Research Papers

Comprehensive Online Control Strategies for Plastic Injection Molding Process

[+] Author and Article Information
Jaho Seo

Korea Institute of Machinery and Materials,
156 Gajungbukno,
Yuseong-gu, Daejeon 305-343,
Republic of Korea
e-mail: seojaho@kimm.re.kr

Amir Khajepour

Department of Mechanical
and Mechatronics Engineering,
University of Waterloo,
200 University Avenue West,
Waterloo, ON N2L 3G1, Canada
e-mail: akhajepour@uwaterloo.ca

Jan P. Huissoon

Department of Mechanical
and Mechatronics Engineering,
University of Waterloo,
200 University Avenue West,
Waterloo, ON N2L 3G1, Canada
e-mail: jph@mecheng1.uwaterloo.ca

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING. Manuscript received July 28, 2013; final manuscript received April 16, 2014; published online May 21, 2014. Assoc. Editor: Robert Landers.

J. Manuf. Sci. Eng 136(4), 041009 (May 21, 2014) (10 pages) Paper No: MANU-13-1293; doi: 10.1115/1.4027491 History: Received July 28, 2013; Revised April 16, 2014

This study proposes an effective thermal control for plastic injection molding (polymer: Santoprene 8211-45 with density of 790 kg/m3, injection pressure: 1400 psi (9,652,660 Pa)) in a laminated die. For this purpose, a comprehensive control strategy is provided to cover various themes. First, a new method for determining the optimal sensor locations as a prerequisite step for modeling and controller design is introduced. Second, system identification through offline and online training with finite element analysis and neural network techniques are used to develop an accurate model by incorporating uncertain dynamics of the laminated die. Third, an additive feedforward control by adding direct adaptive inverse control to self-adaptive PID is developed for temperature control of cavity wall (cavity size: 52.9 × 32.07 × 16.03 mm). A verification of designed controller's performance demonstrates that the proposed strategy provides accurate online temperature tracking and faster response under thermal dynamics with various cycle-times in the injection mold process.

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Fig. 1

Laminated die with cavity and conformal cooling channel

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Fig. 2

Monitored nodes of mold (side view (a) and top view (b))

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Fig. 3

Input conditions of the FEA for clustering

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Fig. 4

Four optimal sensor locations for thermocouple installation

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Fig. 5

System identification procedure

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Fig. 6

Training data using all flow rate ranges (0, 1, 3, 4, 5, 6, 8 gpm) and one cycle-time (91 s) at node Mo484

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Fig. 7

Schematic of NARX model

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Fig. 14

Experimental validation results (error between yN and y)

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Fig. 13

Experimental validation results (comparison between model (yN) and actual outputs (y))

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Fig. 12

Input conditions for experimental validation

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Fig. 11

Experimental setup: (a) installation of laminated die on molding machine, (b) laminated die with thermocouples, and (c) host PC with USB DAQ

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Fig. 10

Offline training results (error between yN and y)

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Fig. 9

Offline training results (comparison between model (yN) and actual outputs (y))

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Fig. 8

Training results with ARX, ARMAX, and NARX models at node 484 using training data in Fig. 6

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Fig. 15

Direct adaptive inverse control

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Fig. 16

Additive feedforward control

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Fig. 17

Final product of plastic injection molding

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Fig. 18

Linear relationship between an average of four Ta at four nodes and cavity wall temperature immediately after ejection

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Fig. 19

Performance of direct adaptive inverse controller (InvOnly), conventional PID (ConPID), AFC with self-adaptive BP PID (InvBPPID), AFC with self-adaptive RBF PID (InvRBFPID), and AFC with conventional PID (InvConPID) for multisetpoints with various cycle-times

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Fig. 20

Coolant flow rate (control variable) of direct adaptive inverse controller (InvOnly), conventional PID (ConPID), AFC with self-adaptive BP PID (InvBPPID), AFC with self-adaptive RBF PID (InvRBFPID), and AFC with conventional PID (InvConPID) for multisetpoints with various cycle-times



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