Abstract: This paper analyzes die-casting forming structure of an aluminum alloy camera housing and conducts detailed analysis, calculation, and process processing of main aspects of mold design. Expansion force of die-casting part was calculated, and die-casting machine was selected based on clamping force selection method. Gating system and overflow system of die-casting part were analyzed in detail, designed and fabricated in full 3D. Finally, CAE mold flow analysis of designed gating system was performed using AnyCasting software. Based on simulation results of temperature distribution and air entrapment during filling process, layout of gating system was adjusted, and the overall structural design of mold gating system was improved.
In modern society, for safety and convenience, real-time surveillance using cameras has become an indispensable standard feature in building installations. From city streets to residential communities, cameras are likely deployed in every corner, whether in public or private areas, facilitating tracking and investigation of past events, uncovering truth, ensuring social security, and improving people's quality of life. Camera housing is made of aluminum alloy, which improves service life of camera's electronic equipment. Using die-casting molds allows for mass production and reduces costs.
This paper takes an aluminum alloy camera housing as an example, using UG software to analyze its die-casting process and design a full 3D die-casting mold gating and drainage system. AnyCasting software is used for die-casting simulation analysis to verify rationality and filling effect of designed gating and drainage systems, to make improvements and refinements.

As shown in Figure 1, structure of this component is basically symmetrical, and its shape is that of a cover-type component. Average wall thickness of this component is 2.29 mm, and the thickest part does not exceed 10.83 mm. Thick wall is mainly located at reserved drilling position, and structural complexity is moderate. According to material selection of general structural components, there are assembly requirements for top surface and eye hole position, and CNC machining is used. Finished product is free of burrs and obvious casting defects, and surface is shot blasted.

 

Fig. 1 Part drawing and design of feeding position on inner gate side
Camera housing also functions as a bracket, so it needs sufficient strength and corrosion resistance. Material selected is ADC12 aluminum alloy, which is characterized by high specific strength and corrosion resistance. This material is widely used and is suitable for making cylinder heads, cylinder blocks and electronic product brackets, etc. Its chemical composition is shown in Table 1.
Tab.1 ADC12 Chemical composition of die cast aluminum alloy

 

Silicon can improve casting performance of aluminum alloy, magnesium can improve strength and yield strength, copper and zinc can improve fluidity, tensile strength and hardness of alloy, iron can reduce phenomenon of sticking to mold, and manganese and nickel can neutralize harm of iron. As shown in Figures 1 and 2, if material is fed from side, pouring direction needs to both climb upwards and ensure stable filling of side-mounted electronic eye area. Structure has a large gap in the middle of shell and two holes on the side. As can be seen from point 3 in Figure 2, these two holes are slightly complex, increasing filling resistance. Improper design can easily lead to casting defects such as cold shuts and insufficient end-pouring. Therefore, a reasonable design of gating and overflow systems is crucial to ensuring casting quality.

 

1. Install an internal sprue on the ground side. 2. Separate the moving and fixed molds. 3. Install two side core pulls here. 4. Install an overflow groove on the top side.
Fig.2 Analysis of slope of moving and fixed mold parting surface

Through slope analysis, as shown in Figure 2, a side core-pulling structure needs to be made at eye holes on both sides of camera shell. Upper part of part has a clear front and rear mold boundary, and enclosed area has partial undercuts, requiring process processing.
After precise analysis of camera housing shape, considering slotted structure at natural parting line and thin wall, front and rear mold parting line was raised by 1.2 mm to create sprue location. Parting surface at sprue was set as a plane to avoid thin-walled area and facilitate smooth demolding of front and rear molds. As shown in Figures 3 and 4, sprue is fed laterally to minimize damage to casting during sprue removal.
Figure 3 shows a plane segmentation of casting 1.2 mm above natural parting line on sprue side, forming designed parting surface. Draft angle is 1°. Analysis of slope in Figure 3(b) shows that moving and stationary molds can easily demold.

 

Fig.3 Boundary between moving and fixed diese
Figure 4 shows 3D model of gating and overflow system design. Sprue is located on stationary mold side, and runner is located on moving mold side. Side core pullers are provided on both sides. For undercut position on moving mold side, side core pullers are used to compensate (as shown in circles in Figure 4), allowing for smooth demolding of moving mold.

