REG NASA-LLIS-1860--2008 Lessons Learned - Inherent Difficulty in Manufacturing Small Fillet Welds in 6000 Series Aluminum.pdf

1、Lessons Learned Entry: 1860Lesson Info:a71 Lesson Number: 1860a71 Lesson Date: 2008-6-25a71 Submitting Organization: GSFCa71 Submitted by: Robert Verniera71 POC Email: Robert.J.Verniernasa.govSubject: Inherent Difficulty in Manufacturing Small Fillet Welds in 6000 Series Aluminum Abstract: The lesso

2、n learned is that when producing small size fillet welds in 6000 series aluminum there is an inherent risk that the welded part can be produced in accordance with approved manufacturing standards and inspection techniques, and yet result in a weld that has subsurface cracks. These cracks can result

3、in a part with less than the required design strength and fail under load. The recommendation is that designers should be trained to understand the risk inherent in designing load carrying parts that incorporate critical welds in 6000 series aluminum.Description of Driving Event: A battery lift adap

4、ter manufactured to support ground processing for the HST Servicing Mission 4 failed during proof testing. A failure occurred in a critical weld which propagated to other welds as the failure progressed and the load path changed. A failure analysis of the welds showed that although the welds were pr

5、oduced in accordance with accepted design and manufacturing standards, the welds had subsurface cracks that propagated under load and caused the failure. The cracks were caused by insufficient filler material being introduced into the weld as it was formed. For 6000 series aluminum, filler material

6、is required to dilute the base alloy into an alloy that will weld without cracking. The weld was specified as a 1/8“ fillet weld. The small weld size contributed to the degree of difficulty in producing a weld with sufficient filler to prevent cracking, and yet meet the size specification.Lesson(s)

7、Learned: The lesson learned is that there is inherent manufacturing difficulty in producing small fillet welds in Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-6000 series aluminum. These welds can be designed and manufactured in accordance with ac

8、cepted standards and yet produce a weld that has subsurface cracks and does not meet the required design strengthRecommendation(s): The recommendation is that designers should be trained to understand the risk inherent in designing load carrying parts that incorporate critical welds in 6000 series a

9、luminum. Special attention as appropriate needs to be paid to these welds to reduce risk of failure, such as ensuring sufficient weld size, x-ray inspection, require weld samples for destructive analysis, verification of welder training certification, or design out critical welds. Evidence of Recurr

10、ence Control Effectiveness: N/ADocuments Related to Lesson: N/AMission Directorate(s): a71 ScienceAdditional Key Phrase(s): a71 Manufacturing and Assemblya71 Mission Operations and Ground Support Systems.a71 Mission Operations and Ground Support Systems.Ground support systemsa71 Additional Categorie

11、s.a71 Additional Categories.Ground EquipmentAdditional Info: a71 Project: Hubble Space Telescope Servicing Mission 4Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Approval Info: a71 Approval Date: 2009-06-03a71 Approval Name: mbella71 Approval Organization: HQProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-