What is Resistance Welding?
Resistance welding is a method of joining metals by applying force through a weld electrode and then passing current for a specified amount of time through the metal area that is to be joined together.
The main benefit with resistance welding is that no other materials are needed to produce the bond which is an extremely cost-effective procedure.
There are several different types of resistance welding (e.g., spot and seam, projection, flash, upset) that are distinguished primarily by the types and shapes of weld electrodes that are used to not only apply pressure but to also conduct current.
Weld electrodes are made from various copper based alloys because the copper (which has the greatest conductive properties) also helps to dissipate heat away from the weld interface.
As the heat is produced a tinny-wash (melted area) of the materials being joined, it requires a cooling connection with the weld electrodes or tooling also made from copper alloy as part of the water cooled system for resistance welding.
Resistance welding machines are built for many automotive, aerospace and industrial applications. Resistance welding can be automated and produce repeatable actions to a high degree of control so that manufacturers can have regular and reliable production.
How Does Resistance Welding Work?
Resistance welding is typically utilized to join two flat metal workpieces. An electric current is supplied to the metal sheets (or any workpieces being welded) via weld electrodes, which exert weight to the sheets.
This weight is converted into heat. Heat is developed so that it melts the metal at the location the two sheets come together at the point where the “resistance” happens at the faying surfaces. The electrode then pulls heat from the melted weld area, which forms a weld nugget at the location where it solidifies.
A force is exerted before, during and after a current is being provided, which limits the contact zone.
Types of Resistance Welding
1. Spot Welding and Seam Welding
Resistance Spot Welding, like all Resistance Welding Processes, produces welds by using the heat generated by resistance to the flow of welding current through the faying surfaces, as well as any force used to push the work pieces together, that is applied over a defined period of time.
Resistance Spot Welding uses the face geometries of the welding electrodes in order to focus the welding current at the specified weld location, as well as the force of the electrodes against the workpieces. Once there is sufficient resistance, a weld nugget is formed, and the materials are brought down or brought together.
Resistance Seam Welding is a sub-group of Resistance Spot welding that uses wheel-shaped electrodes to deliver both the force and welding current to the parts. The difference is that the workpiece rolls between the two wheel-shaped electrodes while the weld current is applied.
Depending on the specific weld time and weld current settings, the welds may be overlapping, forming an entirely welded seam, or they may simply be individual spot welds made at specified intervals.
2. Projection Welding
Like the other Resistance Welding Processes, Projection Welding fundamentally relies on heat generated through resistive heating from the flow of the welding current, and then applying the projected force to bring the weld pieces together, for a defined period of time.
Projection Welding localizes welds at points defined by projections, embossment, or intersections, using these features to focus the heat generation at the point of contact.
Once the resistive heating has reached a point where sufficient resistance has formed at the point of contact, the projections collapse, forming the weld nugget.
Solid projections are commonly employed when welding fasteners to parts. Embossments are commonly utilize for joining plate or sheet material. A form of Projection welding (using material intersections) is cross-wire welding.
In this case, the intersection of the wires themselves localizes the heat generation and therefore the resistance. The wires set down into one another creating a weld nugget in the process.
3. Flash Welding
Similar to other Resistance Welding Processes, Flash Welding generates heat from the resistance to current flow, as well as applied force to push the workpieces together, in a defined amount of time. Flash Welding is a Resistance Welding Process that uses flashing action to create a resistance.
This is accomplished by using extremely high current density at extremely small contact points between the workpieces.
Once a predetermined point is reached, after the flashing has started to take place, force is applied to the workpiece, and they are fed together, at a controlled rate. The rapid upset from this force will push oxides and contaminants from the weld.
4. Upset Welding
While the process of upset welding works similarly to other resistance welding processes, the heat generated by the resistance to welding current is used, along with the force to push the workpieces together, over a selected amount of time.
Upset welding is different than flash welding in that the workpieces are already in firm contact with one another; therefore, no flashing occurs. Pressure is applied prior to the beginning of the current and continues throughout the process until completed.
Applications Of Resistance Welding
- Resistance welding is utilized for production welding of sheet metal, wire, and tubes.
- It is utilized in welding bars, boxes, cans, rods, pipes and frames with medium and higher resistance materials (e.g. steel, stainless steel, silicon bronze) that are easy to weld.
- It is utilized in welded aircraft and automobiles parts.
- It is utilized in making cutting tools.
- It is utilized in making fuel tanks of cars, tractors, etc.
- It is utilized in making wire fabrics, grids, grills, mesh welds, containers, etc.
Advantages of Resistance Welding
- Similar and dissimilar metals can be effectively welded
- Extremely automated
- High efficiency with high production and high welding rates
- Economical
- Environmentally friendly, very low waste & pollution
- No filler metal or other materials such as rods, fluxes, inert gasses, oxygen or acetylene is needed
Disadvantages of Resistance Welding
- A resistance welding machine usually requires a high level of technically trained personnel to operate since it is typically complex and expensive machinery.
- The thickness of the completed workpiece is often limited
- It is mechanically and thermally less efficient for high-conductive materials
- Requires an extremely high electric power input
FAQs
What is the most common form of resistance welding?
Spot welding is the most common form of resistance welding. Opposing electrodes or tips conduct and concentrate welding current and apply forging force to form each weld.
What are 2 advantages of resistance welding?
In addition to the speed, consistency is the other great advantage resistance welding has to offer. Because the heat generated during the welding process is controlled by electrical resistance, the process is highly repeatable and produces consistent, high-quality welds every time.
Is TIG welding resistance welding?
Yes and no. Stick welding uses resistance to melt the filler electrode to perform the weld, MIG uses resistance to melt the filler wire to make the weld, TIG uses the arc caused by current jumping from the TIG electrode to the work piece, into which the operator feeds the filler material.
What is the difference between resistance welding and soldering?
The main difference between welding and soldering is melting. In soldering, metal producers heat up the metal to be bonded but never soften them. In welding, metal producers melt the base metal.
What is another name for resistance welding?
Resistance welding, sometimes called electric resistance welding (ERW),is a process by which metals can be joined together by applying pressure and conducting a strong electric current through the metal combination to heat up the welding joint and melt the metals, forging them together.
Is resistance welding the same as induction welding?
This process is very similar to resistance welding, except that in the case of resistance welding the current is delivered using contacts to the workpiece instead of using induction. Induction welding was first discovered by Michael Faraday.