Research Papers

Printing Three-Dimensional Electrical Traces in Additive Manufactured Parts for Injection of Low Melting Temperature Metals

[+] Author and Article Information
John P. Swensen

Department of Mechanical Engineering and
Materials Science,
Yale University,
9 Hillhouse Ave., Mason Lab 110,
New Haven, CT 06511
e-mail: john.swensen@yale.edu

Lael U. Odhner

Right Hand Robotics LLC,
Medford, MA 02155
e-mail: lael@righthandrobotics.com

Brandon Araki

Massachusetts Institute of Technology,
Cambridge, MA 02139
e-mail: br.araki@gmail.com

Aaron M. Dollar

Department of Mechanical Engineering and
Materials Science,
Yale University,
15 Prospect Street,
New Haven, CT 06520
e-mail: aaron.dollar@yale.edu

1Corrresponding author.

Contributed by the Mechanisms and Robotics Committee of ASME for publication in the JOURNAL OF MECHANISMS AND ROBOTICS. Manuscript received September 2, 2014; final manuscript received December 12, 2014; published online February 27, 2015. Assoc. Editor: Satyandra K. Gupta.

J. Mechanisms Robotics 7(2), 021004 (May 01, 2015) (10 pages) Paper No: JMR-14-1236; doi: 10.1115/1.4029435 History: Received September 02, 2014; Revised December 12, 2014; Online February 27, 2015

While techniques exist for the rapid prototyping of mechanical and electrical components separately, this paper describes a method where commercial additive manufacturing (AM) techniques can be used to concurrently construct the mechanical structure and electronic circuits in a robotic or mechatronic system. The technique involves printing hollow channels within 3D printed parts that are then filled with a low melting point liquid metal alloy that solidifies to form electrical traces. This method is compatible with most conventional fused deposition modeling and stereolithography (SLA) machines and requires no modification to an existing printer, though the technique could easily be incorporated into multimaterial machines. Three primary considerations are explored using a commercial fused deposition manufacturing (FDM) process as a testbed: material and manufacturing process parameters, simplified injection fluid mechanics, and automatic part generation using standard printed circuit board (PCB) software tools. Example parts demonstrate the ability to embed circuits into a 3D printed structure and populate the surface with discrete electronic components.

Copyright © 2015 by ASME
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Fig. 1

The process of creating circuits by designing hollow channels in 3D printed parts and injecting with low melting point metals to create complete electrical traces: (a) a schematic capture of a 555 timer circuit, (b) a PCB board layout for the timer circuit, and (c) an operating circuit after injection

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Fig. 2

A schematic of the integrated wiring process, including the syringe pump, reservoirs, checks valves, and printed channels into which liquid metal is injected. Each trace within the part has a sprue, or injection point, used to fill the trace and the outlet of the injection device seals into the injection port using standard slip tip syringe connectors. The check valve ensures that the injection pathway remains primed with liquid metal between injections.

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Fig. 3

Channels for electrical traces were made using square profiles in the printed parts. To avoid printing support material into the traces, a diamond-shaped channel may be necessary.

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Fig. 4

The channels must be spaced so that two widths of the printed ABS filament can fit between them

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Fig. 5

The advancing fluid flow with branching where the branching flow is determined by relative fluid flow resistance in each channel: (a) the first branch point has been reached and (b) multiple branches have occurred

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Fig. 6

A diagram of the types of circuit elements that must be converted from the layered PCB format to an equivalent three-dimensional representation

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Fig. 7

The complete process of conversion of a single trace from circuit board cad software (EAGLE PCB) to the equivalent 3D printed part with channels ready for injection: (a) the EAGLE PCB representation of a single trace of the circuit, (b) the extracted tree representation of the trace starting at the injection point and ending at each component pin location, (c) a plot of the extracted tree with layer depths and channel diameters specified, and (d) the conversion of the circuit trace tree representation to STL format using the programmatic solid modeling language and software openscad

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Fig. 8

A spiral-shaped trace 465 mm long was printed into a test part to demonstrate lengths at which the traces can be cast, and the ability to make three-dimensional circuits. The sectioned part shows that the trace has completely filled the channel without leakage.

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Fig. 9

The expected and actual resistance measurements for three test pieces each of three different channel cross-sectional areas and/or lengths

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Fig. 10

The branching test piece and visual tracking of fluid advancement through background image subtraction using a visible light camera: (a) the branching test piece where the diameter of the channels in each of the four branches can be varied and (b)–(d) the advancing liquid metal for a single injection at three different times

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Fig. 11

Injection experimental results including potential error conditions: (a) the branching test piece used to compare injection simulations with experimental results, (b) a typical good injection, and (c) a problematic injection where an air bubble had formed in the injection apparatus, thus causing a delay when the bubble reached the injection point. Because the visual fluid tracking only allowed us to tracked fluid in the horizontal direction, only the position of the fluid head in each horizontal channel is plotted.

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Fig. 12

Injection simulations (dashed lines) and experimental results (solid lines): (a) all channels are 1.6 × 1.6 mm2, (b) the first channel is 0.8 ×0.8 mm2 and each successive channel has 2-, 3-, and 4-times the cross-sectional area, and (c) the optimized channel diameters. Note that in the case of the optimized channel diameters that a bubble in the injection pathway caused a delay during injection, but that the variance in final arrival time was less than the nonoptimized cases despite the delay.



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