| Which Laser is Right for You? |
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| This can be a very tricky question to answer.
There are lots of factors to take into account, including the following: |
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• The Proof is in the Samples
• Quality of Mark
• Speed of Mark
• Capital Cost of Laser
• Consumable Cost of Laser
• Sorting out Laser Specifications
• Support
• Expected Operating Conditions |
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>> The Proof
is in the Samples
The number one thing to look for when choosing a laser is the sample.
All the laser vendors will make samples for free, and Exatron can arrange
for this to happen for you. Be aware that the vendors will each need
a pretty good supply of samples, as there will be test pieces to find
the right sets of parameters for your parts.
Ultimately, the main concern will be which vendor made the best looking
samples for the amount of money you are willing to spend. The proof
really is in the samples. |
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>> Quality
of Mark
Laser marking is an art, not a science. Gather a dozen engineers and
marketing people, and you’ll get a dozen opinions on what laser
mark looks good. In some cases, it matters greatly whether the mark
looks good. This is especially true in consumer or high-value products
where the customer expects the product to look very nice. There are
other applications where it does not matter at all, such as a production
lot number buried deep inside some assembly.
The problem with getting a quality mark is that it often requires a
sacrifice of processing speed. Blazing across the surface of the target
may leave a slightly ragged-looking line, but going slow may leave perfect
crisp edges. It’s a judgment call that requires coordination between
production and marketing as to what is acceptable.
Higher quality may also mean a more expensive laser. In particular,
there are plastics which will mark O.K. with a 1064 YAG laser, but will
be much prettier with a 532 Vanadate laser. The trouble is that the
532 may initially cost $20,000 more than the 1064. |
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>> Speed
of Mark
Speed is always music to the ears of the production guys. Speed is often
a function of power – More Power! (There are limits with some
materials that simply will not go faster, no matter how much power
you throw at it.)
As there is an inverse relationship between dwell time on target and
power delivered to the target, to get speed you have to add power. More
powerful lasers are more costly to purchase initially, and have slightly
higher consumable costs over time.
The key question for speed is: How many units do you need to process
in a day/hour/minute
Remember that processing time is a function not only of the laser but
also the material handling system feeding the laser. No matter how fast
the laser mark is, if the whole system is slow, the laser is slow. Given
the expense of lasers, it is worth while to support them with fast production
machines to feed them.
However, if your process produces only limited quantities of products,
you may be able to get away with a lower power laser and move it slowly.
If your laser is waiting for product to arrive, it’s a waste of
time and money. If you can get away with lower power due to lower throughput
requirements, you’re money ahead. |
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>> Capital
Cost of the Laser
The initial capital cost for laser marker can be surprising. Some will
be surprised they’ve become so inexpensive, while others will
wonder how they could possibly cost so much. Lasers sold by Exatron
currently have a price range of $25,000 up to well over $100,000, and
that’s just for the laser. The handler is extra. It’s difficult
to say what a typical system will cost as there is no “typical” system.
The old adage “You Get What You Pay For” is only partially
applicable to laser markers. Certain vendors have higher costs than
others, and the extra money may or may not buy you a better laser. Again,
the proof is in the samples. |
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>> Consumable
Costs of the Laser
The Diode-pumped Nd:YAG and YVO4 lasers have essentially no consumables.
They require power (although usually not a great deal of it) and some
require deionized water that is replaced every so often. The major
cost associated with these lasers is replacement diodes. The diode
pump modules will degrade over time and eventually lose enough power
that the system fails to perform well. The time of decay varies between
vendors and even different lots. All vendors guarantee their diodes
for a period of time, with a minimum being 5,000 hours of operation
or one year. The guarantees vary by vendor. The replacement diode packs
can be several thousand dollars, so do not be surprised by this expense. |
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>> Sorting
out Laser Specifications
Laser product data sheets will have many specifications, some of which
are relevant and others not. Ultimately, the measure of a laser is
how much work it can get done on the surface of the target material.
This can depend on wavelength, power rating, beam quality, spot size,
pulse frequencies and software. This section will try to explain these
parameters:
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• Wavelength
Just as materials absorb and reflect different wavelengths of visible
light, giving those items their color, materials will absorb, transmit
or reflect different wavelengths of laser light. For example, plain
glass will absorb CO2 laser light at 10600nm, but is transparent
to the YAG wavelengths of 1064nm and 532nm.
How the laser will perform on the material is first and foremost
a function of how that material reacts to that wavelength of light.
There are some general guidelines on this, but in general it is a
function of applications testing to determine which laser wavelengths
work best with a given material. There are only about 5 commonly
available wavelengths for commercial marking lasers, so the choices
are fairly limited. |
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• Power
The most common measure of a laser, Wattage, is also very misleading.
The power of laser is not so much the raw power output by the crystal
or gas, but the effective power delivered to the surface of the
target material.
Some things to watch out for:
Flashlamp power ratings. Older flashlamp-pumped YAG lasers typically
have very high power ratings. These lasers created a great deal of
power in the raw form, but that raw beam was not suitable for most
marking purposes. After the beam is passed through the appropriate
optics and apertures to get a good marking beam, as much as 75% of
the power will disappear from the final beam. Newer diode-pumped
systems have much less fallout in power and so it is entirely fair
to compare a 50W flashlamp to a 10W diode-pumped system.
