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How orbital milling machines are used for wind turbine manufacture

Posted by Alan Hillier on Jul 6, 2016 9:30:00 AM


    

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2015 was an unprecedented year for the wind industry with more than 63 GW of new wind power capacity being brought on line.  Construction of huge turbines to meet this increased demand presents difficult challenges for manufacturers, including the accuracy of the machined faces on the tower and on the rotor blades.

Over the years, Mirage has been approached by several manufacturers to design and supply portable machining tools to carry out these difficult tasks.

As you might expect, the key challenge is to deliver accurate results across such large diameters, but at the same time to keep set-up and machining times to a minimum and also ensuring the safe handling of such heavy machines.

Solutions developed by Mirage over the past few years has included:

  • Developing an orbital milling machine using a 3 point mounting system.
  • Following this, developing a patented hydraulic mounting chuck, enabling reduced set up times, regulated clamping force and known blade stress.
  • Machining times achieved of up to 400mm per minute.
  • Guaranteed flatness and surface finish.
  • Introducing a range of machines to machine blade sizes from 30m to 65m.

Download orbital milling buyers guide

 

Trolley development

With the considerable weight of the machines and the need to operate them vertically, Mirage developed a range of trolleys on which each orbital milling machine is mounted and then offered up to the blade or tower flange.

These height adjustable and portable trolleys include also space for the hydraulic power unit and a platform to ensure safety of the machine operators. Some are supplied with an extractor unit to capture the dust fibreglass produced when machining.

 

Example 1: Wind blade machining

Machines used: Mirage WP2500, WP3500 with adapted bases.

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  • A leading manufacturer of wind turbines required the face of the composite rotor to be machined at 2.4m diameter.
  • The rotor blade had composite structure with both steel and GRP.
  • The flatness tolerance was to be within 0.20mm at 2.4m and machining time within 1 hour.

Method

  • The high spots on the flange were recorded and depth of cut set with the digital scale.
  • The machine fitted was with a 125mm face mill and machining commenced at 400 mm/min, giving a rotation time of 20 mins.
  • Floor to floor machining times of 30 minutes is now possible
  • Machines have since been used in the production of over 10,000 blades.

 

Example 2: Wind tower machining

Machine used: Mirage WP4300

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Above: orbital milling a tower section

  • End flange of the tower to be machined within 1 hour
  • Flatness tolerance of 0.15mm at 2.7m diameter.
  • The fabrication required the WP4300 to clamp into the tower and machine the flange.

 Method

  • The machine was mounted using the eight jaw chucking system with four off having an adjusting feature built in to allow fast easy levelling.
  • Four off additional jaws were used to provide rigidity and the machine has a hydraulic rotary distributor to enable correct hose orientation.
  • The machine was mounted to the tower fabrication, locked in place, levelled and then machining commenced.
  • High spots removed locally
  • Completion of 3 flanges per day a saving of over 80% on previous methods.
  • Flatness tolerance achieved: 0.30mm with 0.8 –1.6 μm Ra Finish

Download the Orbital Milling Buyers Guide here, or if you have a potential project needing this product right now  please click here to get in touch.

Topics: On-site machining, wind turbine blade repair, orbital milling machine

   

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