 

1. Sprue 2. Runner 3. Ingate 4. Enlarged section 5. In Figure 6. Side core pull (two locations) 7. Venting groove 8. Overflow groove
Fig. 4 Design of pouring system of camera casing

Selecting a die casting machine based on clamping force is a traditional and widely used method. Model of die casting machine is defined by magnitude of clamping force. Formula for calculating clamping force for die casting selection:

 

Where: F_lock is clamping force required for die casting, N; K is safety factor, taken as 1.3; F_main is main expansion force, N; F_division is sub-expansion force, N.
Formula for calculating main expansion force is:

 

Where: A is projected area of casting on parting surface, m2, generally plus 40% as projected area of gating system; p is injection pressure, MPa, its value is 40 MPa for general parts and 70 MPa for load-bearing parts. Camera housing described in this article belongs to general parts, and p value is calculated as 40 MPa. Formula for calculating expansion force is:

 

Where: A core is sum of projected areas of forming end face of side core pulling mechanism, m2; α is wedge angle of side core pulling wedge block, with a value range of 10°~25°, and 23° in this example.
Maximum outline size of casting is 156 mm*180 mm*80 mm. Projected area measured in UG software is 15 694 mm2, and projected area of side core pulling is 6 467 mm2 (two places). These data are substituted into formula for calculating clamping force. F lock = 1 965 kN. According to selection parameter table 2 of LK die casting machine, DCC280 LK die casting machine is initially selected, with a punch diameter of 60 mm and a pressure chamber filling degree of about 38%.
Tab. 2 IMPRESS series parameter table for Lijin coldchamber die-casting machine (excerpt)

Gating system is an important factor in determining filling condition and also an important factor in determining internal quality of die casting. Designing a reasonable gating system is an important part of die casting mold design work. Design of gating system for camera housing is shown in Figure 4.

Formula for calculating cross-sectional area (Ag) of ingate is:

 

Where: G is mass of molten metal passing through ingate. In actual calculations, filling mass of overflow groove should be considered, and it is taken as 1.2~1.5 times mass of casting, kg; ρ is density of liquid metal, kg/m3; vg is filling speed, m/s; t is filling time of cavity, s.
Mass of camera housing casting is 0.399 kg. Considering that mass of overflow groove accounts for 30% of mass of casting, G is taken as 0.52 kg; density of liquid aluminum alloy is 2.4*103 kg/m3; according to corresponding conditions in Table 3, die-casting filling speed Vg is taken as 42 m/s; cavity filling time corresponding to Table 4 is selected as 0.03 s. Substituting these data into formula, Ag can be calculated to be approximately 170 mm2. Ratio of injection punch area to ingate cross-sectional area selected earlier is 16.6, which meets requirements. Ingate thickness is 1.4 mm.
Tab. 3 Relationship between average thickness of die casting and filling speed

Tab. 4 Relationship between quality of die castings and filling time

Connection positions and feed angles between ingate, runner, and casting are shown in Figure 5.
In Figure 5(a), molten aluminum alloy is injected into casting cavity from runner through ingate. End angle of runner is set to 50°, and its flow trend is towards upper left of casting to avoid direct impact of high-speed, high-pressure liquid on mold core. Casting is a circular cap shape, and ingate is a fan-shaped runner, layout of which is shown in Figure 6. Runners 2 and 3 are main runners, pointing towards center (as shown by red line in figure), and blue arrows indicate flow direction of ingate. Runners 1 and 4 are auxiliary runners, mainly filling shape in straight direction of sides. Figure 7 is a liquid flow tracking cloud map of gating system analyzed using CAE software. From this figure, it can be concluded that gating design meets expectations.

 

Fig. 5 Design of pouring system

Fig. 6 Layout of inner gate position

 

Fig.7 Simulation analysis of liquid flow tracking

Horizontal sprue adopts a tree structure. Front end connecting to ingate is designed and calculated according to 3 times cross-sectional area of ingate. Remaining area follows principle of gradually decreasing from end of vertical sprue to end of horizontal sprue, effectively reducing air entrapment or suction.
Sprue slab is designed according to parameters of LK DCC280 die casting machine selected above. Its punch diameter is equal to that of the sprue, which is 60 mm. Its thickness is designed to be 1/3 of diameter, i.e., 20 mm. Slab is 5 mm higher than the highest point of casting. Thus, a smooth and fluid gating system channel is designed. As shown in Figure 5(b).
Figure 7 is a cloud diagram of liquid flow tracking simulation analysis of gating system. Its simulation results are basically consistent with expectations. Two main channels in the middle are inclined upwards, filling top part and continuing to advance to one side of overflow channel. Auxiliary channels on both sides mainly complete filling task in straight direction of side.

