A methodology for determination the inlet velocity in injection molding simulations

Miranda, Diego Alves de; Rauber, Willian Kévin; Vaz Jr., Miguel; Zdanski, Paulo Sergio Berving

doi:10.1590/0104-1428.20230099

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ORIGINAL ARTICLE • Polímeros 34 (1) • 2024 • https://doi.org/10.1590/0104-1428.20230099 copy

A methodology for determination the inlet velocity in injection molding simulations

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

The inlet velocity of thermoplastic in injection molds plays a crucial role in obtaining high-quality polymer parts and the final performance of the product. It is known that the way the polymer is injected into the mold can directly affect important properties, such as the distribution of internal stresses, the cooling rate and the formation of surface defects. However, there are injection molding machines that only control injection pressure and dosage, making it difficult to obtain the gate inlet velocity into the mold cavity. Besides, some molds have many injection channels as well as complex inlet geometries, which make a challenging task to identify the inlet velocity. This study presents numerical and experimental approaches on how to determine the entry velocity in thermoplastic injection molds. The main results showed that these methods are highly efficient and contribute to identifying the gate inlet velocity with good accuracy.

Keywords:
inlet velocity; injection molds; numerical/experimental methodologies

Geometric Properties			Boundary Conditions			Rheological Properties
Parameter	Value	Unit	Parameter	Value	Unit	Parameter	Value	Unit
H₀	1	mm	ρ₀	810	kg∙m^-3	η₀	3,600	Pa∙s
L₀	10	mm	Cp₀	2,500	J∙kg^-3∙K^-1	λ	1.62	s
Z₀	10	mm	k₀	0.16	W∙m^-1∙K^-1	n	0.3	–
			U₀	10	mm∙s^-1	α	0.00931	K^-1
			T₀	230	℃	β	1	–
			T_w	50	℃

h [mm]	u*	${\tilde{p}}_{h_{1}}^{u^{*}}$	$ε_{h_{1}}^{u^{*}}$	$u_{e x a c t}^{*}$	T*	${\tilde{p}}_{h_{1}}^{T^{*}}$	$ε_{h_{1}}^{T^{*}}$	$T_{e x a c t}^{*}$
0.50	1.2140	–	–	–	0.9179	–	–	–
0.25	1.2101	–	–	–	0.9140	–	–	–
0.125	1.2092	2.0739	-2.8857×10^-4	1.2089	0.9131	2.0739	-2.9218×10^-4	0.9128
0.0625	1.2089	1.6937	-1.2814×10^-4	1.2088	0.9127	1.6937	-1.2974×10^-4	0.9126
0.03125	1.2088	1.6408	-4.3354×10^-5	1.2088	0.9128	1.6407	-4.3896×10^-5	0.9126

h [mm]	u*	${\tilde{p}}_{h_{1}}^{u^{*}}$	$ε_{h_{1}}^{u^{*}}$	$u_{e x a c t}^{*}$	T*	${\tilde{p}}_{h_{1}}^{T^{*}}$	$ε_{h_{1}}^{T^{*}}$	$T_{e x a c t}^{*}$
0.50	1.2466	–	–	–	0.8755	–	–	–
0.25	1.2426	–	–	–	0.8716	–	–	–
0.125	1.2417	2.0739	-2.9401×10^-4	1.2414	0.8707	2.0738	-2.8670×10^-4	0.8704
0.0625	1.2414	1.6937	-1.3056×10^-4	1.2413	0.8704	1.6937	-1.2731×10^-4	0.8702
0.03125	1.2413	1.6408	-4.4170×10^-5	1.2412	0.8703	1.6407	-4.3072×10^-5	0.8702

Lines	Δt = 0.10 s		Δt = 0.20 s		Δt = 0.30 s
Δx₁ (mm)	4.89		9.76		14.56
Δx₂ (mm)	5.03		10.04		14.98
Δx₃ (mm)	5.06		10.10		15.07
Δx₄ (mm)	5.13		10.23		15.27
Δx₅ (mm)	5.10		10.17		15.18
$\bar{Δ x}$ (mm)	5.042	±0.0931	10.060	± 0.1823	15.012	± 0.2754
Calculated Velocities
${\bar{U}}_{0 s i m}$ (mm∙s^-1)	50.42	± 0.9311	50.30	± 0.9117	50.04	± 0.9182

Lines	Δt = 0.10 s		Δt = 0.20 s		Δt = 0.30 s
Δx₁ (mm)	4.95		9.88		14.75
Δx₂ (mm)	5.01		10.01		14.94
Δx₃ (mm)	5.03		10.03		14.97
Δx₄ (mm)	5.09		10.16		15.16
Δx₅ (mm)	5.06		10.10		15.07
$\bar{Δ x}$ (mm)	5.028	± 0.0531	10.036	± 0.1055	14.978	± 0.1542
Calculated Velocities
${\bar{U}}_{0 s i m}$ (mm∙s^-1)	50.28	± 0.5310	50.18	± 0.5275	49.9267	± 0.5139

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