Productive Times

CNC Onsite A/S in Vejle, Denmark, has delivered its custom-built Goliath machine tool to wind tower manufacturer Welcon A/S in Give, Denmark. Welcon is milling 97 bottom tower flanges for 15mW V236 turbines for projects in Germany and the Netherlands. Production began in April 2025, and the first flanges have already exceeded flatness specifications, ensuring a precise fit with the transition piece — enhancing reliability and design flexibility and significantly reducing costly post-production checks.

The milling process ensures that the tower and transition piece align, forming a flat, stable connection between the two flanges, a critical mechanical joint held together with bolts. By implementing CNC Onsite’s machining process, tight tolerances are achieved, which eliminates the need for heat straightening, a common post-production step to correct flatness issues, while also optimizing the maintenance of bolts during operation.

Heat straightening is a method used to correct distortions in metal components, such as wind turbine flanges, caused by manufacturing, welding or operational stresses. The process involves applying controlled heat to specific areas, causing the metal to expand. Once cooled down, it contracts, helping to restore the component’s original shape.

CNC Onsite specifically designed Goliath to ensure flat flanges for structural strength and fatigue resistance.

“On the first flange, we have achieved a global flatness tolerance of 0.21 mm. The required 1 mm for this project is already well below the common industry standard of 2.5 mm, so we are, of course, very pleased with the machine’s performance,” said Soren Kellenberger, sales director and partner at CNC Onsite. “Ensuring a tolerance of 1 mm or better is a significant benefit when it comes to ensuring correct bolt tightening. With 160 bolts in a flange, reducing maintenance costs and downtime due to loose bolts is a considerable cost saver.”

Welcon will integrate the flange facing process as a standard manufacturing step, replacing the traditional heat straightening method after welding. By employing Goliath to machine the 97 bottom flanges, the tower manufacturer can ensure a faster, more uniform method.

The consistent flatness across all flanges will provide Vestas Wind Systems A/S, Welcon’s customer, with greater flexibility in flange designs and dimensions, as well as a broader choice of bolt sizes.

“The industry demand for fine tolerances is increasing,” said Johnny Hauggaard Skov, vice director of Welcon. “To meet flatness requirements, we need a machine-based process, as heat straightening cannot achieve the necessary precision. We also expect this to improve health and safety by eliminating manual work.”