Laser Transmission Welding of Thermoplastic Composites

Laser Transmission Welding of

Thermoplastic Composites

Dr. Stefanos Giannis

Technical Manager,

Composites & Adhesives

Contents

September 15, 2016 ADMACOM Workshop, Brussels, BE 2

• …about Element Materials Technology

• Overview of Laser Transmission Welding (LTW)

• LaWoCS project

• Case study 1: Plastic pin

• Case study 2: Stiffened beam

• Case study 3: Lap joints

• Conclusions

• Future steps

Business By Industry Sector


Three Services


Materials

Product Qualification

Failure Analysis

Late R&D

Prototype

Production

We Work With Industry Leaders


These logo’s are used without the direct permission of the Trademark

owners and are used in a nominative to indicate that Element is either

currently or has in the past successfully completed testing tasks and

projects on behalf of these organisations













Polymer Matrix Composite Materials


• Fibre Reinforced Plastics (FRP) are essential

for light weight constructions

• Low density compared to traditional materials

• Excellent strength and stiffness properties

• Thermoplastics are currently used in many

different industrial applications (Aero, Auto,

Energy etc.) and demand is growing rapidly

• Attractive for their formability, mechanical

properties and recyclability

• To increase uptake many sectors require faster

manufacturing and joining techniques

Laser Transmission Welding – An Established Technique


• Contact-free technology

• High flexibility of process

• Low permeability of welded

seams

• Decrease of cycle times

Source: Laserline Source: LPKF Source: LZH

Source: Leister

+

In cooperation with: Aqua Select GmbH

Laser Transmission Welding (LTW)


• Based on the optical characteristic of polymers

• Local energy absorption at focussed interface

• No preparation or further treatment required

• Often no visible witness marks on joined partners

• Welding of 3D parts is relatively easy

Clamping pressure

Clamping pressure

Laser absorbing

part (LA)

Laser transparent

part (LT)

Laser beam

Welding area

Weld seam

Laser absorbing material

Laser transmitting material

Laser Transparency


• The transmissivity of the material is influenced by… – the material thickness

– the type of reinforcements and their volume fraction

• Ideal level is around 15% transmissivity

0

5

10

15

20

25

30

35

40

45

50

250 500 750 1000 1250 1500

Tra

ns

mis

siv

ity [

%]

Wavelength [nm]

PEI Glass 1,2 mm

PEI Glass 1,7 mm

PEI Glass 2,4 mm

940 nm

Influence of Fibre Direction – Bead on Plate Welding


Unreinforced vs. Reinforced – Lap Shear Specimens


• Homogeneous weld seam width for unreinforced polymer

• Fluctuating weld seam characteristics for reinforced composite

5 mm 5 mm

PPS + Carbon Black PPS + Carbon Fibre

LT

LA

Temperature Monitoring


• PPS containing carbon black

• Quasi-simultaneous welding, 400mm/s

• Homogeneous temperature distribution

• Carbon fibre reinforced PPS

• Quasi-simultaneous welding, 400mm/s

• Inhomogeneous temperature

distribution

LaWoCS – Laser Transmission Welding Of Thermoplastic Composite Structures


• Development of laser welding process for thermoplastic

composite materials and welding of real parts

• Development of adapted thermoplastic base materials and

manufacturing of real components

• Testing of novel

thermoplastic composite

structures and real parts

according to industrial

specifications

Case Study 1: Plastic Pin


• Injection moulded pins used in aircraft interior (Airbus A330)

• Passenger cabin (floor panel in pantry)

• Sandwich panel made of CFRP laminates and honeycomb structures

Source: EADS Source: DEVA /

LZH



• Laser Transmission Welding compared with adhesive bonding

• Pin: thermoplastic polymer based on PA 6.6 with fire retardant additives

• Production volume: ~ 300,000 p.a.

LT

10 mm 10 mm 10 mm

LT

LA LA

LT Weld or bond

LA LA

Weld or bond

10 mm

Laser absorbing part:

PA 6.6 + carbon black

Laser absorbing part

PA 6.6 + carbon fibre

LT

Laser Transmission Welding of the Pin


• Laser transmitting part – PA6.6

• Laser absorbing part – carbon black filled PA6.6

– carbon fibre reinforced PA6.6

Laser transmission welded pin Source: LZH



• Bonded samples prepared based on same joint area as welded samples

• Used high temperature epoxy for bonded samples

• Set of bonded and LTW samples exposed to the following conditions: – Reference (i.e., ambient laboratory conditions)

– Elevated temperature wet (80°C/85%RH) for 6 weeks

– Elevated temperature dry (80°C) for 6 weeks

– IRM902 oil at 80°C for 6 weeks

• Samples tested at RT, 80°C and -50°C in a ‘push-off’ test



• Significant knockdown for bonded samples after ETW exposure

ETW (80°C/85% RH) exposure for 6 weeks Reference



• LTW samples less sensitive to ETD conditioning when tested at 80C

• LTW samples have similar performance to bonded samples after oil exposure

IRM902 0il at 80°C exposure for 6 weeks ETD (80C) exposure for 6 weeks

• Bonded – Cohesive / interfacial

• Welded – Fibre pullout or failure

of the pin

Case Study 1: Plastic Pin - Failures


Case Study 2: Stiffened Beam (Torsion)


Source: AGC AeroComposites /Element

Case Study 2: Stiffened Beam (Flexure)


Typical failure in bonded sample - adhesion

Typical failure in welded sample – bulk material

Source: AGC AeroComposites /Element

Case Study 3: Creep of Joints


• 1.7mm thick Tencate Cetex PEI/GF

• Bonded using high temperature epoxy

• Loads applied: 15kg, 10kg and 5kg

• Temperature ramp 1C/min

Conclusions


• Laser Transmission Welding can be used for joining some long fibre

thermoplastic composites

• The weld seam quality is influenced by the type and layout of reinforcements

• The temperature in the weld seam can be monitored (pyrometer) and used as a

feedback for automatic temperature control

• LTW made specimens were less sensitive to environmental conditions with failure

occurring in the matrix rather than at a bonded interface

• Specimens preparation for LTW is minimal i.e., intimate contact is required but no

other surface preparation

• Processing time is significantly reduced compared to bonding (seconds vs. hours)

• Part design can be optimised for LTW to further reduce weight without large

compromises in other areas

Future Work


• Expand the LTW development for: – Larger structures and more complex geometries

– Other long fibre reinforced thermoplastic composites

• Enhance the quality control during the welding process

• Integrate LTW with typical manufacturing processes to realise the significant

process savings (vs. time for bonding, surface preparation steps removed)

Acknowledgements


• The author would like to thank Innovate UK (formerly UK Technology Strategy

Board) and the German Federal Ministry of Education and Research (BMBF) for

their support of these investigations within the Eurostars project LaWoCs

(Project No. 01QE1002D)

Thank you for your attention!

Any questions?

Documents

Laser Transmission Welding of Thermoplastic Composites