Multi-Axis Laser Technology Soars To New Heights: An Update of the Last 10 Years

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Laser Machining
Subcomponents are more tightly integrated into highly productive system

By Terry L. VanderWert and Michael D. Polad
Laserdyne Systems Division
PRIMA North America, Inc.

CHAMPLIN, Minn.—As the next generation of commercial aircraft takes center stage, behind the scenes multi-axis technology has quietly become a major player in the manufacturing of these aircraft. Critical aerospace components—such as turbine engine blades, nozzle guide vanes, shrouds, combustors, and even air frames—have become increasingly dependent on an enhanced multi-axis laser capability, providing a significant impact on manufacturing speed, quality and reduced part costs.

In addition to aerospace component manufacturing, multi-axis laser technology has become an important manufacturing process for many product categories, ranging from automotive prototyping to medical component manufacturing. Integral to this trend of the last decade is that an ever-increasing number of products are now designed to reflect the capabilities and benefits of laser processing. Multi-axis laser now opens a new frontier of design possibilities, whereas before, applications for laser processing largely arose as lasers were demonstrated to be more cost-effective than established, incumbent processes.

Designing for laser processing today has in itself contributed to huge cost and quality benefits.

Multi-Axis Laser Technology Matures

The most striking change in multi-axis laser system technology within the past 10 years has been in the degree of integration of subsystems. Today's laser systems have evolved from a collection of individual components—laser, CNC, motion devices, and motors—into truly integrated machine tools with each component working together and optimized based on an overall system perspective.

Looking at today's laser systems, one sees tight integration of the laser, motion system, control, user interface, sensors, and CAD/CAM programming software, all based on new and more advanced process knowledge and capability. For example, motion parameters are optimized for the components being processed, capability (processing speeds) of the laser source, and ability of process and workpiece sensors to adaptively correct for part-to-part variations. The result is more productive multi-axis laser systems that yield more consistent output. Following is an overview of important areas that have experienced major leaps in multi-axis laser technology within the last 10 years:

Laser Power Sources Provide New Part Features And Quality

The workhorses of industrial laser processing continue to be the flashlamp-pumped, pulsed Nd:YAG, CW Nd:YAG, and CO2 lasers. Integration of beam conditioning optics (e.g., beam expanding/reducing telescopes) within the laser has provided the basis for process improvements in laser drilling. With the ability to change the size of the laser beam before it is focused, one can change the focused spot size and, therefore, hole diameter while maintaining the advantages of drilling at focus.

Recently, there has been much discussion in technical literature and at conferences about new laser types, including ultrashort (picosecond, femtosecond) pulse length lasers and Yb-doped fiber and disk lasers. These lasers are in various forms of development and evaluation. Those which demonstrate reliability and performance in industrial processing may become significant within the next few years.

Improved Process Control through Integration of Sensors and Software

Improved process control has accompanied integration of sensors and software that provide capability for fully integrated laser beam focus control. The pioneer of this technology is Laserdyne Systems, which holds several patents for these laser system designs.

Today's modern multi-axis systems include one or more of these workpiece/fixture sensors. These sensors are typically capacitive or optical and are used to measure and automatically control the distance between the laser processing beam and the work piece.

In the past, automatic focus controls often used a small motor to move the cutting/drilling nozzle directly, thereby always moving the focusing lens parallel to the laser cutting beam. However, in applications requiring drilling holes at shallow angles to a surface (such as aerospace turbine engine combustors), it is advantageous to move the nozzle in other directions to maintain the correct hole location. Today's fully integrated multi-axis laser system moves the nozzle by moving the main system axes, thus allowing the user to specify any direction desired for the motion.

More recent addition of a laser-based sensor (optical focus control/OFC) has addressed limitations of capacitance sensing to "side sense" or to also detect surfaces of the part adjacent to the one being processed. Optical focus control also avoids errors that occur with debris buildup on the assist gas nozzle and is applicable to surfaces that are not electrically conductive. With OFC has come capability to measure or map the run-out (actual vs. design shape) at several levels on a ceramic-coated cylindrical part while the part is moved in front of the OFC sensor, storing that data to control the laser beam position when the part is processed. Mapping of run-out can occur in two directions with both sets of data then applied simultaneously during processing.

