Automatic Plate Nesting System
Hitachi Zosen Corporation developed the automatic nesting system (JNEST+) by the use of genetic algorithm (GA). This report shows that JNEST+ can reduce man-hours of nesting work and reduce the scrap ratio (weight of scrap/weight of uncut steel plate) because it can be utilized for nesting in both material removal and cutting of steel.
1. Introduction
Nesting in shipbuilding is defined as the work of arranging the most possible hull structure parts onto the least possible material steel plates. In the past, the work had been time-consuming and therefore, done by specialists. Other industries had already developed and utilized some automatic nesting systems, but these systems could not be applied to ship- building. Some of the reasons were that some parts of a ship have complicated shape and various sizes and that the nesting in ship- building has few constraints compared with those of other industries. It was and is, therefore, very difficult for these other nesting systems to solve questions in combination with the above conditions within a practical time frame.
2. Applied algorithms
Use of genetic algorithm is one of the techniques used to solve questions in combination and leads an optimal solution by simulating a process of biological evolution in computers. It is said that the use of algorithm is one of the most practical methods compared with conventional ones. But in case of solving a combination in nesting within a practical time frame, in addition to the use of algorithm, the following constraints which are rooted in the specialists' know-how are introduced by JNEST+.
(1) Simplifying
Parts having complicated shapes can be formed into simplified ones, when this formation does not effect the scrap ratio negatively. For example, small holes, cut-outs, and scallops included in parts can be omitted to simplify their complicated shapes.
(2) Pairing
When there are two similar parts and their shape is triangle or the L-type, they are regarded as pair parts. For example, two similar brackets are regarded as pair parts and can be treated as one part.
(3) Grouping
Rectangular parts can be arranged in a material steel plate at one time, when they are the same in height or width. For example, collar plates can be arranged in parallel at one time.
In addition to the above, parts that are possible to turn over and parts that are possible to cut symmetrically are also considered as
