Abstract:
The protective parts used in oil drilling machines serve a crucial role in safety protection. This paper focuses on ductile iron protective parts and employs a combination of Pro/E and ProCAST software to numerically simulate the casting process of the original investment casting. The objectives are to identify the causes of casting defects such as shrinkage and dispersed shrinkage, improve the gating system, and study the effects of pouring temperature, filling speed, and shell preheating temperature on casting quality. Optimal process parameters are obtained through analysis, and numerical simulation verifies a significant reduction in the casting’s shrinkage rate, which is further confirmed through actual casting production.
1. Introduction
Protective parts, as vital components of oil drilling machines, play a significant role in ensuring safety. Ductile iron, known for its high strength and good ductility, is commonly used to manufacture these parts. However, defects such as shrinkage and dispersed shrinkage often occur during the investment casting process, affecting the quality of the castings. This paper aims to optimize the investment casting process for ductile iron drilling machine protective parts by numerically simulating the casting process and analyzing the impact of various process parameters.
2. Structure of Ductile Iron Drilling Machine Protective Parts
The ductile iron protective parts for drilling machines are important components that provide safety protection. The casting has a relatively simple structure with uniform wall thickness, averaging 20 mm. It is a hollow cylinder with three asymmetrical slots on one end, eight through-holes between the two end faces, and tooth-shaped grooves on the outer contour. The outer dimensions of the casting are 148.49 mm × 148.49 mm × 71.1 mm. The material of the casting is QT600, with specific chemical compositions and mechanical properties as summarized in Table 1.
Table 1: Chemical Composition and Mechanical Properties of QT600
| Chemical Composition (mass fraction, %) | Mechanical Properties |
|---|---|
| C: 3.0 ~ 3.5 | Tensile Strength ≥ 600 MPa |
| Si: 2.4 ~ 2.8 | Hardness: HB 190 ~ 270 |
| Mn: 0.3 ~ 0.5 | Density: 7,300 kg/m³ |
| S: 0.03 ~ 0.035 | Solidification Temperature Range: 1,129 ~ 1,194 ℃ |
| P < 0.1 | |
| Mg: 0.045 ~ 0.050 |
3. Investment Casting Process Design
3.1 Gating System Selection
Based on the structural characteristics of the ductile iron protective parts, which are straight-cylinder-shaped with thick walls, the gating system adopts a combination of a sprue, runner, ingate, and vent to improve production efficiency and ensure sequential solidification, thereby preventing defects such as shrinkage and dispersed shrinkage.
3.2 Determination of Filling Speed
The filling speed is calculated using the Carlkin formula:
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where v_{充} is the minimum allowable rise speed of the metal liquid level in the mold cavity (cm/s), h is the height of the casting (cm), δ is the wall thickness of the casting (cm), and T is the pouring temperature (℃).
The calculated filling speed is 0.4577 m/s, and after comprehensive consideration, it is set to 0.458 m/s.
3.3 Main Process Parameters
The main process parameters for investment casting are summarized in Table 2.
Table 2: Main Process Parameters for Investment Casting
| Parameter | Value |
|---|---|
| Alloy Pouring Temperature | 1,300 ℃ |
| Filling Speed | 0.458 m/s |
| Shell Preheating Temperature | 900 ℃ |
| Shell Material | Refractory Quartz Sand |
| Binder | Silica Sol |
| Cooling Method | Natural Cooling |
4. Initial Process Numerical Simulation Results and Analysis
4.1 3D Modeling and Mesh Division
The 3D model of the ductile iron protective part was created using Pro/E software. Based on this, the 3D model of the gating system and mesh division were completed, resulting in a total of 67,010 nodes for the casting.
4.2 Simulation Parameter Settings and Results Analysis
The material and boundary conditions were set in ProCAST software. The heat transfer coefficients were determined based on experience and typical values: 1,000 W/(m²·K) between the shell and casting, 1,000 W/(m²·K) between the casting and air, and 50 W/(m²·K) between the shell and air. The casting gravity direction was set to the negative X-direction with a value of 9.8 m/s².
The initial filling process and solidification situation were simulated, and the results showed that the metal liquid was injected smoothly, with minimal impact on the mold cavity wall. The filling process and solidification sequence were analyzed, and it was found that shrinkage and dispersed shrinkage defects were prone to occur in the sprue, ingate, and their connecting parts, with a shrinkage rate of 13.2603%.
