1. No load test: if the working current is normal, it may be that the welding head contacts the objects that should not be contacted or the parameter conditions between the welding head and the welding seat fail;

2. If the no-load test is abnormal, first observe whether the welding head of ultrasonic welding grading card slabs has cracks and whether the installation is firm, and then remove the welding head for no-load test to eliminate the problems of transducer and horn step by step. Remove and replace the new welding head for judgment after eliminating the possibility of problems in the transducer and horn;

3. Sometimes no-load is normal but can not work normally, which may be due to changes in sound energy components such as welding head, resulting in poor sound energy transmission.