Original Date: 07/21/2003
Revision Date: 01/18/2007

Electric Boat Corporation, Quonset Point Facility automated its pipe marking, cutting, and bending processes by implementing Direct Numerical Control and Computer Numerical Control systems. These systems enable the company to increase product quality, decrease staff requirements, and reduce turnaround time.

Electric Boat Corporation, Quonset Point Facility (EBQP) automated its pipe marking, cutting, and bending processes into a streamlined operation by implementing Direct Numerical Control (DNC) marking, cutting, and bending machines. Automated pipe marking and cutting use a single, custom-built machine supplied by Dante Precision, with a customized Human Machine Interface. The automated pipe bending machines are DNC Swartz- Wirtz CNC40, 60, 100, 265 benders that strictly perform cold bending for pipes with diameters ranging from ¼” to 10”. All machines are part of an ethernet network that automatically downloads up-to-date pipe design data at regular intervals during the day.

The U.S. Navy has extensive requirements for pipe marking on nuclear submarines. Pipes must be permanently marked with at least 10 sets of information to establish a pedigree for every piece installed. Previously, pipe- marking operations were performed manually using “vibro-etching” tools. EBQP devoted 10 individuals working up to three shifts per day to manage this operation. The manual transcription of data from drawings to pipe was error prone, and markings were often difficult to read, and the risks of injuries (cutting and repetitive motion strains) were high. An additional eight to 10 mechanics performed cutting operations, requiring review of design drawings, manual layouts of bend lines and cutting measurements, and cutting to prescribed lengths. Cutting accuracy was held to ± 0.2”, but true accuracy rested with the mechanic as mark interpretation was subject to human error.

Pipe bending was accomplished by manual entry of bending information into the machine controller. Operators reviewed requirements from the bend data sheet, part of the drawing package. While the bend data sheet called out the necessary bend angles, it did not provide the operator with information on the degree to which the machine should over-bend the pipe. Over-bends are necessary because pipes will “spring-back” to some extent. Spring-backs vary by material type, bend angle, and pipe diameter. Operators were required to have enough experience and knowledge of spring-back amounts to perform manual over-bend calculations; therefore, they could not enter the bend angles from the bend data sheet, but had to correct for spring-back and radial growth on a pipe-by-pipe basis, making transcription and over-bend calculation errors an issue.

Automation of the marking and cutting operation resulted in reduced labor (from 10 operators to one operator per shift), thus reducing process time for individual operations from 15 minutes to four minutes per pipe detail, and accomplished in two shifts instead of three depending on volume. Marking legibility and transcription errors are no longer a problem since the pipes are stamped in uniform script and the data is automatically sent from design to the marking mechanism. Safety, a high priority at EBQP, increased considerably due to the near elimination of vibration injuries and a 25% reduction in cutting injuries.

Pipe details emerging from the marking/cutting process are loaded into a rack for transportation to the nearby pipe bending stations. As with the marking/cutting system, operators enter a part number into a workstation PC with commercial-off-the-shelf CAD/CAM integration software. All numerical control bending programs necessary to bend all the pipes arriving at each station are automatically distributed. The software is sophisticated to automatically calculate over-bend angles per part and download producibility information (e.g., shop floor and ceiling height limitations) so pipe bending will not be obstructed. EBQP uses four Computer Numerical Control (CNC) machines for pipe bending. The CNC machines can produce bends of two-, three-, or five-times a pipe’s diameter in pipes with diameters of 0.250" to 10.000" with varying wall thicknesses. Because there may be up to 22 bends per pipe detail, EBQP’s CNC machines use an automated power boost and mandrels to minimize wall thinning. The software also manages the timeliness of data, regularly expunging old design information from the system.

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