The invention relates to a method of manufacturing a rotor blade for a wind turbine , more speci fically a method of manufacturing a first hal f rotor blade shell , a second hal f rotor blade shell and a spacer forming a leading edge closure of the rotor blade designed to receive in an assembled state a leading edge of the first hal f rotor blade shell and on the opposed side a leading edge of the second hal f rotor blade shell .

To achieve manufacturing cost reduction of rotor blades , large scale production is a first solution to limit downtime while allowing purchasing cost reduction . Di f ferent manufacturing processes are available for mass production of rotor blades .

Resin trans fer molding (RTM) is a well-known production process in which a reactive resin in the form of a resin-hardener mixture is inj ected into a closed mold, usually a two-part mold, in which dry fiber plies have been previously placed . In this process , the fiber plies are placed in the mold . The mold is then closed, and reactive resin is constantly inj ected via a sprue at an inj ection pressure of between 0 . 5 and 8 bar . The components of the resin system are mixed in advance in a pressure head . The fiber plies are thus impregnated with the resin . Excess resin escapes at vents . The resin is cured under holding pressure and with the vents closed . When the reactive resin has cured, the mold is opened, and the finished part is extracted from the mold . This process allows to obtain high performance structural parts by directly combining reinforcement in the form of fiber plies and matrix in the form of the reactive resin .

In high-pressure resin trans fer molding (HP-RTM) the inj ection pressure can be increased to up to 200 bar . A fully cured composite part can be obtained in a time less than 10 minutes , depending on selected chemicals and on the process parameters . The high-pressure process allows a high throughput reducing manufacturing costs .

Compression molding using sheet molding compound ( SMC ) is another well-known production process that allows high volume production and cost-ef fective manufacturing typically with reduced scrap . Weight reduction of manufactured parts is also achieved due to lower dimensional requirements .

It is an obj ect of the present invention to provide for a method of manufacturing a rotor blade for a wind turbine that allows the combination of di f ferent production processes selected to optimi ze manufacturing of each component of the rotor blade , thereby reducing manufacturing costs at the level of the components of the rotor blade .

This obj ective is met according to the present invention by providing a method of manufacturing a rotor blade for a wind turbine according to claim 1 . Further advantageous embodiments of the invention are subj ect of the dependent claims .

A method of manufacturing a rotor blade for a wind turbine is disclosed, comprising the step of providing plies of fibrous material and stacking the plies in a first mold for a first hal f rotor blade shell and in a second mold for a second hal f rotor blade shell , the first mold and the second mold being designed for use in a high-pressure resin trans fer molding process . The first hal f rotor blade shell and the second hal f rotor blade shell include each a plurality of circular passages arranged inboard and designed to mate with a plurality of bushings for fastening the rotor blade to a hub of the wind turbine . Preferably, the plies are made of dry fibrous material to produce homogeneous laminates with a minimum of defects . Typically, plies of triaxial non-crimped fabric in carbon fiber can be used . Recycled carbon fiber can also be used as an ecological alternative . Preferably, two circular passages are provided to receive each time a bushing .

Further, the method comprises the step of inj ecting a resin by high-pressure resin trans fer molding process in the first mold and in the second mold to bond the plies and manufacture the first hal f rotor blade shell and the second hal f rotor blade shell .

The method comprises also the step of providing the plurality of bushings each formed as a solid cylindrical sleeve having a wall protrusion extending radially outwards from an outer surface of the sleeve . The presence of a wall protrusion extending radially is advantageous to increase the circumferential contact surface with the material surrounding each bushing and improves the fixation of the bushing in an axial direction of the bushing . Preferably, the plurality of bushings are made of steel to provide for the required mechanical resistance , wherein the bushings can have undergone an electrostatic coating to limit the risk of corrosion .

In addition, the method comprises the step of manufacturing and providing a spacer . The spacer comprises a rotor blade root , preferably solid, defining a reference plane and including the plurality of bushings arranged with their axial direction perpendicular to the reference plane . The wall protrusion of the plurality of bushings is each time embedded in the rotor blade root during manufacturing to ensure their anchoring in the rotor blade root . Advantageously, the method eliminates a step of fixation of the bushings , for example with an adhesive agent , after manufacturing the rotor blade root .

In a known manner, the rotor blade comprises the rotor blade root for fastening the rotor blade to a rotor shaft or to a hub of the wind turbine . The hub is typically attached to the rotor shaft . In operation, the rotor shaft or its axis of rotation is at least approximately aligned in the direction of the incoming wind .

Further, the spacer comprises a leading edge closure and a rotor blade tip, the leading edge closure extending from the rotor blade root outboard into the rotor blade tip facing away from the rotor blade root .

