production of fuel cell components

PRODUCTION OF FUEL CELL COMPONENTS

Gerd KriegerManaging Director of the Fuel Cell Working [email protected]

VDMA

The German Mechanical EngineeringIndustry Association (VDMA) representsmore than 3200 companies in themechanical and plant engineering sector.The Fuel Cell Working Group supportsmore than 50 leading manufacturers andsuppliers of fuel cells in the expansion ofthe industrial network and in the politicalrepresentation of interests. To this end,technical solutions for the optimizationand cost reduction of fuel cell systemsand components as well as for theestablishment of series production arebeing developed in project groups.

PEM of RWTH Aachen University isconcerned with the production technologyof fuel cells. Within the mechanicalengineering sector, the field of activityranges from the cost-efficient productionof hydrogen-powered drive traincomponents to innovative mobilitysolutions and overall emission reduction.Through national and internationalprojects with small and large companies atdifferent stages of the value chain as wellas participation in various researchprojects, PEM offers extensive expertise.

Authors

VDMA Working Group Fuel Cells

PEM of RWTH Aachen University

Any questions?

Chair of Production Engineering of E-Mobility Components (PEM)RWTH Aachen UniversityBohr 1252072 Aachen www.pem.rwth-aachen.de

Philipp Reims, M. Sc.Research Associate Fuel [email protected]

Peter Ayvaz, M. Sc. M. Sc.Chief [email protected]

Christoph Schön, M. Sc. Group Lead Fuel [email protected]

Prof. Dr.-Ing. Achim KampkerInstitute [email protected]

Contact us!

Aachen, November 20201st Edition, Printed by

PEM of RWTH Aachen University and VDMA, ISBN: 978-3-947920-16-7

VDMA Working Group Fuel CellsFriedrichstraße 9510117 Berlin

bz.vdma.org

Overviewof PEM fuel cells

Technology developmentof PEM fuel cellsA widespread deployment of fuel cell technology requires product and processinnovations aimed at reducing production costs. This requires a scaling ofproduction volumes while at the same time meeting quality requirementsuniformly. PEM of RWTH Aachen University has set itself this goal and hastherefore identified the following research topics, among others:

Component production● Substitution of the decal process● Increasing the proportion of roll-to-roll

processes in productionStack production● High-speed stacking● Reduction of the stack activation time

Process Innovation (example)Component production● Development of bondable BPP● Construction of bondable "intermediate

plates" to increase product modularityStack production● Combination of membrane electrode

assembly (MEA) and bipolar half plates(BPHP) into one component

Product Innovation (example)

In this brochure, manufacturing of fuel cell components as part of theproduction process of polymer electrolyte membrane fuel cells (PEM fuel cells)is shown schematically.The fuel cell components bipolar plate, gas diffusion layer and catalyst coatedmembrane are manufactured using different materials through variousproduction processes. Based on the current state of the art, this brochureshows a possible production sequence for component production. It should benoted that the present selection serves as a basis for discussion within theindustry and that further process step configurations are conceivable - indeedeven desired. For this reason, to some extent, alternative manufacturingprocesses to produce fuel cell components are referred to in this brochure.Alternative process variants can be specified in more detail in joint discussionwith the PEM chair or the VDMA.

Fuel Cell System

Fuel Cell StackFuel Cell Components

Stack productionComponent production System production

Operating principleof PEM fuel cells

Fuel cell typesin comparison

Structural Setupe- Electrical

load

H2H2

H+e-

e-e- H+

e-

O2

H2OH2OH2H2 outlet O2 & H2O

outletO2

H2H2 inlet O2 O2 inlete-

O2

Bipolar half plate Gas diffusion layer Catalyst Membrane Gas diffusion layer Bipolar half plateCatalyst

2 H2 4 H+ + 4 e-Anode oxidation

O2 + 4 H+ + 4 e- 2 H2OCathode reduction

2 H2 + O2 2 H2OOverall reaction

The diagram shows an overview of different fuel cell types currently available inindustry and research, their reaction media and the usual operatingtemperature.

