Research On The Ultrasonic Detection Method And System Of Detecting And Evaluating The Spot Weld Quality In Car Body

Resistance spot welding is the main connection method in the assembly of automotive body,the quality of spot welding is the key to ensure the structure security and appearance quality of the automotive body.The traditional method of inspecting spot welding quality is destructive sampling test,which is hard to fully reflect the welding quality of automotive body,and can't satisfy the welding quality detecting demand of high reliability and low cost with the development of automobile industry.For increasing the detection efficiency to satisfy the growing detection demand,a kind of nondestructive,efficient and accurate inspection method of testing the spot welding quality is urgently needed.Based on the fundamental principle of detecting spot welding quality using ultrasonic A-scan method,this thesis establishes corresponding mathematical and simulation models,analyzes the effects of the error factors on the detection results,designs the clamping device of probe and circulation supply system of couplant,and programs the software of evaluating spot welding quality.Finally the system of automatically detecting and evaluating the spot welding quality of automotive body is established,the main research contents are as follows:(1)The theoretical A-scan expression of different materials,plate thickness and nugget diameter is deduced based on the basic theory of acoustic propagation,and the mathematical calculation formulas of nugget diameter is established,which realize the quantitative calculation of spot welding quality detection using ultrasonic A-scan method;The effect of spot welding structure and material on ultrasonic attenuation coefficient is studied,and the corresponding measurement experiment has been finished.It's found that,with the increase of nugget diameter,the attenuation coefficient increases generally,and structure factor turns form the major factor to secondary factor of acoustic attenuation.(2)The transient acoustic simulation models are established,the results reveal the acoustic propagation mechanism during the detection process,and the influence of diffraction effect,indentation depth,indentation angle,air hole,probe deviation on the detection results are analyzed.Besides,the appeared reason and condition of “Napoleon's Hat” phenomenon is studied,which is caused by air-hole in welds during detecting process.The simulation results provides the basis for amending the theoretical calculation formula of nugget diameter and establishing evaluation algorithm of the spot welding quality.(3)Combining the results of experiment and simulation,the recognition algorithm of spot welding quality is established and programmed in the spot weldingevaluationsoftware,the software can calculate many parameters such as nugget diameter,attenuation coefficient and indentation depth,and the quality of spot welding can be identified through these parameters;The system ofdetecting and evaluating the spot welding quality has been built,it can automatically test many welds during short time.Based on partial immersion method,the probe clamping device and circulatorysupply system of couplant is designed,which can ensure the precise location of the probe and the circulation supply of couplant.This thesis perfects the theory of detecting spot welding quality using ultrasonic A-scan method,designs a system of detecting and evaluating spot welding quality in automotive body,provides the theoretical basis and technology method of online detecting the welding quality of automobile.It is valuable not only in theory but also engineering practice for evaluating the spot welding quality and ensuring the security of automotive body.