Research On Detecting System Of Leakage Welding Of Nut In Projection Welding Process

With the constant development of production technology,nut projection welding technology is more and more widely used in the manufacturing process of white car body by virtue of its advantages of excellent quality and high efficiency.Projection welding is a special form of resistance spot welding,whose operation and control are completely done by the workers with hand,so leakage welding phenomenon occur sometimes in the actual production site.Therefore,a complete and reliable quality monitoring system is urgently needed in the nut projection welding process at the production site,to find and promptly deal with the problem of nut leakage welding in the production process,ultimately providing a good guarantee for the assembly of automotive white body.The basic principle of the monitoring of leakage welding of nut projection welding is to monitor the position signal of the workpiece and the electric signal to record the actual welding number,if the actual number is less than the designed number,so the leakage welding occurs.The difficulty of this research is that the workpiece can not be effectively monitored in the motion state.At present,the feasible method is to monitor the position of the workpiece by means of sensing range.Due to more stringent requirements on environmental conditions of the existing laser sensors and Hall proximity switches,their application are limited in the actual site.Traditional conductive proximity switches' s effective recognization distance is only 0.4 times of the measured coil probe,it's hard to satisfy the need of application.The latest digital inductance sensor LDC1614 is the best choice for this subject,which is based on the characteristics of its anti interference,oil resistant and the range large and so on.In order to verify the function of the monitoring system,using the advanced ARM microcontroller,high accuracy ballscrew and advanced step motor controller and high resolution optical-electricity encoder,this topic designed and built a electrical experiment platform and tested the monitoring system.The control accuracy is up to 1.25 um,and the measure resolution can up to 0.5um.The results of test based the long distance approaching switch using advanced digital concuctive integration chip LCD1614 shows that when there is no microwave absorbing matterial,the effective working distance can up to 1.5 times of diameter of the measured coil probe.With the NFC-130 matterial,the effective working distance can up to 1.68 times of diameter of the measured coil probe.With the WPC-2800 matterial,the effective working distance can can up to 1.92 times of diameter of the measured coil probeFinally the test welding current is as high as 6000 A completed in the resistance projection welding machine whose type is DN63,proving that the interfere of the strong magnetic field and the power frequency signal is not obvious to the test process of the monitoring system,and the monitoring system can effectively identify the process of the welding stamping parts feeding and leaving.In the way,the problem of monitoring workpiece is efficiently solved in the leakage of the convex welding of the nut,providing the technical support for the monitoring of the leakage welding.