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Research Papers

Hybrid Extrusion Force-Velocity Control Using Freeze-Form Extrusion Fabrication for Functionally Graded Material Parts

[+] Author and Article Information
Bradley K. Deuser

e-mail: bkd4k3@mst.edu

Greg E. Hilmas

Department of Mechanical and Aerospace Engineering,
Missouri University of Science and Technology,
Rolla, MO 65409

Contributed by the Manufacturing Engineering Division of ASME for publication in the Journal of Manufacturing Science and Engineering. Manuscript received August 16, 2012; final manuscript received April 27, 2013; published online July 17, 2013. Assoc. Editor: Tony Schmitz.

J. Manuf. Sci. Eng 135(4), 041015 (Jul 17, 2013) (11 pages) Paper No: MANU-12-1249; doi: 10.1115/1.4024534 History: Received August 16, 2012; Revised April 27, 2013; Accepted April 30, 2013

Freeze-form extrusion fabrication (FEF) is an additive manufacturing (AM) process that uses an aqueous-based paste loaded with ceramic or metal powder to build complex, three-dimensional parts by extruding the material from a syringe onto a solid substrate in a subzero temperature environment. This paper describes the development of an intelligent control methodology for paste extrusion that utilizes a hybrid extrusion force-velocity controller. A plunger velocity controller was used to ensure a steady extrusion flow rate, and an extrusion force controller was developed to precisely regulate the starting and stopping of the extrusion process. Both controllers were coupled with a hybrid control scheme for extrusion-on-demand and air bubble release compensation. The plunger velocity controller successfully regulated the output material composition from two syringes, and the extrusion force controller precisely controlled the extrusion start and stop. Air bubble release compensation reduced the severity of extrusion gap defects and extrusion track thinning resulting from air bubble releases. Monolithic and functionally graded parts were fabricated to illustrate the functionality of the hybrid extrusion force-velocity controller.

Copyright © 2013 by ASME
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References

Figures

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Fig. 2

Triple-extruder mechanism for mixing of up to three colloidal pastes to form an FGM part

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Fig. 6

Plunger velocity controller response to a pyramid step input reference velocity trajectory

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Fig. 5

General tracking velocity controller block diagram

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Fig. 9

Linearized extrusion force model open-loop time constant and plunger velocity coefficient with respect to nominal extrusion force

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Fig. 10

Linearized general tracking force controller block diagram

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Fig. 4

Linear cylinder 1 velocity model and experimental results

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Fig. 12

Plunger velocity and extrusion force responses for step change in extrusion force reference from 50 to 500 N to start extrusion and from 500 to 50 N to stop extrusion

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Fig. 13

Extrusion segment deposition using the dwell-based method. (a) Dwell start from 100 to 600 ms at the beginning of each segment with 200 ms stop dwell and (b) dwell stop from 100 to 600 ms at the end of each segment with 200 ms start dwell.

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Fig. 14

Extrusion segment deposition using trajectory-based method. (a) Early start from 100 to 400 ms in advance with 400 ms stop dwell and (b) early stop from 20 to 100 ms in advance with 400 ms start dwell.

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Fig. 15

Experimental plunger velocity and extrusion force responses to an air bubble release for (a) velocity controller with uref = 0.01 mm/s, and (b) extrusion force controller with Fref = 630 N.

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Fig. 16

Parts with gap defects caused by an air bubble release for (a) velocity controller with uref = 0.01 mm/s and (b) extrusion force controller with Fref = 630 N

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Fig. 3

FEF system schematic for extrusion and motion control

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Fig. 18

Measured extrusion force and plunger velocity for air bubble release when using the hybrid force-velocity controller

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Fig. 19

Tool path generation flow chart for FEF part fabrication. Fabricating this part necessarily involves several discrete tool path segments, each marked by a different color and thus requires multiple starts and stops

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Fig. 20

Demonstration of fabricating a functionally graded material part using two CaCO3 pastes

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Fig. 7

Measured and modeled steady-state extrusion forces

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Fig. 8

Simulated and measured extrusion forces for p0 = 218 Pa and l0 = 0.9 mm. An air bubble release occurred at 720 s.

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Fig. 11

Extrusion force general tracking controller experimental results

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Fig. 17

Parts with defects due to air bubble releases using (a) velocity controller with uref = 0.01 mm/s and (b) extrusion force controller with Fref = 630 N

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