Atmospheric Plasma Bracket Bonding Surface Preparation

Team: Braden Hastings, Ryan Higdon, Andrew Nelson

Sponsor: Northrop Grumman Corporation

Project Description

Northrop Grumman attaches instrumentation to the sides of rockets via proprietary brackets. These Brackets are epoxied to the sides of the rockets. The surface of the backs of the brackets need to be prepared in order to bond better. The current process is slow and inefficient. NGC has tasked us with finding a better surface processing method using atmospheric plasma.

Current Process

  • Involves hand grinding, degreasing, and drying. 
  • Takes two to three days for a batch of approximately 50 brackets.
  • Hand grinding can cause natural defects through human error.

Solution

  • Atmospheric plasma can treat the surfaces more quickly and more efficiently.
  • The surface treated by atmospheric plasma is more conducive for bonding than the surface treated by the current process.

Requirements

  • Limited number of jigs to hold all types of brackets
  • Even treatment of each bracket surface via atmospheric plasma

Design Description

model
Atmospheric Plasma Jet
  • Atmospheric Plasma Jet
  • Powered by compressed air and high voltage
  • Used to clean and prepare the surfaces of the brackets for bonding
  • Array of four jets cover area needed to prepare the largest bracket
Coverage area of the 4 jets

Coverage area of the 4 jets

Universal Jig
  • Universal Jig
  • Used to hold all variations of the brackets
  • Holds the bracket in the correct place while passing underneath the jets
  • Designed to allow for easy placement and removal of brackets
  • Jigs are bolted to the slats on the slat conveyor
Slat Conveyor
  • Slat Conveyor
  • Base of the system used to pass the brackets under the jets
  • A slat conveyor was chosen to allow the operators to fix the Universal Jig to the conveyor
Enclosure
  • Enclosure
  • Isolates operators from jets during operation
  • Includes sensors to ensure safety of operators and plasma jets
  • Infrared Sensors, proximity sensors, emergency stop buttons, and PLC logic are what constitute the safety system

Performance Review

  • Bracket Fitment Test Tested to ensure that all brackets fit within the jig
  • Bracket Placement Test Tested to ensure ease of placement and removal of brackets
  • Sensor Test Tested control logic of sensors to ensure system shutoff
  • Surface Disturbance Test Tested bracket removal to ensure treated surface remains undisturbed
Requirement/Constraint Target Threshold Predicted Performance Actual Performace
Electrical grounding 5e5 ohms 1e6 ohms 5e5 ohms Not tested
# of jig types needed 1 1 1 1
Precision of bracket placement in jig 10 mm 20 mm 5mm 7.6mm
Easy to place brackets in jigs 5 sec 15 sec 3 sec 2 sec
Fits in warehouse 1x3x3 m 5x3x3 m 3x1.65x1.5 m 3x1.65x1.5 m per specifications
Easy to move 250 kg 500 kg 318 kg Unknown
Speed of bracket movement 150 mm/s 100 mm/s 150 mm/s 150 mm/s per specifications
Ease of maintenance 0 Inaccessible Subsystems 1 Inaccessible Subsystems 0 Inaccessible Subsystems 0 Inaccessible Subsystems
Safety shutoff 4 Devices 2 devices 7 devices 7 devices
Overal spped of process 60 sec/bracket 300 sec/bracket 10 sec/bracket 4 sec/bracket
Tipping Angle 45° 30° 31° Unknown

Conclusion

  • A universal jig was made to fit all brackets
  • The system was designed to treat a full set of brackets in 1 hour
  • A redundant safety system was designed to protect operators of the system

Lessons Learned

  • Simplifying the design and reducing moving parts has a major benefit
  • Work with commercially available parts when possible (limit custom parts)
  • Communicate questions quickly and often

Future Work

  • The system should be assembled and tested to find the optimal height of the plasma jets over the brackets
  • More investigation into specific slat conveyors and manufacturers to find the best solution for the conveyor needs to be done