Microcellular injection molding process for producing lightweight thermoplastic polyurethane with customizable properties

doi:10.1007/s11465-018-0498-6

Front. Mech. Eng.

2018, Vol. 13

Issue (1) : 96-106 https://doi.org/10.1007/s11465-018-0498-6

RESEARCH ARTICLE

Microcellular injection molding process for producing lightweight thermoplastic polyurethane with customizable properties

Thomas ELLINGHAM^1,², Hrishikesh KHARBAS^1,², Mihai MANITIU³, Guenter SCHOLZ³, Lih-Sheng TURNG^1,²(

)

¹. Department of Mechanical Engineering, University of Wisconsin-Madison, Madison, WI 53706, USA
². Wisconsin Institute for Discovery, University of Wisconsin-Madison, Madison, WI 53715, USA
³. BASF Corporation, Wyandotte, MI 48192, USA

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Abstract

A three-stage molding process involving microcellular injection molding with core retraction and an “out-of-mold” expansion was developed to manufacture thermoplastic polyurethane into lightweight foams of varying local densities, microstructures, and mechanical properties in the same microcellular injection molded part. Two stages of cavity expansion through sequential core retractions and a third expansion in a separate mold at an elevated temperature were carried out. The densities varied from 0.25 to 0.42 g/cm³ (77% to 62% weight reduction). The mechanical properties varied as well. Cyclic compressive strengths and hysteresis loss ratios, together with the microstructures, were characterized and reported.

Keywords thermoplastic polyurethane microcellular injection molding cavity expansion compressive strength hysteresis loss ratio

Corresponding Author(s): Lih-Sheng TURNG

Just Accepted Date: 12 December 2017 Online First Date: 09 January 2018 Issue Date: 23 January 2018

Cite this article:

Thomas ELLINGHAM,Hrishikesh KHARBAS,Mihai MANITIU, et al. Microcellular injection molding process for producing lightweight thermoplastic polyurethane with customizable properties[J]. Front. Mech. Eng., 2018, 13(1): 96-106.

URL:

https://academic.hep.com.cn/fme/EN/10.1007/s11465-018-0498-6
https://academic.hep.com.cn/fme/EN/Y2018/V13/I1/96

Fig.1 Schematic of an injection-molded component part and the direction of core retraction

Fig.2 Schematic representation of the three-stage molding process and the corresponding part thicknesses at various stages (unit: mm). From left to right, the first three images correspond to the part dimensions of the original part, the part after Stage 1, and the part after Stage 2, respectively. Stage 3 is includes (a) Part 1: Straight profile; (b) Part 2: Varying profile

Tab.1 Processing conditions for injection molding

Fig.3 SEM images of the edge (left) and center (right) of the part after (a) Stage 1, (b) Stage 2, and (c) Stage 3

Fig.4 Graphical representation of (a) bulk density, (b) cell size, (c) hysteresis loops, and (d) hysteresis loss ratio results at the end of different stages in the three-stage molding process of the flat profiled part (Part 1)

Fig.5 Location of SEM samples and uniaxial compression samples for the tapered profile part (Part 2) (unit: mm)

Fig.6 SEM images at 15× magnification at the center of cross sections at (a) Section 1, (b) Section 2, (c) Section 3, and (d) Section 4 of the tapered profile part (Part 2)

Fig.7 SEM images at 200× magnification of the center of cross sections at (a) Section 1, (b) Section 2, (c) Section 3, and (d) Section 4 of the tapered profile part (Part 2)

Fig.8 Graphical representation of (a) bulk density, (b) cell size, (c) cell aspect ratios, and (d) hysteresis loop results at different sections in the tapered profile part (Part 2)

Fig.9 Plot of (a) uniaxial compression hysteresis loops and (b) hysteresis loss ratios at different sections in Part 2 with a maximum load of 2000 N

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