Product diagram of cushion sealing cover is shown in Figure 1. Maximum dimension is ø42.40 mm * 76.70 mm, average thickness of plastic part is 1.70 mm, and weight of plastic part is 8.2 grams. Material of plastic parts is PP, and shrinkage rate is 1.015. Technical requirements of plastic parts are that there should be no defects such as peaks, underfilled injection molding, flow lines, pores, warpage deformation, silver streaks, cold materials, jet lines, etc.

 

Figure 1 Product Picture of Cushion Sealing Cap
It can be seen from Figure 1 that appearance of plastic part is a bottle cap-shaped circle, with a number of evenly distributed raised ribs on outer circle. There is a column in the center of plastic part, there is a small step inside column near top, and there are 4 special-shaped through holes on the step. Shape of plastic part has an inverted button, and it is necessary to design Hough slider to be out of mold. There is a circle of double-threaded threads inside plastic part, and there is a circle of inverted buckles on the top surface of plastic part to form a buffer ring. After being assembled with container, it plays a role of buffering and sealing.

 

Cushioning sealing caps belong to category of daily chemical packaging container caps. Production batches of products are huge, and it is necessary to design a multi-cavity mold to meet production capacity requirements. Shape of mold in plastic part needs to be designed with a Hough slider. Slider mainly contains a hollow column in the middle. Parting line is at arc of large-diameter shoulder of plastic part, so it belongs to front mold slider (here slider cannot be designed to ribs on outer edge of plastic part, otherwise it will affect appearance of plastic part, which is a bad design solution). See figure 2 of mold design. For double-end thread inside plastic part, based on empirical judgment, this thread needs to be demolded forcedly. Thread suitable for forced demolding generally has a small number of turns, a larger pitch, and a triangular tooth shape, which consists of an arc at the top and root of triangle. A complete buffer ring at the top of thread also constitutes a mold undercut, which requires forced demolding. Two forced demolding of back mold requires mold plate to be split twice. Because front mold is designed with a semi-hot runner gating system and Huff slider, it also requires multiple parting of mold plate in order to get out of gating system aggregate and slider parting. Therefore, multiple sequential parting of front and rear templates constitutes difficulty of mold design.
Mold design cavity is layout in 24 cavities, divided into 3 rows and arranged in a straight line, with 8 holes in each row. Mold base is a non-standard mold base 7385. On small step near top of center column of plastic part, point gate is designed at the center of 4 special-shaped through holes. Due to large number of mold cavities and long runners, molten plastic is easy to cool in flow, which affects filling. For this reason, mold is designed with a hot runner system, molten plastic is injected into runner of manifold, then filled through nozzle runner. At the same time, a heat shield is designed on mold panel to prevent heat loss. This hot runner combined with cold runner mold design method is a semi-hot runner mold. Hot runner system includes a splitter plate and 8 hot nozzles. Each hot nozzle feeds 3 mold cavities. Runner is approximately Y-shaped, which is roughly close to a balanced design.

 

Mold base assembly diagram is shown in Figure 4. Panel, hot nozzle mounting plate 1 and hot nozzle mounting plate 2 are connected together to provide installation space for hot runner system. A plate and A pallet 2 are also assembled together with screws and fixed with positioning pins. B plate and the B pallet are also connected together with screws. Core fixing plate and bottom plate are also fixed together. For complex molds with multiple sub-types for bottle caps, there are more template layers. To analyze mold structure, you must first analyze which mold plates are connected together (where are connecting screws?), which mold plates are operated separately, what is sequence of separate actions, what is positioning and guiding system (guide pin and guide sleeve) , where is control mechanism for sequence classification of each mold plate, how is deduction machine designed, and which mold plate is it designed on? Where are limit screws for separation of mold plate and what is stroke?
This set of molds is a multi-cavity mold. Installation holes of cavity parts of mold base need to maintain high accuracy. Mold base is made of mold steel 738 as a whole, and center distance tolerance between two adjacent cavities is ±0.02mm. Cavity parts need heat treatment to make a hard mold.
Due to complex structure of mold, forced demolding of mold requires multiple mold opening actions to achieve. Mold opening action is divided into 6 mold opening operations. The first mold opening PL1-130 is to open 130 between nozzle plate and A pallet 1, take out nozzle material. The second mold opening is that nozzle plate is separated from nozzle mounting plate 2 by PL2-10, distance is 10, nozzle plate pushes nozzle material away from nozzle mounting plate 2. The third mold opening is A pallet 1 and A pallet 2 minutes 40, PL3-40, this parting is driven by an oil cylinder to complete core pulling of front mold Hough slider. The fourth parting is separation of A plate and the push plate, which belongs to main parting surface opening, front and rear molds are parted from here, PL4-150; the fifth parting is separation between B pallet and core fixing plate, PL5 -50, where parting is driven by cylinder. Push plate and movable inner mold insert 33 jointly push plastic part away from forming thimble 32 in the center of plastic part. The sixth time mold was opened, plastic part was completely forced off from back mold in two places.

 

3D water transportation diagram of each template of mold is shown in Figure 3.

 

 

 

 

 

Figure 2 Mould diagram of cushion sealing cap

 

Figure 3 3D diagram of water transport in front and rear mode

 

Figure 4 Mold base assembly diagram