Vertical injection molding machine molded article shrinkage (1)

Date：2015-09-25 01:08:54

The first chapter
        1.1 engineering background
        All dimensions of the practice of using the same shrinkage rate applies only to the central gate of disk products. Since the tolerance value ordinary injection molding products are great, so the above practices have little impact on the success rate of such mold. However, more stringent requirements for tolerances precision injection molding products, injection molded products in order to ensure precision can be achieved, can not ignore the value of shrinkage errors.
        Vertical injection molding machine mold design, manufacturing and assembly and injection molding process, precision injection molded products are influential. First, in the mold design stage, to reduce the value of the error shrinkage, and tolerance of each part of the mold making reasonable provision; secondly in the mold manufacturing stage, all parts of the mold manufacturing error specified to be controlled in a mold designer within the range of tolerance; then the mold assembly process, pay attention to prevent moving dislocation scheduled to die, and to die sports organizations to put in place; the final stage in injection molding, injection molding process configuration parameters to be reasonable, to avoid the emergence of various molding defects, such as cylinder temperature is too high vertical injection molding machine injection molding material thermal degradation and injection molding products dark spots left on the surface, if the packing is not sufficient or in-mold cooling time is too short then injection molded products prone warped etc. . To ensure the accuracy of the injection molded article, the above-mentioned four stages are important, which select the correct shrinkage played a groundbreaking role, if the value of the shrinkage error has exceeded the tolerance allowed for the injection molded article of degree, then in later session further efforts are to no avail.
        Xi light Kanzaki Japan Corporation proposed tolerances precision injection molding products, the table minimum limit refers to the single-cavity mold plastic molding precision attainable dimensional accuracy limits, practical limit is that the use of the following four cavities mold plastic molding precision attainable dimensional accuracy limits.
        Tolerance value is divided by the corresponding basic size and converted into a percentage, and then compared with the molding material shrinkage fluctuation range, you will find precision injection molding products tolerance percentage share in its basic dimensions fluctuations molding material shrinkage is often beyond . So when the shrinkage differences precision injection molding products each point is large, if mold designers still use the same shrinkage value of all size to injection mold design, mold tolerance even if very strict regulations, die size processing was extremely accurate, by the pair of molds molded plastic products are also likely to substandard products in order to meet the dimensions of injection molded plastic products under the drawing, in the design of injection molds, we need vertical injection molding machine according to the respective size of the injection molded article shrinkage Molding dimensions give compensation.
        Shrinkage vertical injection molding machine injection molding products is affected by many factors, so the injection molding related reference books provided by the shrinkage of the molding material is usually possible fluctuation range rather than a fixed value. Currently in the design and manufacture of injection molds in the value of the shrinkage problem is relatively simple process. Plastic mold designers get the drawings, it is often selected in the shrinkage of the molding material fluctuation range of intermediate values, or taking an average shrinkage of plastic molding material provided by the supplier, and will be selected in accordance with the contraction of all dimensions values ​​amplification, obtained molding die size. The essence of this practice, means that no matter what the shape of plastic products, mold has several gates and gate location where each dimension of the plastic shrinkage are the same.
        In fact, only in the single-gate and temperature conditions are identical for each point on the boundary of the article, the size of each plastic shrinkage will be the same, in line with these conditions, only the gate located in the center plastic disc. That is, the engineering background to date, in the national economy and the plastic from steel, wood, cement three traditional material par important material in all areas of people's lives instead of part of metal, wood, glass and leather and developed into We are able to see the plastic products. The reason why the rapid development of the plastics industry, not only because of the development of the petrochemical industry to provide a wealth of basic raw materials, and with in-depth study of physical chemistry of polymers, plastics and mechanical properties of heat resistance, continue to improve, plus light weight plastic itself has, corrosion resistance, good insulation properties, muffler damping characteristics of the plastic used in construction, automotive, machinery, instruments, electronics, household appliances, health care, sports and other aspects of the increasingly wide.
        At the same time, used in automobiles, machinery, instruments, electronics and other industrial sectors plastic vertical injection molding machine, its precision requirements are also getting higher and higher. The plastics industry is made, development and application of plastics processing industry in three areas of industrial synthetic resin and plastic products thereof. Plastics processing industry plays a role in the past and is connected to link raw materials and products. Many plastics molding method, such as injection molding, extrusion, blow molding, calendering, slush and so on. Since the injection molding process of molding cycle is short, a variety of plastics processing adaptable, capable of producing complex shape, size, or more precise with metal inserts of plastic products, plastic products, has therefore become the main method of forming. Vertical injection molding machine plastic products, more than 80% of plastics are processed by injection molding.
        In the vertical injection molding machine injection molding production process, the plastic particles from the hopper into the injection machine cylinder, in the cylinder is heated and melted plastic plastics become viscous fluid, when it is driven by the injection screw, i.e., at high pressure and relatively high speed through the injection machine nozzle, the mold sprue, runner, gate and into the mold cavity, since the mold temperature is lower than the softening temperature of the plastic, the plastic melt is rapidly absorbed and therefore mold The heat outside to the inside to make it solidify, when the plastic products condense to an appropriate thickness, mold open, an ejection mechanism would plastics ejection from the mold cavity.
        To complete this cycle of time, depending on the size and thickness of the plastic products, from a few seconds to several minutes. After stripping the plastic products, the mold was cooled to room temperature outside continues. Plastic injection molding cycle is experienced by the solid particles are heated to become molten state and fill the mold cavity, and then closed in the colder mold is cooled to a solid state products of the entire process.
        Vertical injection molding machine plastic thermal expansion and contraction of the phenomenon is more significant than the metal, cooled to room temperature is always less than the volume of plastics mold cavity volume at room temperature, which is injection molded article shrinkage Iz], in order to normal bet molded Dalian Li Ding university dissertations 博卜 grid: On the contrary, if we can make the mold before the design in line with the actual situation of qualitative predictions about trends in the distribution of products throughout the shrinkage of injection molding, then by adjusting the injection molding process parameters you can get a qualified plastic products.
        Research content of this paper is to explore practical, reasonable vertical injection molding machine injection molding shrinkage rate prediction method, and then applied to the design and manufacture of precision injection molds. This is an effective means of vertical injection molding machine injection mold design quality and vertical injection molding machine precision injection molding products and the passing rate of increase.

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