In the field of advanced manufacturing, rapid prototyping technologies have revolutionized the production of complex components, particularly in the realm of sand castings. Among these, inkjet three-dimensional printing (3DP) has emerged as a pivotal method for fabricating sand molds and cores due to its efficiency, cost-effectiveness, and ability to produce intricate geometries without residual thermal stresses. As a researcher deeply involved in additive manufacturing for sand castings, I have focused on optimizing key process parameters to enhance the mechanical properties and reduce material waste, thereby improving the overall quality and sustainability of sand castings production. This study delves into the influence of recycled sand proportion, layer thickness, and X-direction resolution on the tensile strength and loss on ignition of 3D printed sand castings molds and cores, aiming to establish guidelines for industrial applications.
The adoption of inkjet 3DP for sand castings offers significant advantages over traditional methods like selective laser sintering (SLS), including faster production times and lower operational costs. However, the performance of printed molds and cores is highly dependent on material composition and printing parameters. In practice, a substantial amount of unused sand is generated during the cleaning process, prompting the need for recycling to reduce costs and environmental impact. By integrating recycled sand into new sand mixtures, we can achieve economical production, but this requires careful parameter tuning to ensure that the mechanical integrity of sand castings is not compromised. This research employs an orthogonal experimental design to systematically evaluate the effects of these variables, providing a data-driven approach to optimize sand castings manufacturing.
To conduct this investigation, I utilized silica sand with a particle size range of 70–140 mesh, commonly employed in sand castings for its refractory properties. The sand particles exhibited irregular shapes, which can influence bonding characteristics. Recycled sand, collected from previous 3DP runs, had a loss on ignition of approximately 0.28% due to residual curing agents. The binder consisted of furan resin, and the curing agent was p-hydroxybenzenesulfonic acid. The printing was performed on an ExOne MAX inkjet 3DP system, capable of handling large build volumes up to 1,800 mm × 1,000 mm × 700 mm, which is ideal for producing sizable sand castings molds and cores. Tensile strength specimens were printed according to standardized dimensions, and their mechanical properties were measured using a hydraulic strength tester after a 24-hour curing period. Loss on ignition was determined by combusting the resin content at high temperatures and calculating the mass reduction percentage.
The experimental methodology centered on an orthogonal array to efficiently explore the multi-factor space. Three critical parameters were selected: recycled sand proportion (Factor A), layer thickness (Factor B), and X-direction resolution (Factor C). Each factor was tested at four levels, as summarized in Table 1. This design allowed for a comprehensive analysis of main effects and interactions without requiring an exhaustive full-factorial approach, which is crucial for practical applications in sand castings production. The response variables included tensile strength (in MPa) and loss on ignition (in %), both of which are key indicators of mold/core quality for sand castings.
| Level | (A) Recycled Sand Proportion (%) | (B) Layer Thickness (mm) | (C) X-Direction Resolution (mm) |
|---|---|---|---|
| 1 | 0 | 0.24 | 0.06 |
| 2 | 30 | 0.28 | 0.07 |
| 3 | 60 | 0.32 | 0.08 |
| 4 | 90 | 0.36 | 0.09 |
The orthogonal experiment comprised 16 trials, with results for tensile strength and loss on ignition presented in Table 2. From these data, it is evident that parameter combinations significantly affect the performance of sand castings molds and cores. For instance, Trial 1 (0% recycled sand, 0.24 mm layer thickness, 0.06 mm X-direction resolution) yielded the highest tensile strength of 3.61 MPa, while Trial 4 (0% recycled sand, 0.36 mm layer thickness, 0.09 mm X-direction resolution) resulted in the lowest loss on ignition of 1.93%. These variations underscore the importance of parameter optimization in achieving desired properties for sand castings.