AFC Alkaline Fuel Cell

LT-PEMFC Low Temperature Polymer Electrolyte Membrane FC

HT-PEMFC High Temperature Polymer Electrolyte Membrane FC

DMFC Direct Methanol Fuel Cell

PAFC Phosphoric Acid Fuel Cell

MCFC Molten Carbonate Fuel Cell

SOFC Solid Oxide Fuel CellFuel cell type Anode in / out Cathode out / in

OH-

H+

H+

H+

H+

O2-

CO32-

Ion transport

air

O2CO2

H2O

H2O

H2O

H2O O2

O2

O2

O2

O2

O2

air

air

air

air

air

gaseous

gaseous

liquid

liquid

pure substance

COH2

CO2H2O

H2

H2

H2

H2

CH3OH CO2

H2O

natural gas

COH2 CO2

H2Onatural gas

Temp. [°C]

8090

0 65

022

090

160

Energy conversion from chemical to electrical energy within a PEM fuel cell isbased on the following operating principle:● Flow channels of the bipolar half plates (BPHP) are used to supply

hydrogen to the anode and oxygen to the cathode.● Via the gas diffusion layer (GDL), hydrogen diffuses to the anode side of the

catalyst coated membrane (CCM).● Hydrogen is catalytically oxidized, releasing electrons and forming H+-ions.,

H+-ions pass through the moist membrane to the cathode side. Electronsare conducted to the cathode side via an external circuit.

● Oxygen on the cathode side is reduced by the electrons and reacts with theH+-ions from the membrane to form H2O (water), which is purged.

StackStacking &

Preassembly Compressing Tensioning LeakageTesting Finalization Break-in &

Testing

Stack production:*

System production:*

Syste

m

Balance-of-Plant Assembly Electrical Integration End of Line-Testing

Component Production:

BPPCoating Forming Separating &

Cutting Joining LeakageTesting

Gasket application

Process step Intermediate product End product

MEAJoining &

Seperating

*Essential part of the brochure "Production of Fuel Cell Systems“

Production processof PEM fuel cell components

GDLChopping

Carbon FiberImpreg-nating Graphitizing Water-

proofingCC

MMixing Subgasketapplication

Hot Pressing &Decal Removing

Coating Decal &Drying

MPL application& Sintering

FormingCarbon Paper

● Due to the small production volumes of fuel cells, there is currently nogenerally valid process chain for the series production of PEM fuel cellcomponents.

● Production of a PEM fuel cell system can be divided into three superordinatesteps: component production, stack production and system production.

● This brochure presents the process steps that constitute the current state ofthe art in the production of PEM fuel cell components.

● Production of the fuel cell stack and system is explained in more detail in aseparate brochure entitled "Production of Fuel Cell Systems”.

Overviewof PEM fuel cell components

Catalyst coated membrane

Gas diffusion layer

Bipolar plate

● The bipolar plate (BPP) usuallyconsists of two bipolar half plates,which are formed, coated and joineddepending on the material (metal* orgraphite).

● Reaction media are transported viathe BPP and the reaction heat isremoved from the fuel cell.

● The BPP is electrically conductive andthus feeds the electrons into theconsumer circuit.

● The gas diffusion layer (GDL) consistsof carbon paper or nonwoven andhas a significant influence on theefficiency of the fuel cell.

● The GDL enables a uniformdistribution of the reaction media onthe catalyst layers of the anode andcathode side.

● The microporous layer (MPL)improves the regulation of the waterbalance at the electrodes.

● The polymer membrane coated withplatinum catalyst is called a catalystcoated membrane (CCM).

● There is one catalyst layer each onthe anode and cathode side. Thelayers differ in their chemicalcomposition and thickness.

● Hydrogen ion transport takes placevia the CCM, the catalyst layersenable oxidation or reduction.

