1.What are the key influencing factors?
Material Thickness: This is the most crucial determining factor. The thicker the material, the more heat is required, and the higher the current. It's usually calculated based on the thickness of a single plate or the total thickness.
Material Type: Although all are cold-rolled steel, different grades (e.g., SPCC, SPCD, SPCE) have slightly different resistivity and melting points.
Electrode Type and End Face Diameter: The electrode diameter determines the current density. The smaller the diameter, the higher the current density and the more concentrated the heat. The electrode diameter (usually the radius R of a sphere) needs to be selected based on the plate thickness.
Electrode Pressure: The pressure must be high enough to ensure stable contact resistance between the plates and to compress the weld nugget into a dense structure. Insufficient pressure will cause spatter; excessive pressure will reduce contact resistance, requiring a higher current.
Welding Time: The time the current passes through (usually calculated in cycles, 1 cycle = 0.02 seconds). Time and current can compensate for each other (high current for short time, or low current for long time), but each has its applicable range.
2.What is the golden rule for determining the optimal current?
Test Welding: Set the current, time, and pressure based on experience.
Inspection:
Destructive Testing (Most Reliable): Perform a peel test or shear test. A successful weld should leave a complete "button" (melt nugget) on one of the plates. Measure the button diameter; it should meet the requirements (usually, the weld nugget diameter should be ≥4√t, where t is the thickness of the single plate).
Non-Destructive Testing: Ultrasonic testing, etc., can be used.
Adjustments:
Insufficient weld strength (small or non-formed weld nugget): Gradually increase the current or extend the welding time.
Severe spatter: Possible causes include: excessive current, insufficient pressure, electrode wear, or poor alignment. First, check and increase the electrode pressure; if ineffective, appropriately reduce the current.
Excessively deep weld indentation: Excessive current, excessive welding time, or insufficient electrode pressure.
3.What are the important safety and operational guidelines?
Apply pressure before applying current: Ensure the electrode is firmly pressed against the workpiece before connecting the welding current. This is a fundamental principle to prevent spatter and equipment damage.
Cooling is crucial: Sufficient cooling of both the electrode and the workpiece is essential; otherwise, the electrode tip will wear and deform rapidly, leading to inconsistent weld quality.
Surface cleaning: Rust-preventive oil, grease, or oxides on the surface of cold-rolled coils can severely affect contact resistance, causing fluctuations in weld quality. The surface must be kept clean before welding.
Parameter recording: For mature products, once the optimal parameters are determined through testing, a welding process specification should be established and strictly adhered to.
4.What are some methods for estimating current?
Empirical formula (for spot welding of low carbon steel):
Current (kA) ≈ (9～11) Plate thickness (mm) *
For example: Welding a 1.0mm + 1.0mm cold-rolled plate, the total welding current is approximately 9～11 kA (9000～11000 amperes).
This is a very rough initial value and must be adjusted according to the actual situation.
5.What factors need to be considered when determining the welding current?
For resistance welding of cold-rolled coils, the welding current is a range that needs to be determined comprehensively based on the plate thickness, electrode, pressure, and time. For spot welding of 1.0mm thick cold-rolled plates, the typical starting point of the current is around 8-11 kA. The most scientific method is to start from empirical values and find the most suitable current parameters for your specific production conditions (equipment, materials, speed) through process experiments and destructive testing of weld joints.