Rapid investment casting process based on SLS

With the continuous rise and popularization of 3D technology, China’s manufacturing industry has gradually achieved upgrading, especially in the mold processing and production, domestic automobile, aerospace and other industries, which has a huge market demand for the integrated manufacturing of new complex structural functional parts and rapid mold manufacturing. At present, due to the need of traditional sand mold technology for mold development, especially in the early stage of parts design and development, the long time of mold design and development has seriously hindered the experimental verification and production equipment of new equipment. According to the existing 3D rapid prototyping technology, in order to meet the diversified needs of the market. The rapid investment casting process not only shortens the development cycle of castings from several months to several days, but also greatly reduces the processing cost compared with traditional manufacturing.

The main process of rapid investment casting based on SLS is as follows: importing the layered CAD model into SLS rapid prototyping computer, manually supporting and cleaning the residual powder of the fired SLS prototype, and testing the SLS After post-treatment, design and adding gating system, through shell preparation, shell baking, alloy casting and other casting processes, the alloy castings meeting the requirements were manufactured. The research content mainly focuses on the application and promotion of rapid casting technology in the early stage of product development in aerospace, ship power, mold and other industries, such as the rapid manufacturing of single test parts, small batch test prototype, and mold required for early product development and test in aerospace and other fields. It can effectively shorten the R & D and manufacturing cycle of new products and reduce the cost of mold design in the early stage.

This paper mainly studies the size error transfer law in the process of rapid casting based on SLS, applies the size error transfer law to compensate the size of complex parts, and formulates the corresponding casting process, so as to shorten the preparation time of qualified wax mold, improve the size accuracy and surface quality of parts, and has important guiding significance for the subsequent production and processing of complex parts.

The rapid investment casting process, particularly when based on Selective Laser Sintering (SLS) technology, represents a significant innovation in manufacturing, combining the advantages of traditional investment casting with the precision and speed of modern 3D printing techniques. This method allows for the production of complex parts with excellent surface finishes and high dimensional accuracy, catering especially to industries like aerospace, automotive, medical devices, and tooling. Here’s an overview of how the process works and its benefits:

Overview of the Process

  1. Design and 3D Modeling: The process begins with the creation of a detailed 3D model of the part to be cast. This model is then used to generate the design of the mold.
  2. SLS of the Pattern: Instead of creating a wax pattern, as is traditional in investment casting, an SLS machine is used to directly 3D print the pattern using a powdered material (such as polystyrene or a special investment casting resin). The laser selectively fuses the powder particles layer by layer, building up the pattern.
  3. Shell Building: The SLS pattern is then coated with a refractory material to create the mold shell. This step may involve dipping the pattern into a slurry of refractory material, then sprinkling it with a stucco material, and allowing it to dry. This process is repeated several times to build up the thickness of the shell.
  4. Pattern Removal: Once the shell is complete and has hardened, the pattern material inside is removed. For patterns made from materials with a low melting point or those that can be chemically dissolved, this can be done by heating the shell (autoclaving) or placing it in a chemical bath, leaving a hollow mold.
  5. Pouring: Molten metal is poured into the hollow mold. After the metal has cooled and solidified, the mold material is broken away to reveal the cast metal part.
  6. Finishing: Any necessary finishing processes, such as machining, polishing, or painting, are performed on the metal part to achieve the desired final specifications.

Benefits of SLS-Based Investment Casting

  • Complex Geometries: SLS allows for the creation of patterns with complex internal structures and fine details that would be difficult or impossible to achieve with traditional pattern-making methods.
  • Reduced Lead Times: Directly 3D printing patterns eliminates the need for tooling production, significantly reducing lead times from design to final casting.
  • Cost Efficiency: For short production runs or prototypes, SLS-based investment casting is more cost-effective than traditional methods, which require expensive molds for pattern making.
  • Material Options: A wide range of materials can be used for casting, giving designers and engineers flexibility in material selection to meet specific property requirements.
  • High Accuracy and Surface Finish: The precision of SLS, combined with the investment casting process, results in parts with high dimensional accuracy and excellent surface finishes.

Challenges and Considerations

While the SLS-based investment casting process offers numerous benefits, it also presents some challenges, such as the need for specialized equipment (SLS machines) and expertise in both additive manufacturing and casting technologies. Additionally, the cost of SLS machines and materials can be high, though this is often offset by the savings in tooling and reduced waste.

The integration of SLS technology into the investment casting process is a testament to the ongoing evolution of manufacturing techniques, offering a powerful tool for producing high-quality, complex parts efficiently and effectively. This approach is particularly valuable in applications where precision, material properties, and design complexity are critical.

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