Membrane

Catalyst coating

Microporous layer

Carbon paper or nonwoven

H2-supplyCoolant supply

Flow field (H2)

O2-, H2O-removal

Flow field (coolant)

Gasket

*Focus of this brochure

O2-supply

H2-removal

Sub-gasket

MixingCCM production

Catalyst powder:Platinum coated carbon substrate (approx. 15 wt%)Solvent:Deionised water (approx. 40 wt%) and e.g. methanol (approx. 40 wt%)Binder:ionomer solution (approx. 5 wt% )

Anode formula (example)

Catalyst powder:Platinum coated carbon substrate (approx. 20 wt%)Solvent:Deionised water (35 wt%) and e.g. methanol (35 wt%)Binder:ionomer solution (approx. 10 wt%)

Cathode formula (example)

Heat source

E.g. water, ionomer,

isopropanol

ω1

Dry catalyst powder(e.g. platinum,

carbon substrate)

ω2

● Through energy input, several separate starting materials are combined toform a catalyst ink by means of a rotating tool.

● The catalyst ink consists mainly of carbon substrate (e.g. Carbon black) andcatalyst material (e.g. platinum, platinum-ruthenium, platinum-cobalt). Forthe production of the catalyst ink, ionomer and solvent (e.g. water,isopropanol) are also required.

● Mixing of the catalyst ink for the anode layer and the cathode layer of theCCM takes place separately due to the different compositions.

• Porosity• Uniform loading of platinum• Viscosity

Quality criteria• Mixing duration• Mixing temperature• Mixing tool• Environmental conditions

Influences on quality

• Platinum load cathode: approx. 0.4 mg/cm²• Platinum load anode: approx. 0.1 mg/cm²• Atmosphere: contamination-free• Merging time: > 1 h• Merging temperature: 2 °C• Merging speed: 600 - 4000 rpm

Process parameters & requirements• Paddle mixer• Rotary ball mixer • Ultrasonic mixer

Alternative technologies


Intensive mixer with mixing tool

XRF IR/DC

Convection ovenDecal

Slot die

Pump

Catalyst ink

Catalyst layer

● The Decal Process is an indirect coating of the polymer membrane bymeans of a decal transfer carrier film, hereinafter referred to as 'decal'. Theprocess enables the application of a pre-dried coating onto the moisture-sensitive polymer membrane.

● The catalyst ink produced in the previous step is applied to the decal (e.g.polytetrafluoroethylene [PTFE], polypropylene [PP]) via a slot die.

● The coated decal is then transferred to a convection oven and dried.● After evaporation of the solvents, the decal is tested for homogeneity,

particle size and thickness of the catalyst layer. This can be done usinginfrared / direct current (IR/DC) and/or X-ray fluorescence (XRF) systems.

Coating Decal & Drying

• Layer homogeneity• Particle size• Layer thickness• Residual moisture after drying

Quality criteria• Viscosity of the catalyst ink• Application tool• Oven temperature


• Coating thickness (anode): 3 - 15 µm• Coating thickness (cathode): 10 - 30 µm• Path speed: 0,1 - 1 m/min • Drying time: approx. 4 min• Drying temperature: approx. 30 - 70 °C (air)

120 - 160 ° C (heated rolls)

Process parameters & requirements• Transfer Roller• Screen printing, inkjet printing, gravure

printing• Doctor blade• Infrared drying, laser drying• Extrusion



CCM production

Tempered rollers

F

F

CCM

Tempered top roller

Temperedbottom roller

Polymer membrane

Used cathode decal

(waste product)

Usedanode decal

(waste product)Catalyst coatedanode decal

Catalyst coated cathode decal

Catalyst layer

Hot pressing & decal removing


CCM production

● Transfer of the dry catalyst layer from the decal to the polymer membraneis realized by hot pressing. Since the productivity of this step dependslargely on the hot pressing method, a roll-to-roll process is suggested.

● Cathode and anode decal are fed simultaneously to the top and bottom ofthe polymer membrane and are placed between the pair of rollers.

