WO2011119099A1

WO2011119099A1 - Method and arrangement for machining of a hub

Info

Publication number: WO2011119099A1
Application number: PCT/SE2011/050330
Authority: WO
Inventors: Michael Larsson
Original assignee: Carlstad Machinetools Ab
Priority date: 2010-03-23
Filing date: 2011-03-23
Publication date: 2011-09-29
Also published as: SE535645C2; EP2550124A1; EP2550124A4; SE1000275A1

Abstract

This invention relates to a method for machining of a hub, wherein said hub (1) comprises a geometrical center axis (C), a bottom section (10) extending in a perpendicular plane relative the center axis (C) and a plurality of symmetrical placed flange surfaces (12) for blades/wings, said flange surfaces (12) extending in a plane creating a sharp angle (a) with said center axis (C), and wherein said method comprises arranging of a converting machine (3) and a machining table (2) belonging thereto, arranging of said hub (1) on the machining table (2) through fixation of the bottom section (10) parallel with the upper surface (20) of the table (2), and machining of a flange surface (12) according to the above, wherein a plurality of converting machines (3) are symmetrical arranged around said machining table (2), each converting machine is arranged with an angle machining arrangement (30-33) that enables machining of said angled flange surface (12) when said table surface (20) is horizontal, and a plurality of machines are used simultaneously to machine a plurality of flange surfaces (12).

Description

METHOD AND ARRANGEMENT FOR MACHINING OF A HUB

FIELD OF THE INVENTION

The present invention relates to a method for machining of a hub, wherein said hub shall have a rotational symmetric body with a geometrical center axis, a bottom section extending in a perpendicular plane relative the center axis and a plurality of symmetrical placed flange surfaces for blades/wings, said flange surfaces extending in a plane creating a sharp angle a with said center axis, and wherein said method comprises arranging of a converting machine with a machining table belonging thereto, arranging of said hub on the machining table through fixation of the bottom section parallel with the upper surface of the table, and machining to obtain flange surfaces as mentioned above.

BACKGROUND INFORMATION

Machining of hubs for wind turbines is in capacity point of view a significant bottleneck for producers of wind turbines. To a large extent this depends on that the investment in machine equipment is large and the efficiency relatively low, which in turn means that nobody will invest in over-capacity. Today's machine equipment are also bulky which implies large, and consequently expensive locals. The invention in this document eliminates the machining of a hub as a dimensional factor regarding the production capacity of wind turbines.

A hub is normally manufactured in cast iron with a machinery allowance about 12 to 15 mm. Machining takes place in the "bottom", the side that is attached against the generator shaft, on the "top", corresponding side to the "bottom" where the nose cone is attached. Machining of means for attachment of gear boxes/engines for blade turning may also be here. Machining is also made on surfaces and holes of means of attachment for the propeller blade, referred to below as "flange surfaces". These flange surfaces are in general angled, 2 to 4 degrees against the direction of the wind. This angle is to a large extent the basis for the common method for machining of blade flanges, which is as referred below.

Operation 1 : The "bottom" and the "top" of the hub are machined in a horizontal miller. Possible machining of attachment surfaces for gear boxes/engines for blade turning on the "top" is excluded from this operation since these shall follow the same angles as the flange surfaces. Operation 2: The hub is placed on a tilted circular table or on a tilted rotary fixture in front of a miller ( see fig. 1). The machined surface "the bottom" is used as fixation. Thereafter a blade flange surface is machined one at a time. Normally spindle motors with high power are used, often between 20-50 kW to obtain high milling grade, which upwards is limited by weaknesses in machine assembly respectively arising vibrations. When a surface is finish-machined the circular table/ fixture is turned 120 degrees and thereafter next blade flange is machined etc. Finally a 90 degrees angular cutter-head is changed in and the machining of the fastening surfaces for the gear boxes for blade turning is performed.

There are several disadvantages with this method. The largest efficiency restrain factor is that since the hub is tilted during the machining only one side of the hub can be machined. Another disadvantage is that many rotations of the work piece is made, which is ineffectively since no machining can be performed under the rotation. A third is that angular cutter-heads must be used under parts of the operation. Partly it takes time to change these heads on and off the machine, partly angular cutter-heads are sensitive for torque which limits the possibility to optimize machining data.

