Experimental Study On Weak Magnetic Testing Technology Of Weld Nugget Quality

With the continuous progress of science and technology,the requirements for welding quality are getting higher and higher in all walks of life.As the weld penetration,welding pool width,and actual throat are important signs of welding mechanical properties.How to effectively detect these quality parameters of weld nugget has become a frontier issue for evaluating and testing welding quality.However,at present,there are not many methods to detect the quality of weld nugget quality,and these detection methods have obvious limitations.In order to effectively evaluate welding quality and measure the quality parameters of weld nugget efficiently and accurately,a weak magnetic detection method based on geomagnetic field is proposed to detect the quality of weld nugget and evaluate the quality of welding quality.Firstly,the automobile brackets(two-point control arm weldments made of high-strength steel and torsion beam rear axle weldments)used in automobile industry were took as research objects based on the basic principle of field weakening detection.Depth of the weld(distance from the weld surface to junction of the brazing material and the parent metal)was calculated by various inversion methods based on the inversion theory of magnetic anomalies and the basic Biot-Savart law.The caculation results of these inversion methods were compared to obtain the optimal approach for caculating weld depth.Secondly,in terms of hardware,a miniature single TMR sensor with a thickness not more than 1 mm and an array type TMR sensor with a thickness not more than 10 mm are designed for weak magnetic signals collecting to detect welds in car brackets with complex geometry and narrow detection positions.Signal-to-noise ratio of the weak magnetic signal was enhanced by using the singular data filtering method based on the Layda criterion to filter original collected magnetic signal.Weld depth of the tested part can be obtained from the weld depth calculation method.Comparing the calculated weld depth results with the metallographic experimental results,we can see that the calculation results of weld depth based on the weak magnetic detection method are consistent with the actual depth values of the welds.The maximum error is 0.24 mm,which verifies the feasibility of the TMR sensor.Finally,based on the calculated weld depth value,a mathematical model for calculating the quality parameters of weld nugget was established according to shape of the weld nugget and size and placement of the sensor.A visual software system for detecting quality parameters of weld nugget was written under the framework of the C# program.The comparison between the results used Array type TMR sensor and the metallographic experiment results showed that the weld nugget quality parameters tested by the weak magnetic detection method were consistent with the actual quality parameter values of the weld nugget.The experimental study in this paper provides a new idea for the detection of weld nugget quality.