ABSTRACT INTRODUCTION

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1 The CAD/CAM system as a central information source in a shipbuilding environment K. Johansson Kockums Computer Systems AB, Box 50555, S Malmo, Sweden ABSTRACT In a shipbuilding CAD/CAM system a product model is built up, during the design process, with geometric as well as non-geometric information. This information is used for producing drawings, different kinds of production information (inch NC-information), etc. Information needed for parts lists, production planning, material handling, etc., can be derived from the product model instead of being created manually. The paper discusses important characteristics of a shipbuilding CAD/CAM system. The perspective is the CAD/CAM system as a part of the total information flow within a shipyard. INTRODUCTION Ships and offshore structures are often built in short series or as individual made-to-order products. The high complexity of the products implies an intensive design and planning process, where many tasks have to be performed in parallel. Often, manufacture of one part of the product is going on at the same time as the detailed design of another. The main functions within a shipyard and the information flow between them are illustrated in figure 1. The flow Tendering-Design-Production is the main information flow. The shipbuilding CAD/CAM system deals mainly with this information flow. Planning, Materials, Finance and Follow-Up can be considered service functions created to support the main flow.

2 iviciiiiie. Product Figure 1: The Shipyard Information Flow. THE SHIPBUILDING CAD/CAM SYSTEM The product model When developing the layout of a complex area like an engine room, there are frequent needs to analyse the arrangement from different views, to make sections and projections to verify clearances, etc. To do this with manually produced drawings is a heavy task when all sections and projections must be updated as work proceeds. For years, many shipyards have used plastic models as a tool to solve these problems, sometimes as a complement, sometimes as a substitute for manual drawings. In the computerized world there is the same need for a 3D model, where the different disciplines can model their parts with access to model information created by other disciplines. It is not enough to store this model as a graphic model. Instead, the model must be a product model containing information about all objects that are involved in the shipbuilding process, such as pipes, brackets, cables, components and their relations. The information stored about the objects is of both numerical and attributal type, the graphical representation is generated when it is needed, e.g. for viewing the model or creating a drawing. In this way, the graphics can be generated as symbolic, 2D or 3D representation depending on the needs at the time of generation. The information stored in the objects is the primary information, the graphical representation, e.g. drawings, is secondary and generated by the CAD/CAM system.

3 The product model also contains information on relations between objects, topological information. These relations are used to maintain consistency in the model and to ensure that when one object in the model is changed, the related objects are modified accordingly. Figure 2: The product model. There are three views of the product model that have to be supported simultaneously by the shipbuilding system: During the early phases of the design the product model is looked upon as a set of systems. During the detailed design phase the model is also looked upon as subdivided into zones or compartments. When the production is planned the model is looked upon as a set of assembly sequences. The Component Data Bank The ship consists, to a great extent, of different types of components. A component stored in a product model requires a lot of technical information connected to it in order to make it possible to analyse the model and to produce parts lists. Since the same component may exist in many different places in the model, the efficient way to handle all component information is to use a component data bank. The component data bank stores simple objects like bars or tubes as raw material, as well as complex objects like pumps and engines. The material

4 4o iviarine rmgmeenng catalogue of a materials handling system contains material number, supplier identity, price, etc. The component data bank should refer to this information and, in addition, contain information about size, shape, technical properties, etc. In an integrated system environment, it is natural to link the component data bank and the materials catalogue of a materials handling system. System characteristics There are some key factors for efficient production of ships, e.g. Design for production Early unit breakdown Prefabrication Preoutfitting. The shipbuilding CAD/CAM system is a system designed to meet the key factors above and other requirements from the shipbuilding environment as opposed to the systems aimed for mechanical design that are generally referred to as CAD/CAM systems. To be efficient, a shipbuilding CAD/CAM system must be based on the product model concept and address all phases in the design process in such a way that information from one stage can be used in the next. It must also use a component data bank. Components Production information Figure 3: Phases in the design process. It is important to have the special conditions in shipbuilding in mind when evaluating the total information flow. To just computerize the existing manual routines will not give as much benefit as taking the opportunity to streamline the information flow where possible, and to adapt the organization and the way

5 Marine Engineering 49 of working to the new tools and methods available. A product model based system must understand what the different parts of the model really represent, and be able to interpret the rules and restrictions connected to each type of object. For example, to produce bending information for a pipe or to check the possibilities to bend a pipe, the system must be able to distinguish pipes from other cylindrical objects that may look like pipes. Other examples would be having the ability to identify the difference between a bend and an elbow, a prefabricated weld and an assembly weld or investigating the surrounding structure of a bracket or a pipe connection, where the system has to know which objects are pipes, stiffeners, seams, valves, etc. The philosophy of a product model based system is that the information in the product model is the basis for the design and production process and contains all technical product definition data. The different views, sections, projections and other information that build up the drawings can be derived from the model. In this way the compatibility between different drawings is automatically secured. There will no longer be a need to restrict the number of views to evaluate a design because of the amount of drawing work. In such a system the drawings are not the primary information source. AUTOMATIC PRODUCTION INFORMATION In shipbuilding, numeric methods have been used for a long time to cut steel plates. The geometry and the marking information for all plate parts can be automatically created based on the product model. The same process can be applied to the handling of stiffeners and pipes. Information about the stiffeners and pipe spools can be automatically retrieved from the product model. The stiffeners can be nested onto standard lengths of bar material. Pipe sketches including parts lists can be produced for each pipe spool. Either a shipyard has chosen manual prefabrication or a fully automated line production, the relevant information can be retrieved from the product model. Also production information and setup information for jigs and different kinds of templates, quality control support, etc can be automatically derived from the product model. When the production information can be produced automatically, very little effort is required to do it once the design is made. This means that the production information can be made just before being required, so that late design changes can be incorporated. The result is less rework and less paper based information floating around with the risk of being out of date.

