DIAMOND E-400 – Increasing the Industrial Standard of Sealed-Off CO2 Lasers
Every aspect of this next-generation sealed-off laser has been optimized to deliver
superior performance, lower cost of ownership and higher reliability
Summary
Over the past decade, the sealed-off CO2 laser has revolutionized cutting of plastic, thin metal,
fabrics, leather, wood & other organic materials as well as drilling of paper & plastic, providing a
turnkey, compact tool that can be confidently integrated into a wide variety of production line
equipment. Analysis of these applications indicated the only way to further improve process
economics and thereby increase the applications space was to increase the performance, lower
the cost of ownership and extend the reliability of these workhorse lasers. This was no small
challenge given the maturity of sealed-off CO2 lasers in the 100-500 Watt power range.
Coherent has shipped more of these lasers than any other manufacturer, and more importantly,
has thoroughly investigated possibilities of improvement over the years. Analysis of this data
has enabled our engineering team to design a next generation product – the DIAMONDTM E
series, which will increase the industrial standard of sealed-off CO2 laser technology. The first
member of this family is the DIAMOND E-400, which delivers 400W of output power backed by
an unconditional 24 months warranty. The DIAMOND E-400 is the first pulsed laser in its power
class built in this integrated format (see Figure 1). This redesign effort has included an
improvement in beam quality, reduced cost of ownership through modular design, and a new
integrated power supply, extensive use of on-board diagnostics and ease of service.
Improvements in reliability have also been incorporated, including improvements to the
convenient new integrated but easily detachable RF power supply.
Superior beam quality
Many details within the laser head have been analyzed and optimized which lead to improved
beam parameters in comparison to current field proven DIAMOND K-Series. Specifically, the
new electrode design yield a highly consistent and uniform plasma, resulting in superior beam
quality and power stability of +/-5%.
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We’ve also taken the definition and
specifications of beam quality to a new
level with the DIAMOND E-400. We still
provide a value for M2 (<1.2), which
defines the overall focus ability of the
beam as it exits the laser. But we’ve also
worked on measuring and improving other
important beam parameters – those that
critically impact how the laser beam is
delivered and ultimately how it cuts and
drills.
These parameters are mainly
determined
by
the
laser’s
beam
Figure 1: A key development in the DIAMOND E-400 laser
conditioning optics which are located
is elimination of the RF power umbilical by integrating a
outside the cavity itself and include turning
compact power supply within the laser head (photo)
and focusing mirrors.
These optics now remove all beam astigmatism, producing a single, fixed beam waist location
as well as beam ellipticity of less than 1:1.2.
Ellipticity and astigmatism errors which could cause the beam to cut differently in orthogonal
directions have been dramatically reduced.
Moreover, the optics are configured to produce a
smooth Gaussian beam with an output beam diameter (1/e2) of 12 mm and a beam divergence
of < 1.6 mrad. Thus, the beam is well collimated when it leaves the laser head. The advantage
is that the integrator often does not need to include a beam expander for beam delivery, even in
systems with long beam paths. In the far- and near field, the laser delivers a smooth Gaussian
beam with very little side mode energy (see Figure 2). Optics can be placed closely to the laser
output window, without degrading the beam quality in the focus by introduction of side modes.
This is important because ultimately it’s the far-field optical performance – at the work surface –
that determines how the laser cuts and drills.
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In addition to its optical characteristics, the
materials processing capabilities of a
pulsed CO2 laser are also dependent on
the temporal (pulsing) characteristics of
the laser. Specifically, pulses with faster
fall time deliver more of the total pulse
energy above the material processing
threshold. Just as superior beam quality
leads to tighter spatial focus, faster fall
time translates into tighter temporal focus.
Both effects maximize the ratio of usable
power/total power.
Far-field focus
Figure 2: In the DIAMOND E-400 the beam conditioning optics ensures superior beam characteristics in both the
near-field and far-field, without the need for a beam expander.
The end result is both faster cutting and
reduced HAZ (heat affected zone), as well
as faster piercing during drilling and cut
initiation. With the new power supply and
electrode design, and the elimination of the
RF umbilical, the DIAMOND E-400 has
pulse fall times on the order of only 50
microseconds (see Figure 3). In terms of
performance metrics, even at 5 kHz and a
60% duty cycle, the DIAMOND E-400 still
delivers a modulation depth of 100% (see
Figure 3).
Near-field focus
Actual results from beta-site testing indicate the DIAMOND E-400 cuts up to twice as fast as
competitive 400 watt lasers.
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Simplified integration into OEM workstations
The DIAMOND E-400 laser simplifies integration into OEM equipment due to several factors.
As shown in Figure 4. the laser output beam is aligned precisely to the kinematic mounting feet.
This not only simplifies integration but also greatly simplifies laser exchange when a laser
reaches the end of its life.
The carefully pre-defined beam characteristics also impact the ease of integration. The far-field
beam parameters are extremely consistent eliminating the need for extra optical adjustment.
And as already noted, the large collimated beam means that most OEMs can avoid the cost and
complexity of a beam expander.
