Abstract: This paper delves into the application of 3D printing in rapid investment casting, showcasing its capability to directly manufacture complex and high-precision castings through digital modeling. This innovative approach reduces the cost of new product development and shortens the production cycle. By taking a small impeller as an example, the paper highlights the groundbreaking application of 3D printing’s light-cured molding process in investment casting, addressing challenges faced in traditional methods. It optimizes traditional casting processes, fostering the widespread adoption of 3D printing across various fields and bringing revolutionary changes to the manufacturing industry, ultimately promoting the high-quality development of the casting industry.
1. Introduction
With the rapid advancement of technology, 3D printing has gradually integrated into various aspects of our daily lives. Within the industrial sector, it has sparked a new production revolution. Investment casting, also known as lost-wax casting, is a precision casting technique utilizing wax molds as the patterning material. This process is known for producing castings with complex structures, uneven wall thicknesses, and high dimensional accuracy, making it widely applied in industries such as aerospace and automotive electronics. However, traditional investment casting faces challenges like long mold-making cycles, high costs, and specific material requirements for molds. 3D printing, which creates objects by depositing material layer by layer, can significantly shorten the mold-making process, reduce costs, and fabricate intricate shapes unachievable by traditional methods. Thus, the integration of 3D printing into investment casting injects new vitality into this traditional craft.
2. Materials Used in Investment Casting and 3D Printing
Table 1. Common Materials for Wax Molds in Investment Casting
| Material Type | Main Components | Melting Point Range (°C) |
|---|---|---|
| Wax-based | Paraffin, stearic acid, etc. | 60~70 |
| Resin-based | Natural resin | 70~120 |
| High-temp | Rosin, beeswax, polystyrene, etc. | >120 |
| Medium-temp (Rosin-based) | Rosin, wax, etc. | 90~110 |
| Medium-temp (Wax-based) | Paraffin, other additives | 80~100 |
Table 2. Melting Points of Common Materials for 3D Printing
| Material | Melting Point Range (°C) |
|---|---|
| ABS | 210~240 |
| PLA | 170~220 |
| PETG | 220~250 |
| TPU | 190~230 |
| Photosensitive Resin | 60~90 |
| Nylon | 235~270 |
Considering the requirement for wax molds to melt during the dewaxing process, the low melting point of materials suitable for 3D printing makes it feasible to use 3D-printed products as substitutes for wax molds.
3. The Process of Applying 3D Printing in Rapid Investment Casting
The application of 3D printing in rapid investment casting mainly replaces two parts of the traditional casting process: mold pressing and wax mold manufacturing.
Taking a small impeller (with a bottom diameter of 100 mm, a top diameter of 26 mm, and a side width of 45 mm) as an example, this section explores the application of SLA (Stereolithography Apparatus) 3D printing in rapid investment casting.
3.1 Digital Modeling
Using modeling software, a digital model is designed and generated. Alternatively, a digital model can be created through reverse engineering or 3D scanning. The digital model file is converted into an STL file, sliced, and processed to generate Gcode. Throughout this process, the focus is on ensuring the professionalism and scientificity of the output model based on the integration of 3D printing and rapid investment casting technologies.
3.2 Printing the Model
Photosensitive resin (with a melting point of 70 °C) is selected as the 3D printing material. The 3D model is imported into the slicing software of the SLA machine, where it is sliced into layers. A scanning path is designed, and a scraper or brush is used to evenly coat the resin on the bottom plate to ensure the flatness and uniform curing of the molded product. The coated resin or mold is placed in the SLA equipment, where UV light activates the photosensitive curing agent, rapidly solidifying and hardening the resin. Final surface finishing (such as sanding and polishing) is done to achieve the desired shape and surface quality.
3.3 Shell Making
Facial and backing coatings are prepared, and the model surface is dipped into the mixed coating and sprinkled with refractory sand. The coating and sand are allowed to dry and harden under specific temperature and humidity conditions, forming a refractory layer. The steps of coating, sanding, and drying are repeated 5 to 6 times to ensure sufficient strength and refractoriness of the shell. During the entire shell-making process, strict control over process parameters is necessary.
3.4 Dewaxing, Firing, and Pouring
The prepared shell is soaked in hot water at 85~95 °C. The heat melts the photosensitive resin-formed model inside the shell, which flows out, leaving a castable mold. The mold is fired at about 900 °C for 1 to 2 hours to further remove moisture, residuals, and impurities. To prevent deformation and cracking during pouring, the mold is compacted with dry sand before pouring to form the required casting.
After further grinding, the actual dimensions of the casting are obtained, as shown in Table 3.
Table 3. Measured Dimensions of the Casting
| Theoretical Dimension (mm) | Actual Dimension (mm) |
|---|---|
| Bottom Diameter: 100 | Bottom Diameter: 99.80 |
| Top Diameter: 26 | Top Diameter: 26.12 |
| Side Width: 45 | Side Width: 45.23 |
The analysis of Table 3 reveals that the theoretical and actual dimensions of the casting are close, with small errors and high accuracy, indicating good integration between rapid investment casting and 3D printing.
4. Advantages of 3D Printing in Rapid Investment Casting
Table 4. Comparison of Advantages of 3D Printing and Traditional Processes
| Advantage | Effect |
|---|---|
| Fast molding speed | Traditional wax molds take an average of 5 days, while 3D printing can complete them in 1 to 2 days |
| High precision | Accuracy can reach 0.5 mm or even higher |
| Strong customization capabilities | Meets over 90% of personalized design needs |
| High material utilization | Material utilization rate can reach over 80%, while traditional methods are around 50% |
- Cost Savings in Development and Trial Production: The combination of 3D printing and rapid investment casting improves product development and trial production efficiency, eliminating the costs of tooling and mold manufacturing, labor, and other expenses.
- Reduced Process Complexity: Traditional manufacturing processes are complex. The integration of 3D printing and rapid investment casting simplifies the process, enabling the completion of tasks that were previously difficult or of low quality.
- Industrial Application: With the development and industrial application of 3D printing technology, efficiency continues to increase, and manufacturing costs decrease, making mass production feasible.
- Increased Production Efficiency and Manufacturing Flexibility: The integration of 3D printing and rapid investment casting effectively addresses issues of low production efficiency and manufacturing flexibility in the past.
5. Conclusion and Outlook
- The SLA process of 3D printing can be tightly integrated with rapid investment casting. Finished products made of photosensitive resin can replace traditional wax molds in investment casting, achieving high precision and satisfactory appearance quality.
- 3D printing is visual, controllable, intuitive, and highly operable, making it well-suited for rapid development and trial production of small-batch new products.
Despite the rapid development and widespread application of 3D printing technology, challenges remain. The cost of 3D printer equipment is relatively high, and it requires professional operation, increasing production costs. Additionally, 3D printing has specific material requirements, and achieving high-precision printing with certain special materials may be difficult.