Induction Thermographic Inspection of Friction Welding Joints in Automobile Engine Valves

An active infrared thermography system based on induction heating was developed to inspect the joint quality of friction-welded shafts in automobile engine valves. Two types of engine valves were sampled from a manufacturing factory and tested using induction thermography. One valve demonstrated a good welded joint, whereas the other exhibited a joint with incomplete fusion. The engine valve samples underwent pulsed induction heating and were imaged with an infrared camera to capture the temperature distribution at the welded joint of the valve shaft. The infrared images provided clear insights into temperature changes at the welding interface caused by defects, enabling successful defect detection. The specimen with a perfect weld displayed only the interface contour of the joint of two different materials, whereas the infrared image for the imperfect joint showed a significant temperature rise at the interface due to discriminatory Joule heating in the welding defects (typically incomplete fusion). In addition, the engine valve samples were inspected using the ultrasonic pulse-echo method for qualitative comparison with the induction thermography results. Experimental results revealed that induction infrared thermography is an effective tool for inspecting defective friction welds in automobile engine valves due to its non-contact nature and ability to quickly and clearly visualize welding defects.