Fuel Cell Stack Frames CNC Machining for Hydrogen Energy

Because it has great corrosion resistance and it keeps its mechanical properties between 60 and 90 degrees centigrade, stainless steel 316L has been preferred in fuel cells. Having reasonable corrosion resistance for structural components and avoiding hydrogen embrittlement for 1 to 3 bar hydrogen in 5,000 to 10,000 hour lifetime, pH 2 to 4 stack operation for between 60 and 90 degrees centigrade saves considerable weight in automotive applications (20 to 40 percent) when system power density is critical (1.5 to 3 kW/kg). Also, it has good biocompatibility for medical devices. Fuel cell applications.
Aluminum 6061-T6 Type III hard anodizing 25–75 microns thickness within anodizing range, exceptionally good thermal 167 watts per meter Kelvin, still good for heat spreading in end plates. Low density 2.7 grams per cubic centimeter reduces stack mass by 60 percent compared to steel. Adequate strength with aluminum compression anodized yield strength 276 megapascals supporting strength loads. Also, there is electrical insulation resistance above 1000 megohms per square centimeter, preventing parasitic counter current paths. The anodized aluminum oxide layer. Corrode the base material under acid condensate.

5-axis CNC machining centers generate end plates during Flatness ± 0.003 inches over a 300 to 600 mm sq active areas using precision face milling multiple shallow depth cuts 0.1 to 0.3 mm are made and high stiffness fixturing is used to reduce workpiece deflection, then made manifold port features positions ±0.005 inches for alignment with bipolar plate channels, and made tie rod holes patterns with perpendicularity 0.010 mm to ensure equal clamping force distribution over parallel clamping zones. Decks of which are made with full CNC integration with flatness of 0.002 inches and surface finishes of 0.4 to 0.8 suspected microns worked to ensure even gasket compression needed for high integrity of hydrogen and air seals, ≤ 5 standard cubic centimeters per minute leakage at differential pressure of 3 bars per SAE J2578 during leak testing. For the CNC stack surface, ports are 10 to 35 mm pd cut and 0.005 pd and 0.010 mm perpendicular to the stack surface to ensure proper sealing with an O-ring or gasket, and tie rod holes are 8 to 16 mm dd with positional accuracy ±0.010 inches for blind assembly without thread damage.
Wire EDM makes complicated coolant channel patterns in end plates where the channel widths are 3 to 8 millimeters. The end plates have a surface finish from 1.6 to 3.2 microns. CNC tapping is done to make the M6 to M12 threaded holes, which are used for compression bolting. These have a thread class 6H tolerance. Gold plating or graphite coating is done to the current collectors, which are 0.5 to 2 microns thick, and reduces contact resistance to 5 to 10 milliohms per square centimeter. Stainless steel is passivated with the ASTM A967 standard or undergoes nitric acid treatment, which forms a stable chromium oxide layer. A 20 to 50 micron thick epoxy or phenolic resin is layered on the non-contact surfaces to prevent metallic ion contamination of the membrane electrode assemblies.

For frames, we accomplish sealing surfaces with a flatness tolerance of 0.002 inches for surfaces between 300 mm and 600 mm and maintain uniform gasket compression between 0.2 mm and 0.5 mm and leak rates below 5 standard cubic centimeters per minute per SAE J2578 for fuel cell testing standards, leak rate manifold ports and position accuracy of ±0.005 inches for alignment with bipolar plate or gas diffusion layer flow field patterns and keeping flow distribution uniformity ±10 percent within the active area, port diameter within ±0.005 inches for O-ring grooves of 10 to 35 mm diameter and ensuring a 15 to 25 percent squeeze and preventing extrusion during 1 to 3 bar pressure cycling, position of tie-rod holes within ±0.010 inches across a bolt circle diameter of 250 to 550 mm, enabling blind assembly and stack compression of 20 to 100 kN avoiding binding during compression, perpendicularity between sealing surfaces and tie-rod holes of 0.010 mm, maintaining parallel plate alignment within 0.05 mm across a stack of 200 to 800 mm in height containing 100 to 400 cells, and sealing surface finishes of Ra 0.4 to 0.8 microns for minimizing leak paths and obtaining stable contact resistance of 10 to 30 milliohms per cm2 on current collector interfaces.
Critical compression surfaces, which are responsible for the flatness of the membrane assembly, are flat within 0.001 inches over local areas from 50 to 100 millimeters square. This prevents over-compression from non-uniform assembly pressure.

