Lasers for low stress, hermetic welding that maintains the ... 30 April 2008.pdf · Title:...

Copyright GENTEX® Corporation 2008

Lasers for low stress, hermetic welding that

maintains the integrity of fluid path channels

for fuel cells and batteries

Gareth McGrath

www.clearweld.com

Lasers in emerging energy marketsMIWL

30th April 2008


Advanced Energy Solutions

The biggest problems facing power utilities worldwide are blackouts, brownouts and the huge capital investments required in upgrading the transmission and distribution networks to deliver the increasing demand for energy.Fuel cells - batteries

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Fuel Cells vs. Batteries

A fuel cell is an electrochemical energy conversion device. It produces electricity from external fuel (on the anode side) and an oxidant (on the cathode side). These react in the presence of an electrolyte. The reactants flow in and reaction products flow out, while the electrolyte remains in the cell. Fuel cells can run almost constantly as long as the flows are maintained.

Fuel cells are different from batteries in that they consume reactant, which must be replenished, whereas batteries store electrical energy chemically in a closed system. Additionally, while the electrodes within a battery react &change as a batteryis charged or discharged, a fuel cell's electrodes are catalytic and relatively stable.

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Flow Batteries

A flow battery is a form of rechargeable battery in which electrolyte containing one or more dissolved electroactive species flows through a power cell / reactor that converts chemical energy to electricity. Additional electrolyte is stored externally, and is usually pumped through the cell (or cells) of the reactor. Flow batteries can be rapidly "recharged" by replacing the electrolyte liquid (in a similar way to refillingfuel tanks for internal combustion engines)while simultaneously recovering the spent material for re-energization

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The Zinc/Bromine Battery

The zinc/bromine battery is very different in concept and designfrom more traditional batteries such as the lead/acid battery. The battery is based on the reaction between two commonly available chemicals, zinc and bromine

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The Stack Assembly

The bromine storage medium is immiscible with an aqueous solution containing zinc bromide.

All battery components are made from a bromine inert plastic

www.clearweld.comCourtesy ZBB


Fuel Cells

The alkaline fuel cell (AFC), also known as the Bacon fuel cell after its British inventor, is one of the most developed fuel cell technologies and is the cell that flew Man to the Moon. NASA has used alkaline fuel cells since the mid-1960s, in Apollo-series missions and on the Space Shuttle.

AFCs consume hydrogen and pure oxygen producing potable water, heat, and electricity. They are among the most efficient fuel cells, having the potential to reach 70%.

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Neah Power Systems

• Neah Power part ,showing the results of micro-fluidic DOE. The photo is of a two part weld consisting of a thick base part and a much thinner middle layer. To complete the unit a third thick part is welded to the middle layer, which is not shown here. The photo is a depiction of the channel integrity.

• Neah’s unique Si electrode architecture allows for industry leading power density and operation in a non air-breathing environment.”

Courtesy Neah Power Systems


Advantages of Laser Welding

• High Strengths

• Repeatable and Consistent

• Hermetic Seal

• No Particulates

• Low or No Flash

• Low Residual Stress

• Color Flexibility (in some cases)

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Critical Factors

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Substrate Materials

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Substrate Materials• Top substrate must be transmissive at the laser

wavelength, while the bottom substrate must absorb the laser either throughout the bulk of the material or at the surface only

• Most thermoplastics are highly transmissive from approximately 700nm to 2000nm– NIR lasers pass efficiently with little or no heat

generated– To utilize laser welding one substrate has to be

altered to absorb the laser energy

• Must be in contact and miscible when heated• Must have similar or overlapping melting

ranges and be chemically compatible

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Laser AbsorberSomething is needed in or on the bottom substrate to harness the laser energy and make the plastic laser weldable

• Carbon can be used for black and dark opaque parts

• Other organic additives can be used to increase color flexibility

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Laser Absorber• Gentex® developed a method to increase color

flexibility

• Complex organic additives are used to absorb laser light, two product forms: 1. Coating—additive is dissolved in a solvent,

which absorb between 940-1100nm2. Resin—additive is dissolved/dispersed

throughout and absorbs between 800-1100nm

• Absorb only at targeted NIR wavelength ranges to weld efficiently while reducing color in the visible range

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Joint/Part Design

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Joint/Part DesignSurface Quality…

• Clean surfaces at interface and any area exposed to the laser (top surface of transmitting substrate) to prevent marking or burning the surfaces

• Smooth surfaces preferred

– Matte surfaces can be welded but the surface irregularity may result in reduced strength

• Parallel surfaces to ensure complete contact

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Surface Flatness…

The fit between the two substrates to be joined may be important depending on:

• Substrate polymer and grade—melt flow

• Amount of clamping pressure that can be applied

• Weld parameters—for example, higher power may cause more material to melt

• Laser configuration—welding simultaneously can overcome some tolerance issues

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Joint/Part Design


Fixturing/Clamping

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Factors affecting clamping pressure:• Materials to be welded – for example, melt flow

varies from plastic to plastic, and grade to grade• Thickness of substrates – thin substrates are

more flexible, therefore require less pressure• Surface finish• Parallelism between substrates• Strength requirements• Welding parameters • Laser configuration• Joint design

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Fixturing/Clamping


Experience and Know-how

Experience and know-how help avoid “reinventing the wheel” and bring an application to fruition in a short period of time, as shown at Barkston Plastics

www.clearweld.comCourtesy TWI


Sliding Clamp

Courtesy TWI www.clearweld.com


Laser Technology

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Laser - Single Beam

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Laser - Quasi-simultaneous

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Laser - Simultaneous

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Laser - Curtain

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Parameter Selection

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Parameter Selection

Weld parameters:• Laser power• Weld speed (time)• Beam size• Clamping Pressure• Absorber concentration

Energy Density

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Multi-Axis System Barkston Plastics

Courtesy TWI


Conclusion• There are many benefits to using laser

welding; however there are critical factors that must be tied together properly in order to achieve these benefits.

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Critical Factors for Laser Welding

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