Sequential Overmolding (Bi-color) Injection Technology And Application Research

Nowadays, with the peoples' improving quality demands to injection products, more and more innovative injection processes and technologies have being developed and applied. Among them, the sequential overmolding or bi-color injection technology has been widely spreaded and applied as one advanced manufacture technology in China's injection molding.As one manufacture technique earliest appeared in 1961 of Arburg Company's multi-color injection machine, its aim was to improve the sequential overmolding or bi-color products' efficiency. During the early years, the main method was an inserting and encapsulating technology. Now, this is a hot field of research and application in China, but has a great difference with single-component injection, especially in injection molding equipments and injection processes. Because of high cost of imported equipments and complex processes and mold sutructure, the sequential overmolding or two-component injection process had not been wildly introduced and used in our country, instead of many substitute methods to produce the overmolding or two-component parts.At present, to ordinary injection molding process, most CAE software can simulate well for single-material molding process, but can't make an accurate simulation for sequential overmolding (bi-color) injection molding process, due to its process parameters' quantities and uncertain factors of coupling interface between the overmolding and substrate material are twice than or more than the single-material injection, therefore, in the stage of process parameters setting, mold design and simulation analysis the research and application are limited very much. In so many CAE software, no one can simulate sequential overmolding (bi-color) injection comprehensively and concretely. So simulation results are just a reference to practical production.In this thesis, extensive reading were adopted at home and abroad, summarized five typical and improved sequential overmolding (bi-color) mold structure such as the core rotary-type bi-color injection structure, the contraction core-type bi-color injection structure, the de-part plate rotary-type bi-color injection structure, the core slide-type bi-color injection structure, seesaw mold structure; analysed the processing characteristics and adaptability of mold structure respectively; summarized key points of sequential overmolding mold design and products design; finally established the main influence factors to product quality such as melt temperature, hold pressure, injection velocity, mold temperature and so on. From the melt rheology, the rheological application were discussed in sequential overmolding injection, such as melt rheology index n vs volume fraction of the second melt and stress analysis of sequential overmolding melt flow; at the same time made a mold structure design to sequential overmolding seal shell according to products requirements; and simulated the product combining MPI/Overmolding module with robust design-orthogonal tests; analysed influence of the injection process parameters such as melt temperature, hold pressure, injection velocity, mold temperature on sequential overmolding injection, and obtained influence degrees of main factors, such as melt temperature is greater than hold pressure and injection velocity than mold temperature for volumetric shrinkage; and hold pressure is more than melt temperature than injection velocity than mold temperature for sink index. The research of this paper can supply guidance to practical overmolding injection production.