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Seam welding is the process of joining two similar or dissimilar materials at the seam by the use of electric current and pressure. The process is mostly used on metals since they conduct electricity easily and can sustain relatively high pressures.
Seam welding is possible thanks to contact resistance created between the two metals.
As current passes between the metals, heat gets generated at the small gap. Electrodes maintain and control the flow of electricity.
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Let’s get into the details about this welding technique used across a diverse set of industries.
What is resistance seam welding?
Seam welding or resistance seam welding is a subset of resistance welding, which is the process of welding two materials using electric current.
There are mainly four types of electric resistance welding:
- Resistance spot welding
- Resistance projection welding
- Resistance butt welding
- Resistance seam welding
Resistance seam welding is one among the most common welding processes used to join metal sheets with a continuous weld.
When two similar or dissimilar materials are pressed together, there will be a slight gap between them due to surface irregularities. In resistance seam welding, this gap creates an electrical resistance between the two materials and causes them to heat up at the seam.
This is also known as contact resistance.
The welding current is of primary importance in seam welding. The amount of heat generated at the seams will depend on the magnitude of the current flowing through it.
However, cranking up the electricity too much can cause expulsions and electrode deterioration. Alternating current (AC) is still the most preferred type of electric current used in seam welding.
The seam welding process uses wheel-shaped electrodes. These wheels apply force and electricity to the workpieces.
The welding force should be proportional to the hardness of the materials. Hence, harder metals need more welding force compared to softer metals.
In a broader sense, resistance seam welding is categorized into:
Intermittent motion seam welding
The rollers and the electric current application stays active until the weld position is obtained. This means that weld occurs at specific spots or area rather than as a continuous line.
Intermittent motion seam welding is useful for welding thicker metals where a continuous weld is not possible. There are two types of intermitted seam welding:
- Roll Spot weld
- Overlapping seam weld
Continuous motion seam welding
In continuous seam welding, a continuous weld is possible. The metal joins as it passes through the electrodes at a constant roller speed. It produces a uniform overlapping weld as the workpieces remain under constant pressure.
The type of electrodes used in resistance seam welding is dependent on the material that is to be weld. For example, if we use seam welding to weld aluminum, then copper electrodes are often avoided. This is because copper alloys with aluminum, resulting in much faster deterioration of the electrode.
Laser seam welding and resistance seam welding
The term seam welding has become almost synonymous with resistance seam welding. However, there is also another seam welding process called laser seam welding.
Laser seam welding is a variation of laser spot welding. In laser spot welding, a high-intensity laser is pointed at a spot where the beam causes the target spot to melt and weld.
However, in this case, the laser tool head is stationary. In this welding technique, the laser moves along the seam to create a constant weld.
This type of welding technique is typically used to weld sensors, radar components, insulin pumps, battery housing, and pacemaker cases.
Advantages of resistance seam welding
Resistance seam welding has a unique set of advantages which makes it very favorable in many industries.
Airtight welds: One of the most important characteristics of a continuous weld is that it can create airtight and watertight seals. This is very important in creating metal structures that need air or water leakage protection, like air or liquid-tight vessels.
Fast weld process: Weld is possible at high speeds. And, since the whole process is automatic, resistance seam welding is faster than other alternatives like spot welding.
No filler/flux required: The weld is possible without using any filler or flux material.
Disadvantages of resistance seam welding
The way resistance seam welding is set up, some disadvantages come with it. The following are some of the limitations or disadvantages of resistance seam welding.
Limited weld lines: Since seam welding apparatus consists of rollers, only straight line or uniformly curved line welds are possible.
Thickness limitations: There are limitations when it comes to the thickness of the sheets because seam welding can become quite cumbersome when the thickness of a single sheet is more than 3mm.
Applications of seam welding
Resistance seam welding finds its application in the assembly of fuel tanks as it needs to be liquid-tight. It is also used for welding parts of vessels that need to be water or airtight.
Some other forms of welding can also create water and airtight seals, but they do not necessarily ensure a clean weld. Similar to what is achievable through seam welding.
The other common application is in welding pipes and tubes. Resistance seam welding is especially used in this field because it doesn’t use any fusion metals in the process.
Hence, there are no weld beads that would ruin the aesthetics of the tubes or pipes. This welding technique is capable of producing seamless joints that are hard to even feel at the joining surface.
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Seam welding is also used in manufacturing sheet metal tanks used as containers for kerosene, gasoline, and other fluids. Both the airtight and liquid-tight welds play a role in such an application. This is because liquids like gasoline vaporize when in contact with the air.
Resistance seam welding finds itself in many industries due to the unique weld capabilities. Like every welding process, it has its set of advantages and disadvantages.
However, for a particular set of requirements, resistance seam welding is ideal in its performance and weld capabilities.