Abstract: A die cooling system combining 3D-printed water channels and high-pressure cooling achieves uniform cooling of pure electric vehicle motor housing mold. Sensors and solenoid valves are connected to die-casting equipment control system to intelligently control mold operating temperature, addressing aluminum sticking to mold and improving internal quality of casting and production efficiency. Research results have both reference significance and application value for development of similarly complex automotive parts.

Drive motor housing, as shown in Figure 1, consists of four functional areas: first area for mounting motor inner housing, stator, and rotor; second area for mounting output shaft assembly; third area for mounting internal circulating water cooling pipes; fourth area for mounting and fixing motor.

 

Figure 1 Motor Housing Model
To reduce motor weight and increase electric vehicle range, finite element analysis was used in casting structural design. Wall thickness of motor housing cylinder was reduced to 4 mm, and H-shaped reinforcement ribs were added. Wall thickness of output shaft assembly mounting area was reduced from 15 mm to 6 mm, and special-shaped reinforcement ribs were added. As a result, weight of motor housing casting was reduced from 15 kg to 8 kg. Optimized casting structure design presented significant challenges in designing die-casting mold cooling system and die-casting process parameters. This paper primarily studies die-casting mold cooling, intelligent temperature control systems, die-casting process parameters, housing casting quality, and production efficiency.

Figure 2 shows a photo of actual motor housing. Porosity is no more than 4%. Cylindrical portion of motor housing is relatively large, 500 mm long and 4 mm thick. Long distance of molten aluminum filling cavity inevitably leads to a sharp rise in mold temperature. Mold flow simulation temperature field shown in Figure 3 shows that wall thickness and temperature are highest in Zone G, deep within housing cavity, where complex reinforcement ribs are located. This inevitably leads to aluminum sticking, internal porosity, air holes, and shrinkage cavities, making high-pressure cooling channel impossible to machine. Designing this area as an insert and using 3D-printed cooling channels directly connected to high-pressure cooling water pipes in mold core solves cooling problem in Zone G. As shown in Figure 4, 1 shows partial implementation of conformal cooling channels in mold insert. To minimize distance between cooling channels and outer surface of mold cavity, only 1 mm diameter 3D-printed channels were used at sharp corners of irregularly shaped structure in Figure 1. This ensures that outer wall of channel in high-temperature zone G in Figure 3 is less than 8 mm from mold surface. This achieves precise conformal cooling and ensures a roughly equal distance between cooling channels and outer surface of mold cavity, resolving issue of uneven thermal conductivity on complex mold surfaces. 2 shows high-pressure inlet and outlet channels, one end of which is connected to high-pressure cooling device and the other end to the workshop return water pipe.

 

Figure 2 Actual Motor Housing

 

Figure 3 Temperature Field

 

Figure 4 3D-Printed Insert

High-purity, high-flowability, and high-sphericity alloy powders composed primarily of iron, manganese, nickel, chromium, molybdenum, and tungsten were selected. 3D conformal cooling channel inserts were fabricated using laser melt deposition. After hot isostatic pressing, vacuum quenching, solution annealing, precision machining, and surface laser coating, mechanical properties of 3D-printed inserts are shown in Table 1.

Table 1 Material Mechanical Properties

Analysis of temperature field data in Figure 3 reveals that temperature in zone G of casting is the highest, significantly impacting casting quality. Controlling temperature in zone G essentially guarantees the overall quality of casting. Installing a thermocouple on opposite side of zone G of 3D-printed insert provides optimal mold temperature monitoring, as shown in Figure 5. Within 3 ms, thermocouple converts thermoelectric potential generated by temperature changes into a digital temperature signal. This signal is connected to die-casting machine (Figure 6) via a thermocouple plug. Die-casting machine stores received temperature signal in a memory and compares it with mold temperature setpoint. When mold temperature exceeds set upper limit of 205℃, as shown in Figure 7, all three parallel cooling water control solenoid valves open, increasing mold cooling water flow rate (Figure 8), and mold temperature rapidly decreases. When mold temperature falls below set lower limit of 190℃, three parallel solenoid valves close sequentially until mold temperature rises within set range. Remaining solenoid valves are then closed, achieving moving mold temperature equilibrium, as shown in Figure 9.

 

Figure 5 Mold Temperature Monitoring

 

Figure 6 Die-Casting Machine

 

Figure 7 Solenoid Valve

 

Figure 8 Mold Cooling Device

 

Figure 9 Mold Temperature Monitoring System Interface

After three batch production trials, three sets of process parameters were optimized for small-batch production. Die-casting process parameters are shown in Table 2.

Table 2 Die-Casting Process Parameters
A trial production of 1,000 units was conducted using each of three sets of die-casting process parameters. Motor housing castings were inspected for external quality, CT scans were performed, and average cycle times were calculated. Results are shown in Table 3. Shell castings have widely varying wall thicknesses, resulting in different heat storage capacities in different mold areas. Thicker walls increase heat storage capacity. Test results show that optimal mold temperature for areas with wall thicknesses greater than 10 mm is between 180℃ and 195℃, respectively, for areas with wall thicknesses between 4 and 6 mm. Optimal mold temperature is between 195℃ and 205℃ for areas with wall thicknesses between 4 and 6 mm. Ingate velocity directly impacts filling time, mold life, and casting surface quality. Excessive speeds can prematurely erode mold surface, leading to significant air entrainment during injection process and poor exhaust flow, resulting in defects such as porosity in casting. An ingate velocity of 46 m/s achieves optimal external and internal quality, as shown in Figure 10. Gate ratio, a key parameter for controlling filling speed and pressure transmission, was designed based on CAE simulation analysis. Third set of process parameters exhibited the best production efficiency, but yield rate was low. Considering both production efficiency and quality, first set of process parameters was found to be optimal. Among top ten internal defects in casting, the largest diameter is 1.539 mm and porosity is 3.5%, which is far lower than VW 50093:2012-075 die casting porosity standard of 5%.

Table 3 Production statistics

 

Figure 10 Motor housing CT report

(1) 3D printing additive manufacturing technology can provide good technical support for design and manufacture of die casting molds, realize conformal cooling of complex structural parts of the , and completely solve defects such as aluminum sticking, die pulling, and air holes in die castings; 3D printed water channel can be as small as 1 mm in diameter and can be within 8 mm from mold surface, achieving precise cooling of mold.
(2) Mold working temperature is controlled by using thermal sensors, solenoid valves, and mold temperature control system of die casting machine. Mold temperature information is directly connected with cooling water flow control information to realize intelligent control of mold temperature, which has reference significance and application value for development of similar complex automotive parts.