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Research Papers

Development of Freeze-Form Extrusion Fabrication With Use of Sacrificial Material

[+] Author and Article Information
Ming C. Leu

Department of Mechanical and
Aerospace Engineering,
Missouri University of Science and Technology,
Rolla, MO 65409
e-mail: mleu@mst.edu

Diego A. Garcia

Department of Mechanical and
Aerospace Engineering,
Missouri University of Science and Technology,
Rolla, MO 65409
e-mail: daghd3@mst.edu

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING. Manuscript received April 15, 2014; final manuscript received September 4, 2014; published online October 24, 2014. Assoc. Editor: Darrell Wallace.

J. Manuf. Sci. Eng 136(6), 061014 (Oct 24, 2014) (9 pages) Paper No: MANU-14-1200; doi: 10.1115/1.4028542 History: Received April 15, 2014; Revised September 04, 2014

The development of freeze-form extrusion fabrication (FEF) process to fabricate three-dimensional (3D) ceramic parts with use of sacrificial material to build support sections during the fabrication process is presented in this paper. FEF is an environmentally friendly, additive manufacturing (AM) process that builds 3D parts in a freezing environment layer-by-layer by computer controlled extrusion and deposition of aqueous colloidal pastes based on computer-aided design (CAD) models. Methyl cellulose was identified as the support material, and alumina was used as the main material in this study. After characterizing the dynamics of extruding alumina and methyl cellulose pastes, a general tracking controller (GTC) was developed and applied to control the extrusion force in depositing both alumina and methyl cellulose pastes. The controller was able to reduce the time constant of the closed-loop system by more than 65% in comparison to the open-loop control system. Freeze-drying was used to remove the water content after the part has been built. The support material was then removed in the binder burnout process. Finally, sintering was done to densify the ceramic part. The fabrication of a cube-shaped part with a square hole in each side that requires depositing the sacrificial material during the FEF process was demonstrated.

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References

Figures

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Fig. 1

Experimental setup of the multi-extruder FEF machine

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Fig. 2

Comparison of simulation and experimental results based on the gains and time constants for alumina paste extrusion in Table 1. The curves with dashed lines are obtained by fitting the force-time experimental data with a first-order model for the paste-extrusion dynamics.

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Fig. 3

Relationship between steady-state force and ram velocity for alumina paste extrusion

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Fig. 4

Relationship between time constant and ram velocity for alumina paste extrusion

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Fig. 5

Comparison of modeled and measured results with a step reference input alternating between 1 and −1 mm/s for extrusion of alumina paste

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Fig. 6

Block diagram of the GTC

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Fig. 7

Response with the use of the GTC for extrusion of alumina paste

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Fig. 8

Reference versus measured force using the GTC with a rise time of 1 s for extrusion of alumina paste

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Fig. 9

Reference extrusion force versus extrudate velocity for alumina paste

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Fig. 12

CAD model of a cube with a square hole on each side (top), the extruded part with sacrificial material (middle), and the sintered part (bottom)

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Fig. 11

Different table speeds for extrusion of alumina paste at 400 N extrusion force (left) and for extrusion of methyl cellulose paste at 350 N extrusion force (right)

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Fig. 10

Cross sections of rectangular blocks with the stand-off distance of (a) 600 μm, (b) 500 μm, and (c) 400 μm

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