Printer ink cartridge holder product is shown in Figure 1. Maximum dimensions of product are 92.44 mm * 96.00 mm * 70.82 mm; average thickness of plastic part is 2.00 mm, material of plastic part is ABS, shrinkage rate is 1.005, and weight of plastic part is 31.25 grams. Technical requirements for plastic parts are that there should be no defects such as peaking, underfilling injection molding, flow lines, pores, warping deformation, silver streaks, cold material, and jetting lines, and meet ROSH environmental protection requirements.

 

Figure 1 Product picture of printer ink cartridge holder
Printer cartridge holder is a cartridge holder for a famous Japanese brand printer. There are at least two types of ink cartridges that need to be installed inside a color inkjet printer. One is black and the other is colored. Colors contain three colors, usually red, yellow and blue. Three primary colors can be used in different proportions to bring out various other colors and print colorful documents. Ink cartridge is a high-tech product in printer, and its application includes complex electrochemical principles. Installation accuracy of ink cartridge holder is high, ensuring that four ink cartridges are in ideal design position. Only in this way can the normal operation of color printer be guaranteed. 
It can be seen from Figure 1 that structure of plastic part is very complicated, design of slider contains many details and techniques, which are difficult to describe completely and accurately in words. In the face of such a complex plastic part, it is first necessary to analyze structural manufacturability of plastic part, and secondly to analyze plastic part using three elements of mold design in order to determine a reasonable mold structure.
Cavity design of mold is 4 cavities, because two sliders of plastic part are opposite to each other. Therefore, cavity arrangement is 4 cavities, arranged in a straight line, and two sliders are arranged on both sides of mold core. Structure of slider is shown in Figure 7. Slider on the right is made of a large insert, which is a typical method of inserting a large insert, and it is convenient to arrange a cooling water transport apron between slider insert and slider seat.
Arranging 4 cavities in a straight line makes mold longer. Mold base is a non-standard mold base 4080. Due to complex structure of plastic part and long distance between 4 cavities, if a three-plate mold is designed, flow path will be very small if gate is injected with glue. Long, molten plastic is easy to cool and difficult to fill, so a needle valve hot runner system is designed, and system is YUDO hot runner system. Gate position is on the top surface of plastic part, as shown in Figure 1. Needle valve gate can control opening and closing time, which greatly improves appearance quality of plastic parts.

 

 

Figure 4 Insert structure
Advantages of using needle valve hot nozzle:
(1) On the appearance of product, inlet gate is smooth, without traces of raised gates, and does not affect performance of paper surface;
(2) A gate with a larger diameter can be used, which can speed up filling of cavity, further reduce injection pressure, and reduce deformation of product;
(3) It can prevent wire drawing and salivation when opening mold;
(4) When screw of injection molding machine retreats, it can effectively prevent material from being sucked back from cavity;
(5) For larger products with more than two gates, sequence control can be realized, and injection volume of each gate can be controlled to reduce product weld marks;
(6) It can shorten processing cycle and improve production efficiency;
(7) Since cold runner is replaced, there is no material handle, which can save a lot of raw materials.

 

Figure 5 Explosion diagram of rear mold
The most common control methods for needle valve hot nozzle needle are air pressure control and hydraulic control. Because air pressure control uses air, it is clean and environmentally friendly, and has obvious advantages. Therefore, needle valve hot runner of printer ink cartridge holder adopts air pressure control. Way. Needle valve nozzles have a variety of optional specifications and models, which are generally determined according to different needs of customers or for different plastic properties. For cylinder needle valve hot nozzle used in this example, in process of assembling it with mold, in order to ensure high-precision (coaxiality) cooperation with cavity plate, runner plate, and upper bottom plate of mold, it is necessary to improve machining accuracy of corresponding matching parts of mold.
Edge of plastic part adopts a flat thimble, and inner design thimble is ejected. A travel switch is added to thimble plate to facilitate confirmation of accurate return of ejector system.

 

Figure 6 Exploded view of front mold

 

Figure 7 Slider structure diagram