The development and application of a multiple wavelength illumination technique for the vision-based process monitoring of aero-structure riveting

Airframe riveting is a critical process that requires high levels of process monitoring and quality assurance due to the very high risk associated with the failure of such joints. This paper describes the development of the enabling technology developed for a machine vision-based process monitoring system. One of the key factors affecting the performance of a machine vision system is the quality of the lighting. In the application described in this paper the available lighting was severely limited by the confined space in which the system had to operate. The problem was also compounded by the reflective nature of the objects to be examined. The initial images obtained were not suitable for further processing due to the presence of significant shadows and specular reflections. A novel solution to this problem based on multiple wavelength illumination and signal processing is presented along with results from experimental trials of the approach.     

A general methodology for bearing design in non-symmetric T-shaped sections in extrusion process

In this study, a general methodology has been developed to design the proper bearing in order to eliminate the curvature of the final product in extrusion process. Three smooth curved (advanced-surface) dies with non-symmetric T-shaped sections and different off-centricities have been studied. For each die, the proper bearing has been designed and physical and numerical modeling have been performed to validate the design. The design procedure is as follows: A formulation, based on Bezier curves, has been used to determine the exit velocity profile. Since the result of Bezier method is different from the actual velocity profile, the Chitkara corrective function has been modified and applied to improve the velocity field. A deviation function has been developed to measure the curvature of the final product in terms of the exit velocity field. Considering the obtained velocity field, the friction effects, and the geometry of the dies, the proper bearing for each die has been designed. Finally, numerical and physical modeling have been performed on the die-bearing combination. According to the results, the curvature of the final product was eliminated to a great extent.     

Comprehensive study on hydrogen induced cracking of electrical resistance welded API X52 pipeline steel

Different heat treatment cycles were designed in order to investigate the effect of microstructural changes on hydrogen induced cracking resistance (HIC) and mechanical properties of the electric resistance welded steel. The heat treating of the as-welded specimen improved the ductility and impact toughness. After heat treatment, the uniform hardness profile was obtained for the welded specimens. The removal of local hard zones reduced the risk of HIC. The chemical composition and clustering of inclusions have a deleterious effect on cracking resistance in the H₂S environment. Aluminosilicate compounds and MnS inclusions were favorite sites for HIC. The most promising post weld heat treatment for improving mechanical properties and the resistance to HIC was the application of two-cycle quenching followed by tempering.     

Transient analysis of diffusion least‐mean squares adaptive networks with noisy channels

In this paper, we study the effect of noisy channels on the transient performance of diffusion adaptive network with least‐mean squares (LMS) learning rule. We first drive the update equation of diffusion LMS which incorporates the effects of noisy channels. Then, using the framework of fundamental weighted energy conservation relation, we derive closed‐form expressions for learning curves in terms of mean‐square deviation and excess mean‐square error. We also find the mean and mean‐square stability bounds of step‐size for diffusion LMS with noisy channels. We show that although noisy channels affect the performance of the diffusion LMS network, the stability bounds of the step‐size are the same form as in the ideal channels case. The derived closed‐form expressions are shown to provide a good match with values found by simulation. Copyright © 2011 John Wiley & Sons, Ltd.     

Optimal assignment of human resources for maintenance departments using fuzzy queuing systems

Maintenance-related costs are one of the main components of overhead costs and constitute an important part of a product’s actual cost. Therefore, making proper efforts to reduce and optimise maintenance costs could be one way of gaining competitive advantages. A major part of maintenance-related costs is the salaries paid to the workforce in the maintenance department. This paper seeks the optimal assignment of human resources to the maintenance department to reduce the related costs. First, we model the maintenance department using fuzzy queue models. Then, a cost function is proposed which includes the costs of workforce shortage and workforce overload. The optimal size of workforce is obtained by considering different numbers and choosing the one which minimises the total costs. Some parameters are fuzzy outputs of the queue models, which make fuzzy results of the cost function. In order to find the minimum fuzzy cost function, we use Lee and Li fuzzy ranking method. Finally, our model is tested in a spiral-tube company and a sensitivity analysis is performed.