Digital Materials: hybrid printing process for large scale production

Abstract

Lithography based additive manufacturing technologies (L-AMTs) are well known for their excellent surface quality and precision as well as for their nearly unlimited freedom of design. However, in some cases L-AMTs are limited in thermomechanical properties of the final part material or turnover quantity. This is of specific concern for photopolymers which typically exhibit rather low fracture toughness values. Therefore, a newly designed hybrid printing concept with large build platform was developed in order to expand the field of industrial applications. By combining inkjet printing with dynamic digital light processing, such toughening concepts relying on heterogeneity can be realized. A digital light process unit (used wavelength λ = 365 nm, pixel size 50 μm) and an inkjet unit (λ = 455 nm, resolution 600 dpi) are utilized to produce bioinspired heterogenous materials. The brick-and-mortar structure or the alternating hard and soft phases of nacre or glass sponge lead to crack deflection and branching, or crack propagation can be stopped in the soft layer called shielding effect. Fratzl et al. figured out that an effective shielding effect can be observed if the difference in elastic moduli of soft and hard phase is factor 5 or higher. By printing the primary hard matrix material by a lithography-based AMT-printer (usable build volume: 1000 x 280 x 300 mm³) and adding a soft ink as secondary material by an inkjet-printer, toughening of the digital material could be achieved. Tensile testing, stress relaxation nanoindentation and impact testing were performed to characterise thermomechanical properties. Furthermore, light, and scanning electron microscopy were utilized to assess properties of fractured samples and inkjet droplet quality. Assessed values agree with high performance polymers and printed digital materials reach an increase in tensile toughness of more than 60 %.