注塑模外文翻译

International Journal Conference on Manufacturing and Mechanical Engineering (IJCMME'13) October 4-5, 2013 Dubai (UAE).

Numerical Analysis of Transient Fluid Flow and Heat Transfer in a Process of Plastic Injection of a Mold of Renewable Paint Bucket.

Ali Kargar

Abstract

This research investigates the numerical analysis of heat transfer and fluid flow in transient conditions in plastic injection process on a mold of renewable paint bucket using mold flow software and also analyzes the effective factors such as injection pressure and the form and time of cooling and the heat factors.The main equations include; the equations of continuity, momentum and energy. The induced thermal stresses are analyzed in different points of the component.The thermal analysis of plastic injection mold provides the possibility to investigate the effect of thermal residual stress in changing the sample form and tensile stress analysis in order to achieve the tolerance limit of the sample under tensile load before failure.The analysis results lead to achieve the primary materials reduction value without any change in form or contortion in component (bucket). Also, for the gained input conditions, in general, the least consumption materials attained with the maximum injection efficiency.

Keywords— plastic injection mold, thermal residual stress, injection pressure, cooling time

I. INTRODUCTION

PLASTIC industry is of the world developing industries. Plastic components exist in almost products in everyday life and they are mostly made in injection style.The molding process of plastic injection is of the known industries in production field of components with varied and complex forms and also with low cost.The molding process of plastic injection is

a cyclic process. Four major steps of the process include filling, molding, cooling and component ejector [1].

Molding process of plastic injection starts with casting resin and the required additives in the funnel of the system for heating in cylinder and injecting in injection machine.This is the feeding step, which the mold cavity would be filled with the hot and melted polymer in injection temperature.

After filling the mold cavity, the additional polymeric materials would be injected with higher pressure to compensate the expected contraction simultaneously with the component freezing.Hereafter, the cooling step starts and continues up to the time that the component reaches the sufficient rigidity for ejection[2].

The next step is ejection, which the mold will open in this step and the component would be ejected and the mold would be closed for the next cycle. Design and construction of injection molds of polymeric components with the required characteristics,is an expensive process and needs experience and repeated modifications in construction and machining.Also, designing the mold appurtenances including; muscle (or core) design which is a very difficult and complicated work because of its ups and downs.There are some other important factors in mold design, which include; mold size, number of cavities, cavities layout, runner system, gates system, shrinkage and ejection.In mold thermal analysis, the goal is to investigate thermal residual stress or input stresses in mold to the product sizes[3].Generally, creating thermal stresses in molded injecting component occurs in cooling process and such matter is because of low heat transfer and the heat difference between melted resin and the mold.During the cooling time, the temperature around mold cavity is not uniform. During the cooling time, the places near to cooling flumes,has higher cooling rate than the places far from the flumes. Such matter leads to varied contractions and following that, it causes to thermal stress.Such thermal stresses lead to major residual stresses. So, in cooling process, the extended simulation of thermal residual stresses would be so important in molded components.So, understanding the distribution style of thermal stress, the form variations of thermal residual stresses would be predicted. In this section, mold injection design is given to investigate sample of torsion test and the thermal analysis of the form to understand the effect of the thermal residual stress in mold[4,5].

II. PHYSICAL EXPRESSION

The studied case in the present research is an renewable pain bucket of cylindrical ABS with 2 mm thickness which is shown in figure (1).According to the almost conical shape of the paint bucket, the bucket bottom diameter is about 262/17 mm and its height is about 235/62 mm. the injection input data to construct the bucket include;120 mpa pressure, injection time 1 sec., melt temperature 230°c, and the clamping force5600 ton. Figure (2)

shows the main mold and figure (3) shows its designed sample.

Fig. 1 Renewable paint bucket

Fig. 2 The main mold

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Fig. 3 The mold designed model

III. THE GOVERNING EQUATIONS

Te main equations to determine the pressure, speed and temperature distribution, in injection process of mold plastic of renewable paint bucket are continuity equations,

momentum and the energy equation which include[6,7,8]:

IV. GEOMETRICAL GRATING

In figure (4), the considered geometrical grating is performed, using irregular and prismatic mesh. The important points in meshing include: the meshes portion should not be more than 1 to 7 and their compression percent should be at least 85%.

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Fig. 4 The grating type of renewable paint bucket

V. RESULTS

Next to operating the input conditions and determining the most suitable inlet as shown in figure (4),the studied model would be analyzed and in result, heat distribution, pressure, filling time, freezing time and other effective parameters on the injection process

would be gained, as shown in the following figures, representatively.

Fig. 5 Heat distribution at the end of injection