Resistance Welding by Hongyan Zhang download in ePub, pdf, iPad
Thus the contact resistance generally decreases with increasing temperature. Electrode materials have also been used to influence the heat balance in resistance welding, especially for joining light and non-ferrous metals.
In projection welding, the welding force causes the collapse of the projection in the workpiece, which changes the contact area and thereby the contact resistance and the current density. The resultant bond has definite interfaces with minimum grain growth. When the welding current is high enough, the size of the weld nugget increases with increasing welding time until it reaches a size similar to the electrode tip contact area.
This allows the electrodes to stay in constant contact with the material to make long continuous welds. The thickness is limited by the output of the welding power source and thus the equipment range due to the current required for each application. It is also widely used for manufacturing of furniture and domestic equipment etc.
Resistance Weld Bonding Is a combined joining process with adhesive bonding and resistance welding. The resistivity of material influences the heat generation. In a solid state bond, also called a thermo-compression bond, dissimilar materials with dissimilar grain structure, e. The adhesive is applied to the faying surfaces of sheets to be welded, and subsequently resistance spot weld is made through the sheets before curing of the adhesive. The seam may be a butt joint or an overlap joint and is usually an automated process.
Care is taken to eliminate contaminants between the faying surfaces. It is often the tedious job of the welding engineers to find the optimized welding current and time for each individual welding application.
The higher current needed with the larger tip diameter may be optimized through welding tests or by support of numerical simulations. Mechanisms of electrode degradation The severe conditions of high current and pressure during resistance welding expose the electrode tips at a high risk of degradation. They are rather difficult to weld with resistance welding. In continuous seam welding, the wheels continue to roll as each weld is made.
Both effects lead to progressively reducing weld nugget sizes. The geometry of electrodes in spot welding controls the current density and the resulting size of the weld nugget. Typically, high weld energies at either short or long weld times, depending on physical characteristics, are used to produce fusion bonds.