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LASER CUTTING AND JOINING OF HYBRID-POLYMER-METAL PARTS

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JEC 2017, Paris15th March 2017

Frank Schneider1, Kira van der Straeten1, Stefan Janssen2

1Fraunhofer Institute for Laser Technology ILTAachen

2Chair for Laser Technology LLT, RWTH Aachen University

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OUTLINE

Laser Cutting

Process fundamentals cutting FRP

Cutting of hybrid parts

Laser Joining

Surface structuring

Direct joining

Further approaches

Summery and Outlook

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MotivationMulti Material Laser Cutting

Lasers cut all kind of light weight materials:- metals: high strength steel, aluminum,

titanium- fiber reinforced polymers: GFRP, CFRP

Wide spread use in metal cutting

Multi material applications benefit from Laser cutting

Edge preparation for joining in overlap or butt joints

Common processingstacked or pre-assembled metal and FRP parts

Cutting of materials with inlays

Cutting for insert integration

Hybrid Parts and Materials

- wear-freeconstant quality

- contact-free, no forcesno vibration, high precision, reduced clamping

- flexibleeconomic from individual to mass production

Laser Cutting Features

Laser Applications 2016

Source: Strategies Unlimited

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Thermal Cutting Process Comparison Metals and FRP

Metals

FRP

Mean process temperature between melting and evaporation temperature of the metal

Most of the material is ejected as melt

Adequate gas assistance ensures minimum recast layer

Process temperature >> decomposition temperature of the matrix

High ratio of evaporated material

Short interaction times ensures minimum heat affected matrix

Examples: Laser cutting of high-strength steel

Laser cutting of GFRP

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Multi-kW-Laser Cutting - Two Dedicated Processes

Local melting or evaporation of the material with a focused laser beam

Material removal by a gas jet or evaporation pressure gradients

1st pass

2nd pass

Second last pass

Remote cutting

multi-pass process

- CFRP

- Low heat impact

cutting direction-->

Gas assisted cutting

single-pass process

- Metals, Plastics, GFRP

- High throughput

- Good 3D suitability Seite 5

Laser beam

Nozzle

Cutting gas

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CFRP Cutting up to thick sections

Kerf shaping by adapted scan strategy and

beam orientation

Deep cut accessibility

One-sided perpendicular cut flank

Minimized heat load

Heat affected zone <200 µm (8 mm thickness)

Left side Right side

500 µm 2 mm

Carbon Fiber UD plies [0/90]Epoxy matrixFiber volume 59%

CFRP cut egde (8 mm)

Demonstrated up to 10 mm thickness

4 kW fiber laser

Multi-pass cutting with 5 m/s scan speed

Effective cutting speed 0.4 m/min (10 mm thickness)14 m/min (2.6 mm thickness)

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1st StepCutting of CFRP in a multi-pass process

last pass

Cutting of Stacked MaterialTwo Step Process

1st pass

Cut edge and cross section of stacked CFRP/Ti sheets

2nd StepCutting of the metal (Al, Ti, steel) in a gas assisted fusion cutting process (single-pass)

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Cutting Holes for Inserts with Ultrafast Lasers Drilling contoured holes in preforms with ultra short pulsed lasers

- pulse duration ~ 7ps- average power up to 400 W, pulse energy up to 1 mJ

High quality: no fiber swelling or layer deformation

Process time longer than with fiber laser cutting (4s <-> 40s)

In combination with innovative fasteners increase in - breaking torque +15%- pull-out force +125%

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10 mm© Fraunhofer ILT

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Cutting Form Locking Contours

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Individual process steps for cutting each side for the butt joint

Multi material combinations possible

Fixing with cover plate in overlap joint by - adhesives- laser thermal direct joining- laser transmission joining

Thermoplastic FRP or

Metal

Thermoplastic FRP

Thermoplastic GFRP

Overlap joint area

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Multi Material JoiningMotivation

