Resistance Welding - How It Works

Resistance welding is a process that utilizes electricity, and mechanical pressure along with the inherent electrical conductivity (resistance) of the work-pieces to form a weld joint. Electric current is delivered to the work-pieces through electrodes and converted to heat that produces instantaneous fusing and joining of the work-pieces.

Without the physics of Joule Heating, resistance welding cannot work. According to Joule’s first law the heat produced is a function of the current (amps), the electrical resistance (ohms), and time according to the relation:

Q(heat) = I2×R×t. , where i= current (amps), R= electrical resistance(ohms) , and t= time.

This relation shows the sensitivity of the heat produced to the electric current applied; doubling the current (amps) will result in a fourfold increase in heat produced at the weld. Heating continues until the materials to be joined are fused; the addition of pressure applied through the electrodes completes the fusion process. The final function of the electrode utilizes the relatively high thermal conductivity of the electrode material to extract heat from the molten weld area to form a solidified weld nugget. Water cooling is often utilized to remove the heat and cool the molten nugget along with the electrodes.

As the key properties of the electrodes are hardness (indicative of strength) and electrical conductivity, electrode alloys have been designed by metallurgists to yield varieties of these properties in the electrode alloys. These electrode alloys are conveniently grouped by the industry into classes according to their hardness and electrical conductivity. The RWMA (Resistance Welding Manufacturer’s Alliance), a standing committee of the American Welding Society (AWS), defines these groups by their physical and mechanical properties, namely hardness and electrical conductivity.

Water cooling of the electrode is typically provided to improve nugget solidification and prolong electrode life, but eventually most electrodes require replacement due to wear and erosion. The integrity (dimension) of the electrode face must be maintained to provide a consistent current density in the weld area. This is accomplished by re-dressing the deformed electrode, or simply replacing it.

Resistance welding systems are designed so the electrode is easily removed and replaced. Electrodes are fastened to an electrode holder by various means. Many are press fit with matching tapered surfaces on the holder and electrode, while others may be threaded. A specially formulated, conductive lubricant, such as Cadi’s Copper-Lube, may be applied on the holder to facilitate removal and extend holder life. Electrodes are designed with various fit-up characteristics; some have protruding “male” tapers, while others have internal, “female” tapers that match the counterpart holder’s taper. The RWMA describes the numerous standard combinations of electrode styles and tapers and defines a numbering system to identify these electrodes.

Resistance welding systems can be simple or complex. Long semi-continuous welds can be made using a rotating electrode (welding wheel) or complex electrode tools can be used to weld nuts or studs onto a base metal.

Cadi Company manufactures electrodes in all styles and configurations used in the industry for spot welding, seam welding, stud and nut welding, butt welding, projection welding, and many more.

For more information about resistance welding or a free quote,
contact Cadi Company at 800- 243-3650.

Cadi Company’s View on:

  • Materials - Cadi Company manufactures resistance welding electrodes and components using the highest quality materials.

  • Technology - Cadi’s proprietary processes use technology to drive the manufacturing of copper alloys to develop properties in the components that continue to exceed industry standards.

  • Facility - Cadi’s unique physical plant and streamlined systems ensure uniformity and exactness in each part or component manufactured.

  • Overall – Cadi continues to invest in a well- trained and experienced work force; implement ISO 9001:2015 business operating standards; and works with each customer to understand their needs.

Cadi Company has been and will continue to be a competitive reliable supplier in an ever-changing resistance welding industry.