Modern utility-scale wind turbine blades are hollow, near-100 m composite shells produced in matched heated metal molds, with plug-and-mold tooling from suppliers such as Gurit covering 126 m mold assemblies for offshore prepreg/infusion routes [S2].
The dominant process family is resin infusion of dry glass and carbon fabrics inside a closed mold under vacuum — variants include VARTM, SCRIMP and prepreg autoclave — followed by root insert bonding, demold, post-cure and trailing-edge/leading-edge finishing, with each step gated by geometric and NDT inspection and the mold vacuum line monitored by a pressure transmitter [S1][S2].
Process Map: Plug, Mold, Infusion, Cure, Demold
The canonical build sequence starts with a precision master plug (typically a CNC-machined or composite-trimmed male surface), which is used to lay up the female mold shell; Gurit's portfolio includes master plugs, milled parts, root plates, bonding flanges and full mold metal frames with integrated heating and vacuum channels [S2].
Once the mold is heated, dry multi-axial glass or carbon fabrics (often combined with balsa or PVC foam cores) are laid onto the lower shell, root inserts are positioned, the upper shell is closed, and resin is drawn in under vacuum; the heated mold then drives the cure cycle, after which the blade is demolded using blade-shell turning and clamping devices that protect the laminate [S2].
Tooling Stack: From Master Plug to 126 m Mold
Gurit explicitly markets itself as a global leader in industrial plugs and molds, with a Manufacturing Solutions Business Unit that ships wind blade molds up to 126 m, including modular designs, integrated electric/liquid heating systems, optimized vacuum processing and air heaters/coolers to shorten cure [S2].
The company's accessory list — hinges, automated layup and finishing devices, webs gantries, assembly stations, resin traps and covers — is the de facto bill of materials for a turnkey blade cell, and the same engineering design and analysis group is used for both prototype and full-scale serial production [S2].
Composite Layup and Resin Systems
Blade composites are typically glass-fibre-reinforced epoxy, with epoxy vinyl ester resin called out specifically in the literature for wind blade matrix systems and carbon-fibre reinforcements used selectively on the spar cap and root for stiffness [S3].
PROPID-class design tools generate the NURBS-based airfoil geometry, and the same database feeds the layup table that drives preform cutting; cunninghamia lanceolata (Chinese fir) veneer impregnation studies have been used as a low-cost test substrate for evaluating resin uptake versus impregnation time in wind-blade composite coupons [S3].
Cure Monitoring and Anomaly Detection
Frequency Modulated Continuous Wave (FMCW) radar is increasingly specified for in-mold cure monitoring because it gives a full view of the laminate during the exotherm; the radar head is set up and verified against reference standards with a multifunction process calibrator, and the arXiv 2306.10808 paper uses the analytic (complex) Intermediate Frequency signal of FMCW to separate material-specific reflection from round-trip delay, then strips healthy features with a complex-valued auto-encoder that uses an Exponential Amplitude Decay (EAD) activation exploiting the Rayleigh distribution of the instantaneous amplitude [S1].
On the residual, a focus Support Vector Data Description (focus-SVDD) defines the anomaly boundary, and the authors report superior performance over state-of-the-art unsupervised anomaly detection on collected data — directly addressing manufacturing defects that would otherwise push operation and maintenance cost upward [S1].
Comparison: Infusion Routes on Engineering Criteria
For blade builders, the four practical infusion/lamination routes stack up as: VARTM/SCRIMP infusion of dry fabrics (lowest tooling capex, room-temp cure possible, longer cycle, ~60-70% fibre volume fraction typical, with the resin front tracked by an inline flow meter), prepreg autoclave (highest mechanical performance and lowest porosity but requires an autoclave large enough for the blade, driving factory capex), resin transfer molding with heated matched tooling (Gurit's default, mid capex, integrated heating shortens cure and tightens dimensional control), and pultrusion of spar caps (high throughput for the heavily loaded structural element, used as a sub-component rather than full shell) [S2][S3].
The trade is per-blade capex versus mechanical reproducibility: prepreg/autoclave wins on stiffness-to-weight and defect rate, VARTM wins on tooling cost and energy, and the heated matched-metal mold route is the mainstream compromise at 80-126 m blade lengths where autoclaves do not exist [S2].
Post-Mold Operations and Repair
Post-demold, blades are post-cured, trimmed, drilled for lightning receptors and root bolts, surface-finished, balanced and painted; Springer chapter 10.1007/978-3-319-78166-2_8 documents advanced composite blade repair procedures and the parallel advanced manufacturing of metal gearbox components that the same wind-turbine service chain depends on, since a blade and its gearbox share a 20-25 year service horizon [S4].
Repair scope — gel-coat restoration, scarf-bonded patch, trailing-edge rebuild, leading-edge erosion shield replacement — is dictated by the defect type the FMCW + focus-SVDD pipeline is designed to flag during manufacture rather than in service [S1][S4].
Standards, Limits and What the QA Stack Must Catch
Defect classes that the in-mold non-contact QA must resolve include porosity, dry spots, race-tracking, misaligned ply drops, incorrect core placement, root-bondline voids and improper cure degree — all of which are listed in the arXiv 2306.10808 motivation as the failure modes that drive operation and maintenance cost upward [S1].
For simulation and controls work downstream, MathWorks' Wind Turbine block in Simscape Driveline provides the plant model that blade aerodynamic profiles are coupled into, and Qingdao Jintaida is one of the many Chinese Tier-2/Tier-3 OEMs advertising finished blades and turbines on Made-in-China, with a sourcing-AI channel running over the catalog [S5][S6].
For related composite-process reference, see our coverage of anode material manufacturing line decisions, and for inline AI inspection in adjacent cells the separator smart manufacturing AI/MES stack is a useful comparator. Where blade plants overlap with storage and inverter assembly on the same renewable EPC, the solar inverter smart manufacturing power-band audit anchors the controls-side spec.