

Sand casting is the oldest method of metal casting, where molten metal is poured into a sand mold and solidifies, forming a part. While modern companies like The Federal Group use advanced technologies in sand casting manufacturing, the fundamental techniques have remained unchanged for thousands of years.
An Overview of the Sand Casting Process
There are plenty of reasons why sand casting continues to be an effective metal casting technique. In addition to being cost-effective, sand casting is suitable for a wide range of applications and offers major advantages like versatility and design flexibility.
Pattern Creation
The sand casting procedure begins with pattern creation, where a prototype or model is made from another material like wood, plastic, or metal. The mold cavity is formed by pressing the model into a mixture of sand and binders. It’s typically formed in two parts, the cope (or top) and drag (the bottom). When combined, these form the complete mold for casting.
Pouring the Molten Metal
In the next stage, the molten metal is poured into the mold cavity and allowed to cool. The amount of time it takes to cool depends on factors like the type of metal, the complexity of the shape, and the size of the component. The casting must be properly cooled to achieve the proper specifications and ensure safe handling.
Shakeout and Post-Processing
After the part cools and solidifies, the sand mold is broken apart to reveal the casting. This stage is called the shakeout, where residual sand is removed from the part. The newly cast component then undergoes post-processing, which includes everything from removing excess material to surface finishing and inspection.
Materials Used in Sand Casting and Their Properties
Several types of sand, binders, and additives are used in sand casting. Different materials used in sand casting offer a variety of benefits. By carefully selecting the right combination of materials, sand casting manufacturers can optimize the process to ensure the highest quality parts at the lowest cost to their clients.
Common materials used in sand casting include:
- Silica Sand: The most widely used sand, known for its affordability and ability to withstand high temperatures.
- Chromite Sand: Valued for its high thermal conductivity and stability under extreme temperatures, making it ideal for casting high-performance alloys.
- Zircon Sand: Offers low thermal expansion, ensuring precise castings and minimal defects.
- Resin Binders: Added to hold the sand mold together during the casting process.
- Clay Binders (e.g., Bentonite): Often used to improve mold strength and stability, ensuring the mold can handle the molten metal without breaking.
- Additives (e.g., Coal Dust, Sea Coal): Used to improve surface finish and minimize casting defects.
By choosing the right combination of these materials, sand casting manufacturers can improve both the quality and cost-effectiveness of the final product.
Choosing the Right Sand Type: Green Sand vs. Resin-Bonded Sand
As a mold material, sand has several advantages over other materials. The most important advantage of using sand as a mold material is that it can handle the high temperatures of various molten metals. It’s also inexpensive and recyclable.
In sand casting, green sand and resin-bonded sand are the most common types. Manufacturers choose between these two types based on factors like part size, shape complexity, and surface finish requirements.
Green sand isn’t actually the color green. It’s called green sand because it contains moisture, similar to green wood. The moisture content, which comes from adding clay and water, helps the sand stick together and creates a strong mold. The sand remains uncured and “green” when the molten metal is poured into the mold. This type of sand casting offers greater flexibility and the sand is highly reusable because it’s free of chemical additives.
Resin-bonded sand, on the other hand, uses chemical binders. Some of these resins are self-hardening, but others harden when triggered by heat or a gas catalyst. This type of sand molding provides better dimensional accuracy and a superior surface finish but increases production costs.
Choosing between resin-bonded and green sand castings depends on the specific requirements of your project. Factors like budget and production volume also help determine the type of sand used.
Other Essential Materials: Binders, Cores, and Additives
Anyone who has ever made a sand castle understands that sand needs something added to hold its shape. A variety of materials and techniques are used as binders and additives in sand casting to ensure that molds are stable, detailed, and accurate. While bentonite clay is one of the most commonly used organic binders, binders can include everything from coal and iron oxide to cereal grains and molasses.
Chemical binders, such as phenolic or furan resins, improve the dimensional accuracy of molds and are becoming more commonly used. The type of resin is usually determined by the metal alloy being cast, as different types of resins work better with certain types of metals.
Metal castings that require hollow spaces or complex internal geometries use cores to create cavities, angles, and detailed features that can’t be achieved with the mold pattern alone. Sand cores are typically made with the same binders as the mold itself.
Advantages and Limitations of the Sand Casting Method
Sand casting stands out as one of the most widely used casting techniques in the manufacturing world. However, like any manufacturing method, sand molding has advantages and limitations that are important to understand when determining if it’s the right method for your custom parts.
Pros
Sand casting is ideal for low- to medium-volume production runs, prototype castings, and the conversion of welded components to castings. Sand casting is a highly sustainable manufacturing process, even though each mold is used only once.
The main advantages of sand casting include:
- Lower production cost: Cost effective for low-volume production runs
- Large part capabilities: Suitable for fabricating large parts and components
- Material flexibility: Compatible with both ferrous and non-ferrous metals
- Faster turnaround times: Shorter lead time compared to other metal manufacturing processes
One of the most attractive features of sand casting is the low initial setup cost. It’s also easier and less expensive to modify sand casting molds if your design changes.
