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Projection Welding Basics


Projection Welding - An Overview

Projection welding is a kind of resistance welding processes in which the welds are created by the heat obtained from the resistance to the flow of current through two work pieces held together under pressure with the help of electrodes. The projections by embossing, stamping, casting, or machining helps to localize the area of welding.

Projection welding is almost similar to the spot welding process except the electrodes used; for, the tips are flat in projection welding, and the amount of current to be passed and the pressure applied is higher than in spot welding. This is mainly due to the large numbers of welds required to be created through projection welding.

Projection Welding Basics - Process

The two parts to be welded are held together as such that the projections on one piece are in contact with the other piece, which is under pressure by the electrodes. As the current passes through and localize around the region of weld, making the metal of the area to the plastic state, these softened projections collapses under pressure results in formation of a weld.

However, the success of the weld widely depends upon the preparation of the surfaces of the work pieces. The effectiveness of projection welding depends greatly on the projections that are created on the surface of the work pieces to be welded. Also, pulsation timings are included to regulate the current, as it is helpful in welding thick work pieces.

Equipment used for Projection welding

The process of projection welding is undertaken with the help of a press type machine with both single-phase and three-phase transformers. Platens with T-slots are employed to hold electrodes, and the welding head is guided with the help of bearings and is made to move in straight line. It is actuated with air, hydraulics or springs. The controls used for this process are of synchronous type.

Metals that can be welded by Projection welding

Projection welding involves preparation of surfaces, and not all the surfaces can be worked upon. However, there are some of them that can be worked upon with projection welding, and are listed below:

" Stainless steel
" Low carbon steel
" Coated materials such as galvanized
" Naval bars, etc.

Advantages of Projection Welding process

Some of the advantages of employing Projection Welding process are as follows:

" A large number of welds can be created, as projections can be made available in large numbers. However, for this, press has to be capable of distributing the pressure equally.
" Life of electrodes is more, as only the flat surfaces are required to be worked on. The maintenance involved in the process is also far less in this case, making it an easier process.

Disadvantages of Projection welding

The initial cost is little high, as the press type machine is required to be employed for the process. This is a major drawback for this process; however, as the work can be done on large number of pieces, the cost is usually compensated.

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