Product demoulding mode refer to which method is used to eject product after injection molding is completed. Injection mold demoulding methods include following.
(1) Ejector pin, tube, straight and oblique ejection.
(2) Push-out mode.
(3) Pushing block ejection method.
(4) Ejection method of floating slider.
(5) Air-blown ejection method (also known as wind support ejection).
(6) Elevated teeth ejection mode of thread mold.
(7) Pull out by hand (usually used on ultra-soft materials).
Among them, thimble, tube, straight top and oblique ejection are most commonly used. This example is used to complete this ejection. After demoulding method is determined, following issues need to be considered:
① Judge sticking force of front mold.
② Judge sticking force of back mold.
③ Understand assembly requirements of related assemblies.
④ Understanding and checking of thimble arrangement space.
⑤ Arrangement of size of thimble, size of thimble requires mold structure.
⑥ Influence of ejector pin position on cooling water, fastening screw position and inserts of various sizes.
⑦ Thimble, thimble hole processing method.
⑧If judgment is wrong and ejection is not smooth, second and third solutions are prepared, space is reserved, and so on.
Determination of adhesive force is based on the shape of plastic mold. Order of adhesive force is as follows:

(1) Square internal holes, circular internal holes, special-shaped internal holes, tooth-shaped internal holes, etc. As shown in the figure below, this is part with the largest mold force. Products with these shapes often have these parts in back mold when designing. Injection position of these shapes, the larger shape, the greater mold force, the higher height, the larger mold force, the rougher surface, the larger mold force, the smaller inclination of mold, the larger mold force, the greater number of mold force.

 

Although size and surface area of M part is smaller than that of N part in above figure, adhesive force is larger than that of N part because plastic will be tightly wrapped on square hole core due to thermal expansion and contraction when cooling, as shown in figure below:

 

From picture above, we can see that plastic product starts to cool after injection molding is full, and there will be a phenomenon of shrinkage during cooling. It is because of shrinkage of plastic part that exterior of product will leave front mold cavity, see first surface in figure above. It is also because of shrinkage of plastic parts that product will be tightly wrapped on back mold core, that is, square inner hole core, see second surface in figure above.
(2) Large-sized shape, which is second largest mold force, see N-plane part in figure above.
(3) Small-sized square holes, square bones, round holes, round bones, round columns, special-shaped holes, special-shaped bones, deep bones (deep reinforcing ribs), which is third largest mold force. When there are a large number of them, their total sticking force will exceed sticking force of large-shaped inner hole. In addition, these shapes of rubber bits are widely used, can be used as positioning, fixing, locking, and functional positions. For example, screw columns, key guide rubber bones, stiffeners, switch positioning square bones, and crisscross meshes of force parts, etc., this part of mold force is the most difficult to judge mold force of all mold forces, but also the most difficult factor in designing size of ejector pin.
(4) Inverse buckle position, functional buckle position, core pulling hole position, which is the fourth largest "mold sticking force". Strictly speaking, this part does not belong to category of mold sticking force, but at the moment when mold is opened, it actually plays role of retaining mold. Magnitude of this part of sticking force depends on size and strength of buckle. When buckle is large, deep and thick enough, its mold retention force is the largest, but it only has a large mold retention force when mold is opened. When mold is opened or ejected, this part of "sticking force" will disappear, because these parts are usually designed as slider cores or inclined top core when mold is designed. Once mold opening or ejection is completed, "sliding force" disappears automatically because slider or inclined top has been evacuated.
(5) Small glue position, small and shallow bone position (reinforcing position), small and low column position, which are fifth largest sticking force. This part of mold force is small, usually not considered as main object, just pay attention when designing ejector pin. This is just an explanation of relationship between shape of plastic product and mold force. In fact, in addition to shape and size of product, factors that affect mold force have two large influencing factors, namely: processing equipment, methods, and product surface roughness. These two factors are closely related, because plastic products tend to be thinner. If surface roughness is to be improved, it must be polished. Such a small space is difficult to achieve. In many cases, there is a problem that product cannot be polished after processing to improve its surface smoothness, that is, it cannot improve its sticking force. When mold is tested, mold structure is changed because it cannot be ejected or whitened.

(1) Size of commonly used ejector pin is φ3 ～ φ8mm. In general, there is no special structure, and most of them are designed according to this. If product is large and mold is very large, when ejector pin is very long, choose a larger one. Ejector pin commonly used in large molds is φ6 ～ φ16mm. Ejector pin smaller than φ2.5mm, its ejection force is small, easy to break, and difficult to process, it should be used with caution.
(2) If space permits, design a larger ejector rather than select a smaller ejector.
(3) When judging sticking force is not sure, select as many thimbles as possible.
(4) When designing thimble position, to balance ejection force, one or two thimbles can be added.
(5) Ejector position should be arranged in a hidden place, a place where there is no requirement, not easy to eject, and with high ejection force.
(6) Ejector pin has function of exhausting, so it should be exhausted as far as possible without affecting ejection.
(7) Try not to line up thimble where it may collide with slider.
(8) Do not place thimble on setting line, and do not place it too close to setting line.
(9) Don't design a flat thimble, tube that can use a round thimble. According to above thinking, use AutoCAD to open 2D drawing of this example on a computer, and use a mouse to arrange thimbles of various sizes. After adjusting position, consider comparison between ejection force and mold force to determine size of ejector pin and ejection pin design.

