REG NASA-LLIS-1226-1998 Lessons Learned - Stripping of insulation from small-gauge wires.pdf

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1、Lessons Learned Entry: 1226Lesson Info:a71 Lesson Number: 1226a71 Lesson Date: 1998-10-21a71 Submitting Organization: JSCa71 Submitted by: Roger Parks/ Ronald A. MontagueSubject: Stripping of insulation from small-gauge wires Description of Driving Event: Qualification test failures of RM2679 transf

2、ormers were discovered after vibration screening. Post-test analysis of the failed transformers revealed there were gaps between internal contacts. Further analysis revealed that wires had broken off where the transformer coil wire is soldered to larger terminals.Root cause: Nicks were discovered on

3、 the coil winding wire near its attachment point. Further investigation determined that assembly personnel were using mechanical strippers to strip the coating off the ends of the wire. These nicks became stress concentrators leading to subsequent failure during vibration testing.Lesson(s) Learned:

4、Routine manufacturing processes such as wire stripping techniques must be carefully evaluated and re-evaluated to ensure their satisfactoriness for use in fabrication of flight hardwareRecommendation(s): The transformer vendor has stopped performing the mechanical stripping operation. To prevent reo

5、ccurrence of this problem, the vendor has been instructed to use either thermal or chemical stripping of coil wire. No additional vibration failures occurred after replacing the mechanical stripping process. Stripping of such small wires, regardless of application, should avoid mechanical methods si

6、nce they have been shown to damage the wire. This process change is particularly recommended for transformer and inductors designed with coil wire between 38 and 32 AWG. Evidence of Recurrence Control Effectiveness: Provided by IHSNot for ResaleNo reproduction or networking permitted without license

7、 from IHS-,-,-N/ADocuments Related to Lesson: N/AMission Directorate(s): N/AAdditional Key Phrase(s): a71 Flight Equipmenta71 Ground Equipmenta71 Hardwarea71 Human Resources & Educationa71 Industrial Operationsa71 Parts Materials & Processesa71 Safety & Mission Assurancea71 Test & VerificationAdditional Info: Approval Info: a71 Approval Date: 2002-06-27a71 Approval Name: Ronald A. Montaguea71 Approval Organization: JSCa71 Approval Phone Number: 281-483-8576Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-