▪ Fast and cheap process

▪ Established in serial production

Holes destroy fibers and the strength of the composite

Additional weight of the fasteners

▪ Potential for a fast and reliable process

▪ High joint strength without additional materials

▪ Potential for serial production

Accessibility necessary

Only thermoplastics

▪ Broad range of adhesive for different applications

▪ Suitable for composites

Extensive surface pretreatment

Long process times

Additional material

Mechanical Joining Laser-based ApproachAdhesive Joining

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Hybrid Joining of FRP and MetalLaser-based Process Chain

Microstructuring of the metal surface to create undercuts and enlarge active surface

Heat conduction joining by irradiation of the metal surface and melting polymer through thermal contact

1. Metallic JoiningPartner

2. Laser Microstructuring of

the Surface

3. Thermal Contact ofthe Samples by

Applying Pressure5. Hybrid Connection

4. Joining by Heatingwith Laser Radiation

Metal Plastic

Laser BeamLaser Beam

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Laser MicrostructuringLine Structures with High Power Fiber Laser

Laser beam with high intensity (single mode)

Combination of sublimation and melting

Recoil pressure moves melt from the bottom to the side of the structure

Material recasts there

Repetitions create undercut structure

Short process times (~400 mm²/s)

N+1 Seite 12

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Thermal Direct Joining through Heat ConductionLaser Joining Process

Zoom

Optics

Joining

device

6-Axis-

Robot

Clamping

frame

Metal

specimen

Plastic

specimen

Lifting

Cylinder

Heat conduction joining with diode laser (Pmax = 3kW)

Beam delivery adapted to joining zone

Simultaneous joining e.g. zoom optics with adaptable rectangular spot

Continuous joining e.g. line optics with different line lengths

Clamping pressure to ensure thermal contact between joining partners

Other heating methods possible

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Hybrid-Joining of FRP and MetalLaser Joining Results

Material:

Tepex 102 RG600

laserstructured 1.4301

Results:

Increasing number of lines (structure density) Increasing shear strength

Structure pattern can be optimized regarding loads

Shear strength for crossed lines ~20 MPa

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ApplicationPM Join: Car door

Car door with GFRP reinforcement bar (DuPont)

Simulation of joint behavior and required transferred forces

Structure distance, structure orientation and incident angle of laser beam are adjusted for the joining zone

Achieved tensile shear strengths >20 N/mm²

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Other Joining ApproachesHybrid Injection Molding

Combination of laser microstructured metal inserts and injection molding for joining

Besides density and orientation of microstructures, joint strength strongly depending on process parameters for injection molding

Joint strengths > 22 MPa achieved

Collaboration with BARLOG GRUPPE

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New Laser Microstructuring ApproachSpongy Structures with Ultrafast Laser

Formation of Cone-like Protrusions (CLP) during ablation of metals at medium and high fluences (energy/area)

Dots and holes appear which grow to small clusters with increasing number of ablated layers (N)

Visually detected by blackening of the surface

Spongy structure characterized by

Random orientation

Microstructures with nano-substructures

Structure depth between 50-150 µm and width between 10-50 µm on steel

High process times

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Experimental Results Spongy StructuresShear Strength of PA6/GF47 with Steel

23,725,0

26,0

0

5

10

15

20

25

30

CR300LADCR210LAD

Sh

ear

stre

ng

th [

MP

a]

CR3DX54D

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Resulting shear strengths >25 MPa can be achieved which is higher than most adhesive joints or other laser-based approaches

Mechanical adhesion improved by increased specific adhesion

So far no industrial relevance due to high process times Deep drawing steel High strength steel

HyBriLight

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Summary and Outlook

High demand for reliable joining techniques for FRP and metal

Laser cutting allows edge preparation and contour cuts both in metal and FRP with one wear-free tool

Laser-based process chain enable reliable, adhesive-free joining of polymers and metals due to mechanical interlocking

Different microstructuring and joining approaches possible

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Acknowledgements: The PMJoin project has received funding from the European Community's Seventh Framework Program (FP7-NMP-2012-SMALL-6) under grant agreement no 309993.

The HyBriLight project is supported by the German Federal Ministry of Education and Research (BMBF) under the reference code 13N12718.

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Thank you for your Attention

Contact

Dr. Frank Schneider Macro Joining and CuttingFraunhofer-Institut für Lasertechnik (ILT) frank.schneider@ilt.fraunhofer.de