Large injection mould for car front bumper
The front bumper of a car is one of the most important exterior parts of a car. It must not only have sufficient strength and rigidity, but also play a buffering role in the event of a collision and protect the car body. It must also pursue harmony and unity with the car body shape, and Realize its own lightweight. In order to achieve this purpose, the main body of the front bumper of the current car is made of plastic, commonly known as plastic bumper.
1. Structural analysis of plastic parts
The shape of the front bumper of a car is similar to that of a saddle. The specific structure is shown in Figure 1. The material is PP+EPDM-T20, and the shrinkage rate is 1.0095. Among them, EPDM can improve the elasticity of the bumper, and T20 means that 20% of talcum powder is added to the material, and the purpose is to improve the stiffness of the bumper.
The characteristics of plastic parts are:
(1) The shape is complex, the size is large, and the wall thickness is relatively small. It is a large thin-walled plastic part.
(2) Plastic parts have many collisions and insertion holes, many reinforcing ribs, and large melt flow resistance.
(3) There are three undercuts on the inside of the plastic part, and it is quite difficult to pull the core laterally at each point.
2. Mould structure analysis
The injection mold for the main body of the front bumper adopts an internal parting surface, passes through a hot runner, and is controlled by a sequence valve to enter the glue. The inverted buckle on both sides adopts the structure of large inclined top sleeve, horizontal inclined top and straight top, the maximum external size is 2500×1560×1790mm, and the detailed mold structure is shown in Figure 2.
2.1 Forming part design
In the automobile front bumper injection mold, there are two types of parting surfaces: outer parting surface and inner parting surface. The outer parting bumper has the same parting method as the ordinary mold, the mold structure is relatively simple, but the parting clamping line can be seen, which affects the appearance. After the inner parting bumper is assembled, the parting clamp line cannot be seen, and the parting clamp line is hidden on the non-appearance surface of the plastic part. The technical difficulty and structure of the inner parting bumper are more complicated than that of the outer parting bumper, and the technical risk is higher. The mold cost and mold price will be much higher than that of the outer parting bumper, but the appearance is beautiful, and it is in the middle and high-end. It is widely used in automobiles. This mold forming part adopts an advanced and complex design scheme of internal parting, and has achieved good results, as shown in Figure 3.
In addition, this plastic part has a large number of through holes, some of which are larger in area. The venting groove and the avoiding groove are designed at the collision point, and the insertion angle is greater than 7°, which can increase the service life of the mold and prevent flash .
The front bumper injection mold molding parts and the template are integrated, and the template material can be P20 or 718.
2.2 Design of gating system
The mold casting system adopts an integral hot runner system. Its advantages include convenient assembly and disassembly, low machining accuracy requirements, no risk of glue leakage, reliable assembly accuracy, and no need for repeated disassembly and assembly, and low maintenance and repair costs.
The front bumper is an exterior part, and the surface is not allowed to have weld marks. The weld marks must be driven to the non-appearance surface or eliminated during injection molding. This is one of the key and difficult points of the mold design. Although the traditional simultaneous multi-point pouring can fill the entire cavity with melt, it is difficult to achieve the desired product quality due to the existence of weld marks. to this end
This mold adopts 8-point sequential valve hot runner gate control technology, namely SVG technology. This is another advanced technology used in this mold. It controls the opening and closing of eight hot nozzles through the drive of a cylinder. The ideal effect of no weld marks on the surface of the plastic part is achieved. The location of the hot runner gate of the front bumper injection mold is shown in Figure 2.3 Design of side core pulling mechanism
Since the front bumper adopts an internal parting surface, the parting line at the undercut of the fixed mold A plate is located under the inclined top of the movable mold side. In order to avoid the risk of mold damage during the operation, the core is pulled when the mold is opened The steps must be strictly controlled, see the mold working process for details. This mold adopts a straight top and a lower inclined top design, and a complex structure of horizontal inclined top is designed in the inclined top. In order to pull the core smoothly, there must be enough space between the inclined roof and the straight roof, and the contact surface of the inclined roof and the straight roof shall be designed with a slope of 3°～5°. The large inclined roof and the large straight roof on both sides of the injection mold of the inner parting bumper should be designed with cooling water channels. The side hole of the fixed mold of the inner parting bumper should be designed with a fixed mold elastic pin structure, as shown in the enlarged view at E in Figure 2. What I want to explain here is that the internal parting bumper injection mold is different from the general injection mold. The side core 43 of the mold is ejected during the mold opening process, and the plastic part will follow the fixed mold for a certain distance.
