Vertical injection molding machine shrinkage rate (4)

Date：2015-10-08 23:15:14

1.4 The main work
        Solve vertical injection molding machine injection molding simulation methods needed material constants problem difficult to obtain, this paper presents some kind of plastic to plastic manufacturer provided an average shrinkage to represent the characteristics of a batch of vertical injection molding machine injection molding material, Numerical simulation methods for structure prediction based on molding shrinkage vertical injection molding machine injection molding products distribution trends, draw qualitative conclusions, then combined with the average shrinkage rate of vertical injection molding machine injection molding materials, predict vertical injection molding machine Injection Molding shrinkage products, the value of each point, draw quantitative conclusions.
        According to the prediction of vertical injection molding machine injection molding around the mold shrinkage of molding size is determined, in the production of vertical injection molding machine injection molding process by adjusting the parameters so that the vertical injection molding machine injection molding products actual shrinkage values ​​to predict shrinkage value approach, resulting in a qualified plastic products.
        To take advantage of the numerical simulation method to predict vertical injection molding machine injection molding shrinkage rate distribution trends, we also need to participate in the material constants calculation. Since the aim is to get the numerical simulation shrinkage distribution trends, want is qualitative rather than quantitative conclusions conclusion, therefore can choose between two constants have been measured plastic material to represent the non-crystalline plastic with crystalline plastic.
        Since the material constants imprecise, making numerical simulation can not be used to determine the appropriate vertical injection molding machine injection molding process parameters, required vertical injection molding machine injection molding production personnel in the test mode debugging a reasonable injection molding process parameters. In the simulation, when it is assumed that under ideal conditions the injection molding process, which does not produce charge injection molded article is insufficient, shrinkage, scorch, overflow mold, warped and other molding defects. Research will focus on the impact of molding shrinkage distribution structure, because so vertical injection molding machine injection molding products throughout the contraction was mainly due to different molding structure, but also from the perspective of the service object, the mold designers Injection molding shrinkage rate distribution of most concern is the structure of the vertical injection molding machine.
        Based on the above analysis, this paper prediction method for injection molding shrinkage rate was studied, mainly as follows:
        (1) vertical injection molding machine injection molding process in motion analysis of the characteristics of the polymer, combined with experimental studies to explore the vertical injection molding machine Shrinkage of injection molded products. After the current numerical simulation of the injection molding process, is the desire to obtain narrow plastic hematocrit level, which was converted into an equivalent temperature load, and then the mold and the mold cooling stage outside the cooling stage separately using linear viscoelastic constitutive heat Model and thermo-elastic model to solve vertical injection molding machine injection molding products deformation under load and deformation restraint effect. But if we can clear shrinking direction injection molding products, it can reduce the hematocrit level of desire according to which he is bound to shrink displacement situation translate directly into injection molded products, so that the calculation process is simplified. For this purpose shrink mechanism analysis of injection molding products.
        (2) According to the characteristics of the injection molding of the three basic equations of fluid mechanics were simplified equations establish vertical injection molding machine injection molding products temperature and pressure.
        Shrinkage of injection molded article is achieved by specific volume shrink, because plastic hematocrit changes in pressure strain, thermal strain, strain crystallization and chemical reactions strain, specific volume change produced by a chemical reaction which is not within the scope of this article. In the flow and packing stage, plastic pressure in the cavity around the continuous improvement of plastic hematocrit compressive strain; after holding pressure disappears, plastic hematocrit spontaneous reply from the compressed state to the equilibrium state, but by the cavity plastic hematocrit limit can not be expanded, specific volume contraction tendency to rely on the temperature drop generated than the absorption capacity of the expansion trend, so at the beginning of a period of time in plastic mold cooling phase hematocrit value does not change, plastic pressure as the plastic temperature Bu drop and continue to decrease, has been reduced to equal to atmospheric pressure, specific volume expansion trend was completely disappeared, the temperature drops and crystallization can make tears' plastic molded article shrinkage.
