Shrinkage Prediction for Slowly-Crystallizing Thermoplastic Polymers in Injection Molding

1997 ◽  
Vol 12 (3) ◽  
pp. 228-237 ◽  
Author(s):  
S. Han ◽  
K. K. Wang
Keyword(s):  
Injection Molding ◽  
Thermoplastic Polymers

Reaction Injection Molding

2006 ◽  
Author(s):  
Chang Dae Han
Keyword(s):  
Injection Molding ◽  
Cross Sections ◽  
Elevated Temperatures ◽  
Three Dimensional ◽  
Industrial Applications ◽  
Processing Temperature ◽  
Thermoplastic Polymers ◽  
Reaction Injection Molding ◽  
Rapid Injection ◽  
Sink Marks

Reaction injection molding (RIM) is a thermoset processing operation during which the incoming feedstream(s) undergo cure reactions that give rise to a three-dimensional network structure (Becker 1979; Macosko 1989). Different from the operation of injection molding thermoplastic polymers presented in Chapter 8, in RIM operation the component(s) must cure rapidly (say, within 90 seconds) and a finished product is removed in 1−10 minutes, depending on the chemical systems, the part thickness, and the capabilities of the processing machine. The chief advantages of RIM over the injection molding of thermoplastic polymers are: (1) large parts can be produced at low energy consumption, (2) large parts with varying cross sections with or without inserts can be produced without the problem of sink marks, and (3) lightweight parts, owing to the microcellular structure, can be produced. However, the predominant industrial applications are in the automotive industry; for instance, in the production of automobile fascia. In the 1970s and 1980s, very intensive research activities were reported on a better understanding of the RIM operation. Thermosets must meet with some stringent requirements for RIM operation. These are: (1) viscosities must be fairly low at processing temperature, so that a rapid injection of the feedstreams can be realized; (2) the feedstreams must have sufficient compatibility for efficient mixing by the static impingement mixing technique; (3) cure reaction must be sufficiently fast, such that a finished product can be removed in a very short time after injection is completed; (4) a finished product must have sufficient stiffness and resiliency at elevated temperatures; and (5) a finished product must be released easily from the mold surface, etc. It is then clear that not many thermosets meet these requirements. It has been found that urethanes, with proper chemistry of the components, meet with the requirements. For this reason, urethanes have been the most widely used resin for RIM, although other thermosets (e.g., epoxy) have also been used to some extent.

On the packing–holding flow in the injection molding of thermoplastic polymers

1988 ◽  
Vol 35 (6) ◽  
pp. 1483-1495 ◽  
Author(s):  
G. Titomanlio ◽  
S. Piccarolo ◽  
G. Levati
Keyword(s):  
Injection Molding ◽  
Thermoplastic Polymers

scholarly journals Tuning Power Ultrasound for Enhanced Performance of Thermoplastic Micro-Injection Molding: Principles, Methods, and Performances

Polymers ◽  
2021 ◽  
Vol 13 (17) ◽  
pp. 2877
Author(s):  
Baishun Zhao ◽  
Yuanbao Qiang ◽  
Wangqing Wu ◽  
Bingyan Jiang
Keyword(s):  
Injection Molding ◽  
Morphological Evolution ◽  
Rapid Development ◽  
Commercial Application ◽  
Efficient Production ◽  
Thermoplastic Polymers ◽  
Micro Injection Molding ◽  
Replication Fidelity ◽  
Power Ultrasound ◽  
Research Activities

With the wide application of Micro-Electro-Mechanical Systems (MEMSs), especially the rapid development of wearable flexible electronics technology, the efficient production of micro-parts with thermoplastic polymers will be the core technology of the harvesting market. However, it is significantly restrained by the limitations of the traditional micro-injection-molding (MIM) process, such as replication fidelity, material utilization, and energy consumption. Currently, the increasing investigation has been focused on the ultrasonic-assisted micro-injection molding (UAMIM) and ultrasonic plasticization micro-injection molding (UPMIM), which has the advantages of new plasticization principle, high replication fidelity, and cost-effectiveness. The aim of this review is to present the latest research activities on the action mechanism of power ultrasound in various polymer micro-molding processes. At the beginning of this review, the physical changes, chemical changes, and morphological evolution mechanism of various thermoplastic polymers under different application modes of ultrasonic energy field are introduced. Subsequently, the process principles, characteristics, and latest developments of UAMIM and UPMIM are scientifically summarized. Particularly, some representative performance advantages of different polymers based on ultrasonic plasticization are further exemplified with a deeper understanding of polymer–MIM relationships. Finally, the challenges and opportunities of power ultrasound in MIM are prospected, such as the mechanism understanding and commercial application.

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