Using Computer Aided Designs and Manufacturing (CAD/CAM)
Ship designs are now days made by computer aided process and thus many computer aided design (CAD) systems are available like TRIBON, FORAN, Autoship etc. The information provided by these designs are integrated into computer aided manufacturing (CAM) systems. Production information is provided directly for use by computer numerical control (CNC) machines. Thus the production process of cutting and shaping plates and section, panel assemblies etc can be done automatically with the help of computer.
A wire-frame model is a visual presentation of a three-dimensional (3D) or physical object used in 3D computer graphics. It is created by specifying each edge of the physical object where two mathematically continuous smooth surfaces meet, or by connecting an object’s constituent vertices using straight lines or curves. The object is projected onto a display screen by drawing lines at the location of each edge. The term wire frame comes from designers using metal wire to represent the three-dimensional shape of solid objects. 3D wire frame allows to construct and manipulate solids and solid surfaces. Using a wire-frame model allows visualization of the underlying design structure of a 3D model. Traditional two-dimensional views and drawings can be created by appropriate rotation of the object and selection of hidden line removal via cutting planes.
When greater graphical detail is desired, surface textures can be added automatically after completion of the initial rendering of the wire frame. This allows the designer to quickly review solids or rotate the object to new desired views. Wire-frame models are also used as the input for computer-aided manufacturing (CAM).
There are mainly three types of 3D CAD models. Wire frame is one of them and it is the most abstract and least realistic. Other types of 3D CAD models are surface and solid. This method of modeling consists of only lines, points and curves defining the edges of an object.
Method for creating 3D wireframe
Extrusion is a technique for creating a 3D wire-frame model by copying a 2D profile and extending it to a depth defined by the operator. The result is a 3D wireframe of the profile.
- Rotation produces wire-frame models by rotating a cross section or profile of the part about an axis. It is similar to extrusion except it is swept about an axis.
- Extrusion with scale technique consists of defining the depth along with the facility of enlarging scale uniformly.
- Using primitive shapes to build models.
Wire Frame Model of an Oil Tanker
This involves shaping and cutting of steel plates to a particular shape using manual methods or automatic methods like CAM. Computer aided machinery uses Numerically Controlled (NC) system. Nesting refers to the process of laying out cutting patterns to minimize the raw material waste.
NC system is one in which a machine is operated and controlled by insertion of Numerical Data. Numerical Data is a sequence of numbers which fully describes the part to be produced. Additionally certain instructions can be fed in to a CAM for operating it automatically. These instructions are also fed numerically in to the computer.
Once the numbers are fed then there is a reading device which converts these numbers into electrical impulses. These electrical impulses become control signals for various parts of the machine which produces the desired finish product. The input data to the cutting machine goes from CAM system. If several parts are to be cut from a single plate, these parts are nested or economically fitted into the plate from where the parts are going to get cut, before the actual cutting starts. This is helpful in avoiding the wastage.
Nesting software must take into account the limitations and features of the machining technology in use, such as:
- Machining cannot take place where the raw material is clamped into place;
- Some machines can access only half of the material at a particular time; the machine automatically flips the sheet over to allow the remaining half to be accessed;
- When punching, the width of the punch tool must be considered;
- Shearing may be permitted only in certain areas of the sheet due to limitations of the machinery
- Defects on material that must be discarded;
- Different quality areas that must match corresponding quality levels required for different parts;
- Direction constraints, that may come from a printed pattern or from fiber direction;
Once the plate is nested then the parts can be joined and sub-assemblies can be prefabricated. Sub assemblies and assemblies can be joined to form a unit. These units are put together or assembled to form a complete ship.