Seven ejection mechanisms
1. Push block ejection mechanism
For flat plastic parts with flanges, if ejection with a push plate will adhere to the mold, a push block ejection mechanism should be used. Because the push block is an integral part of the cavity, it should have higher hardness and lower surface roughness.
There are two types of reset: one relies on plastic pressure, and the other uses a reset rod.
two. Utilize molded parts ejection mechanism
Due to the structural shape and the plastic used, some plastic parts are not suitable to use ejection mechanisms such as ejector pins, ejector tubes, push plates, and push blocks. In this case, molding inserts or concave molds can be used to bring out the plastic parts. The push block mentioned earlier belongs to the forming insert ejection mechanism.
three. Multi-component comprehensive ejection mechanism
It refers to the combination of the several ejection mechanisms mentioned above to achieve the purpose of ejection. Commonly used ones include ejector rod plus top plate, ejector tube plus top plate
Four. Air pressure escape mechanism
The use of air pressure demoulding requires the installation of compressed air passages and valves. The processing is relatively simple and is suitable for demoulding light and thin soft plastics.
five. Inclined slider escape mechanism
When the plastic part has inner and outer holes or undercuts that are different from the mold opening direction, which hinders the direct demoulding of the plastic part, an inclined slider demoulding mechanism must be used. Parts with side holes or undercuts are made into movable cores. When the plastic part is demoulded, the movable core is first pulled out, and then the plastic part is ejected from the mold. The mechanism that completes the extraction and reset of the movable core is called a core-pulling mechanism.
6. Bending pin parting and core pulling mechanism
Its principle is the same as that of the inclined guide post core-pulling mechanism, but the difference is that the inclined guide post is replaced by a bent pin with a rectangular cross-section. Its advantage is that the bevel angle can be made larger.
7. Inclined guide groove parting and core pulling mechanism
<1>﹑Design method of sloping roof and determination of various dimensions:
1. Determine the core pulling distance based on the shape of the product: S drawing = S undercut + (2~3) mm.
2. According to the ejection stroke, calculate the angle α of the inclined roof (tgα = S pumping / S lifting). The α value should not be too large. If it is too large, the bending force on the inclined roof will be large, which will easily lead to breakage. Generally, it is 3≦ α≦8˚.
3. Confirm that the position of the reference point P of the inclined roof in the mold is an integer.
4. Confirm the thickness L1 of the sloped roof. L1 is determined according to the actual situation, but this value should not be too small, otherwise the strength of the sloped roof cannot be guaranteed.
5. The breaking distance H between the inclined top and the mold core is generally 5~10mm (depending on the thickness of the mold core).
<2> Issues to note during the design process:
1. The inclined roof cannot damage other parts of the product when ejecting the product.
2. The hole in the body plate of the inclined roof should be able to fully accommodate the inclined roof.
3. Determine the size and direction of the sliding groove of the inclined top seat on the upper ejection plate. To make the inclined roof work smoothly, that is, to ensure smooth movement of the inclined roof on the upper ejection plate and sufficient space for movement, so we It is necessary to make sure that the space in the direction of movement of the inclined top seat is large, and ensure that L2>S is drawn.
<3>﹑Parting line design
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1. Basic mold splitting (Figure 1 and Figure 2)
2.R corner processing (Figure 3)
3. Interference 1: Insufficient travel space (as shown in Figure 4)
Solution: (1) Move or cut the finished product; (Customer recommended) as shown in Figure 5
(2) Reduce the thickness of the sloped roof; (to ensure strength)
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(3) Change the direction of core pulling; (lengthen the stroke) as shown in Figure 6
4. Interference 2: Along the direction of core pulling, the finished product has a downward arc, and the inclined top cannot retreat.
Solution: (1) Reduce glue in the finished product (recommended for customers) as shown in Figure 7
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(2) Make a slope b at the bottom of the inclined roof base to delay the ejection of the inclined roof, as shown in Figure 8
Requirements:﹕ｽb≧ｽa˚ ｽc≧ｽb˚
5. The demoulding angle is ≧2. Due to the small core pulling force of the inclined top, demoulding is difficult.
<4>﹑The inclined roof is matched with the male mold core
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1. Basic matching (as shown in Figure 9), the male mold core line is cut with oblique holes.
2. Add guidance (Figure 10).
When the inclined top is wide or the slope of the mold core (guide) is too short, the inclined top will tilt toward the finished product during ejection, shortening the design stroke and making demoulding difficult. Guides should be added, in the form of:
a. Add a T-shaped hook on one side (single);
b. Add a hook or dovetail groove on the back;
3. Mold core insert (Figure 11)
When the male mold core is too thick (such as >150mm), the wire cutting accuracy (line bending) will be reduced, the processing time will be long, and the threading hole will be difficult to drill. Inserts should be considered.
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<5>﹑Male model steals holes
Key points: a. First drill round holes, then square holes, then special-shaped holes;
b.1KP stealing hole size and location are checked by double-section method
(As shown in Figure 12);
c. Stealing holes must be drawn on the assembly plane for inspection
Does it interfere with sealing rings, water pipes, thimbles, screws, etc.?
d. The location and size of the stolen holes will be rounded first.
<6>﹑Connection of inclined roof and ejection plate
Connection 1: The inclined roof and the inclined roof base are connected with a T-shaped hook (Figure 13).
If the thickness of the inclined roof is too small, use a single-sided hook; a wear-resistant plate needs to be added to the bottom of the male mold; adjustment is difficult, so you can
Reserve 1~2mm at the bottom of the top base for adjustment during assembly.
Connection 2: The inclined roof dome is connected to the inclined roof base, and the rest is the same as before (Figure 14).
Connection 3: The inclined roof is lengthened and the inclined roof is shortened (to enhance the stiffness). The male mold does not need to add a wear-resistant plate (as shown in Figure 15).
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Connection 4: Use a round pin with a hook as the inclined top seat (Figure 16).
