CNC Onsite, a Danish expert in mobile machining, has delivered its custom-built machine called “Goliath” to tower manufacturer Welcon. The machine is now milling 97 bottom tower flanges for Vestas’ 15 MW V236 turbines. These turbines will be used in projects in Germany and the Netherlands. Production started in April. The first flanges have already exceeded flatness requirements. This ensures a perfect fit with the transition piece. The result is improved reliability, more design flexibility, and fewer costly post-production checks.
The milling process helps align the tower and the transition piece perfectly. This creates a flat and stable connection between the two flanges. The joint is held together by bolts. By using CNC Onsite’s machining process, Welcon achieves industry-leading tolerances. This process removes the need for heat straightening, a common step used to fix flatness problems after production. It also helps maintain bolt tightness during operation.
The “Goliath” machine is custom-built by CNC Onsite. It is specifically designed to create flat flanges that provide structural strength and resist fatigue.
Bolted Connections Provide Long-Term Benefits
On the first flange, the machine achieved a flatness tolerance of 0.21 mm. The project requires 1 mm tolerance. This is much tighter than the usual industry standard of 2.5 mm. Soren Kellenberger, sales director and partner at CNC Onsite, said, “We are very pleased with the machine’s performance.”
Having a tolerance of 1 mm or less is important for correct bolt tightening. Each flange has 160 bolts. By reducing the risk of loose bolts, maintenance costs and downtime are lowered. This saves money.
Welcon plans to make this flange milling process a standard part of production. It will replace heat straightening, which uses controlled heating and cooling to fix flatness after welding. Using the Goliath machine on all 97 bottom flanges will make the process faster and more uniform.
The consistent flatness of these flanges will give Vestas, Welcon’s customer, more design options. This includes more choices in flange dimensions and bolt sizes.
Johnny Hauggaard Skov, Vice Director at Welcon, said, “The industry demands finer tolerances. To meet these flatness needs, we need machine-based processes. Heat straightening cannot reach this precision. We also expect better health and safety by reducing manual work.”
Peter Sigfred Mortensen, senior specialist in Offshore Tower Structure at Vestas, added, “If this precision milling is used industry-wide on all flanges, it will offer many benefits. Perfectly flat flanges eliminate costly measurements at sea and before shipping. It will also allow more design freedom, including the use of smaller or even maintenance-free bolts.”
Facing New Challenges with Larger Flanges
Wind turbine tower flanges are increasing in size. For example, Vestas’ new 15 MW turbines use flanges up to 7.5 meters in diameter. This growth raises the need for even tighter tolerances.
Soren Kellenberger explained, “It is already difficult to achieve required precision for 4-5 meter flanges. For flanges larger than 7 meters, the tolerances are even stricter. The combination of larger size and tighter tolerances makes it nearly impossible to meet standards with traditional methods.”
The Goliath machine is designed for efficient work. It mounts directly onto the flange. It uses adjustable legs with hydraulic cylinders or electric actuators to secure its position. This design allows easy switching between different flange sizes.
Designed for Flexibility and Speed
The machine uses powerful electric motors to mill quickly and precisely. It can handle flanges from 6.5 to 10 meters in diameter in its standard form. It can also be adapted for larger flanges. The fully CNC-controlled machine can mill flat, tilted, and double-tilted flanges. It can also cut features such as gasket grooves.
Goliath is the result of over 12 years of CNC Onsite’s experience machining wind industry flanges. It was developed and built based on this expertise. The machine sets new standards for precision and efficiency.
The machine delivered to Welcon is the third custom-built Goliath model for large diameter flanges since its launch in 2022. It can be leased or bought. It is currently used by offshore customers in Denmark and Spain.