In mold processing, ejector pin and cooling water conflicts the most. Without cooling water or ejector pin, mold will not be able to be injection molded. Sometimes thimble needs to "make way" for cooling water, and sometimes cooling water is "make way" for thimble. Design principle is to ensure cooling performance of mold and product can be ejected smoothly, both of which are indispensable.

There are many methods of thimble hole processing, following four are commonly used. (1) Directly drilled with a drill, usually used on less demanding molds. (2) Use a reamer to drill out after drilling with a drill. Usually, it is used on molds with medium or upper requirements. (3) Use a drill bit to drill lead hole and then cut it with fast-moving wire. It is usually used on a medium or medium-upper mold. (4) Use a drill bit to drill lead hole and then cut it with a slow wire. It is usually used on high-demand molds.

When ejector pin design is completed, second or third solution is often thought out in advance, in case problems occur in the future test mode, alternatives can be found in time.

 (1) Maximum adhesive force of this product picture is on four faces "A-side", "B-side", "C-side", and "D-side" as shown in Figure 11.17. Do not consider ejection force of other parts at first, only consider pushing out these four faces. Figure 11.18 shows a partial ejection ranking map. Diameter of thimble is φ3.0mm and φ2.0mm.

 

 

① φ3.0mm is arranged in four positions of "1", "2", "3", and "4", which are respectively distributed at four outer corners, because adhesive force on corners is the largest.
② φ2.0mm is arranged in four positions of "5", "6", "7" and "8", which are respectively distributed on four corners. It is definitely not enough to rely on 4 φ3.0mm thimbles to eject large frame. Therefore, 4 thimbles are added to 4 inner corners, space on inner side is limited, large thimble cannot be arranged, so φ2.0mm thimble must be arranged. According to this ejection force, ejection of four corners of large frame and two short sides should be no problem, but middle section of long side is questionable.
③ Put two thimbles, "9" and "10" in the middle of two long sides. Due to large space, "9" thimble can be arranged with a φ3.0mm thimble, "10" thimble can only be arranged with a φ2.0mm pre-needle because of small space.
(2) "E", "F", "G", and "H" planes shown in partial map of thimble in Figure 11.19 and perspective view in Figure 11.20. Although these four planes are small, they are very high and their adhension is not small. Inclination of these four faces is above 2 °, which can greatly reduce sticking force. Figure 11.19 shows partial arrangement of thimbles. Firstly, φ2.0mm thimbles are arranged on four corners. Positions of four thimbles are shown in positions "11", "12", "13", and "14" on Figure 11.19.

 

(3) Ejection of "A position" in Figure 11.21. Ejector pins "13" and "14" in Fig. 11.19 have an effect on ejection of "A position". However, there are adhesive forces on "H" plane and two sides near "H" plane. A thimble is designed on back and bottom of "A position" to solve ejection problem of "A position". Due to limited space, up to two ejector pins can be arranged, as shown in Figure 11.21, the largest "1" can only be φ2.0mm, "2" can only be φ1. 5mm. Because glue position of “A” is small, surface area is not large, depth of ribs is not deep, these two thimbles can not only eject “A” surface, but also support two thimbles “13” and "14" on Figure 11.19.

 

