1. Casting Analysis and Design
1.1 Casting Material and Structure
- Material: The material of the product frame is ZTC4 titanium alloy.
| Element | Ti | Al | N | Others |
| Mass Fraction (%) | Balance | 5.5 – 6.8 | 3.5 – 4.5 | 0.15 (max), 0.3 (max), 0.1 (max), 0.015 (max), 0.05 (max), 0.2 (max) |
- Structure: The casting has a frame structure with external dimensions of 348.0mm x 283.5mm x 198.0mm and an average wall thickness of 3mm. It contains multiple rib plates and bosses.
1.2 Pouring System Design
| Pouring System | Section Ratio | Characteristics |
|---|---|---|
| Top Pouring Type | 1 : 1.25 : 1.75 | Simple structure, easy to fill the cavity, conducive to molding and sequential solidification of the casting. |
| Bottom Pouring Type | 1 : 1.25 : 2.2 | Stable filling, good for venting, and realizes bottom-up sequential solidification. |
2. Numerical Simulation and Analysis
2.1 Boundary Condition Settings
| Parameter | Value |
|---|---|
| Contact Type between Shell and Casting | COINC |
| Interface Heat Transfer Coefficient | 1000W/(m^2•K) |
| Pouring Type | Gravity Filling |
| Pouring Temperature | 1750°C |
| Shell Initial Temperature | 25°C |
| Pouring Time | 3s |
| Shell Material | CBSMS – M Chemically Bonded Shell Molding Sand – Mold |
| Stress – Strain Setting (Casting) | Linear – Elastic |
| Stress – Strain Setting (Shell) | Rigid |
2.2 Filling Process Analysis
| Pouring System | Filling Characteristics |
|---|---|
| Top Pouring Type | At t=0.6s, alloy liquid flows to the bottom rapidly, causing strong impact on the shell. At t=1.02s, the liquid level is uneven, with poor filling stability, especially in the rib plate area. At t=1.78s, the casting body is basically filled, and the upper pouring system is gradually filled. The process has problems such as interrupted metal liquid flow, turbulence, and insufficient filling. |
| Bottom Pouring Type | At t=1.68s, alloy liquid starts to fill the casting body from five ingates, with stable confluence and no air entrainment. At t=2.17s, the filling process is stable. At t=2.81s, the filling rate reaches 99%, and no turbulence occurs. The temperature of each region in the casting is above the liquidus line, with a low probability of cold shut. |
2.3 Solidification Process and Defect Distribution
| Pouring System | Solidification Time and Defect Distribution |
|---|---|
| Top Pouring Type | The inner runner solidifies earlier than the middle rib plate and sidewall of the casting, resulting in self – shrinkage of the alloy liquid near the middle and bottom of the casting body. The total shrinkage porosity is mainly distributed at the rib – rib and rib – tendon junctions, with strong discreteness. The casting has obvious shrinkage porosity due to turbulent filling and air entrainment. |
| Bottom Pouring Type | The solidification time is from top to bottom and from outside to inside. The top riser is designed reasonably to achieve good feeding function. More than 80% of the shrinkage porosity is concentrated in the riser and pouring system, and there are no defects in the casting body. |
2.4 Effective Stress Distribution
| Pouring System | Effective Stress Distribution |
|---|---|
| Top Pouring Type | The stress at the corner R angle and the junction of the rib plate and sidewall of the frame is large, exceeding 750 MPa, and cold cracks are prone to occur at the end of the solidification process. |
| Bottom Pouring Type | The large stress is mainly concentrated in the anti – deformation rib area, and the stress distribution in the main part of the casting is uniform and lower than the yield stress, so it is not easy to crack. |
2.5 Deformation Result Analysis
| Pouring System | Deformation Characteristics |
|---|---|
| Top Pouring Type | The total deformation of the casting body exceeds 1mm, mainly concentrated at the opening and inner wall. |
| Bottom Pouring Type | The total deformation at the opening is reduced to less than 0.5mm, and the deformation is mainly in the riser and the plane where the riser is located. |
3. Test Results
3.1 Surface Quality
| Pouring System | Surface Quality |
|---|---|
| Top Pouring Type | The casting is formed completely without defects such as underfilling, bulging, and cold shut, which is consistent with the simulation prediction. |
| Bottom Pouring Type | The casting is formed completely without defects such as underfilling, bulging, and cold shut, which is consistent with the simulation prediction. |
3.2 Metallurgical Quality
| Pouring System | Metallurgical Quality |
|---|---|
| Top Pouring Type | There are many internal shrinkage holes, mainly distributed at the rib plate corner, rib – tendon junction, and boss. The shrinkage hole position and volume are basically consistent with the computer simulation results. After hot isostatic pressing, there are multiple static pressure pits on the surface. |
| Bottom Pouring Type | The overall internal quality is good, with only one large shrinkage hole at the hot joint where the outer wall meets the tendon. After hot isostatic pressing, there is only one static pressure pit on the surface, which can be repaired by welding. |
3.3 Casting Dimensions
| Pouring System | Casting Dimensions |
|---|---|
| Top Pouring Type | The overall contour deformation exceeds 1mm, and the local surface contour exceeds 3mm. |
| Bottom Pouring Type | The surface contour can be controlled within 1mm, and the wall thickness deviation can be controlled within ±0.3mm, meeting the design requirements. |
4. Conclusions
- Bottom pouring in investment casting of titanium alloy frame has a more stable filling process, smaller shrinkage porosity, reduced effective stress, and lower deformation compared to top pouring.
- ProCAST simulation can accurately predict casting defects, effective stress, and displacement, providing a reliable basis for process selection.