5. Process Optimization and Simulation
5.1 Defect Analysis and Modification of the Initial Process Scheme
Based on the numerical simulation results of the initial scheme, it was found that the area around the sprue, ingate, and their connecting parts were prone to shrinkage and dispersed shrinkage defects. Two optimized schemes (a and b) were proposed, by adding additional ingates on the rectangular side and the pipeline part, respectively.
5.2 Results and Analysis of Different Process Schemes
The shrinkage distribution of the two optimized schemes was simulated, and the results showed that the shrinkage rate of scheme a was 6.9025%, and that of scheme b was 1.3675%. Scheme b had the lowest shrinkage rate and no shrinkage defects in the casting body, making it the more reasonable option compared to scheme a and the initial scheme.
6. Optimization of Casting Process Parameters
To further improve the casting quality, an orthogonal experiment was conducted to study the effects of pouring temperature, filling speed, and shell preheating temperature on the shrinkage rate of the casting. The factors and levels of the orthogonal experiment are summarized in Table 3.
Table 3: Factors and Levels of Orthogonal Experiment
| Factor | Level 1 | Level 2 | Level 3 |
|---|---|---|---|
| A: Pouring Temperature (℃) | 1,250 | 1,280 | 1,300 |
| B: Filling Speed (m/s) | 0.450 | 0.455 | 0.460 |
| C: Shell Preheating Temperature (℃) | 800 | 900 | 1,000 |
Nine experimental schemes were designed based on the orthogonal experiment, and the finite element modeling and numerical simulation were completed for each scheme. The filling time and shrinkage rate of each scheme were recorded and summarized in Table 4.
Table 4: Orthogonal Experiment Schemes and Results
| Test No. | Factor A | Factor B | Factor C | Filling Time (s) | Shrinkage Rate (%) |
|---|---|---|---|---|---|
| L1 | 1 | 1 | 1 | 4.881 | 1.451 |
| L2 | 1 | 2 | 2 | 3.925 | 1.433 |
| L3 | 1 | 3 | 3 | 3.869 | 1.442 |
| L4 | 2 | 1 | 2 | 3.961 | 1.551 |
| L5 | 2 | 2 | 3 | 3.918 | 1.452 |
| L6 | 2 | 3 | 1 | 3.869 | 1.402 |
| L7 | 3 | 1 | 3 | 3.820 | 1.589 |
| L8 | 3 | 2 | 1 | 3.771 | 1.370 |
| L9 | 3 | 3 | 2 | 3.858 | 1.321 |
Based on the nine experimental schemes designed through the orthogonal experiment, finite element modeling and numerical simulations were conducted for each. The recorded filling times and shrinkage rates for each scheme have been summarized in Table 4 above.
Analysis of the orthogonal experiment results reveals that the combination of factors providing the lowest shrinkage rate, indicating higher casting quality, is A3B3C1. Specifically, this optimal combination corresponds to a pouring temperature of 1,300°C, a filling speed of 0.460 m/s, and a shell preheating temperature of 800°C. With these parameters, the filling time was 3.858 s, and the shrinkage rate was 1.321%.
The distribution of shrinkage in the optimal casting scheme for the drilling machine protective parts. The shrinkage is minimal and well-distributed, confirming the effectiveness of the optimized parameters.
To validate the simulation results, actual investment casting of the ductile iron drilling machine protective parts was carried out based on the optimized parameters. The obtained castings, exhibited improved quality with a reduced rate of defective products.
7 Conclusion
(1) The ProCAST software effectively simulates the investment casting process of ductile iron drilling machine protective parts. By optimizing the gating system design, including increasing the number of runner and gate channels, casting defects were minimized, providing practical guidance for actual production.
(2) An orthogonal experiment was conducted to analyze the three process parameters affecting the quality of the ductile iron drilling machine protective parts. Based on the principle of minimizing the shrinkage rate for better casting quality, the optimal combination of parameters was determined as a pouring temperature of 1,300°C, a filling speed of 0.460 m/s, and a shell preheating temperature of 800°C. This combination significantly improved casting quality, as verified through both simulations and actual casting production.