(4) Ejection of "B" and "C" positions in Figure 11.21. These two parts are almost same. "B" position is used to explain working process. There is a through hole on "B" position. If adhesive force of through-hole is on the side of back mold, it will undoubtedly be a great resistance to ejection of "B" position on back mold. It can be seen from front parting that collision surface of all small through holes is on bottom surface, die sticking force is on the side of front mold. Therefore, when mold is opened, die holding force of small through holes is already disappear. In this way, ejection resistance of ejector pin is much smaller, but there is still sticking force. Thimble "14" originally hit on Figure 11.17 is near "B" position. When it is ejected, it can provide an ejection force at "B" position. But even if it has enough force to push out "B" position, force it pushes out is not allowed to bypass small through hole to transfer force to "X point", because this will deform product. In other words, a thimble must be designed near "point X", as shown in "3" position shown in Figure 11.21. Because space is small, maximum can only be φ2.0mm. In this way, ejection force of "B" position is sufficient, and "C" position can be solved by same method.
(5) Ejection of "D" and "E" positions on Figure 11.21. From analysis of parting surface, it can be seen that glue positions of "D" position and "E" position are both in front mold, and there is almost no glue position left on rear mold. In other words, if a thimble is designed at these two positions, thimble at this position is hardly subject to resistance when ejected, that is, no thimble is designed at "D" position and "E" position.
(6) Ejection of "F" bit on Figure 11.21. Shape of ”F” position is very representative. It is a fully symmetrical shape from top to bottom and left to right. Of course, its adhesive force is also fully symmetrical. Designed ejector pin should also be fully symmetrical. Only in this way can force balance be guaranteed during ejection. Before arranging thimble position, understand function of this part of position. From perspective of assembly relationship, "F" position has only its height to play a positioning function. Its positioning position is at the highest surface of middle rib position. All other "F" positions are used only for reinforcing ribs, and there is no assembly relationship. During processing, draft angle can be made larger to reduce sticking force. From Figure 11.21, it can be seen that there are 8 semicircular ring bones and a straight bone in the middle of "F" position. These two parts can be drafted at a large slope to reduce sticking force. See Figure 11.21 for ejector pin arrangement. One ejector pin is arranged every other row, with 4 punches on each side, a total of 8 ejector pins. Maximum allowable ejection pin is φ2.0mm. From a strength point of view, every two thimbles are responsible for overcoming combined adhesive force of connecting bones between two semicircular ring bones and two ring bones. Because height of semicircular ring bone and straight bone is not high, draft angle can be increased, at this time, ejection force of 2 thimbles will be greater than comprehensive mold force, that is, ejection forces of these 8 fully symmetrical ejector pins can not only eject "F" position, but also help ejector pins of "11", "12", "13", and "14" on Figure 11.17.
(7) Ejection problems of "G" and "H" positions on Figure 11.21 are similar to ejection problems of "B" position. Design of ejector pins is similar, but orientation is slightly different.
(8) Ejection of "J" position on Figure 11.21, "J" position is small, depth is not deep but not shallow, and draft angle is about 1°. Ribs of this "U" -shaped structure must have a balanced ejection force during ejection, otherwise ribs may have a "snap" mode, that is, some or all of ribs will be broken and left on back mold when ejected, will not come out with large glue position. From Figure 11.21, you can see that there are three thimbles designed around "J" position. They are "4", "8", and "11", of which power of "4" and "8" is sufficient. "11" can only push out "E" face (see Figure 11.17). At this time, you can consider adding one to opposite side of "4" thimble. Because of space, it can only be arranged on the top surface of bone. There is no other requirement for ribs except for strengthening effect, so it is allowed to design a thimble on its top surface, see "12" on Figure 11.21, but maximum can only be a φ2.0mm thimble. In this way, ejection problem of "J" position is solved.
(9) Ejection of the "K" bit. “K” position is connected to inner side of short side of large position, and “K” position is small. As long as short side of large position can be ejected, it can also be taken out along with it, it is usually not solved independently as main object.
(10) Ejection of "M" bit on Figure 11.21. "M" position is a straight tendon, bone is shallow, its adhesive force is not too large, and there are many ejectors around "M" position, auxiliary ejection is very powerful. Even if you do not add an ejector pin to "M" position, it is possible to eject it. In addition, when ejecting pin in "J" position, a φ2mm ejector pin has already been placed on this bone position, but considering that "K" position still lacks a little ejection force. Therefore, in order to ensure ejection problem in this area, it is better to add an ejector pin. Ejector pin at "13" position on Figure 11.21 is also arranged on the top surface of straight bone, and φ2mm can be used.
(11) Ejection of "N" position on Figure 11.21. “N” position is a deeper small square counterbore, four sides of square counterbore have a large slope (greater than 2 °), so adhesive force displayed at “N” position is greatly weakened. There are already two ejector pins of φ3.0mm on two sides of "N" position. When ejecting product, these two ejectors have a great force for ejection of "N" position; but considering that original ejection tasks of these two ejectors are not light, for sake of safety, they should be added with more ejection forces, add ejector pins "14" and "15", take φ3.0mm. "14" thimble has formed a balanced ejection pattern for "N" position with "9" top in Figure 11.17, but considering that "N" position is deeper, "15" thimble is added. Through design of these three φ3.0mm ejector pins, ejection problem of "N" position is ensured.
(12) Ejection of "P" bit on Figure 11.21. "P" position is two small positions, which are very shallow and mold force is not too large. In addition, a φ3.0mm thimble has been designed at the center of "P" position. In addition, ejection force of “N” position is left, which can help ejection of “P” position. If it cannot be pushed out, because two sides of "P" position have no assembly requirements, you can increase draft to reduce sticking force; or arrange a thimble in the middle of "P" position as a preliminary solution. "J", "K", and "N" positions are symmetrical, corresponding positions on this side can be handled by corresponding thimble design method. Now first draw "design of thimble" solution we have already thought of above, and draw it on 2D plan of product 1: 1, as shown in Figure 11.22.

 

Design of thimble on Figure 11.22 is a preliminary confirmation scheme. If there is a conflict with other structures, fine-tuning is performed.