Outer shell of speaker is shown in Figure 1. Maximum size of product is 132.61 mm * 78.21 mm * 42.81 mm, average thickness of plastic part is 1.80 mm, material of plastic part is ABS, shrinkage rate is 1.005, and weight of plastic part is 24.17 grams. Technical requirements of plastic parts are that there must be no defects such as peaks, underfilling of injection molding, flow lines, pores, warpage deformation, silver streaks, cold materials, jet lines, etc.

 

Figure 1 Product Picture of Speaker Outer Shell
Structure of plastic part is a heterosexual shell, design of plastic part structure and 3D mold is shown in attached 3D drawing. Production batch of plastic parts is relatively large. Considering structure of plastic parts and existing injection molding machine tonnage, mold design cavity ranks 1 cavity. When tonnage of injection molding machine is large, you can also choose cavity rank 2 cavities. Three sides of plastic part have flanges facing movable mold, and edge of the largest side has holes to form an inverted buckle. Edges of two outer sides are perpendicular to top surface, that is, two sides also need to design slider core. Therefore, difficulty of mold design is design of three sliders.
When designing mold, it is necessary to make demolding angle for plastic part. Plastic material is different, bone height is different, and angle value of demolding angle is different. If demolding slope is too large, it will affect appearance of plastic part; if demolding slope is too small, plastic part will be dragged or deformed during demolding process. Product design engineers sometimes do not design draft angle in product 3D drawing. When designing mold, mold designer needs to work with product design to determine mold ejection slope of plastic part.

 

 

 

In this set of molds, two sides of outer side of plastic part have no demolding inclination, so when designing mold, it is necessary to design slider forming, that is, slider 2 and slider 3. These two sides must not be designed for demolding oblique. Therefore, mold design engineers need to make correct judgments.
3 side of plastic part needs to be designed with a slider, and slider is designed on operating side, counter-operating side and ground. There is no slider on top side, and gate is designed at the center of mold. Gate is a horn gate, which can be automatically broken when mold is opened, and mold can be automatically injected. Positioning ring and K.O hole of mold are all eccentrically designed by 30mm. Three sliders of mold are driven by oblique guide posts. Glue position part is designed with slider inserts, and slider inserts are fixed on the slider seat from side.
There are two undercuts on the back of plastic part, which need to be designed for inclined top demoulding. Therefore, ejection of plastic parts adopts thimble, cylinder and inclined ejection.
Design of injection mold cooling system is often regarded as a secondary issue. Not enough attention has been paid to size and structural design of cooling system. Unreasonable cooling system design will cause internal stress for small plastic parts, deformation and even stress cracking for large plastic parts with thin walls. Moreover, inadequate cooling will lead to prolonged molding cycle, thereby reducing production efficiency. For cooling of injection molds, the most efficient is direct water transport. As shown in Figure 2, movable and fixed molds of mold are designed for direct water transport.
There is a basic difference in cooling between molds for mass production of plastic parts and molds for production of precision plastic parts. For molds for mass production of plastic parts, in order to shorten cycle time, it is best to use "quick" cooling, which may cause large dimensional fluctuations, rough, uneven structures and large internal stress in plastic parts. "Quick" cooling means that distance between cooling channel and cavity is very close, mold temperature is low. For production of precision parts, narrow tolerance bands and good mechanical properties are required. This requires "slowing down" cold. Considering filling of mold and mechanical properties of plastic part, it is ideal that mold temperature is close to melting point temperature at the moment of injection, then slowly cooled to demolding temperature. Outer shell products of sound boxes are produced in large batches, and cooling system is designed to pursue rapid cooling.

 

 

 

 

Figure 2 Mold diagram of outer shell of speaker