What is seam welding?

Short Answer:

Seam welding is a type of resistance welding process used to join two overlapping metal sheets continuously along a seam or joint. In this process, a series of overlapping spot welds are produced by rotating wheel-shaped electrodes, which apply both pressure and current while moving along the joint.

This method is mainly used for producing leak-proof and continuous joints in fuel tanks, pipes, drums, and containers. Seam welding provides strong, uniform, and airtight joints, making it ideal for applications where fluid or gas leakage must be avoided.

Detailed Explanation :

Seam Welding

Seam welding is a resistance welding process that forms a continuous joint between two or more overlapping sheets of metal. Instead of using stationary electrodes as in spot welding, seam welding employs rotating wheel-shaped electrodes that roll along the joint while simultaneously applying pressure and passing electric current. The heat generated at the contact point melts the metal surfaces, and as the wheels move, a series of overlapping weld nuggets are produced. When these nuggets overlap properly, they form a continuous and strong seam.

This process is commonly used where continuous and leak-proof joints are required, such as in tanks, pipes, fuel containers, and sealed metal enclosures. Seam welding is an automated and efficient process suitable for thin to medium-thickness metal sheets, typically up to 3 mm.

Principle of Operation

Seam welding works on the same principle as resistance spot welding, where heat is produced by the resistance of metal to the flow of electric current. The formula used is:
H = I² × R × t
where

  • H = Heat generated
  • I = Current
  • R = Electrical resistance
  • t = Time of current flow

The metal sheets are held together under pressure between the rotating electrodes. As current flows through the joint, heat is generated due to electrical resistance at the contact surfaces. This heat melts the metal locally to form a weld nugget. The rotating electrodes move continuously, forming a series of overlapping weld spots that create a continuous seam.

Equipment Used

A basic seam welding setup consists of the following components:

  1. Power Source:
    Supplies low voltage, high current to produce the required heat.
  2. Rotating Electrodes:
    Wheel-shaped copper alloy electrodes act as both conductors of current and means of applying pressure.
  3. Workpiece:
    Usually two or more thin metal sheets that are overlapped and welded together.
  4. Control System:
    Regulates current, electrode pressure, welding speed, and duration of current flow to ensure consistent weld quality.
  5. Cooling System:
    Water cooling is used to prevent overheating of electrodes and workpieces.

Working Process

  1. Preparation:
    The metal sheets are cleaned and overlapped properly along the seam.
  2. Clamping:
    The sheets are held tightly between the two rotating wheel electrodes.
  3. Current Flow:
    Electric current passes through the joint, generating heat due to electrical resistance at the interface.
  4. Welding:
    As the wheels rotate, the current is applied either continuously or in pulses, producing a line of overlapping weld nuggets.
  5. Cooling and Solidification:
    The molten metal solidifies under pressure, forming a continuous and strong seam.

Depending on the type of current flow, there are two main types of seam welding:

  • Continuous Seam Welding: Current flows continuously, forming a continuous joint.
  • Intermittent Seam Welding: Current is applied in pulses, forming a chain of overlapping weld nuggets.

Advantages

  • Produces leak-proof and continuous joints.
  • High welding speed and good repeatability.
  • No need for filler materials or flux.
  • Easy to automate for mass production.
  • Produces uniform and neat welds with good strength.

Disadvantages

  • Limited to thin metal sheets (usually below 3 mm).
  • Difficult to weld irregular or non-linear seams.
  • High equipment cost and complex setup.
  • Overheating of electrodes may occur if cooling is insufficient.
  • Maintenance of electrode shape and alignment is critical.

Applications

  • Automobile industry: Welding of fuel tanks, mufflers, and radiators.
  • Aerospace and defense: Fabrication of sealed containers and ducts.
  • Electrical industry: Manufacturing of transformers and metal enclosures.
  • Home appliances: Used in making washing machines, ovens, and drums.
  • Pipe and drum manufacturing: To create continuous joints along cylindrical bodies.

Precautions

  • Ensure clean and oxide-free surfaces for good electrical contact.
  • Maintain proper electrode pressure and speed for uniform welds.
  • Use effective water cooling to prevent electrode wear.
  • Regularly check welding parameters like current and time for consistent quality.
Conclusion

Seam welding is an efficient and reliable resistance welding process that creates continuous, leak-proof joints using rotating wheel electrodes. It is widely used in industries where air or fluid tightness is essential. The process is clean, fast, and suitable for automation, making it ideal for high-production applications. Despite limitations in material thickness and shape, seam welding remains one of the most effective methods for producing durable and continuous joints in sheet metal fabrication.