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Aluminum alloy motor housing casting process development

In recent years, with the demand for energy conservation, emission reduction and environmental protection, the research and development focus of automobile manufacturing companies is shifting from traditional fuel vehicles to new energy vehicles. The aluminum alloy motor casing is the core casting of the new energy vehicle powertrain. The top (open side) is connected to the inverter, the bottom is connected to the reducer, and is connected to the main shaft bearing through an inlaid bearing bushing. The side wall is often connected to the inverter through a suspension. Subframe connection.


The structure of the motor housing is relatively complex. The side wall of the motor casing surrounds the cooling water jacket. Ensuring the sealing of the water jacket is an important technical requirement for the product and the biggest difficulty in the casting process. At the same time, shrinkage on the upper and lower end surfaces and side walls of the motor housing are also casting defects that need to be avoided during process development.

The structural characteristics and common casting defects of the motor casing. On this basis,We discussed and shared the casting process design of the motor casing and the application of computer simulation technology in the rapid trial production of motor casing castings.

1 Motor housing product features1.1 Basic product information

The motor housing is the core component of new energy vehicles. One end of it is connected to the reducer and the other end is connected to the inverter. The diameter of the motor casing is generally ϕ350~ϕ400 mm, and the height is generally in the range of 200~300 mm. Figure 1 shows two common motor housings for different powers. The main wall thickness is 5~6 mm. The side water jacket has various structures, but most of them are spiral structure or semi-spiral structure (Figure 2). The water jacket wall The thickness is generally 6~7 mm. The weight of the motor shell is generally 4~10 kg, and the material is generally aluminum alloy A356.2 with T6 heat treatment.

motor casing

(a) 140 kW motor housing

(b) 160 kW motor housing


Figure 1 Two different power motor housing



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Figure 2 Motor housing water jacket structure

1.2 Technical requirements

Mechanical properties generally require that the hardness of the bottom and top surfaces is not less than 90 HBW, and that the tensile strength of the furnace test rod or the designated sampling part of the body is ≥275 MPa, and the elongation is ≥2%. The air tightness requirement is: the water jacket has no bubble leakage under 600 kPa for 10 minutes. Casting defects such as pores, shrinkage porosity, cold shut, cracks, slag inclusions, etc. are not allowed on the surface and machined surfaces of the castings. The internal defects of the castings must be controlled to ASTM E155 Level III, and the dimensions of the castings must meet the requirements of CT7 level.

1.3 Common casting defects

The motor housing casting has a complex structure and is difficult to cast. Once the casting process is unreasonable, it is very easy to produce waste products. Common casting defects are shown in Figure 3. Defects caused by insufficient feeding include concentrated shrinkage cavities and local shrinkage, air bubbles caused by poor exhaust, insufficient pouring or cold insulation caused by poor mold filling. These defects are also the main reasons for the unqualified air tightness of the motor housing. factor. In addition, there are defects such as water jacket core breakage, poor bearing bushing fit, and severe sand adhesion in parts of the casting. Among the above-mentioned defects that are prone to occur during the motor housing casting process, defects caused by poor feeding are the most important. Therefore, the main focus in casting process selection is the feeding problem of castings.


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Figure 3 Common casting defects

2 Motor housing casting process plan2.1 Core making and core assembly solutions

Using the core assembly process to produce motor casing castings is one of the mainstream process solutions in the industry. The motor casing casting process flow is shown in Figure 4.

For the core making and core assembly process, the mass production of water jackets for motor casings generally uses hot core box core making, and the outer contour core uses cold core box core making. In the early trial production stage of the motor housing, due to the complex structure of the water jacket core, a 3D printed sand core can be used. The outer contour sand core can be 3D printed or made using a processable plastic manual core box. In the early trial production stage of the product, in order to achieve rapid trial production, the mold removal direction of the core box can be ignored, and there is no need to follow the mold splitting method of the batch production process (Figure 5a), but use the partial sand core integration solution (Figure 5b).




(a) Core assembly method of batch production process


(b) Core assembly method during trial production


2.2 Casting process selection and pouring system design

In the core forming process, the choice of specific casting process mainly depends on the product structure characteristics and workshop production conditions, and then the choice is made based on process reliability, cost and the convenience of on-site core forming, pouring and cleaning operations. For integral structure motor housings with water jackets on the side walls, the most commonly used casting method currently is low-pressure casting or low-pressure mold filling and flip solidification. If the structure of the motor housing is suitable, gravity casting or tilt casting can also be used.