The rotor blade root and the leading edge closure have a receiving region designed to receive on one side a leading edge of the first hal f rotor blade shell and on the opposed side a leading edge of the second hal f rotor blade shell to form a leading edge of the rotor blade . The spacer forms a supporting structure for the first and the second hal f rotor blade shell and delimits with the first and the second hal f rotor blade shell a hollow body of the rotor blade . The spacer is designed to maintain at a distance a trailing edge of the first and the second hal f rotor blade shell to form the trailing edge of the rotor blade .

Preferably, the receiving region is formed with a profile on the one side complementary to the leading edge of the first hal f rotor blade shell and on the opposed side complementary to the leading edge of the second hal f rotor blade shell . This arrangement forms a seamless transition from the leading edge closure to the first and second hal f rotor blade shells .

After preferably cleaning contact surfaces of the first hal f rotor blade shell and the second hal f rotor blade shell , the method comprises the step of positioning the first hal f rotor blade shell and the second hal f rotor blade shell in the receiving region with the plurality of circular passages mounted around the plurality of bushings . Further, the step of bonding the first hal f rotor blade shell , the second hal f rotor blade shell and the spacer to form the leading edge of the rotor blade and bonding the first hal f rotor blade shell and the second hal f rotor blade shell to form a trailing edge of the rotor blade is performed .

As a further step, a plurality of washers having an internal diameter corresponding to the external diameter of the plurality of bushings are provided to mount a washer at each end of the bushings . To mount the washer, it is inserted at each end of the bushing and a pair of washers can be maintained at each end of the bushing by a bolt used to fasten the rotor blade to the rotor shaft or to the hub of the wind turbine .

Advantageously, the method allows the use of the high-pressure resin trans fer molding process for the manufacturing of the first hal f rotor blade shell and the second hal f rotor blade shell , for which the process is particularly well adapted in terms of costs . Further, the leading edge closure of the rotor blade can be manufactured by a di f ferent method that is better adapted for that type of part . Therefore , the method optimi zes cost by allowing the use of di f ferent manufacturing processes for the adapter and the first as well as the second hal f rotor blade shell , each process being independently optimi zed . Further, this method allows scalability of manufacturing by using production processes that are adequate for small as well as large production quantities . In addition, the bushings are integrated to the rotor blade during the manufacturing process of the rotor blade itsel f such that an additional step is not necessary anymore after molding the rotor blade to fix the bushings .

In a preferred embodiment , the thickness of the spacer is designed to allow the bushings to protrude on each side of the spacer at least by a height corresponding to the thickness of the second hal f rotor blade shell and the first hal f rotor blade shell , respectively, and by a height corresponding to less than the combined thickness of the second hal f rotor blade shell with the washer and the combined thickness of first hal f rotor blade shell with the washer, respectively . This arrangement forms a seamless transition from the bushings to the first and second hal f rotor blade shells .

In a preferred embodiment , the spacer is manufactured by compression molding using sheet molding compound, preferably of glass- fiber reinforced polyester . This process allows cost optimi zation for manufacturing the spacer . Further, in the absence of an impregnation step of the fibrous material , a wide range of dry fibrous material can be used like recycled fibrous material or fibrous material coming from renewable sources , what would not be the case with resin trans fer molding .

In a preferred embodiment , the spacer is manufactured by inj ection molding, preferably of thermoplastic foam . This process allows also cost optimi zation for manufacturing the spacer while thermoplastic foam allows weight reduction of the spacer .

In a preferred embodiment , the step of manufacturing the spacer by molding comprises the step of manufacturing the spacer in a plurality of spacer segments and the step of assembling the plurality of spacer segments to form the spacer . Preferably, the spacer is manufactured in two to six spacer segments . Most preferably, four to six spacer segments are provided . Advantageously, this step allows to reduce tooling si ze .

In a preferred embodiment , the spacer segments are assembled by form fit connection . Such a connection allows an assembly of the spacer segments to form the spacer without using mechanical elements or adhesive agents , what limits the manufacturing costs .

In a preferred embodiment , the trailing edge of the first hal f rotor blade shell and the trailing edge of the second hal f rotor blade shell are assembled directly with each other to form a trailing edge of the blade . This embodiment allows a further weight reduction because the trailing edge is free from spacer .

In a preferred embodiment , the trailing edge of the first hal f rotor blade shell and the trailing edge of the second hal f rotor blade shell are milled to si ze before being assembled .

