In order to eliminate the shrinkage cavity and porosity defects caused by solidification shrinkage of molten iron, take the relatively complex lower box as an example (and apply it to the upper box), and design three process schemes, as shown in the table.

Scheme No	Pouring position	Sprue position	Casting mass/kg	Pieces per type/piece	Size of sprue/mm	Size of runner/mm × mm	Size of sprue/mm × mm	Sprue ratio Σ F straight: Σ F horizontal: ΣF in	Pouring time/s	Pouring system mass/kg	Chilled iron mass/kg	Riser mass/kg	Process yield/%	Cold iron usage/%
Scheme I	Vertical pouring	Top pouring	121	1	φ40	2-40×40	4-50×10	1:2.55:1.59	26	20	8.4	86	53.3	6.9
Scheme II	Inclined pouring	Intermediate pouring	121	2	φ50	2-63/52×33	4-80×15	1:1.94:1.63	21	38	65	58	71.6	26.9
Scheme III	Horizontal pouring	Bottom pouring	121	1	φ44	2-52/42×26	2-80×15	1:1.6:1.53	18	19	24.5	34	69.5	20.2

Scheme I: vertical top-side pouring and multi-riser feeding process (as shown in Figure 1) is adopted. In order to facilitate sand cleaning and cold iron bonding, the process sand core is divided into six sand cores for printing, as shown in Figure 2. The whole production process includes: 3D printing sand core, printing core sand cleaning, dip coating, drying, placing cold iron, core assembly, screw clamping and locking sand core, placing air jacket seat nozzle basin and pouring. The core separation and core assembly process is shown in Figure 2 and Figure 3.

Scheme 2: adopt the inclined vertical side pouring and multi-riser feeding process, as shown in Figure 4, and the 3D printing core process is shown in Figure 5. During the assembly process, the sand core must be assembled horizontally outside the mold and fastened with bolts, and then the assembled sand core shall be erected and placed in the lower mold, and the upper mold shall be closed. As shown in Figure 6, the operation of ductile iron is relatively complex.

Scheme III: adopt horizontal split, bottom side pouring, side hot/blind riser feeding process, as shown in Figure 7, and 3D printed sand core as shown in Figure 8. During the core assembly process, the bottom core is placed on the core plate, and the core is vertically lowered. After the core assembly, use the clamp bolt to press and then pour, as shown in Figure 9.

The three schemes are simulated and analyzed with MAGMA software. According to the simulation criteria of MAGMA software, the three schemes can meet the quality requirements of ultrasonic and radiographic inspection of ductile iron castings, and can realize the sequential feeding of riser to ductile iron castings.

The molten iron in Scheme III enters the mold cavity (as shown in Figure 10) from the bottom side of the gear box junction surface through the side hot dark riser at low flow rate (within V=0.6~0.9 m/s) to reduce the MgO slag generated by the contact oxidation of Mg and the mold cavity air. Set chills at the farthest distance from the riser. The chills become thinner and point to the riser. The chills+side concealed risers+top concealed risers are adopted to make the modulus distribution as M riser: M neck: M casting: M casting end=(1.35~1.55): 1.1:1: (0.5~0.6) large gradient modulus (as shown in Figure 11), so as to realize the sequential feeding of the riser to the ductile iron castings. The simulation results of shrinkage distribution are shown in Figure 12 Quality requirements for radiographic testing.