Method of manufacturing wind turbine blades comprising composite materials

1. A method of manufacturing a wind turbine blade comprising composite materials, comprising:

selecting an outer mould part;

selecting an inner mould part, wherein at least a substantial part of the surface of the inner mould part comprises a compressible layer being covered by an airtight membrane;

evacuating the compressible layer, thus causing the compressible layer to become compressed;

positioning, after the evacuating, materials to be bonded in a mould cavity between the outer mould part and the inner mould part;

wherein after positioning, the outer mould part encloses the inner mold part;

evacuating the mould cavity; and

bonding the materials;

wherein the inner mould part is selected such that a force of expansion of the compressible layer provides sufficient pressure for the bonding;

and wherein the inner mould part is selected such that it exceeds the hollow space provided by the outer mould part when the compressible layer is not compressed.

2. The method according to claim 1 , further comprising:

detecting a leak in the airtight membrane.

3. The method according to claim 2 , wherein the detecting the leak is based on detecting an air pressure within the mould cavity.

4. The method according to claim 2 , wherein the detecting the leak is based on detecting an air pressure within the compressible layer and/or measuring an amount of air flowing into the compressible layer and/or measuring an amount of air flowing out of the mould cavity.

5. The method according to claim 2 , when a leak being present the method further comprising:

re-evacuating the compressible layer.

6. The method according to claim 1 , wherein air is allowed to flow into the compressible layer while evacuating the mould cavity.

7. The method according to claim 6 , further comprising:

re-evacuating the compressible layer occurs after the materials have bonded.

8. The method according to claim 1 , wherein the inner mould part is selected to comprise a rigid core part with a compressible coating being covered by a vacuum bag.

9. The method according to claim 8 , wherein the vacuum bag is dimensioned to fit over the rigid core part with its compressible coating in an uncompressed state.