| Injection molding technology is an important molding method of plastics, now it has been widely used in almost all fields of the national economy, such as household appliances, automobiles, electronics, aerospace, commodities and so on. However, as the complexity of the injection molding process, there are always many problems on the parts produced by conventional injection method, such as weld mark, flow mark, fiber exposure and so on. As a result, the appearance of the parts is seriously affected. The mechanical properties are decreased as well, leading to a hidden danger for the application of the parts. Therefore, spraying and coating have to be employed after injection molding process so as to improve the part's performance or appearance. These subsequent re-processing operations increase the part manufacturing processes, waste raw material and energy. Especially, they also increase the production cost and cause environment pollution inevitably. How to reduce the defects of the injected polymer parts, improving the product quality and canceling the spraying or coating process is one of important research subjects of the injection molding technology. In order to meet the requirements of the customers on the appearance, performance cost and environment of the plastic parts, rapid heat cycle molding (RHCM) technology is developed in recent years. Using this technology, high-quality plastic parts with excellent appearance and no weld marks can be produced and fiber exposure on the part surface can be avoided as well. Especially, the subsequent processing processes, such as spraying and coating which seriously pollute the environment can be eliminated. Thus, the whole production process flowchart is shortened. The energy, material and production cost are decreased. RHCM is a kind of potential green manufacturing technology and has a broad application prospect in plastic injection molding industry.Based on the principles of the rapid heat cycle molding technology, firstly, the compositions of this new injection method are researched and the requirements of the production line established in the enterprise are discussed. Compared with the conventional injection molding process, the differences between the RHCM injection process and the conventional one are studied. The design rules of the products and molds for RHCM technology are established and the processing method of the mold is also discussed. Secondly, considering the working conditions of the mold in practical production process, the temperature and stress field during the injection process are studied. The service lifetime of the mold is estimated. Thirdly, in order to improving the production efficiency and the part quality, optimization models for different layouts of heating channels in the mold are proposed, the structures of the mold are then optimized according to the models. According to the characteristics of the RHCM technology, a mold temperature control equipment and a cooling system for the electrical experiment mold are developed. By using them, the mechanical properties and appearance of the glass-fiber reinforced parts which are injected by RHCM injection method are researched.Different from the conventional injection molding process, the mold must be rapidly heated and cooled down to designated temperatures in RHCM injection molding cycle. In heating stage, the cavity surface of the mold should be heated up to the heat distortion temperature of polymer for ensuring good filling state of the plastic melt. In cooling stage, the mold and the polymer melt must be cooled down to ejected temperature of the polymer part rapidly in order to reduce the molding cycle. According to this characteristic, the structures of the products and mold for the technology are analyzed, and the principles that are needed to follow in structure design of RHCM products and the mold are presented. By researching on the mold material, machine method and polishing techniques, the precision machining of the mold cavity plate is achieved. Aiming at reducing the warpage and sink marks that are usually appeared on the RHCM injected parts, the mechanisms of the two defects are analyzed. The influence of the injection parameters on the warpage and the sink marks are also studied. Based on the researches above, the Steam-assisted Rapid Heat Cycle Molding (SRHCM) and electrical Rapid Heat Cycle Molding (ERHCM) are discussed respectively. The compositions of the two systems in which the molds are heated in different ways are analyzed. The requirements of both the two systems for the vapor source or heating rods, cooling water, mold temperature control equipments, process monitoring supervisory system and mold structures are proposed, and the key technologies for the application of the two different systems are studied.As the temperature distribution of the mold has significant effect on the part quality, the heat transfer process among the mold, heating system, plastic part, cooling system and ambience are all analyzed according to the heat transfer theory. The temperature field models for both the SRHCM mold and the ERHCM mold are established based on the above analysis and the finite element simulation theory. The instantaneous temperature of the cavity plate are obtained through the finite element simulation and the factors that influence the heating efficiency and temperature distribution on the mold cavity, including the spaces between channels, the diameters and numbers of channels and the distances from the cavity surface to the channels are all discussed. By using death-to-birth element technique, the temperature of the ERHCM mold during the whole injection molding cycle are obtained which is of great help to grasp the mold temperature and set the parameters values of the injection process.During the practical injection process, as the rising of the mold temperature and the restriction between the mold plates, the thermal distortion and stress are brought inevitably. Meantime, the mold also suffers great clamping pressure, injection pressure and other mechanical stress during the injection cycle. As a result, a much larger deformation of the mold is induced. The precision, cost and the surface quality of the part are affected. With the continuous production, fatigue cracks are much easier to generate on the RHCM mold due to the great stresses, and the mold lifetime becomes shorter. Therefore, the stress and strain analysis model for the mold is established according to the restriction state of the mold plates. The stress and strain distributions of the mold and the factors that affect the mold deformation and the lifetime are discussed. A new fixing mode called "partial cold gap" fixing mode for the RHCM mold is proposed. With this method, the thermal expansion of the mold is compensated effectively which is of much help to decrease the stress and improve lifetime of the mold. At last, the lifetimes of the mold with different "cold gap" are estimated in this section, and the recommendations for the mold assembly are proposed.During RHCM process, the production efficiency and the part's quality are seriously affected by the temperature and its distribution uniformity on the mold cavity surface. Warpage and weld mark are easy to be formed if the temperature is low or distributed unevenly on the mold cavity surface after heating and cooling processes. Therefore, there is a strict requirement on the temperature of mold cavity surface after heating process in order to obtain high-quality plastic parts and ensure the production efficiency. Commonly, there are much more heating channels in RHCM mold, the layout of them has a great effect on the heating efficiency and the temperature distribution of the mold. Optimization modes integrated the finite element technique with the artificial intelligence algorithm together are proposed to optimize the channels layout. For the purposes of achieving a uniform temperature distribution on the cavity surface of the mold, the distances between the neighbor heating channels were considered as the main design variables for plane surface LCD TV model. An objective function to optimize the temperature distribution uniformity is proposed. By using a quadric response surface equation genetic algorithm, the layout of the channels is optimized. For arc surface LCD TV model, the center coordinates of the heating channels are considered as the main design variables. Multi-objective functions for optimizing the temperature distribution uniformity and heating efficiency are established. The layout of the heating channels is optimized by integrating the establishment of CAD model, the finite element method and Pareto-based genetic algorithm.As the fiber reinforced plastic products have much more excellent mechanical and thermal properties, they have occupied an important position in the injection field. By using the RHCM technology, the fiber exposure on the fiber reinforced products surface can be avoided and the surface appearance can be greatly improved, so the fiber-reinforced products can be used more widely. For studying the performances of the fiber reinforced products injected by RHCM technology, the layout of heating rods for the designed experiment mold is optimized and a mold temperature controlling system for ERHCM mold is developed. A production line for experiment is established in our laboratory. The fiber reinforced ABS is used as an example to study the relationship between the mechanical properties and the mold temperature. At the same time, the formation of the weldline on the fiber reinforced product is described. The relationship between the surface quality and roughness of the part and the mold temperature are also researched.Although RHCM technology is a new injection method, it has become a very important molding way of the polymer. Studying the molding mechanism of the RHCM technology, promoting the application of the new injection method is one of important issues for the technology. Researches on the key technologies of the related products and the mold are of great industrial interest for its practical application. The established production line for experiment based on the RHCM theory is of much help to research the mechanism of the technology and also has a very important effect to promote the application of the technology.
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