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WHAT IS WELDING?

Resistance welding is a fusion process which takes place between two metals under a certain load and heat without any demand of additional materials. The heat required during welding process is generated from the electrical resistance of the materials. There are four types of welding methods in resistance welding: Spot Welding, projection welding, seam welding, and flash butt/ butt welding. The Flash Butt / Butt Welding method requires no overlapping of the joining metals. Furthermore, there are four types of output current solutions: Single phase AC, capacitor discharge DC, three phase rectified DC, and three phase inveter DC respectively. Capacitor Discharge DC is not applicable in Seam Welding and Flash Butt / Butt Welding methods due to its intrinsic nature of instantaneity on current flow time.

4 WELDING METHODS

Resistance Welding can be divided into four welding methods and four output current solutions.

Welding Methods

4 OUTPUT CURRENT SOLUTIONS

Single Phase AC

Single Phase AC

Single Phase AC  is the most fundamental type of output solution. Current returns to zero every half cycle. This type of current solution creates a “no current flow” period and induces intermittent heating phenomenon. AC welding machines with Constant Current Controllers possess the functions of primary voltage compensation and primary/secondary constant current feedback control which automatically adjust power fluctuations.

Capacitor Discharge DC

Capacitor Discharge DC

Capacitor Discharge DC is one of the direct current series which extracts energy from the power over a period of time for storing in capacitors. The stored energy is rapidly discharged to transformer producing a flow of electrical current for welding. Capacitor Discharge solution is the best application in welding products in hot rolled sheet or thick steel sheet with multiple embossments.

Three Phase Rectified DC

Three Phase Rectified DC

Three Phase Rectified DC is with three-phase balanced input operating at 50 or 60Hz. It was widely adapted before the emergence of Three Phase Inverter DC. The diodes on the transformers convert AC to DC. Three Phase Rectified DC solution saves 40% of energy with comparison to Single Phase AC solution.

Three Phase Inverter DC

Three Phase Inverter DC

Three Phase Inverter DC utilizes three-phase balanced input. Current is in full wave form rectified to DC and switch to 1000Hz to produce AC supply to primary transformer. The current is rectified into DC for welding afterwards. Three Phase Inverter DC solution has the following advantages:

 

Three Phase Inverter DC solution has the following advantages:

  1. It does not have blank period in the current wave form. Heat produced is continuous and efficient. The fast feedback control (roughly 0.1 millisecond) ensures stable welding quality and controls welding splash.
  2. High frequency means high current density. It easily generates the required welding heat in the shortest time interval. Thus, welding is completed in a faster approach with minimum power consumption.
  3. High-frequency switching technology also reduces power consumption to 60-70% comparing with Single Phase AC solution.
  4. High-frequency transformer makes wide-range welding possible. Traditional AC transformer may induce insufficient current disperse with poor welding quality.
  Schematic Diagram
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