(1) Gravity casting

Gravity casting is the most convenient process. The biggest advantage of this casting process is that the pouring process is fast. It can achieve continuous pouring of products with a single-piece cycle of 8 to 12 seconds. It is the fastest production cycle among these casting processes. Gravity casting is used. In order to ensure smooth mold filling, bottom pouring pouring scheme is often used. The pouring system is shown in Figure 6.


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Figure 6 Design of gravity casting pouring system

The cross runner using bottom injection gravity casting can be designed as a ring around the outside of the motor housing casting. The inner runner extends from the bottom of the cross runner to the flange surface of the casting, with a riser placed on the top, and two pieces in one box can be realized. Feed at the same time.

The disadvantage of this casting method is that since the material is fed from the bottom, the temperature field distribution of the material liquid in the cavity after the mold filling is completed is hotter at the bottom and colder at the top. This temperature distribution pattern is very unfavorable for the sequential solidification of the casting, so It is extremely easy for parts of the casting to be insufficiently compressed to produce shrinkage porosity or even shrinkage cavities, which may lead to unqualified air tightness of the motor casing after processing.

(2) Low pressure casting

Low-pressure casting is the most common forming process for producing motor casings. The biggest difference between it and gravity casting is that low-pressure casting can feed the casting in the anti-gravity direction through the inner runner during the solidification process, so as to ensure that the bottom of the casting The shrinkage can be effectively solved. The sprue design is shown in Figure 7.

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Figure 7 Low pressure casting runner form

The advantage of this runner design is that the process yield is high, but the disadvantage is that it is difficult to solve the feeding problem. Since the wall thickness of the bottom surface of the motor housing is generally relatively thin, it will solidify first during the solidification process of the casting, causing the feeding channel connecting the casting area above it to the sprue to be closed in advance, resulting in the thermal joint area above the casting being ineffective. Feeding, as shown in Figure 8.

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(a) Packing channel interruption

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(b) Hot section area on the side wall of the casting

Figure 8 Low-pressure casting is prone to shrinkage defects

Based on the above reasons and according to the structural characteristics of the casting, the bottom of the casting can be partially thickened, as shown in Figure 9(a), or a runner design as shown in Figure 9(b) to (e) can be adopted. From the aspects of casting mold filling and feeding, the design of the above gating system is feasible.

aluminum casting parts

(a) Partial thickening of the bottom

sand casting

(b) Sprue plan I

(C) Sprue plan II

(d) Sprue plan III

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(e) Sprue scheme IV



The core assembly of the sprue plans (a) ~ (c) is relatively simple, but it will increase the burden of the cleaning process and needs to be removed by turning. The cleaning of the plans (d) and (e) in Figure 9 will be easier. The gating system can be removed by sawing.

There are also many design options for the top riser, as shown in Figure 10. The specific solution to choose mainly depends on the structure of the product. The optimal riser solution can be determined through simulation analysis of hot node distribution and prediction of shrinkage cavities and shrinkage porosity defects.

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(a) Riser scheme I

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(b)Riser scheme II


sand casting

(c)Riser scheme III


(3) Low pressure filling, flipping and solidification

The low-pressure mold filling flip solidification scheme eliminates the top riser of the low-pressure casting scheme and replaces it with a cold iron. The runner design is no different from that of low-pressure casting (Figure 11). After the mold filling is completed, the manipulator or turning mechanism is used to turn the sand bag 180°. The basic design intention of this solution is that after the turning, the inner runner and the runner will act as a riser for feeding, and the cold iron will be under the casting after turning. Chilling, castings and gating systems form an ideal temperature field distribution, which is more conducive to sequential solidification. Moreover, due to the elimination of the riser, the process yield rate of the product is higher. However, this process requires the cooperation of a manipulator and a flipping mechanism to achieve it.

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Figure 9Low-voltage flip-chill design scheme

(4) Tilt pouring

Tilt pouring generally involves setting a pouring cup on one side of the riser and then flipping it 90°, as shown in Figure 12. The entire flipping process can be controlled within 7 to 12 s, but during the flipping process, one side of the shell will be overheated, the temperature field distribution is difficult to control, and the risk of shrinkage and porosity of the product is greater. Moreover, core drift and core breakage are prone to occur during the turning process, which requires high strength and positioning of the sand core, and the workshop needs a turning mechanism to realize the turning action.

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Figure 10 Tilt pouring scheme

Based on the above analysis, low-pressure casting is the most common casting process for producing motor casings. As for whether to use standard low-pressure casting or low-pressure flip casting, the choice must be made based on the specific structure of the product and the workshop production conditions.


Source: FAW Casting Co., Ltd.