Temperature control of injection molds is a very important issue, but it is often not paid attention to in domestic molds. A particularly obvious example is to wait for mold to be tested, there is no problem before drilling and transporting water. That is, qualification of mold is obtained in an environment where there is no water. In export mold design, customer pays great attention to cooling problem, water transportation must be processed once during mold processing, test mold can be carried out after water transportation if finished.
If cooling system design is unreasonable, internal stress will be generated for small plastic parts, deformation and even stress cracking will occur for large plastic parts with thin walls. Moreover, insufficient cooling will lead to prolonged molding cycle, thereby reducing production efficiency. For cooling system design, extensive research has been conducted at home and abroad for decades, many formulas have also been summarized. These formulas are introduced in common mold design manuals. But in reality, mold design is based on similar product analogies to design cooling systems, few people calculate, because of cycle of product processing, time left for mold design is very limited. Current mold flow analysis software can also simulate effectiveness of cooling system. So as to find the best cooling system design scheme.
In order to make mold have a higher mold temperature during forming, improve fluidity of material, be easy to fill, ensure quality of product, after filling is completed, in order to make molten resin filled in mold solidify quickly, heat must be effectively removed, so design of water transport is to strive for a short molding cycle time.
Purpose of cooling:
A. Balance cooling and improve quality of plastic parts
B. Effective cooling, shorten injection cycle
C. Mechanism is cooled to ensure mold operation
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, and mold temperature is relatively low.
For production of precision plastic parts, narrow tolerance bands and good mechanical properties are required. This requires "slow cooling". Considering filling of mold and mechanical properties of plastic part, it is ideal that mold temperature is close to melting point temperature at instant of injection, and then slowly cooled to demolding temperature. However, this is unrealistic, because considering thermal inertia of mold, injection molding has a short periodic strength change and a reasonable cycle time, so "slow cooling" can only provide a general criterion.
Prerequisite for injection molding precision plastic parts is that mold temperature is high. In order to obtain required "slow cooling" effect, configuration and diameter of cooling channels are different, rapid heating and cooling of high temperature molds are often required.
In actual injection molding production, cooling water should be closed before last 30 molds, so that mold has enough heat to prevent condensation on inner wall of cavity.

Direct water transport is the most commonly used water transport circuit design, as shown in Figure 1. In all cooling circuits, flow rate of through water is large, cooling efficiency is high, and heat is taken away the most. Figure 2 shows through water parameters.
Actual structure of plastic parts is often very complicated. Straight-through water cannot always be drilled horizontally, pond cannot be same height. So-called conformal and straight-through water transportation design means that water transportation needs to be combined with shape of plastic parts to maintain uniform cooling. Therefore, during mold design, for irregular plastic parts, determination of water transport height dimension needs to be carried out with help of 3D software to avoid errors.

 

Figure 1 Design of direct water transport

 

Picture 2 Through water parameters

 

Figure 3 Direct water transport design for large molds
Figure 3 shows direct water transport design for large molds. Three pieces of moisture are shipped in a fixed mold. Through water of middle insert is connected to mold base to enter and exit from left and right sides, water of left and right inserts are also through water, which enters and exits from mold base in long direction. Plastic position of plastic part is in movable mold, and multiple water transport lines are designed along plastic part. Both sides of movable mold insert are large inclined roofs, cooling of core is designed for cross-drilled water transport.

Spoke-type water transportation of large disc-shaped plastic parts is shown in Figure 4. Spoke-type water transportation is also a kind of direct water transportation. Large disk-shaped plastic movable mold has multiple deep bone positions, arranged along radius, water transportation must correspond to these deep bone positions.

 

 

Figure 4 Large disc-shaped plastic parts and spoke water transport
Figure 5 shows water transport design of large thin plastic parts. Butt drill holes along shape of molded product to plug unnecessary parts. Cooling effect is good and it is suitable for products that are approximately round.

 

Figure 5 Water transportation design of round sheet plastic parts