Aerospace Titanium Alloy Repair on Landing Gear Bracket

Case Study 2: Aerospace Titanium Alloy Repair on Landing Gear Bracket

Scenario An FAA-certified MRO facility performed a critical repair on a Ti-6Al-4V (Grade 5) landing gear bracket after FOD-induced surface cracking. Due to titanium’s low thermal conductivity and high sensitivity to thermal cycling, the WPS mandated a maximum heat input of 0.45 kJ/mm to avoid α-case formation, embrittlement, and distortion. The repair required GTAW with pulsed current, but only average current and voltage were logged by the machine; travel speed was manually measured using laser tachometry. Tight tolerances (±0.1 mm fit-up) and post-weld HIP requirements added zero-margin-for-error pressure.

Given Data

• Welding Current: 132 A
• Welding Voltage: 11.8 V
• Travel Speed: 210 mm/min

Calculation Using the same formula:

$$ \text{Heat Input} = \frac{11.8 \times 132 \times 60}{210} $$

Step-by-step:

• $11.8 \times 132 = 1557.6$
• $1557.6 \times 60 = 93,456$
• $93,456 \div 210 = 445.0286... , \text{J/mm} = 0.4450... , \text{kJ/mm}$
• Rounded to two decimal places: 0.45 kJ/mm

Result and Decision The calculated heat input (0.45 kJ/mm) exactly matched the upper WPS limit. To build in safety margin without sacrificing penetration, engineers reduced travel speed to 205 mm/min and lowered current to 130 A—recomputing to 0.44 kJ/mm—ensuring robustness against minor measurement drift. All repaired brackets passed 100% UT and microhardness mapping (no >350 HV α-case detected).

Lesson When operating at the absolute thermal limit—especially for reactive alloys like Ti-6Al-4V—treat the calculator’s output as a boundary condition, not a target: engineer deliberate conservatism into parameter selection, and validate with direct thermal monitoring (e.g., IR thermography), not just calculation.