Mold Analysis: Automotive fan base plastic mold design

Time:2019-11-08 16:17:47 / Popularity: / Source:

Mold is an important process equipment of modern industry and an indispensable part of production of many industrial products. In recent years, with continuous development and mass production of new models in automotive industry, some internal structural parts have been basically plasticized, new injection molding technology has played an important role in promoting launch of new models. In particular, development of automotive plastic parts molds is closely related. In recent years, continuous maturity of CAD/CAM/CAE has enabled many sophisticated and complex products to be designed and produced. In design of molds, we can design better institutions based on strong processing capabilities, improve production efficiency, ensure product quality, reduce costs, labor intensity, and mold production cycle.
Fan on car's fan base is designed to dissipate heat from heat sink. It includes engine cooling water pipe, water chamber, fan base, fan rotor and air conditioning radiator core. When both of them have a temperature that is too high, fan will start. Mixing with fan is noise from fan. Balance of blade rotation and flatness of fan base assembly will affect noise level of car. Car fan base is divided into integral type and split type. Split type should pay attention to roundness and profile requirements of product, while integral fan base requires flatness on the basis of roundness and profile. Only better assembly with heat sink can further reduce noise and energy consumption. Fan motor will vibrate during operation, so fan base is required to have a certain shock absorption, as shown in Figure 1: Assembly position of fan base in the car.
Fan base molds 
Figure 1 Assembly position of fan base

Process analysis of parts

Fan base is a structural part belonging to automobile engine cooling circulation system. It is divided into an integral type and a split type according to different models and sizes. Following product (Fig. 2) is an integral fan base. Mold adopts a mold with one cavity. Maximum size of product is 736x441x137. Shape is more complicated and matching requirements are high. Long glass fiber requires less fiber breaking rate and shape deformation is below 1mm. Among them, there are 6 small sealing doors, 3 holes for assembling with fan rotor, 3 metal inserts, and 4 positioning slots for heat sink. Middle circumferential ribs require small deformation and high assembly requirements. Moving mold side of whole product is covered with 1.6mm stiffeners. Reinforcing ribs are 0.5 degrees on one side, big end is 1.6, and small end is 1.5. Middle reinforcing ribs have a small force range, product is long glass fiber and harder, so exit angle is large, unilateral angle is more than 1 degree, and all ribs are required to be above R1mm. To ensure smooth release at deep ribs on fixed mold side, three fixed-mode blocks are designed.
plastic mold design 
Figure 2 Product plan
Material selection: PP-LGF30, shrinkage rate: 0.3%, average wall thickness: 2.5mm, injection molding machine: 780T.

Mold flow analysis

Fan base molds is designed as a mold with one cavity, according to shape of product and injection molding process, mold flow analysis is carried out with gate with 3 drops, 4 gates and 5 gates to find the best glue way and gate type, finally choose gate with 4 drops (Figure 3), because material is long glass fiber, so to prevent long glass fiber from being broken when filling, it is necessary to reduce corner on its flow path, that is, try to increase R angle.
plastic mold design 
Figure 3 product feeding solution
In terms of cooling system, fan base molds adopts a full-inlaid structure, requiring each large insert to have a separate water channel + water tower for cooling. If necessary, mold temperature can be used to control deformation of product. Water path diameter is set to 12 mm and water tower is 18 mm. (Figure 4)
mold temperature 
Figure 4 Dynamic mold waterway diagram
Through mold flow analysis, results show:
Figure 5 shows position of product's fusion line. Temperature of junction is higher, and junction is more obvious. Mainly in the place where stream meets, generation of weld line will reduce structural strength of product and cause surface defects. However, choice of gate with 4 drops, it can be seen more welds, but not very obvious.
Fig. 6 shows shrinkage of product when it is ejected. Since product is not uniformly solidified, shrinkage is inconsistent, and it is necessary to strengthen mold temperature, correct water passage, and control cooling. It can be seen from results that shrinkage index of this scheme is small, less than 0.5%.
Mold flow analysis 
Figure 5 Distribution of fusion line   Figure 6 Distribution of contraction situation
In summary:
1. Product bonding line is many and not obvious, but it is necessary to pay attention to exhaust gas at the end.
2. Product is solidified evenly, causing shrinkage to be less large. It is recommended to cool evenly.