        To calculate the contraction process visible injection molded products each point, the need for liquidity and packing stage temperature and pressure calculation calculate vertical injection molding machine injection molding products, and equal to the pressure in the mold according to the plastic cooling simulation and simulation-mold cooling atmospheric pressure after the specific volume decreases with temperature and reduced shrinkage process to determine the circumstances of each time step. To solve the temperature and pressure of injection molding products, we must first establish the appropriate equations. The various stages of equations established in this paper in vertical injection molding machine injection molding are considered vertical injection molding machine injection molding products in the flow surface and heat transfer between the mold wall and plastic specific heat with respect to time changes.
        (3) to be used in the control equation plastic viscosity, thermal conductivity, specific heat, specific volume calculation method will be discussed, and relaxation properties of polymers based on the calculation of the specific volume of plastics Tait equation of state to be amended. Plastic hematocrit is not only the physical properties of the data to be used in the control equation, and the calculation procedure is in accordance with the degree of shrinkage shrink plastic hematocrit to carry out, so the correct calculation of plastic hematocrit is very important. Tait equation of state is currently widely used to calculate the specific volume of plastic, but plastic is non-crystalline and crystalline plastic Tait equation of state as described in the minimum rate of temperature change VT produced and maintained under constant relationship. The actual injection molding process, the cooling rate of injection molded articles not only changes in time, and throughout the cooling rate difference is very large, which makes a p vT relationship provided Tait equation of state can not be applied directly, but it needs to be amended to obtain several VT relations with non-crystalline plastic case of changing the cooling rate and crystalline plastics.
        (4) The forecast plastic melt during filling the forefront of the equivalent distance method, and according to the forefront of the plastic melt injection mold cavity in the flow path of the flow field is divided, each of flow paths and at different times of the plastic melt front intersection as a mesh node, the completion of the vertical injection molding machine injection molding products within the flow surface meshing. This article established injection molding machine injection molding products each point contraction in the flow surface is carried out along its flow path, so the front of the injection molded products for processing and the flow path of the meshing link.
        Since the division of the flow path is based on the plastic melt front location, so that you need to predict the distribution of plastic flow analysis before the melt front, and to this end proposes the equivalent distance calculation method to determine the use of the plastic melt front position equivalent distance.
        (5) on the injection-molded article temperature boundary condition issue, the manner of superposition of point sources on the field to get the mold wall temperature distribution trends, and the flow and packing stages of vertical injection molding machine product temperature calculated using the non- symmetrical temperature boundary conditions, consider the space within the mold cooling stage vertical injection molding machine injection molding products arising due to shrinkage of the mold wall. Then solved by the finite difference method vertical injection molding machine injection molding temperature and pressure control products party a ride, carry out flow, pressure, numerical simulation of the die-mold cooling and cooling process to obtain a contraction of vertical injection molding machine injection molding products rate distribution trends.
        Now widely used in the Boundary Element Method mold wall dimensional temperature field, boundary element method because the coefficient matrix of the resulting large linear algebraic equations is the full array and asymmetry, so the amount of data occupied by the coefficient matrix is ​​very large, very complex data management, Equations for a long time, and in order to determine the heat flux density injection molded products and mold between the walls, we need to calculate the temperature field of the mold wall and the calculation of the vertical injection molding machine injection molding products temperature field were evil co iteration until the convergence in order to obtain the steady-state temperature field in the mold wall (if the die temperature fluctuations into account changes, the mold wall temperature field as transient temperature field processing is to be performed at each time step mold wall temperature field and vertical injection molding machine Injection Molding Woe product temperature field of combined iterative calculation).
        Given by the Boundary Element Method mold wall three-dimensional temperature field to spend a lot of computing time, and this article studied in predicting shrinkage always focused on the distribution of the grasp of the overall trend, and therefore quantitative mold wall temperature field in solving qualitative solving instead, by superimposing the flow channel, the impact of cold source of the mold cavity inner wall of the heat source and the cooling circuit points each point, to get the mold wall temperature distribution trend, temperature boundary condition as vertical injection molding machine injection molding products.
        (6) obtained by the numerical simulation of vertical injection molding machine injection molding shrinkage rate distribution vertical injection molding machine injection molding material average shrinkage trend and plastic manufacturers to provide combined, forecasting around vertical injection molding machine injection molding shrinkage values. Finally, the shrinkage rate prediction methods herein experimentally verified.

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