Design of the injection mold for the hottest draw

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Design of injection mold for pull hook plastic parts

Abstract: "pull hook" or "hook" is a kind of commonly used structural modified polyphenylene oxide in plastic products. It is also used in TV parts, connectors of telex terminal equipment and other structures. Its function is to use the elastic deformation of plastic materials to complete the connection with other parts. Such structures often use the inclined jacking mechanism in the molding mold to complete the molding and disengagement of its side recess, In view of the problems that may be encountered in the mold design, manufacturing and production of the tilting mechanism, an example is analyzed, hoping to provide a reference for similar molds

key words: hook plastic parts inclined top injection mold

1 product structure

product shape and structure such as spring tension and compression testing machine should pay attention to the jaw or relatively sliding surface of the fixture should be clean, as shown in Figure 1, and the material is POM

the product is equipped with 4 hooks, which are distributed on the left and right sides of the trunk. The horizontal spacing is 20mm, the longitudinal spacing is 5mm, the thickness of the hook is 2mm, the height is 11mm, and there is a 0.5mm on its head × O. 5mm anti slip reinforcement

2 key points of conventional design of the mold

according to the structural characteristics of the product, the forming of the hook adopts the inclined top block mechanism, which is ejected symmetrically between the four hooks. According to the matching and batch requirements, the mold is designed into 8 pieces. The inclined top block is used to eject, and the glue is injected through the large gate at the tail. The cavity and core materials are s136h. The mold base adopts the standard CI mold base. The ejection stroke of the inclined top block is 25mm, and its lateral displacement is 2.4mm (see Figure 2)

3 problems after mold test

the products are biased in the ejection process, and there is inclined top block on the side, which makes it difficult to take parts

4 problem analysis

in the ejection process, because the cavities at the hook are all located on the inclined top block, and the anti deformation ability of the material in the cantilever state at the hook is not enough to resist the cavity wrapping force, causing the hook to deform (it cannot be instantly separated from the cavity, and the existence of anti slip reinforcement aggravates its severity)

in addition, when the ejection reaches the side arm and disengages from the mold core (as shown in Figure 3), the product has no other mechanism support except that the hook is still on the inclined top block, and the force of the product by the inclined top block is not balanced in practice, so the product is very easy to move to one side, and the original design of 2.4mm horizontal displacement space is not enough to compensate for the deformation of the hook and the movement of the product, resulting in the hook unable to disengage from the inclined top block

5 solution this 1 cut started from April 24, 1967, 50 years ago

reduce the height of the hook anti-skid rib to 1mm, and the forming of the hook is completed by the core insert 3 (see Figure 4), while the inclined ejector block 5 only plays the role of ejecting the hook. During the ejecting process (especially the first 11mm), the hook will be guided by the forming position added to the core, so as to ensure that the hook is slightly deformed until the hook is separated from the core 4, At this time, the anti-skid bar of the hook just disengages from the inclined top block 5 (because the height has been reduced to 1mm), so that in the continuous ejection process, the product will only bear the upward jacking force and the friction of lateral movement relative to the inclined top block. In order not to cause the hook to be clamped into the inclined roof block again due to the uneven force on the left and right of the product relative to the inclined roof block, flat ejector pins are added at the tail of the product to support both sides as the positioning after ejection. When the ejection reaches 20mm, the inclined roof block 5 has completely got rid of the hook (0. For example, the implementation plan for methane use in landfills (LMOP) 9mm). At this time, the flat ejector pin limit sleeve 7 stops, and the inclined roof block 5 continues to eject, The product is separated from the flat ejector pin 6 to complete the ejection of the product, so that the parts can be easily taken out

6 conclusion

for such products ejected by the inclined ejector block, attention should be paid to the design of its ejection mechanism and the positioning of the product:

(1) the product structure should be optimized

(2) whether the product will swing during ejection

(3) whether the product, especially the hook, will deform with the ejection of the tilting block, or cannot be separated from the tilting block

(4) strictly control the ejection stroke of the inclined ejector block, and detect whether there are interference and other problems after ejection

(5) considering the stability of the tilting block mechanism, to avoid blocking due to poor resetting of the tilting block in the actual production process, an auxiliary first resetting mechanism is designed to avoid damaging the cavity

(6) nitriding treatment should be considered for sliding parts such as inclined top block to increase their wear resistance. (end)

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