Through EP0032890 is known a machining arrangement with the aim to give an increased flexibility and efficiency, through a method in which machining of work pieces can be done simultaneously by several machines. The machine equipment is principally directed to achieve streamlining through 180° symmetrical placing of machine equipment that performs different operations with respect to the symmetry line them between, in order to be able to machine two work pieces at the same time and through a 180° turning make two different operations on respective work piece, by which streamlining occurs thanks to simultaneously machining of the both symmetrical placed machines. To achieve large flexibility, to be able to carry through many different work operations, the machines are movable in their stand parts in three orthogonal directions and are arranged with a spindle joint that gives swiveling feature in the horizontal plane, around a vertical axis. The objective of the known machine

arrangement is to lead to the greatest possible flexibility. A disadvantage with a machine arrangement like this is that it is relatively weak, especially by a spindle joint that admits swiveling feature around the vertical plane. A machine arrangement like that in EP0032890 is therefore not suitable for machining of work pieces as mentioned above, i.e. large work pieces that by efficiency reasons requires large cutting. SUMMARY OF THE INVENTION

It is an object of the present invention to minimize the above mentioned disadvantages, which is obtained by a method in accordance with claim 1. Thanks to this invention many advantages are obtained. The evident benefit with this invention is that the machining of the blade flanges is performed in less than a third of the time compared with usual methods. In addition to that, an important additional benefit is gained, that a single operator can accomplish, what according to usual methods requires 3 operators. Altogether this means not only saving of time but also a saving on a surprising level, as it has been shown that the costs for the machining can be reduced by more than 50% by the use of the method according to the invention.

Furthermore is gained that a much more stable machine arrangement is allowed to be utilized, since the combination of the fixation of the work piece and the machine abutment can admit reduced vibration excitation and resulting torque of the work piece, which in turn results in that larger power is allowed to be used with a higher/faster cutting as a result. Moreover the invention results in the possibility that fewer spare parts is needed to be stored ( compared with to use revolving spindle heads), and also results in the possibility to minimize stop time and maintenance costs respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in more detail with reference to the enclosed figures, in which: Fig.1 shows the principles for machining of a hub according to prior art,

Fig.2 shows the principles for machining of a hub according to the invention, seen in a lateral view,

Fig.3 shows the principles for machining of a hub according to the invention, seen from above, and

Fig.4 shows the principles for a machinery according to the invention.

DETAILED DESCRIPTION

In figure 2 there is shown a hub 1 , in the form of a larger conically hub for a wind turbine, which comprises a rotational symmetric body 1 with a geometrical center axis C. The hub 1 has a bottom section 10 extending in a perpendicular plane relative the center axis C and a plurality of symmetrical placed flange surfaces 12 for attachment of blades/wings (not shown). The flange surfaces 12 extends in a plane that creates a sharp angle a relative the center axis C. Further a converting machine 3 is shown with a machining table 2 belonging to it, above which said hub 1 is attached by fixation of the bottom section 10 fixed-up onto and consequently parallel with the upper surface 20 of the table 2. Machining of a flange surface 12 is made by a converting machine 3 arranged with an angle machining arrangement 30-33 that enables machining of said angled flange surface 12 when said table surface 20 is horizontal. Fundamentally the machine 3 comprises a pillar 32 that may be moved in an arrangement 34 in x-direction relative its foundation 35. The pillar 32, in turn, supports a positioning means 33 that on one hand may be moved in y-direction (i.e. up and down along the pillar 32) and partly may be angled an angle a. At said positioning means 33, an arm 30 is arranged, that by means of a telescope arrangement gives displacement possibility in z-direction by a machining spindle 31 arranged at the arms outer end, e.g. a milling tool, that is driven by a spindle motor (not shown) with relatively high power, preferably exceeding 40 kW, with the aim of obtaining particularly fast/high cutting, more preferred the power of the spindle motor is exceeding 50 kW, implying that the machining power applied on the work piece at the same time exceeds 100 kW, more preferred exceeding 110 kW. In an optimal machine equipment according to the invention, wherein the included spindles are programmed ( e.g. according to simulation tests or practical tests) to machine the piece 1 so that arising torque on the work piece 1 is balanced to the utmost possible extent, total power may exceed 120 kW, e.g. 180 kW, resulting in enormous fast machining. In figure 3 is shown that according to the preferred embodiment of the invention there are three converting machines 3, symmetrical placed around the machining table 2, and that each converting machine 3 is allowed to machine each flange surface 12. Further is indicated a control unit 5 that enables (wireless and/or wire-bound) control of all the machines 3 by one operator.