100% depth
of modulation
Figure 3: The DIAMOND E-400 is characterized by very short pulse fall times, which translates into increased cutting
efficiency and reduced HAZ.
The integrated power supply is another obvious benefit for OEM tool builders. Machinery does
not have to be designed with the additional space and support necessary to accommodate a
separate power supply. And the potential geometry/space constraints and head associated with
an RF umbilical are also things of the past. Similarly, the laser’s on-board beam diagnostics
mean that separate sensors do not have to be built into systems to duplicate their purpose. And
as a general rule, each such sensor would need its own beamsplitter and optical train. Plus all
the other sensors such as RF power, temperature monitors and operational logs eliminate the
need for system builders to duplicate these.
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Lower cost of ownership
The ultimate aim of many of these developments is to lower the total cost of ownership for the
laser.
Specifically, improvements in economy can be seen in four different areas: lower
purchase cost, lower cost of integration, reduced downtime and lower service costs.
The lower purchase price is a direct result
of the reduced cost of the integrated but
easily detachable RF power supply and
Laser Beam aligned
to Mounting Feet
(Golden Axis)
the total elimination of the RF umbilical
and its connectors. The cost of integration
is decreased because of the enhanced
software suite and interface, and again,
the possible elimination of the beam
expander.
Operational
cost
is
lower
because of minimized downtime of this
high-reliability design (backed by a 24
months warranty).
And lastly, if any
problems do occur, the powerful on-board
suite of self-diagnostics means that the
cause is immediately obvious, so the laser
is serviced in the minimum time and cost.
Elimination of the “discovery” phase in any
problem reduces the time and hence cost
Kinematics Mounting Feet
Figure 4:
to fix that problem on site. In some
industries, for example for first tier
The output beam is aligned precisely to the kinematic
automotive manufacturers, one hour of
mounting feet, simplifying integration into OEM equipment.
unexpected downtime on a line can cost
up to $100,000.
Possible preventive maintenance in the future may further reduce downtime, as the user is
warned and has spare parts on site and available to plan on a routine service interaction.
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Increased reliability
The most significant design innovation has been to integrate the power supply within the laser
head, with the specific purpose of eliminating the RF power cable that normally links the two.
This cable has to carry multiple kilowatts of RF power in a 400 Watt laser. As a result, the
length of the cable must be fabricated very accurately; otherwise the impedance is too high
resulting in a very high power load (i.e. thermal build-up) at the connectors. Similarly, the
connector contacts must be very accurately machined – even tiny spaces could lead to arcing.
Eliminating this cable altogether removes the cable as a manufacturing challenge and cost item,
as well as a potential source for laser failure, thereby improving reliability.
The new integrated but easily detachable RF power supply has been subjected to the same
level of scrutiny and re-optimization as the plasma tube. Most importantly, taking advantage of
advances in integrated electronic components for high power circuitry has enabled a dramatic
60% reduction in total parts count, with a corresponding increase in inherent reliability, not to
mention lower manufacturing and testing costs. Power supply size has also been decreased.
Many details in the laser head have been analyzed and re-designed.
For example, new
materials and manufacturing protocols will improve lifetime of gas and internal optics. Plus, a
new electrode design includes novel geometry to deliver both longer-life joints and increased
efficiency. Increased efficiency means that the laser head is leading to both longer lifetime and
more stable mode output. The use of a new type of igniter, specifically designed to lower the
stresses associated with plasma ignition has been introduced as well and thereby increasing the
overall tube lifetime.
On board control & diagnostics
Another key to minimizing downtime in any laser is to expect the unexpected. It’s not enough to
design and manufacture a product with inherently high reliability, it’s also necessary to build in
intelligent systems to monitor all critical operational parameters (see Figure 5). The laser acts
like a server; the diagnostic & control software can be accessed by a PC through the Ethernet
port either directly or through Internet. The DIAMOND E-400 includes a full complement of onboard sensors and diagnostics, including temperatures sensors in the head and at key locations
in the power supply.
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In addition, there are sensors that monitor both the forward and reflected RF power levels. The
laser also includes a laser power meter as a standard tool. The on-board computer monitors all
of these sensors in real time and stores the readings in a time-log.
Figure 5:
The DIAMOND E-400 is a
smart laser with a
comprehensive suite of
sensors and software to
analyze and long all key
operational and performance
metrics (screen capture).
There can be two important benefits from this comprehensive approach to self-monitoring.
First, if a problem does occur, its source can be immediately identified from the error code
generated by this system, so downtimes are reduced. However, the ultimate long-term goal with
this approach is complete preventative maintenance, where the operator, and in some cases
the laser manufacturer, can be automatically alerted to a potential operational problem before it
ever affects the actual laser performance.
Conclusion
Enlarging the applications space for sealed-off CO2 lasers requires expanding their process
capabilities and improving overall economics. But, for a mature technology, this can be difficult
to accomplish. Through a willingness to re-evaluate all aspects of laser design and diligent
attention to detail, however, Coherent has been able to significantly enhance the performance
and cost characteristics of this technology, resulting in the new DIAMOND E-400.
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