Knowledge

I. Core Characteristics of the Lost Foam Casting Process for Gearbox Housing

 

1. Foam Model Disappearance: This is the foundation of the process. The precise shape of the casting (gearbox housing) is first made into a model using expandable polystyrene or polymethyl methacrylate (EPS or EPMMA) foam plastic. During pouring, the molten metal rapidly vaporizes and replaces the foam model.

2. No-bonding Agent Dry Sand Molding: The foam model is buried in dry sand (without any bonding agent added) such as quartz sand or zircon sand (usually compacted under negative pressure).

3. No Mold Removal or Parting Surface: Traditional sand casting requires a parting surface between the upper and lower sand boxes and considers draft angles for removing the wooden or metal mold. In lost foam casting, the "mold" is the vaporizable foam model, which directly "disappears" in the metal, not limited by the shape of the traditional parting surface. In theory, draft angles can be eliminated.

4. No Core Required: The complex internal cavities, oil channels, waterways, etc., of the gearbox housing, which require a large number of cores to be combined in traditional casting, are directly made on the foam model (including cavity cores) in lost foam casting. The sand naturally fills and supports them, and after pouring, the foam vaporizes to form the cavities. There is no operation or error of inserting cores.

5. Simplified Process: Due to the absence of parting, mold removal, box assembly (upper and lower box combination), and core insertion, the process is greatly simplified.

6. One-time Forming: The "integrated" foam model can precisely integrate structures that originally required multiple castings or were split in traditional casting (such as flanges, reinforcing ribs, bosses, connection interfaces, and complex internal channels) into a single model, ultimately casting it into a single integral casting.

7. Precise Replicability: Foam models can be machined or molded with high precision, accurately replicating complex three-dimensional curved surfaces.

8. Environmental Tendency (Relative): There are no harmful bonding agent emissions or waste sand treatment problems from traditional clay sand, sodium silicate sand, or resin sand molding (the sand recovery rate is extremely high).

 

 

II. Main Advantages of Using Lost Foam Casting for Gearbox Housing

 

1. Greatly Increased Design Freedom - Complex Structure Integration:

a. Core advantage! It is particularly advantageous for extremely complex gearbox housings (especially large ones with complex internal flow channels, installation interfaces, multi-bend oilways, reinforcing rib networks, etc.).

b. It can design and manufacture integral parts that are difficult or extremely costly to achieve in traditional sand casting or even precision casting, reducing the assembly or welding processes after separate casting.

c. Topology optimization for weight reduction: More complex topology optimization structures can be boldly adopted to maximize the removal of redundant materials, reducing the weight of the housing without sacrificing strength and rigidity.

 

2. Improved Casting Precision and Geometric Dimensional Stability:

a. Without parting surfaces and core insertion operations, problems such as lower box misalignment, box expansion, and core insertion errors are avoided.

b. The model itself has high precision, and during pouring, the model is completely wrapped and supported by rigid dry sand, with minimal interference from external forces.

c. Result: The dimensional accuracy of the casting can reach CT7-CT9 level (far higher than ordinary sand casting), with good shape and position tolerances and high wall thickness uniformity. It provides a good foundation for subsequent processing.

 

3. Significantly Reduced or Eliminated Machining Allowance:

a. oPrecise dimensions, good surface quality (up to Ra 12.5-25μm), and the requirement for minimal or no draft angles mean that many critical installation surfaces (such as bearing housing flange surfaces, box mating surfaces, etc.) only require minimal machining, sometimes only local pouring points need to be cleaned for assembly. This greatly reduces material loss and machining time costs.

 

4. Excellent Surface Quality:

a. High dry sand compactness, good filling ability of liquid metal under negative pressure, smooth surface, and clear contours. It is less likely to have defects such as sand sticking or scarring. The smoothness that traditional sand casting can only achieve with high-quality coatings and good molding sand is relatively easy to achieve and stable in lost foam casting. The surface roughness (Ra) is usually better than that of sand castings of the same type.

 

5. Simplify production processes and improve efficiency:

a. Significantly reduce tooling (eliminate wooden molds/metal molds, core boxes).

b. Eliminate processes such as sand mixing, box assembly, and core insertion.

c. Significantly reduce the amount of post-casting cleaning work (no flash or burrs, minimal core residue, and easy recovery of dry sand).

d. Overall, shorten the production cycle and increase labor productivity.

 

6. Highly flexible production:

a. Suitable for multi-variety and medium to small batch production (especially for small batches or during the R&D stage). The cost and time for making new foam models are much lower than those for wooden or metal molds.

b. Has significant advantages for single-piece trial production or sample manufacturing.

c. The gating system can be conveniently integrated into the model to optimize the layout.

 

7. Environmental advantages:

a. Dry sand is nearly 100% recyclable with minimal additions.

b. No harmful fumes from organic binders (such as furan or phenolic resins) used in traditional sand casting.

c. Improved working environment and reduced dust hazards (especially the risk of silicosis).

d. Significantly less waste sand compared to traditional sand casting.

 

8. Reduce casting stress:

a. The cooling rate of the casting in dry sand is relatively uniform, resulting in less stress tendency compared to cold-hard sand casting methods.

 

Summary and key points of application

For products like reducer housings that require structural complexity, geometric precision, lightweight design, and medium to small batch production (especially on the smaller side), lost foam casting offers a highly competitive solution. Its greatest value lies in the liberation of design freedom (integration of complex structures), improvement in manufacturing precision, and significant reduction in subsequent processing costs.

 

However, this process also has strict requirements for the early stage foam model making (precision, density, coating control), gating system design, process parameters (negative pressure, pouring temperature), and control of casting metallurgical quality (preventing carbon increase, porosity). The development of early-stage molds (foam mold foaming molds) is a key investment. When the shell wall thickness is particularly thick and the production volume is extremely large, a comprehensive cost-benefit analysis with traditional high-pressure casting or hard mold casting is necessary.

 

Overall, within the appropriate range of reducer housing products and production capacity, the lost foam casting process, with its characteristics of high integration of complex structures, high precision, minimal machining allowance, and clean production, can provide high-quality, high-performance, and competitively priced solutions.

 

China Vigor has more than 20 years of experience, a strong technical team, and production capabilities in lost foam casting technology. If you have any questions, demands, related parts development, or to improve your supply chain, please feel free to contact us at info@castings-forging.com