Resistance welding is the process of joining metals using pressure and passing electric current to get a period across the part of the metal being joined. Since resistance welding is among the most inexpensive welding processes on the market today since it doesn’t require other materials to generate a bond.
It’s worth noting that resistance welding will come in several forms which differ primarily from the shapes and kinds of weld electrodes used to conduct the electrode and apply pressure. The electrodes are generally manufactured from copper alloys and are cooled by water which flows through conductive tooling of the machine along with the cavities in the electrodes.
Machines created for resistance welding are made and manufactured for a wide array of industrial, automotive, and aerospace industry applications. And since the majority are automated, the working of these machines is well-controlled and will be repeated, based on information found at this guide on seam welds. Consequently, they make it simpler 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 in between the surface in contact with a joint and force, which pushes the workpieces together. Both are applied for a defined period for your weld being complete. It’s worth noting that spot welds use the face geometries of whichever welding electrode is now being used to apply force on the workpiece and focus the current on the weld location. After the resistance generated is sufficient, the metals “set down” and combine, as well as a nugget of weld forms.
Seam welding is actually 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 as being a current is now being applied. Depending on 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 a similar 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, all of these focus the generated heat to your specific point. After the current has generated enough resistance on the POC, the projections fall off, developing a weld nugget.
The flash welding process leverages a similar principle as other resistance welding processes. However, with flash welding, resistance is generated using flashing action which is achieved by utilizing a high current to your small contact point in between the workpiece. After the flashing process has started, force is applied to your specific point on the workpiece. It’s worth noting how the workpieces are slowly moved at the determined rate.
Upset welding uses a similar principle as other resistance welding processes. And though it may be similar to flash welding, the main difference in between the two is the pieces being welded are actually in contact, meaning no flashing occurs. Here, pressure on the workpieces is applied prior to the current starts and is sustained up until the welding process is complete.
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 current that’s passing throughout the metal combination
- R – represents the base metals’ and make contact with interfaces’ resistance
- t – represents time/time of current flow
Even though the principle may appear simple, there are a huge selection of parameters that influence the results of actual welding processes. To know resistance welding technology better, here’s a look at a number of the parameters that influence welding results:
The welding current is an important parameter in relation to resistance welding as it determines the quantity of heat generated by a power of square. It’s worth noting that weld nugget sizes increase using the increasing welding current however, when the current is way too high, it could result in electrode deterioration and expulsions. To avert this, welding engineers need to look for the optimal welding time and current for each welding application.
Heat generation in resistance welding is directly proportional to welding time. On account of heat transfer from weld zones to electrodes along with the base metals, in addition to a loss of heat from surrounding surfaces, a minimum welding time and current are needed to build a weld. In the event the current is not sufficient, increasing welding times alone won’t generate a weld. However, when the current is strong enough, the weld nugget size improves as weld time increases until it’s a similar size as being the contact portion of the electrode tip. If welding time is protracted, expulsion might occur or maybe the electrode could end up sticking with the workpiece.
Welding force impacts the resistance welding process through its result on contact resistance on the contact area as well as the interfaces because of material deformation. The pieces being worked tirelessly on needs to be compressed by a certain force over the weld zones to permit current to move. In the event the welding force isn’t strong enough, expulsion might occur once the current starts flowing because of high contact resistance – and this might lead to rapid heat generation. On the other hand, when the force is higher than normal, that could increase the risk for contact area being larger than normal, something that might lead to low current density. Simultaneously, it may possibly result in low contact resistance, and this 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. Which induces changes for 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 in relation 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 true 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. As most metal surfaces have contaminants like oil, dirt, water vapor, and oxides to 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 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 that 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, very little heat is produced despite having quite high welding currents and is quickly dissipated. Such metals take time and effort to weld using resistance welding. However, they create very good electrodes. When unlike metals are welded together, metal with higher resistivity will normally generate more heat. This can be something which should be thought of upfront when building welding parts for projection welding and when choosing the kind of electrodes for use 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 since their surface asperities are not as easy to deform. That leads to much smaller contact areas. It’s worth noting how the materials used as electrodes have been 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, such as welding rods, brazing materials, or solder.
- Its processing time is very short.
- It includes operator-safety as being the machines only require low voltage to function.
- Resistance welding doesn’t create messes like other welding techniques it’s neat and environmentally-friendly.
- It generates reliable electro-mechanical joints.
Resistance Welding Shortcomings
- The electrodes used should be able to reach either sides of the metal pieces they can be bonding. Some spot-welding machines is only able to hold a definite metal thickness, usually 5-50 inches. Even though the electrode’s position might be adjusted, most electrode holders simply have 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 electrodes touch the metal. when the current isn’t hot or strong enough, or maybe the metal isn’t held together good enough, the spot weld might turn out to be weak or small.
- A loss of strength and warping can take place around points where workpiece continues to be spot-welded. The joint’s appearance is frequently quite ugly and can have cracks onto it. The metal could also end up becoming less resistant to corrosion.