Original Date: 05/23/1994
Revision Date: 01/18/2007
Information : Environmental Testing
Naval Undersea Warfare Center (NUWC) Division Keyport has improved its environmental test area capabilities and procedures. These improvements include an upgrade of the vibration systems, development of new dynamic test fixture designs, and use of a computer-aided status system.
Keyport had eight 1960s vintage vibration systems that required excessive maintenance and down time, and replacement parts were expensive and difficult to obtain. The new test requirements for the MK 50 torpedo could not be met with the existing equipment because of excessive crosstalk in the slip tables, excessive shaker body motion at low frequencies, and tolerances that were beyond the capabilities of the controllers. The oil-film slip tables also would bind during low temperature testing.
Since funding for upgrades was limited, the entire vibration system could not be replaced. Individual system components were procured as funds became available using competitive procurement with compatibility requirements. This technique caused the systems to become mixed, since the low bidder was not necessarily the system manufacturer. The shaker trunnions, armatures, and load supports were upgraded using this technique. Many of the components procured were the first of their types such as the large solid state class AB linear amplifiers, large air-cooled class D switching amplifiers, new controller models from a first time manufacturer, and the all-bearing slip-table design. No compatibility problems were experienced between components supplied by different manufacturers. Most of the manufacturers worked closely with Keyport to fix any problems with the equipment. Using this piecemeal technique allowed Keyport to obtain the equivalent of a new vibration system with a limited budget.
Combining components from different manufacturers has given Keyport enhanced capabilities over those with a complete system from a single manufacturer. The all-bearing slip table crosstalk meets all weapon specifications and has eliminated binding problems. The upgraded shaker body trunnions have provided improved response with no excessive body movement at low frequencies.
Keyport also previously used the standard welded magnesium plate fixtures for dynamic test fixtures requiring time-consuming and expensive welding and machining operations to construct. The magnesium fixtures were easily damaged and had high maintenance costs due to severe oxidation of the magnesium. A new method was engineered to use a bolt-and-epoxy method of building fixtures with aluminum plate. New inserts were also designed and built in house for the fixtures to eliminate a problem where the inserts were constantly pulling out of the fixture. The new inserts had a larger outer diameter and a longer length and resulted in an 80% cost reduction per year (from $65K to $12K). The bolt and epoxy assembled fixtures are as durable as the welded magnesium fixtures and are exceeding the 10 year design life cycle by 140%. The new fixtures are cheaper and can be made more quickly, have less corrosion problems, 75% less maintenance cost, and have a longer life cycle.
Formerly, all environmental test status was kept on a database requiring manual entry at test completion. Tests were run at a 30K per year rate and were required to be completed within 60 days of receipt. No priority system existed and no tracking of the status was available. A database system was developed that provided for barcode wanding stations at each test site for test personnel to enter the date and test sequence before and after each test. The on-line, current status of individual test items was then available, including percentage of test completion, number of days in test, number of days remaining, and number of days waiting for test. Historical event sequences and final dispositions were also available, as well as flexible report formats on the network. The system now allows the test personnel to set priorities and meet contract schedule commitments.
These changes have made the environmental test area more responsive to advanced torpedo design enhancements and provided the capability to perform more comprehensive, extensive controlled tolerance tests that were previously beyond the range of the equipment.
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