OSG end mills demonstrate high-quality, high-precision milling in fuel cell mold plate production
Peter Cramer Jensen | OSG Scandinavia
In recent years, fuel cell powered systems have emerged as an efficient and reliable alternate technology for electricity generation, and are finding applications in various industries globally. The surge in adoption is driven by growing environmental concerns, as well as increasing government initiatives for hydrogen fuel cell infrastructure.
Hjerno Tool Factory in Odense, Denmark recently received an order that involves the machining of mold plates made of 59 HRC tool steel used in fuel cells. Established in 1946 as one of the largest and oldest tool factories in Scandinavia, Hjerno Tool Factory specializes in the production of injection molding tools with the highest attention to quality and detail. Utilizing some of the latest machineries and equipment, Hjerno Tool Factory is able to provide innovative tool design solutions for intricate parts with tolerances as low as two microns. With more than 50 tool specialists stationed at its 4,000-square-meter modern manufacturing facility, Hjerno Tool Factory is able to produce on average one new injection molding tool per day.
A majority of Hjerno Tool Factory’s orders are complicated, involve difficult-to-machine materials, require strict tolerances and short cycle time for maximum cost efficiency. Hjerno Tool Factory’s recent fuel cell project for an international client was one of such orders.
About Fuel Cells
A fuel cell is an electrochemical cell that is powered by forcing hydrogen gas through a catalyst-coated membrane where it bonds with oxygen from the air. This electrochemical reaction creates water vapor and a stream of electrons that can power the same electric motors found in a battery-electric vehicle. Although expensive when compared with gas generators and lithium-ion batteries, fuel cells are capable of producing electricity continuously as long as hydrogen and oxygen are supplied. Moreover, the only emissions from fuel cells are water and heat, thus many see fuel cell technology as a new sustainable and low-carbon based energy source.
Machining the Fuel Cell Mold Plates
The fuel cell consists of a number of components required for it to function. The proton exchange membrane (PEM) plates are especially critical to the fuel cell as it serves as an energy generator where the chemical reaction of converting hydrogen and oxygen into electricity and heat takes place. The thin steel flow plates are composed of complex channel patterns for the hydrogen and oxygen gas to flow through.
Several months of non-stop precision machining was required of Hjerno Tool Factory to machine eight molds for these fuel cell power stack separator plate membranes with extreme tolerance requirement in 59 HRC tool steel. The project included uninterrupted 0.4 mm ball milling over several months, eight days of non-stop finishing milling and tolerances within three microns.
All of these factors combined made it a one-of-a-kind project, said Peter Jørgensen, Managing Director of OSG Scandinavia, who supplied the cutting tools to Hjerno.
“In OSG Scandinavia’s 40 years of existence, it is the first time we’ve been involved in a project as remarkable as this one,” said Jørgensen. “The requirements from the machine, tool fixture and the tool itself were all on the verge of impossibility.”
To tackle the challenge, Hjerno Tool Factory relied on a V33i milling machine from the Japanese machine tool builder Makino; the shrink fit tool holders came from MST, while OSG supplied two different sets of cutting tools – the WXS-LN-EBD ball nose carbide end mill and the CBN-SXB ball end mill.
The WXS-LN-EBD is a 2-flute, long-neck ball nose carbide end mill designed for high-precision milling of hardened steels up to 65 HRC. Equipped with OSG’s original WXS coating for superior heat and wear resistant, this rib processing end mill series is able to achieve optimal performance with high precision and efficiency under aggressive machining conditions.
The CBN-SXB is a small-diameter 2-flute super ball end mill designed for high-precision finishing. Its spiral gash end cut geometry provides a strong and sharp edge with cutting performance equivalent to carbide tools. The CBN-SXB is especially effective in profile milling and workpieces with large inclines. It is most ideal for finishing long distance high-hardness materials above 50 HRC.
“Initially, we also discussed developing customized cutting tools for this specific project, but it quickly became clear that our standard cutting tools should be able to do the task,” said Jørgensen.
The OSG end mills were able to provide high-quality machined surface even at high-feed rate while maintaining the strict accuracy required by the fuel cell project. However, as milling progressed, it became clear that the machines milled with a variation, for which Hjerno Tool Factory’s technicians could not account the reason.
For quite some time, it was believed that the variance was caused by a mechanical problem in the machines or in the cutting tools. However, it was later discovered that there was an inaccuracy in the advanced CAM system that Hjerno Tool Factory uses.
Specialist Summit in Denmark
In order to resolve the inconsistency, Hjerno Tool Factory called for assistance from all over the world. Shortly after, various stakeholders of the project – Hjerno Tool Factory, OSG, Makino and the CAD/CAM supplier – all met up at Hjerno Tool Factory’s headquarters in the Danish town of Odense.
The system developer ended up spending 14 days in Denmark, where he recoded the entire program structure so that the CAD software could handle the extremely large files. At the same time, OSG and Makino’s specialists developed new suggestions for milling optimization.
The team efforts have proven to be a tremendous success. From then on, Hjerno Tool Factory’s machines stayed within the required tolerances, which enabled it to complete the fuel cell mold plates with superior quality. The customer, a Swedish manufacturer of fuel cells, was so pleased with the final result that they placed another long-term order with the Danish factory afterward.
A major take-away from this fuel cell project was that the milling machine is not always the one to blame.
“It is always incredibly easy to place the blame on the milling machine because that’s where the symptoms of a disease appear,” said Hjerno Tool Factory Tool Maker Kristian Jessen Hansen. “This project has really helped us to not only gain a far better understanding of how to optimize the use of our milling machines, but also to spot the built-in weaknesses of a CAD/CAD system,” said Hansen.
For OSG Scandinavia, the fuel cell project served to prove that a tight-knit relationship between supplier and customer is vital, when tolerances and competencies are put to the test.
“Although we have worked together with Hjerno Tool Factory for the past 15 years, it is on projects like this one that you really come to recognize the know-how and expertise of your partners,” said Jørgensen.
Hjerno Tool Factory prides itself in precision, professionalism and uncompromising quality. It is a forward-thinking company that continuously invests in new production facilities and tooling solutions in order to provide the best results for its clients.
“The wonderful thing about projects that are technically challenging is that we learn to raise the bar of our company,” said Hjerno Tool Factory Managing Director Aage Agergaard. “To succeed, you just need stamina and persistence.”