Empirical Characterization of Lattice, Spring, and Non-Assembly Mechanisms Fabricated With Nylon Polymer Powder Bed Fusion

Abstract

Emerging additive manufacturing technologies are enabling the design of engineered parts with complex geometries and mechanical capabilities. Polymer powder bed fusion (PBF) printing is a promising process that is becoming more economically accessible while providing capabilities for printing non-assembly mechanisms. These processes could enable the automated design of complex personalized biomedical designs, such as prosthetics with integrated lattices, springs, and joints. However, manufacturing constraints and mechanical capabilities of these 3D printed designs requires further investigation to determine their feasibility and capabilities. Here, we conduct dimensional characterization and mechanical testing of Nylon 11 printed parts. Minimum fabrication constraints were measured to determine the smallest beam size as approximately 0.7 mm with a minimum gap size between beams of 0.35 mm. Mechanical testing demonstrated low anisotropy of parts in compression/tension which led to the testing of mechanical lattices with approximate elastic moduli of 25 MPa to 55 MPa. Helical springs worked in compression with a stiffness of approximately 0.2 N/mm to 16.8 N/mm for 3 mm to 7 mm wire diameters. Minimum printable gap sizes were used to inform the fabrication of a fully functional finger prosthetic with joints working directly after print post-processing, with no assembly required. Overall, these are foundational steps in demonstrating design rules and constraints for automating customized designs from polymer powder bed fusion printing, which offers unique capabilities for diverse and mechanically complex engineering applications.

Design for Additive Manufacturing: Recent Innovations and Future Directions

“…Powder printing processes are particularly useful for non-assembly mechanism creation since unused powder is present in areas between components of joints that, once removed, enables the movement of mechanisms requiring no further assembly. A recent study on nylon-powder-printed prosthetics found that relevant mechanisms operated best within a specified range of gap sizes from about 0.2 to 0.4 mm [13]. Further studies with geometric tolerances of laser powder bed fusion found that 15 mm diameter holes had mean printed diameters of 15.05 and 15.03 mm with standard deviations of 0.04 mm [54].…”

“…A table is provided at the end of the section that highlights the relevant materials and processes for each application area considered. [95], (B) a lightweight steering wheel [96], (C) bridge construction [97], (D) a chocolate printed geometry [98], (E) a finger prosthetic [13], and (F) a soft tensegrity robot [99]. Images adapted with permission.…”

“…When considering AM in the aircraft industry, fuzzy systematic approaches have identified five critical factors for its success: (1) cost effectiveness, (2) special demand capabilities, (3) part printability, (4) a lack of manufacturing technologies, and (5) the size of Figure 8. Representative innovative AM applications in diverse fields demonstrating (A) an unmanned aerial vehicle [95], (B) a lightweight steering wheel [96], (C) bridge construction [97], (D) a chocolate printed geometry [98], (E) a finger prosthetic [13], and (F) a soft tensegrity robot [99]. Images adapted with permission.…”

“…These DfAM endeavors provide a context for reviewing recent research in the framework proposed in Figure 1, in which Fabrication, Generation, and Assessment phases are considered during AM research and development. The Figure 1 framework demonstrates a case study with Nylon 11 material printed with powder bed fusion, which is a novel AM process that facilitates printing integrated parts and non-assembly mechanisms [13]. The Fabrication phase is demonstrated with a lattice design, in which minimum manufacturing constraints were measured during the Assessment phase using microscopy and mechanical testing to define a design space for configuring lattice structures in the Generation phase.…”

“…If the Generation phase were initiated prior to having this knowledge, it is highly likely a designer could explore infeasible solutions of the design space that would not result in manufacturable designs. In other cases, a designer may begin with generation steps that focus on innovations by proposing The Figure 1 framework demonstrates a case study with Nylon 11 material printed with powder bed fusion, which is a novel AM process that facilitates printing integrated parts and non-assembly mechanisms [13]. The Fabrication phase is demonstrated with a lattice design, in which minimum manufacturing constraints were measured during the Assessment phase using microscopy and mechanical testing to define a design space for configuring lattice structures in the Generation phase.…”