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Reliability of Ultrasonic Technique Used for Defect Detection of Spot Welded Plates in Automotive Industry

Amiri, Nima | 2019

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 52153 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Farrahi, Gholamhossien; Chizari, Mahmoud; kashizadeh, Kazem Reza
  7. Abstract:
  8. Resistance Spot Welding (RSW) is one of the common techniques for connecting steel sheets in automotive industries. There are about 3000-5000 RSWs in the automotive chassis and body. Therefore, health and quality of RSW play a critical role in the final product performance. Also, welding process should be performed in a fully controlled program to ensure the durability of the vehicle body. In the automotive industry, there are various non-destructive methods (i.e., Chisel and Ultrasonic tests) and peel test as a destructive test (DT) to control the quality of RSW. Since the DT method is costly (waste of time, manpower, and materials), the main aim of the present research is to evaluate the reliability of non-destructive tests (NDTs) and use its results for decreasing the number of DT’s bodies. Therefore, Non-destructive tests (ultrasonic and chipping test) and destructive tests were performed on 5 car bodies as the real samples. Then, the reliability of the ultrasonic test was calculated using Binomial distribution and Bayesian criteria based on three types of quality including good weld, Undersize weld, and Stick weld. Finally, by providing standard samples at different dimensions and materials, the number of different sheets (two-sheet and three-sheet) and various strength (good weld, undersize weld and stick weld), it has been attempted to provide a more reliable instruction that Improves detection of spot-weld defects.The results of various tests on 5 car bodies in the first part of the study show that the overall reliability of the ultrasonic device is about 95% based on previous instructions. However, the calculated reliability for the detection of the undersize defect was estimated to be around 48%. The new instruction increased the overall reliability to about 98 percent, And the detectability of undersize defect increased by up to 70%. Moreover, the new instruction gives descriptions to how correctly distinguish each type of welding (good weld, undersize weld and stick weld) separately
  9. Keywords:
  10. Resistance Spot Welding ; Ultrasonic Test ; Reliability ; Bayesian Updating ; Spot Weld Defects

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