During manufacturing of a mold made of composite material, the material undergoes a pre-curing and a final post-curing, both constituting a high temperature thermal cycle permitting the polymerization of the resin and thus attaining the mechanical properties required in the mold.
Later, during production of pieces made of composite material with this mold, it is common to undergo phenomena derived from expansion and contraction of the material, namely Spring-back (recovery of material elasticity) and Chemical Shrinkage (increase of the density of the material during the curing process).
These effects provoked by thermal cycles result in permanent geometrical deformations in the bed of the molds that will later be transmitted to the products made in the mold.
These effects intensify as the surface and geometrical complexity of the molds increase (double curvature and sharp angles).
The lack of repetitiveness in the behavior of pieces of large dimensions makes the correction of these deformations using a geometric factor applicable to the geometry of the model for which the mold is obtained unfeasible. Thus, these effects need to be mitigated by other means, whose objective is to keep the model of the mold from altering the geometry of the manufactured piece on the mold itself.
Some of these solutions are based on laminating the bed of the mold using a lamination made of fiberglass fabrics interwoven and pre-impregnated with a low content of resin and following a balanced lamination sequence (in % of fiber) and symmetrical in the orientation of the fibers. Likewise, in order to reduce these deformations, the molds are manufactured on models having the same or similar coefficient of thermal expansion (CTE). Notwithstanding the above, these solutions failed to eradicate all the cited deviations.
In this respect, Spanish patent ES2208028, held by the same applicant of the present invention, is known to address this issue and describes the production of a mold of wind turbine blade shells comprising two parts, upper and lower, joined together by a pivoting mechanism that permits attainment of all positions necessary to manufacture a blade. Each part of the mold, semi-mold, comprises a bed or cradle of composite material resting on a structure braced against some ribs distributed along the bed.
The bed is the part that gives the final product its aerodynamic geometry, likewise serving as a base for its production. In the cited Patent, this bed is formed by a sandwich structure with skins of composite material (pre-impregnated) and an aluminum honeycomb core that acts as a thermal chamber by the introduction of hot air through some conduits situated along the bed.
The conduits are coupled to the surface of the bed by some ribs that, by some runners secured to a pivoting system and some hinges on the legs of the mold structure, are designed to absorb the deviations of the mold.
However, once the aforementioned deformations have occurred in the bed, they cannot be corrected with the ribs mentioned in the patent and the deformations could end up exceeding the mold bed's required surface tolerances and hence the final product obtained.
Other solutions in the State of the art are known to attempt to solve the deformations in the mold bed, particularly international patent WO2010103493, which describes a mold solution incorporating a longitudinally-laminated tube together with some actuators fitted in various sections perpendicular to the mold surface. These sections are in turn reinforced by a rib that joins the different actuators in a single section. Nonetheless, this solution obtains an elevated longitudinal rigidity and little cross rigidity, thus the adjustment or correction of the mold section is carried out lengthwise. On the other hand, this solution is not equipped with an expansion system and therefore not only fails to solve the aforementioned problems but also applies solely to low-temperature molds for infusion mold blades.