Technique Used in Drilling 170-Micron-Diameter Holes
Summary:
Laser Fare, Inc. (Smithfield, RI), has patents pending on a new laser drilling technique combining beam splitting and low-power optical trepanning. The main advantage to the technique is speed; other techniques can drill precision holes, but several orders of magnitude more slowly. MDA interest in high-speed precision hole drilling was driven by its Airborne Laser program requirement. The technique has several potential commercial applications in the aerospace, automotive, and precision-valve (''inkjet spray'') technology industry.
Technology Description:
Laser Fare, Inc., has filed two process patents for a hole-drilling technique combining low-power optical trepanning with beam splitting. A primary laser beam is generated by a commercially available Nd:YAG laser operating at a wavelength of 1064 nanometers (nm). Through the use of a wavelength-specific optical beam splitter, this primary beam is split into three individual beams of roughly equal power. An optical trepanning subsystem converts an input Gaussian beam into an output annular beam. The system then drills holes in target plates as they are moved past the apparatus.
In the Phase II work, the target plates were Inconel 600 with a plate thickness of 635 microns. Laser Fare worked with a number of partners who operated primary lasers at varying pulse repetition rates, pulse durations, pulse energies, and average output power ranging from 1.4 to 14.8 watts. The test results showed that the lower power output created holes with desirable properties of eccentricity, taper, recast thickness, extent of the heat affected zone, and plate distortion. According to minimum adiabatic energy calculations for drilling a perfect right-cylindrical 170-micron hole through a 635-micron-thick Inconel plate, trepanning requires only about 30 percent of the output power that percussion drilling does, assuming fixed quality requirements.
The importance of the technique is primarily manufacturing speed as measured by drilling time per hole. Mechanical drilling might take one minute per hole; the ABL objective was to get drill time per hole down to 0.75 second. Laser Fare's technique, if all works as planned using reasonable downtime calculations, would reduce the drill time per hole to 0.42 seconds.
MDA Origins:
In 2002, MDA awarded a Phase I SBIR contract to Laser Fare and three subcontractors to address a unique hole-drilling requirement. Laser Fare considered the results of the Phase I work ''fair'' but too slow and with too much taper. Optical trepanning and beam splitting showed promise of increasing the drilling rate and decreasing taper. In December 2003, MDA awarded Laser Fare a Phase II SBIR contract to investigate the technique of low-power optical trepanning using beam splitting.
Spinoff Applications:
Precision hole drilling has a direct application in any technology that requires a uniform spray, either into a combustion chamber or at a target.
One obvious application is fuel injection. A single automotive fuel injector does not require millions of holes, but millions of cars would benefit from highly precise and smooth microcylinders that make for a uniform spray into a combustion chamber. Another similar application is precision holes for inkjet technology. As the uses for inkjet technology go beyond printers, demand will rise for the ability to create holes with diameters in the submillimeter range.
A futuristic application is modifying the surface of airplane wings. Microholes drilled into the skin of a wing far enough to reach a plenum at a negative pressure can create boundary layer suction. This in turn overcomes boundary layer separation, one cause of drag. Remove that drag, and the efficiency of a wing surface can be improved by several percentage points, which translates into improved capability and fuel efficiency. The problem is that many millions of holes would be required on each wing section. To date, nobody has developed a cost-effective means to accomplish this challenging requirement.
Commercialization:
Laser Fare has filed two process patents on precision high-speed laser-trepanning. The company has held discussions with several aerospace companies to use the low-power optical trepanning technique (but not beam splitting) for shaped holes for cooling jet engine components. Most turbine blades are coated with a thermal barrier to help resist high-temperature malfunction; this coating is non-conductive and electric discharge machining cannot be used to drill through it. High-power lasers can do the task but can cause collateral damage to surrounding material. However, using low-power optical trepanning, it might now be possible to use lasers to cut complex three-dimensional shapes inexpensively and quickly.
Company Profile:
Laser Fare, Inc., is a privately held corporation founded in 1979. Located in Smithfield, RI, the corporation is divided into two main groups, the Materials Processing Group and the Advanced Technology Group. The former offers value-added services including design services, parts assembly, airflow testing, and gross leak testing; it has in-house tooling, design, and engineering staff as well as an in-house metallurgical testing center. The latter focuses on the advancement of laser materials processing and the development and commercialization of new laser-based technologies, and works both independently as well as in conjunction with universities, national laboratories, and corporations. In 2004, the company employed between 40 to 50 full-time employees and generated revenue on the order of between $4 and $5 million. Laser Fare operates in a facility that is approximately 20,000 square feet of mixed office, laboratory, and shop floor space. Its primary business is laser cutting, laser drilling, laser welding, and laser engraving.
Contact Information:
Dr. Paul F. Jacobs
Laser Fare, Inc.
One Industrial Drive South
Smithfield, RI 02917
Tel:(401) 231-4400
Fax:(401) 231-4932
email: pjacobs@laserfare.com
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