The wall thickness of the trai ling edge of the first and second hal f rotor blade is thinner than the wall thickness in the rest of the first and second hal f rotor blade and is designed such that , in the assembled state , both trailing edges assembled directly to each other form the trailing edge of the rotor blade without a portion of the spacer necessary at the trailing edge . Milling the trailing edge of the first and second hal f rotor blade to si ze , i . e . to give them their final form for the assembly as the rotor blade , allows removing irregularities at the edges of the first and second hal f rotor blade before bonding them .

In a preferred embodiment , the rotor blade tip forms a tip closure of the rotor blade , the tip closure being arranged at an outboard end of the second hal f rotor blade shell and at an outboard end of the first hal f rotor blade shell . Outboard defines a position or direction farther from the center and inboard defines the opposed direction .

Preferably, the rotor blade tip has a tip receiving region designed to receive on one side a tip edge of the first hal f rotor blade shell and on the opposed side a tip edge of the second hal f rotor blade shell to form a tip edge of the rotor blade .

Preferably, the rotor blade tip has a profile in the form of a wedge tapering in the direction from the leading edge to the trailing edge to follow the shape of the outboard end of the second hal f rotor blade shell and at an outboard end of the first hal f rotor blade shell . Preferably, the tip receiving region is formed with a profile on the one side complementary to the tip edge of the first hal f rotor blade shell and on the opposed side complementary to the tip edge of the second hal f rotor blade shell . This arrangement forms a seamless transition from the tip closure to the first and second hal f rotor blade shells .

In a preferred embodiment , the rotor blade root forms a trailing edge closure arranged at an inboard end of the second hal f rotor blade shell and at an inboard end of the first hal f rotor blade shell .

In a preferred embodiment , the wall protrusion of the plurality of bushings is in the form of at least one rib arranged at mid-height of the bushings . This embodiment provides for a strong anchoring of the bushings in the rotor blade root .

Bolts made of glass fiber reinforced or carbon fiber reinforced thermoplastic materials can be inserted in the washers and bushings for fastening the rotor blade to the rotor shaft . The use of such materials reduces weight and cost while avoiding corrosion problems .

Description of the figures

The present invention will now be described by way of an example with reference to the accompanying drawings in which :

Fig . 1 shows a perspective view of the components of the rotor blade before assembly; Fig . 2 shows a top view of the rotor blade in the assembled state ;

Fig . 3 shows a cross section of the rotor blade along the section A-A illustrated in Fig . 2 ;

Fig . 4 shows a cross section of the rotor blade along the section C-C illustrated in Fig . 2 ;

Fig . 5 shows a cross section of the rotor blade along the section D-D illustrated in Fig . 2 ;

Fig . 6 shows in a cross sectional view a portion of a rotor blade root after the step of manufacturing the rotor blade root with an embedded bushing;

Fig . 7 shows in a cross sectional view the same portion as of Fig . 6 after a next step with a first hal f rotor blade shell and a second hal f rotor blade shell accommodated around the bushing; and

Fig . 8 shows in a cross sectional view the same portion as of Fig . 6 after a next step with washers arranged around the bushing .

Fig . 1 shows a first hal f rotor blade shell 10 and a second hal f rotor blade shell 20 manufactured according to the invention for a rotor blade 30 for a wind turbine .

The method of manufacturing the rotor blade comprises the step of providing plies of fibrous material in the form of triaxial non-crimped fabric in carbon fiber and stacking the plies in a first mold for a first hal f rotor blade shell and in a second mold for a second hal f rotor blade shell , the first mold and the second mold being designed for use in a high-pressure resin trans fer molding process . Further, the method comprises the step of inj ecting a resin by high-pressure resin trans fer molding process in the first mold and in the second mold to bond the plies and manufacture the first hal f rotor blade shell 10 and the second hal f rotor blade shell 20 .

The first hal f rotor blade shell 10 and the second hal f rotor blade shell 20 include each a plurality of circular passages 40 , here each time two circular passages . The circular passages 40 are arranged inboard to mate with a plurality of bushings 50 for fastening the rotor blade to a hub of the wind turbine .

The rotor blade comprises a rotor blade root 42 for fastening the rotor blade 10 to a not represented rotor shaft or to a hub of the wind turbine . The hub is typically attached to the rotor shaft . In operation, the rotor shaft or its axis of rotation is at least approximately aligned in the direction of the incoming wind . The rotor blade has a leading edge 44 and a trailing edge 46 extending from an inboard end 45 to an outboard end 47 .

The method comprises also the step of providing the plurality of bushings 50 made of steel each formed as a solid cylindrical sleeve having a wall protrusion 52 extending radially outwards from an outer surface of the sleeve as illustrated in Fig . 6 . The wall protrusion 52 is in the form of at least one rib arranged at mid-height of the bushing . The rib provides for a strong anchoring of the bushing in the rotor blade root 42 .

