TERRY L. VANDERWERT
MICHAEL D. POLAD
Laserdyne Systems Div.
PRIMA North America Inc.
As the next generation of commercial aircraft takes center stage, behind the scenes multiaxis lasers have quietly become major players in aerospace manufacturing. Turning out critical components such as turbine-engine blades, nozzle guide vanes, shrouds, combustors, and even air frames increasingly depends on advances in multiaxis lasers that speed manufacturing, improve quality, and reduce part costs.
In addition to aerospace components, multiaxis lasers have become important systems for making everything from automotive prototypes to medical devices. An everincreasing number of products are now designed with the capabilities and benefits of laser processing in mind. In the past, applications largely arose only when lasers were more cost effective than incumbent production processes. Now, manufacturers are taking advantage of laser's capabilities to generate components that would be cost prohibitive or impractical with other methods.
The most striking change in multiaxis laser technology over the last decade has been the degree of integration of subsystems. These include the laser, motion system, motors, controls, user interface, sensors, and CAD/CAM software. Today's laser systems have evolved from a collection of individual components into truly integrated machine tools, based on advanced process knowledge and improved capabilities. For example, today's systems typically optimize motion parameters based on the components being produced, laser processing speeds, and the ability of workpiece sensors to detect and the controls to adaptively correct for part-to-part variations. The result is more productive multiaxis lasers that yield more consistent output.
The workhorses of industrial laser processing continue to be the flashlamp pumpedpulsed Nd:YAG, continuous-wave Nd:YAG, and CO2 lasers. However, adding conditioning optics — such as beam expanding and reducing telescopes — to the laser has improved drilling capabilities. And the ability to change beam size before it focuses permits quick hole-diameter changes while maintaining the advantages of drilling at focus.
Sensors and software for laser-beam focus control have also improved. Today's multiaxis systems include one or more workpiece/fixture sensors. The sensors, typically capacitive or optical, measure and help automatically control the distance between the laser-processing beam focal point and workpiece.
In the past, automatic focus controls often used a small motor to directly position the cutting/drilling nozzle, thus moving the focusing lens parallel to the laser-cutting beam. However, when drilling holes at shallow angles (such as on turbine-engine combustors) it is advantageous to move the nozzle in other directions to maintain the correct drilling location. For instance, integrated multiaxis laser systems move the nozzle via the main system axes, thus letting the user specify any desired direction of motion.
The recent addition of laser-based sensors, termed Optical Focus Control (OFC), addresses limitations of capacitance sensors to "side sense," or detect part surfaces adjacent to the one being processed. It also avoids errors caused by debris buildup on the assist gas nozzle. OFC can, for example, measure or map the run-out (actual versus design shape) at several levels on a ceramic-coated cylindrical part as it moves in front of the OFC sensor. Stored data, in turn, helps control the laser-beam position during part processing. Run-out can be mapped in two directions with both data sets applied simultaneously during processing.
Other capabilities now routine on multiaxis lasers include:
Feature finding determines the location of key workpiece and tooling features such as tooling balls. Measurements are typically used to adjust the reference positions on which program datums are based.
AutoNormal determines surface orientation and adjusts machine axes so the workpiece is perpendicular, or at a user-specified angle to the laser beam. It locates three points on a surface using noncontact sensors and, in seconds, calculates the plane and normal vector of the surface. Users specify point spacing, letting AutoNormal sense a wide range of surface radii, a practical addition to cutting and drilling programs.
AxisAlign measures certain points on a part or fixture using noncontact sensors such as capacitance (axis focus control) or OFC. The software redefines machine axes to match actual part orientation, eliminating the need for precise, expensive fixtures and long setup times. The feature helps improve part accuracy.
Additional features developed in recent years concentrate on making systems more user friendly. These include:
- Ready connectivity to networks, simplifying loading, backup, and storing part programs and CNC software.
- Access-control systems built into the CNC that assign different system privileges and configurations to different users.
- Online manuals with extensive hypertext links, making it quick and easy to access programming and operating information.
Like most industrial systems, improvements in computer speed and hardware have greatly improved laser-system controls. For example, 10 years ago, two 8 x 10-in. DSP boards controlled the motion of a typical Laserdyne eight-axis system. Servo positions were calculated once every 5 msec, and the servoloop was updated every 250 msec. Today, a single DSP board that fits in a PC card slot controls all axes. Servo positions are calculated every 1 msec and the servoloop is updated every 200 msec. The improvement is obvious: more-accurate motion at much higher speeds.
And a decade ago a typical state-of-the-art system from Laserdyne had a MS-DOS-based user interface. That was upgraded to Windows NT in 1998 and is now the more powerful and stable Windows XP Pro. The latest touchscreens are much easier to use and more flexible than previous versions, letting users configure displays and controls to suit individual needs.
Faster processing and more memory have also brought about several part-programming features that simplify complex programs. They include:
- Arrays of any desired length, with userassignable names.
- Vectors — specialized arrays that usually hold axis positions.
- Named system parameters that let users easily read axis positions, laser and sensor data, and other system-status conditions.
Combining the laser and system control also means higher throughput and quality. For example, controls can make laser power proportional to velocity (cutting or welding speed) of the laser-beam focal point. This simplifies part programs and yields higher quality parts. In another example, the drillonthe-fly feature pulses the laser as a function of axis position (such as rotary-axis position for a cylindrical part). This can significantly increase drilling speed. The time needed to produce a hole in a typical part has dropped from about 5 to 1 sec or less.
Interfacing to external devices has also become easier with software for RS-232 serial communications. From the part program, users can interrogate external devices, wait for a response, and modify the program based on that response. External devices, such as remote laser-beam power meters, are also routinely added to document process parameters as part of a process history or SPC record.
Multiaxis laser systems are highly sophisticated machine tools that require significant investment. But by integrating process knowledge into the overall system, lasers have become more intelligent, more productive, and capable of producing higher quality components — in most cases more than justifying the expense. For example, understanding the factors affecting airflow consistency in laser drilling has led to processes such as drilling at focus. Sensors such as OFC and breakthrough detection have significantly increased component quality, accompanied by cost reductions due to less inspection, scrap, and rework.
When a laser system is matched with the right applications, return on investment can be impressive. Hundreds of companies ranging from Fortune 100 manufacturers to small subcontract shops have accelerated investments in laser systems as the capability of these systems increases.
Advances in multiaxis laser systems will continue. Recently, for example, there has been much discussion about new laser types, including ultrashort (picosecond, femtosecond)pulse-length lasers and Yb-doped fiber and disk lasers. These are in various stages of development, and may become significant players in industrial settings within the next few years.
Software and hardware improvements will also continue. As more intelligence is built into laser systems, the skill level required of operators will be reduced. And efforts to better model laser processes will further enhance integration of system components. As more-powerful and sophisticated laser power sources are designed, they too will further improve capabilities in current applications and enable new ones.
Laserdyne Systems Div., (763) 433-3700, prima-na.com