Production Techniques for 3D Printed Inflatable Elastomer Structures: Part II—Four-Axis Direct Ink Writing on Irregular Double-Curved and Inflatable Surfaces

Abstract

This article is the second in a two-part series describing a process for conformal 3D printing onto inflated substrates. The article describes the design and build of a custom-built four-axis 3D printer with the ability to measure the shape of any uneven substrate, and to then accurately extrude a thixotropic silicone onto the substrate by using Direct Ink Writing techniques. Details of strategies for 3D scanning a double-curved tubular inflated substrate using an industrial triangulation laser measurement device are given. Methods to import scan data and create a digital representation of the surface within the parametric design software Grasshopper 3D are explained. Geodesic print paths are created over the surface of the computed substrate, and these are the basis for calculating 3D printer toolpaths. A constant surface linear velocity strategy is developed, allowing the printer to move the print nozzle at a varying speed over the substrate surface. The change in speed is correlated with changes in the surface linear velocity of a fourth axis rotation of the variable radius balloon substrate. This ensures that the extruded bead maintains a constant thickness, even while using a constant flow rate deposition. The process is achieved by adapting cartographic techniques to re-project to the desired print paths. The efficacy of this technique is analyzed by 3D scanning a printed patterned balloon, then measuring and comparing multiple cross-sections of the extruded beading.

Additive Manufacturing of Multi‐Scale Porous Soft Tissue Implants That Encourage Vascularization and Tissue Ingrowth

“…[24] In a second application (coating a mammary implant), we coated the gypsum form of a human breast with a 250 µm thick silicone membrane (Figure 3G-I). The substrate curvature was measured using a laser [25] and a spray deposition toolpath was derived, ensuring that the nozzle tip is maintained at 85 mm from the surface. Three rope-coil layers (A = 3.5 mm,) were then deposited over the surface (using NuSil MED 4820).…”

“…We print open-pore structures over highly curved surfaces, using multi-axis printing techniques. Building upon pre-existing principles, [24,25] we show that a substrate can be coated by first ascertaining the surface topology using laser measurements, and then calculating a toolpath over that surface -resulting in an evenly distributed coating. This shows that varying LRC loops can be used to completely coat complex shapes.…”

Curved-layered material extrusion modeling for thin-walled parts by a 5-axis machine

“…However, both of them did not resolve the problem of non-support additive manufacturing. Coulter et al (2018) creatively used a four-axis machine to deposit fibers in a shaped rotator around a special rotary axis. However, this method can only form structures conformal to the shape of the rotator.…”

Bioinspired Heart Valve Prosthesis Made by Silicone Additive Manufacturing

“…This was possible by rastering over the substrate surface with a 1D measurement laser and then using the resulting spatial information to design the printer's tool path. 42 Leaflets and fibers were over-sprayed with the soft silicone solution to improve the smoothness of the leaflet surface. Finally, a stiff silicone composition featuring hardness of 80 A and modulus of 13.52 MPa was used for the directed deposition of inter-leaflet triangles that precisely match the anatomy and mimic the elastic modulus 43 of the native aortic root ( Figure 4D).…”