In traditional sand casting production, skilled workers are required to create sand molds based on drawings and patterns. Processes such as mold making and core making often consume significant labor and time, especially during the development phase of castings, where the production cycle can be considerably extended. For example, when using metal patterns on a production line to manufacture a forklift transmission system housing, the sample development phase typically lasts as long as 2–3 months.
3D printing casting technology offers advantages such as rapid prototyping, elimination of the need for molds, and the ability to print complex sand molds. It is widely applied in metal castings and new product development stages, significantly accelerating the casting research and development speed, reducing process research costs and risks, and achieving personalized, diversified, and rapid development of casting production. Moreover, the printed sand molds have excellent quality, ensuring the castings’ quality. In this paper, we present the application of 3D printing casting in the development of a drive axle housing casting, demonstrating its effectiveness through a real case study.
Process Analysis
The drive axle housing casting is made of material QT500-7, with a mass of 76 kg. The overall dimensions are 730 mm × 411 mm × 362 mm. The main wall thickness is 20 mm, the maximum wall thickness is 48 mm, and the minimum wall thickness is 8 mm. The dimensional accuracy requirement is CT-9. No internal defects that could affect performance are allowed, and the delivery time is 10 days. Due to the complex structure of the bridge housing, features such as heat dissipation ribs on the outer wall of the bridge package and bolt bosses on the connecting plate cannot be directly demolded, requiring several cores to form, which brings great difficulty to the mold design. If traditional resin sand methods were used for development, the cost would be high and the R&D cycle long. Using 3D printing casting eliminates the need for pattern making, offers flexible process design, and saves substantial cost and time. Therefore, 3D printing technology was adopted for sample development.
| Parameter | Value |
|---|---|
| Material | QT500-7 |
| Mass | 76 kg |
| Overall dimensions | 730 mm × 411 mm × 362 mm |
| Main wall thickness | 20 mm |
| Maximum wall thickness | 48 mm |
| Minimum wall thickness | 8 mm |
| Dimensional accuracy | CT-9 |
| Delivery time | 10 days |
3D Printing Technology
The three-dimensional powder binding technology (3DP) works by first spreading a layer of powder, then using a nozzle to spray binder onto the areas that need to be formed, causing the powder material to bond and form a cross-section of the part. This process of powder spreading, spraying, and bonding is repeated layer by layer to obtain the final 3D printed part.
A German Exone-SMAX 3D sand printer was used in this development. The working area of the printer is 1800 mm × 1000 mm × 700 mm, and the printing speed is 60 L/h. The materials used were silica sand, furan resin, and a curing agent. The properties of the silica sand are listed in Table 2. The furan resin addition was 1.2%, the curing agent addition was 0.18%, the layer thickness was 0.28 mm, and the tensile strength of the printed sand mold was 1.6 MPa.
| Property | Value |
|---|---|
| w(SiO₂) / % | > 99.1 |
| Medium sand grain size / mm | 0.13 – 0.14 |
| AFS value | 97 |
| Specific surface area / (cm²·g⁻¹) | 176 |
| pH value | 6.9 |
| Refractoriness / °C | > 1550 |
| Ignition loss / % | 0.2 |
The combination of 3D printing casting technology with high-quality silica sand and binder system ensures that the printed sand molds have sufficient strength and dimensional accuracy, enabling complex geometries that are difficult to achieve with conventional mold making.
Casting Process Design
The drive axle housing casting material is QT500-7, with a casting mass of 56 kg and a pouring mass of approximately 140 kg. The pouring time was controlled within 20–25 s. The casting process is shown schematically in the detailed design description below. A middle injection gating system was adopted, with the gating system cross-sectional area ratio of ∑Fdirect : ∑Fhorizontal : ∑Finternal = 1.25 : 1.5 : 1.
Risers were placed at each hot spot of the casting to provide feeding. A hot riser with a diameter of 120 mm was placed at the root of the connecting plate, and a cold riser with a diameter of 90 mm was placed at the connecting arm area of the frame. Additionally, a chill with dimensions 80 mm × 50 mm × 60 mm was placed on the bottom surface of the connecting arm to improve the temperature field. To ensure core strength, a ø25 mm round steel bar was placed in the center of the core as a core rod. A ceramic foam filter (125 mm × 125 mm × 22 mm, 10 ppi) was placed in the gating system. The layout was one casting per box.
