Building big in Japan

By Russ Olexa

With some ships approaching 900 ft. in length or even larger with a beam of 100 ft. or more, enormous is probably the right word to describe the steel sub-fabrications used to build them. These sub-fabrications can easily be 60 ft. tall by 30 ft. wide and 40 ft. long.

Having the right equipment to build them efficiently to make a profit is crucial, especially when a company is faced with competition from low-wage countries like China.

Building a ship is similar to building any final product such as an automobile. Often the shipbuilder itself doesn't build the entire structure, but only assembles the pieces that are produced at supplier facilities. But because these fabrications are extremely large, they are difficult or impossible to transfer by any overland transportation, therefore suppliers and ship assemblers are usually located within a short distance from each other. In fact, some fabrications require special vehicles to even move them around a fabricator's facility. Large cranes that can lift 600 tons are also a common way of moving fabrications from one area to another in a shipyard, especially to join the fabrications together.

FFJ joined a contingent of people from around the world involved with shipbuilding for Koike Aronson's 2006 Shipbuilding Conference in November. We visited several Japanese shipyards to see how they construct large-scale fabrications. Although none of the fabricators we visited built entire ships, each one had a specialty in constructing specific parts, such as the large 60-ft. square doors that enclose the holds and sections of a hull. A cross section of ships produced in Japan includes container carriers, cargo ships, roll-on-roll-off vehicle carriers, car carriers, bulk carriers, fishing ships, passenger vessels and tankers.

As most people would suspect, the primary fabrication work done at these shipyards includes cutting and welding of primarily A36 steel with a yield strength between 782 psi and 996 psi in thicknesses from 1/4 in. to 2 in., with 1/4 in. to 1 in. being the norm. Common cutting systems include oxy/acetylene, laser and plasma systems; however, shipbuilders' needs are a bit different from those of most other fabricators. Primarily due to the scale of fabrication, they need large-bed cutting systems, as well as automated welding systems. Also, because of metal distortion from cutting or welding, large sheets of metal have to be straightened before they can be used as part of a fabrication, which is usually done by experienced personnel using hydraulic jacks. Stainless steel, aluminum, brass and copper are also used in building ships, but usually not for the super structure. While aluminum is typically used to build entire ships, the material wasn't prevalent at the yards FFJ visited.

Often, a fabricator will be dealing with 1/2-in.-thick plates that are welded together to form a final sheet that is roughly 60 ft. long by 20 ft. wide. Try moving this around without bending it. To weld these 20-ft.-by-20-ft. sheets together to form one long one is often done using an automated welding machine and submerged arc. One machine that FFJ witnessed used three MIG guns using 1/4-in. filler wire to simultaneously weld the seam. Each gun penetrated one area of the seam to fill it while traveling automatically by an overhead gantry system.

So what type of equipment do these companies need that most other fabricators would probably never use? Again, it's a matter of size, but some equipment is unique to this business. One example is a high-volume plasma beveling machine. Often plate has to be beveled for welding, but shipbuilders need so much beveled plate that they have their own dedicated equipment or employ separate companies that offer beveling exclusively.

One company that FFJ visited was a subsidiary of a fabricator that used a Koike plasma bevel-cutting unit and cutting table within a specially designed system to bevel sections of angle bars up to 100 ft. long. By switching from a different beveller to the Koike equipment, the company went from needing six operators to just two to get the same output. This has helped the company to considerably boost production. It also took the pressure off finding qualified personnel and allowed the company to move some operators to other positions.

Processing plate
Another piece of equipment unique to shipbuilding is a CNC full-surface cutting machine. Although shipbuilders can use a plasma cutting system to mark steel plate, this isn't the best use of the plasma cutter. Therefore Koike, along with the Universal Shipbuilding Co. (Japan), developed a CNC full-service printer that is guided by NC and CAM data. This type of equipment is crucial to efficient shipbuilding operators.

Without a printer, information has to be added to the plate manually, which means workers spend hours laying out guidelines and information on a plate for downstream operations. If they make any type of error, it could be disastrous.