By means of the invention the process may on a advantageously manner optimize the machining of the wing flanges. The equipment according to the preferred embodiment, as shown in figure 4, comprises three milling machines 3, with a tilt able arm/spindle 30/31. The machines 3 are placed with 120 degrees angle in between, with the same distance in proportion to a centrally placed rig station 2,4 (see figure 2 and 3) for the hub. A palette (not shown) may be used to couple the hub 1, before the unit is fastened on the rig station 2,4. After that all the flange surfaces are machined at the same time. By the inclination of each mill spindle to the desired angle, e.g. two to four degrees, it is possible to machine 3 sides at the same time, by one operator.

The most evident benefit with the invention, in the above exemplifying case, is that the machining of the blade flanges is performed in less than a third of the time. Partly, all three sides are machined at the same time and, partly, all rotations of the work piece are avoided. This results in a machining time of about 28 to 30 %. If same productivity will be achieved with a traditional method it requires 3,2 machines. The investment for these 3,2 machines is 200% of the investment of an arrangement according to the invention. In addition to that, 3,2 machines naturally requires 3,2 operators. Taken together, this implies that the costs for the machining of the blade flanges on a wind turbine hub are more than halfed through the use of the invention. In addition to that the big advantage is won that the machine equipment according to the invention is less vibration prone and more stable (e.g. through the use of a fixation between the spindle arm 30 and the pillar 32), which enables that the total cutting may be kept very high.

Claims

1. Method for machining of a hub, wherein said hub (1) comprises a geometrical center axis (C), a bottom section (10) extending in a perpendicular plane relative the center axis (C) and a plurality of symmetrical placed flange surfaces (12) for blades/wings, said flange surfaces (12) extending in a plane creating a sharp angle (a) with said center axis (C), and wherein said method comprises;

-arranging of a converting machine (3) with a machine tool (31) and a machining table (2) belonging thereto,

-arranging of said hub (1) on the machining table (2) through fixation of the bottom section (10) parallel with the upper surface (20) of the table (2), -machining of a flange surface (12) according to the above,

characterized in,

-that three converting machines (3) are symmetrical arranged, with an angle of

120 degrees in between, around said machining table (2),

-that each converting machine is arranged with an angle machining arrangement

(30-33) that enables machining of said angled flange surface (12) when said table surface (20) is horizontal, wherein said angle (a) is between 2-4 degrees and is achieved by means of a spindle arm (30) arranged on the machine (3), which spindle arm (30) is adjusted in said angle (a) in relation to the horizontal plane for application of the machine tool (31), and

-that all machines are used simultaneously to machine a plurality of flange surfaces (12).

2. Method according to claim 1 , characterized by a control unit (5) that enables controlling of all converting machines by an operator.

3. Method according to claim 1 or 2, characterized in that said machine tool (31) is arranged at the outer end of the spindle arm (30), that by means of a telescope arrangement yields the possibility of displacement of said machine tool (31) to and from said center axis (C).

4. Machine assembly for machining of a hub, wherein said hub (1) comprises a geometrical center axis (C), a bottom section (10) extending in a perpendicular plane relative the center axis (C) and a plurality of symmetrical placed flange surfaces (12) for blades/wings, which flange surfaces (12) extends in a plane creating a sharp angle (a) with said center axis (C), and wherein said machine assembly comprises; -arranging of a converting machine (3) with a machine tool (31) arranged at a spindle arm (30) and a machining table (2) belonging thereto,

-arranging of fixation means arranged to fix said hub (1) on the machining table (2) with the bottom section (10) parallel with the upper surface (20) of the table

(2) ,

-arranging of a control unit (5) arranged to control said machine (3) for machining of a flange surface (12) according to the above,

characterized in,

-that three converting machines (3) are symmetrical arranged with an angle of 120 degrees in between around said machining table (2),

-that each converting machine (3) is arranged with an angle machining arrangement (30-33) that enables machining of said angled flange surface (12) when said table surface (20) is horizontal,

-that said spindle arm (30) is arranged to be adjusted in said angle (a) in relation to the horizontal plane for application of the machine tool (31) in an angle (a ) that lies between 2-4 degrees and is acquired through a arranged on the machine

(3) and

-that said control unit (5) is arranged to control said three machines (3) for simultaneously tooling of three flange surfaces (12).