MAGMA software was used to simulate the filling and solidification processes. The simulation results showed that the filling process was stable, with no obvious turbulence or sand erosion (as observed in the simulation). The solidification results indicated no significant shrinkage defects.
| Parameter | Value |
|---|---|
| Casting material | QT500-7 |
| Casting mass (part) | 56 kg |
| Pouring mass | 140 kg |
| Desired pouring time | 20 – 25 s |
| Gating ratio (∑Fdirect:∑Fhorizontal:∑Finternal) | 1.25 : 1.5 : 1 |
| Hot riser diameter | 120 mm |
| Cold riser diameter | 90 mm |
| Chill dimensions | 80 mm × 50 mm × 60 mm |
| Core rod diameter | 25 mm (round steel) |
| Filter specification | 125 mm × 125 mm × 22 mm, 10 ppi |
| Layout | One casting per box |
The simulation also helped verify the feeding efficiency. The relationship between the riser volume and the casting hot spot modulus can be expressed by the following equation applied in MAGMA:
$$ M_{riser} \ge 1.2 M_{casting\;hotspot} $$
where \(M\) is the modulus (volume-to-surface area ratio). For the hot riser placed at the connecting plate root, the modulus calculation ensured adequate liquid metal supply during solidification. The actual pouring time achieved during casting was 19 s, which fell within the desired range.
Sand Mold Design and Production
To ensure the quality of the sand mold production, the design followed these principles: (1) Ensure that there are no dead corners for cleaning sand in any part of the mold; (2) Avoid accumulation of coating during flow coating, or ensure easy cleaning if accumulation occurs; (3) Minimize the number of assembled mold parts to avoid dimensional deviations. The mold was divided into two halves (upper and lower) along the horizontal gate, along with three cores. The lower mold contained the lower part of the casting, the horizontal gate, the filter seat, and the recess for the chill. The upper mold contained the upper part of the casting, the horizontal gate, and the overflow vents. Core #1 formed the internal cavity structure, while cores #2 and #3 formed the mounting holes of the connecting arm.
Based on field experience, the parting line offset for non-flow-coated surfaces was set at 0.2 mm, and for flow-coated surfaces at 0.5 mm. The core print clearance was 0.2–0.5 mm.
Commercial alcohol-based coating was applied by flow coating, and after ignition, the residual heat dried the coating. Manual mold assembly was performed. After assembly, the mold was fastened with bolts and placed into a self-made sand flask, with surrounding molding sand compacted to prevent lifting or running out of metal. A matching pouring cup was placed on top. The mold was then poured. The actual pouring time was 19 s, the pouring temperature was 1400 °C, and the pouring mass was 140 kg.
| Parameter | Value |
|---|---|
| Parting line offset (non-flow-coated) | 0.2 mm |
| Parting line offset (flow-coated) | 0.5 mm |
| Core print clearance | 0.2 – 0.5 mm |
| Coating type | Alcohol-based, flow-coated |
| Drying method | Ignition (heat drying) |
| Mold assembly | Manual, bolted |
| Back-up filling | Molding sand in flask |
Casting Finishing and Inspection
A total of five molds were poured. After shakeout and cleaning, all castings were acceptable (Figure showing the final casting). Three-dimensional scanning was used to check dimensions, and all measured values were within the required tolerances. The mechanical properties met the specification. The surface quality of the castings was superior to that of conventional resin sand products. After sample delivery, machining and bench testing were performed, followed by final vehicle assembly. The entire process was fully compliant. This batch of sample castings, from casting process design to sample delivery, took a total of 9 days.
| Parameter | Result |
|---|---|
| Number of molds poured | 5 |
| Qualification rate | 100 % |
| Dimensional inspection method | 3D scanning |
| Dimensional compliance | Within specification |
| Mechanical properties | Passed |
| Surface quality | Better than conventional resin sand |
| Development cycle (design to sample) | 9 days |
Conclusion
The development of the drive axle housing casting using 3D printing casting technology demonstrates the following advantages:
- Flexibility in process design: 3D printing casting allows casting process design without being constrained by product structure, enabling simplified and innovative designs. Traditional methods would require complex pattern and core box tooling, which is both time-consuming and expensive. With 3D printing casting, the gating system, risers, chills, and cores can be optimized freely.
- Superior casting quality: The printed sand mold exhibits high dimensional accuracy and excellent surface finish. Consequently, the castings produced have better surface quality and fewer defects compared to those made with conventional resin sand processes. The mechanical properties and dimensional accuracy meet all requirements.
- Dramatically shortened development cycle: The entire process from casting design to sample delivery was completed in only 9 days, compared to the typical 2–3 months required for traditional methods. This acceleration is critical for rapid prototyping and time-to-market in new product development.
Moreover, the use of 3D printing casting eliminates the need for physical patterns and core boxes, reducing tooling costs and enabling design changes without additional expense. The technology is particularly well-suited for complex castings like drive axle housings, where internal cavities, intricate ribs, and multiple cores are required. The successful application of 3D printing casting in this case confirms its potential to revolutionize the casting industry for small-batch, high-complexity production.
In summary, 3D printing casting provides a powerful tool for foundries to accelerate innovation, reduce risk, and achieve high-quality castings in a fraction of the traditional time. As 3D printing casting technology continues to advance, its adoption in the production of critical components such as drive axle housings will likely become standard practice.