| Welding is a kind of permanent connection method of materials. The strength of the welding joint generally needs to reach a certain value. The welding joints always serve in extremely harsh environment, such as corrosive, high-temperature, low-temperature. So it must have strong corrosion resistance and excellent performance in high or low temperatures. In order to prevent the failure of a welding joint in its normal life span, in welding process the quality of welding joint should be controlled through the real-time quality control and the external or internal quality testing welding process.Ultrasonic testing has been applied widely, because of its high sensitivity and harmless. It can show the inside case of materials directly by the ultrasonic imaging technique. In this paper, a new method for the ultrasonic located or quantitative test in welding joint was proposed. The method of measuring the spatial position of flexible arm measurement system is applied in ultrasonic testing,this method can play the role of positioning, and then aims to quantitative test. This testing system has not a motor driven device, the probe can be manual operated, that means one can carry on ultrasonic testing for the welding joint at surface of different sites or the internal parts of materials with a cavity. Compared with the motor driven probe locate system, it has many advantages, such as flexibility and wide testing range.In this paper, a basic principle of ultrasonic located or quantitative test for welding joint was designed at first. Starting from the freedoms choice, the lever lengths design, joints design,the mechanical of flexible arm was designed, and a kind of suitable angle encoder was chosen. The obtainment of rod angle information was relying on the data collect system. An optimal counting method was discovered, and a series of program was compiled to acquire positional information;An ideal mathematic model of the flexible arm measurement system was established to obtain the spatial position and verify the correctness of the ideal mathematical model. Finally the matrix equation which set the six corners as independent variable and the spatial coordinates as variable was established. Based on detailed analysis of the source of the spatial position measurement errors, the error mathematical model of the spatial location was established;To improve the measurement accuracy of the flexible arm measuring system, a research on the specific impacts and weights of each structural parameter error for the spatial position measuring accuracy of the flexible arm measurement system was done, and a study on calibration algorithm of each structural parameter based on the L-M algorithm in the least squares method was conducted, all that led to the establishment of a single point model and distance calibration model. The results of simulative experiments for both of the models indicated that: the most structural parameters can be calibrated accurately; the errors of the structural parameters were less than 10%, when the accidental errors of the flexible arm measurement system were so small;A calibration experiment scheme is developed, and calibrated the structural parameters of the flexible arm measurement system by using the single point calibration model, then selected the optimal structural parameters from three groups of calibrate results and tested the distance between any two points for ten pairs of trials. The results showed that: all the measurement errors were less than 0.5mm; it can meet the accuracy requirements;Take an example, tested the located or quantitative testing for spot welding joint by using the flexible arm ultrasonic testing system, the C-scan images and C-scan images with grids of the nugget areas of spot welding joints were obtained, then compared the measured nugget diameter and the actual nugget diameter. The results demonstrated that it can achieve positioning or quantitative test for spot welding joints by using this flexible arm ultrasonic testing system. |
PDF Full Text Request