NOW IT’S COLORFUL - treffert.k0v.detreffert.k0v.de/treffert/treffert/img/laserwelding_en.pdf ·...
-
Upload
vuongkhanh -
Category
Documents
-
view
224 -
download
0
Transcript of NOW IT’S COLORFUL - treffert.k0v.detreffert.k0v.de/treffert/treffert/img/laserwelding_en.pdf ·...
Every new technology must
have strong arguments to
replace established
methods. Why use lasers
for polymer welding? There
are four significant argu-
ments:
• Laser welded connections
resist high mechanical
loads, they are gas tight
and often achieve the same
strength as the base
material.
• With lasers, almost any
kind of seam weld contour
can be realized and there
is a solution for nearly
every workpiece geometry.
• Minimal thermal and
mechanical stress input is
applied: What you weld is
what you see. The welding
is so precisely localized,
that even sensitive
components very close to
the weld remain unaffected.
• The results are surfaces
with perfect quality,
no micro particles, glue or
roughness.
WHY LASER WELDING?
In summary, all thermopla-
stics and almost all thermo-
plastic elastomers, unfilled
or filled to a degree can be
welded. For example, in
current applications, poly-
mers with a glass fiber
percentage of up to 30%
are laser welded. Also
different kinds of polymers
can be joined without pro-
blems - provided they are
chemically compatible and
the two melting temperature
ranges are sufficiently over-
lapping. Some examples of
materials which can be
welded: PE, PP, PVC, PS,
ABS, SAN, PA6, PA6.6,
PC, PMMA, PSU …
There is also a rule of
thumb for natural
materials: What you can
weld ultrasonically, can
also be laser welded.WHAT CAN BE WELDED?
ApplicationsProcess
AdvantagesRules of Thumb
As with any other process,
laser welding of polymers
needs specific conditions to
be a success. There are
four key factors:
• Choice of suitable poly-
mers and pigments
• Use of the right laser
source with suitable optics
• Appropriate joint
configuration and small
gap width
• Optimized clamping
technology, allowing free
access of the laser beam to
the seam and applying
sufficient pressure to the
components.
Glueing polymers often
requires pre-processing of
the surface with organic
solvents. This rules out
glueing for certain applica-
tions. Apart from that,
some very common unipo-
lar polyolefins (PE and PP)
are difficult to glue.
Welding with heated
elements or hot air is
inexpensive but slow and,
in the first case, wears off
the tools due to direct
contact with the polymer.
These processes apply heat
to a large area, which is
unsuitable for sensitive
components. Friction,
vibration or ultrasonic
welding methods all subject
the workpieces to high
mechanical stress.
Consequently, complex
design and regular mainte-
nance of the machines is
required. Ultrasonic wel-
ding, in particular, requires
specifically designed work-
piece geometries in order
to transfer the sonic energy
to the right locations.
Laser welding of polymers
is already successfully
implemented in numerous
applications.
The main areas of use are
automotive, electronic and
telecommunication indu-
stries, medical device tech-
nology, human care and
household devices.
FOUR FACTORS FOR SUCCESS
DIRECT COMPARISON
ApplicationsProcessAdvantagesRules of Thumb
The low heat conductivity
and viscosity of polymers
means that the most prac-
tical welding geometry in
most cases is overlap wel-
ding. Here, the laser beam
penetrates the upper mate-
rial and is absorbed by the
lower material. The heating
of the latter leads to plasti-
fication which bridges the
workpiece gap and melts
the upper material by heat
transfer. Therefore, having
a small workpiece gap is
an important success factor.
As a rule of thumb the
gap width should not
exceed 100 microns in
contour welding.
PROCESS OVERVIEW
All commonly used poly-
mers are more or less
transparent (in undoped
condition) in the infrared
wavelength range of the
laser sources (except CO2
lasers). Filler materials,
usually pigments, provide
for the absorption of laser
energy. Many color
pigments absorb within the
infrared range and can be
used for laser welding.
