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LESSON 25

Welded Joints

Welding is defined as the localized, intimate union of metal parts in the plastic, or

plastic and molten states, with the application of blows or mechanical pressure; or

the union of parts in the molten state without any pressure. There are three mainmethods of welding, forge welding, electric resistance welding and fusion

welding which may be further classified as shown in Fig 3.12

Fig.3.12 Spectrum of welding methods.

Of the many type of welding, the one commonly used in the manufacture of

machinery is arc welding, next comes gas welding. There are two general fields ofapplication for welding:

(1) When welding is substituted for riveting, and

(2) When welding is used as an alternate method for casting or forging.The main advantages of welded joints over riveted joints are:

1. Lighter weight, due to elimination of straps, gusset plates etc.

2. The efficiency of the joint can be as high as 100 per cent.3. Lower cost.

4. Ease of fabrication.5. Less noisy.

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Type of Welded Joints

There are five basic forms of welded joints

(1) Edge

(2) Butt

(3) Tee(4) Lap

(5) Corner

Fig.3.13 Types of welded joints.

The lap or fillet joint is obtained by over lapping the plates and then welding the

edges of the plates. The lap joint may be single transverse fillet, double transverse

fillet or parallel fillet as shown in Fig. 3.14

Fig.3.14 Types of fillet welded joints.

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Fig.3.15 Types of butt-welded joints.

The butt joint is obtained by placing the two plates edge to edge-: and then

welding them. Various forms of butt-welded joints are shown in Fig. 3.15

Edge Preparations

Fig.3.16 Joint preparation dimensions.

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Before welding two plates their edges have to be prepared. Fig. 3.16shows edge

preparation method for various types of joints.