Evaluation Method for Ship Hull Plates’ Process Molding

Abstract

The evaluation procedure is an important step for the ship hull plates automatic processing, which serves as a basis for secondary processing. In this paper, an evaluation method was proposed, based on the experienced workers' knowledge. The design surface and the measured surface were registered by transforming to the new coordinate system. Then the profile errors were evaluated and decomposed into three directions: transverse, longitudinal, and torsional. Finally, the experiment results shown that the evaluation indexes, which were based on the errors decomposed result, can be served as the basis for secondary processing of the ship hull plates. 1. Introduction Ship hull plates are thick large steel plates with arbitrary threedimensional (3D) shapes. Usually, the steel plates are plastically deformed to the design shape by line heating process. And the shapes of the machining plates are evaluated by the wooden bending templates, which are generated by ship's design data. Experienced workers can evaluate the transverse bending, longitudinal bending, as well as torsional angle of the plates by this process, and get the essential factual basis for the secondary processing. However, this process has no clear-cut methodology, the evaluation results and the secondary processing plan are heavy, depending on the tacit knowledge, skill, and experience of the craftsmen during the line heating processing (Woo-Jae et al. 2010; Hiekata et al. 2011; Seong et al. 2013; Sun et al. 2013). For ship hull plates profile error evaluation, Hiekata et al. (2011) had put forward an accuracy evaluation system, using 3D laser scanner to measure the ship hull plates, and then evaluated the displacement errors by comparing the measured surface with the design surface. This system had achieved digital evaluation, but the evaluation indexes were difficult to guide the secondary processing. Sun et al. (2013) evaluated the ship hull plates by the virtual templates, and generated the processing plan, according to the evaluation results. Nevertheless, this method only evaluates the longitudinal bending and torsional condition. it still needs to be improved. Also, other researchers (Wen et al. 2013; Liu 2014; He et al. 2015; Nasri et al. 2015) had put forward various evaluation methods, but the purposed methods were aimed to improve the evaluation accuracy, seldom consider the line heating process. Thus, these methods have failed to provide the factual basis for the secondary processing.