Weld Quality Inspection Research Articles

Development of a Flexible Laser Ultrasonic Probe

Ultrasonics is a widely used nondestructive testing technique, which is often applied off-line for weld quality inspection. Laser ultrasonic (LU) inspection systems have the potential for on-line application, providing the means to identify unacceptable welds as they are formed. Because LU systems are non-contacting, they can be used for testing moving specimens or for operation in hazardous and/or high temperature environments. A highly versatile system can be created when an optical fiber delivery system is incorporated into the design. Introduction of a focusing objective increases the allowable working distance and permits stronger generation using material ablation as the generating mechanism. This paper describes the development of a laser ultrasonic probe using an optical fiber delivery system with a distal end, focusing objective. The optical fiber delivery system can be configured as a single fiber source, a linear array (fiber bundle) or a phased array. Results include experimentally obtained directivity patterns demonstrating ultrasonic generation using ablation sources. Thermoelastic source results are also included. This paper demonstrates the potential of the fiber tool and presents an overview of the weld control scheme.

A quality assurance technique for resistance spot welding using a neuro-fuzzy algorithm

Abstract Resistance spot welding is widely used in the field of plate assembly; however, there is currently no satisfactory nondestructive quality evaluation for this type of welding, either in real time or on-line. Moreover, even though the rate of welding under conditions of expulsion has been high until now, there is still no established method of quality control against expulsion. Accordingly, this paper proposes a quality assurance technique for resistance spot welding using a neuro-fuzzy algorithm. Four parameters from an electrode separation signal, in the case of non-expulsion, and dynamic resistance patterns, in the case of expulsion, are selected as the fuzzy input parameters. These parameters are determined using a neuro-learning algorithm and then are used to construct a fuzzy inference system. When compared with the real strength for the total strength range, the fuzzy inference values of strength produced a specimen error within ±4%, and the percentage of specimen errors within ±1% was 88.8%. The tensile-shear strength limit for electrically coated zinc is 3,920 kN/mm 2 . When evaluating whether the quality of the welding was good or bad according to this criterion, the probability of misjudgment that a good quality weld was a poor one was 0.43%, and the reverse was 2.59%. Finally, the proposed neuro-fuzzy inference system can infer the tensile-shear strength of resistance spot welding with a high efficiency in cases of both non-expulsion and expulsion. It is also anticipated that an on-line welding quality inspection system will be realized in the near future.

On-Line Estimation of Laser Weld Penetration

High-power CO2 laser welding has been widely used in the industry because of its high productivity and excellent weld quality. In order to tap the potential of this process completely, it is important to have on-line weld quality inspection methods to improve the process productivity and reliability by achieving 100 percent weld inspection. Weld penetration is one of the most important factors critical to the quality of a laser weld. However, it is very difficult to directly measure the extent of penetration without sectioning the workpiece. In this paper a model-based penetration depth estimation technique suitable for the production environment is developed. The proposed model relates the temperature measured on the bottom surface of the workpiece, weld bead width, laser beam power and welding speed to penetration depth. The closed-loop depth estimator combines the model and a model-error compensator to compensate for the uncertainty in the measurement of the laser power and absorptivity. Other effects considered are the averaging due to the finite size of the sensor, delay based on the sensor location and the process and sensor dynamics. Several bead-on-plate and butt welds were made on low carbon steel plates to validate the static process models and the depth estimation scheme. Temperatures on the bottom surface of the workpiece during welding were measured using infrared thermocouples. The welds were sectioned longitudinally to obtain the penetration profile. The penetration profiles estimated by the depth estimator matched satisfactorily with the measured penetration profiles. The results validate the capability of the proposed depth estimator to estimate penetration depth and its ability to trace the dynamic changes in penetration depth.

IBM France Pioneers Applications of Neural Networks

Few industrial applications of neural networks are yet in operation. One company making exceptional progress, however, is IBM France whose team of specialists are implementing pioneering applications with machine vision and diagnostic sensing. This team is using the novel technology to tackle such problems as character recognition, weld quality inspection and machine diagnostics.

Abstract: Leak testing large vacuum systems

Testing of large vacuum systems for leaks may best be described as a problem in high vacuum engineering with leak detection methods as a tool for its accomplishment. Before any leak testing is performed, it is necessary to determine the operating limits for the vacuum system which in turn are used as the boundary conditions for specification of acceptable leak rates. After determination of the leak rates which are acceptable to the overall vacuum system operation, a leak testing system design and procedure is developed to satisfy the leakage criteria. The leak testing philosphy to be followed is little different than any other leak testing problem.Differences found in leak testing of large vacuum systems as compared to laboratory systems are primarily ones of physical magnitude and emphasis. For example, the roughing cycle commonly used on small components, i.e., laboratory vacuum systems and components of less than 50 ft 3 volume, is of little concern when making use of a mass spectrometer leak detector ...