Mold design of inner buckle window lower edge hand

2022-08-11
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Design of the mold for the lower edge handrail of the automobile inner buckle window

Abstract: the lower edge handrail of the automobile inner buckle window is a kind of special-shaped material with hard and soft materials, which is produced by extrusion molding technology. The design of die head and setting die are described in detail. Theoretical calculation and practical experience are combined in the design of die

key words: profile; Extrusion molding; Mold

introduction

Figure 1 is the part drawing of the armrest at the lower edge of the inner buckle window of the car. It uses rigid PVC as the main body, elastic rubber as the soft edge, and is produced by CO extrusion molding technology. At the same time, the product optimizes its storage life, oxidation resistance, UV resistance and other properties. The shape and structure are complex, and the matching size and accuracy requirements are high. Therefore, the mold design should not only consider the fusibility of hard and soft materials during coextrusion, but also consider the matching coordination between the head and the setting die

1 design of machine head

Figure 2 is the structure diagram of machine head, which is composed of feeding section, transition section and die. The die head is the key part of profile extrusion. Its flow channel, structure and accuracy are the main factors that determine the shape, dimensional accuracy and apparent quality of the extrudate. However, the design of the die is still mainly based on the experience design and die test correction, and the emphasis should be paid to the flow consistency of hard and soft materials and how to make the hard and soft materials have better fusibility at the die

1.1 die design

(1) relationship between die shape and product cross-section shape. For example, generation 8 and 8.5 LCD panel production lines have been successfully put into production. The die is a forming part of the product cross-section. When the material leaves the die, there is obvious expansion and deformation, which is caused by the uneven flow rate of molten material in the die cavity, uneven resistance, improper temperature adjustment or fluctuation, and the viscoelastic effect of melt expansion from the die. Therefore, the cross-sectional shape of the channel gap should be similar to the shape of the product, and the specific size should be determined by combining the expansion of the material, the contraction of the material during cooling, the traction and stretching and other factors to make the corresponding correction, but this correction is difficult to calculate in theory, and can only be determined by experience and multiple mold trials

(2) empirical calculation of die size die size = product size × K ± 0.2 (k is the molding shrinkage; 0.2 is the polishing amount) for example: the length of the die of one-sided plastic section = 50 × 1.046+0.2 = 52.5mm (Fig. 2) the thickness of the die channel is taken as the thickness of the product due to small shrinkage

(3) calculate the length of the die forming section. Generally, the length of the die section is corrected by comparing the calculation method and the empirical method, and a suitable size is selected

there are calculation methods and empirical methods for calculating the forming length of the die:

① calculation method

the shape of the profile designed in this design can be regarded as a kind of gap, and the flow of the material is considered to be one-dimensional flow. The flow parameter formula of the molten material in the die expressed by its rheological principle formula is:

P = 12qhl/wh3

where:

p - extrusion pressure, MPA

Q - volume flow, cm3/s

L - length of forming section, CM

W - equivalent width of gap, CM

H - equivalent height of gap, CM

length of forming section is converted according to the above formula: l = pwh3/12qh

② empirical method takes the gap height of die as the main parameter

if the gap height is h, then the length of the forming section L = (20 ~ 30) h, H = 0.9h, and H is the nominal size of the wall thickness of the profile

to sum up, the length of the forming section of the die is determined to be 75mm (Fig. 2)

1.2 design of feeding section and transition section

the key to the design of feeding section is to have no dead corners and corners. The design of transition section should adjust the flow rate according to the principle of "equal pressure and equal speed", and the slow flow should be enlarged to speed up

according to the empirical data provided by Wuhan modern rubber and Plastic Technology Co., Ltd., the lengths of feed break and transition section are 81mm and 49mm respectively. The head compression ratio e is taken as 3 ~ 6

2 setting die design

2.1 setting die structure design

Figure 3 is the setting die structure diagram. The selection of upper and lower parting surfaces of the setting die should be easy to operate, with good sealing, large and uniform vacuum adsorption force, and good processing technology of vacuum holes and cooling water holes. The setting mold is fixed on the setting table and can be opened and closed. The lower part is fixed on the channel steel of the sizing table, and the sizing table can move on the steel rail. The upper part shall be easy for quick loading and unloading, easy to clean, and firmly locked

2.2 design of vacuum adsorption hole

due to the large adsorption force of the groove, the vacuum width adsorption hole adopts the groove structure, and the width is generally f 0.8mm ~ f1.2mm. The adsorption force should be evenly arranged, and the vacuum adsorption grooves of the upper and lower halves of the setting mold should be aligned and connected respectively, but generally not connected with the atmosphere. The parts of the ribs and corners should be designed with large adsorption force to ensure the molding quality of the profile. In order to achieve this goal, the air extraction port is designed to align the ribs and edges. Since the base parison is still in viscous flow state when entering the first section of the setting mold, it is easy to be sucked into the groove, resulting in excessive resistance, so the width of 1 ~ 6 vacuum adsorption grooves in front of the first section of the setting mold is preferably 0.8mm, and the rest can be 1 ~ 1.2mm. The distribution of vacuum adsorption area from the inlet to the outlet of the setting mold should be from large to small, and the number of vacuum grooves should also be from dense to sparse. The front part of the first section should have enough adsorption force to improve the surface quality of the profile, so the spacing of 1 ~ 6 vacuum grooves in front is 25 ~ 30mm, and the rest can be 30 ~ 40mm. The edge of the groove should be chamfered with oilstone, but it should not be too large

2.3 calculation of the length of the setting die

the total length of the setting die is determined by the area of the vacuum adsorption circuit and the area of the water cooling circuit according to the section size of the profile. At the same time, it is also affected by the performance of the extruder, the size of the traction force, the size of the vacuum hole, the cooling speed and other factors. The actual total length is difficult to be accurately calculated. It is generally estimated according to the empirical formula: l = 400t2v. In this design, the length of the vacuum setting die is taken as 208 mm (Fig. 3)

3 conclusion

at present, the relevant theory of profile forming is not mature, and the theoretical calculation and practical experience are combined in the mold design. Therefore, in the mold manufacturing, it is necessary to repeatedly try and trim the mold, and the trimming of the die should be tested and adjusted online with the shaping device. The mold is easy to operate in the process of use, and can continuously and stably produce qualified products

About the author: Qi Xinghong (1968 ~), female, lecturer

author unit: Qi Xinghong (Huazhong University of science and technology, College of mechanical science and engineering, Hubei, Wu constantly arouses the endogenous power of enterprises, Han, 430070; Wuhan University of technology, College of mechanical and electrical engineering, Hubei, Wuhan, 430070)

Hu Ping (Wuhan University of technology, College of chemical engineering, Hubei, Wuhan, 430070)

Gong Zhihai (Wuhan University of technology, College of chemical engineering, Hubei, Wuhan, 430070)

References:

[1] Fu Xiujuan, Liu Changsheng, Zhou Aijun Design of extrusion die for heat insulation strip profile [j] Application of engineering plastics, 2004, (8): 55 ~ 57

[2] thorough Development of extrusion die for UPVC profile [j] Mold industry, 2001, (2): 34 ~ 37

[3] Wu Qinghe Plastic extrusion molding [m] Beijing: Chemical Industry Press, 2004

[4] LV Boyuan, Tang Yue, etc Extrusion molding and product application [m] Beijing: Chemical Industry Press, 2002 (end)

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