Casting has external dimensions of 176.99 mm * 171.11 mm * 90.88 mm, with an average wall thickness of 2.87 mm. Wall thickness analysis is shown in Figure 1. Casting material is AlSi8Cu3, with a tensile strength σb ≥ 195 MPa and elongation δ ≥ 2%. AlSi8Cu3 alloy, as a high-performance aluminum alloy material, plays an important role in automotive industry. Its unique properties make it a reasonable choice for manufacturing critical automotive components. High strength, good casting performance, and corrosion resistance of AlSi8Cu3 alloy enable it to meet stringent casting requirements. Through reasonable casting processes, AlSi8Cu3 alloy can be processed into various complex-shaped parts, improving the overall performance and reliability of automobiles.

 

Figure 1 Wall Thickness Analysis
Based on casting die-casting tolerances and technical requirements, mold design and sufficient machining allowance are determined, as shown in Figure 2. Surfaces indicated by arrows are the areas requiring machining after die casting. Machining allowance is adjusted to 0.3 mm for subsequent processing.

 

Figure 2 Casting Machining Allowance

Difficulties in casting formation: ① Cage-like structure is complex, and intricate reinforcing ribs affect melt flow. Solving problem of trapped air during melt impingement requires precise control of runner flow rate and reasonable design of overflow and venting channels; ② Casting has significant wall thickness variations, making cavity filling difficult at the end; ③ There are six mounting holes at the end of casting, as shown in Figure 3.  It is necessary to ensure internal density of casting, free from defects such as pores and shrinkage cavities, to meet installation strength requirements of main unit bracket.

 

Figure 3 Forming Difficulty Analysis

Casting weight is 285.9 g, and projected forming area is 16,935 mm². Due to complex structure and difficulty in filling end of cavity, mold needs to be designed with multiple sliding core mechanisms. Casting requires high strength, necessitating high clamping force and pressure.  Based on die-casting machine parameters (see Table 1), a DCC280T cold-chamber die-casting machine was selected as molding equipment, equipped with a φ60 mm diameter plunger.

Table 1 Die-casting machine parameters

Based on technical requirements analysis, parting line is set as shown in Figure 4(a). Dark surface is main parting surface PL1, which includes contact surface PL2. Opening direction of PL2 is mold opening direction. Three side cores SC1, SC2, and SC3 are set in the area perpendicular to mold opening direction. SC1 slider is shown in Figure 4(b), SC2 slider in Figure 4(c), and SC3 slider in Figure 4(d).

 

Figure 4 Parting line design
Gating system design is shown in Figure 5. Main runner Z controls flow rate of the entire gating system, with a cross-sectional size of 25 mm * 11 mm. Following principle that main runner cross-section is larger than branch runners, i.e., Z > 1+2+3+4, where 1, 2, 3, and 4 are branch runners, gating system uses runners 1, 2, 3, and 4 to fill areas a, b, c, and d respectively. Runner 1 is an auxiliary runner: its cross-sectional size is 7 mm * 6 mm, and gate cross-sectional size is 1.6 mm * 8 mm, responsible for compensating for pressure loss of runner 2 due to slope of parting surface. Runner 2 is main runner, responsible for filling area b, with a cross-sectional size of 10 mm * 8 mm and a gate cross-sectional size of 1.2 mm * 25 mm. Runner 3 is a secondary main runner, responsible for filling area c, with a cross-sectional size of 10 mm * 8 mm and a gate cross-sectional size of 1.2 mm * 20 mm. Runner 4 is an auxiliary runner, responsible for filling area d, with a cross-sectional size of 8 mm * 6 mm, a gate cross-sectional size of 1.2 mm * 9 mm.

 

Figure 5. Gating System Design
Due to four-runner gating system and cage-like reinforcing rib structure of casting, cold material can easily accumulate at intersection of multiple material flows. If this cold material is not promptly removed from mold cavity, it can lead to cold shuts on casting surface, internal shrinkage cavities, gas entrapment, and even affect its strength, leading to fracture. Therefore, four 25 mm * 25 mm * 12 mm overflow grooves and four 12 mm * 0.1 mm venting grooves were designed on core side, as shown in Figure 6. A 25 mm * 25 mm * 5 mm overflow groove was designed on inner side of reinforcing rib at the top of mold cavity, with a 30° draft angle on the side wall and a R3 mm radius at the bottom. Molded casting is carried out by inner gate connected to overflow groove. To ensure smooth removal of molded casting, inner gate size was designed to be 20 mm * 1 mm, used to promptly remove cold material at intersection of runners 2 and 3. Corresponding overflow grooves were also opened in mold cavity plate corresponding to core to increase slag removal capacity, as shown in Figure 7.

