Influence of Heat Sink on the Mold Temperature of Gypsum Mold Used in Injection Molding

Chung-Chih Lin,Hon-Chih Yeh,Kun-Chen Chen

doi:10.3390/polym12030701

Abstract

Gypsum molds have been developed as an alternative for the Rapid tooling (RT) method used in injection molding. However, the poor capability of the heat delivery forces the gypsum mold to operate under a high-risk condition, and distortion of the molded part becomes apparent. The goal is to investigate the effect of a heat sink on the reduction of the gypsum mold temperature and to establish a methodology for the heat sink design. The methodology used the advantage of the electrical circuit concept to analyze the mold temperature. The heat transfer of a mold was modeled using an equivalent thermal circuit. After all the components on the circuit were determined, the heat transfer rate could then be calculated. Once the heat transfer rate was known, the mold temperature could be easily analyzed. A modified thermal circuit considering transverse heat conduction was also proposed, which estimated the mold temperature more accurately. The mold temperature was reduced by 16.8 °C when a gypsum mold was installed with a 40 mm thick heat sink in a parallel configuration. Moreover, the reduction of the mold temperature improved the deflection of the molded part from 0.78 mm to 0.54 mm. This work provides a quick approach to analyze the mold temperature based on the thermal circuit concept. As the cooling system of the mold was modularized analytically, important properties of the cooling system in the heat transfer process were revealed by analyzing the thermal circuit of the mold, for example, the heat transfer rate or the mold temperature.

Highlights

When a customer requests the development of a new product, a small quantity of the prototype is usually prepared for validation
The volume of a gypsum block expands after the gypsum paste becomes solidified and the gypsum mold does not suffer from the volume shrinkage that is a known processing issue for many polymer-based Rapid tooling (RT) materials
In our previous work [1], we developed gypsum inserts and gypsum molds for the RT method to be used in plastic injection molding

Summary

Introduction

When a customer requests the development of a new product, a small quantity of the prototype is usually prepared for validation. The volume of a gypsum block expands after the gypsum paste becomes solidified and the gypsum mold does not suffer from the volume shrinkage that is a known processing issue for many polymer-based RT materials. This specific material property improves the replication capability. In our previous work [1], we developed gypsum inserts and gypsum molds for the RT method to be used in plastic injection molding. Since gypsum is a natural material and can be recycled, gypsum molds provide an ecofriendly approach for producing a limited quantity of prototypes made by using thermoplastic materials, with the injection molding method as the intended production line.

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Conclusion