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Conformal Cooling Channel Design For Plastic Injection Molding

The constant temperature mold of molding plastic parts with high precision contours is of significance in determining not only the productivity of the injection molding process but also the product quality. A solution to this challenge is the rapid thermal response molding process in which uniform temperature overall the mold part ensures the product quality by preventing differential shrinkage, internal stress and mold release problems (Li, 2001). Many Computer-Aided-Engineering (CAE) and optimization methods have been carried out to observe and fine-tune the influences of the thermal system (Park et al., 1998).

The results of these research works are obtained by using thermal analysis modules of commercial CAE packages such as C-Mold or Moldflow which are based on the initial designs generated by the human. By given an initial thermal configuration design, efficiency and quality of the molded part can be predicted before an actual plastic mold is manufactured. One more necessary step for the complete automation in the molding thermal system is to generate the initial design for the conformal cooling channels.For example casting mould,mold making,plastic injection mold etc. In this paper, a featured-based approach to this problem is proposed. Super-quadrics is presented as a tool for recognizing the plastic part shapes and an algorithm is applied for generating the center line of the thermal sub-system of each individual surface. Finally, these sub sets of center lines are combined to create a unique center line which is the guide line for generating the cooling channel of the thermal system.

Conformal cooling channel, as the name implies, refers to the channels that conform to the surface of the mould cavity. Conformal cooling channels have demonstrated simultaneous improvement in production rate and part quality as compared with conventional production tools. In the previous researches, cooling line design and fabrication have been confined to relatively simple configuration, primarily due to the limits of the fabrication method used to make tools, but also due to the lack of appropriate design methodology. Emergence of Solid Freeform Fabrication processes with the ability to fabricate 3-D feature with almost arbitrary complexity is exceedingly useful to mould design process (Xu et al., 2001). The remaining problem to be solved is how to optimize the design process of the thermal system. In this paper, a systematic method for designing cooling channel is proposed. Firstly, the feature recognition algorithm is applied to identify and decompose the moulded part into manageable sections so-called cooling zones. In the next step, a sub-system of cooling channel is generated for each cooling zone. These sub-systems of cooling channels are further decomposed into smaller elements called cooling cells which are easy to be analysed. Lastly, the combination process of these sub-systems is done to create a complete conformal cooling system for the whole plastic part based on the constraints of the combination algorithm and design rules.

Nowadays, feature-based modeling has been a standard for 3D designs. Most of the complex shapes are obtained by synthesizing from sets of simple features. This design strategy is not sensitive to the part geometry; therefore, it keeps the simplicity of the design routine no matter how complicated the geometry of the part is. For the same purposes of simplicity and efficiency, the molded part is segmented into sub-features that must be recognized for the partial thermal system designs. Feature recognition has drawn much attention from researchers and been proposed in literatures (Lentz et al., 1993). The majority of these has based on machining feature recognition techniques which can be classified in three categories: graph-based methods, volumetric methods and hint-based methods. Although recent machining feature recognition technique can be a good solver for parts with complicated intersecting feature, this technique is not appropriate for detecting shape feature for thermal system design of plastic products. In plastic products, free-form surfaces are mostly used and hence, free-form features have to be processed. Furthermore, a shape feature in a plastic part may blend smoothly to another feature and the boundaries between features can not be explicitly defined. With these two reasons, neither graph-based methods, volumetric methods nor hint-based methods can be applied.