Developed High Pressure Crimping Process
A key technical challenge stood in the way of our launching an important new line of solenoid products. A reliable method of joining the solenoid flux tube to the pole end had to be developed. The joining method had to withstand high fatigue loading and also had to remain tight throughout its life since any gap in the joint would adversely affected magnetic performance.
A number of joining methods were considered including brazing, threading, and roll forming but we decided that a segmented crimp joint had a number of advantages. It was easy to assemble, it “drew up” any gap between the parts, and it avoided the thread locking issue. It also had disadvantages, namely the potential of producing life-limiting stress risers. The challenge was to identifying and optimizing the key design parameters required to make the joint capable of 10,000,000 impulse cycles to 5000 psi.
The design team could not identify any useful theoretical models and had little confidence in the ability of current FEA software to predict fatigue life.
We decided to use a series of designed experiments to develop an empirical model. We used Resolution IVscreening experiments to identify the key factors followed by factorial experiments to identify interaction. Simplex optimization was used as required.
After optimization, the solenoid, including the crimped joints, was rated for 10,000,000 pressure cycles to 5000 psi at 99.5% assurance. The crimping method allowed for through processing of the tube ID and easy single axis assembly.