Yes. Zintilon gives quick prototyping for 2 to 10 functional stack frame sets sent to you in 3 to 5 weeks. This includes single-cell and short-stack testing for validation of the stack frames. They also perform electrochemical leak testing, and, per SAE J2578, compression testing, and uniform load distribution analysis. Zintilon does low-volume production of 50 to 500 frame sets for pilot fuel cell vehicle programs and demonstration systems with first article inspection and material traceability. They perform high-volume production for commercial fuel cell vehicles with automated machining cells and real-time statistical process control that achieves process capability indices Cpk greater than 1.67 for critical flatness and sealing dimensions.
In each stage of production, we do full validation including inspections using coordinate measuring machines, touch-trigger, and scanning probes for measuring flatness deviation maps for the entire surfaces, leak testing helium mass spectrometry detecting leak rates up to 1×10⁻⁶ standard cubic centimeters per second, measuring contact resistance on the surfaces of current collectors at several points for uniformity where 5 to 15 milliohms per square centimeter supports uniformity, certification of materials for alloys with specific documented mechanical properties, and alloy composition and mechanical property documentation, and corrosion testing including potentiostatic holds at 0.6 volts versus standard hydrogen electrode in 0.5 molar sulfuric acid at 80 degrees measuring corrosion current of 1 mic amp per square centimeter per DOE technical targets for 5,000 hour endurance in automotive duty cycles at 80 degrees with sulfuric acid to meet the 5,000 hour corrosion performance target of automotive duty cycles.

There is complete traceability regarding the materials; each fuel cell stack frame is constructed under the ISO 9001:2015 quality management system, verified for dimensions, and validated according to functional specifications. Each component is compliant with the fuel cell component testing standards stated in the SAE J2578 technical information report including leak testing and the specifications of leak rates of 5 to 20 standard cubic centimeters per minute under a differential pressure of 1 to 3 bar, the SAE J2579 technical information report on fuel systems in fuel cell and hydrogen vehicles which covers material compatibility with hydrogen gas up to 70 megapascals and water, ISO 14687 criteria concerning hydrogen fuel quality specifications for fuel cell applications which mandates at least 99.97 % hydrogen and impurity levels that do not poison the catalyst and degrade the membrane, UN ECE R134 uniform provisions concerning hydrogen and fuel cell vehicles that cover the safety of hydrogen systems, and the DOE technical targets for fuel cell components on stipulated target durability of 5,000 automotive hours, 40,000 stationary hours of operation, automotive stacks maintaining a power density of 650 watts per kilogram, $30 per kilowatt cost at 500,000 systems annually, and other specified targets.
Manufacturing procedures have material certifications indicating documents describing the composition and sulfur, chlorine, and fluorine restriction thresholds of less than one part per milliontoo avoid membrane contamination, dimensional inspection reports in conjunction with measurement uncertainty analysis, electrical contact resistance verifications weighing between 5 and 30 milliohms per square centimeter on the current collector surface with measurements corrosion resistance proved by potentiostatic tests at fuel cell operational potentials of 0.6 to 0.9 volts versus the standard hydrogen electrode, and mechanical tests validating compression load capacity and fatigue resistance by simulating fuel cell operating conditions with 10,000 compression cycles at 1 to 3 megapascals.

Some examples are passivation of SS per ASTM A967, electrochemical polishing, gold plating, and deposit-etch graphite and titanium nitride coatings. With passivation, I’m using nitric acid to remove free-iron contaminants and then to form stable chromium-oxide layers. I also eliminate corrosion and achieve measured corrosion currents below 1 microampere per square centimeter in an acid fuel cell environment. Gold and titanium nitride (TiN) PVD coatings are at 0.5-2 microns and 1-5 microns thickness, respectively, and achieve contact corrosion of 5-10 milliohms per square centimeter and corrosion for 5,000 hours. Also, corrosion-resistant and electrically conductive Gold and graphite PVD coatings achieve a thickness of 0.5-2 microns and contact corrosion of 5-10 milliohms per square centimeter and 5,000 hours for corrosion. Also, achieve a corrosion-resistant and electrically conductive surface at 10-20 milliohms per square centimeter.
Coating non-contact surfaces with epoxy or phenolic resin adds an electrophoretic coating that adds 20 to 50 microns in thickness while offering electrical insulation and preventing metallic ions from dissolving that poison the membrane electrode assembly catalysts, reducing 10 to 30 percent of the performance over 1,000 hours of operation. Anodizing Type III hard coat 25 to 75 microns on aluminum frames provides electrical insulation resistance over 1,000 mega-ohms and corrosion protection while dimensional tolerances are maintained, adding 0.013 to 0.038 millimeters per surface. All surface coatings and treatments meet the purity standards for fuel cells with extractable ionic contaminants of less than 1 part per million of chloride, fluoride, or sulfate. This prevents membrane degradation and poisoning of the catalysts.

For standard fuel cell stack end plates and current collector frames (80 to 120-kilowatt designs) we have on the books, it takes 6 to 10 weeks to deliver, including the designed hydrogen-compatibility CNC machining, precision grinding, protective coating, and quality control, including flatness and leak testing within the range of 100 to 1,000 frame set production lot sizes. Custom designs for stationary fuel cell systems or specialized automotive configurations with unique manifold geometries or integrated cooling require an 8 to 14 week lead time, depending on complexity, coating, and validation testing scope, including testing in operational fuel cell stacks.
If you need prototypes made for developing fuel cell stacks, we can get those to you in about 3 to 4 weeks. Choose a 77-day rush on machining, then we can do basic surface finishing so assembly frames can be done for quick assembly of single cell testing, little stacks, or short-stack testing. If we receive production orders for over 5,000 frames annually, setup will require at least 12 to 18 weeks to account for work process optimization of CNC machining programs, automated grinding cells, integrated coating lines that can process up to 5,000 parts weekly, and completion of PPAP. All phased delivery for stacks in support of vehicle production will also be synchronized to yearly stacks of 10,000 to 100,000 units and include linear delivery synchronized to fuel cell stacks.