● For good transferability of the catalyst layer, the tempered pair of rollers(100 - 170 °C) brings the polymer membrane to glass transition temperatureand generates a constant line pressure.

● Subsequently, cathode and anode decal are peeled off, analogous to theremoval of a sticker (decal), and are treated as waste.

● The CCM is finished and is wrapped up into a coil.

• Residue free decal• Non-destruction of catalyst layer and

polymer membrane• Uniform adhesion of the catalyst layer

Quality criteria• Decal quality• Combination of roller temperature, feed rate

and contact pressure• Duration of active force application


• Line force: 150 - 250 N/cm• Temperature: 100 - 170 °C

Process parameters & requirementsDirect membrane coating • Screen, inkjet or gravure printing, doctor

blade, additive layer productionIndirect membrane coating• Transfer roller• Coating of the GDL (GDE approach)


Compressive force

GDE approach:

GDL

Catalyst ink

Doctor blade tool● The catalyst ink is applied

directly to the GDL, a so-calledgas diffusion electrode (GDE) iscreated.

● The GDE is then applied to thetop and bottom sides of apolymer membrane andlaminated to form the MEA.

● The figure shows coating bydoctor blade, where thethickness of the catalyst ink canbe precisely adjusted.

Indirect coating by transfer roller:

C

Slot die

Polymer-membrane CCM

Coatedroller

● Catalyst ink is applied to ateflon coated intermediateelement (e.g. a roller) and(partially) dried.

● Following the example of hotpressing, the transfer takesplace on the underside of theintermediate element, wherethe polymer membrane isguided along.

● The intermediate element mustbe cleaned before it is coatedagain.

CCM direct coating:

Catalyst ink

Polymer membrane

Slot die● The polymer membrane is

coated on both sides in verticaldirection by means of slot dies.

● The vertical alignment enablesassembly space savings andcoating on both sides with thesame coating quality.

● Due to the high sensitivity ofthe polymer membrane tomoisture, crack and waveformation must becounteracted.

The previously shown decal method is considered one feasible option formembrane coating. Alternatively, the following procedures seem plausible:

Alternative catalyst applicationCoating concepts and research approaches

Subgasket application

Gasket material(top half)

Gasket material(lower half)


CCM production

• Precisely positioned gasket • No contamination on the MEA surface• Strength of the joint

Quality criteria• Axial, radial and angular offset of the rollers

in relation to each other• Position tolerance between gasket and CCM


• Feed rate: up to 30 m/min• Die roll geometry: product dependent• Contact pressure during joining process:

material dependent

Process parameters & requirements• Injection moulding of a frame gasket• Application of the sub-gasket by robot


CCM

= Counter roll= Die roll= Guiding roll= Laminating roll

= Vacuum die roll

Release film

Adhesive

CCM

Gasketlayer

CCM with gasket (sub-gasket)

Waste product

Waste product

Carrier material

Perforation

Waste product

Shown procedure is based loosely on patent US2011/0151350A1

● The upper half of the sub-gasket consisting of carrier material, adhesive,PET gasket layer and release film, is first perforated by means of a die rolland then excess release film is removed.

● From the supplied CCM, a vacuum die roll is used to separate material in adefined shape and staple it to the upper half of the gasket.

● The lower half of the gasket, consisting only of a carrier material and PETgasket layer, is also first perforated and pressed onto the underside of theCCM material by a laminating roll.

● At the same time, the perforated part of the upper carrier material togetherwith the release film is removed and disposed.

● Finally, the perforated part of the lower carrier material is removed.

Chopping carbon fiberPress roll

Blade roller

Crushed carbon fibers

Cutting head


GDL production

● As an initial step for GDL production, dry carbon fibers are chopped.● The fiber strand is guided over a steel roll with polymer teeth (blue) and

held in position by a press roller.● The cutting heads of the rotating blade roller apply pressure to the fiber

strand in transverse direction and cause the fiber filaments to break untilthe fiber is completely cut through. Polymer teeth filled with air (orange)silently expel the cut fibers.

