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The injection mold is an important tooling and production of various industrial product, along with the popularization and application of plastic mold design industry and the rapid development of the plastic products in aviation, aerospace, electronics, machinery, shipbuilding and automobile industries, products to the mold of the increasingly high deman, plastic mold design and the traditional approach has been unable to adapt the product updates update and improve the quality of requirements. Computer Aided Engineering (CAE) technology has become a plastic product development, mold design and product processing these weak links in the most effective way.
USA listing Corporation Mold Flow Company is specialized in injection molding CAE software and consulting company, since 1976, issued the first set of flow analysis software, has been leading the plastic molding CAE software market. In recent years, is widely used in the field of automobile, home appliance, electronic communication, chemical industry and etc.
CAE can be used in the mold processing, in the computer the entire injection molding process analysis, accurate prediction of the melt filling, packing, cooling condition, as well as the products of the stress distribution， molecular and fiber orientation distribution, the shrinkage and war page, so that designers can find problems early， modify the part and mold design in time, ather than wait until later to repair the mold test mold. This is not only the traditional design method of plastic mold a breakthrough, and even avoid mould repair scrap, improve product quality and reduce the cost to reduce, is of great significance in technology and economy.
Plastic mold design not only adopts CAD technology, but also by CAE technology. This is the inevitable trend of development. Injection molding is pided into two stages, namely the development/design stage (including product design, mold design and mold manufacturing) and production (including the purchase of material, mold and molding). The traditional injection method is before formal production, because the designer's experience and intuition, die design, die assembly is completed, usually need several test mode, found problem, not only need to set the process parameters, and also need to modify the design of plastic mould products and plastic mold design, which will increase the cost of production, to extend the product development cycle.
2. Design and fabrication of the heat-generable mold insert
Fig. 1 presents the concept of the heat-generable mold insert. This mold insert is made of a P-type single-crystal silicon wafer. Silicon processes are used to build micro-cavities of specified dimensions and shapes on the surface of one side of the mold insert. Ion implantation process is utilized to dope N-type phosphorus ions into specific areas under the surface on the same side of the silicon mold insert to make these areas electrically conducting. Consequently, silicon-based electric-conductible micro lines with required resistance and pattern are formed at a fixed range of depth under the surface of the mold insert. These silicon-based conducting lines act as electrical heaters when connected to an external electrical power supply. Therefore, they can be applied to heat the wall of micro-cavities and the plastic near the wall at the right moment in the molding process to control the temperature distribution, the cooling rate and the solidification sequence of the plastic.
Fig. 1. (a) Cross-section of heat-generable mold insert in use， (b) expected temperature distribution of the plastic during cooling in the molding process. Tg: glass transition temperature of molding plastic; Tde: de-molding temperature; t0: start time of the cooling stage; t1: several seconds after the powering one of the electrical heating lines; t2: time to power off of the electrical heating lines; t3: time to beginning the de-molding.
Fig. 1(b) illustrates the expected temperature distribution of the plastic used in the developed novel mold insert during cooling in the molding process. d is the thickness of the part that is between the high-temperature plastic in the micro-cavities and the low-temperature plastic in contact with the cooling metal mold plate at time t = t2. The part of the plastic with thickness d has a large temperature gradient and is cooled from time t = t2 to t = t3, inducing thermal stress and the effect of gripping of the mold insert by the plastic. Accordingly, the thickness d is important in determining the gripping force F which the molded micro-structured component grips the mold insert in de-molding.