Laser Welding of Transparent Plastics Clear-To-Clear Polymer Bonding with High-Wavelength Lasers

Live!

Shane Stafford Market development representative, LPKF Laser & Electronics North America

Josh Brown Laser plastic welding sales associate, LPKF Laser & Electronics North America

Dr. Tony Hoult West coast general manager, IPG Photonics

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1. What is LWTP?

2. How it works

3. Industries

4. Materials

5. Applications

6. Equipment

Laser Welding of Transparent Plastics

• Polymer bonding with laser energy • Clear-to-clear bonding (also translucent/natural polymers) • Requires no special additives or absorbers • AKA - 2µm welding (2 micron)

Through-transmission Laser Laser Welding of Welding Transparent Plastics (TTLW) (LWTP)

800nm – 1064nm wavelengths 1500nm – 2000nm wavelengths

Requires NO absorbers, can Absorbing layer required bond clear/natural/translucent thermoplastics

• Changes in laser wavelength affect transmission/absorption in thermoplastics Natural polycarbonate

Goldilocks' Zone

X-axis – wavelength in nanometers Y-axis – % of laser radiation transmitted by PC

Near 100% transmission Partial, natural absorption

Goldilocks' Zone • Right balance of transmission and absorption

Volumetric Heating • Laser passes through all pieces, but enough energy is absorbed in each to create melt

“Lens” Effect • Majority of energy tends to stay at interface

• Laser beam with a wavelength >1500 nm • 2 or more clear/natural/translucent thermoplastics • Clamping force • Material compatibility (i.e. similar melt temp, surface energy and chemical makeup)

Clamping force Clamping force

Transparent plastic Weld zone

material fusion Transparent plastic

Workpiece carrier

Laser Motion Control

• Beam controlled by galvo-scanning mirrors, traces joint pattern • Typical travel speeds 20 – 80mm/s, usually a single pass

LWTP Specific Advantages • No absorbers! • New possibilities for laser entry/joint designs • Great for films and multilayer applications

Laser welding v. other joining methods (i.e. gluing, ultrasonic, vibration) • Particulate free – cleanroom rated process up to class 5 • Localized heat • No mechanical stress • Hermetic seals • High strength bonds • Excellent repeatability/low maintenance - excellent for high-volume production • Flexible process • Low scrap/reject rates

Disadvantages of absorbers

• High cost • Even “optically clear” absorbers have some color effect • Difficult/costly to apply • Disadvantageous for approval procedures (e.g. FDA-certification)

Medical • Microfluidics and lab-on-a-chip • Catheters/tubing • Bags and connectors

Biotech • Cell culture flasks/cases

Consumer - broad • Design elements and aesthetics

Rigid • Polycarbonate • PMMA (acrylic) • PS • COP/COC • PEEK

Flexible • TPU/TPE • PET • PVC

Welding of 2 PMMA-foils (thickness 250 µm)

0,4 mm

0,25 mm

1 mm Scale-up of weld seam

Quadratic weld seam Weld zone PMMA-foil PMMA-foil

Welding multiple foil-layers

5 mm

Four layers of a PU-foil Weld zone 4 PU-foils

Welding one PC-foil between two PMMA-sheets

PMMA-sheet (0,8 mm)

0,9 mm

PC-sheet (0,1 mm)

1,5 mm

Scale-up of weld seam PMMA-sheet (1,0 mm)

5 mm Weld zone Example of a weld contour PMMA-sheet PC foil PMMA-sheet

COC-Foil (150 µm) on a microfluidic-sheet (COC)

Microfluidic channels

Weld seam embed channel

1 mm

Weld seam in a microfluidic channel system Weld zone

COC foil COC-microfluidic

Plane welding of a foil on a microfluidic-sheet (thickness 1,0 mm)

Unharmed channel boarders

2,5 mm

Plane welding 2,5 mm

Scale-up of weld area

Two translucent PC-sheets (thickness 1 mm)

10 mm

Weld contour: LPKF-logo (width of weld seam: 0,6 mm) Weld zone

PC-sheet PC-sheet

Two super-transparent PC-sheets (thickness 1 mm)

10 mm

Weld contour: LPKF-logo (width of weld seam: 1 mm) Weld zone PC-sheet PC-sheet

Appearance of fracture of two transparent PC-sheets

Material break-out

3 mm MaterialWeld zone break -out PC-sheet Appearance of fracture (welding of two transparent PC-sheets) PC-sheet

• Clear PC welded to an optically opaque, yet laser transmissive black dyed PC • Laser could theoretically enter from either side as both parts are transmissive to the laser

New approach: • Long wavelength approach produces volumetric absorption of the laser beam • More recognizably a welding process • Enables butt welds or lap welds • Obeys Beer-Lambert absorption law

22 layers of 0.1 mm thick LDPE

26 26 Micro-welding polymers with 2um lasers

Figure 1. 1” PMMA discs PMMA (acrylic) welding • volumetric absorption • no absorption enhancers • no material modification Test results: • 3 mm thick samples, fig. 1 • Melt features on surface • 30W, 100 mm/s speed • 163 mm scan lens Figure 2. • Films can be welded onto PMMA surface

27 27 Polymer Joining Example

Welded Tritan® co-polyester containers Weld line, 3 pass Weld line, single pass

0.8 mm thick flexible TPU Range of fibers can be incorporated into film

28 Weld widths and joints

Beam spot size = joint width • Can vary from <100µm to 3mm • Depends on optics set and focal depth

Joint Types

Lap Joint T Joint Butt Joint

29 Clamping – Glass Plate

• Clamping force ensure contact between parts • Workpiece carrier provides support along entire joint • Glass clamp plate – must be glass, not acrylic (acrylic will absorb laser)

Glass Clamp Plate

Workpiece carrier

• All metal tooling provides support as close to joint as possible without blocking beam

Workpiece carrier

Details • Not “fiber delivered” - fiber lasers use actual optical fiber as the lasing chamber rather than a gas or crystal • 120 watt – average power, scalable in future • CW – continuous wave • Can create very small beam spot profiles < 100 µm

Diode Lasers – also available in >1500nm wavelengths • Requires special wafers to reach higher wavelengths, can be expensive • Wattages tend to be lower than fiber lasers • Shorter focal length lenses required

Easily integrated into existing standard laser welding systems, requires only a different laser source, usually a fiber laser at 1940nm.

Automation Stand-alone Systems for Automated Integrated Systems Cells or Manual Loading

• Laser welding is a particulate free process making it ideal for cleanrooms • LPKF application center cleanroom is rated at ISO Class 5

LPKF Laser & Electronics · 12555 SW Leveton, Tualatin, OR 97062 Josh Brown – 503.454.4231, [email protected] – www.lpkfusa.com

Submit questions via… • Your GoTo Webinar panel • Twitter • #LPKF • @LPKF_USA