| Wind power


The We4Ce and CNC Onsite method provides significant advantages: up to 60% in cost savings; reduced downtime; and environmental benefits from eliminating potential blade waste and blade transportation, which would typically incur high logistical costs and carbon dioxide emissions.


CNC Onsite designed and built a custom machine to drill out defective bushings from the rotor blades’ composite laminate, creating accurately dimensioned holes for replacements. “Drilling in fibreglass is typically hard on tools, causing them to wear out quickly. That is why


as part of this project, we developed special drills to achieve high precision and efficiency,” explains Soren Kellenberger, partner and sales director, CNC Onsite.


Infusion technology ensures long-lasting bushing bond We4Ce applied its patented infusion technology to fasten the new replacement bushing in place, ensuring exact centring. Epoxy resin was infused through an inlet tube into the base of the bushing, with vacuum processing ensuring even distribution around the cavity.


The blade root bushing, or insert, is a safety-critical component that connects the rotor blade to the turbine hub. In some blades, polyester is used to embed the bushing. If during the original manufacturing process this material shrinks or is unevenly distributed, microcracks can arise with cracks developing over time. Such cracks reduce the bonding surface and increase the risk of the bushing loosening — potentially leading to blade failure. Further remanufacturing projects with significant potential, include those in Brazil and the USA.


Goliath’s high precision milling of Vestas tower flanges


Another recent project undertaken by CNC Onsite was the milling of Vestas tower flanges to better than 1 mm tolerance using one of its Goliath precision milling machines installed at the premises of tower manufacturer Welcon. The Goliath machine was used for milling 97 bottom tower flanges for Vestas 15 MW V236 wind turbines destined for projects in Germany and the Netherlands. The flanges have exceeded flatness specifications, ensuring a ”perfect fit” with the transition pieces. The milling process ensures that the


tower and transition piece align perfectly, forming a flat, stable connection between the two flanges, a critical mechanical joint held together with bolts. By implementing CNC Onsite’s machining process, ”industry leading tolerances are achieved”, the company says, which eliminates the need for ”heat straightening”, a common post-production step to correct flatness issues. Goliath is a custom-built precision milling machine from CNC Onsite, specifically designed 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 plans to integrate the flange facing process as a standard manufacturing step, replacing traditional heat straightening, a controlled heating and cooling process used to correct flatness distortions after welding. The consistent flatness across all flanges will provide Vestas with ”greater flexibility in flange designs and dimensions, as well as a broader choice of bolt sizes,” says CNC Onsite. “The industry demand for fine


tolerances is increasing. To meet flatness requirements, we need a machine-based process, as heat straightening cannot achieve the necessary precision,” says Johnny Hauggaard Skov, Vice Director,


Welcon.“We also expect this to improve health and safety by eliminating manual work.”


“If applied throughout the industry on all flanges, from tower to transition piece, I believe this precision milling will offer a range of benefits. When all flanges are completely flat, it eliminates the costly measurements we have seen both at sea and prior to shipping. It will also provide design freedom, including the option of smaller and even maintenance-free bolts,” says Peter Sigfred Mortensen, senior specialist, Offshore Tower Structure, Towers R&D, Vestas. As wind turbine tower flanges grow in diameter — now reaching 7.5 m for Vestas’ new 15 MW turbines – the demand for even finer tolerances increases. “It is a challenge to achieve the required


precision for 4-5-meter diameter flanges. But on today’s seven-plus meter flanges the tolerances are even tighter. This combination of larger diameter and stricter tolerances makes it nearly impossible to meet standards with traditional methods,” says Soren Kellenberger, sales director and partner at CNC Onsite. The Goliath milling machine is mounted


Goliath precision milling machine prior to installation on flange (photos: CNC Onsite)


Goliath at work, precision milling on 7.5 m diameter Vestas wind turbine tower flange


directly onto the flange. Using adjustable legs with hydraulic cylinders or optional electric actuators, the machine is securely positioned, allowing easy switching between different flange diameters. Powerful electric motors enable fast, high-precision milling. The machine handles flanges from 6.5 to 10 meters in diameter in the standard configuration and can be adapted for larger sizes. Fully CNC-controlled, the machine can mill flat, tilted, and double-tilted flanges, as well as features like gasket grooves. The machine for Welcon is the third custom-built Goliath machine, designed for large diameter flanges, since its launch in 2022. It can be leased or purchased and is currently in use by offshore customers in Denmark and Spain.


www.modernpowersystems.com | September 2025 | 39


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