Resistance welding is the method of joining metals using pressure and passing electric current for any period over the portion of the metal to be joined. Since resistance welding is one of the most inexpensive welding processes available today because it doesn’t require other materials to make a bond.
It’s worth noting that resistance welding will come in several forms which differ primarily by the shapes and kinds of weld electrodes utilized to conduct the electrode and apply the strain. The electrodes are mainly made from copper alloys and so are cooled by water which flows through conductive tooling of your machine along with the cavities in the electrodes.
Machines designed for resistance welding are created and manufactured for a variety of industrial, automotive, and aerospace industry applications. And also since many are automated, the working of such machines is well-controlled and may be repeated, based on information found at this piece of content. As such, they make it simpler for companies to staff their production easily.
Resistance Welding Types
Seam and Spot Welding
Like resistance welding applications, spot welding creates welds by making use of heat that’s been generated by welding current flow resistance in between the surface in contact with a joint and force, which pushes the workpieces together. The 2 are requested a defined period to the weld to be complete. It’s worth noting that spot welds make use of the face geometries of whichever welding electrode has been utilized to apply force about the workpiece and concentration the present on the weld location. When the resistance generated is enough, the metals “set down” and combine, as well as a nugget of weld forms.
Seam welding is basically a subcategory of spot welding. However, under this option, wheel-shaped electrodes are widely used to deliver welding current and force on the parts. Under seam welding, workpieces roll between wheel-shaped electrodes as being a current has been applied. Dependent upon the time settings and current, the resulting welds might end up forming complete welded seams, overlapping seams, or individual welds at specified intervals.
Projection welding applies a similar principles as other resistance welding processes. However, with projection welding, the welds are localized at preset points by making use of intersections, projections, or embossments, all of these focus the generated heat to your specific point. When the current has generated enough resistance on the POC, the projections fall off, making a weld nugget.
Flash welding applies a similar principle as other resistance welding processes. However, with flash welding, resistance is generated using flashing action which can be achieved by applying a high current to your small contact point in between the workpiece. When the flashing process has started, force is applied to your specific point about the workpiece. It’s worth noting how the workpieces are slowly moved with a determined rate.
Upset welding uses a similar principle as other resistance welding processes. And while it is just like flash welding, the main difference in between the two is the fact that pieces being welded are already in contact, which suggests no flashing occurs. Here, pressure about the workpieces is applied ahead of the current starts and is also sustained until the welding process is complete.
Resistance Welding Parameters
Resistance welding works in line with the principle of Joule Heating, where heat, denoted Q, is generated reliant on three factors:
- I – represents the present that’s passing through the metal combination
- R – represents the base metals’ and contact interfaces’ resistance
- t – represents the time/time period of current flow
As the principle might seem simple, you can find hundreds of parameters that influence the final results of actual welding processes. To learn resistance welding technology better, here’s a peek at a number of the parameters that influence welding results:
The welding current is a vital parameter when it comes to resistance welding mainly because it determines the amount of heat generated from a power of square. It’s worth noting that weld nugget sizes increase using the increasing welding current however, if the current is simply too high, it could result in electrode deterioration and expulsions. To avert this, welding engineers need to determine the optimal welding efforts and current for every welding application.
Heat generation in resistance welding is directly proportional to welding time. Because of heat transfer from weld zones to electrodes along with the base metals, and also a loss in heat from surrounding surfaces, the absolute minimum welding efforts and current are necessary to create a weld. When the current is just not sufficient, increasing welding times alone won’t generate a weld. However, once the current is sufficiently strong enough, the weld nugget size improves as weld time increases until it’s a similar size because the contact area of the electrode tip. If welding time is protracted, expulsion might occur or perhaps the electrode might end up sticking to the workpiece.
Welding force impacts the resistance welding process through its impact on contact resistance about the contact area and at the interfaces as a result of material deformation. The pieces being handled must be compressed from a certain force across the weld zones allowing current to successfully pass. When the welding force isn’t sufficiently strong enough, expulsion might occur after the current starts flowing as a result of high contact resistance – and therefore might lead to rapid heat generation. However, if the force is greater than normal, which may make the contact area to be greater than normal, something which might lead to low current density. At the same time, it could result in low contact resistance, and therefore could reduce the actual size of the weld nugget as well as heat generation. In projection welding, it’s the force applied that causes projections in the workpiece to collapse. Which induces changes on the contact area and, consequently, contact resistance and density. Furthermore, in addition, it influences welding results as well as heat development.
Contact resistance at weld interfaces is one of the most influential parameters when it comes to materials. However, it’s worth noting it has highly-dynamic interactions with process parameters. When welding forces increase, contact pressure also increases, meaning that the real contact area on the interface also increases as a result of the rough surface asperities deforming. Which induces contact resistance on the interface to lower, reducing heat generation and weld nugget size. Since the majority metal surfaces have contaminants like oil, dirt, water vapor, and oxides to them, when temperatures rise, many of them – mainly oil-based and water contaminants – dissipate in the initial few cycles, while metals soften due to the high temperatures. Consequently, contact resistance will usually decrease as temperatures rise. While contact resistance only affects results during the initial few cycles, it’s a decisive affect on how heat is distributed as a result of how heat is generated and distributed initially.
Almost all material properties alter as temperatures fluctuate, something which adds to the dynamics of resistance welding. It’s worth noting that material resistivity influences how heat is generated. Heat capacity and thermal conductivity influence how heat is transferred. In metals with high thermal conductivity and low resistivities like copper and silver, minimal heat is produced even with extremely high welding currents and is also quickly dissipated. Such metals take time and effort to weld using resistance welding. However, they are very good electrodes. When unlike metals are welded together, metal with higher resistivity will usually generate more heat. This is certainly something that ought to be considered ahead of time when making welding parts for projection welding so when choosing the particular electrodes to be utilized in spot welding. Welding material hardness also affects contact resistance. Metals that happen to be harder (have higher-yield stress) will usually have higher contact resistance at similar welding forces his or her surface asperities are harder to deform. That contributes to smaller contact areas. It’s worth noting how the materials used as electrodes are also utilized to influence how heat is balanced in resistance welding, particularly when joining non-ferrous and lightweight metals.
Resistance Welding Advantages
- Resistance welding has no consumables, such as welding rods, brazing materials, or solder.
- Its processing time is extremely short.
- It gives you operator-safety because the machines only need low voltage to work.
- Resistance welding doesn’t create messes like other welding techniques it’s neat and environmentally-friendly.
- It produces reliable electro-mechanical joints.
Resistance Welding Shortcomings
- The electrodes used should certainly reach both sides of your metal pieces these are bonding. Some spot-welding machines could only hold a definite metal thickness, usually 5-50 inches. And although the electrode’s position might be adjusted, most electrode holders have only limited movement.
- The shapes and measurements of electrodes used will determine the strength and measurements of the weld. The joints only form on the spots where the electrodes touch the metal. if the current isn’t hot or sufficiently strong enough, or perhaps the metal isn’t held together sufficiently, the spot weld might wind up being weak or small.
- A loss in strength and warping can happen around points where the workpiece is spot-welded. The joint’s appearance is frequently quite ugly and may also have cracks into it. The metal may also wind up becoming less resistant against corrosion.