Resistance welding is the method of joining metals using pressure and passing electric current for the period over the area of the metal to become joined. Since resistance welding is amongst the most inexpensive welding processes now available simply because it doesn’t require many other materials to produce a bond.
It’s worth noting that resistance welding comes in several forms which differ primarily from the shapes and kinds of weld electrodes employed to conduct the electrode and apply the stress. The electrodes are generally made from copper alloys and therefore are cooled by water which flows through conductive tooling from the machine as well as the cavities inside the electrodes.
Machines created for resistance welding are created and manufactured for a variety of industrial, automotive, and aerospace industry applications. And since nearly all are automated, the working of the machines is well-controlled and can be repeated, at least according to a site I found. Therefore, they make it easier for companies to staff their production easily.
Resistance Welding Types
Seam and Spot Welding
Like resistance welding operations, spot welding creates welds through the use of heat that’s been generated by welding current flow resistance between your surface in touch with a joint and force, which pushes the workpieces together. Both the are requested a defined period for that weld to become complete. It’s worth noting that spot welds use the face geometries of whichever welding electrode will be employed to apply force about the workpiece and focus the current at the weld location. After 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 alternative, wheel-shaped electrodes are utilized to deliver welding current and force for the parts. Under seam welding, workpieces roll between wheel-shaped electrodes being a current will be applied. Based on 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 exactly the same principles as other resistance welding processes. However, with projection welding, the welds are localized at preset points through the use of intersections, projections, or embossments, which all focus the generated heat into a specific point. After the current has generated enough resistance at the POC, the projections fall off, building a weld nugget.
Flash (or butt) welding actually uses exactly the same 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 into a small contact point between your workpiece. After the flashing process has begun, force is applied into a specific point about the workpiece. It’s worth noting the workpieces are slowly moved with a determined rate.
Upset welding uses exactly the same principle as other resistance welding processes. And while it is just like flash welding, the visible difference between your two would be that the pieces being welded are already in contact, which implies no flashing occurs. Here, pressure about the workpieces is applied prior to the current starts which is sustained until the welding process is complete.
Resistance Welding Parameters
Resistance welding works depending on the principle of Joule Heating, where heat, denoted Q, is generated dependent on three factors:
- I – represents the current that’s passing throughout the metal combination
- R – represents the base metals’ and contact interfaces’ resistance
- t – represents some time/time of current flow
As the principle may appear simple, there are hundreds of parameters that influence the outcomes of actual welding processes. To comprehend resistance welding technology better, here’s a look at several of the parameters that influence welding results:
The welding current is an important parameter in relation to resistance welding as it determines the volume of heat generated by way of a power of square. It’s worth noting that weld nugget sizes increase together with the increasing welding current however, if the current is too high, it could cause electrode deterioration and expulsions. To avert this, welding engineers need to look for the optimal welding some time and current for each welding application.
Heat generation in resistance welding is directly proportional to welding time. Because of heat transfer from weld zones to electrodes as well as the base metals, in addition to a reduction in heat from surrounding surfaces, the absolute minimum welding some time and current are necessary to create a weld. If the current is not really sufficient, increasing welding times alone won’t generate a weld. However, as soon as the current is sufficiently strong, the weld nugget size boosts as weld time increases until it’s exactly the same size as the contact portion of the electrode tip. If welding time is protracted, expulsion might occur or the electrode might end up staying on the workpiece.
Welding force impacts the resistance welding process through its impact on contact resistance about the contact area as well as at the interfaces because of material deformation. The pieces being handled needs to be compressed by way of a certain force along the weld zones to enable current to move. If the welding force isn’t sufficiently strong, expulsion might occur once the current starts flowing because of high contact resistance – and that might bring about rapid heat generation. On the other hand, if the force is more than normal, that may make the contact area to become larger than normal, something which might bring about low current density. Simultaneously, it may bring about low contact resistance, and that could reduce the size of the weld nugget and also heat generation. In projection welding, it’s the force applied that causes projections inside the workpiece to collapse. That triggers changes for the contact area and, consequently, contact resistance and density. Furthermore, it also influences welding results and also heat development.
Contact resistance at weld interfaces is amongst the most influential parameters in relation to materials. However, it’s worth noting which it has highly-dynamic interactions with process parameters. When welding forces increase, contact pressure also increases, which means that the actual contact area at the interface also increases as a result of the rough surface asperities deforming. That triggers contact resistance at the interface to reduce, reducing heat generation and weld nugget size. Since most metal surfaces have contaminants like oil, dirt, water vapor, and oxides upon them, when temperatures rise, a number 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 normally decrease as temperatures rise. While contact resistance only affects results during the initial few cycles, it’s a decisive impact 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 increases 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, very little heat is produced despite quite high welding currents which is quickly dissipated. Such metals take time and effort to weld using resistance welding. However, they are great electrodes. When unlike metals are welded together, metal with higher resistivity will normally generate more heat. This is something that needs to be considered beforehand when designing welding parts for projection welding and once choosing the sort of electrodes to use in spot welding. Material hardness also affects contact resistance. Metals that happen to be harder (have higher-yield stress) will normally have higher contact resistance at similar welding forces his or her surface asperities are harder to deform. That brings about much smaller contact areas. It’s worth noting the materials used as electrodes have also been employed to influence how heat is balanced in resistance welding, particularly if joining non-ferrous and light metals.
Resistance Welding Advantages
- Resistance welding has no consumables, for example welding rods, brazing materials, or solder.
- Its processing time is extremely short.
- It provides operator-safety as the machines only require low voltage to operate.
- Resistance welding doesn’t create messes like other welding techniques it’s clean and environmentally-friendly.
- It creates reliable electro-mechanical joints.
Resistance Welding Shortcomings
- The electrodes used should be able to reach either sides from the metal pieces they are bonding. Some spot-welding machines can only hold a certain metal thickness, usually 5-50 inches. Even though the electrode’s position can be adjusted, most electrode holders just have limited movement.
- The shapes and dimensions of electrodes used will determine the strength and dimensions of the weld. The joints only form at the spots where electrodes touch the metal. if the current isn’t hot or sufficiently strong, or the metal isn’t held together well enough, the spot weld might end up being weak or small.
- A reduction in strength and warping can take place around points where workpiece continues to be spot-welded. The joint’s appearance is usually quite ugly and may have cracks upon it. The metal may also find yourself becoming less resistant to corrosion.