6 DU marine engineering DRAWING PRODUCTION Traditionally, the production drawings were just a refinement of the design drawings. The prefabrication information (plate part geometries, pipe spool details, etc.) was obtained from these drawings which were also used for assembly purposes. Such production drawings and their parts lists usually showed the whole arrangement and consequently the different assembly phases could not be distinguished. When using a product model as the basis for drawing generation, it is easy to present one set of views from the model suitable for the designers, and another suitable for the production people. The prefabrication drawings, e.g. burning sketches and pipe sketches, can be extracted from the model and the assembly drawings can be composed in a way that reflects the assembly sequence.,.,,. :,y.i.i,m.s,!«" - iaii izi! M ui. :«\:!u\! i w!;z!.5s;..i... i kz:.;;;:!:;:5:! «i;. i i.j. iik.i Figure 4: Assembly drawing. There are typically about 8000 pipe sketches in a ship. It takes about 3 manhours to manually produce a pipe sketch from arrangement drawings or from a plastic model. Most of this time is spent on drawing work but the time to make the parts list, the bending instructions, etc. should not be

7 Marine Engineering 51 underestimated. There are a lot of manhours to be saved when these drawings and related information are automatically created by the system. When the pipe sketches and the corresponding parts lists are produced by the system, also the possibility of manual mistakes in transforming the arrangement to pipe sketches will be eliminated. In many cases the drawings look very similar, e.g. a drawing for an assembly operation. Figure 4 shows a subassembly in two standard views and includes a parts list. These types of drawings could be automatically derived from the product model, saving a lot of drafting work. PARTS LISTS PRODUCTION Parts lists are the fundamental source of information on material to be used. Traditionally the parts lists were produced manually during or after the drawing work. However, the designers already enter most of the parts list information into the product model during the design work. It saves work to extract the parts lists from the product model and then transfer the information to e.g. the materials and planning systems. There are three major types of parts lists: Parts lists connected to early design documents like diagrams. These parts lists are used mainly for material ordering purposes. Parts lists for prefabrication of e.g. pipes and hull parts. Parts lists for the different assembly stages. The first two types of parts lists will mainly refer to components, while the assembly parts lists will refer to components and prefabrication parts lists as well as to other assembly parts lists. Depending on the production method and the layout of the working drawings used, the assembly parts lists can be split up into several levels, reflecting the Work Breakdown Structure. The production information for prefabrication of pipes is presented on pipe sketches, one sketch for each pipe spool, or on isometric drawings showing a few pipes each. In both cases, the drawings have a corresponding parts list, showing the material needed. The drawings and the parts lists can automatically be retrieved from the product model. The prefabrication parts lists for plate parts and stiffeners contain the part identification, the raw material identification, the NC tape identification, etc. They are produced in the nesting process. Typically about 2500 tapes are used for plate part production on a ship.

8 PRODUCTION LINES AND ROBOTS Many different types of production lines and robots exist or are part of on going development projects. All of these different types of equipments can get the necessary product information from the product model. For example a welding robot can get the nominal welding trace and the type of the weld from the product model. The model can also provide the necessary geometry for interference control. It is important to find methods to define the movements of the robot based on the information in the product model and on standards, patterns and macros. Otherwise the tool path definition and the movement control can easily become a bottleneck with a lot of intensive manual work involved. With a careful selection of methods and standards the product model can be used for analysis of the context and minimize the manual interactions. ABOUT THE COMPANY KOCKUMS COMPUTER SYSTEMS During the 1960s, the development of systems to support the technical and management information flow started at Kockums Shipyard Kockums Computer Systems AB was founded. In 1988 KCS acquired the rights to the Norwegian AUTOKON system and, in 1992, to the German SCHIFFKO system. These systems have been installed in more than 125 sites all over the world. KCS has now developed the next generation of shipbuilding software. The new TRIBON system was announced at the Nor-Shipping Fair in Oslo in June. This new system incorporates all the best features of its predecessors and at the same time has a more extensive capability. KCS has 160 employees and belongs to the Celsius Industries Corporation which employs approximately people. REFERENCES Some information in this paper has been fetched from: TRIBON information published by Kockums Computer Systems AB. Kaj Johansson, 'CAD/CAM, Automation and Robotization' To be presented at WEMT 93 in Madrid Oct 20-22, Kaj Johansson, 'Integration of CAD/CAM and Management Information Systems'. Presented at ICCAS 88 in Shanghai.