In recent years, with rapid development of 3D printing technology, great progress has been made in moulding manufacturing process applications, printing material development and processes at home and abroad. Metal 3D printing technology has been widely used in cutting-edge fields such as aviation, aerospace and medical. At present, direct use of laser 3D printing technology in China to directly manufacture molds has not yet achieved scale application in mold enterprises, but a few mold enterprises have tried to use 3D printing technology to print mold parts, to achieve internal complex shape-following cooling channels that cannot be processed by traditional processes (see figure 1) to improve cooling uniformity and efficiency of precision mold.

 

Figure 1 3D printed parts and their internal conformal cooling channels

3D printing technology can greatly improve performance of mold parts and extend service life of molds, which is a breakthrough point in moulding manufacturing process technology. Main technical advantages of molds made with 3D printing technology are reflected in two aspects: reasonable and efficient cooling, flexible exhaust design.

Use of 3D printing technology to design and manufacture cooling water channel has following advantages: 1 can be free from shape of plastic part, arbitrarily construct a 3D conformal cooling water channel; 2 no cooling dead zone, shorten injection molding cycle; 3 mold temperature is uniform, reduce deformation of plastic part and improve quality of plastic parts.

Taking plastic parts of mobile power source as an example, plastic part has a size of 67 mm × 23 mm × 130 mm, and material is PC. Mold insert size is 172.26mm×62.2mm×23mm, material is 1.2709 metal powder, hardness is 52~54HRC, and mold adopts 1 die 2-cavity structure, as shown in Fig. 4(a).

 

a. Feeding

 

b. 3D printed parts

 

c. Parts

 

d. Positional relationship between cooling water channel and mold

Figure 4 3D printing in plastic injection molding process

In order to ensure surface quality of plastic parts, gate is located at inner edge of plastic part. Constrained by size of plastic part and feeding mode, traditional cooling method (cooling water channel passes through inside of plastic part) cannot achieve better cooling and cooling effect is poor. Using 3D printing technology to print mold parts and conformal cooling water channels for production, cooling effect of plastic parts is obviously improved. Application of 3D printing in molding process of plastic parts is shown in Figure 4.

 

a. 3D printing process

 

b. Traditional crafts

Figure 5 Comparison of cooling system design between 3D printing process and traditional process

Figure 5 is a comparison of simulated cooling effect of conformal cooling water channel of 3D printing process and traditional process cooling water channel. It can be seen from Fig. 5 that there is a high temperature zone near plastic gate during cooling of traditional process cooling water channel, application of 3D printing design conformal cooling water channel significantly improves local high temperature of cooling of plastic injection molding, and effectively improves cooling effect of mold.

 

Table 3 compares effect of 3D printing process conformal cooling water channel with traditional process cooling water channel injection molding. Compared with traditional cooling water channel process, application of 3D printing conformal cooling water channel shortens cooling time from 12s to 9s, molding cycle is shortened from 25s to 21s, deformation of final plastic part is reduced from 0.17mm to 0.03mm, and molding quality of plastic parts is improved.

Fig. 6(a) shows positional relationship between plastic parts structure of automobile glove box and 3D printing conformal cooling water channel insert. Outer dimensions of plastic parts are 480mm×340mm×250mm, material is ABS/PC, and mold temperature during plastic injection molding is 75~85℃. According to structural analysis of plastic parts, there are many reinforcing ribs on the side of plastic parts, and two ends are dense. According to traditional cooling water channel arrangement, cooling effect is shown in Fig. 6(b). It can be seen from Fig. 6(b) that cooling uniformity is poor, surface temperature of plastic part is 73~118.6℃, and temperature at both ends is higher than about 40℃ in middle part, which is easy to cause warping deformation of plastic part.