Koike's printer allows a DXF file to be interfaced between a CAD and CAM system so the computer operator can plan where information and lines are needed on the plate. It also allows lines, letters, marks and figures to be freely sized. Plates go through the printer and then move on to other operations.

Shinichi Yamawaki, director of the machinery sales division at Koike Japan, says the reason that shipbuilders buy dedicated machinery such as a printer is that "they want to make large improvements in their productivity, because there is more demand in this business sector compared to other industries. So they look for dedicated technology to improve their production."

Laser systems
Koike Aronson produces oxy-fuel cutting systems, plasma cutting systems and laser cutting machines. The company's niche is cutting large plate using either Fanuc 2kW and 4kW resonators or a Trumpf 6kW resonator mounted on a carriage. Instead of mounting the resonator alongside the table and using flying optics to direct the beam to the workpiece, Koike's laser systems have the resonator mounted on top of the carriage with a beam delivery system called Sigma Box. This creates a fixed beam path with little diffusion as the cutting head moves over the workpiece. It also eliminates the bellows system that a flying optics laser uses. Koike feels that this is a more efficient way to achieve a good beam quality for the long term and that it reduces the periods between routine maintenance. It's able to reduce maintenance because the Sigma Box will not draw factory air inside the laser beam path, which can cause dirt to accumulate on the focusing lens and mirrors. This design also makes service easier because all the reflecting mirrors are fixed and set in the Sigma Box, which makes them simpler to clean.

In shipyards, laser cutters are used in two areas, for plate thicknesses below 1 in. and for parts that need precise cuts. Plate over 1 in. thick is usually done with oxy-fuel or a plasma cutter. When it comes to a laser bed, Koike will build one to order. One shipyard has a laser bed measuring 120 ft. long by 15 ft. wide. In fact, several laser heads can be placed on this type of bed so multiple part cutting can be done or so parts that are 100 ft. long can be cut.

So many systems
For cutting that doesn't require the precision of a laser, Koike also produces plasma cutting systems. The company makes laser beds with multiple cutting gantries similar to the lasers, as well as 3-D link plasma bevel systems.

Another product that Koike produces for greater efficiency when working in plate is a portable-automatic gas cutting machine called the Weasel. Using a unique drive mechanism and guided by a rail, it allows hands-free automated operation for straight cuts that are either vertical or beveled.

Koike also produces a double-bevel edge cutting machine called the Edge-Cut that takes the place of two portable cutting machines. It maintains a constant speed while cutting by using side guide rollers to move along the plate.

When welding stringers to plates that can be 20 ft. to 30 ft. long, welding personnel can easily get tired and lose productivity. In response, Koike developed a portable fillet welding carriage called the Wel-Handy Multi RC. It uses a motorized small carriage with a permanent magnet and runs automatically along the stringer using guide arms and guide rollers. A MIG gun is inserted into the carriage and aligned to the weld. When welding begins, the Wel-Handy moves along at a predetermined rate to expertly weld a seam without operator guidance or intervention. A remote control is also available.

Yamawaki says that along with shipbuilding, "There's a strong demand coming from the construction machinery industry for our type of equipment. The laser equipment can easily be used for steel bridge building, steel fabrication, construction and industrial machinery."

However, the software that controls the equipment for cutting can be different. He adds, "In shipyards, they want software to program straight and bevel cuts or blind bevels and to produce a small corner loop. Steel bridge manufacturers ask for very accurate holes, sharp corners and sharp edges. Therefore we have to produce cutting software for each industry."

Making sure that plate is cut accurately is important for improving the final welding process, says Yamawaki. "If a precision-plasma cutting system or a laser can offer close tolerances, it will improve downstream welding processes, which saves labor and money in the long run."

Although shipbuilders have a niche for producing fabrications and some use dedicated cutting equipment, much of this equipment can be used in other industries, as Yamawaki points out. With this equipment, companies can gain productivity without adding personnel that are so difficult to find. FFJ

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