Polymer Weldingwith Lasers

NOW IT’S COLORFUL

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

info@treffert.orgwww.treffert.org

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