| Trial No. | A: Recycled Sand (%) | B: Layer Thickness (mm) | C: X-Direction Resolution (mm) | Tensile Strength (MPa) | Loss on Ignition (%) |
|---|---|---|---|---|---|
| 1 | 0 | 0.24 | 0.06 | 3.61 | 3.67 |
| 2 | 0 | 0.28 | 0.07 | 3.10 | 2.67 |
| 3 | 0 | 0.32 | 0.08 | 2.32 | 2.22 |
| 4 | 0 | 0.36 | 0.09 | 1.48 | 1.93 |
| 5 | 30 | 0.28 | 0.06 | 3.02 | 2.97 |
| 6 | 30 | 0.24 | 0.07 | 3.22 | 2.74 |
| 7 | 30 | 0.36 | 0.08 | 1.70 | 1.99 |
| 8 | 30 | 0.32 | 0.09 | 1.82 | 2.04 |
| 9 | 60 | 0.32 | 0.06 | 2.47 | 3.09 |
| 10 | 60 | 0.36 | 0.07 | 1.73 | 2.23 |
| 11 | 60 | 0.24 | 0.08 | 3.03 | 2.72 |
| 12 | 60 | 0.28 | 0.09 | 2.19 | 2.18 |
| 13 | 90 | 0.36 | 0.06 | 2.04 | 2.70 |
| 14 | 90 | 0.32 | 0.07 | 2.27 | 2.17 |
| 15 | 90 | 0.28 | 0.08 | 2.41 | 2.38 |
| 16 | 90 | 0.24 | 0.09 | 2.69 | 2.34 |
To quantify the impact of each factor, analysis of variance (ANOVA) was performed on both tensile strength and loss on ignition data. The ANOVA results for tensile strength, shown in Table 3, reveal that layer thickness exerts the most significant influence (F-value = 217.18), followed by X-direction resolution (F-value = 59.81), and recycled sand proportion (F-value = 9.67). All factors are statistically significant at the chosen confidence level, emphasizing their critical roles in determining the mechanical properties of sand castings molds and cores. Similarly, for loss on ignition (Table 4), X-direction resolution is the dominant factor (F-value = 64.82), with layer thickness also being significant (F-value = 27.9), while recycled sand proportion shows a lesser effect (F-value = 3.89). These findings guide the optimization process for sand castings production, highlighting parameters that require precise control.
| Variance Source | Sum of Squares (S) | Degrees of Freedom | Mean Square | F-Value | Critical Value (α=0.05) |
|---|---|---|---|---|---|
| Recycled Sand Proportion | 0.19371 | 3 | 0.06457 | 9.67 | 4.76 |
| Layer Thickness | 4.34845 | 3 | 1.44948 | 217.18 | |
| X-Direction Resolution | 1.19759 | 3 | 0.39920 | 59.81 | |
| Error | 0.04004 | 6 | 0.00667 | — | — |
| Variance Source | Sum of Squares (S) | Degrees of Freedom | Mean Square | F-Value | Critical Value (α=0.05) |
|---|---|---|---|---|---|
| Recycled Sand Proportion | 0.13103 | 3 | 0.04368 | 3.89 | 4.76 |
| Layer Thickness | 0.93854 | 3 | 0.31285 | 27.9 | |
| X-Direction Resolution | 2.18077 | 3 | 0.72692 | 64.82 | |
| Error | 0.06728 | 6 | 0.01121 | — | — |
The main effects plots derived from the experimental data further illustrate the relationships between parameters and response variables. For tensile strength, increasing the recycled sand proportion leads to a gradual decrease in strength, which can be attributed to the formation of weak interfacial layers on sand particles due to contaminants in the recycled sand. This weakens the adhesive bonds between the binder and sand, a common issue in sand castings when using recycled materials. The effect of X-direction resolution is directly tied to binder content: smaller resolutions correspond to higher binder deposition, enhancing strength but also increasing loss on ignition. This trade-off is crucial for optimizing sand castings molds and cores, as excessive binder can lead to casting defects like gas porosity. Layer thickness inversely affects strength, with thicker layers reducing interlayer bonding and capillary action, as described by the Laplace equation for capillary pressure:
$$ \Delta P = \frac{2\gamma \cos\theta}{r} $$
where $\Delta P$ is the capillary pressure, $\gamma$ is the surface tension, $\theta$ is the contact angle, and $r$ is the pore radius. As layer thickness increases, the effective pore radius decreases, reducing $\Delta P$ and hindering binder penetration, which compromises the integrity of sand castings.
