Method for manufacturing a wind turbine blade and mandrel tool

1. A method for manufacturing a wind turbine blade, comprising:

a) arranging a fiber lay-up on a mandrel tool, the mandrel tool comprising a frame and, as seen in cross-section, at least two mandrel portions connected to the frame, and wherein at least a portion of the fiber lay-up is supported by an outer surface of the at least two mandrel portions,

b) reducing a cross-section size of the mandrel tool by retracting at least one of the at least two mandrel portions towards the frame,

c) arranging the mandrel tool inside adjacent blade sections,

d) increasing the cross-section size of the mandrel tool by extending at least one of the at least two mandrel portions away from the frame, and

e) infusing at least a portion of the fiber lay-up with a resin and curing the resin to obtain a cured joining portion joining the blade sections inside.

2. The method according to claim 1 , wherein the cross-section size of the mandrel tool is reduced by reducing a height of the mandrel tool and/or a width of the mandrel tool.

3. The method according to claim 1 , including, during step b) or between step b) and step c) the step of folding the fiber lay-up inwards.

4. The method according to claim 3 , wherein the mandrel tool comprises at least one gap extending along a longitudinal direction of the mandrel tool and arranged, as seen in cross-section, between two adjacent mandrel portions of the at least two mandrel portions, and wherein the fiber lay-up is folded inwards into the at least one gap.

5. The method according to claim 3 , wherein the fiber lay-up is tensioned during and/or after folding it inwards.

6. The method according to claim 4 , including, after step a) and before step b) the step of fixing at least one moveable longitudinal member to the mandrel tool such that it is arranged along the longitudinal direction of the mandrel tool and outside the at least one gap, and wherein the fiber lay-up is folded inwards by moving the at least one longitudinal member into the at least one gap.

7. The method according to claim 1 , wherein:

the at least two mandrel portions comprise at least two upper mandrel portions and at least two lower mandrel portions,

the method includes, during step a), the step of arranging

a web element between the at least two upper mandrel portions and between the at least two lower mandrel portions,

the web element includes a first portion, a second portion and a middle portion arranged between the first and second portions,

the method includes, before step b), the step of removing the middle portion, and

the method includes, after step d), the step of re-arranging the middle portion between the first and second portions of the web element.

8. The method according to claim 1 , including, after step b) and before step c), the step of strapping the fiber lay-up to the mandrel tool.

9. The method according to claim 1 , wherein:

the fiber lay-up comprises a fiber lay-up forming, once infused and cured, a shell joint joining a shell of a first one of the adjacent blade sections with a shell of a second one of the adjacent blade sections,

the fiber lay-up comprises a fiber lay-up forming, once infused and cured, one or more beam joints joining one or more beams of a first one of the adjacent blade sections with one or more corresponding beams of a second one of the adjacent blade sections, and/or

the fiber lay-up comprises a fiber lay-up forming, once infused and cured, a web joint joining a web of a first one of the adjacent blade sections with a web of a second one of the adjacent blade sections.

10. The method according to claim 1 , wherein the mandrel tool is arranged partially inside a first one of the blade sections such that a portion of the mandrel tool protrudes from the first one of the blade sections, and a second one of the blade sections is arranged adjacent to the first one of the blade sections such that the second one of the blade sections receives the portion of the mandrel tool protruding from the first one of the blade sections.