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Technical Briefs

Adaptive Extrusion Force Control of Freeze-Form Extrusion Fabrication Processes

[+] Author and Article Information
Xiyue Zhao

Department of Mechanical and Aerospace Engineering, Missouri University of Science and Technology, Rolla, MO 65401-0050xzd2c@mst.edu

Robert G. Landers

Department of Mechanical and Aerospace Engineering, Missouri University of Science and Technology, Rolla, MO 65401-0050landersr@mst.edu

Ming C. Leu

Department of Mechanical and Aerospace Engineering, Missouri University of Science and Technology, Rolla, MO 65401-0050mleu@mst.edu

J. Manuf. Sci. Eng 132(6), 064504 (Dec 17, 2010) (9 pages) doi:10.1115/1.4003009 History: Received April 22, 2009; Revised October 28, 2010; Published December 17, 2010; Online December 17, 2010

Freeze-form extrusion fabrication is an additive manufacturing process that extrudes high solids loading aqueous ceramic pastes in a layer-by-layer fashion below the paste freezing temperature for component fabrication. Due to effects, such as the air bubble release, agglomerate breakdown, and change in paste properties during extrusion as a result of liquid phase migration, the extrusion force is difficult to control. In this paper, an adaptive controller is proposed to regulate the extrusion force. Recursive least-squares is used to estimate the extrusion force model parameters during fabrication and a low-order control scheme capable of tracking general reference trajectories is designed and implemented to regulate the extrusion process. The controller is implemented for sinusoidal reference trajectories and the results demonstrate excellent tracking performance of the adaptive extrusion force controller. Several parts were fabricated with the adaptive extrusion force controller. These results illustrate the need for extrusion force control and that variable reference extrusion force profiles are required to fabricate complex features.

Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Gantry motion system (left) and extrusion mechanism (right)

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Figure 2

Extrusion mechanism schematic

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Figure 3

FEF process control system schematic

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Figure 4

Extrusion force response to a constant command voltage of 30 mV

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Figure 5

Discontinuous paste flow on top of a hollow cone

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Figure 6

Extrusion force (top) and command voltage (bottom). The sudden drop in extrusion force is due to the release of an air bubble.

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Figure 7

Commanded voltage (upper left), modeled and measured extrusion forces (bottom left), and estimated model parameters a (upper right) and b (lower right)

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Figure 8

Estimated model parameters a (top) and b (bottom) during steady-state for the experiment in Fig. 7

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Figure 9

Model time constant (top) and model gain (bottom) as functions of paste volume in a material reservoir

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Figure 10

Reference and measured extrusion force (top) and command voltage (bottom) responses for a sinusoidal reference with a frequency of 0.1 Hz. The reference and measured extrusion force signals are hardly distinguishable.

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Figure 11

Reference and measured extrusion force (top) and command voltage (bottom) responses for a sinusoidal reference with a frequency of 1 Hz

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Figure 12

Experimental extrusion force closed-loop magnitude (top) and phase (bottom) frequency responses for sinusoidal reference extrusion forces

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Figure 13

Extrusion force average error (top) and error standard deviation (bottom) for sinusoidal reference extrusion forces

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Figure 14

Small ogive cone fabricated with a constant ram velocity of 10 μm/s

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Figure 15

Extrusion force for the part in Fig. 1 fabricated with a constant ram velocity of 10 μm/s

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Figure 16

Small ogive cone fabricated with an extrusion force controller

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Figure 17

Extrusion force (top) and command voltage (bottom) for the part in Fig. 1 fabricated with an extrusion force controller. The reference and measured extrusion force signals are hardly distinguishable.

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Figure 18

Large ogive cone fabricated with an extrusion force controller

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Figure 19

Extrusion force (top) and command voltage (bottom) for the part in Fig. 1 fabricated with an extrusion force controller. The reference and measured extrusion force signals are hardly distinguishable.

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Figure 20

Square part fabricated with an extrusion force controller and a constant reference force of Fr=311 N

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Figure 23

Reference and measured extrusion force (top) and command voltage (bottom) for the square part in Fig. 2 fabricated with an extrusion force controller and a variable reference force

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Figure 21

Reference and measured extrusion force (top) and command voltage (bottom) for the square part in Fig. 2 fabricated with an extrusion force controller and a constant reference force of Fr=312 N. The reference and measured extrusion force signals are hardly distinguishable.

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Figure 22

Square part fabricated with an extrusion force controller and a variable reference force

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