To model the tensile strength as a function of these parameters, I developed an empirical equation based on the experimental data. Assuming linear effects, the relationship can be expressed as:
$$ \sigma_t = \beta_0 – \beta_1 A – \beta_2 B – \beta_3 C + \epsilon $$
where $\sigma_t$ is the tensile strength, $A$ is the recycled sand proportion (%), $B$ is the layer thickness (mm), $C$ is the X-direction resolution (mm), $\beta_i$ are coefficients, and $\epsilon$ is the error term. From the ANOVA results, $\beta_2$ (for layer thickness) is the largest, confirming its dominant role. For sand castings applications, a more refined model might include interaction terms, but for simplicity, this linear approximation suffices to guide parameter selection.
In terms of loss on ignition, the relationship with X-direction resolution is particularly important for sand castings quality. Higher binder content, associated with smaller X-direction resolutions, increases organic material that combusts during casting, potentially causing gas-related defects. Thus, optimizing this parameter is essential to balance strength and casting performance. The loss on ignition can be approximated by:
$$ LOI = \alpha_0 + \alpha_1 C – \alpha_2 B + \delta $$
where $LOI$ is the loss on ignition (%), $\alpha_i$ are coefficients, and $\delta$ is error. The positive coefficient for $C$ indicates that finer resolutions increase $LOI$, while thicker layers reduce it due to less binder penetration.
Based on industry standards for sand castings, which typically require a tensile strength of at least 1.75 MPa and a loss on ignition below 2.2%, I identified optimal parameter sets from the orthogonal trials. Trials 8, 12, and 14 met these criteria, with Trial 12 (30% recycled sand, 0.28 mm layer thickness, 0.09 mm X-direction resolution) offering a balanced combination: tensile strength of 2.19 MPa and loss on ignition of 2.18%. To validate this, I conducted confirmation experiments using these parameters, resulting in a tensile strength of 1.97 MPa and loss on ignition of 2.2%, which adequately satisfies the requirements for sand castings production. This optimal setup enables efficient use of recycled sand while maintaining mechanical performance, contributing to sustainable manufacturing practices for sand castings.
The implications of these findings extend beyond laboratory settings to industrial sand castings production. By integrating recycled sand at 30%, manufacturers can reduce material costs without sacrificing quality. The layer thickness of 0.28 mm ensures sufficient strength while maintaining reasonable print speeds, and the X-direction resolution of 0.09 mm controls binder usage to minimize casting defects. For complex sand castings molds and cores, such as those used in engine blocks or turbine blades, these parameters provide a reliable foundation. Furthermore, the study highlights the importance of parameter interactions; for instance, at higher recycled sand proportions, adjusting layer thickness and resolution becomes even more critical to compensate for strength loss.
In conclusion, this research demonstrates a systematic approach to optimizing inkjet 3DP parameters for sand castings molds and cores. Through orthogonal experimentation and statistical analysis, I have shown that layer thickness is the most influential factor for tensile strength, while X-direction resolution primarily governs loss on ignition. Recycled sand proportion, though less impactful, still plays a significant role in material sustainability. The recommended parameters—30% recycled sand, 0.28 mm layer thickness, and 0.09 mm X-direction resolution—offer a practical solution for producing high-quality sand castings with reduced environmental footprint. Future work could explore additional factors, such as binder chemistry or sand particle morphology, to further enhance the performance of 3D printed sand castings. As additive manufacturing continues to evolve, such optimizations will be pivotal in advancing the sand castings industry toward greater efficiency and innovation.