Blister Formation in Film Insert Moulding.

Area of Science:

• Manufacturing Engineering
• Materials Science
• Polymer Processing

Background:

• Blister formation in injection molded parts, particularly film insert molded (FIM) components, is a significant cause of product rejection.
• Existing literature lacks a comprehensive understanding of the underlying mechanisms and physics governing blister formation in molded parts.

Purpose of the Study:

• To enhance the fundamental understanding of the causes of blister formation in injection molded parts.
• To identify processing parameters that influence blister formation and establish a method for producing blister-free parts.

Main Methods:

• Overmolding a 5 mm membrane strip with Polypropylene (PP) to create a disc-shaped part (17.25 mm diameter, 500 µm thickness).
• Utilizing a full factorial design of experiments (DoE) varying mold temperature (Tm), barrel temperature (Tb), injection speed (Vi), and packing pressure (Pp).
• Characterizing blistering using areal surface roughness parameters (Spk, Smr1) measured by confocal laser microscopy and simulating the FIM process to analyze substrate shrinkage.

Main Results:

• Investigated the influence of key processing parameters (mold temperature, barrel temperature, injection speed, packing pressure) on blister formation.
• Quantified blistering using surface roughness parameters (Spk, Smr1) on the membrane surface.
• Simulated the FIM process to understand substrate shrinkage effects.

Conclusions:

• A method and specific processing window were defined to successfully produce blister-free injection molded parts.
• The study provides fundamental insights into blister formation, aiding in defect reduction for FIM components.