Key Points of Injection Mold Design for Scanner Base

Time：2023-10-27 07:27:24 / Popularity： / Source：

Scanner base products are shown in Figure 1. Maximum dimensions of product are 371.37 mm * 285.93 mm * 65.83 mm; average thickness of plastic part is 2.50 mm, material of plastic part is PS HI, shrinkage rate is 1.005, and weight of plastic part is 391.30 grams. Technical requirements for plastic parts are that there should be no defects such as peaking, underfilled injection molding, flow lines, pores, warping deformation, silver streaks, cold material, and jetting lines, and meet ROSH environmental protection requirements.

Figure 1 Scanner base product map

Figure 2 3D diagram of rear mold core and parting surface
It can be seen from Figure 1 that the overall shape of plastic part is a flat shell, and one side of plastic part has a demoulding slope of 1゜, but there are four U-shaped buckles with different heights on the shoulder. In order to avoid affecting product function, there must be no step difference and clamping line on this side of plastic part, so a large slider needs to be designed on this side. In addition, there is a protruding lug on top surface of plastic part, where there is a mold undercut, and undercut of lug is solved by slider, which is combined with the entire side to form a large slider, as shown in Figure 2.
This scanner is a famous brand in Japan. This article shares all materials of mold parting surface jointly analyzed and formulated by domestic mold design experts and Japanese experts, provides reference for everyone. Readers can understand essentials of parting surface design in detail through these materials and combined with 3D drawings. Scanner base product looks like a simple mold at first glance. In fact, parting surface of mold is not a plane, many places are alternately high and low. Because parting surface of part of product is relatively complicated, it needs to be determined by segment-by-segment analysis with 3D software. For complex parting surfaces with large ups and downs, it is necessary to analyze function of product at this part, combine product tolerances, determine appropriate demoulding slope, and reduce plastic draft, so that parting surface can be determined. For fixed mold core corresponding to outer surface of high-gloss product, special attention should be paid when selecting parting surface so that step difference between movable and fixed mold cores is as small as possible, and appearance must not be affected. On premise of ensuring function and tolerance of product, choose a flat parting surface as much as possible to facilitate mold processing and assembly. Analysis diagram of parting surface of mold is shown in Figure 3.

Size of plastic part is large, and mold design cavity is 1 cavity. Due to YUDO hot runner system, mold base is non-standard 6570, injection molding machine matched with mold is 650 tons, and mold weight exceeds 2 tons. In order to ensure rigidity of mold system, mold adopts three-level positioning. The first level of positioning is positioning of guide post and guide sleeve of mold base itself, diameter of guide post is ø60. Taper positioning blocks are designed on three sides without sliders to improve accuracy of mold clamping; four corners of front and rear mold cores are respectively designed to position tiger mouth, which is conducive to precise mold clamping, which is called three-level positioning of mold. Due to large number of front mold plates and heavy weight of hot runner mold, it is necessary to design a positioning pin of ø40. A ø25 positioning pin is also designed between B plate, square iron and bottom plate of rear mold to increase rigidity of mold and improve precision of injection molded parts. Locating pin of rear mold ø25 passes through 3 mold plates. In order to facilitate removal, locating pin needs to be made with M12 threaded holes at both ends.
Gating system is YUDO hot runner, needle valve hot nozzle, two-point glue injection. Valve needle type hot nozzle, with good color change performance, suitable for most plastics, good flow performance, with minimal gate marks and smooth and beautiful gate, etc. Needle valve gate hot runner system has same structure as ordinary multi-head hot runner system, there is an additional set of valve needle transmission device to control opening and closing movement of valve needle. Transmission device is equivalent to a hydraulic cylinder, which is connected with mold by the hydraulic device of injection machine to form a hydraulic circuit to realize opening and closing movement of valve needle, and can control injection of molten plastic into cavity through timing.

Because valve gate is closed by mechanical action of valve needle, it is not limited by cooling time of plastic at gate, so valve gate runner system can sometimes greatly shorten production and molding cycle of plastic parts. Gate size can also be opened larger, which is good for processing plastics that are sensitive to shear. Valve gate method can process small parts weighing a few grams, as well as large parts weighing several kilograms. Various engineering plastics can be processed to produce parts with valve gates. If there are multiple cavities of different sizes in a mold, if a valve runner system is used, flow of each cavity can be adjusted and controlled separately by controlling opening and closing time of each gate. This is especially significant for multi-cavity molds with widely different shapes and sizes. Also, for molds with high productivity and multi-layer parting surfaces, it can only be realized by using a valve-type hot runner system.
For demanding flat plastic parts, preventing their deformation is an important task in injection molding work. For this reason, a straight-through water delivery is designed for both front and rear molds, and a straight-through cooling circuit is also designed for slider. Layout of cooling system is shown in Figure 4.
Both front and back of scanner base plastic part belong to appearance surface, so traces of thimble must be beautifully designed. Ejection element of this set of mold has a cylinder, which is located at the bottom of column, which will not affect appearance of plastic part, and has a large ejection force; multiple slanted ejectors have a large ejection force, and can also be pulled out of buckle. For rest of parts, since appearance of flat thimble is better than that of round thimble, several rows of flat thimbles are designed, arrangement is neat and beautiful.

Exterior surface of scanner base plastic part needs to be etched in many places, and back also has an etched surface. When designing ejector component, etched surface must be avoided, and attention should be paid to it when designing mold.

Figure 3 Analysis diagram of mold parting surface

Figure 4 Cooling system layout

Gud Mould Industry Co., Ltd

Key Points of Injection Mold Design for Scanner Base

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