Ships have holes and pipes with various functions. In general, with previous systems, when hole outfitting design information is supplied to hull design, holes are marked on drawings in the hull design stage. Then, the drawings are supplied to the production stage and field workers use production drawings for the construction of ships. To produce a member marked on the drawings, workers must enter the information and coordinates of every hole while checking the drawings and then insert them into modeling tools [1]. In this process, design drawing errors occur frequently due to the transfer of incorrect hole information. Design errors lead to losses related to the reconstruction of holes, degradation of design quality, and increased design man-hours. These errors account for a large proportion of design errors in shipyards.

To address this problem, numerical control (NC) cutting is performed in advance through a hole plan system for holes penetrating hull fittings and pipes, thus, shortening the processing time; however, this is limited to the automation of inner plate hole generation [2][3]. Furthermore, the automatic generation of shell plate holes has been difficult due to the limitation of the existing two-dimensional design software until recently. Particularly for curved shell plates, secondary accidents frequently occur due to field construction instead of hole construction in the NC processing stage. In this study, the limitations of existing 2D design software were overcome using the 3D CAD system AVEVA Marine (hereinafter referred to as “AVEVA Marine”). Modern design software applications must provide factory automation data and detailed production information as well as various modeling and drawing automation features to improve design efficiency [4]. For the hull surface information, 3D information such as 3D shell plate hole automation is essential and the developed software system has advantages in this respect.

Figure 1 compares the processes before and after using the NC cutting system. In the past, holes were constructed in the field by workers using drawings, but the developed system can generate holes and perform NC processing with the coordinates of the holes only. According to the system flow, the outfitting design department first creates virtual holes with the hole information and coordinates and stores them in the database. The stored data can be modified and deleted as needed. The developed system ensures safe work and accurate construction. The main content of this paper is to propose an automatic generation system that can perform 3D modeling of holes using accurate hole design data and generate shell plate holes in the NC processing stage. This paper is organized as follows. After the Introduction section, Section 2 introduces the overall system structure, Section 3 describes the system configuration, Section 4 presents the system application results, and finally, Section 5 draws relevant conclusions.

Figure 1: 
Previous system and developed system process

The overall structure of the developed system is shown in Figure 2. The left side of this figure consists of the “Outfitting Hole Manager,” which generates virtual holes with the hole shape information and coordinates and stores them in the database, and AVEVA Marine for managing the information on the hole shapes and shell plate to be constructed.

Figure 2: 
System architecture

The right side of Figure 2 consists of the “Hull Hole Manager” for generating actual holes through the hole information and “Hole Information Database” for managing the hole coordinates and other hole information.

Figure 3 shows the input window for receiving the hole information of the shell plate in the hole drawing work as a tool of AVEVA Marine [5]. This input window is composed of several sections. Users can select the hole shape in “Designation,” select the reference axes (X,Y) of the holes in “Approx. Coord.,” choose whether to process the holes as “Marked” or “Burnt”, and enter the coordinate point of the hole in Point 1. “Marked” and “Burnt” indicate virtual and real holes, respectively. The reason for distinguishing virtual and real holes is to distinguish whether the hole can be finally processed in the NC workshop or whether it needs to be modified.

Figure 3: 
Hole information input window

Figure 4 shows a virtual hole generated through the input window using the hole coordinates and other information found with the developed algorithm. The drawing worker verifies the hole position and information through 3D modeling and stores them in the database. The conventional method has a high possibility of construction error because the shell plate holes are processed manually. However, the NC hole cutting illustrated in Figure 4 can improve production efficiency and minimize construction errors.

Figure 4: 
Example of virtual hole generation

Previous works have proposed process automation systems related to outfitting-related members (pipe hole, plumbing hole, and cable hole) and inner holes but shell plate work was performed manually due to the nature of the curved shell plate. Manual cutting, in particular, requires high-place work depending on the cutting position, prior marking for the cutting position and shape, and additional grinding work if the cut shape is not good.

In this study, the outfitting and hull departments jointly proposed the shell plate automation hole generation process. The outfitting department stored the hole information and modeling of the virtual hole in a database. Based on the stored data, the hull department created the real hole and performed the NC process.

Table 1 shows a photograph before applying the shell plate hole processing system on the left and a photograph after applying the shell plate hole processing system on the right. The feasibility of this method has been verified by its application to a bulk ship built in a shipyard in 2018. For the cutting equipment, manual cutting with an oxygen welder was performed before applying the system; however, the NC automatic cutting system was used for the shell plate automatic hole generation system. The developed system can reduce casualties by preventing falling risks and improve the final quality of the cutting surface with minimal errors compared to conventional methods. Furthermore, the hole processing time was reduced to approximately 10 min to reduce the cutting man-hours compared to the existing manual cutting system (approximately 3 h).

	Before application to system	After application to system
Cutting equipment	ㆍManual cutting with an oxygen welding machine	ㆍNC automatic cutting equipment
Cutting man/hour	ㆍApproximately 3 M/H per hole	ㆍApproximately 0.1 M/H or lower per hole
Cutting quality	ㆍVaries by the worker’s skills	ㆍExcellent
Additional work	ㆍWork at a high place may be required depending on the cutting position ㆍPrior marking of the cutting location and shape may be required if it is not a pipe hole. ㆍAdditional grinding may be required if the cutting shape is not good.	ㆍCutting work when there is a bridge ㆍAdditional finishing process is not necessary.
Cutting shapes

In this study, the 3D CAD system AVEVA Marine was used instead of existing 2D design software. The objective of this study is to apply the developed system to the hull surface. As 3D information is essential for the hull surface, the 3D CAD system can improve the process throughout the process covering 3D modeling, design, and construction. This software is especially popular in the outfitting design and construction fields.

The developed shell plate hole processing system is an automation system that can model holes using the hull surface and hole information and be applied to shell plates as well as the inner plates of ships. According to the “2018 Shipbuilding Industry Disaster Cases” [7] published by the Korea Occupational Safety and Health Agency, many falling accidents occur during the shell plate work. Through the developed system, shell plate hole construction can be done automatically using NC cutting equipment instead of field construction. Consequently, safety problems such as production accidents that may occur in the field, hole accidents at high positions such as workers falling, and secondary accidents due to falling work tools can be prevented. Furthermore, its implementation is expected to improve the quality of ships by reducing hole cutting man-hours and improving the efficiency of production and design processes. However, it was difficult to adjust the intervals of intersections in this study. In the future, we will research more accurate slope calculations and their application to holes by making it possible to adjust the distance between intersections.

As shown in Figure 14, the results of applying the developed shell plate hole processing system showed that for some holes that are large or located at the edge of a member, there is a possibility of deformation of the shape or position of the hole due to plate forming. Hole shape changes due to plate forming can be prevented through “bridge work,” which is often used in shipyards, and problems can be minimized by standardizing bridge construction methods.