Titanium Bipolar Plate Machining: Flatness and Channel Accuracy Achieved

Product Introduction

As hydrogen energy plays a bigger role in the shift to clean power, many leading companies are increasing their investment in its development. There is a company that has spent nearly a decade working across the entire hydrogen value chain and taking part in key green hydrogen research projects.

During the development of a new proton exchange membrane electrolyzer, their R&D team came for high-precision bipolar plates. These components, made from stainless steel or titanium alloys, include complex flow channels and demand strict flatness and surface quality.

With our 5-axis precision machining capabilities and strong experience in processing titanium alloys, WayKen provides customized solutions that combine functionality, reliability, and production stability.

Part Structure Analysis

The bipolar plate is a uniform thin plate made of titanium, with a size of170mm*130mm*2mm. Grooves are evenly distributed on one side, with a width of less than 1mm, which requires a precision of +-0.05mm. In addition, the flatness required is +-0.01mm, which increases the machining difficulty.

Machining Solutions for High-Precision Bipolar Plates

Manufacturing bipolar plates with both micro-scale precision and stable performance poses unique challenges, especially when working with thin-walled titanium components and narrow flow channels.

Design Requirements and Machining Points for Precision Flow Channels

The flow channel is an important structure. Its main function is to evenly and accurately distribute hydrogen, oxygen, and electrolyte, to ensure that the electrolysis reaction occurs evenly on the surface of the membrane electrode. Therefore, to obtain qualified flow channels, many details are worth noticing during the production process.

It can be seen in the picture below that the flow channels are 0.81mm wide and 0.51mm deep. And bipolar plates are often stacked in multiples to distribute the medium evenly, so the accuracy requirements are very important, up to ±0.005mm.

To achieve this precision, we typically adopt a multi-step machining strategy:

• Rough Machining: Remove the bulk of excess material, leaving a uniform allowance for finishing.
• Semi-finishing and Finishing: Use a small-diameter tool with a low feed rate to carefully mill out the detailed structure.
• Tool Material Selection: Due to the small tool diameter, the breakage risk is high and affects dimensional accuracy. We use K10-grade tools with a high cobalt content, which offer excellent hardness and impact resistance, ensuring stable performance throughout the process.

Surface Cleanliness and Burr Control in Channel Machining

In these bipolar plates, pure liquid will flow through during the entire electrolysis process, so there must be no impurities. Obvious tool traces will also cause uneven pressure distribution after the product is bonded, affecting the function of the bipolar plate.

To prevent these issues, the channels must remain clean, and surface roughness should be kept within Ra0.8. Our five-axis machines, capable of speeds up to 32,000 rpm, can achieve roughness as low as Ra0.2 without any post-processing. However, to balance machining cost and efficiency, we typically use a three-axis machine in production. By setting high spindle speeds and low feed rates during the finishing stage, we can still achieve the required Ra0.8 surface finish.

In addition, titanium alloy has a tendency to stick to the cutting tool, often causing burrs. To minimize this, we select tools with TiAlN coating, which reduces adhesion and improves surface quality. After machining, we use a hard-bristle brush to remove residual burrs, inspect the surface under magnification at an oblique angle, and finish with compressed air to ensure all debris is cleared.

How to Meet High Flatness Requirements?

Bipolar plates are used in multiple stacks. If the flatness is out of tolerance and the local pressure is insufficient, gas leakage may occur. Due to such functional requirements, the flatness accuracy of the bipolar plate is 0.01mm.

As it’s a thin plate, bipolar plates are prone to deformation. And all channels are distributed on one side, the deformation is hard to control by flipping processing. Based on our experience, we’ll use a grinder to machine the plate. Compared with CNC, a grinder generates less heat, less deformation, and can achieve better flatness and finish.

Flatness Control Strategy in Thin Plate Machining

First, we’ll grind the red surface to directly achieve the 0.01 flatness, and no further processing will be performed on this surface. Then, the red surface will be used as the reference to mill out other structures on the opposite side. Finally, we’ll clamp the reverse side as the bottom, and the channels will be milled out in this clamp.

Given the thin structure, minor deformation is unavoidable without external force intervention. To address this, we proposed applying an external force during flatness inspection to simulate actual assembly conditions. Since the bipolar plate will be installed under pressure during use, the customer reviewed and accepted this inspection method as reasonable and aligned with practical application scenarios.

Feedback

After receiving the parts, the customer shared the following comments:
“The bipolar plates have passed inspection and meet all requirements. The flatness of 0.01 mm and the precision of the flow channels are well beyond our expectations. The parts have been successfully installed, and the electrolysis system is operating smoothly. We look forward to placing more orders with you.”

With advanced CNC machining, tight tolerance control, and deep expertise in complex geometries, WayKen delivers high-precision components that meet the strictest quality standards. From prototyping to low-volume production, we provide reliable machining solutions for critical applications across energy, automotive, medical, and industrial sectors.