● The rotary cutting tool is able to work at high speed. The cutting head weartypical of the process is minimized by cutting "into the void".

● The 6 - 12 mm large fibers are collected in a collecting container and usedfor the subsequent carbon paper production.

• Particle shape• Surface morphology

Quality criteria• Sharpness of the cutting heads• Shape of the cutting heads• Material of the cutting heads


• Cutting rate: 9 m/min• Particle size: 6 - 12 mm• Contact pressure of the press roll: 0,1 MPa

Process parameters & requirements• Guillotine cuttingAlternative technologies

Carbon fiber

Steel roll Polymer tooth filled with air

Polymer tooth

Calendering zone(optional)

Forming carbon paper

Heated roll

Pressing zone Drying zone

Flow box

Wet non-woven fabric

(„paper“)

Wastewater


GDL production

• Uniform material thickness• Smoothness of the material• Wet strength of the paper• Damage-free surface

Quality criteria• Water content of the suspension• Gap or force measurement during

calendering• Quality of the fiber dispersion• Homogeneous binder distribution• Web tension


• Productivity: 300 - 320 m²/h• Specific weight: 15 - 70 g/m²• Material thickness: 150 - 300 µm• Binder content: < 25 %

Process parameters & requirements• Spunlace nonwoven fabric production• Fabric production


● Cut carbon fibers are processed together with a binder polymer inside a so-called “Flowbox" to form a suspension and are uniformly applied to aninclined screen.

● The inclined screen is covered with plastic fabric and allows water to drainoff but retains the carbon fibers.

● During the subsequent pressing process, the solids content of the papersuspension is increased by further removal of water, resulting in wetnonwoven fabric ("paper").

● While maintaining the sheet structure, the volume of the paper is reducedin the drying unit and the binder is hardened.

● Optionally, the surface structure is determined by calendering. Cooledrollers compress the carbon paper and remove the last fibers and spongestructures.

Carbon fiber suspension

Inclined screen

Press roll

Distribution zone

Mass sensor

Carbonpaper

Impregnating


GDL production

● Carbon paper is impregnated with a thermosetting resin (e.g. phenolicresin), so that a desired material strength and porosity are achieved. Inaddition, the electrical and thermal conductivity are increased after passingthrough the graphitization process.

● After passing through the impregnating bath, excess liquid is removed by apressing process.

● Remaining solvents are evaporated inside a convection oven at approx.150 °C and the resin is cured.

● As an alternative to the continuous process, the carbon paper is separatedafter drying, alternately stacked with separator paper at elevatedtemperature and then pressed.

• Material thickness• Material density

Quality criteria• Composition of the impregnation material• Drying temperature• Drying duration


• Drying temperature: 150 °C• Material thickness: 200 - 270 µm

Process parameters & requirements• Infrared drying• Stacking with separator paper


OutputImpregnated carbon

paper(< 270 µm)

Convection oven

Carbon paper

Impregnating bath

Pressing processExcess liquid

Idler pulley

Graphitizing


GDL production

● Graphitization (also high-temperature carbonization) of the thermosettingresin leads to a higher modulus of elasticity, increased electrical andthermal conductivity and oxidative resistance.

● The carbon paper is heated in a furnace under inert gas atmosphere(nitrogen, argon) or in vacuum to temperatures of approx. 1400 -2000 °C (more than 2000 °C in the batch process).

● The reel material passes through different temperature zones within theheating zone and is finally cooled down to room temperature in a coolingzone.

● The final product has a material thickness of 150 to 300 µm.

