Variation Propagation Analysis of Hull Flat Block Construction Process Based on State Space Model

Hull flat block (HFB) construction is a typical discrete manufacturing process, during which block deviation is accumulated. To satisfy the dimensional requirements of shipowners, the variation propagation during HFB construction must be modeled and analyzed. Based on the stream of variation theory, the construction process is analyzed to provide a reference for controlling the deviation. In the hull construction process, the deviation is categorized into part deviation, location deviation, and welding deviation. By analyzing the causes of the different deviations, the different deviations and their accumulations can be calculated. A HFB is used to verify the proposed model, and the results show that the method can be used to calculate the deviation to the HFB. As a typical large-scale complex equipment, the hull construction process is extremely time-consuming and laborious. The final hull is composed of intermediate products, such as subassemblies, unit assemblies, and grand-assemblies (Cho et al. 1999). Since the group technology was applied in hull construction, a series of production lines has been established based on the process similarity of parts, components, blocks, and grand blocks. The actual dimension of parts would inevitably deviate from the theoretical dimension (Mandal 2017), i.e., dimensional and shape deviations will occur owing to many factors (Okumoto 2002). In the hull construction process, the deviation from the previous process will be propagated to the current process and coupled with the deviation in the current process, thereby affecting the accuracy of the product. Hence, the product must be repaired to satisfy the design requirements (Takechi et al. 1998). This will prolong the production cycle and reduce the production efficiency (Heo et al. 2015). It was discovered that the man-hours of the main operations during hull assembly constituted only one-sixth of the total assembly manhours, whereas the man-hours used for adjustment constituted one-third (Chen et al. 2020). Currently, shipyards need to eliminate the adjustment operation to avoid unnecessary rework, as well as reduce human and material resources in subsequent processes. Tanigawa (2003) estimated that an ideal ship construction accuracy control plan can reduce the production cost by 5%. Therefore, the accuracy of the hull construction process must be controlled and improved in shipyards, and a reasonable accuracy control plan should be devised to improve the product quality.