Design and CAE of large injection mold for bumper

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Design of large injection mold for car bumper and CAE

[Abstract] it is the development trend of the automotive industry that plastic bumper replaces metal bumper, but the design of plastic bumper still adopts the traditional mold design method. Therefore, aiming at the product structure of the car front bumper, this paper uses the software of HuaSu CAE (HsCAE) to optimize, analyze and simulate the cavity pressure, melt temperature and flow front of the car bumper injection mold, and check the main parameters of the bumper injection mold at the same time. The research results show that the design method used in this paper can greatly improve the efficiency of the design and development of the bumper injection mold

keywords bumper injection mold hot runner CAE

1 preface

with the development of automobile industry, all metal bumpers are increasingly not suitable for the requirements of modern vehicles in lightweight, high functionality and integration with body modeling. Especially in cars and light vehicles, there is a trend to replace all metal bumpers with plastic bumpers. As a substitute for steel parts, automotive plastic bumpers occupy a place in the automotive industry because of their beautiful appearance, light weight, easy molding, corrosion resistance, low cost, good comprehensive mechanical performance, and easy to achieve large-scale production. At present, cars in China. Manufacturers of mini cars and light vehicles are gradually upgrading their products

2 geometric structure analysis of car front bumper

the part shown in Figure 1 is Mazda car front bumper, with a wall thickness of 3.5mm. Generally, the surface of the part is required to be smooth without defects, and there is no high requirement for its shape accuracy. As shown in Figure 1, the bumper is saddle shaped, Length 1925 "Our TORLON reg; Pai processor certification work is mm, 715mm wide, 538mm high, and the average wall thickness is 3.5mm. There is an oval lamp hole on the left and right, a ventilation grid in the middle, and a number of inner stiffeners. The tail has inner curling, so it needs to use inner core pulling.

bumper materials require good rigidity, impact resistance, dimensional stability, solvent resistance, and coating performance in a wide temperature range. Propylene integrated function Better, so polypropylene (modified) is selected here as the bumper material

the features of the designed bumper mold are: the overall dimension of the mold is large (2400mm × 700mm × 11oomm), volume weight (25~40t), complex structure, similar to a medium level machine tool; The mold pouring system is a hot runner, which needs electric heating; The cooling system of cavity and core is complex, and the hot runner of cavity and gating system is contradictory; The ejection system of products is complex, which is usually combined with hydraulic and mechanical ejection, and the products are automatically taken out by manipulator; The product size is large, the gating system is often cold, and the scribed line on the hot runner phase support is combined with the position of the idler centerline

3 CAE optimization analysis

based on the overall structure of the injection mold for the front bumper of the car, the use function control and the specific design of the mold structure (including the design of the molding parts and guiding devices of the gating system, the direction finding and parting core pulling mechanism, the mold temperature control device, etc.), the optimization and dynamic simulation analysis are carried out by using the HsCAE (HuaSu CAE) software developed by the national mold Key Laboratory of Huazhong University of science and technology, Thus, the backward method of designing the gate position and size of the mold only by human experience in the past, which requires multiple mold trials and repeated modifications, can be finally designed, finalized and manufactured. The development of this subject will greatly reduce the complicated labor of designers to repeatedly estimate the size of the mouth, and accelerate the process of large car injection mold design, manufacturing and product serialization in China

during plastic injection molding, the flow and molding of plastic in the mold cavity are related to a series of factors, such as the performance of materials, the shape and size of plastic parts, molding temperature, molding speed, molding pressure, molding time, surface condition of mold cavity and mold design. CAE optimization analysis is to use the high-speed computing function of the computer and comprehensively consider various factors to obtain the simulation results of flow field, temperature field, pressure field, shear stress field and so on, so as to evaluate the advantages and disadvantages of the scheme used. Here, the hscae5.0 software developed by the State Key Laboratory of mold of Huazhong University of science and technology is used for optimization analysis

the analysis results of flow field are shown in Figure 2, and its flow is balanced. Combined with the analysis results of fusion mark behind, it shows that the gate opening is reasonable

the temperature field results are shown in Figure 3. The temperature difference at the end is relatively large, which may be due to the hot runner technology adopted by this mold, and the CAE analysis results are calculated according to the cold runner juice. If the temperature difference at different positions at the end of injection is too large, it is difficult to obtain uniform cooling. Different temperatures will lead to changes in the density and properties of the polymer, which will lead to warpage. At the same time, large residual stress caused by temperature difference may be generated

the results of pressure field are shown in Figure 4. Because of hot runner, slight pressure is not a phenomenon. In case of insufficient pressure, the following factors should be considered: ① insufficient liquidity of materials; ② The product is too large and the wall thickness of the part is very thin; ③ The length of runner is too long; ④ Graded injection is required

the results of shear stress field are shown in the picture. The stress field is uniform and there will be no spray phenomenon

stl used in CAE optimization analysis must be considered. The file has no coordinates, so it cannot be accurately positioned, and the flow imbalance factor will be artificially introduced. The common hot runner or the combination of cold and hot runner technology of large injection mold is very different from the cold runner assumed by CAE analysis, which also brings great errors to the analysis