Additional integrated capabilities that are now routine with multi-axis laser systems include the following:

Additional multi-axis laser system convenience features that weren't around 10 years ago include:

Faster, Lower-cost Computing of the Machine Control

Improvements in computer speed and hardware have greatly increased computing power and laser system control capability. Ten years ago, motion of a typical LASERDYNE system's 8-axis motion was controlled by two 8- by 10-inch DSP boards. Servo positions were calculated once every 5 milliseconds, and the servo loop was updated every 250 microseconds. Today, a single DSP board that fits in a PC card slot controls all axes. Servo positions are calculated every millisecond, and the servo loop is updated every 200 microseconds. The improvement is obvious—more accurate motion at much higher speeds.

The user interface has also benefited from computer advances. Ten years ago, Laserdyne's user interface was MSDOS-based. That was improved with a system based on Windows NT in 1998. Laserdyne's latest system with touch screen is much easier to use and more flexible than the previous systems. Many of the display features and controls can be configured by the user to suit individual needs. Also, today's operating system, Windows XP Pro, is much more powerful and stable than Windows NT.

Faster processing and more memory have brought about several part programming features that simplify complex programs: arrays (of any desired length, with user-assignable names), vectors (specialized arrays that usually hold axis positions), and named system parameters (user can access axis positions, laser data, sensor data, and other system parameters).

Integration of the laser and system control also has addressed the need for higher throughput and quality. For example, the control includes the ability to make laser power proportional to the velocity (cutting or welding speed) of the laser beam focal point, thereby simplifying part programs and making higher quality parts. Drill on the fly, whereby the laser is pulsed as a function of axis position (e.g., rotary axis position for a cylindrical part), significantly increases drilling speed.

Today's interfaces to external devices have also become easier with RS-232 serial communications from within a part program. From the part program, a user can interrogate an external device, wait for a response, and modify the part program based on the 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.

Design for Better Manufacturability Justifies Today's Multi-Axis Laser System Cost

Multi-axis laser systems are highly sophisticated machine tools that require significant investment. But by integrating knowledge of the process into the system, laser systems have become more intelligent, more productive, and produce higher quality components, justifying their use. For example, in laser drilling, understanding the factors affecting air flow consistency has led to processes such as drilling at focus. Addition of sensors, such as optical focus control and break through detection, has created significant increases in component quality with accompanying major reductions in costs due to reduced inspection, scrap, and rework costs.

When matched with the right applications, the return on investment can be impressive.

Future is Limited Only by Imagination

Capabilities for multi-axis laser systems will continue to advance. New software and hardware features that make laser processing more productive, enabling them to produce higher quality parts, are on today's design screens for practical application in the months ahead. Further integration of system components will be derived from systematic efforts to model laser processes. As more intelligence is built into these new laser systems, the skill level required of operators will be reduced. And as more powerful and sophisticated laser power sources are designed, they too will appear in systems on the factory floor, not only to further improve capability in current applications and enable new applications.

For more information from Laserdyne Systems Division, visit www.primapower.com/en/products/thelaser/laserdyne-795-en/.

About the Authors

Terry L. VanderWert is vice president, Laserdyne Systems Division, PRIMA North America, Inc. and is responsible for design, development, production and support for the Laserdyne family of multi-axis laser processing systems. Mr. VanderWert has been involved in applying lasers to materials processing (drilling, cutting, welding, heat treating) for more than 25 years. He holds a master of metallurgy and materials science degree and bachelor of metallurgical engineering degree from the University of Minnesota and is a registered professional engineer in Minnesota.

Michael D. Polad is software engineering manager, Laserdyne Systems Division, PRIMA North America, Inc. and has been responsible for software design of Laserdyne CNC controls from 1981. Having designed the company's first CNC because no suitable one was available for the first integrated system, Polad has managed the design of CNC's written in assembly language, CNC's designed to run under MS-DOS and two major CNC designs with Windows interfaces. He holds a bachelor of aerospace engineering degree from the University of Minnesota.

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