Resistance welding is the method of joining metals using pressure and passing electric current for the period over the area of the metal to get joined. Since resistance welding is probably the most inexpensive welding processes available today since it doesn’t require many other materials to generate a bond.
It’s worth noting that resistance welding can be purchased in several forms which differ primarily from the shapes and types of weld electrodes used to conduct the electrode and apply pressure. The electrodes are generally created from copper alloys and they are cooled by water which flows through conductive tooling of your machine along with the cavities in the electrodes.
Machines made for resistance welding were created and manufactured for a wide array of industrial, automotive, and aerospace industry applications. And because nearly all are automated, the working of those machines is well-controlled and might be repeated, based on content from [dcl=8635]. Consequently, they make it easier for companies to staff their production effortlessly.
Resistance Welding Types
Seam and Spot Welding
Like resistance welding processes, spot welding creates welds by making 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. The two are applied for a defined period for that weld to get complete. It’s worth noting that spot welds take advantage of the face geometries of whichever welding electrode will be used to apply force around the workpiece while focusing the current on the weld location. After the resistance generated is plenty, the metals “set down” and combine, as well as a nugget of weld forms.
Seam welding is essentially a subcategory of spot welding. However, under this choice, wheel-shaped electrodes are employed to deliver welding current and force towards the parts. Under seam welding, workpieces roll between wheel-shaped electrodes as a current will be applied. According to the time settings and current, the resulting welds could 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 by making use of intersections, projections, or embossments, which focus the generated heat to your specific point. After the current has generated enough resistance on the POC, the projections fall off, making a weld nugget.
The flash welding process leverages exactly the same principle as other resistance welding processes. However, with flash welding, resistance is generated using flashing action which can be achieved by using an increased current to your small contact point between your workpiece. After the flashing process has started, force is applied to your specific point around the workpiece. It’s worth noting that this workpieces are slowly moved at the determined rate.
Upset welding uses exactly the same principle as other resistance welding processes. And while it is much like flash welding, the real difference between your two is the pieces being welded are actually in contact, meaning no flashing occurs. Here, pressure around the workpieces is applied just before the current starts and is sustained before the welding process is finished.
Resistance Welding Parameters
Resistance welding works in line with the principle of Joule Heating, where heat, denoted Q, is generated dependent on three factors:
- I – represents the current that’s passing from the metal combination
- R – represents the base metals’ and contact interfaces’ resistance
- t – represents enough time/time period of current flow
While the principle might seem simple, there are numerous parameters that influence the outcomes of actual welding processes. To understand resistance welding technology better, here’s a short look at a number of the parameters that influence welding results:
The welding current is a vital parameter in terms of 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 prevent this, welding engineers need to ascertain the optimal welding time as well as 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, as well as a loss in heat from surrounding surfaces, the absolute minimum welding time as well as current are needed to create a weld. When the current is not really sufficient, increasing welding times alone won’t produce a weld. However, once the current is sufficiently strong enough, the weld nugget size boosts as weld time increases until it’s exactly the same size since the contact section of the electrode tip. If welding time is protracted, expulsion might occur or even the electrode could end up sticking to the workpiece.
Welding force impacts the resistance welding process through its effect on contact resistance around the contact area and at the interfaces as a result of material deformation. The pieces being worked tirelessly on needs to be compressed from a certain force across the weld zones to allow current to move. When the welding force isn’t sufficiently strong enough, expulsion might occur once the current starts flowing as a result of high contact resistance – and that might cause rapid heat generation. On the flip side, if the force is beyond normal, that might make the contact area to get bigger than normal, something which might cause low current density. At the same time, it might cause low contact resistance, and that could reduce how big the weld nugget and also heat generation. In projection welding, it’s the force applied which induces projections within the workpiece to collapse. Which causes changes towards 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 probably the most influential parameters in terms of 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 the real contact area on the interface also increases as a result of the rough surface asperities deforming. Which causes contact resistance on the interface to diminish, reducing heat generation and weld nugget size. Since most metal surfaces have contaminants like oil, dirt, water vapor, and oxides to them, when temperatures rise, a few of them – mainly oil-based and water contaminants – dissipate in the first few cycles, while metals soften due to the high temperatures. For that reason, contact resistance will normally decrease as temperatures rise. While contact resistance only affects results during the first few cycles, it’s a decisive effect on how heat is distributed as a result of how heat is generated and distributed initially.
Just about all material properties alter as temperatures fluctuate, something which enhances 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 higher thermal conductivity and low resistivities like copper and silver, minimal heat is produced even with high welding currents and is quickly dissipated. Such metals are difficult to weld using resistance welding. However, they are excellent electrodes. When unlike metals are welded together, metal with higher resistivity will normally generate more heat. This really is something which should be considered upfront when designing welding parts for projection welding so when choosing the type of electrodes to be utilized in spot welding. The hardness of your welding material also affects contact resistance. Metals that are harder (have higher-yield stress) will normally have higher contact resistance at similar welding forces as their surface asperities are harder to deform. That contributes to smaller contact areas. It’s worth noting that this materials used as electrodes are also used to influence how heat is balanced in resistance welding, particularly if joining non-ferrous and light-weight 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 since the machines only require low voltage to work.
- Resistance welding doesn’t create messes like other welding techniques it’s neat and environmentally-friendly.
- It makes reliable electro-mechanical joints.
Resistance Welding Shortcomings
- The electrodes used should certainly reach either sides of your metal pieces they are bonding. Some spot-welding machines is only able to hold a definite metal thickness, usually 5-50 inches. And while the electrode’s position might be adjusted, most electrode holders have only limited movement.
- The shapes and size of electrodes used will determine the strength and size of the weld. The joints only form on the spots the location where the electrodes touch the metal. if the current isn’t hot or sufficiently strong enough, or even the metal isn’t held together sufficiently, the spot weld might become weak or small.
- A loss in strength and warping can happen around points the location where the workpiece continues to be spot-welded. The joint’s appearance is usually quite ugly and can have cracks into it. The metal may also end up becoming less immune to corrosion.