Automated cutting of submarine components

July 1, 2002
The concept and realization of this modern operation advances the technology for custom cutting applications

David A. Belforte

The concept and realization of this modern operation advances the technology for custom cutting applications

Let's face it. Most of us, who are not associated with submarines, gained knowledge of underwater vessels from the movies. "Das Boot" or "Hunt for Red October" may have served as an introduction to submersibles used in the past 50 years.

Building a nuclear submarine today is facilitated by computer design operations.
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This writer gained some first-hand experience in submarine construction while directing studies on laser welding of thick-section HY80, 100 and 120 alloys used in the fabrication of nuclear submarines. So an invitation to visit General Dynamics Electric Boat's Quonset Point, Rhode Island, facility was welcomed on two levels: both as an opportunity to see the company's new fabricating facility and then to gain a view of modern submarine construction practices.

First, let me supply a little history. Isaac Rice founded Electric Boat (EB) in 1899 when the company built the world's first practical submarine, the Holland. During World War I the company built 85 submarines for the U.S. Navy. Technology was always the company's bent, and in 1934 the Cuttlefish was the first welded submarine and the first to be built at the company's Groton, Connecticut, shipyard. It built 74 submarines for the Navy during World War II, and, again showing a technology influence, in 1954 it launched the world's first nuclear-powered sub. In April of 1952, company President John Jay Hopkins restructured EB to create General Dynamics as the company began a diversification into other industrial sectors.

In 1972 it laid the keel for the first of the Los Angeles class attack subs, followed in 1979 by the first of the Tridents. In 1996 the company started design of the Virginia class attack subs, the successor to the 1996 Seawolf class.

In 1999 the keel for the SSN 774, Virginia was laid as the company celebrated its 100th birthday. Along the way the company acquired the U.S. Navy's former Quonset Point air facility and in 1978 turned it into an automated frame and cylinder facility. This facility was updated in January of 2002 with the dedication of the new automated steel-processing center. These events are the reason this writer was invited to visit.

All of the submarines mentioned above, except the Virginia, have a common factor: they were built from blueprints. And we all know that translating blueprints into steel fabrications can, for example, lead to errors and multiple engineering changes that in turn can lead to more errors. So management at EB decided to automate its steel cutting operations by downloading CAD data directly to the cutting shop, eliminating errors that had occurred working from drawings.

To do this EB had to develop a means to mark out the cutting patterns so that the newly installed cutting equipment could cut to exact dimension without scrap or rework. It was aided in this by the fact that the Virginia class of submarines was completely designed by CATIA, an IBM CAD/CAM program, and the cutting systems control used in the new facility are compatible with CATIA.

AT EB's new $12.4 million Automated Steel Processing Center (see Figure 2), opened last December, steel sheet and plate stored outside is brought to a conveyor system that feeds material into the new building to an automated smart blaster that cleans only the surface area that will be cut and used in assembly operations. The smart blaster reads a barcode that identifies the material and the part area that will be cut.

After cleaning, the steel is moved via conveyor to a station where reference holes are drilled and then to a marking station. Here a 500W Nd:YAG laser marker (Rofin Sinar; Plymouth, MI) lays out the near-side cutting patterns, marks attachment locations and identifies the part to be cut. From there the material moves to a flipper station, which turns the plate over for far-side marking by the laser. Steel is then moved by overhead crane to one of three cutting machines; a plasma cuter handles all material in excess of 1.5 in., a laser system cuts up to 1.25 in. or a water jet cutter that cuts up to 8.0-in. thickness. All three systems were supplied by ESAB (Florence, South Carolina), one of the reasons this company was selected as the vendor.

Figure 2. Floor plan of EB's new automated steel processing center.
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According to John Holmander, site manager, the ESAB laser system, which is powered by a 5.0kW Trumpf (Farmington, CT) CO2 laser, is used to cut about 60 percent of the steel used in the assembly of the internals of a nuclear sub. Think of a sub as a cylinder within a cylinder. It's the metal in the interior cylinder we are interested in as this is used as the walls (bulkheads) of the sub, performing duties as a sound barrier and as a hanger for the myriad pipes that carry utility service though the boat. Stainless steel (304L) in thickness up to 1.5 in. is used exclusively.

Even though EB has a commitment only for the first sub, the Virginia, the automated cutting facility is run on a three-shift-per-day schedule. This is accommodated by a central control operation where three people can oversee all the cutting operations from a central location. Here the advantages of dealing with one supplier become obvious, as all the control software is compatible with each machine's control and with the company's central computers.

After component parts are cut they are delivered to the assembly area for integration into the internal structure of the sub. Scrap steel, if of a size that can be used later, is returned to the outside storage area, where it can be retrieved easily.

When one looks at this highly automated facility and then considers that the company has a commitment for only one sub at this time, the obvious question arises: is this facility cost effective. The answer, according to Holmander, is a definite yes. He says that the cutting facility is exceeding plan in terms of cost effectiveness. Holmander explains that the company is turning out a more precise part, which means that downstream operations are improved and this means a better final product with less rework. In the long haul this means that submarines can be built at a lower cost, which enables the Navy to modernize it's fleet at a cost that tax money can support without breaking the budget.

Setting aside the mission of this facility—cutting steel for submarines—the concept and realization of this modern automated cutting operation is a major undertaking; one that advances the technology for any company engaged in custom cutting applications.

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