Abstract:
The structural optimization design of the sand spreader for sand casting 3D printing equipment. By addressing the varying printing requirements of different types of sand, the design aims to improve the sanding density, strength, efficiency, and quality of the 3D printing process.
1. Introduction
Sand casting 3D printing technology represents a significant advancement in the foundry industry. It effectively shortens production cycles, enhances casting accuracy, reduces costs, and enables the manufacture of complex structures through digital design, thereby meeting customized demands. Additionally, this technology promotes environmental protection by minimizing material waste, aligning with sustainable development requirements. In modern manufacturing, sand casting 3D printing plays a crucial role in enhancing production efficiency and innovation capabilities.
2. Role of Sand Spreading Device in Sand Casting 3D Printing
2.1 Influence on the Sand Casting 3D Printing Process
The printing quality and efficiency of sand casting 3D printing equipment largely depend on the sand spreading device. A critical indicator for evaluating the performance of a sand spreading device is its sand discharge volume, as well as the density and strength of the spread sand.
Currently, conventional sand spreading devices used in sand casting 3D printing equipment have a fixed sand outlet size of approximately 3mm. With the same sand outlet size, different types of sand result in varying sand discharge volumes and printed product quality. Due to the diversity of sand types available in the market, achieving consistent product quality on a single device necessitates adjustable sand outlet sizes based on the type of sand used. When the sand discharge volume meets the required specifications, the compactness of different sands varies, leading to differences in density and strength. However, for a given product, the density and strength specifications must remain consistent. Thus, an ideal sand spreading device should be capable of compacting different sands to achieve uniform density and strength.
2.2 Existing Issues
The widely used sand spreading equipment in the market currently faces three primary issues:
- Non-adjustable Sand Outlet Volume: For different types of sand, the required sand outlet volume should vary with a fixed sand outlet. This non-adjustability often results in unsatisfactory sand discharge volumes and defective products.
- Lack of Automatic Compaction Mechanism: Manual adjustment of sand spreading equipment parameters based on experience is required in actual production, leading to inefficiencies and numerous issues.
- Improvement Needed in Sand Bed Flatness, Compactness, and Uniformity: Addressing the control of sand discharge volume and varying compaction of different sands is crucial to achieving consistent sand density and strength.
3. Principle and Structure of the New Sand Spreader
To enhance sand spreading quality, control over three aspects is essential:
- Addressing the diversity of sand outlet sizes to ensure compatibility with various sands using a single sand spreader.
- Adjusting the sand outlet size without replacing the sand spreading equipment to improve print quality.
- Ensuring identical sand density and strength for different sands during the spreading process.
3.1 Structural Composition of the Sand Spreading Device
The sand spreading device primarily consists of a sand tank for holding sand. The sand tank is welded from profiles and thick plates. Below the sand tank is installed a V-shaped groove, which connects to a transition groove at the lower part. The transition groove further connects to the sand outlet, formed by maintaining a certain distance between two scraper plates. Inside the transition groove is the V-shaped groove, with a sand outlet at the bottom. Above the V-shaped groove is installed a T-shaped plate, which has threaded holes at both ends. Above the transition groove, there are fixing blocks, and the T-shaped plate and fixing blocks on the V-shaped groove are connected by a spiral scale connecting rod.
At both ends of the sand tank are installed lifting cylinders, with the cylinder arms connecting to both ends of the compacting axis. The compacting axis is supported by bearings on support plates. The lifting cylinders are equipped with force sensors to detect the compressive force between the compacting axis and the sand surface.
3.2 Working Principle of the Sand Spreading Device
The working principle of the sand spreading device is as follows: Sand enters the sand tank through a sand receiving opening. During the sand filling process, a spiral drive motor operates continuously, driving synchronous pulley rotation. The synchronous pulley is connected to the driven wheel at the end of the screw rod via a belt. The turning driven wheel rotates the screw rod, which evenly transports sand to the other end of the sand tank. Once the sand tank is full, the sand spreading device begins to operate. During operation, an eccentric mechanism generates vibration through eccentric rotation, causing sand to flow out through the sand outlet.
4. Methods for Improving Sand Spreading Quality
4.1 Optimizing the Sand Discharge Structure
In practical applications, sand varies in several aspects:
- Types: Ceramsite sand, chromite sand, thermally recycled sand, silica sand, etc.
- Age: Adjusting the amount of resin curing agent based on the ratio of new and old sand.
- Particle Size: Selecting sand mesh sizes based on product precision.
Therefore, different sand types require varying sand outlet sizes.
4.1.1 Adjustable Sand Discharge Volume
The newly designed sand spreader allows for adjusting the spiral scale connecting rod for different sands. The spiral scale connecting rod connects to the T-shaped plate via a threaded scale. The amount of sand discharged from the sand outlet directly depends on the gap between the bottom of the T-shaped plate and the bottom of the V-shaped groove. Different markings on the spiral scale connecting rod correspond to specific gap distances between the T-shaped plate and V-shaped groove. For example, when using thermally recycled sand during printing, the gap between the T-shaped plate and V-shaped groove for ceramsite sand, chromite sand, and thermally recycled sand is 3mm. When using smaller-grained ceramsite sand, the spiral scale connecting rod is rotated to set the marking to 2, adjusting the gap to 2mm. Similarly, when using a mixture of new and old sand, the gap is adjusted to 4mm.
During the printing process, the marking on the spiral scale connecting rod is adjusted based on working conditions and sand type to meet different sand discharge volume requirements.
4.1.2 Automatic Adjustment of Density and Strength
Once sand spreading begins, the lifting cylinders raise the compacting axis to an appropriate position. During sand spreading, friction between the compacting axis and sand surface causes the compacting axis to continuously rotate and compact the sand. Additionally, factors such as varying sand types or external influences may affect the density and strength of the spread sand. At this point, the force sensor on the other end of the lifting cylinder detects the force exerted on the cylinder, feeding back the detection result to the system. The cylinder adjusts the distance between the compacting axis and sand surface based on the required force, ensuring uniform sand compression and meeting density and strength standards. This mechanism was not present in the original equipment.
4.2 Application Effects of Sand Spreading
The proposed sand spreading improvement method significantly enhances the flatness, compactness, and uniformity of the sand bed. Table 1 presents the sand mold density statistics before and after the improvement, the sand mold density distribution before and after the improvement.
Table 1. Sand Mold Density Before and After Improvement (g·cm-3)
| Test Block | Before Improvement | After Improvement |
|---|---|---|
| 1 | 1.37 | 1.37 |
| 2 | 1.29 | 1.37 |
| 3 | 1.32 | 1.36 |
| 4 | 1.30 | 1.37 |
| 5 | 1.33 | 1.36 |
| 6 | 1.35 | 1.38 |
| 7 | 1.37 | 1.37 |
| 8 | 1.30 | 1.39 |
| 9 | 1.39 | 1.36 |
| 10 | 1.38 | 1.38 |
The standard density of the sand mold is 1.35 g/cm3.
Before the improvement, sand mold density fluctuated widely between 1.29 g/cm3 and 1.39 g/cm3, lacking stability. Some sand cores had densities below the standard, potentially leading to casting quality issues. After the improvement, sand mold density variation decreased significantly, with a higher consistency within the range of 1.36 g/cm3 to 1.40 g/cm3. The sand core density exceeded the standard, providing a better foundation for casting.
The comparison before and after the improvement shows that effective measures significantly improved sand mold density stability, enhancing casting quality and reducing defective rates in production.