Types of Resistance Welding Tests

The application scenarios of resistance welding are extremely diverse, covering almost all types of metal joining. Inspection of resistance-welded products serves as a critical quality control measure and is of utmost importance. Inspection methods for resistance-welded products can be categorized into destructive testing and non-destructive testing. Destructive testing is often used as a sampling method for spot checks, while non-destructive testing is applied in both process and final product inspections. Below is a brief overview.

Destructive Testing of Resistance-Welded Products

Destructive testing methods for resistance-welded products primarily include push-pull force, shear force, torque, bending, vibration, and penetration depth testing.

In the automotive industry, where resistance welding is most widely used, welding is generally divided into spot welding and projection welding.

Spot Welding Inspection: Mainly conducted through offline destructive testing, such as measuring the nugget diameter of the weld spot, testing the shear strength of the weld spot, and determining the penetration depth. These methods are used to quantify whether the connection strength, nugget diameter, and penetration rate of the weld spot meet standards.

Projection Welding Inspection: Primarily involves push-out testing, torque testing, and penetration depth testing. The main inspection criteria include the push-off force, torque, and penetration depth of the projection after welding, which determine whether the welded fasteners meet strength requirements. Fatigue resistance testing is Mainly evaluated through bending and vibration tests. For example, after butt welding sheet metal, the joint is assessed based on whether it can withstand a specified bending angle and number of bending cycles. Similarly, projection-welded nuts undergo extreme vibration for a set duration to simulate performance under harsh dynamic and static loads, with pass/fail criteria based on whether the nuts detach.

Non-Destructive Testing of Resistance-Welded Products

Non-destructive testing methods include visual inspection, X-ray inspection, ultrasonic testing, and welding process monitoring.

In the military and aerospace industries, where products have unique requirements, welds must meet aviation or military standards. In addition to sampling inspections, these standards often require full weld-point visual inspection, X-ray inspection, and ultrasonic testing to ensure the highest welding quality.

– Visual Inspection: Primarily checks the appearance of weld spots, including dimensions, indentation depth, and color, providing a preliminary assessment based on visible characteristics.

– X-ray and Ultrasonic Testing: Use radiation and ultrasonic waves to inspect the weld nugget, including its diameter, penetration rate, and any welding defects.

As the most promising non-destructive testing method today, welding process monitoring is increasingly being adopted. It involves real-time data tracking of welding current, time, voltage, pressure, displacement, and resistance. Through data comparison, curve generation, and analysis, weld spots can be evaluated during or after the welding process, effectively preventing defective products from being released.