Mold design features and mold structure

Mold design concepts and features:

mold base 
Figure 7 mold base target size value
1: Size of mold base is reasonable (Fig. 7), and guide pillar is used. Dynamic mold is set with insert structure. Mold base material is S50C, and all insert materials of dynamic mold are 2343. Mold is easy to disassemble and deform, convenient to maintain, and convenient to control shrinkage of mold temperature.
2: Fully consider cooling, waterway should be arranged as much as possible, diameter is large, and middle annular waterway is evenly cooled.
3: Ejection is safe, reasonable and even.
4: Parting surface is set reasonably, it is convenient to process, and R angle parting surface is processed into a smoothing difference.

Mold peripheral accessories design:

Basic appearance structure of mold
hot runner protection block, positioning ring, lock module, die pit, ring screw hole, water path, water collecting block.
a: Protection block is 10mm or more higher than hot runner, plays a protective role in production and transportation.
b: Size of die hole between each two plates is set to 60x60 and 8mm.
c: Set die on the ground side of mold.
d: A and B plates are lifted at 8 point each time, and position of rings is set on both sides of mold as much as possible.
mold base 
Figure 8 basic appearance of fan base molds
Mold positioning system (four-ply structure)
Mold base is matched with a 10 degree taper to form overall mold positioning and anti-rolling mode, wear plates are added as needed. Four-ply margin is 80-85mm, height is 58mm, bottom R5 is above, and top corner C3 is finished by mold base company.
Mold positioning 
Figure 9 mold positioning system diagram
Hot runner system:
Long glass fiber can effectively improve rigidity, impact strength, creep resistance and dimensional stability of product, and can make complex automotive module products. Due to long fiber length of this material, it poses certain difficulties for conventional injection molding, and may be damaged during injection molding process without obtaining required strength. Long glass fiber reinforced polypropylene injection molding technology has been successfully developed in foreign countries. Technology includes two aspects: one is material modification of glass fiber reinforced polypropylene, that is, an ultra low melt viscosity polypropylene resin is used (Resin melt flow rate is 300g/10min), so that glass fiber wrapped therein is subjected to a small screw pushing shear force during injection molding process to reduce length loss of glass fiber, and at the same time a polypropylene resin with a high crystal structure is added to ensure strength of injection molded part.
Second is improvement of injection molding process, that is by improving geometry of screw, such as deepening screw groove, widening pitch of screw, optimizing design of screw head, expanding hot runner to make glass fiber reinforced resin flow smoothly during injection process to reduce high shear force of resin during plasticizing process, thereby reducing length of glass fiber. Following is an improved method starting from hot runner.
Hot runner system using long glass fiber is quite different from ordinary hot runner system. Ordinary needle valve has a round shape of about 0.2mm on product (see Figure 10). However, in order to prevent long glass fiber from breaking during filling, it is necessary to reduce corner on flow path. Product should be smooth as much as possible. A 7X7 frustum is added at four glue points, and a split groove is added to movable mold side of product to facilitate flow of long glass fibers (see Figure 11). In hot runner system, in order to prevent long glass fiber from breaking during flow, large R angle is added by insert at the corner (see Fig. 12).
Hot runner system 
Figure 10 Common material into glue point Figure 11 Long glass fiber into glue
Hot runner system 
Figure 12, long glass fiber hot runner diagram

Pre-deformation of fan base molds:

We know that product deformation is caused by three factors: uneven cooling; uneven shrinkage; inconsistent molecular orientation. Through actual simulation analysis, these methods have limited effect, and still can not meet product deformation and product tolerance requirements. In this case, we need to make product's anti-deformation according to results of mold flow analysis. In order to obtain qualified products, following (Figure 13, Figure 43 is a pre-deformation of prior mold) is a reference for pre-deformation of fan base.
Fan base molds 
Figure 13, same type of mold product pre-deformation program
Fan base molds 
Figure 14, same type of mold product pre-deformation program
According to experience of previous mold and results of fan base mold flow analysis, following figure is shown (Figure 15).
Mold flow analysis 
Figure 15, fan base mold flow analysis
According to mold flow analysis, fan base is generally farther away from center of circle, and deformation is larger. Based on this set of data, following anti-deformation mold design is performed (Fig. 16).
Fan base molds 
Figure 16, first pre-deformation design of fan base molds
Fan base molds 
Figure 17, second pre-deformation design of fan base molds
Middle ring part is symmetrical because of product structure, and there is an increase of ribs. Deformation X and Y directions are small and can be neglected, but Z direction is greatly deformed. Product has a deformation of 1.5-2.8mm at both ends. Outside ring, farther away from center of circle, the greater deformation. Pre-deformation can be designed according to a certain gradient angle, but it should be considered in combination with distance from center of circle, product structure and joint position of gate. Deformation of end of product and body are basically same. Key parts such as buckles are designed to be inlaid in order to be easily modified in the future. Make first pre-deformation size according to mold flow analysis. After test, second pre-deformation was made due to amount of product deformation, product tolerances, etc. (Fig. 17). Finally, requirements of product were met.

Molded part design:

According to customer's requirements, each part of product needs to be cooled, so mold adopts a full-inlaid structure (Fig. 18), and each molding insert has a separate cooling water passage.
Fan base molds 
Figure 18, moving mold core insert
Each of inserts on fixed mold has a mounting sequence, and each insert has a mounting angle to protect molded part and fitter from ease installation, strengthen assembly relationship between inserts. In order to prevent product from being firmly fixed, three fixed-mode spring blocks are added on side of fixed mold, which can play a safety protection role when mold is generated.
Mold flow analysis 
Figure 19, moving mold inlaid block waterway
All molded inserts pass through water path (Figure 19): in general terms to control mold temperature. 1. Cool cavity to achieve rapid product formation. 2. Because material is long glass fiber, it is necessary to maintain temperature of cavity, thereby controlling molding time to ensure that product does not warp and rubber compound is insufficient. 3. Circular water path in mold core insert is reasonably distributed according to shape of product. 4, single cooling waterway can be achieve which part of warpage is serious, deformation is large, you can immediately control product quality through process adjustment of single cooling waterway.
Support column, travel switch and forced reset hole (Figure 20):
a: Number of supporting columns should be as large as possible, diameter should be as large as possible, and position should be distributed below pouring point and parting surface.
b: Travel switch is set diagonally for a total of two.
c: Number of forced reset holes is set to 4, which matches top hole of machine.
plastic mold design 
Figure 20 support column, travel switch, forced reset hole diagram

Mold work process

When mold is opened, moving and fixed molds are divided, three fixed-mode elastic blocks and plastic parts are pushed out with moving mold. After mold is opened for a certain distance, moving mold stops moving, pushing mechanism moves forward under forced resetting force of injection machine, pushing ejector pin on top plate to push out plastic part. When mold is closed, pushing mechanism is first reset under forced resetting action. After stroke switch is touched, injection molding machine starts to close mold.

Key points and difficulties in mold design and manufacturing

(1) Fan base has a short manufacturing cycle and a long procurement time for mold base. It also needs to be pre-deformed. Material is long glass fiber, which brings pressure to design and order. It needs to be experienced and purchased in early stage.
(2) Long glass fiber material is relatively hard, mold is ejected and reset is unbalanced, product size is large and easily deformed. Top plate guide column is increased by 2, thimble plate screw is increased to prevent deformation, and fixed mold block is added to prevent die from being fixed.
(3) Elimination of fusion line. After mold was tested, it was found that sintering line was obvious, and it was solved by improving injection molding process and strengthening exhaust.
(4) It is necessary to install molded inserts in order during assembly. Molded inserts are angled to ensure post-assembly quality.
Summary: In actual production, when fan base is smoothly ejected, product is balanced, which can prevent deformation of product without whitening, reduce and control position of fusion line. Through continuous accumulation of experience in manufacture of fan base molds, coordination between design, processing, assembly and mold base factory is more orderly, guaranteed in mold cycle, processing of mold problems is targeted and specialized. These summaries have reference for making similar molds in the future. Sexuality, guidance. With the continuous development and development of technology, Fan base products are trending towards high efficiency, tightness, shorter injection molding cycle and 1+1 design of mold products.

Go To Top