In addition, the method comprises the step of manufacturing and providing a spacer 60 . The spacer 60 comprises the rotor blade root 42 defining a reference plane and including the plurality of bushings 50 arranged with their axial direction perpendicular to the reference plane . The rotor blade root 42 is formed as a solid inboard end of the rotor blade extending from the leading edge 44 to the trailing edge 46 .

The wall protrusion 52 of the plurality of bushings is each time embedded in the rotor blade root during manufacturing to ensure their anchoring in the rotor blade root 42 .

Further, the spacer comprises a leading edge closure 64 of the rotor blade extending from the rotor blade root 42 outboard into a rotor blade tip 68 facing away from the rotor blade root .

As shown in Fig . 3 , 4 and 5 , the spacer 60 has a receiving region 70 designed to receive on one side the first hal f rotor blade shell 10 and on the opposed side the second hal f rotor blade shell 20 to form the rotor blade . The receiving region extends over the rotor blade root 42 , the leading closure 64 and the rotor blade tip 68 . The receiving region is formed with a profile on the one side complementary to the leading edge of the first hal f rotor blade shell and on the opposed side complementary to the leading edge of the second hal f rotor blade shell . This arrangement forms a seamless transition from the spacer to the first and second hal f rotor blade shells .

After cleaning contact surfaces of the first hal f rotor blade shell and the second hal f rotor blade shell , the method comprises the step of positioning the first hal f rotor blade shell 10 and the second hal f rotor blade shell 20 in the receiving region 70 with the plurality of circular passages 40 mounted around the plurality of bushings 50 as shown in Fig . 4 and Fig . 7 . Then, the step of bonding the first hal f rotor blade shell , the second hal f rotor blade shell and the spacer 60 is performed to form the leading 44 and trailing edge 46 of the rotor blade as well as the inboard end 45 and the outboard end 47 .

In a previous step, the trailing edge of the first hal f rotor blade shell and the trailing edge of the second hal f rotor blade shell have been milled to si ze before being bonded directly to each other to form the trailing edge as shown in Fig . 4 .

Fig . 4 shows the receiving region 70 of the leading edge closure 64 in which on one side a leading edge of the first hal f rotor blade shell 10 and on the opposed side a leading edge of the second hal f rotor blade shell 20 are accommodated to form the leading edge 44 of the rotor blade .

Fig . 5 shows the receiving region 70 of the rotor blade tip 68 in which an outboard end of the first hal f rotor blade shell 10 and on the opposed side an outboard end of the second hal f rotor blade shell 20 are accommodated to form the outboard end of the rotor blade .

As a further step, a plurality of washers 80 having an internal diameter corresponding each time to the external diameter of the plurality of bushings 50 are provided and a washer is mounted at each end of the bushings as shown in Fig . 8 . The thickness of the spacer 60 is designed to allow the bushings 50 to protrude on each side of the spacer at least by a height corresponding to the thickness of the second hal f rotor blade shell 10 and the first hal f rotor blade shell 20 , respectively, and by a height corresponding to less than the combined thickness of the second hal f rotor blade shell with the washer and the combined thickness of first hal f rotor blade shell with the washer, respectively, as shown in Fig . 6 , Fig . 7 and Fig . 8 .

The spacer 60 is manufactured by compression molding using sheet molding compound of glass- fiber reinforced polyester, wherein the spacer 60 is manufactured in a plurality of , here four, spacer segments 60a, 60b 60c and 60d illustrated in Fig . 2 and the plurality of spacer segments are assembled by form fit connection to form the spacer 60 . A first spacer segment 60a comprises the rotor blade root 42 with an adj oining portion of the leading edge closure 64 . A second 60b spacer segment adj oining the first spacer segment and a third spacer segment 60c adj oining the second spacer segment form each a section of the leading edge closure 64 . A fourth spacer segment 60d adj oining the third spacer segment comprises an outboard section of the leading edge closure 64 and the rotor blade tip 68 .

The rotor blade tip 68 has a profile in the form of a wedge tapering in the direction from the leading edge to the trailing edge to follow the shape of the outboard end of the second hal f rotor blade shell and at an outboard end of the first hal f rotor blade shell .

List of reference signs first hal f rotor blade shell 10 second hal f rotor blade shell 20 rotor blade 30 circular passages 40 rotor blade root 42 leading edge 44 inboard end 45 trailing edge 46 outboard end 47 bushings 50 wall protrusion 52 spacer 60 spacer segments 60 a, 60b 60c and 60d leading edge closure 64 rotor blade tip 68 receiving region 70 washers 80