Cons
While offering significant benefits like flexibility and cost-effectiveness, sand casting is not a viable option for all applications. Here are some of the major drawbacks to sand casting:
- Rough surface finish: Not suitable for all types of components
- Less dimensional accuracy: Sand casting lacks the precision of other processing methods unless secondary machining is performed
- Likelihood of defects: Additional finishing is often needed to achieve desired specifications
- Quality control: Depending on the specifications of your parts, it can require extensive testing and inspections
When the disadvantages of sand casting are properly understood, manufacturers can overcome them. By making production decisions that mitigate these issues, sand casting companies can help clients enjoy the benefits of sand casting.
What Is Sand Casting Used For?
Sand casting can make metal parts for every size – from small to large pieces. The dimensional accuracy and low cost benefits make sand casting a great solution for a range of products and assemblies.
In addition, sand moulding can form castings with excellent exterior and inner cores. Almost anything that is metal is possible for sand casting. Hollows can be made from moist sand containing molten metal, then cooled.
Below are a few products that are typically produced using the sand casting manufacturing process:
- Axles
- Engine blocks
- Exhaust manifolds
- Gearboxes
- Impeller housing (pictured above)
- Pistons
- Pumps
- Turbine housings
Modern Innovations and Sustainability in Sand Casting
Innovations in sand casting have enabled more complex designs with faster lead times. New binders, better recycling processes, and improved mold pattern technologies have improved the sand casting process while lowering costs and increasing sustainability.
Advances in sand casting have significantly transformed the sand casting process, improving the efficiency of manufacturing and the quality of components. Key innovations include everything from automation of mold handling and pouring and 3D printing to solidification modeling and non-destructive testing (NDT).
Modern innovations in sand casting have also improved sustainability by reducing waste and energy consumption. By recycling sand and using sustainable binders, sand casting manufacturers comply with regulations and appeal to environmentally conscious consumers.
Sand Casting vs. Other Casting Methods: A Comparative Analysis
When evaluating sand casting as an option for manufacturing metal components, it’s important to understand other casting methods like die casting and investment casting. Each method offers distinct benefits and drawbacks, and it’s essential to explore the differences when making informed decisions for your projects.
What’s the Difference Between Die Casting and Sand Casting?
Sand casting is not the only metal casting solution. Die casting is also a viable option for certain parts. Compared to sand casting, die casting may reduce the need for additional tooling.
Die casting also relies on liquid metal or molten metal. Instead of forming a mold cavity in the sand, a steel mold is created in the size and shape of the product; this mold is also referred to as the “die.” The molten metal is forced into the die. After the metal cools and solidifies, the die may be reused, which allows for a quicker cycle compared to casting with sand.
Possible casting defects include pores, hot tearing, and surface projections. These defects are often caused by issues with the manufacturing processes. For example, porosity often occurs when the liquid metal is heated too high or the sand has a low permeability.
Raw castings may also require additional finishing. The surface finish often has a rough texture and with die casting, the finish is smoother. The die also allows for more complex shapes for parts with tight tolerances.
Sand casting is a low cost casting solution especially for low-volume runs. When creating thousands of castings, cost-effectiveness tends to decrease. With die casting, the reusable mold allows for faster production and lower costs, especially when dealing with high-volume orders.
What’s the Difference Between Sand Casting and Investment Casting?
The sand casting and investment casting processes are both used to produce metal parts by pouring molten metal into a mold. Besides that similarity, there are many differences between these two metal casting processes.
Surface Finish
Investment casting typically has a higher quality surface finish in comparison to sand castings. This is because the sand mold in sand casting can produce a more textured surface finish on the final product. Although, the surface finish created by sand casting can be adjusted via secondary machining methods.
Dimensional Accuracy
Sand casting generally doesn’t offer high dimensional accuracy compared to some other casting methods. It’s known for its versatility and cost-effectiveness rather than precision. For tighter tolerances and higher precision, processes like investment casting or die casting are often preferred.
The Molds
If you anticipate any changes to the design of the mold, then sand casting is right for you. Sand casting molds are much easier to adjust than the molds used in the investment casting process.
Conclusion: Is Sand Casting Right for Your Manufacturing Needs?
When selecting a casting method, factors like budget, production volume, and part complexity are crucial in determining the best manufacturing process for your project. TFG specializes in a variety of metal manufacturing solutions and provides assistance with material selection and design optimization.
Contact us today to learn more about sand casting options for your manufacturing needs.
Holly Cacilhas
Quality Manager
Holly has over 18 years of experience in quality and has worked with brands such as Tesla, BMW, and Chrysler. She has led, trained, and managed teams between 25 and 400 people. Holly enjoys camping, boating, and spending time with her family.
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