Miyachi Unitek is no stranger to patented inventions (at last count, I think the company has 19), and the patent recently issued to NASA raises that number by 1...IMHO.
That’s because NASA’s newly patented Dynamically Variable Spot Size (DVSS) laser system (US patent #8,290,006) for bonding metal components used our LW300A 300W Nd:YAG high speed industrial laser in its development process. Miyachi Unitek engineers John Hurst and James Middleton are both listed as inventors on the patent, and much of the early work was done as part of a partnership development effort right here at Miyachi Unitek headquarters in Monrovia, CA!
It all began when NASA engineers at the Marshall Space Flight Center in Huntsville Alabama were looking for a better way to braze highly reflective alloying material on the main engine cooling tubes of the space shuttle. This repair work takes place deep inside the engine, so the brazing equipment had to be compact and delivered using a fiber optic cable.
NASA welding engineers reached out to Ed Turner of MUC during the “Moon Buggy Challenge” at Space Camp to provide laser and systems design expertise. Safety and operator ergonomics were the obvious challenges in a high powered hand-held laser brazing “torch,” as well as fiber breakage detection for the entire length of the fiber optic delivery cable.
The equipment had to be powerful enough to braze gold over high temp alloy and give the operator the feel of a traditional brazing torch. This was the genesis of the hand-held laser brazing torch project-named “silver bullet.”
John Hurst and Jim Middleton designed some breakthrough features that made this project successful, including a three-step laser safety interlock. Safety features include:
- Laser proximity at lasing surface detection – a safety interlock optical sensor that would not allow the laser shutter to open unless it was in the focusing range of the material.
- Finger switch and foot switch actuation –another safety/ergonomics feature that also gave the operator the feel of a traditional “Miller” type foot-pedal actuator.
- Built-in fiber breakage detection – built into the torch and control box.
Figures above, L to R: Optical Safety Sensor, Laser Torch, Laser Control Pendant
The LW300A pulsed ND:YAG laser was chosen for its high peak power (6 kilowatts), dynamic pulse width range (0.25-99.9 milliseconds) and high repetition rate capabilities (500 Hertz).
NASA deployed three complete laser and optical beam delivery systems to the shuttle repair facilities at Huntsville Alabama Marshall Space Flight Center, Stennis Mississippi, and Kennedy Space Flight Center in Florida.
The DVSS system is housed in something about the size of a size of a desktop computer. It contains a light entry aperture coupled to a laser beam transmission cable and a light exit aperture. Multiple lenses contained within the housing focus a laser beam from the light entry aperture through the light exit aperture. The lenses can be dynamically adjusted to vary the spot size of the laser, from 0.002-0.075 inches.
The nifty system also contains a number of interoperable safety devices that prevent activation of the laser and DVSS laser system if each safety device does not provide a closed circuit. I am impressed with these features, especially the manually depressible interlock switch, an internal proximity sensor, a remotely operated potentiometer, a remotely activated toggle, and a power supply interlock. The remotely operated potentiometer also provides continuous variability in laser energy output.
I think one of the important things about the new system is that NASA only recently sanctioned the use of lasers in very controlled and restricted settings, despite the fact that lasers are widely used for sensitive welding and brazing operations on small, thin-walled components. The ability to flexibly change the spot size of the laser beam is critical in some operations, and NASA considers it important to accommodating varying sizes of filler metal used during brazing processes.
The DVSS lens system is designed so that the optimal brazing distance is in a de-focused area of the lens, which allows for a larger spot size for heating the joining area and accommodates varying sizes of filler metal. That optimal working distance can be in a focused area for zoom lens assembly for welding; in some applications, two separate DVSS laser systems may be used for both brazing and welding applications. DVSS dynamically changes the energy density of the laser beam focused spot, which means the heat or energy can automatically adjust from just heating the material (brazing) to melting it (welding).