• Degree of pyrolysis of the resin > 99,5%.• Deposit-free product• Conductivity of the material• Carbon content

Quality criteria• Temperature profile• Low temperature carbonization gas routing

(removal of the pyrolysis products)• Inerting the furnace


• Process temperature: 1400 - 2500 °C• Material thickness: 150 - 300 µm• Density of the paper: 0,2 - 0,3 g/cm³.• Process duration < 5 min (< 15 min for

batch process)• Vacuum or inert gas atmosphere

Process parameters & requirements• Graphitizing under inert gas atmosphere• Batch carbonization under vacuum or inert

gas


Water cooling

Nitrogen removalNitrogen injection

Heating zone

Nitrogen atmosphereCooling zone

Impregnated carbon paper

Lock

Lock

GDLsubstrate

Waterproofing


GDL production

● The GDL substrate is dipped into an aqueous polytetrafluoroethylene (PTFE)suspension, whereby excess suspension is removed by a pressing process.This process helps to improve the hydrophobic properties.

● The PTFE content of the later GDL is adjusted by the amount of PTFE in thesuspension.

● Remaining solvents are removed by oven drying and the PTFE particles arebound to the base material by sintering at approx. 300 °C - 350 °C.

● The speed of the drying process influences the PTFE distribution in thematerial. Due to fast drying, the PTFE remains in surface zones, while slowdrying ensures an integral distribution.

• Homogeneous PTFE distributionQuality criteria

• Composition of the impregnation material• Drying temperature• Drying duration


• Drying temperature: 300 °C - 350 °C• PTFE mass fraction: 5 - 10 wt%• Paper thickness: 200 - 270 µm• Alternative material: fluoroethylene-

propylene (FEP)

Process parameters & requirements• Infrared drying• Air drying• Spraying• Brush application


Convection oven

Graphitized carbon paper

Aqueous PTFE suspension Pressing processExcess liquid

Deflection roller

OutputHydrophobic carbon

paper(< 270 µm)


● The microporous layer (MPL), consisting of carbon or graphite particles andpolymeric binder (e.g. PTFE), has a pore size between 100 and 500 nm,whereas the carbon paper has a pore size of 10 - 30 µm.

● The primary function of the MPL is water management, as it effectivelyremoves liquid water from the catalyst layers.

● Here, the MPL is applied to the carbon paper with a layer thickness of lessthan 50 µm using a doctor blade method.

● To reduce crack formation, the solvent is slowly evaporated. Sinteringallows sufficient adhesion of the MPL.

● Finally, the material is trimmed, checked for quality defects and marked.Wrapping up is carried out with the aid of release film.

• Adhesion of the MPL to carbon paper• No exceeding of the melting point• Damage-free MPL surface• Smoothness

Quality criteria• Sintering time• Temperature profile during sintering• MPL material


• Pore size: 100 - 500 nm• Layer thickness: < 50 µm• Duration of the sintering process: < 10 min• Sintering temperature: approx. 300 - 350 °C

Process parameters & requirements• Slot die coating• Screen printing• Spray application


MPL application & sinteringGDL production

Preheating(250 °C)

Sintering(350 °C)

Convection oven

Doctor bladeMPL material

Release filmCutting toollengthwise

Markers (ink)

Camerasystem

Quality assurance

GDL

F

F

Joining & separating

GDL


MEA production

● The CCM is connected to the GDL on both sides and then separated. AMEA with gasket is formed.

● Adhesive is applied on the GDL, which is perforated according to the givengeometry.

● The perforated GDL is stapled to the top and bottom of the MEA withgasket.

● Joining is then carried out by means of hot pressing.● The process step is completed with the separation. At this point, in addition

to crosswise separation, lengthwise separation is also possible, dependingon the product and process design.

● Since the MEA is the "less accurate" component compared to the bipolarplate, it requires special attention in tolerance management.

