getting a hip replacement expects the implant to be certified
and last a long time. The same goes for new and replacement parts
in aircraft. The assumption is that critical partsespecially
those used in applications where safety is paramountare
certified by the manufacturer and the government and are made
to exact specifications. Lawrence Livermore and Metal Improvement
Company, Inc., have developed a system that helps identify certified
and other high-value parts.
The Lasershot Marking System
imprints permanent, high-resolution identification marks that
are difficult to counterfeit, readable by machine, and strengthen
the part at the site of the mark, in contrast to other marking
methods, which can actually weaken the part. Before Lasershot,
there was no way to permanently mark parts used in safety-critical
applications without inducing the danger of fatigue and stress-crack
corrosion, notes Livermore physicist Lloyd Hackel, primary
developer of the system.
Hip Implants to Space Stations
The Lasershot Marking System
has the potential to be of great use not only to makers of medical
and aircraft components, but also to aerospace organizations such
as the National Aeronautics and Space Administration (NASA). It
is a prime candidate for imprinting safety-critical parts with
the Air Transport Association 2000 Data Matrix, a high-data-intensity,
two-dimensional, machine-readable symbol recently adopted by NASA.
NASA plans to use this data matrix to identify and track the millions
of parts used in the space program. Currently, the matrix is imprinted
on the thousands of heat-resistant tiles on the Space Shuttle
using a traditional marking technique. However, safety-critical
metal parts are not marked at all because of the risk of marking-induced
failure. The invention of the Lasershot Marking System means that
NASA may soon be able to mark and track these important parts
NASA has added Lasershot
marking to its Data Matrix Direct Part Marking Standard and Handbook
and included three samples imprinted with the mark in its Materials
International Space Station Experiment, which was launched on
the STS-105 in August. The sample parts were bolted onto the space
station to face the slipstream solar wind. After one year, they
will be retrieved and examined to evaluate how well they held
up in the hostile space environment. NASA and the Department of
Defense are also conducting ground, flight, and in-orbit tests
of laser-peened marks to certify Lasershots use in current
and future programs.
Air Transport Association, the Electronic Industry Association,
the Automotive Industry Action Group, and the Semiconductor Equipment
Manufacturers Institutehave chosen the Data Matrix
standard as the preferred one for parts marking, thereby extending
the potential applications for the Lasershot system. Components
that could be marked with this method include fan blades, disks,
rotors, and integrated rotor assemblies as well as components
A mark created by the Lasershot
system allows manufacturers and users to positively identify each
individual part and trace each part from manufacture to retirement.
In addition, Lasershot peen marking will be a valuable tool in
combating counterfeit parts by providing a unique, permanent,
and difficult-to-reproduce tracking symbol, one that also strengthens
the part at the site. The mark contains fine detail nearly impossible
to counterfeit, much like the watermark on modern currency. Part
counterfeiting is a growing concern. According to government estimates,
as much as $2 billion in unapproved parts are now sitting on the
shelves of parts distributors, airlines, and repair stations.
Lasershot peen-marking station. The Lasershot Marking System
(shown in action in the background of the opening image) uses
laser pulses to safely and permanently impress identification
markings on metal components without weakening them. The system
is thus ideal for marking parts used in situations where safety
is criticalfrom hip-joint replacements to commercial
Chip off the Laser Peening Block
technique common in metalworkinguses a ball-peen hammer
or pneumatically shot small metal balls to pound a piece of metal
into shape and strengthen it against fatigue failure. Replace
the hammer or metal balls with a laser and the blow of metal on
metal with the pressure wave of a laser light pulse on metal,
and laser peening results. (See S&TR, March
and Stressed, Metals Get Stronger.)
In the Lasershot peen-marking
process, a layer of absorptive material is placed over the area
to be peened, and a thin layer of water is flowed over the absorption
layer. A high-intensity laser with an energy density (fluence)
of about 100 joules per square centimeter illuminates and ablates
material from the absorption layer, creating an intense pressure
pulse that is initially confined by the water. The absorption
layer protects the part surface from material removal or melting.
The pressure pulse creates a shock wave that strains the surface
in a two-dimensional pattern that mirrors the lasers intensity
profile. By creating the desired pattern upstream in the light
and then imaging this pattern onto the metal, a complete mark
can be made with a single laser pulse.
laser system projects the pattern on the part in much the same
way that a slide projector creates an image on a screen,
explains Hackel. A slide projector without a slide in place
projects a light field of uniform intensity on the screen. No
image or pattern appears. When a slide is inserted between the
projector bulb and lens, the light and dark areas of the slide
provide an intensity profile pattern that is imaged onto the screen.
