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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. Designing for laser processing today has in
itself contributed to huge cost and quality benefits.
Multi-Axis Laser 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, motors,
etc.—into truly integrated machine tools with all components 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, CAD/CAM programming software, etc, 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 technology within the last 10 years:
Laser Power Sources
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 stages of development and
evaluation. Those demonstrating reliability and performance in industrial
processing may become significant within the next few years.
Improved Process Control
Improved process control has
accompanied integration of sensors and software that provide capability for
fully integrated laser beam focus control. A 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.
(See photo page 18.)
More recently, 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. OFC 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
Additional integrated capabilities
that are now routine with multi-axis laser systems include the following:
Feature Finding™ automatically
determines the actual location of key workpiece and tooling features (e.g.
tooling balls). These measurements are typically used to adjust the reference
positions from which program locations are based.
AutoNormal™ automatically determines
the orientation of a surface and adjusts the machine axes so that the workpiece
is perpendicular (normal) or at any user programmable angle to the laser beam.
In seconds, this process measures the location of three points on a surface
using one of the non-contact sensors integrated into the system and calculates
the plane and normal vector of the surface. Spacing of these points is user
programmable, making the feature useful for sensing a wide range of surface
radii and a practical addition to a cutting or drilling program.
AxisAlign™ automatically measures
the location of certain points on a part or fixture, using a non-contact sensor
such as capacitance (Axis Focus Control/AFC) or optical (OFC). Machine axes are
re-defined in software to match the part orientation, thereby eliminating the
need for precise, expensive fixtures or long setup times, and improving part
accuracy.
Additional multi-axis laser system
convenience features that weren’t around 10 years ago include:
Easy connectivity to networks,
simplifying loading, backup, and storage of part programs and CNC executive
software.
Sophisticated operating systems that
can limit access to capability for editing part programs or changing system
parameters.
Access control systems built into
the CNC, providing the ability to assign different system privileges or system
configurations to different users.
On-line manuals with extensive
hypertext links, making it quick and easy to access programming or operation
information.
Faster, Lower-Cost Computing
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” x 10” 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 also has
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.
Benefits of Faster Processing
Faster processing and more memory
has brought about several part programming features that simplify complex
programs: (1) arrays (of any desired length, with user-assignable names), (2)
vectors (specialized arrays that usually hold axis positions) and (3) 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 axes position (e.g. rotary axis
position for a cylindrical part), significantly increases drilling speed
(Illustration One).
Today’s interfaces to external devices has 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.
Cost Justification
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. The number of users
with multiple laser systems is testimony to this return on investment. Hundreds
of companies ranging from Fortune 100 manufacturers to small subcontract shops
have accelerated their investment in additional laser systems as their business
grow and the capability of these systems increases.
The Future
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. n
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