• Position accuracy of the GDL• Strength of the joint connection• Dimensional accuracy of the cutting

geometry

Quality criteria• Axial, radial and angular offset of the rolls• Combination of roller temperature, feed rate

and contact pressure• Duration of active force application


• Hot pressing temperature: 100 - 160 °C• Contact pressure: 1.000 - 10.000 kg/cm²

Process parameters & requirements• Discontinuous hot pressing process• Additive layer production


Cutting toolcrosswise

ConveyorbeltCutting tool

lenthgwise (optional)

MEA

Adhesive

= Counter roll= Die= Guiding roll

Waste product

Tempered top roller

Temperedbottom roller Compressive

force

Top viewGDL

CCM with subgasket

Shown is a procedure based on the patent US2011/0151350A1

Coating

NN

SS N

S

Vacuum pump

sN

Plasma

Substrate heater

Atom

Magnet

Target (e.g. gold, titanium,

aluminium)

Ion

X-ray testing device

X-rays

Ar

Aspiration

mm

Raw material

BPHP


BPP production

● Coating of the raw material for the bipolar half plates is carried out usingPhysical Vapour Deposition (PVD).

● First, the surface of the raw material is cleaned from both sides and itsquality is checked.

● The raw material is positioned inside a vacuum chamber filled with inert gas(e.g. argon), the inert gas is ionized and forms a plasma.

● The target (coating material, e.g. gold, titanium, aluminum) is bombardedwith ions formed by the plasma. Atoms of the target dissolve, move to thesubstrate (here the raw material) and diffuse into its surface.

● After the coated raw material leaves the vacuum chamber, its layerthickness can be measured using X-rays.

• Electrical conductivity• Corrosion resistance

Quality criteria• Inert gas• Coating material• Substrate shape


• Temperature: 450 - 500 °C• Vacuum pressure: 1x10-1 - 1x10-7 mbar• Layer thickness: 0,1 – 6,3 µm• Cycle time: approx. 2 - 5 min

Process parameters & requirements• Alternative coating materials: titanium

nitride, chrome nitride, amorphous carbon• Chemical Vapour Deposition (CVD)• Nitriding• Electroplating


Coated raw material

Output

Cleaning device

Quality control

● The (coated) raw material for the bipolar half plate (e.g. 1.4301, 1.4404) isuncoiled from a coil, fed into the hydroforming system and positionedunder the moulding tool.

● By lowering the upper die, a contact pressure (also clamping force) isapplied to the material, moulding tool and lower die.

● Afterwards, water is brought under high pressure by means of a pressureintensifier and passed through the perforated plate. This leads -predetermined by the design of the moulding tool - to plastic deformationof the material and thus to the formation of the part geometry.

● Several part geometries can be formed simultaneously to increase theoutput rate.

● A final cleaning process cleans the formed material of residues.

Forming


BPP production

• Freedom from breakage and damage• Uniform flow field structure• High repetition accuracy• Very low springback

Quality criteria• Forming pressure• Clamping force• Forming properties of the base material• Part geometry• Machine stiffness


• Forming pressure: 1.000 - 4.000 bar• Process time: approx. 2 - 10 sec. per plate • Working medium: water• Possible material thickness: 0,05 - 1 mm

Process parameters & requirements• Stamping• Deep drawing• Injection moulding• Embossing• Rubber pad pressing• Roll-to-roll moulding


Pressure intensifier

Geometry of the bipolar half plate

Output

(Coated) raw material

Bipolar half plate with part geometry

Water

Upper die

Perforated plate

Moulding tool

Bipolar-half plate

NozzleLaser beam

Separating & cutting

Component production

Conveyor belt Bipolar half plate

(BPHP).

Cuttinghead


BPP production

● The bipolar half plates are separated and brought into the desired contourby laser cutting.

● Inside the cutting head, the laser beam is focused through a lens andprojected onto the metal sheet. The high energy input leads to a separationof the material.

● The cutting optics are mounted on a so-called XY-portal and allow thecutting head to move precisely within a specified range.

● Coated and uncoated materials can be processed.

• Burr-free edges• No impairment of the coating• Warp-free cut

Quality criteria• Type of laser• Cutting speed• Focusing• Process related contaminations


• Working range: 500 - 1.500 mm• Laser output power: 500 – 2.000 W• Feed rate: 20 - max. 300 m/min with

0,2 mm wall thickness• Accuracy: 10 - 50 µm

Process parameters & requirements• Stamping• Fineblanking, shearing• Remote laser cutting


Bipolar half plate(BPHP).