 

Figure 6. Core Overflow Grooves and Venting Grooves

 

Figure 7. Mold Cavity Overflow Grooves
In cooling system design, pressure chamber uses a double-circulation water circuit to ensure cooling effectiveness and improve durability of punch. Sprue cone uses a water well cooling design. Two water channels with a diameter of φ8 mm are arranged in core and mold cavity plate, as shown in Figure 8, 25 mm away from casting. Water channel connectors use 1/4PT pipe threads. All cooling water pipes pass through mold base and are directly locked to sides of core and mold cavity plate. This effectively prevents water leakage caused by aging of sealing rings.

 

Figure 8. Cooling System

Mold structure is shown in Figure 9. Mold cavity insert 12 is fixed to fixed mold plate 3 with screws, and core insert 11 is fixed to movable mold plate 4 with screws. Guide pins are designed on fixed mold plate side to facilitate robotic part removal after mold opening. Pressure chamber 1 is cooled by a double-layer water circuit, and sprue cone 2 uses water well cooling, with bottom of water well sealed with brass. Mold base consists of a fixed mold plate 3, a movable mold plate 4, and spacers 5. Both fixed and movable mold plates must undergo heat treatment. Main parting surface of cavity plate insert is flush with fixed mold plate surface, while main parting surface of core insert is 0.15~0.2 mm higher than movable mold plate surface, resulting in a designed mold closing gap of 0.15~0.2 mm. Movable mold plate has a vent groove with a depth of 0.1 mm at the corresponding overflow channel position. To prevent mold deformation, support columns are placed below sprue cone 2 and also in the middle of mold plate, avoiding ejector pin holes. Ejector plate 8 is guided by four return pins 9, and spacer block 5 is machined as a single piece and also serves as base plate. Four corners of movable mold plate are designed with 30 mm * 30 mm * 8 mm pry slots. Four large holes are provided on both movable and fixed mold plates for easy disassembly and assembly of core and cavity plate inserts. Mold lifting holes on mold plate are M24 mm, with two lifting holes on the top side to avoid top slider pull rods.

 

Figure 9 Mold Structure
1. Pressure chamber 2. Sprue cone 3. Fixed mold plate 4. Movable mold plate 5. Spacer block 6. Support column 7. Ejector plate 8. Ejector pin fixing plate 9. Return pin 10. Angled guide pin 11. Core insert 12. Cavity plate insert 13. Spring 14. Pull rod 15. Slider 16. Slider 17. Slider

Core insert 11, cavity plate insert 12, and sliders 15-17 are all made of imported alloy steel 8418. 8418 mold steel is a high-performance hot-work tool steel containing chromium, molybdenum, and vanadium, possessing excellent resistance to thermal fatigue cracking, thermal shock cracking, thermal wear, and plastic deformation. These properties make it the optimal choice for die casting, hot forging, and hot extrusion molds. After rough machining and before heat treatment, mold parts must undergo stress relief treatment, and quenching hardness is 46-48 HRC. After mold parts are machined, core and cavity plate inserts undergo shot peening treatment. Shot peening is a surface treatment technology specifically for die-casting mold parts. Its main purpose is to improve wear resistance, corrosion resistance, and thermal fatigue performance of mold parts, thereby extending service life of mold. External dimensions of core and cavity plate inserts should be 0.05~0.08 mm smaller than moving and fixed mold frames, and four-corner positioning fit tolerance should be 0.03~0.05 mm.

After mold assembly and quality inspection are completed, ensuring that all mold opening and closing actions (opening, closing, ejection, etc.) are smooth, a trial run is performed. Based on casting information and die-casting machine parameters, parameters for the first trial run are set, as shown in Table 2. Sample casting from the first trial run is shown in Figure 10.

Table 2 Trial Run Report

 

Figure 10 Sample Casting from the First Trial Run