Bipolar plate machining: Why fuel cell engineers should consider chemical etching

International pressure on energy diversification has led to a dynamic investment environment for alternative energy options, and fuel cells are close to being the most efficient, with the global fuel cell market set to reach upwards of $25 billion by 2025.

The demand is for more and more efficient, and increasingly cost-effective fuel cells, which influences both material choice and the chosen technology for manufacture.

Traditional bipolar plate machining

Bipolar plates, a key component of a fuel cell, have traditionally been CNC-machined from graphite, an extremely expensive and highly permeable material that is not ideally suited to mass manufacturing applications. So saying, numerous materials have been assessed as alternatives, and because of the demand for competitively priced, relatively-easily to manufacture, durable materials, metals (especially stainless steel and titanium) have become increasingly popular. Stainless steel exhibits an array of characteristics that make it ideally suited for bipolar fuel cell plates, including its inherent strength, chemical stability, low cost and relative ease of mass production.

Fuel cells are produced by stacking precise and intricate plates machined with complex grooves or channels which enable liquid and gases to flow and can be variously manufactured using CNC-machining, hydroforming and stamping, but there are question marks over the scalability and capability of these processes.

Traditional metalworking technologies such as stamping – and more recently hydroforming – compromise planarity (flatness) and introduce stresses and burrs. Single-point machining processes and presswork tooling can also be slow and uneconomical to produce, especially during R&D.

Benefits of chemical etching bipolar plates

Photo chemical etching process offers manufacturers significant advantages when producing complex components such as bipolar fuel cell plates.

Low-cost tooling

First, and most importantly, photo etching requires no hard tooling, the use of digital tooling being inexpensive to produce and adapt, and therefore allowing designs to be optimised at minimal cost.

Speed of supply

The process also allows speedy ramp up from prototype volumes to high volume manufacture, offers almost unlimited part complexity, produces burr- and stress-free components (especially important for fuel cell plates where imperfections can compromise stack bonding), does not affect metal properties, is appropriate for all grades of steel and achieves accuracy to ±0.025 mm — all at lead times measured in days, not months.

Channel complexity

Photo chemical etching removes metal simultaneously, meaning complex channels or flow fields can be etched on both sides of the plate. This versatility enables designers to vary the size and shape of channels and incorporate headers, collectors and port features without additional cost, not possible with alternative technologies.

Suitable materials

Precision Micro typically manufactures bipolar plates from 316L-grade stainless steel in plate sizes to 1500mm x 600mm, but plates can also be specified in exotic and hard to machine metals (such as titanium) for lighter-weight and corrosion resistance in high-temperature fuel cell applications.

The versatility of the photo chemical etching process, coupled with Precision Micro’s 50 years of etching expertise, makes it a compelling option for the manufacture of complex sheet metal parts across numerous exacting applications and stimulates innovation as it removes obstacles for design engineers inherent in traditional technologies.