Output

Joining

High resolutioncamera

Weld points


BPP production

● In the joining process two bipolar half plates are welded together to form abipolar plate.

● A focused laser beam and the resulting high energy input into the metalsurface heats the metal to melting temperature and creates a material joint.

● In order to avoid oxidation, the welding process is carried out in an inertgas atmosphere.

● For process monitoring and quality assurance, the welding process can berecorded and evaluated using sensors.

• Component warping• Strength of the weld points• Media-tight welding• No traces of powder

Quality criteria• Positioning and tensioning of the bipolar

half plates• Size of the heat-affected zone• Process temperature in the weld points• Wavelength of the laser beam• Type of inert gas


• Cycle time: 10 - 120 sec.• Feed rate: < 60 m/min• Laser power: approx. 500 - 1000 W• Wall thickness material: approx. 100 - 250

µm

Process parameters & requirements• Adhesive bonding technology• Brazing• Additive manufacturing


Output

Bipolar half plates

Inert gas nozzle

Laser beam

Bipolar plate(BPP)

Remote scannerArm robot apparatus

Laser

Leakage testing

Component production

Nozzle

Vacuum chamber (for vacuum test)

Leak detector

Test medium (e.g. air, helium)


BPP production

• No deformation or destruction of the bipolar plate

• Leak tightness of the bipolar plate

Quality criteria• Test pressure• Accuracy of the leak detector• Geometry of the combustion gas ducts


• Test pressure: approx. 1 – 1,5 bar• Cycle time: approx. 20 - 60 sec.• Test sensitivity: 3x10-2 mbarl/s (air)

2x10-6 mbarl/s (helium)• Test gas: air, helium, nitrogen, hydrogen

Process parameters & requirements• Flow test• Ultrasonic detection• Outside-in procedure


● Finally, the bipolar plates are checked for leaks.● In the vacuum test, these are placed inside a vacuum chamber, filled with a

test medium (e.g. helium) and its partial pressure is measured.● At increased test medium partial pressure in the chamber, leaks of the

bipolar plates can be identified with a mass spectrometer leak detector(MSLD). This method can be used for more stringent test specifications.

● In the pressure drop test, air as a testmedium is fed into the test object andleaks are detected by a drop in air pressure in the system.

● The basic conditions for passing the leakage test shall be determined by themanufacturer. After passing the leakage test the production of the bipolarplate is finished.

Bipolarplate

End plates

Gasket applicationStencil carrierImage area

Barrier layer

Screen framesAutomatic valves

Doctor blade

Bipolar half plate

Hydraulicarm

Printed gasket

Fibers

Bipolar half plate

Image position

Gasket material


BPP production

• Position accuracy of the gasket • Uniform gasket

Quality criteria• Process speed• Distance between the fibers of the stencil

carrier• Dosing quantity


• Cycle time: < 3 sec.• Wall thickness gasket: 0,3 – 0,5 mm• Doctor blade speed: 50 mm/s

Process parameters & requirements• Dispensing• Formed-in-Place-Foam-Gasket (FIPFG)• Insert moulding• Stamping


● The BPP gaskets are applied to the bipolar plate by screen printing.● The gasket material is applied to the stencil carrier via a nozzle and pressed

through the image areas by the movement of the doctor blade.● While the barrier layers cannot transfer gasket material to the bipolar plate,

the image areas of the stencil carrier are permeable. These zones areindividually adjustable.

● The bipolar plate is brought into close proximity of the stencil carrier bymeans of a hydraulic arm, so that a perfect application of the gasket ispossible.

● The doctor blade conveys the unecessary printing substance to the edge ofthe printing plate which is used for the next printing process.

OutputCoated bipolar

plate with gasket

production of fuel cell components

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