Process comparison on the microstructure and mechanical properties of fiber-reinforced polyphenylene sulfide using MuCell technology

Abstract

The MuCell process is a special injection molding process which utilizes supercritical gas (nitrogen) to create integral foam sandwiches. The advantages are lower weight, higher specific properties and shorter cycle times. In this study, a series of glass fiber-reinforced polyphenylene sulfide foam blanks are manufactured using the MuCell injection molding process. The different variations of the process (low-pressure also known as structural foam injection molding) and high-pressure foam injection molding (also known as “core back expansion,” “breathing mold,” “precision opening,” decompression molding) are used. The sandwich structure and mechanical properties (tensile strength, bending strength, and impact behavior) of the microcellular and glass fiber-reinforced polyphenylene sulfide foams are systematically investigated and compared to compact material. The results showed that the injection parameters (injection speed, foaming mechanism) played an important role in the relative density of microcellular polyphenylene sulfide foams and the mechanical properties. It could be shown that the specific tensile strength decreased while increasing the degree of foaming which can be explained by the increased number of cells and the resulting cell size. This leads to stress peaks which lower the mechanical properties. The Charpy impact strength shows a significant dependence on the fiber orientation. The specific bending modulus of the high-pressure foaming process, however, surpasses the values of the other two processes showing the potential of this manufacturing variation especially with regard to bending loads. Furthermore, a high dependence of the mechanical properties on the fiber orientation of the tested specimens can be found.

A Design of Experiment Approach for Surface Roughness Comparisons of Foam Injection-Moulding Methods

“…Furthermore, when injection speed is increased from 100 mm/s to 267.8 mm/s, the mean R a decreased from 1.297 µm to 1.072 µm. This reduction in surface roughness with an increase in injection speed can be attributed to the cavity being filled earlier hence the frozen layer may have started to freeze thus mitigating the polymer/gas solution from reaching the moulding surface [43,44]. When processing with a higher melt temperature, the R a decreased from 1.324 µm to 1.045 µm.…”

Investigation on the Crystallization Process of Microcellular Injection Moulded Parts and the Influences of Parameters on the Crystallization by Simulation

“…Moreover, the use of MuCell ® to produce lightweight parts for automotive and aerospace applications reduces fuel consumption and contributes to reduce CO2 emissions [9][10][11]. However, the light weight can lead to poor mechanical properties, and consequently several authors investigated strategies to improve mechanical properties of MuCell ® parts [12][13][14][15][16][17][18].…”

Modelling and Simulation of MuCell®: The Effect of Key Processing Parameters on Cell Size and Weight Reduction

“…A non-linear impact of mould temperature and cell size was also reported, with results indicating that by increasing the mould temperature, the cell size initially decreases and then increases [ 33 ]. Contrarily, Lohr et al [ 34 ] found that the influence of the injection velocity can be neglected. Liu et al [ 35 ] concluded that the cell density decreases in a linear way by decreasing the shot volume and that the effect of gas content on the cell density can be neglected.…”