 

a. Positional relationship between inserts and plastic parts

 

b. Traditional process cooling channel cooling effect

 

c. 3D printing conformal cooling water channel cooling effect

Figure 6 car glove box cooling system design

In view of this situation, designing cooling water channel shown in Fig. 6(a) is designed. Cooling simulation effect is shown in Fig. 6(c). Surface temperature of plastic part is 57.6~67.8℃, and surface temperature of whole plastic part is uniform and cooling effect is good.

 

a. Insert and position on plastic part

 

b. Conformal cooling channel design

 

c. 3D printing mold inserts

Figure 7 Application of shaped water channel on insert

Position of other car glove box insert on plastic part is shown in Figure 7(a). Shape of plastic part is 523mm×310mm×317mm. TMaterial is: ABS/PC. Mold temperature is 75~85℃ during injection molding. As shown in Figure 7(b), 3D printed conformal cooling water channel is shown in Figure 7(c). Insert size is 172.26mm × 62.2mm × 23mm and material is 1.2709 metal powder, hardness is 52~54HRC.

 

a. Conformal waterway

 

b. Traditional waterway (yttrium copper material)

 

c. Traditional waterway (mold steel material)

Figure 8 Comparison of three process cooling effects

Figure 8 shows cooling simulation results of three different cooling modes at side ribs. It can be seen from Fig. 8(a) that surface temperature is 59.34~76.4℃, surface temperature is uniform, and forming effect is good. Figure 8(b) shows cooling simulation results of traditional cooling method (yttrium copper material). Surface temperature of plastic part is 65.81~78.45℃, and surface temperature is uniform. However, surface of plastic part using beryllium copper material as cooling medium will produce traces. It is suitable for production of plastic parts with strict surface requirements. Figure 8(c) shows cooling simulation results of traditional cooling water channel (mold steel material). Surface temperature of plastic parts is 82.35~106.8℃. Temperature difference of plastic parts is large, which is easy to cause warpage and deformation, affecting appearance quality of plastic parts, and molding period of plastic parts is long, which does not meet production requirements of plastic parts.

Exhaust system designed and manufactured by 3D printing technology has two major advantages: 1 It can construct internal air holes of material arbitrarily, is applied to internal exhaust and gas-assisted molding of mold; 2 Air holes and water channels can be freely staggered and do not interfere with each other.

 

a. Car door panel CAE bubble distribution

 

b. Cooling channel and exhaust system design

 

c. 3D printing effect on the bottom of insert

Figure 9 3D printing cooling system and exhaust system design

Taking exhaust system design of car door panel as an example, CAE bubble distribution of car door panel is shown in Fig. 9(a). Design method of conventional exhaust system is push rod (plastic part push) + water channel (plastic part cooling) ) + inserts (for exhaust), in order to meet molding quality requirements of plastic parts and a reasonable injection production cycle, exhaust system usually needs to be determined by multiple trials. Using 3D printing technology, cooling water channel and exhaust system can coexist, and best injection molding effect can be achieved, and appearance quality of plastic parts can be obtained.
Design of cooling water channel and exhaust system of car door horn mesh hole is shown in Figure 9(b). When printing, process parameters are set to reduce density of printing of material in a certain thickness of mesh area of mold part molding, forming venting micropores at the bottom of insert. When cavity is filled, gas is collected by venting micropores at the bottom of insert to venting hole of insert, and discharged through venting hole. Venting effect of inserts verified by 3D printing design is consistent with that of ventilated steel, and 3D printing effect at the bottom of insert is shown in Figure 9(c).
There are two types of 3D printing process: integral type and graft type. Monolithic processing refers to laser sintering directly on substrate, and is divided after completion. Grafting processing refers to processing pedestal by a traditional process, fixing pedestal on substrate, and then performing laser sintering on pedestal, and grafting processing process is more advantageous in cost. At present, 3D printing is mainly used in manufacture of molds for some complex mold parts, such as manufacture of cavity plates, cores, etc., which are used in printing conformal cooling water channels, mainly used in: local high temperature areas such as nozzles,hot nozzles, etc., thin parts, special structural parts such as slanted block inserts and top block inserts for cooling.