Even simpler, and therefore
most common, is the use of
carbon black particles
acting as absorbers, typi-
cally in a concentration of
0.05 - 0.5%. However, this
results in darker colors.
There are already standard
solutions for black-black
and transparent- black
welding available.
For clear and bright colors,
pigments which are more
flexible to use, have been
developed. They absorb
only in the wavelength
range which is relevant for
the laser weld, but do not
modify the coloring of the
polymer significantly.
TRANSPARENCY AND ABSORPTION
A B C D
Designs for Laser Welding
and SuitablePigments
Laser Welding Concept:Laser light penetrates the upper
layer and is absorbed by thelower material (A).
The melting of the latter transfers (B)the heat to the upper layer (C).
The mutual melting pool solidifies under external pressure
to a high-quality weld (D).
Transparent/ Black
Black/Black
Colour/Black
Colour 1/Colour 2
Colour 1/Colour 1
Transparent/Transparent
White/White
Black, colored, transparent,
white ... In this order the
complexity of process
requirements for laser wel-
ding of polymers increases.
Applications with black
material as the absorber
are usually easy to realize
or already available as a
standard solution. For wel-
ding of polymers with iden-
tical colors, the necessary
color-identical metamery-
free pigment combinations
are customized in laser-
transparent and laser-
absorbing form - a typical
task for the experienced
master batcher. The wel-
ding of light-colored poly-
mers, which is particularly
required in the medical
device industry, is
successfully realized using
the above mentioned laser
absorbing pigments. For
thin foils and suitable poly-
mers without pigments, CO2
lasers can be used.
White-white welding
requires specific solutions
because of the beam
scattering and the lack of
transparency due to
titanium oxide, which is
used in most cases.
To find the ideal pigmenta-
tion recipe for perfect color
matching and laser welding
characteristics, it takes a
specialist with the knowledge
and experience of
hundreds of thousands of
recipes and with a sophisti-
cated laboratory equipped
with modern extrusion lines
and kneading systems.
Starting with the color
sample given by the custo-
mer, he develops a color
concentrate, which can be
added as a master batch
into the polymer produc-
tion. The master batch is
easy to process, optimally
dispersing and is identical
in color. If requested, the
original material can be
conditioned, which means
it is used as the carrier
material for the master
batch. The characteristics
and the authorization of
the original material are
thus retained, which is par-
ticularly essential in the
medical device industry.
BLACK, COLORED, TRANSRENT, WHITE
PIGMENTING: A FACTOR OF SUCCESS
Designs for Laser Weldingand Suitable Pigments
Increasing degree of complexity inoverlap welding of polymers. Formany applications a well-functioningpartnership between master batcherand laser manufacturer is of greatadvantage.
The wavelength is the deci-
sive feature which makes
diode lasers, Nd:YAG
lasers and CO2 lasers the
most suitable lasers for
polymer welding. The latter
is absorbed by most poly-
mers and can weld them
directly (limited to foils).
Apart from the wavelength
difference and the absorption
behaviour of certain pig-
ments, the following rule
applies: Nd:YAG lasers are
particularly suitable for
welding seam widths below
1 mm and for plane wel-
ding geometries with scan-
ning head applications.
Diode lasers, however, are
preferred for wider welding
seams, circular seams and
simple spot welds. In most
cases the required power
ranges from 30 to 150 W,
which is achieved by both
laser technologies effort-
lessly and cost-effectively.
WHICH LASER SOURCE?
These two processes have
the best market penetration
presently. In the case of
contour welding, the laser
beam follows the welding
seam, similar to the wel-
ding of metal. The laser
beam is often delivered via
glass fiber to robot-control-
led optics. Almost any
workpiece size can be
welded. The tolerable gap
width (approximately 100
microns) often determines
the limit of this technique.
In the case of quasi-simul-
taneous welding, the laser
beam passes over the enti-
re welding contour several
times very rapidly. Beam
deflection is done using
galvo scanning heads and
therefore higher beam qua-
lity is essential. The entire
welding path melts simulta-
neously due to heat buffe-
ring and allows the
materials to move against
each other easily. The pres-
sure on both materials and
a suitably constructed set-
ting way can bridge larger
gaps. However, quasi-
simultaneous welding
requires higher laser
powers and the heat load
on the components
is higher.
