1. Introduction
Volute products play a crucial role in various industries, such as fluid – handling systems, turbines, and compressors. Their unique curved structure poses significant challenges in the casting process. The design of a three – dimensional casting process for volute products is a complex task that requires a deep understanding of both the product’s geometry and the principles of casting technology. This article aims to comprehensively explore every aspect of this process, from model preparation to the final design of sand cores and molds, with a focus on enhancing design efficiency and product quality.
1.1 Significance of Volute Products
Volute products are designed to collect, pressurize, and direct fluids or gases. In a pump, for example, the volute helps in converting the kinetic energy of the fluid into pressure energy, ensuring efficient fluid transportation. Their complex shape, resembling a snail shell, is optimized to achieve specific fluid – dynamic performance goals. However, this very shape makes the casting process difficult, as traditional casting methods often face issues related to mold extraction and sand core placement.
1.2 Challenges in Casting Volute Products
The main challenges in casting volute products stem from their non – planar and curved surfaces. When using traditional mold – based casting, determining the proper parting and core – making methods is complex. The non – linear maximum contour of the volute wall makes it impossible to use a simple planar parting surface. In 3D – printed core casting, problems such as sand core cleaning, placement, and fixation arise. These challenges can lead to production inefficiencies, increased costs, and potential product defects if not addressed properly.
2. Simplifying the Model Structure
2.1 Identification and Removal of 精加工结构
Before starting the casting process design, it is essential to simplify the volute product model. such as holes and grooves, which are typically added in the post – casting machining process, are removed from the model. Additionally, all fillets except for the main arc – shaped structures are deleted. This simplification is crucial as these features are not directly cast and their removal does not affect the overall structural integrity of the volute during the casting process. A backup of the original model, named “Body 1”, is created for future reference when adding fillets back.
| Structure Type | Reason for Removal | Impact on Casting |
|---|---|---|
| Holes and Grooves | Not directly cast; added in machining | Facilitates mold design; reduces complexity |
| Non – Main Arc Fillets | For aesthetics or stress – relief in final product, not essential for casting | Simplifies model, eases mold extraction |
2.2 Model Visualization and Efficient Simplification
To simplify the model efficiently, it is recommended to view the model in a mode. This allows designers to see hidden structure lines and surfaces, preventing accidental deletion of important parts. By rotating the model, designers can group the structure lines of the features to be removed in a single area with fewer other structure lines. The features can then be selected using a method, and any unwanted selections can be deselected by rotating the model and . This approach streamlines the simplification process, saving time and ensuring accuracy.
3. Designing the Machining Allowance
3.1 Identifying Machining Surfaces
The first step in designing the machining allowance for the volute model is to identify the machining surfaces. This is done by referring to the two – dimensional drawings provided by the customer and marking the corresponding areas on the 3D model with a distinct color. The volute model has a combination of planar, regular arc – shaped, and curved surfaces. Since the spiral – shaped wall is a non – machining surface, the focus is on the other surfaces.
3.2 Further Model Simplification
After marking the machining surfaces, the model undergoes another round of simplification. Structures such as ，small grooves with narrow spacing (which would make it difficult to remove the sand core after adding the machining allowance), and small steps (where the height difference is too small to be distinguishable after adding fillets for smooth transition) are removed. This ensures that the sand core can be easily removed during the casting process.
| Structure to be Removed | Reason for Removal |
|---|---|
| Beveled faces | Difficult to mold and may cause sand core removal issues |
| Small Grooves with Narrow Spacing | Sand core cannot be extracted due to tight space after machining allowance addition |
| Small Steps | Height difference indistinguishable after fillet addition, causing mold and sand core problems |
3.3 Adding and Verifying Machining Allowance
A backup of the simplified model, named “Body 2”, is created. The machining allowance is then added by thickening the marked machining surfaces according to the specified allowance values. As the allowance is added, each surface is marked with a different color. After completing the addition, the model is carefully inspected. If the machining surface color is completely replaced, it indicates that no machining surface has been overlooked. Additionally, by superimposing the model with machining allowance on “Body 2” and viewing it in mode, any machining allowance added on non – machining surfaces can be identified and corrected.
4. Extracting the Volute Model’s Main Structure
4.4 Impact of Additional Structures on Contour Extraction
Volute models often have structures like on their walls for lifting, assembly, and support purposes. These structures can disrupt the extraction of the maximum contour line of the volute wall when using 3D modeling software’s command. The extraction lines may break at the locations of these structures, leading to an incomplete maximum contour line, which is crucial for determining the parting surface.
4.5 Separating and Simplifying the Main Structure
To address this issue, the additional structures on the volute wall are separated from the wall at their . This separation is done without simplifying any structural features or adding new features not shown on the customer’s 2D drawings. After separation, these structures are hidden, and the remaining volute model is the main structure. However, the separation leaves behind on the wall, which can cause the maximum contour line extraction to be discontinuous. To solve this, these are removed, leaving the volute main structure with a smooth and continuous wall surface.
