With the rapid development of the hydrogen energy vehicle industry, metal bipolar plates have become one of the most critical core components of hydrogen fuel cells. As one of the key parts of a fuel cell, metal bipolar plates offer excellent electrical conductivity, vibration resistance, and impact resistance, while also enabling rapid heat dissipation to maintain uniform battery temperature.

Metal bipolar plates can also be manufactured using relatively thin materials, such as 0.2 mm stainless steel for single-side flow channel half-etching, or 0.3 mm material for double-side flow channel half-etching. Thicker materials can also be used according to specific application requirements.

The main functions of bipolar plates include:

• Gas flow channel distribution

• Thermal management

• Electrical conduction

The manufacturing precision of bipolar plates directly affects the performance of fuel cells.

The manufacturing methods for metal bipolar plates can generally be divided into stamping processes and chemical etching processes. The former uses stamping to form flow channels on metal sheets, while the latter uses chemical corrosion to etch flow channels on both sides of the metal plate. Chemical etching (wet etching), with its advantages of burr-free processing, stress-free manufacturing, and the ability to produce complex three-dimensional flow channels simultaneously, has become a key process for manufacturing stainless steel and titanium alloy bipolar plates. This article provides an in-depth analysis of the core process steps and equipment control points involved.

I. Process Requirements for Metal Bipolar Plate Etching

Fuel cell bipolar plates are typically manufactured from stainless steel (SUS304, SUS316L) or titanium alloy sheets with thicknesses ranging from 0.05 mm to 0.2 mm. Typical flow channel depths range from 0.2 mm to 0.5 mm, while the rib width and channel width can be as small as 0.3 mm.

Core quality indicators include:

Flow Channel Dimensional Accuracy

• Depth tolerance ≤ ±0.02 mm

• Width tolerance ≤ ±0.01 mm

Side Etch Control

• Etch Factor ≥ 2.5

• Minimized lateral etching of flow channels

Surface Roughness

• Ra ≤ 0.8 μm

• Reduces contact resistance and improves coating adhesion

Burr-Free and Curl-Free Edges

• Prevents damage to proton exchange membranes and avoids short circuits

II. Core Process Flow for Metal Bipolar Plate Etching

A complete metal bipolar plate etching production line includes the following key process sections:

1. Pre-Treatment and Lamination

Metal coils or sheets are chemically cleaned (degreasing and oxide removal), followed by double-sided lamination with dry film photoresist or wet photoresist coating. The dry film thickness is selected according to the etching depth requirements, typically ranging from 15–40 μm.

2. Exposure and Development

A high-precision double-sided exposure machine transfers the flow channel pattern onto the photoresist layer. The exposure alignment accuracy must be ≤ ±25 μm. After development, clear opening areas are formed where the flow channels will be etched.

3. Precision Etching (Core Process Section)

This is the most critical stage determining bipolar plate quality. Double-sided symmetrical spray etching is used, where the etchant solution (typically ferric chloride or cupric chloride systems for stainless steel) is uniformly sprayed onto the metal surface through high-pressure nozzles.

Key Technical Control Points:

Spray Pressure and Oscillation

Upper and lower spray pressures are independently controlled. Swing arms or oscillating nozzles eliminate the “pooling effect,” ensuring consistent etching rates between the center and edges.

Temperature Control

The etchant temperature is maintained at 45 ±1°C (for stainless steel). Excessively high temperatures accelerate side etching, while lower temperatures reduce etching speed.

Etchant Concentration and Regeneration

Baumé degree and ORP (oxidation-reduction potential) are monitored in real time. Regenerating agents are automatically added or saturated solution is replaced to maintain stable etching rates.

Endpoint Detection

When the etching depth reaches the target value (through-etching or half-etching), spraying automatically stops to prevent over-etching.

To achieve simultaneous penetration from both sides and form continuous flow channels (such as cathode plates), the etching time must be precisely controlled so that the etching fronts from both sides meet at the center, forming a smooth “hourglass-shaped” cross section. For half-etched anode plates (etched on one side while the other side remains intact), the backside resist layer must be protected while controlling the half-etch depth.

4. Resist Stripping and Post-Treatment

After etching, an alkaline stripping machine removes the remaining dry film. The plates then undergo multi-stage cleaning, including ultrasonic cleaning, to remove etching residues and chloride ions from the surface, followed by hot air drying.

5. Inspection and Slitting

An online vision inspection system is used to check flow channel dimensions and detect defects. Finished products are leveled, cut, or rewound before entering the next surface coating process, such as carbon coating or gold plating.

III. Huazhou Machinery: Metal Bipolar Plate Etching Equipment Solutions for Hydrogen Fuel Cells

To meet the needs of the hydrogen energy industry, Dongguan Huazhou Machinery Technology Co., Ltd. has developed high-precision metal bipolar plate etching production lines with the following advantages:

IV. Why Choose Chemical Etching Instead of Stamping or Laser Processing?

Stamping

For fine flow channels with width-to-depth ratios close to 1, stamping can easily cause tensile cracking or spring-back, and burrs on the edges are difficult to eliminate. Chemical etching, by contrast, is stress-free and produces smooth flow channel sidewalls.

Laser Processing

Laser processing creates heat-affected zones that result in edge oxidation and slag formation. It also has lower efficiency and higher costs. Chemical etching can process entire sheets simultaneously, achieving productivity of several square meters per minute.

Conclusion

Reducing costs and improving efficiency in hydrogen fuel cells rely heavily on high-precision and highly consistent metal bipolar plates. With its unique advantages of stress-free processing, high design flexibility, and scalable mass production capability, chemical etching technology has become one of the mainstream manufacturing processes for bipolar plates.