Sure thing! We develop customized frames for high automotive 100 to 150 kilowatt fuel cell stacks. The frames are 25 to 40 percent lighter due to the optimized topology using finite element analysis to locate opportunities for mass reduction while keeping compression uniformity within ±0.05 MPa across the active area. Integrated thermal management frames are compression coupled with liquid cooling, which has internal channels 6 to 12 mm in diameter, removing 40 to 100 kilowatts of waste heat and eliminating separate cooling plates. This reduces the stack component count by 15 to 25 percent. We also design high-temperature frames for PEMFC, which operate at 100°C to 120°C using titanium alloys or stainless steel 316L to maintain mechanical properties to meet 5 to 8 percent system efficiency improvement through reduced parasitic loads and corrosion resistance at elevated temperatures. The frames help improve the efficiency of the system by 5 to 8 percent through reduced parasitic loads. Heavy-duty frames are for materials handling, fuel cells in forklifts, and ground support equipment with enhanced mechanical durability to withstand shock loads of 10 to 30g and vibration at 10 to 2000 hertz in industrial environments and operating 2,000 to 8,000 hours annually.
The primary need for specialized designs stems from the parts used in military vessels and submarines. Customized fuel cell systems for telecommunications and data center backup power of 5 to 250 kilowatt stationary fuel cell systems have been designed as 40,000-hour life systems. Systems of modular design for rapidly reconfigurable stack arrangements and active areas from 5 square centimeters to 400 square centimeters have been designed in support of fuel cell research and development. Custom designs make use of applied computational fluid dynamics for manifold geometry optimization for equal flow distribution of reactants within a variance of ±5 percent between cells. Structural finite element analysis for uniform compression under ±0.05 megapascals to control membrane damaging, frame mass reduction, and multi-physics modeling to control thermal gradient, humidity gradient, and uniform current density for optimizing performance have also been used.

Precision machining enhances the electrochemical performance of cell stacks by ensuring the flatness of sealing surfaces to within 0.002 inches. This not only prevents hydrogen crossover leakage that decreases cell voltage by 50 to 150 millivolts through the mixed potential effects but also prevents explosion hazards from hydrogen-air mixture formation in oxidant channels. Interfacing manifolds with precision alignment of ±0.005 inches provides uniform stack reactant distribution across cells in 100 to 400 cell stacks and prevents flow starvation. This localized cell voltage loss at varying levels from 100 to 300 millivolts accelerates membrane burnout, and its lifetime decreases from 5000 hours to 2000 hours. Active area compression provides constant uniformity within ±0.05 megapascals of maintained optimal gas diffusion layer porosity, 70 to 80%, and electrical contact resistance, 10 to 30 milliohms per square centimeter, between bipolar plates and gas diffusion layers. This uniform compression prevents voltage loss of 20 to 50 millivolts per cell and prevents the formation of hotspots. The slightly rough sealing surface with a finish of Ra 0.4 to 0.8 microns provides light gasket sealing with no loss of stack structural mass of 10 to 20% maintains leak rates of the stack at less than 5 standard cubic centimeters per minute per SAE J2578 standards, thus saving material.
Keeping compression surfaces and tie rod holes 0.010 millimeters perpendicular ensures that the plates do not tilt during compression. This keeps the membrane electrode assemblies' thickness uniform within ±0.01 millimeters. This thickness uniformity is important for the proton conductivity through the Nafion membranes that are 15 to 50 microns thick and have a conductivity of 0.1 to 0.2 siemens per centimeter at 80°C and 100 percent relative humidity. The low contact resistance of 5 to 15 milliohms per square centimeter on the current collector surfaces is achieved through gold plating or graphite coating. This contact resistance minimizes ohmic voltage loss to 10 to 30 millivolts at a current density of 1 to 2 amperes per square centimeter.
High-quality, corrosion-resistant finishes have been proven to keep working for 5,000 hours of automotive duty cycles, 30,000 of which are start-stop events, all while working on humidity cycling of 30 to 100 percent for 60°C to 90°C operating temperatures, freeze-thaw cycling of minus 40°C to plus 90°C for cold-start capability, and voltage cycling of 0.6 to 0.9 volts. Proper construction allows stacks to reliably operate in fuel cell vehicles for hydrogen. It net outputs 80 to 120 kilowatts of power with an efficiency of 50 to 60 percent, converting the chemical energy in hydrogen to electrical energy, attaining 2 to 3 kilowatts per kilogram and 2.5 to 4 kilowatts per liter for automotive packaging. It also shows a remarkable 5,000 hours of endurance, which translates to 150,000 to 250,000 kilometers of vehicle service life, with only 10 percent voltage loss in the discharge cycle over the lifetime, which includes commercial trucks, passenger vehicles, buses, materials handling equipment, and 1 to 250 kilowatt stationary power systems.