Resistance welding is the process of joining metals using pressure and passing electric current for any period on the section of the metal to become joined. Since resistance welding is among the most inexpensive welding processes on the market today since it doesn’t require many other materials to make a bond.
It’s worth noting that resistance welding will come in several forms which differ primarily from the shapes and types of weld electrodes accustomed to conduct the electrode and apply pressure. The electrodes are mostly created from copper alloys and are cooled by water which flows through conductive tooling of your machine and the cavities inside the electrodes.
Machines designed for resistance welding are designed and manufactured for a wide range of industrial, automotive, and aerospace industry applications. And because many are automated, the working of these machines is well-controlled and may be repeated, based on information found at this. As a result, 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 by using heat that’s been generated by welding current flow resistance between your surface in contact with a joint and force, which pushes the workpieces together. Both the are applied for a defined period for the weld to become complete. It’s worth noting that spot welds use the face geometries of whichever welding electrode is now being accustomed to apply force on the workpiece while focusing the present at the weld location. After the resistance generated is enough, the metals “set down” and combine, and a nugget of weld forms.
Seam welding is essentially a subcategory of spot welding. However, under this alternative, wheel-shaped electrodes are utilized to deliver welding current and force on the parts. Under seam welding, workpieces roll between wheel-shaped electrodes like a current is now being 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 the identical principles as other resistance welding processes. However, with projection welding, the welds are localized at preset points by using intersections, projections, or embossments, which focus the generated heat to a specific point. After the current has generated enough resistance at the POC, the projections fall off, creating a weld nugget.
Flash (or butt) welding actually uses the identical principle as other resistance welding processes. However, with flash welding, resistance is generated using flashing action which happens to be achieved by utilizing a higher current to a small contact point between your workpiece. After the flashing process has started, force is applied to a specific point on the workpiece. It’s worth noting the workpieces are slowly moved in a determined rate.
Upset welding uses the identical principle as other resistance welding processes. And even though it is similar to flash welding, the visible difference between your two is the pieces being welded already are in contact, which means no flashing occurs. Here, pressure on the workpieces is applied ahead of the current starts and it is sustained before the welding process is done.
Resistance Welding Parameters
Resistance welding works based on the principle of Joule Heating, where heat, denoted Q, is generated reliant on three factors:
- I – represents the present that’s passing from the metal combination
- R – represents the base metals’ and make contact with interfaces’ resistance
- t – represents some time/length of current flow
While the principle may seem simple, you can find countless parameters that influence the outcomes of actual welding processes. To know resistance welding technology better, here’s a look at some of the parameters that influence welding results:
The welding current is a vital parameter with regards to resistance welding as it determines the quantity of heat generated with a power of square. It’s worth noting that weld nugget sizes increase with the increasing welding current however, if the current is just too high, it could cause electrode deterioration and expulsions. To avoid this, welding engineers need to determine the optimal welding time and current for each and every welding application.
Heat generation in resistance welding is directly proportional to welding time. On account of heat transfer from weld zones to electrodes and the base metals, in addition to a loss of heat from surrounding surfaces, the absolute minimum welding time and current are necessary to build a weld. If the current will not be sufficient, increasing welding times alone won’t develop a weld. However, if the current is sufficiently strong, the weld nugget size increases as weld time increases until it’s the identical size since the contact part 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 on the contact area and at the interfaces because of material deformation. The pieces being worked tirelessly on needs to be compressed with a certain force down the weld zones allowing current to pass. If the welding force isn’t sufficiently strong, expulsion might occur once the current starts flowing because of high contact resistance – and therefore might cause rapid heat generation. However, if the force is more than normal, which may increase the risk for contact area to become larger than normal, an issue that might cause low current density. At the same time, it may lead to low contact resistance, and therefore could reduce the actual size of the weld nugget and also heat generation. In projection welding, it’s the force applied which induces projections inside the workpiece to collapse. That causes changes on the contact area and, consequently, contact resistance and density. Furthermore, in addition, it influences welding results and also heat development.
Contact resistance at weld interfaces is among the most influential parameters with regards to materials. However, it’s worth noting that this has highly-dynamic interactions with process parameters. When welding forces increase, contact pressure also increases, which means the genuine contact area at the interface also increases on account of the rough surface asperities deforming. That causes contact resistance at the interface to diminish, reducing heat generation and weld nugget size. Because most metal surfaces have contaminants like oil, dirt, water vapor, and oxides about them, when temperatures rise, a number of them – mainly oil-based and water contaminants – dissipate in the initial cycles, while metals soften due to high temperatures. As a result, contact resistance will generally decrease as temperatures rise. While contact resistance only affects results during the initial cycles, it’s a decisive affect on how heat is distributed on account of how heat is generated and distributed initially.
Almost all material properties alter as temperatures fluctuate, an issue that 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 even with quite high welding currents and it is quickly dissipated. Such metals are hard to weld using resistance welding. However, they create excellent electrodes. When unlike metals are welded together, metal with higher resistivity will generally generate more heat. This is certainly something that should be thought about upfront when making welding parts for projection welding and whenever choosing the particular electrodes to be used in spot welding. The hardness of your welding material also affects contact resistance. Metals that are harder (have higher-yield stress) will generally have higher contact resistance at similar welding forces as their surface asperities are harder to deform. That contributes to much smaller contact areas. It’s worth noting the materials used as electrodes have been accustomed to influence how heat is balanced in resistance welding, particularly when joining non-ferrous and light-weight metals.
Resistance Welding Advantages
- Resistance welding has no consumables, such as welding rods, brazing materials, or solder.
- Its processing time is incredibly short.
- It includes operator-safety since the machines only require low voltage to function.
- 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 both sides of your metal pieces they can be bonding. Some spot-welding machines is only able to hold a certain metal thickness, usually 5-50 inches. Even though the electrode’s position could be adjusted, most electrode holders simply have limited movement.
- The shapes and scale of electrodes used will determine the strength and scale of the weld. The joints only form at the spots in which the electrodes touch the metal. if the current isn’t hot or sufficiently strong, or the metal isn’t held together good enough, the spot weld might wind up being weak or small.
- A loss of strength and warping can take place around points in which the workpiece continues to be spot-welded. The joint’s appearance is frequently quite ugly and may have cracks onto it. The metal could also wind up becoming less resistant to corrosion.