Abstract
The formation of blister in the injection moulded parts, especially in the film insert moulded parts, is one of most significant causes of part rejection due to cosmetic requirements or functionality issues. The mechanism and physics of blister formation for molded parts are not well-understood by the state-of-the-art literature. The current paper increases the fundamental understanding of the causes for blister formation. In the experiment, a membrane strip of 5 mm in width was overmoulded with Polypropylene (PP), which formed a disc-shaped part with a diameter of 17.25 mm and a thickness of 500 µm. To investigate the influence of the processing parameters, a full factorial design of experiments (DoE) setup was conducted, including mould temperature (Tm), barrel temperature (Tb), injection speed (Vi) and packing pressure (Pp) as variables. The degree of blistering at the surface was characterized by the areal surface roughness parameters Spk and Smr1, measured with a confocal laser microscope. The measurements were taken on the 10 mm long section of the membrane surface in the centre of the moulded part across the entire width of the film. In addition, the film insert moulding (FIM)-process was simulated and the average shrinkage of the substrate material under the membrane was investigated. Eventually, a method and processing window could be defined that could produce blister-free parts.
Highlights
In film insert moulding (FIM) a preformed film is inserted in the mould and subsequently overmoulded
FIM parts can be found for example in automotive industry, medical technology, design and fashion products, household appliances, as well as for mobile phones and many other applications [1]
The use of FIM to overcome the mechanical problems of weld lines in glass fibre filled thermoplastics has been reported [4]
Summary
In film insert moulding (FIM) a preformed film is inserted in the mould and subsequently overmoulded. C[r7e]asreespwoirthteadn ianncreaassyeminmfilemtrtihcicflknoewss abnedhmavelitotuemr poefraPtuorleyapnrdopylene when a decreases with an increase in mould temperature These results are in good agreement with those ffiolumndwbays Kinimse, retteda,l.w[8h]ewrehothienvmesotiugladtedsidtheecionvcreeraesde biny tthheeafisylmmmshetorywoefdtahefltoewmpleeraadtuirneg effect. The ultimate goal of the work was to use the materials and process for the production of moulding-based methanol fuel cell (DMFC) containers, which are supposed to be used in hearing aid applications [16]. During this investigation, it was found that, for some combinations of the process, parameter blisters occurred in the membrane layer (see Figure 1). Micromachines 2020, 11, 424 moulding and to investigate the relationship between the average shrinkage under the membrane found by means of simulation and the blistered surface analysis
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