2.4 Design of temperature control system
The design of the temperature control system for the injection mold of the front bumper has a great impact on the molding cycle of the mold and the quality of the product. The mold temperature control system is in the form of "straight-through cooling water pipe + inclined cooling water pipe + cooling water well". See Figure 3 for details. The cooling water pipe should be arranged along the shape of the plastic part as far as possible to improve the cooling effect.
The main points of the design of the cooling water channel of this mold are as follows:
(1) The structure of the movable mold is more complicated, and the heat is more concentrated. The cooling should be focused on, but the cooling water channel must be kept at least 8mm away from the push rod, straight top and inclined top hole.
(2) The distance between the water channels is 50-60mm, and the distance between the water channels and the cavity surface is 20-25mm.
(3) The cooling water channel can be made straight holes instead of oblique holes. Oblique holes with an inclination of less than 3 degrees can be directly changed to straight holes.
(4) The length of the cooling water channel should not be too different to ensure that the mold temperature is roughly balanced.
2.5 Guiding positioning system design
This mold is a large-scale thin-walled injection mold. The design of the guiding positioning system directly affects the accuracy of the plastic part and the life of the mold. This mold adopts square guide pillars and 1 ° precise positioning guide positioning. Among them, 4 square guide pillars 80×60×700 (mm) are used on the movable mold side, and 4 square guide pillars 180× are used between the movable and fixed molds. 80×580 (mm). The location is shown in Figure 2 and Figure 3.
In terms of parting surface positioning, the mold adopts two conical surface positioning structures (also called internal mold tube positions) at both ends, and the inclination angle of the conical surface is 5°.
2.6 Design of demoulding system
Plastic parts are large thin-walled parts, and demoulding must be stable and safe. The middle position of the mold adopts straight ejector and push rod ejection, the diameter of the push rod is 12mm. Because the contact area is small, it is difficult to return, and it is easy to cause the putter to collide with the cavity surface of the fixed model, so the inner parting bumper is designed to be straight as possible, and putters are used less.
Due to the large number of push parts, the demolding force and the pusher resetting force are relatively large, so the demolding system uses 2 hydraulic cylinders as the power source. The position of the oil cylinder is shown in Figure 5.
Due to the uneven surface of the moving model core, the fixed ends of all push rods and push tubes must be designed with anti-rotation structures.
3. Mold work process
Because this bumper injection mold uses internal parting technology, the parting line of the undercut position of the A plate is located under the inclined top of the movable mold side. In order to avoid the risk of damage to the mold during the operation, the mold’s working process is very strict. Let's talk about the steps and precautions starting from the clamping.
①The fixed mold A board must be ensured that the push rod plate is in the 50mm state before the mold is closed, so as to ensure that the undercut of the A board does not touch the horizontal small inclined roof protruding from the large inclined roof, and to ensure that the A board can be smooth The clamping action is completed by pressing the reset lever. See Figure 6(a).
②The fixed mold A plate returns the push rod plate and the inclined top pressure, as shown in Figure 6(b).
③The A plate and the push rod plate must be opened 60mm synchronously to ensure that the plastic parts and the horizontal small inclined top are all separated from the inverted surface of the A plate. Before opening the mold, pressure must be applied to the ejection cylinder in advance to ensure that the entire ejection system and the A plate can be opened simultaneously, as shown in Figure 6(c).
④The fixed mold A plate continues to open the mold, and the movable mold keeps the ejection state of 60mm unchanged to achieve the effect of separating the A plate from the straight top, as shown in Figure 6(d).
⑤After the fixed mold is opened to the required space, the movable mold continues to be ejected to a state of 164mm. At this time, the horizontal small inclined top guide rod reaches the inflection point of the changing angle of the guide rail, and the inverted surface of the plastic part is separated from the mold. If the plastic part sticks to a small inclined top at this time, directly pull the plastic part out of the mold by hand, otherwise, continue to push out to the final position of 210mm, as shown in Figure 6(e).
⑥If the product is slightly sticky to the small inclined top, the ejection is completed when the product reaches 164mm. Remove the product and directly cycle to step ① to prevent the product from being pulled back by the horizontal small inclined top, resulting in the inability to remove the product, as shown in Figure 6 ( f).
⑦The non-stick horizontal small inclined top of the plastic part continues to be ejected to 210mm. After the ejection is completed, remove the plastic part and cycle to step ①, as shown in Figure 6(g).
ABIS MOLD TECHNOLOGY CO.,LTD
Daisy Wang (Sales Engineering)
M: +86-150 1652 6799
E: daisy@abismold.com
A: Building B#,YingKeli Industrial Part, LongDong Community, LongGang District, Shenzhen, China 518116
WhatsApp: +86 136 8261 9739
Skype: daisymold@outlook.com