With the Lasershot system, we use a laser and a special telescopic
system to image the pattern of a mark onto the metal part. The
laser fires, and that entire mark is printed on the part in a
This single-pulse technique
is well suited for high-volume marking applications. For low-volume
use, a smaller systemthe multiple-shot matrix marking systembuilds
up a two-dimensional mark using multiple laser pulses.
Breakthroughs Make It Possible
The Lasershot technique
was made possible by a patented breakthrough in laser technology
developed at Livermore involving a neodymium-doped glass laser
and a wavefront correction technology, called phase conjugation.
We can now build laser systems that operate up to six pulses
per second, with output energy of greater than 25 joules,
says Hackel. This means we can peen-mark six data matrices
per second, using the single-shot pattern marking technique.
The phase conjugation provides a high-quality beam that has high,
long-term pointing stability for the high repetition rates needed
for the smaller multiple-shot marking system. As a result, the
Lasershot system can mark parts at a rate comparable to or exceeding
that of conventional marking methods.
The other key to the system
is a specially designed and patented telescopic delivery system,
which precisely relays the image onto the part surface. This
beam delivery is critical for accurately replicating a two-dimensional
marking pattern, notes Hackel. The resulting mark
has uniquely embossed fine detail, making it nearly counterfeit-proof.
10- by 10-character identification markapproximately
0.3 centimeter on a sideimprinted into an aviation-grade
aluminum alloy using the Lasershot Marking System. Unlike
other marking methods, Lasershot increases the marked areas
resistance to fatigue and corrosion failure, and the resulting
high-resolution mark is difficult to counterfeit.
Is Stronger, More Durable
Although other techniques
are available for imprinting identification marks on metal parts,
none measures up to the Lasershot method. The primary techniques
are laser etching, pin stamping, and ink-jet printing. Laser etching
systems work by focusing energy directly onto the surface to be
marked and etching the surface with heat. The heat generated actually
alters the parts surface, even vaporizing the surface in
some cases. Although this technique has good permanence and generates
a clear mark, it modifies the material. In steel, for instance,
the high temperature causes carbon to precipitate out in the area
hit by the laser beam, ultimately degrading the parts strength.
The material modification and strength degradation can lead to
fatigue or stress-corrosion crack failures. In a scanning electron
micrograph study of 10 hip replacement implants that had failed
much earlier than they should have, 5 of the 10 showed fatigue
fractures that began in the characters that had been laser-etched
on the implant surfaces. These failures could have been
prevented by the Lasershot method, notes Hackel.
In pin stamping, a conical
stylus impacts the surface, with the size of the mark controlled
by how deeply the stylus indents the metal. Like peening with
a conventional ball-peen hammer, pin stamping may leave some residual
compressive stress in the part, which would provide some protection
against fatigue and mechanical stress. However, this method also
roughens the surface and concentrates the stress at the bottom
of the sharp indentations. In addition, pin stamping can distort
small or thin parts.
marking using the ink-jet technique does not affect the surface
material, the markings are not necessarily permanent. The permanence
of the mark depends on the chemical interaction of ink and part
as well as on the environment in which the part is used.
or engraving, chemical etching, and welding also degrade strength
and shorten the fatigue lifetime of metals. Other techniques
can cast symbols on parts during manufacturing, notes Hackel.
However, they only work for larger parts and dont
address the need to mark parts already manufactured or those produced
by noncasting methods such as forging and machining.
Unlike laser etching, Lasershot
removes no material, and the marked surface remains chemically
unaltered. Unlike pin-stamped marks, Lasershot does not roughen
the surface. Plus the compressive layer from laser peening extends
as deep as
1 millimeter into the metal, adding strength to this local area.
the Future for Lasershot
The Lasershot Marking System
allows manufacturers for the first time to safely and permanently
mark and label metal parts used in situations where failure means
big trouble. Donald L. Roxby, director of the Symbol Research
Center, an international leader in the development of advanced
symbology solutions for industrial, materials handling, and manufacturing
environments, notes in a recent letter to Hackel, Our organization
was elated when we became aware of your work related to lasershot
peening. The lasershot peening process provides the marking fidelity
required to apply dense symbols to small parts without injecting
risk. The process makes it possible to identify internal engine
components such as aircraft turbine blades and a host of other
difficult marking applications.
The R&D 100 Award judges
voted their agreement. Lasershot is poised to make its mark in
the world of safety-critical parts manufacturing.
Lasershot Marking System, laser peening, R&D 100 Award, safety-critical
metal parts and components.
information contact Lloyd Hackel (925) 422-9009 (firstname.lastname@example.org).