Preparation of the Joints
Correct preparation of the parts to be joined is of great importance in the production of the successful welds. In addition thorough cleaning, ensure that all oil, grease, paint and oxides are removed from the parts. Preparations for the welding may include.
(a) Suitable preparation of the edges along which the weld is to be made.
(b) Accurate setting up of parts in relation to one other.
(c) Preheating or other measures to avoid the stresses and distortion.
Preparation of Edges
Except when thin sheet metal is concerned, it is usually necessary to prepare the edges of the parts to be joined before welding is committed. The method of preparing the edges depends on the material, the thickness and welding technique.
In general, the following points should be observed while preparing the edges.
(a) Flanging may be done to sheet metal of Steel, Brass, Copper or Monel metal upto 1/6” thickness. The edges are turned up at right angles to the depth of about twice the thickness of the metal.
(b) For steel sheet and other metals from 1/16” to 1/8” thickness plain butt joint may be used. No special edges preparation is required here, but the edges must be true and clean.
(c) Where the thickness is above 1/8” the edges must be bevelled on one side forming a ‘VEE’ 80°-90°. This one side bevelling is done upto a thickness of ½”. Beyond this thickness, bevelling on both sides is required. (Double VEE)
(d) The edges must be straight and smooth and the necessary gap must be adjusted.
(e) In corner joints, bevelling and chamfering is to be done whenever it is necessary. Where one side or both sides are to be bevelled depends on the type of the job.
Type of Joints
The main types of welding joints are butt joint, fillet, corner joint and ‘T’ joint.
Butt Joint Welding. In general, butt welds are always preferred to fillet welds, which should be avoided if possible. In the case of butt welds, the parts to be joined are generally in the same plane and this enables different types of preparations to be made. The type of preparation depends on the metal being welded, the thickness of the metal and the welding method adopted. Butt welds are suitable for pressure vessels, storage tanks and whenever it is necessary to join pieces of plates, which can be conveniently arranged to have the edges in one plane. Butt welds have excellent mechanical properties, being strongest in tension.
Fillet Joint Welding. In fillet weld the plates to be joined are not in the same plane and there is the possibility of making many joints depending on the local conditions and requirement. Fillet welds are used in structural work, manufacture of welded articles, for re-enforcement and strengthening purposes. Fillet welds are generally not as strong mechanically as butt welds.
Fillet Weld Position
Outside Corner weld. The outside corner joint is a weld used often in fabrication. It can be made with or without filler material. If the steel pieces are arranged in correct position, excess metal from each piece serves as filler material for fusion.