Welded joints

INTRODUCTION

A welded joint as is clear from its name is obtained by the fusion o the edges of the two metal parts to be joined together, with or without the application of pressure and a filler material. An electric arc or gas is used for fusion of the material.

            A welded joint is a permanent joint used extensively in fabrication process. It is an alternative method for casting or forging and is the replacement for bolted broken off such as gear tooth or to repair a worn surface.

ADVANTAGES AND DISADVANTAGES:

Following are technical advantages and disadvantages

  • Welded joints have low initial cost
  • The process is noiseless.
  • welded joints are greater in strength
  • Less machining is required after welding.
  • Easy to inspect i.e. by x-rays without destroying the piece.
  • Welded joint can easily be repaired.

DISADVANTAGES:

  • Welded joint cannot be used for impact load and vibrations
  • Being permanent joint the welded joint cannot be assembled and reassembled like screwed joints

WELDING PROCESS:

The welding process is mainly divided into two groups.

  • Welding processes that use heat only e.g. fusion welding.
  • Welding processes that use a combination of heat and pressure e.g. forge welding.

FUSION WELDING: In this case, the parts to be joined are held in position while the molten metal is supplied to the joint. Heating the parent metal and the filler metal together forms the molten metal. The joint surfaces become plastic or molten because o the heat from the molten filler metal or other source. Thus, when the molten metal solidifies or fuses, the joint is formed. FORGE WELDING: In this type of welding, the parts to be joined are first heated to a proper temperature in a furnace or forge and the hammered.

TYPES OF WELDED JOINTS:

The welded joint are commonly of two types.

  • Lap joint or fillet joint
  • Butt joint.

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