Research Papers

Real-Time Acoustic and Pressure Characterization of Two-Phase Flow for Quality Control of Expanded Polystyrene Injection Molding Processes

[+] Author and Article Information
James N. Magarian

Mechanical Engineering Department,
Massachusetts Institute of Technology,
Cambridge, MA 02139
e-mail: magarian@mit.edu

Robert D. White, Douglas M. Matson

Mechanical Engineering Department,
Tufts University,
Medford, MA 02155

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING. Manuscript received May 18, 2015; final manuscript received October 7, 2015; published online November 16, 2015. Assoc. Editor: Allen Y. Yi.

J. Manuf. Sci. Eng 138(5), 051002 (Nov 16, 2015) (9 pages) Paper No: MANU-15-1240; doi: 10.1115/1.4031796 History: Received May 18, 2015; Revised October 07, 2015

A method is proposed for real-time process monitoring for expanded polystyrene (EPS) injection molding systems. The method employs measurement of two variables: vacuum pressure in the EPS supply hose and phase difference between two points along an acoustic standing wave generated within the EPS flow path. High-speed videography is utilized as a secondary means of monitoring the injection molding process. Video data are correlated with pressure and acoustic data to substantiate those variables’ validity as indicators of intended molding system performance. Data show recorded parameter curve shapes to be indicative of key injection molding milestone events, such as valve timing and changes in flow regime.

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Fig. 1

Schematic of the experimental setup showing a (a) complete EPS bead flow path from vented hopper, through test section, through injection fill gun, to half-transparent mold tooling, (b) isometric view of the test section, and (c) photograph of the half-transparent mold tooling (injection fill gun can be seen in top right corner)

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Fig. 2

Pneumatic schematic of fill gun test system: (a) fill gun connected to dual air supplies, including separate vacuum drive and fill gun tip control systems and (b) section view of Nymphius JS8/200 G fill gun

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Fig. 3

Dimensional parameters and nomenclature of acoustic portion of test section

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Fig. 9

Vacuum pressure correlations during 552 kPa (80 psi) driven mold fill: (a) correlation between flow velocity and EPS-air vacuum pressure and (b) correlation between bead flow rate (beads/s) and EPS-air vacuum pressure

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Fig. 10

Acoustic phase angle (between microphones) correlations during 552 kPa (80 psi) driven mold fill: (a) correlation between acoustic phase angle and velocity and (b) correlation acoustic phase angle and bead flow rate (beads/s)

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Fig. 8

Parameter profiles during mold fills driven at various pressures: (a) EPS-air vacuum pressure profiles at three distinct drive pressures and (b) test section acoustic phase angle (between microphones) profiles at three distinct drive pressures

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Fig. 7

Complete time-domain characterization of a single mold fill, with fill gun driven at 552 kPa (80 psi): (a) EPS-air vacuum pressure versus time, (b) EPS-air flow velocity versus time, (c) EPS bead flow rate versus time, (d) test section acoustic amplitude ratio (microphone 1/microphone 2) versus time, and (e) test section acoustic phase angle (between microphones) versus time

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Fig. 6

EPS fill gun characterization: inline test section pressure (vacuum) versus applied fill gun drive pressure (positive)

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Fig. 5

High-speed videography and image analysis employed to verify bead velocities and flow rates: (a) screen capture from high-speed video system, depicting two-phase flow just beginning to traverse the transparent test section tube but not yet reaching the mold cavity and (b) view of grid overlay on filled mold image for the purposes of surface bead counting

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Fig. 4

Electrical and data acquisition schematic of the experimental setup




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