During the last few years resistance welding has received wide recognition as the most economical and effective method of joining metals in a great variety of manufacturing operations. Its applications in Spot, Butt and Seam welding are so numerous that any attempt to enumerate them must necessarily fall far short of completeness.

Spot Welding is carried out between two bluntly pointed pencil shaped copper electrodes with points facing and holding the work. On applying the current, a plastic condition is established over an area roughly equal to that of the end of the electrode, and the pressure of the electrodes simultaneously completes the weld. Spot Welding is employed with advantage on sheet metal work, wire meshed fencing, and a great variety of other work.

The Disc Process

Allied to Spot Welding, and performed by means of A-L " Pontelec " Spot Welders, is the patent " Pontelec " " Disc " process which consists in superimposing small pieces of suitable material upon the parts to be welded. The heat is thereby localised at such points, and, under pressure, the added part, or " disc," is forced into the body of the material, thus making an exceptionally strong weld. The patent " Disc " process is applicable with advantage to either repetition or general work where it is important that no mark of the weld should be left upon the finished article. A " Disc " weld remains flush with the surrounding metal and when painted over no trace of its existence is noticeable.

The Ridge Process

The " Ridge " process of spot welding is operated by means of the provision, on the material during rolling, of narrow ridges so that when the parts are brought together, the area of contact is restricted to the desired amount. The electric current rapidly heats these points of contact when the parts are brought together under pressure.

The" Multiple Point " Process

In this operation, a number of projections are formed in articles stamped from the sheet metal, so that, on the parts being brought together contact is confined to such points. In some cases as many as ten points can thus be welded at one operation. The " Multiple Point" process is eminently suitable for high speed repetition work.

Fig. 233.

A-L " Pontelec " Spot welding machines (see Fig. 233) are strongly constructed for continuous operation on work within their rated capacities. They are fitted with water-cooled electrodes the tips of which are renewable, the water circulation being carried close to the working point. Under practical conditions as many as 1.000 Spot welds are normally made, with one trimming up of the tip and ample material is provided to permit the tip to be trimmed up many times. Each machine is fitted with a plug box regulator of ample range to provide adjustment of the heating speed for different thicknesses of material. On the larger machines a trip switch is fitted as a standard part of the equipment. By means of this switch the current can be cut off immediately the weld has taken place. (Messrs. Allen Liversids:e, Ltd.)