Low Carbon Steel Spot Welding Process Parameters (Single-Phase AC, Equal Plate Thickness)
Low carbon steel spot welding is a widely used welding process due to its fast, cost-effective and repeatable production. This welding process can be used to join two or more steel parts (usually any kind of low carbon sheet or plate) when location and surface condition permits. This process produces a joint that is stronger and superior to an ordinary fastener joint.
The Spot Welding Process
Spot welding machines use either AC or DC electric current in order to produce the heat necessary to bond the two pieces of metal together. The AC process is the most common for spot welding of low carbon steel.
The AC welding process consists of welding current alternating from positive to negative in a cycle that is typically set in the range from 0.1 to 3 seconds. In general, the faster the cycle, the faster and hotter the weld. The current is applied through two welding electrodes that squeeze the two pieces of metal together and apply pressure, heat and current simultaneously in order to create the weld. After the desired weld is attained, the current is switched off and the pressure is removed from the parts. Low carbon steel requires an amount of current that is greater than that of stainless steel and other mild steel grades.
Process Parameters
In order to attain a good quality spot weld, it is important to determine the correct process parameters. These parameters include the current, time, pressure and electrode diameter.
Current: The current used for spot welding of low carbon steel should be set at a minimum of 3.5 kA, with a maximum current of around 6kA.
Time: The time or ‘on-time’ of the weld cycle should be kept as short as possible, usually between 0.2 and 0.5 seconds.
Pressure: The pressure applied is also important, as too much pressure can cause the weld to become distorted. A good starting point is 5-7 bar and it can be increased or decreased depending upon the metal thickness and welding requirements.
Electrode Diameter: The diameter of the electrode tip is important as it affects the distribution of the current. For spot welding of equal plate thickness, a diameter of 0.55 inch is a good starting point, with a tolerance of +/- 0.05 inch. For unequal plate thickness a good starting point is 0.50 inch.
Conclusion
When spot welding low carbon steel, it is important to ensure that the process parameters are set correctly in order to achieve a good quality weld. As a general rule, current should be set between 3.5kA and 6kA, the welding time should be kept as short as possible, pressure should be set at 5-7 bar and the electrode diameter should be between 0.50 and 0.55 inch. By following these parameters, a good quality spot weld can be achieved.
