ANA-DIGI Systems was commissioned to transform a manual shot-blasting machine into a fully automated four-axis system for precision shot peening of aluminum airscrew (propeller) blades. This upgrade was essential to improve accuracy, efficiency, and repeatability in the process.
Reinforcing the System for Automation
The existing framework of the manual system required extensive reinforcement to withstand the increased stresses imposed by the automated servo-controlled system. Strengthening the structure ensured that the system could handle the precision demands of shot peening while maintaining durability and stability.
Key System Requirements
To automate the shot peening process effectively, the system needed to:
- Map the blade curvature deviation from a straight line, allowing the shot-blasting head to adjust its position to maintain a consistent distance from the blade surface.
- Track the blade screw to ensure proper rotation during processing, maintaining a constant blasting angle.
- Rotate the blade 180° to expose the opposite side and reverse the above parameters, including any dimensional deviations.
- Shot-blast the inside of the blade end at the feathering bearing fit point.
Shot peening plays a crucial role in airscrew blade maintenance. By reducing air friction losses—similar to how dimples on a golf ball improve aerodynamics—it enhances blade efficiency. Additionally, it significantly reduces stress levels on the blade surface, extending the lifespan of the component.
Advanced System Solution
To achieve these requirements, ANA-DIGI implemented an LS GM6 PLC with a multi-axis APM card, controlling three Mecapion servo drives and servo-geared motors mounted on linear drives. These servos were selected for their high precision, ensuring fine overlapping accuracy of the shot peening runs.
For additional functionality:
- A separate head, fitted to a screw driven by an LS variable speed drive and an AC three-phase geared motor, was used to shot-blast the prop feathering swivel bearing inside the blade end.
- A Mecapion rotary encoder provided depth measurements, feeding outputs into the PLC’s counter inputs. This cost-effective option was chosen as depth measurement requirements were less stringent than surface shot peening accuracy.
Operator Interface and Data Logging
- Recipe selection and operator logging were facilitated through an LS touch-screen HMI.
- The blade profile was displayed on the HMI, allowing for the entry of necessary distance and displacement plot information for various airscrew blades.
- Shot peening results were recorded on a remote computer, with data communicated via the PLC’s built-in RS232 port.
Precision Shot Peening Control
- Peening intensity, adjustable via the HMI, was controlled through the PLC using a pneumatic regulating valve.
- This valve regulated airflow over a venturi, which, in turn, precisely controlled the amount of steel shot used.
Reliable Performance and Long-Term Success
The system has been in operation for 18 months, consistently delivering excellent and repeatable results without major failures. The only minor issues encountered were due to errant shot interfering with the regulating valve’s operation.
By integrating precision control technology, ANA-DIGI Systems has successfully enhanced the efficiency and reliability of airscrew blade shot peening, ensuring long-term performance improvements for aviation applications.