This post includes a Design Failure Modes and Effect Analysis (DFMEA) conducted by me during my Masters of Engineering Science in Materials and Welding. This DFMEA relates to a continuous Friction Stir Welding machine design that I completed as part of my Masters research.
| Item | T = technical F = financial S = Schedule Function | Potential Failure Mode | Potential Effect(s) of Failure | Severity scale is 1 thru 10. 1 is least severe (ie unlikely to pose a problem) 5 is medium severity (ie likely to incur expense or loss of function) 10 is most severe (ie life threatening) Sev | Class | Potential Cause(s)/ Mechanism(s) Failure | Scale is 1 thru 10. 1 is unlikely to occur 5 is medium occurance (ie may or likely to occur) 10 will occur Occur | Current Design Controls | Scale is 1 thru 10. 1 is easily detectable (ie visual) 5 is medium detectable (ie may require tools or procedures to identify problem) 10 is least detectable (ie extremely difficult to detect) Detec | rpn is the product of severity, occurance and detectability rpn < 100 (not significant) 101 < RPN < 300 (requires attention) rpn > 301 (failure is significant) RPN |
|---|---|---|---|---|---|---|---|---|---|---|
| Cable Drive | T | Snaps | No weld travel | 8 | Static overload | 5 | Spreadsheet calculations | 2 | 80 | |
| T | Snaps | No weld travel | 8 | Fatigue failure | 5 | Spreadsheet calculations | 4 | 160 | ||
| T | Stretch | Erratic weld travel speed | 3 | Excessive cable strain | 3 | Spreadsheet calculations | 4 | 36 | ||
| T | No drive | Insufficient motor torque | 2 | Incorrect motor selection | 2 | Objective comparison with similar welds | 2 | 8 | ||
| T | Speed range | Wrong speed range | 5 | Incorrect gearing | 2 | Calculation | 2 | 20 | ||
| Backing Roller | T | Root Backing | Poor weld root profile | 6 | Roll diameter too small | 3 | Subjective decision | 8 | 144 | |
| T | Deflection | Shaft deflection | 6 | Poor bending stiffness | 2 | Calculation | 3 | 36 | ||
| Lateral Alignment | T | Deflection | Weld gap increases | 7 | Excessive compression of nylon roller | 3 | Subjective decision | 5 | 105 | |
| T | Melting | Weld gap increases | 8 | Extrusion temperature exceeds approx 80 degrees | 5 | Subjective decision | 5 | 200 | ||
| Vertical Alignment | T | Deflection | Angular misalignment | 5 | Lack of restraint | 5 | Subjective decision | 2 | 50 | |
| T | Melting | Angular misalignment | 5 | Extrusion temperature exceeds approx 80 degrees | 5 | Subjective decision | 5 | 125 |
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