STEREOLITHOGRAPHY ADDITIVE MANUFACTURED SOFT TOOLING FOR USE IN BLADDER ASSISTED COMPOSITE MANUFACTURING

Nicholas Vaught

Bladder-assisted composite manufacturing (BACM) is an out-of-autoclave (OOA) composite manufacturing process that uses an inflatable internal bladder to compact carbon fiber-reinforced polymer (CFRP) prepregs against a rigid mold during curing, producing hollow CFRP products. Conventional BACM relies on metallic molds that are costly and time-consuming. Additive manufacturing offers a cost-effective alternative for rapidly producing BACM tooling. The objective of this study is to develop and validate a tooling system comprising stereolithography (SLA) tooling. SLA tooling is developed using a hybrid system. Where tooling geometry is produced with SLA inserts and structural rigidity and improved heat transfer is provided by an aluminum casing. Preliminary studies display that tooling manufactured solely from SLA material alone is not feasible for BACM due to the high manufacturing temperatures, poor heat transfer within the SLA material, and the low strength of the SLA material. Topology optimization in ABAQUS CAE is applied to the SLA insert geometry to achieve a 25% reduction in insert volume. This study conducts a design of experiments to evaluate the dimensional accuracy of manufactured CFRP cylindrical tube parts (D = 50.62 mm) as a function of bladder pressure and SLA insert life, while comparing topology-optimized and solid SLA insert designs. Both hybrid mold configurations could produce eight CFRP parts with a dimensional tolerance of up to 0.130 mm. Experimental results show progressive dimensional shrinkage of both the manufactured CFRP parts and SLA inserts with repeated mold use, primarily attributed to the thermoviscoelasticity of the SLA mold material at elevated temperature. The topology-optimized SLA insert resulted in reduced CFRP geometry errors due to reduced material expansion of the optimized region. Finite element (FE) models developed in ABAQUS CAE are used to analyze thermal and stress responses of the hybrid molds during the BACM process. Transient heat transfer models agree with experimental temperature measurements within 10 percent, while transient thermomechanical modeling validates the observed minor shape changes, consistent with the viscoelastic behavior of the SLA insert material.

STEREOLITHOGRAPHY ADDITIVE MANUFACTURED SOFT TOOLING FOR USE IN BLADDER ASSISTED COMPOSITE MANUFACTURING

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