A projection weld is a resistance type weld that is generally applied to a lap or edge joint. The welds to be made are localized at predetermined points and appear as projections or embossments, Figure 19.1. One of the members of the lapped joint is always prepared with an embossed (raised) surface for a projection weld, Figure 19.2. These regularly spaced projections, however, are not shown on any of the views of the drawing. The symbol for this weld is identical to the spot-weld symbol, ^^, and can be applied to the ref­erence line to denote either an arrow side or other side significance. It is not shown astride (centered on) the reference line.

The projection-weld symbol can be distinguished from the spot-weld symbol by the resistance welding process (PW) notation placed in the tail of the arrow. The letters “PW” in the process reference indicates that projection welds are to be made.

PICTORIAL REPRESENTATION FIGURE 19.1 ■ Application of a projection weld to a lap joint.

SIDE VIEW

When the symbol has an arrow side significance, the embossment is located on the arrow side member, Figure 19.3. An other side significance means that the embossment is located on the other side member. Note that the welding process, PW, is always included in the tail for this particular weld.

SYMBOL

EMBOSSMENT REQUIRED BEFORE WELDING

COMPLETED WELD

ARROW SfDE

SYMBOL

EMBOSSMENT REQUIRED BEFORE WELDfMG

COMPLETED WELD

FIGURE 19.2 ■ Side view of a lap joint showing

embossment preparation.

OTHER SIDE

FIGURE 19.3 ■ Application of projection spot-weld symbol.

The elements that can be applied to the projection weld symbol are as follows:

■ Sizes and strength of projection weld. Note the size dimension is preceded by the diameter symbol 0. The strength size is followed by the abbreviation lbs and for metric, mm.

■ Spacing of projection welds

■ Extent of projection welds

■ Number of projection welds

■ Welding process

Several of these elements are applied to the welding symbol shown in Figure 19.4.

The welding symbol for a projection weld can also be used to show the extent of the projection welds. It can be incorporated on the drawing within two extension lines or two centerlines, as shown in Figure 19.5.

FIGURE 19.4 ■ Elements applied to the projection-weld symbol.

FIGURE 19.5 ■ Application of welding symbol to show extent of projection welds.

SYMBOL SIGNIFICANCE

RSW

(3)

(4)

(2)

UNIT 19: REVIEW

1. a. Identify the following symbols.

/

(1)

v> e-

4. a. How does the joint preparation for a projection weld differ from that for a spot weld?

b. Prepare a sketch to illustrate this.

b. Which symbol or symbols in question 1(a) cannot be converted to a projection-weld symbol by changing the welding process?

2. List five elements that can be applied to a projection-weld symbol.

5. Where is the projection-weld symbol located on the reference line? How does this differ from spot-weld symbol locations?

(3)

(2)

3. a. Identify each element given on the following projection-weld symbols (1 through 4). b. Add the element(s) missing in each of the symbols. (1)

6. Apply a welding symbol to Sketch “B” that specifies the data shown in Sketch “A.” Add any other elements necessary to indicate that it is a projection weld. Indicate on the symbol that there are to be three projection welds with diameters, spaced 2" apart. Add any other elements necessary to indicate that it is a projection weld.

7. Is the projection-weld symbol used to denote a both sides significance? Explain.

8. a. Locate the projection-weld symbol on the reference line of the welding symbol in the following sketch to indicate other side projection welds.

b. Add the necessary elements to indicate that six projection welds are required.

c. Add the element that specifies a shear strength of 200 pounds per projection weld.

9. What is the significance of the welding symbol shown in the following illustration?