5. Designing the Process Subsidy for the Volute Wall
5.1 Causes and Consequences of Casting Defects
Casting defects such as are common in the casting process，in particular, is caused by impurities in the molten metal, poor gating system design, or foreign particles entering the mold cavity during the production process. Since slag floats to the top of the casting due to the buoyancy of the molten metal, defects often occur on the top surface of the casting.
5.2 Subsidy Design for the Volute Model
For the volute model, due to its conical – shaped lower casting mold during the process and the difficulty of observing if slag or sand particles enter the cavity, an additional subsidy is required on the top surface of the volute wall. The subsidy is added to both the outer top surface and the inner bottom surface of the volute wall. To add the subsidy, a copy of the volute main structure is made. One copy serves as the main structure, and the other is the subsidy body. The subsidy body is then moved by a distance “a” in the direction of the subsidy.
| Subsidy Location | Method of Addition | Purpose |
|---|---|---|
| Outer Top Surface and Inner Bottom Surface of Volute Wall | Copying the main structure, moving the copy, and adjusting non – wall surfaces | Prevent defects; ensure surface quality |
After that, the subsidy body is simplified by removing parts like，and reducing the height of non – volute – wall top surfaces by at least “a”. Finally, the main structure and the subsidy body are combined to form a volute main structure with an inner and outer top – surface subsidy of “a”.
6. Determining the Parting Surface
6.1 General Principles of Parting Surface Selection
For most casting products, the parting surface is usually located at the maximum plane or the maximum contour to facilitate mold extraction. For volute products, the parting surface is typically at the maximum contour of the volute wall. However, due to the spiral – shaped structure of the volute wall, the maximum contour is a spiral curve rather than a flat line.
6.2 Steps for Parting Surface Design
The first step in designing the parting surface for a volute product is to extract the maximum contour line of the volute wall. Using the mold extraction direction as the vector, the maximum contour line is then stretched into a sheet – like structure. The stretching distance should exceed the farthest point of the volute model in the stretching vector direction. This sheet – like structure is then thickened in both positive and negative directions to form a solid structure, which will be the bottom template of either the upper or lower mold.
| Step | Action | Key Points |
|---|---|---|
| 1 | Extract Maximum Contour Line | Use 3D modeling software tools accurately |
| 2 | Stretch the Contour Line | Set appropriate stretching distance; use mold extraction direction as vector |
| 3 | Thicken the Sheet – like Structure | Ensure sufficient thickness for mold bottom template |
The thickness of the bottom template is adjusted according to the sand box size and the required . The side of the bottom template close to the parting surface, which is formed by extending the maximum contour line of the volute wall, is the parting surface. The bottom template is then trimmed to be in the same shape as the volute main structure to reduce the . The bottom surface of the bottom template is also trimmed to be horizontal and higher than the highest point of the volute model. Finally, the previously separated structures are combined with the volute main structure, and fillets are added based on “Body 1” and the customer’s drawings. The bottom template is then trimmed using the volute model with fillets to ensure a proper fit for mold assembly.
7. Designing the Sand Core and Mold
7.1 Sand Core Design for the Inner Cavity
Volute products have a hollow internal structure, which requires the design of a sand core to form the cavity. Since the inner cavity is a continuous spiral – shaped structure, it can be designed as a single, integrated snail – shaped sand core. Core heads are designed at the openings that connect to the outside, such as the bottom – surface circular hole and the pipe opening, for positioning the sand core. However, no core head is designed at the top – surface circular hole to prevent sand from falling into the cavity during the upper – mold process, which could cause defects.
7.2 Ensuring Sand Core Stability
The volute wall is a thin – walled structure, and the position and horizontality of the inner – cavity sand core significantly affect the wall thickness. Due to the non – central position of the sand core’s center of gravity, an internal fixture can be designed to enhance the sand core’s strength, adjust its center of gravity, and guide the core – setting process. This ensures that the sand core is placed accurately during the casting process, maintaining the required wall thickness of the volute.
7.3 Preventing Core Floating
During the casting process, the inner – cavity sand core, except for the core head at the bottom – surface circular hole, floats on the molten iron, which may cause core floating and dimensional deviations in the casting. To address this, a core – marking hole is designed at the pipe – opening core head, and a corresponding pre – embedded core – marking fixture is designed on the mold. This allows the sand core to be accurately positioned in the lower mold, and the middle part of the sand core is fixed by the upper mold pressing on the top – surface circular hole of the sand core.
8. Conclusion
The design of a three – dimensional casting process for volute products is a multi – step and intricate process. By following the steps of model simplification, machining allowance design, main structure extraction, subsidy design, parting surface determination, and sand core and mold design, manufacturers can effectively overcome the challenges posed by the complex shape of volute products. This approach not only improves the design efficiency but also enhances the quality of the final product, reducing the occurrence of casting defects and production costs. Future research in this area could focus on further optimizing these processes using advanced simulation technologies and new materials to meet the growing demands of modern industries.
