August 2024 Volume 6

There are several quality safeguards that can be employed to avoid shear banding. Furnaces must be uniform within +/- 25F of the setpoint, and efforts should be made to do everything possible to center the range around the setpoint. Cold areas near the exit door of the furnace can be a problem and must be corrected. Transfer time from the furnace to the die must be rapid. Dies should be hot. If your shop is demonstrably colder during the winter it is necessary to shield the press from any open doors and keep the area around the press as close to normal temper ature as possible. Keep fans off the work area to avoid cooling workpieces too fast during transfer and forging. If there remains evidence of shear banding after employing these process controls, you will need to consider adding a forging step to reduce the amount of deformation happening in the blow generating the shear banding. While shear banding can happen in any parts, smaller parts with significant deformation (like a compressor blade) are very sensitive to processing variables and likely to exhibit shear banding if the process controls decline. Titanium remains a critical material for the aerospace industry. It is a very forgeable material provided the forger employs good process modeling, stringent process variable control and well maintained equipment, especially furnaces. MATERIALS

Figure 4: Alpha case on the surface of a titanium forging.

Pat Burke has over 40 years of metallurgical and operations experience in aerospace forging.

You can contact him by email at pmburke5707@outlook.com.

Figure 5: Forging that has been blue etched exhibiting evidence of shear banding (white line).

FIA MAGAZINE | AUGUST 2024 45