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Marking
The generic term for making some kind of readable marking on the
surface of a component. Marks are technically one of the
following kinds of effects: engraving, ablation, annealing, color
change or foaming.
Micromachining
Another generic term used to describe marking on the surface of a
target where the purpose of the mark is not to make a part number or
logo or other readable mark, but to engrave a pattern for mechanical
reasons. These reasons may include liquid conduits through a
metal block, antennae patterns on metal parts, etc.
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The actual processes are called
(alphabetically):
Ablation
This is where one material is removed by laser from the top of
another, dissimilar material. Common example are
“Day/Night” lighted switches in automobiles. These are
commonly translucent white plastic bodies which are dipped in
paint. The paint is then selectively burned off to expose some
pattern or symbol which appears white during the day and which is
illuminated from the rear at night.
Annealing
Annealing is a heating process used on steel and titanium alloys
where the surface of the material is selectively heated with the
laser to near the melting point. This has the effect of
discoloring the material to a black color, which gives excellent
contrast against the surrounding steel. This process when
properly done does not remove material. It is very commonly
used for surgical tools and implants where there is high contrast
and permanence and no trenches or crevices are created for bacteria,
etc., to hide. Annealing has the disadvantage that if the
material is exposed to extreme heat the annealed mark will
disappear. Also, annealing only works on steel and titanium.
Color Change
Color change is a process in plastic where the color of the material
changes under the laser light. Some plastics do this
naturally, and others have additives which absorb specific laser
wavelengths in order to achieve this effect. Typically, no
material, or a trivial amount of material, is removed from the
surface of the target. One of the classic examples, photos of
which can be found on nearly every laser website in the world, is
marking on ear tags for cattle. Many consumer electronics
products have this kind of marking on their cases.
Cutting
Lasers can be used to cut certain materials. Very thin materials (up
to a few thousandths thick) can be cut by normal marking lasers,
although some materials exhibit unsightly heat-effect zones on the
material. Thicker materials can be cut with higher power lasers, and
sheet steel, fabrics, fiberboards, etc., are all cut in industrial
situations with lasers. These lasers can have power in the many
thousands of watts.
Deposition
Commercially available ceramic paints and films can be applied to
the surface of a material and then melted in place with a laser
beam, leaving behind a raised and very permanent laser mark.
Often used with decorative glass items. Somewhat
labor-intensive process to apply the material and then remove the
excess. Also can be expensive. However, the mark can be
very attractive when done properly.
Engraving, light
Probably the most common kind of laser marking is engraving.
This is where the laser beam is used to remove material from the
surface of the device being marked, but the material is
homogeneous. The laser acts like a chisel in this case and
blows away pieces of the subject material. Light engraving is where
a relatively shallow trench is created, between .0001” and
.005”. The depth achievable depends on the material, the
power of the laser and the dwell time of the laser.
Engraving, deep
Deep engraving is something that only high power lasers can do. Deep
engraving is used for making molds and dies, stamps, etc. The depth
that can be achieved is entirely dependent on how the material
absorbs the laser, how much energy the laser has, and how long the
laser can dwell on the target. Deep engraving is usually a fairly
slow process.
Polishing
Similar to annealing is polishing. In polishing, the laser
beam is used to selectively melt the very top few molecules of
material, and when it cools, which is usually instantaneously, the
surface finish will appear different from the surrounding
finish. This will then reflect light differently and while
there is no real color change, it will appear different. This
is often used in electronics for nickel and gold packages.
Welding
Lasers can be used to create weld joints in many materials,
including metals, plastics, and certain ceramics.
Typically, weld lasers are higher power and are used in
systems where the laser beam is stationary and the product
moves underneath the laser - similar to the table travel of a milling machine.
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