4 design of hot runner of bumper large-scale injection mold

when designing the gating system of large-scale plastic mold, it is necessary to ensure that the cavity is full and reduce the defects caused by improper system design. Super large plastic parts often use multi-stage shunt. Multi point simultaneous Pouring Scheme. The complex gating system not only improves the quality of plastic parts, but also increases the difficulty of design. Therefore, the design of gating system is one of the keys to the design of large-scale injection transverse

hot runner technology is not planned to be used this time. The development of this new technology is a major reform of injection mold. Its application not only shortens the forming cycle, improves the production efficiency, but also saves raw materials. In large-scale mold design, hot runner system design is more and more widely used, especially hot runner mold, which is the development direction of large-scale mold

the hot runner mold is discussed below. The reason why the hot runner mold shell is widely used is that it has the following unique advantages: shorten the molding cycle, generally up to 30% - 40%; Avoid recycling a large amount of recycled materials, so as to save raw materials and reduce costs; Because the temperature is strictly controlled, the product quality is improved and the dimensional accuracy and strength of the product are guaranteed; The hot runner is conducive to pressure transmission, which can reduce the injection pressure; Shortening the mold opening stroke is conducive to protecting the mold and prolonging the service life of the mold; There is no need to trim the handle, saving man hours and manpower; Shorten the molding cycle, reduce the product cost, and generally reduce the production cost by 16%

according to the CAE analysis results, AutoCAD software is used for two-dimensional mold design. The mold is designed as single cavity, hot runner, 9-point pouring, inner core pulling and other technologies. The clamping process is guided by two rectangular guide sliders, and finally locked by the conical positioning. The total length of the mold is 2000mm, the width is 1200mm, and the height is 1440mm. The general drawing of the mold structure is shown in Figure 6

The basic steps of two-dimensional mold design are as follows:

(1) draw the two-dimensional structure diagram of the product, and determine the position and size of the parting surface and gate

(2) metal parts are used to surround the inner and outer surfaces of the products

(3) set the pouring system, mold closing guide mechanism, ejection system, heating and cooling system

(4) press and fix the mold parting surface to draw the orientation map of the left and right moving mold

(5) the assembly coordinate positions of relevant parts are shown in the dynamic and fixed mold views respectively

(6) use another view to express the relevant contents of the incomplete main view

(7) draw the product drawing below the main view and mark the size of the product

(8) mark the serial number of parts, and list the technical requirements of materials, pieces, heat treatment, etc. in the parts list

(9) write down the technical requirements and the action principle of the mold in the general assembly drawing

5 verification of main parameters of large injection mold

(1) calculation of thermal power of heating runner plate. The hot runner plate is equivalent to extending the nozzle of the injection molding machine, which greatly shortens the melt flow and is conducive to the filling of melt. However, the hot runner pouring system needs to be equipped with the mold temperature controller of the fine bowl to prevent the melting material from being burnt due to excessive temperature. The power of the heating tube is generally estimated by experience according to the need of 0.1-o.15kw per kg of hot runner plate, which is also called the calculation according to the formula of 3D printing and sensors related to the third industrial revolution

(2) heating and cooling system of the core and cavity

mold temperature is an important factor affecting product quality and molding efficiency. In the mold with hot runner, on the one hand, the hot runner needs to be heated and on the other hand, the mold needs to be cooled. And because of the huge volume of this mold, the mold temperature is low when the mold starts to work, so it needs to be preheated. After working for a period of time, the mold temperature rises and needs to be cooled when it exceeds the specified temperature. The molding temperature of polypropylene (PP) is 160 ℃ -260 ℃, and its mold temperature should be controlled at 55 ℃ ~65 ℃. Large injection mold is best cooled by tap water, which is more economical. The diameter of cooling water hole is generally φ 8- φ 12mm。

the heating device of large injection mold is generally heated by electric heating rods. It has the advantages of convenience and easy control, but it must prevent local overheating

(the 4th International Annual Summit on automotive lightweight technology and material technology innovation and utilization was held in Wuhan in 2014. 3) calculation of cavity side wall thickness

theoretical analysis and practice have proved that the stiffness of large-scale dies is an important problem, while the strength is a secondary problem. Therefore, the dimension of formed parts should be based on meeting the stiffness conditions, and the allowable deflection of polypropylene is 0 04mm。 Regard the side wall as a fixed beam model under uniformly distributed load, and the allowable minimum side wall thickness can be deduced from the deflection formula:

for this bumper mold:

(4) the calculation of force deformation of the dynamic mold base plate, the method and principle are the same as the side wall check, and the allowable maximum deflection is generally 0.05mm

generally, for large injection molds, it is also necessary to calculate the packing force of products on the core and check the jacking force; Strength check of connecting screw ejection rod, etc. Please refer to the design manual of injection molding

6 Conclusion

problems that should be paid attention to in the design of large injection mold for bumper:

(1) the geometric structure of the product should be carefully analyzed and the parting surface should be selected; CAE optimization analysis selects the gate form, size, number and pouring position

(2) determine that raw materials used in products often need to have good fluidity (i.e. plastics with large melt flow index) and be conducive to mold filling; Good mechanical properties can ensure that the car does not deform and has elastic recovery under impact; Resistant to adverse environment and climate change without deformation (warpage)

(3) the design of large or extra large injection mold should consider the use of hot runner or a gating system combining cold and hot runner

(4) heating and cooling are a pair of contradictions that need to be solved in the design of large-scale injection mold

(5) the ejection system of large injection mold is generally very complex, which often requires mechanical and hydraulic combined ejection. (end)

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