Shape Similarity: Methods and Industrial Applications

Mass production, reduced production investment, reduced response time and variability, globalization and increased customization are the most responsible for the need of optimizing the manufacturing process. As companies provide higher levels of customization, the number of products offered increases. Minimizing the cost of providing variety is possible by exploiting shape similarities amongst parts and products. Another reason for utilization of similarity assessment is the cost estimation. Total cost of any part to machine results from material costs, setup costs, tooling costs, and operation costs. Furthermore in very small productions the total cost of new components is affected more than 70% by process planning and CAM (Computer Aided Manufacturing) programming. A relevant part of this time may be saved by modifying the process plan of an old similar part and this is a well known practice in the manufacturing industry. Shape similarity search in a CAD system is an answer to reduce process plan preparation because it finds similarities in geometry by extracting shape signatures from the 3D models and then comparing these signatures exploiting distance functions. This paper presents a review of the methods adopted to generate shape signatures and an analysis of the distance functions suitable for the comparison. The first part of this work investigates the models commonly proposed to extract the shape signature from a solid part. The second part of the paper discusses the choice of the distance function. At the end of this discussion the most appropriate method is proposed to assess the shape similarity, once the part to be manufactured has been assigned: results are shown in terms of accuracy of comparison and computational time, seeking for a trade-off between them.