig. 30.8.


Welding Design GuidelinesFigure 29.15 Design guidelines for welding. Source: J. G. Bralla (ed.), Handbook of Product Design for Manufacturing. Copyright ©1986, McGraw-Hill Publishing Company. Used with permission.


Standard Identification and Symbols for Welds

Figure 29.16


Weld Design Selection

Figure 29.17

Welding Design and Process Selection

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