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.
Highlights
Silicone is widely used in variety of industries such as food, medical, and automotive, because of its good bio-compatibility, thermal insulation, stretchability, and chemical stability
The adhesion strength is 0.115 N/mm2 for poly-vinyl alcohol (PVA) over silicone and 0.047 N/mm2 for poly-lactic acid (PLA) over PVA. In another case of the adhesion strength for silicone over PVA, the breakage always happened in between layers of silicone which means that the adhesion strength between silicone and PVA is stronger than the interlayer strength
It is confirmed that PVA and silicone can adhere properly to facilitate the printing process
Summary
Silicone is widely used in variety of industries such as food, medical, and automotive, because of its good bio-compatibility, thermal insulation, stretchability, and chemical stability. One of the most common processes of manufacturing silicone parts is molding. It is difficult to use molding to manufacture parts with a complicated geometry or undercut features. There is an increasing demand for freeform silicone parts for applications including prototyping of fixtures, soft robotics [1], wearable sensors [2], drug delivery systems [3], and personalized assistive devices [4], etc. It is not cost effective to use molding to manufacture low-volume or personalized products. Additive manufacturing (AM) of silicone has drawn attention to overcome the limitations of traditional manufacturing processes for silicone
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