A Template Model for Defect Simulation for Evaluating Nondestructive Testing in X-Radiography

This paper proposes a new template model for the simulation of casting defects which are classified, according to shape, into three main types: the single defect with circular or elliptical shape, shrinkage defects with stochastic discontinuities, and the cavity or sponge shrinkage defects. For effective simulation, different nesting stencil plates are designed to reflect the characteristics of different casting defects. These include intensity, orientation, size, and shape. The proposed approach also uses geometric diffusion to demonstrate the production of simulated defects with effective shading and contrast when compared to their background. In order to evaluate the effectiveness of the proposed approach, the simulated casting defects are superposed on real radioscopic images of casting pieces and compared with real defects by extensive visual inspection. On the other hand, in order to verify the similarity of the simulated defects and the real defects, we have used our defect inspection algorithm to recognize both real and simulated defects in the same image. The experimental results show that the proposed defect simulation approach can produce a large range of simulated casting defects, which can be utilized as sample images to tune the parameters of casting inspection algorithms.

I. Introduction

Casting defect simulation techniques have received increasing attention in the field of automatic casting inspection [3], [4], [11], [13] to validate the system's sensitivity and to help tune the automatic inspection parameters. Automatic inspection and analysis of casting defects is one of the most important approaches to increasing casting quality. The extraction of the precise shape of the defect is a critical problem which strongly influences the effectiveness of automatic inspection systems [22]. The correct choosing and tuning of the parameters of the inspection algorithm is essential for it to be unaffected by changes across the casting image and is one of the most important steps to guaranteeing the efficiency of the inspection algorithm. The algorithms built for different kinds of casting products vary to some extent, but the tuning of their parameters is a common problem which can be complicated and involves a variety of aspects including consideration of the shapes of the casting defects, the contrast between defects and their background, and the structure of the casting pieces. Before implementing the program to inspect the work pieces, a large number of sample images are needed to tune the algorithm, examine its performance [23], and ensure its accuracy. Product images with defects from the production line are the best; however, they are often not available in sufficient quantities or variety. Simulation of casting defects is an alternative approach to deal with this problem.