With the high-quality development initiatives under the national five-year plan, the demand for superior castings aerospace has intensified, focusing not only on external appearance but also on internal integrity. This process improvement targets internal defects such as shrinkage porosity and coarse microstructure in aerospace casting parts, aiming to achieve ideal cooling conditions—specifically directional solidification—to meet Class I casting standards. Through this endeavor, valuable experience has been accumulated for future advancements in castings aerospace.
The market’s escalating requirements for aluminum alloy products are evident, compelling us to enhance our comprehensive casting capabilities. Failure to adapt would limit our growth prospects, whereas embracing high-value, demanding projects is essential for long-term sustainability. This drive for improvement is not just a necessity but a strategic step toward securing a competitive edge in the aerospace casting parts industry.
The experimental process for refining these castings aerospace involved a systematic approach: initial familiarization with drawings and technical requirements, followed by process formulation and simulation. A review was conducted to identify potential issues, leading to iterative modifications. Upon approval, 3D-printed sand cores were prepared alongside raw materials. Subsequent steps included coating, mold drying, assembly, melting, pouring, and finally, shakeout and post-processing with radiographic inspection. This structured workflow ensured thorough evaluation and optimization.
The component under examination is a complex aerospace casting part, characterized by intricate geometries typical of castings aerospace. Technical specifications mandate that the external surface be free from visible defects such as insufficient filling, gas pores, shrinkage, sand inclusions, and oxidative impurities. Adherence to the QJ3185A-2018 standard for Class I castings is required, with full-body radiographic inspection to validate internal quality. This rigorous standard underscores the critical nature of aerospace casting parts in applications where reliability is paramount.
In the first experimental scheme, the process design incorporated gating and risering systems alongside chill placements to facilitate directional solidification. Differential pressure casting parameters were employed, with key variables including pouring temperature, pressure differential, and cycle time. The simulation of filling and solidification processes provided insights into temperature distribution and defect formation. For instance, the filling sequence was analyzed to ensure smooth metal flow, while solidification modeling highlighted areas prone to shrinkage. The temperature field during solidification can be described using the heat transfer equation:
$$ \frac{\partial T}{\partial t} = \alpha \nabla^2 T $$
where \( T \) is temperature, \( t \) is time, and \( \alpha \) is thermal diffusivity. The solidification fraction \( f_s \) over time can be approximated by:
$$ f_s = 1 – \exp\left(-k t^n\right) $$
with \( k \) and \( n \) as material constants. Simulation results indicated that the gating system functioned effectively, with risers providing necessary feeding. However, radiographic inspection revealed shrinkage porosity at junctions between thick and thin sections, attributed to insufficient riser feeding and localized overheating. Additional factors included excessive pouring temperature and inadequate chill dimensions. A summary of key parameters and observations is presented in Table 1.
| Parameter | Value | Observation |
|---|---|---|
| Pouring Temperature | Higher range | Contributed to shrinkage |
| Chill Width | Insufficient | Limited cooling effect |
| Riser Design | Standard | Inadequate feeding distance |
| Defect Location | Thick-thin junctions | Significant porosity |
The second scheme addressed these shortcomings by modifying chill placements and reducing the pouring temperature by 5°C. This adjustment aimed to enhance cooling rates, shorten feeding distances, and alleviate thermal gradients. The solidification process was re-evaluated using the Chvorinov’s rule for solidification time \( t_s \):
$$ t_s = k \left( \frac{V}{A} \right)^2 $$
where \( V \) is volume, \( A \) is surface area, and \( k \) is a constant. Radiographic results showed minor shrinkage in internal rib areas, but the microstructure appeared finer compared to the initial scheme. This improvement highlighted the role of controlled cooling in refining the grain structure of aerospace casting parts. The relationship between cooling rate \( \dot{T} \) and grain size \( d \) can be expressed as:
$$ d = a \dot{T}^{-b} $$
with \( a \) and \( b \) as empirical constants. Despite progress, residual defects indicated the need for further optimization in chill design and riser efficiency. Table 2 contrasts the two schemes.
| Aspect | Scheme One | Scheme Two |
|---|---|---|
| Pouring Temperature | Higher | Reduced by 5°C |
| Chill Configuration | Basic | Enhanced width and placement |
| Shrinkage Severity | Severe | Minor |
| Microstructure | Coarse | Finer |
In the third scheme, additional chills were positioned at the end faces of internal ribs to target remaining defect-prone zones. Other parameters remained unchanged from the second scheme. Radiographic inspection confirmed the absence of defects and a uniformly dense microstructure, achieving the desired Class I standards for castings aerospace. The success of this approach demonstrates the importance of precise thermal management in producing high-integrity aerospace casting parts. The overall solidification efficiency can be quantified using the Niyama criterion \( Ny \), which predicts shrinkage tendency:
$$ Ny = \frac{G}{\sqrt{\dot{T}}} $$
where \( G \) is temperature gradient. Higher \( Ny \) values indicate reduced shrinkage risk, as achieved in this scheme. A comprehensive analysis of process variables is summarized in Table 3.
| Variable | Scheme Three Value | Impact on Quality |
|---|---|---|
| Pouring Temperature | Optimized low | Minimized superheat |
| Chill Coverage | Extended to ribs | Enhanced directional solidification |
| Riser Efficiency | High | Effective feeding |
| Defect Level | None | Class I compliance |
Reflecting on this comprehensive process, several key insights emerge for improving aerospace casting parts. First, the strategic use of chills effectively mitigates shrinkage by accelerating cooling and promoting directional solidification. Second, chills assist risers by guiding feeding paths and reducing feeding distances, thereby lowering the burden on the riser system. The feeding distance \( L_f \) can be modeled as:
$$ L_f = k_d \sqrt{t_s} $$
where \( k_d \) is a constant dependent on geometry. Third, controlling pouring temperature is critical to avoid localized hotspots that exacerbate porosity. Finally, simulation tools are indispensable for predicting temperature fields and optimizing process parameters in castings aerospace. Continued refinement in these areas will further elevate the quality and reliability of aerospace casting parts, ensuring they meet the stringent demands of modern aerospace applications.
In conclusion, the iterative improvements across three schemes underscore the significance of integrated thermal management in casting processes. By leveraging simulations, adjusting parameters, and implementing targeted chill designs, we achieved a robust process for producing defect-free aerospace casting parts. This experience not only enhances our current capabilities but also sets a foundation for tackling more complex challenges in castings aerospace, driving forward the industry’s pursuit of excellence.