Aluminum alloys are widely used in industry due to their low density, high specific strength and corrosion resistance. Aluminum alloys are often formed by die casting. During die casting process, metal liquid fills mold quickly. If gating system and overflow system are not designed reasonably, defects such as oxidation inclusions and air entrainment will be caused, which will affect quality of casting and reduce its mechanical properties. Traditional die-casting process design relies on experience for multiple attempts, which greatly increases cost and prolongs design cycle.
Based on structural characteristics of three-way valve, gating system and overflow trough of die-casting process are designed, and Flow-3D software is used for numerical simulation of filling process. In initial plan, the overall air entrainment of casting is serious. With gradual optimization of gating system and overflow trough, internal air entrainment of casting is reduced. According to optimized scheme, die-casting mold was designed and manufactured, and production verification was carried out. Through simulation analysis of casting, based on entrainment volume, temperature field and flow characteristics of molten metal, pouring system and overflow trough were designed and optimized. Mold was designed and produced using optimized system, and qualified castings were obtained.
Graphical results
Outline size of three-way valve is 152.5mm×119.5mm×121mm, and average wall thickness is about 5.56mm. Shape of casting is cylindrical, with a circular platform and a stepped through hole on the left side. It is symmetrical up and down, with a boss on lower surface, and a through hole with a partition in the center with a diameter of φ90mm. 1:1 solid three-dimensional modeling is established by UG software, as shown in Figure 1. Selection of casting parting surface should consider complexity of die-casting mold design, ease of processing and dimensional accuracy of casting. According to structural characteristics of casting, because it is completely symmetrical on the left platform, optimized scheme selects horizontal plane of main channel of three-way valve, that is, surface composed of center line of platform and axis of cylinder as parting surface. Parting surface is located at horizontal center of casting, which is conducive to exhaust.

 

Figure 1 Schematic diagram of solid modeling of three-way valve

 

Figure 2 Schematic diagram of parting surface

 

Figure 3 Schematic diagram of preliminary design of pouring system

 

Figure 4 Casting filling process
It can be seen that air entrainment on the front barrel wall of casting is more serious, which will seriously affect quality of casting. For above situation, it may be caused by excessive flow rate of molten metal on horizontal runner. By adding a bend on runner, flow rate of molten metal can be reduced to obtain good filling and improve problem of runner not being filled.

 

Figure 5 Schematic diagram of pouring system of improved scheme

 

Figure 6 Filling process of casting of improved scheme 1

 

Figure 7 Temperature field of casting of improved scheme 1

 

Figure 8 Schematic diagram of pouring system of improved scheme 2

 

Figure 9 Simulation results of improved scheme 2

 

Figure 10 Temperature field after adding auxiliary runners

 

Figure 11 Schematic diagram of pouring system of improved scheme 3

 

Figure 12 Comparison of entrained air volume of different schemes

 

Figure 13 Comparison of oxidized slag of different schemes

 

Figure 14 Volume of entrained air under different pouring systems
As can be seen from Figure 14, entrained air volume in casting is significantly reduced by improved schemes 1 and 3. Although the overall entrained air volume of improved scheme 2 has not decreased significantly, it can be seen from entrained air cloud map that position of entrained air in casting has changed, and part of it has been transferred to overflow tank, which is equivalent to reducing internal entrained air volume. Improvement plan 3 has the lowest air entrainment, good overall filling sequence, no insufficient pouring defects, no significant temperature drop, and less oxide inclusions. It can be used as final trial production plan.

 

Figure 15 Actual production of three-way valve castings

 

Figure 16 X-ray detection results