Nd:YAG Gets a Bead on Reed Switches
Daniel C. McCarthy
Since its development for telecommunications applications, the reed switch has found use in alarm systems and proximity sensors. It generally incorporates two contacts hermetically sealed within a glass capsule. When a magnetic field approaches, the switches either attract to close the circuit or repel to open it.
Inert gas or a vacuum environment within the capsule helps to keep the contacts clean. Laser machining provides unique solutions to fusing the glass around the metal switch. Directed Light, an industrial laser services company that integrated four laser machining systems for a switch supplier, selected Lee Laser's 8250M 250-W continuous-wave Nd:YAG laser for the job.
The unwelded reed switches are connected to the lead frame in groups of 20 to simplify loading and unloading on Directed Light's system. It incorporates two lasers, working in tandem, that weld the glass and metal at one end of the switches. The switches are then rotated, and the lasers repeat the operation at the other end.
Directed Light designed its system to provide a hard-beam delivery using 3-in. dichroic mirrors on each side to locate the beam, said Jeff Smith, vice president and chief operating officer at the company. A cylindrical lens -- a 2x to 8x beam expander -- produces a laser spot 1.5 in. long and 0.1 in. wide. The spot covers several switches at once, and the beam delivery design enables adjustment of the spot in four axes: X, Y, Z and the angle of attack.
"This is an Nd:YAG application," said Smith. "The 1064-nm wavelength operating in continuous-wave mode is ideal for forming this glass-to-metal seal."
The speed at which the switches pass through the spot, the length of the spot, and the laser power are all key process parameters, he added. Lee Laser offered its engineers several choices in 250-W continuous-wave lasers, and they selected the 8250M Nd:YAG for its stability and divergence.
Smith also credited the laser's optical rail configuration, which enabled Directed Light to locate the beam expander and high-speed shutters directly on the rail, simplifying installation and adjustment. Directed Light also incorporated Lee Laser's analog interface to provide programmable power control.
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