Original Date: 07/21/2003
Revision Date: 01/18/2007
Best Practice : Maintaining Dimensional Control of Parts Using Super Piece Process
Because of material purchasing limitations or different plate materials or thickness, super piece parts consist of many different plate sections that are welded together. Electric Boat Corporation, Quonset Point Facility’s Super Piece process optimizes the fit-up process, minimizes root gap to ensure weld quality, and minimizes the effects of tolerance stack-up and weld shrinkage on the over-all dimensional accuracy.
Some plate parts are created by fabricating many small plates and assembling them in a piece-meal fashion into super pieces. In the past, individual small plates were cut to size and formed with edge preparations prior to assembly. Irregular fit-ups typically occurred due to tolerance stack-ups, material mismatch, and weld shrinkage which reduced the end-item dimensional accuracy. In particular, weld root gaps were not consistent and made defect-free welding a difficult task. Shrinkage from each weld also caused distortion in the part allowing the welding process to contribute to inaccuracies. This was exacerbated by irregular weld root gaps which cause uneven heating along the weld line. Electric Boat Corporation, Quonset Point Facility (EBQP) resolved these problems by initiating a Super Piece process, in which several pieces are combined to make one large part.
The Super Piece process enables EBQP to create a part with better weld acceptance that meets tight dimensional tolerances. Edge preparations for parts now exist only on the edges that make up the welded seams of the assembly, and the fabrication of each individual piece is optimized around the welded seams with extra stock in areas that are not welded. This allows the welder to fit the pieces in a manner that ensures a quality weld. After the pieces have been welded into the super piece, reference lines are marked for final trimming.
The Super Piece process enables EBQP to minimize the impacts of irregular fit-ups due to tolerance stack-up, material mismatch, and weld shrinkage, and improves the overall dimensional accuracy of parts. Since the majority of the welding processes are now performed in the flat configuration with the parts fit-up to optimize welding processes, the quality of the weld joints has also improved. EBQP can produce a final assembly configuration within 1/8 inch of the nominal drawing requirements on large-scale submarine components.
For more information see the
Point of Contact for this survey.