Surface Smoothing and Compressive Residual Stress Studies for AM Metals Using Cavitation Abrasive Surface Finishing & Peening for Fatigue Performance

The Additive Manufacturing production process has emerged as a strong contender to meet many of the aerospace industry’s most vital needs. It offers extraordinary design flexibility for shapes with complexities that were previously deemed impossible. The lead time to production is swift and the economics for prototyping and building low to medium volume lots is fiercely competitive when pitted against the conventional alternatives for non-fatigue critical flyaway parts. However, it is clear now that even larger widespread implementations are possible if certain fabrication limitations can be overcome.

Additional gains in surface finishing methods will be needed to bridge the gap between static designed AM structural parts that are routinely being deployed into service now and the needs for structures subjective to high fatigue loads. These critical parts are still faced with difficult smoothing and compressive residual stress surfacing requirements.

Recent studies have been made using cavitation abrasive surface finishing and peening (CASF) that show the combination of material removal with kinetically energized media and high-power fluid shock waves generated by imploding water vapor bubbles is a strong contender to address the needs of both Ra smoothing and fatigue performance. Test data will be shared that compares AM Ti 6Al-4V fatigue coupons in various build conditions: as-built; as-built & HIP; machined; machined & HIP; vs. HIP & CASF. Parts tested were CASF treated with fully automated CNC machines.

CASF is certainly not a panacea for all of the future manufacturing needs, but new fatigue comparison studies are showing that it has great potential, especially for components that have trapped features, stepped bore holes, hidden fluid chambers and non-line-of-sight finishing needs for parts such as heat exchangers that contain long circuitous subterranean passageways.