Overflow system includes overflow channels and venting channels. Overflow channels, in addition to receiving gas, inclusions, and cold metal contamination in cavity, can also regulate local temperature of cavity, improve filling conditions, and, when necessary, serve as a process ejector to remove casting. Overflow channels guide flow of liquid during pouring, and are therefore generally designed at the end of filling path or at confluence of two material flows.
Analysis of casting structure shows that main overflow channels are designed at natural interface of last filling section in opposite direction of gate. Side holes where 1, 2, 3, and 4 converge in Figure 6 are prone to air entrapment. Adding overflow channels to these areas helps improve filling effect. A larger overflow channel is designed in upper cavity.
According to distribution of the total mass of overflow channels to 20%~50% of die casting mass, in this case, the total mass of overflow channels is 123 g, accounting for 31% of casting. Cross-sectional area of overflow outlet of all overflow channels should be 60%~75% of cross-sectional area of ingate. In this case, the total cross-sectional area of overflow channel is 108 mm2, and the total cross-sectional area of ingate is 170 mm2, accounting for 63%, which meets design requirements. 3D drawing of overflow channel was made according to these design principles, as shown in Figure 8. Function of venting channel is mainly to discharge gas in melting cup and mold cavity. Structure design of venting channel is shown in Figure 8. End of overflow channel is collected into a wave plate venting channel.

 

Fig.8 Exhaust system

Gating system was analyzed by CAE using mold flow analysis software AnyCasting. According to relevant parameters of DCC280 die casting machine (Table 2), its process parameters were set as shown in Table 5. Length of pressure chamber is punch stroke, which is less than injection stroke of 400 mm.
Tab. 5 Process parameters of die casting

Filling time simulation effect of gating system was checked in AnyCasting software, as shown in Figure 9. Figure 9 shows simulated effect of liquid aluminum filling ingate. Comparing feeding times of four ingates, two middle ingates have larger areas and are main filling ingates, while two side ingates assist in filling. Middle ingate is faster than side ingates. Cavity is completely filled in 0.26646 s, therefore cavity filling time is approximately 0.029 s, close to 0.03 s calculated in ingate design. Therefore, ingate design and placement are reasonable.

 

Fig. 9 Simulation of filling time

After mold design was completed, a trial mold was performed using a LK DCC280 die-casting machine. 100 trial products were produced for testing and analysis. It was found that 10% of castings had slight cold shuts and slag inclusions in circled area shown in Figure 10. Analysis suggests that this is because it is located at confluence of two material flows or at corner of a tortuous shape, making filling more difficult. Based on mold structure, an overflow groove can be added to guide, remove slag, and maintain heat.

 

Fig. 10 Cloud maps of filling temperature and gas content
Improved mold was simulated using AnyCasting software. Filling time cloud diagram is shown in Figure 11. When filling reaches 97%, casting is fully filled; when it reaches 98%, gas entrainment sequence diagram shows that there is no gas inside casting. Added overflow channels were verified; the total mass of all overflow channels is 156 g, accounting for 39% of casting weight, and filling time is 0.03 s, meeting design requirements. Temperature cloud diagram shows that temperature remains above 620 ℃ when cavity is full, meeting die-casting filling requirements.
After a second trial molding, casting pass rate was 100%.

 

Fig.11 Improved simulation cloud maps

This paper designed mold processing technology for camera housing structure. In parting surface design, three-phase meeting positions of moving mold, fixed mold, and side core-pulling mechanism were rationally allocated, achieving a reasonable parting with minimal modifications to parts. Structural shape and layout of gating system and overflow system were calculated and designed in detail. Designed gating and drainage system was simulated using AnyCasting software. Based on defects of first trial molding and simulation results, quantity and position of overflow system were adjusted accordingly. Finally, a more reasonable gating and drainage system was made, and all castings produced in second trial molding met requirements.