Application of New Triple Hook-Shaped Conformal Cooling Channels for Cores and Sliders in Injection Molding to Reduce Residual Stress and Warping in Complex Plastic Optical Parts.

Abelardo Torres-Alba,Cristina Martin-Doñate,Jorge Manuel Mercado-Colmenero,Juan De Dios Caballero-Garcia

doi:10.3390/polym13172944

Abstract

The paper presents a new design of a triple hook-shaped conformal cooling channels for application in optical parts of great thickness, deep cores, and high dimensional and optical requirements. In these cases, the small dimensions of the core and the high requirements regarding warping and residual stresses prevent the use of traditional and standard conformal cooling channels. The research combines the use of a new triple hook-shaped conformal cooling system with the use of three independent conformal cooling sub-systems adapted to the complex geometric conditions of the sliders that completely surround the optical part under study. Finally, the new proposed conformal cooling design is complemented with a small insert manufactured with a new Fastcool material located in the internal area of the optical part beside the optical facets. A transient numerical analysis validates the set of improvements of the new proposed conformal cooling system presented. The results show an upgrade in thermal efficiency of 267.10% in comparison with the traditional solution. The increase in uniformity in the temperature gradient of the surface of the plastic part causes an enhancement in the field of displacement and in the map of residual stresses reducing the total maximum displacements by 36.343% and the Von—Mises maximum residual stress by 69.280% in comparison with the results obtained for the traditional cooling system. Additionally, the new design of cooling presented in this paper reduces the cycle time of the plastic part under study by 32.61%, compared to the traditional cooling geometry. This fact causes a very high economic and energy saving in line with the sustainability of a green mold. The improvement obtained in the technological parameters will make it possible to achieve the optical and functional requirements established for the correct operation of complex optical parts, where it is not possible to use traditional cooling channels or standard conformal cooling layouts.

Highlights

IntroductionEven if the optical properties of materials such as glass are very stable, their manufacturing process is especially complex considering the time limitations and requirements demanded in the industry
The use of precision polymer optics is becoming an increasing necessity today as products demand sophisticated light handling components to achieve desired results [1,2].Even if the optical properties of materials such as glass are very stable, their manufacturing process is especially complex considering the time limitations and requirements demanded in the industry
The research combines the use of a new triple hook-shaped conformal cooling system with the use of three independent conformal cooling sub-systems adapted to the complex geometric conditions of the sliders that completely surround the optical part under study

Summary

Introduction

Even if the optical properties of materials such as glass are very stable, their manufacturing process is especially complex considering the time limitations and requirements demanded in the industry. Optical pieces manufactured in plastic are sturdy and lowcost, produced in one only step despite the geometric complexity. These reasons make plastic optical parts crucial for contemporary industrial development [3,4,5]. In the injection molding process, the thickest area of the part presents heat accumulation because of slower cooling This fact produces a slower cooling time and an uneven shrinkage [6,7,8] that generates warping, affecting the optical properties of the plastic part [9]

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Conclusion