Description of Driving Event:
Galling of threaded fasteners was experienced in the qualification test program of the Z1 Truss. Fasteners intended to be removable on-orbit galled during test. The fasteners were installed in locking threaded inserts ("KEEN" type). Root cause: The inherent effect of the "Keen"-type, upset thread design is to bite hard into the fastener. After repeated installation and removal, the fastener will gall. These inserts work best engaged once, and are excellent in this application.
Lesson(s) Learned:
A full understanding of the intent of a design is mandatory to ensure that operational requirements can be met
Recommendation(s):
If threaded inserts of this type must be used, "condition" the insert first with a sacrificial bolt of the same type. The sacrificial bolt will cold work the upset thread slightly to help mitigate the probability of galling during repeated use. Lab analysis of this cold working procedure was performed; results are available from the lesson initiator.
Evidence of Recurrence Control Effectiveness:
N/A
Documents Related to Lesson:
N/A
Mission Directorate(s):
N/A
Additional Key Phrase(s):
- Parts Materials & Processes
- Procurement Small Business & Industrial Relations
- Risk Management/Assessment
- Test & Verification
- Test Article
Additional Info:
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