Effects of gate design and cavity thickness on filling, morphology and mechanical properties of microinjection mouldings

Nan Zhang, Quanliang Su, Seong Ying Choi, Michael D. Gilchrist
2015 Materials & design  
Publication information Materials and Design, 83 : 835-847 Publisher Elsevier Item record/more information http://hdl.handle.net/10197/7984 Publisher's statement þÿ T h i s i s t h e a u t h o r s v e r s i o n o f a w o r k t h a t The UCD community has made this article openly available. Please share how this access benefits you. Your story matters! (@ucd_oa) Some rights reserved. For more information, please see the item record link above. ____________ Highlights  Reducing gate size has
more » ... g gate size has conflicting effects on part filling  Increasing cavity thickness can significantly increase polymer melt flow length  Reducing part thickness increases skin ratio and molecular orientation which, in turn, significantly influence mechanical properties  Natural aging increases modulus and yield stress, and decreases failure strain  Design of microinjection molded products requires that special attention be given to material properties at the micro scale Manuscript Click here to view linked References Abstract Miniaturized parts weighing single or tens of milligrams represent a large category of microinjection moulded products. Both miniaturization and extreme processing under microinjection moulding subject material to high shear rates and high cooling rates, and cause the same material to have different morphologies and final properties when used in conventional injection moulding. It also makes mold design challenging. This study investigates the effects of micro gate design (opening and thickness) and cavity thickness (100-500μm) on filling, morphology and the mechanical properties of miniaturized dumbbell parts. It is found that a reduction of gate size has two conflicting effects, namely, increased shear heating increases flow length, and increased cooling rate reduces flow length. Filling increases significantly with an increase of cavity thickness. In addition, the thickness of the skin layer reduces from ~70% to ~10% when part thickness increases from 100μm to 500μm. This oriented skin layer determines molecular orientation and broadly influences Young's modulus, elongation and yield stress. Natural aging at room temperature induces an increase of modulus and yield stress, and a decrease of strain at break. The mechanical properties of microinjection moldings is significantly different from those of conventional injection moldings and measurement at microscale is required for miniaturized product design.
doi:10.1016/j.matdes.2015.06.012 fatcat:z3gr5r2g2vft5ohzzr4ogobe6e