1. Product analysis
This case is a bracket on a sensor of a car. The precision requirements are very high, the material is POM, the product is very small, the longest dimension is 38mm, metal inserts (copper sheets) must be placed during injection molding, and the deformation is required to be very small, see Figure 1.
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figure 1
The non-concentricity of the upper and lower holes of this product is less than 0.02mm. Since POM (polyoxymethylene) products are prone to deformation, in order to minimize the internal stress of the product, the location of the glue inlet point is selected. All aspects must be considered when designing the mold, and the upper and lower holes must be shaped after the mold is released, as shown in Figure 2.
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figure 2
The gap between the upper and lower holes is reversed, and the core must be pulled in two directions before the mold can be released. This brings certain difficulties to the design of the slider, as shown in Figure 3.
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image 3
The core must also be pulled in this direction, see Figure 4.
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Figure 4
During injection molding, an insert must be placed into the movable mold. The insert is a very elastic copper sheet, as shown in Figure 5.
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Figure 5
In order to prevent the copper sheet from being deflected by the plastic during injection molding, two small holes are provided on the copper sheet, and a corresponding core is set in the mold to position it, as shown in Figure 6.
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Figure 6
2. Gate design
After analysis, in order to reduce the stress on the product and minimize deformation, the best location for the glue entry point is here, see Figure 7.
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Figure 7
I adopted the form of point gate, see Figure 8.
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Figure 8
Mold flow analysis is provided by Moldex 3D Company, see Figure 9.
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Figure 9
Due to the tight space, the gate I designed interfered with the fixed mold pins, which was very difficult to deal with. Therefore, I canceled the fixed mold pins and used the original core for the perforations of the fixed mold. , see Figure 10.
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Figure 10
This can leave a reasonable position for the gate tie rod, see Figure 11.
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Figure 11
The overall structure of the mold adopts a simplified small nozzle structure and adopts a first reset device, see Figure 12.
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Figure 12
3. Mold splitting
The lower mold core and three sliders are arranged like this, see Figure 13.
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Figure 13
It looks like this when you drop the mold core and look at it from the other side, see Figure 14.
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Figure 14
The front mold core is designed like this, see Figure 15.
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Figure 15
4. Slider design
This set of molds does not look complicated, but the design of the slider is still a bit difficult, and all aspects must be taken into consideration. Let's look at slider 1 first, see Figure 16.
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Figure 16
The relationship between slider 1 and slider 2 is shown in Figure 17.
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Figure 17
Since slider 1 and slider 2 and their common boundary are the sealing surfaces, they must be treated as a unified plane and have a draft angle to form a plug-in fit with the fixed mold. Moreover, the mating surface must be very precise, so that the bonding line on the product surface is as small as possible, see Figure 18.
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Figure 18
The mating surfaces of all sliders inserted into the mold core must be sloped in the direction of movement to prevent the mating surfaces between the slider and the mold core from being roughened due to friction, see Figure 19.
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Figure 19
The design of slider 3 is shown in Figure 20.
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Figure 20
The end face of the slider 3 collides with the movable mold core to form a sealing position. The mating surface extending into the mold core has a slope of 3° in the direction of movement to ensure that the slider will not be affected by friction during long-term operation. And pulling hair.
5. Design of fixed mold
The power source of the slider is three inclined guide pillars that push the slider apart through the mold opening force of the injection molding machine. The inclined guide pillars are fixed on the fixed template using the inclined guide pillar fixing blocks. The fixed mold side is equipped with a plunger with a reset-first structure, as shown in Figure 21.
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Figure 21
6. Arrangement of moving mold
This set of molds has a very compact structure and uses a standard 1515 simplified small nozzle mold base, as shown in Figure 22.
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Figure 22
This is what the mold looks like after opening and before ejection, see Figure 23.
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Figure 23
The force that pulls off the gate relies on the three nylon rivets in the picture above. In order to make the reset force more balanced, the position of the reset rod is also carefully arranged.
7. Design of ejection mechanism
In order to reduce the internal stress of the product and minimize the deformation, I used more ejector pins to make the ejection force of each part of the product relatively balanced. A total of 10 ejector pins were used, which is rare for such a small product, see Figure 24.
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Figure 24
Since there are five ejector pins that interfere with the slider, a reset-first structure must be set up, as shown in Figure 25.
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Figure 25
8. Design of reset mechanism first
Now let me introduce one of the most common pre-reset mechanisms, see Figure 26.
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Figure 26
The first reset mechanism is also called the pre-reset mechanism. It consists of four major parts: insertion rod, swing rod, roller and stop. When opening the mold, the inclined guide pillars push all the sliders apart, see Figure 27.
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Figure 27
Since the insertion rod has been pulled out, the swing rod has room to rotate. When the top column of the injection molding machine pushes the push plate, due to the action of the roller, the swing rod rotates along the pin axis (here it is rotated 15 degrees), see Figure 28.
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Figure 28
The first reset mechanism is located on both sides of the mold and is completely symmetrical, see Figure 29.
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Figure 29
9. Design of cooling water path
Since the product is relatively small, and the insert (copper sheet) needs to be placed in the injection molding gap, the injection molding cycle is relatively long, so the requirements for the cooling water path of this set of molds are not high. I adopted the simplest design. Since the mold core is relatively small , the water goes directly from the template. The fixed mold has two straight waterways, see Figure 30.
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Figure 30
The same is true for the dynamic mold, see Figure 31.
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Figure 31
The design key points of this set of molds are the arrangement of the boundaries of slider 1 and slider 2 and the selection of the location of the glue entry point.
