Three-dimensional numerical simulation for plastic injection-compression molding

doi:10.1007/s11465-018-0490-1

Front. Mech. Eng.

2018, Vol. 13

Issue (1) : 74-84 https://doi.org/10.1007/s11465-018-0490-1

RESEARCH ARTICLE

Three-dimensional numerical simulation for plastic injection-compression molding

Yun ZHANG¹(

), Wenjie YU¹, Junjie LIANG¹, Jianlin LANG², Dequn LI¹

¹. State Key Laboratory of Material Processing and Die & Mold Technology, Huazhong University of Science and Technology, Wuhan 430074, China
². Beijing Institute of Aeronautical Materials, Beijing 100095, China

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Abstract

Compared with conventional injection molding, injection-compression molding can mold optical parts with higher precision and lower flow residual stress. However, the melt flow process in a closed cavity becomes more complex because of the moving cavity boundary during compression and the nonlinear problems caused by non-Newtonian polymer melt. In this study, a 3D simulation method was developed for injection-compression molding. In this method, arbitrary Lagrangian-Eulerian was introduced to model the moving-boundary flow problem in the compression stage. The non-Newtonian characteristics and compressibility of the polymer melt were considered. The melt flow and pressure distribution in the cavity were investigated by using the proposed simulation method and compared with those of injection molding. Results reveal that the fountain flow effect becomes significant when the cavity thickness increases during compression. The back flow also plays an important role in the flow pattern and redistribution of cavity pressure. The discrepancy in pressures at different points along the flow path is complicated rather than monotonically decreased in injection molding.

Keywords injection-compression molding simulation injection molding melt flow cavity pressure

Corresponding Author(s): Yun ZHANG

Just Accepted Date: 15 November 2017 Online First Date: 29 December 2017 Issue Date: 23 January 2018

Cite this article:

Yun ZHANG,Wenjie YU,Junjie LIANG, et al. Three-dimensional numerical simulation for plastic injection-compression molding[J]. Front. Mech. Eng., 2018, 13(1): 74-84.

URL:

https://academic.hep.com.cn/fme/EN/10.1007/s11465-018-0490-1
https://academic.hep.com.cn/fme/EN/Y2018/V13/I1/74

Fig.1 General description of a mold cavity for injection-compression molding

Fig.2 General polyhedral control volume and the notation used

Fig.3 Molded part. (a) Part dimensions (unit: mm); (b) 3D mesh

Parameter	Value	Parameter	Value
$τ ∗$ /Pa	720887	$C p$ /(J·kg^-1·K^-1)	1880
$n ˜$	0.17	$k$ /(W·m^-1·K^-1)	0.24
$A 1$	38.724	$b 1$ /(m³·kg^–1)	8.65e–4 (melt), 8.61e–4 (solid)
$A ˜ 2$ /K	51.6	$b 2$ /(m³·kg^–1·K^-1)	4.83e–7 (melt), 5.85e–8 (solid)
$D 1$ /(Pa·S)	5.95e15	$b 3$ /Pa	1.74e+8 (melt), 3.43e+8 (solid)
$D 2$ /K	417.15	$b 4$ /K^-1	4.39e–3 (melt), 2.27e–3 (solid)
$D 3$ /(K·Pa^-1)	0	$b 5$ /K	415.98 (melt, solid)
$ρ$ /(kg·m^-3)	1034.7

Tab.1 Material parameters of PC Subic OQ2720

Tab.2 Process conditions for the injection molding and injection-compression molding

Fig.4 Pressures and temperatures along the flow path. (a) Pressures simulated by the presented method; (b) pressures simulated by the Moldflow; (c) pressures by the experiment; (d) temperatures by the experiment

Fig.5 Flow fronts of injection molding at (a) 1.29 s, (b) 2 s, (c) 3.14 s, and (d) 3.18 s

Fig.6 Flow fronts of injection-compression molding at (a) 1.43 s, (b) 2.8 s, (c) 3.63 s, and (d) 3.67 s

Fig.7 Short shot products of injection-compression molding at (a) 0.55 s, (b) 0.8 s, (c) 1.13 s, (d) 2.65 s, (e) 3.13 s, (f) 3.48 s, and (g) 3.82 s

Fig.8 Melt velocities of injection molding at (a) 1.29 s, (b) 2 s, (c) 3.14 s, (d) 3.18 s, (e) 5.7 s, and (f) 8.14 s

Fig.9 Melt velocities of injection-compression molding at (a) 1.43 s, (b) 2.8 s, (c) 3.63 s, (d) 3.67 s, (e) 5.8 s, and (f) 8.63 s

Fig.10 Pressure distributions of injection molding at (a) 3.14 s, (b) 3.18 s, and (c) 8.14 s

Fig.11 Pressure distributions of injection-compression molding at (a) 2.8 s, (b) 3.67 s, (c) 5.8 s, and (d) 8.63 s

Fig.12 Pressure curves of three points along the flow path in injection-compression molding

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