Nd:YAG/THG355 nm
Electronic excitation
Absorption
Additives
Visible regime
Vibronic excitation
Ultra violett Infra red
700 nm
ExcimerArF: 193 nmKrF: 248 nmXeCI:308 nm
Nd:YAG/SHG532 nm
Diode laser808, 940, 980 nm
Nd:YAG1064 nm
CO2
9.4 µm10.6 µm
400 nm
CONTOUR & QUASI-SIMULTANEOUS WELDING
The OptimumLaser for
Every WeldingApplication
Spectrum:Most polymers (grey curve) are
usually transparent or translucent inthe visible and near IR range.
By adding pigments (blue curve), suitable absorption of the laser
wavelength is achieved.
The optimum solution has
to fulfill the requirements of
the production process.
Laser sources with beam
delivery as well as
complete turnkey stand-
alone systems are available:
The StarWeld Diode family
comprises diode lasers and
diode-pumped Nd:YAG-
lasers with galvo scanning
heads or fiber-coupled
optics in different power
ranges. With 808, 940 and
1064 nm, all common
wavelengths for polymer
welding are available.
Depending on the require-
ments, the emphasis can be
on good beam quality or
high output power. The
very compact diode lasers
are especially suitable for
contour welding in small
systems or mounting on
robot arms. PolyScan is a
new turnkey all-in-one
solution for contour and
quasi-simultaneous welding
of polymers. It is most suit-
able for prototype or small
batch production. All lasers
with galvo scanning heads
from the StarWeld Diode
family can be integrated
into this system (diode
lasers as well as Nd:YAG
lasers). Due to the excellent
beam quality of these
lasers, they are especially
suitable for micro welds.
Very simple: Two experien-
ced specialists for the two
main factors of success in
polymer laser welding –
the right laser and the best
pigments – working hand
in hand.
A laser application lab
(Rofin/Baasel Lasertech)
and a color and chemical-
physical laboratory
(Treffert) are ready for
sample processing and
process development.
Within a few days you can
receive the right polymer
solution for your
application, which is
already tested for laser
welding.
We look forward to solving
your task!
INTEGRATED OR STAND-ALONE
WHY ROFIN AND TREFFERT?
The OptimumLaser forEvery WeldingApplication
The successful installation of more
than 15,000 lasers all over the
world has established ROFIN as
one of the leading manufacturers of
lasers and laser based systems.
Macro, Micro and Marking are the
three company competence columns
which allow ROFIN to cover an
extraordinarily wide range of pro-
ducts for industrial material proces-
sing. ROFIN’s high-performance
lasers are used all over the world
for precision cutting, welding, micro-
structuring and marking. More than
1,200 employees in production sites
in the US, Germany, Great Britain,
Japan and Singapore as well as
numerous sales and service branches
ambitiously work on future laser
technology for the industry.
The TREFFERT-group
polymer-technology, with plants in
France and Germany, develops and
produces color systems, additives,
compounds and master batches for
the polymer industry, which are
delivered worldwide. TREFFERT
makes developments for the medical,
automotive and electronic industries,
as well as further technical
applications. The company delivers
batches from the smallest amount as
samples up to several tons. Being a
specialist in this branch of industry
with highest quality standards and
75 years of tradition, TREFFERT
produces just-in-time for specialized
markets. The outstanding strength
of this company is in fulfilling
orders, which require high
performance in development and
consultation.
Carl Baasel LasertechnikGmbH & Co. KG
Petersbrunner Str. 1bD-82319 Starnberg
Tel: +49(0)8151-776-0Fax: +49(0)8151-776-159
www.rofin.com
Treffert GmbH & Co.KGIn der Weide 17D-55411 Bingen
Tel: +49(0)6721-403-0 Fax: +49(0)6721-403-27
© R
OFI
N/T
REFF
ERT
10-2
003
- D
ESIG
N B
Y RO
BI