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Additively manufactured photopolymer mold inserts for low-volume micro-injection molding
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School of Engineering |
Master's thesis
Electronic archive copy is available via Aalto Thesis Database.
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en
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126
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Abstract
Additive manufacturing (AM) enables rapid tooling for low-volume injection molding; however, photopolymer inserts remain constrained by thermomechanical performance. This thesis evaluates additively manufactured photopolymer mold inserts embedded in metallic frames for micro-injection molding of thin-walled, endoscopy-representative components. Four insert materials (Formlabs Rigid 10K, Formlabs High Temp, BASF Ultracur3D RG 3280, and Stratasys Digital ABS Plus) were produced using SLA/MSLA or PolyJet and tested on a Babyplast 6/12 with medical-grade LDPE (Purell 2410T).
To assess feasibility under realistic constraints, three iterative trials evaluated dimensional accuracy, deformation, demolding performance, and durability. Autodesk Moldflow studies supported the workflow through gate-location selection, nominal machine capability checks, and machine-driven shot reconstruction. Geometric fidelity depended strongly on resin-specific behavior and post-curing history. Accordingly, global scaling was not robust, whereas axis-specific compensation improved agreement with target dimensions for Rigid 10K, and Ultracur3D exhibited a stronger overall contraction than the other materials. Demolding remained the dominant bottleneck. To mitigate adhesion, a low-temperature ta-C + TiO PVD coating was evaluated but produced no measurable improvement in release under the applied conditions and was further constrained by limited coverage in deep features. In contrast, a semi-permanent chemical release led to a qualitative reduction in adhesion, without fully eliminating it, where application access was sufficient.
Overall, hybrid photopolymer inserts are feasible within a bounded operating window. Therefore, reliable performance requires (i) co-design of the closure stack-up, (ii) metrology-driven calibration, (iii) conservative process ramp-up, (iv) robust feed-system design, and (v) practical strategies to address adhesion and ensure repeatable demolding.
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Supervisor
Salmi, MikaThesis advisor
Schlund, SebastianJäger, Siim