Where is power measured? Most manufacturers measure power at the
output of the laser crystal, not the workpiece. TRUMPF is the notable
exception to this rule. The power at the crystal will always be higher
than that delivered to the workpiece, even in diode-pumped systems.
So it’s unfair to measure at the crystal. So be careful where
the power rating is taken. |
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• Beam Quality
Different optical setups generate different quality beams. Quality
means how round the beam is, how evenly the power of the laser is
distributed across the face of the beam, etc. Older flashlamps created
such ragged beams that the beam had to pass through metal apertures
to cut off the crummy edges of the beam, thus losing significant
power.
Another element of beam quality is how many ‘hot spots’ there
are across the face of the beam. A good beam will have a single hot
spot in the middle of the beam, with power trailing off to the edges,
like a bell curve. This is called a “single mode” laser
beam. Other lasers will have several hot spots, which gives uneven
marking on the surface of the part. These are called “multi-mode” lasers.
The effective power of a multi-mode laser will be lower as the power
will be more spread out. |
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• Spot Size
The spot size of the laser determines how much power is actually
getting to one point on the target material. As a laser beam is
round, a small difference in beam diameter can mean a big change
in power density:
| Flashlamp: |
Diode-Pumped: |
| Spot Diameter = 120 micron |
Spot Diameter = 60
micron |
| 50W (15 W power at target) |
12 W power at target |
| 15W / (3.1415 x 60 µm2) = 0.0013W/µm2 |
12W / (3.1415 x 30 µm2) = 0.0042W/µm2 |
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By this formula, the “lower power” diode-pumped laser
has more than three times the power density of the flashlamp-pumped
laser.
Smaller spot size also allows for finer writing on ever-smaller electronic
components. Text sizes under 1mm in height are not uncommon. The
smallest text Exatron has ever done was just under .2mm in height.
Spot size is not only a function of the type of laser, but also the
f-theta lens on the system. F-theta lenses which give larger marking
areas also give larger spot sizes and lower power densities. Thus,
a laser which can perform a task on a small target may not be able
to accomplish the same work on a larger target. It is important that
the applications test for a given material use the correct field
lens which will be used in the final system. |
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Pulse Range
This is a simple measure for YAG and Vanadate lasers. Most of these
lasers are pulsed, which means that the beam is turned off and on
at very fast repetition rates. This allows power to build up between
pulses and greatly increases the apparent power of the laser. Most
of these lasers use a thing called a Q-switch which is an electro-optical
switch capable of extremely fast opening and closing.
Lower pulse frequencies usually give higher apparent power, but that
can be overkill with some materials. The preferred pulse frequency
for a given application will depend on the material, so it is important
to match your laser to your application.
Some brands of lasers can operate in Continuous Wave (CW) mode where
they do not pulse at all, but only shoot a straight beam. This can
be useful in certain limited situations.
Modern diode-pumped YAG and Vanadate lasers can pulse between 4000
and 200,000 pulses per second, with some vendors offering a smaller
range. However, YAG gives higher power at low frequencies but peters
out at high frequencies, while Vanadates give lower power at low
frequencies, but maintain higher power at high frequencies. It is
important to understand the difference when comparing different lasers
for a given application. |
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• Software
Most laser marking systems today come with a software package to
develop the mark. For the most part, these software packages are
all pretty good, with some better than others. The more sophisticated
software packages offer greater control over the laser beam itself,
which can offer greater performance in a production environment.
One feature of software that does vary dramatically from vendor to
vendor is self-diagnostics software. Some vendors have dramatically
good diagnostic software while others have essentially nothing. Be
prepared to pay for the better software (although the currently most
expensive laser does not have very good diagnostics software) |
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>>
Support
This is always a tricky business. Exatron tries to provide as much service
as possible for the systems we manufacture. However, there are problems
that we cannot diagnose or deal with, and in those cases we rely on
the vendor of the laser to help.
The simple fact is that laser service can be spotty. Some vendors
don’t
have enough people, other don’t have the right people. Sometimes
the problem can only be solved by getting the factory involved and
if the factory is in Europe this can cause service delays.
Happily, the newer generation of diode-pumped systems have much less
to go wrong with them than older flashlamps. While diode-pumped systems
can have ‘infant mortality’ problems, once they are up
and running in the field they tend to be very reliable, no matter what
brand
you buy.
Some vendors have sophisticated diagnostics hardware and software built
into their systems, while others are very bare-bones. This is as much
a matter of what makes the customer feel comfortable as anything else. |
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>>
Expected Operating Conditions
Part of the decision will rest on the conditions in which the laser
will operate:
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• Operators and Technicians
Will the operators be technically proficient, or not at all? Are
your own repair technicians competent or not? These questions go
to whether to buy a more complicated system which may be more capable,
or a simpler system and sacrifice flexibility for ease of use and
maintenance? |
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• Operating Temperatures
Will the laser system be in an air-conditioned lab, or on a hot production
floor? Air-cooled systems are less expensive and complicated, but
less tolerant of extreme temperature conditions on a production
floor. At high operating temperatures, the diode packs in these
lasers can lose efficiency and drop the power output of the system,
leading to inconsistent marks. In any case, a production floor with
expected temperatures more than 105 F are not good candidates for
laser markers in any case. |
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