Additive Manufacturing of Overhang Structures Using Moisture-Cured Silicone with Support Material

Abstract

Additive manufacturing (AM) of soft materials has a wide variety of applications, such as customized or wearable devices. Silicone is one popular material for these applications given its favorable material properties. However, AM of silicone parts with overhang structures remains challenging due to the soft nature of the material. Overhang structures are the areas where there is no underlying structure. Typically, a support material is used and built in the underlying space so that the overhang structures can be built upon it. Currently, there is no support structure that has been used for AM of silicone. The goal of this study is to develop an AM process to fabricate silicone parts with overhang structures. We first identified and confirmed poly-vinyl alcohol (PVA), a water-soluble material, as a suitable support material for silicone by evaluating the adhesion strength between silicone and PVA. Process parameters for the support material, including critical overhang angle and minimum infill density for the support material, are identified. However, overhang angle alone is not the only determining factor for support material. As silicone is a soft material, it deflects due to its own weight when the height of the overhang structure increases. A finite element model is developed to estimate the critical overhang height paired with different overhang angles to determine whether the use of support material is needed. Finally, parts with overhang structures are printed to demonstrate the capability of the developed process.

A Review of 3D Printing Technologies for Soft Polymer Materials

“…2) Printing multiple materials as the support material. [151,158] Materials with a high Young's modulus can be used to support the softer material to avoid collapse. 3) Embedded printing.…”

“…However, they still used another silicone ink as support, which may have been a problem when printing overhang features (Figure 10B). Muthusamy et al [ 158 ] used PLA, which is much harder than silicone, as the support material. Overhang and spanning features of soft silicone can be printed with high quality in this way (Figure 10C).…”

“…Reproduced with permission. [ 158 ] Copyright 2018, Multidisciplinary Digital Publishing Institute. D) 3D printed organ chips via sacrificial sugar printing.…”

Intelligent Soft Surgical Robots for Next‐Generation Minimally Invasive Surgery

“…Possible solutions include introducing heating beds [ 251 ] or UV lamps, [ 248 ] embedded printing in support fluid (such as Carbopol), [ 253 ] as well as printing easily removed support materials. [ 254 ] We are optimistic about the applications of DIW in future MIS, and it has been demonstrated in the fabrication of various soft devices’ components, e.g., magnetic soft actuators, [ 100 ] fluidic actuators, [ 255 ] DEAs, [ 256 ] sensors, [ 257 ] circuits, [ 153 ] and seamless transition between stiffness gradients. [ 258 ] However, the integrated manufacturing capacity of current DIW technology is still limited, and further research is expected to fill this gap.…”

Multi-material direct ink writing of photocurable elastomeric foams

“…Thus, in order to print soft elastomers, many conventional techniques accept a slower polymerization reaction to allow for the formation of the desired microstructure. As a result of this slower solidification, printed parts are generally limited in terms of geometric complexity (i.e., overhanging features, unsupported walls) and resolution, 8,11,[18][19][20][21][22][23] Recently developed dual cure resins overcome the process-property-structure limitation. For example, numerous systems employ an initial photocuring reaction to create a "green-body" that quickly sets the shape prior to a post-print reaction that improves the mechanical toughness [24][25][26][27] However, these secondary reactions result in an increase in crosslink density and, as a result, the material's modulus.…”