ND:YAG LASER USED FOR COMPLEX HOLE DRILLING IN TURBINE ENGINE COMPONENTS

To meet demands for wider flexibility in hole placement and accuracy, this 5-axis laser machining system allows a precision job shop to process complex turbine engine components along the full travel of the Z-axis at compound angles as shallow as 10 deg to the surface.

Aerofab, Inc. (Indianapolis, IN), a precision sheet metal fabrication and machine shop for commercial aircraft engines and industrial gas turbines, added to its process capabilities by investing in a Laserdyne 795 5-axis laser machining system equipped with a Convergent Lasers CL50k Nd:YAG laser that allows the processing of complex parts along the full travel of the Z-axis at compound angles as shallow as 10 deg to the surface.

This functionality is important in processing turbine engine components where designers require increasingly wider flexibility in hole placement and accuracy to achieve higher performing, fuel efficient engines with less emissions. This is exactly the reason why Aerofab purchased this system, its ninth from PRIMA North America/Laserdyne Systems (Champlin, MN).

“We have developed features within our S94P laser process control that helps the system maintain airflow as tight as ±2 percent on a new generation of aerospace parts, where ±10 percent has been the norm. This, in turn, allows users to manufacture parts with extremely close tolerances and with exceptional repeatability,” explained Terry VanderWert, the president of PRIMA North America. Constructed for high-speed operation without compromising mechanical accuracy, the Laserdyne 795 laser machining system is the first and only standard built multi-axis laser system to guarantee volumetric accuracy. It can drill, cut and weld medium-to-large 3D parts with a unique moving beam motion system.

These capabilities are crucial to Aerofab achieving its stated mission is to be the world’s best manufacturer of complex aerospace and gas-turbine components and meet NADCAP (National Aerospace and Defense Contractors Accreditation Program) requirements. NADCAP is the leading worldwide cooperative program of major companies designed to manage a cost-effective consensus approach to special processes and products, such as laser drilling of aerospace components. The stated NADCAP vision is to develop a world-class special processor supply base for the global aerospace industry using a cost-effective industry managed accreditation process.

The new laser machining system includes a full complement of hardware and software features such as the proprietary Automatic Focus Control (AFC) that guides the motion system to maintain critical focus position and follow the contour of the part regardless of slight surface irregularities. All machine axes react to sensing of the part surface with AFC to create unlimited R-axis correction with high speed and unmatched sensitivity. This control allows top machine speeds so productivity is maximized without downtime or scrapped parts.

The AFC is complimented by the unique Optical Focus Control (OFC) to control the location of the Nd:YAG laser beam focal point relative to both metal and non-metal (not electrically conductive) surfaces. OFC uses a visible (red) laser beam coaxially aligned with the CL50k laser beam to provide an absolute measurement of the distance between the focusing lens and workpiece surface.

The system also uses BreakThrough Detection to maximize throughput and quality in laser drilling turbine engine components by compensating for variations in material thickness and material removal rates. BTD monitors progress of laser drilling for each hole to determine the pulse at which breakthrough first occurs. Once breakthrough has been detected, a user-defined number of additional pulses (any number from 0 and higher) are delivered to the workpiece. The number of additional pulses is determined by factors, such as proximity of the surface being drilled to an adjacent back wall, hole size and taper consistency, and air flow tolerance.

The CL50k Nd:YAG laser is designed specifically for precision hole drilling, including percussion, drill on the fly and trepanning. This laser delivers the highest peak power (50 kW) of any industrial pulsed Nd:YAG laser and is unmatched for drilling deep and high aspect ratio holes at shallow entrance angles. The laser uses an intra-cavity telescope (ICT) to ensure constant beam quality over the entire operating range, with a variable spot module (VSM) that adjusts the beam diameter independent of laser conditions.

A V-rail optical bench setup within the laser head provides superior stability and flexibility. The laser uses two flash lamps that are quickly and easily replaced as needed. Little or no alignment is required after components are changed to further minimize setup and changeover time. The modular design of the optic and electronic assemblies allows for fast and easy replacement of components for processing flexibility and configuration adjustment.

The power supply uses advanced solid-state IGBT electronics for rapid switching of high currents, high efficiency and full programmability of the laser parameters, including pulse shaping. The power supply layout integrates a water conditioning system and heat exchanger inside a compact NEMA 12 enclosure.

All of this combines to provide closed-loop control of hole size. The system also uses SPC Data Acquisition software to capture real-time processing data used in NADCAP reports. The real-time data logs enable the analysis and reporting of laser process information that NADCAP is expected to require in the near future.

Laserdyne Systems, PRIMA North America, Inc., 8600 109^th Avenue North, #400, Champlin, MN 55316, 763-433-3700, Fax: 763-433-3701, www.prima-na.com.