CS Wind Offshore selects CNC Onsite for precision milling of offshore wind farm

Offshore wind foundation manufacturer CS WIND Offshore has begun operating a custom-built, automated milling machine from Danish machining expert CNC Onsite at its Aalborg facility in Denmark to create high-precision cable penetrations in transition pieces destined for offshore wind farms.

This process, the company says, ensures that cables powering external workspace lighting and platform cranes can be sealed with maximum reliability.

Delivering sub-millimeter precision, CNC Onsite’s new magnet-mounted gantry machine replaces manual cutting with a CNC-controlled milling machine that produces clean-cut penetration holes. These six cable holes per transition piece require precise edges to allow for the flawless sealing required around the power cables, a requirement in harsh ocean environments. CS WIND Offshore ordered the customized gantry machine to also mill the 12 pressure relief holes per transition piece, holes designed to relieve pressure and prevent structural warping under rough sea conditions.

“We required a tolerance of one millimeter to eliminate micro-gaps and completely isolate the internal electrical routing,” says Flemming Smidt Pedersen, Senior Manager, Production Engineering, at CS WIND Offshore. “At sea, this watertight integrity is absolute.”
The cables passing through these points power the platform cranes tasked with hoisting critical spare parts to the turbines, as well as the signal lights that illuminate identification numbers on each wind turbine.

“Surpassing our target to achieve a tolerance of just 0.3 millimeters through this entirely dust-free process has allowed us to secure this vital infrastructure while maintaining a cleaner, optimized manufacturing environment,” adds Pedersen.

Large-scale components
With a height of 2 meters, a length of 3.6 meters, and a width of 2.3 meters, CNC Onsite’s 4-axis gantry machine was developed at the company’s headquarters in Vejle, Denmark, in a workshop dedicated to producing customized, high-precision solutions.

“We specially developed the mobile gantry milling system to deliver consistent, high-precision results on steel components. These parts are massive and virtually impossible to move into a standard machine. Therefore, we bring the machine to the workpiece instead. This project was a perfect fit for us, as our specialty is bringing precision machining directly to the component,” says Søren Kellenberger, CEO of CNC Onsite.

Leveraging CNC Onsite’s background in maritime and energy projects, the company designed the mobile gantry machine to produce cable transits in a single automated pass, eliminating the need for manual flame-cutting and grinding.

The company also developed a proprietary magnetic fastening mechanism to provide a stable, vibration-free foundation without the need for traditional, invasive clamping. By utilizing powerful electromagnets, the machine locks directly onto the curved structure of the transition piece with high clamping force, yet leaves the high-grade steel surface completely unmarked. This approach is a significant benefit for transition piece manufacturers, as it prevents surface scarring and eliminates rework.

Managing complex geometry
To accommodate diagonal routing of the cables through the structure, the penetration wall must be at a 45-degree angle. CNC Onsite easily meets this specification with its adjustable machining angle ranging from 28 to 90 degrees. For this specific scope of work, the penetration holes measure 180 millimeters by 350 millimeters. However, the gantry machine is highly versatile, capable of processing openings ranging from minor 50-millimeter-diameter utility holes up to large-scale structural oval penetrations measuring 2,575 millimeters by 550 millimeters.

The 4.8-ton mobile machine handles significant geometric challenges in the manufacturing facility, where each 370-ton transition piece, 7.8 meters in diameter, must be rotated on rollers to align the cutting zones. Equipped with an adjustable wheeled maneuvering setup, the machine tracks the cylinder’s rotation, minimizing manual handling during repositioning.

“This integration of advanced gantry engineering and sub-millimeter precision confirms that manufacturing of large complex steel structures can be optimized to meet the increasingly stringent technical standards of the global offshore energy sector,” concludes Kellenberger.