The term “Sand Casting” can be used to describe the final product and the process to make it. It is a metal casting process done at a place called a “Foundry”. It has stayed as one of the oldest processes. Sand is used as the mould material in this metal casting technique.
Sand casting is a widely used metal casting process that involves creating a mold from a mixture of sand and a binding agent, such as clay. This technique is employed to produce complex metal parts of various sizes and shapes.
The process of sand casting is used to create more than 60% of the metal castings we see in our day-to-day lives. Let us learn the complete definition and process of the technique in this article. We shall also learn the characteristics, advantages, and disadvantages of the process.
This blog provides an overview of the complete sequence of steps involved.
What is Sand Casting?
Sand casting is a widely used metal casting process. A mold is created by compacting sand around a pattern of the desired object. Molten metal is then poured into the mold, allowing it to solidify. After cooling, the sand is removed, revealing the cast metal object. It’s versatile, cost-effective, and suitable for various shapes.
In sand casting, molten metal is poured into a cavity in a disposable sand mould containing a hollow chamber of the desired shape, where it solidifies to create the cavity-shaped component. Clay, epoxy, plaster, metal, and concrete are all examples of casting materials.
The castings produced have exceedingly complicated geometries in a wide range of sizes and weights. The process is often referred to as a sand moulded casting. Metals with high melting temperatures like titanium, steel, and nickel are suitable for sand casting.
The only casting method that works with these materials is this. As a result, the technique is the best option for manufacturing affordable and small parts in the automotive and aerospace industries. The animation below shows the process.
Elements in Sand Casting
Before we learn the steps involved in the process, it is important to understand the parts or the elements used in the casting process. Refer to the sand casting diagram below as you learn about the elements.
Fig 1: Sand Casting Diagram
- Cope and Drag: The top and the bottom part of a casting arrangement are called cope and drag respectively. They are usually wooden frames
- Riser: A riser is often called a feeder. It is a reservoir and a passage included in a metal casting mould to avoid shrinkage of metal.
- Runner: A runner is a channel with a reduced diameter used to allow the flow of molten metal towards the cavity.
- Mould: It is a cavity made out of a pattern (copy of the final desired cast) which is mostly made of sand.
- Core: The core in sand casting is a device inserted into the mould cavity to create interior features in the casting such as holes.
- Gate: It is the point at which the metal reaches the mould cavity and starts to flow into it.
- Base Sand: This is also known as foundation sand and is the purest form of sand (silica).
- Binders: The glue that holds the sand grains together is the binding agent. The most common types of binders are clay & water, Oil, Resin, and Sodium silicate.
Step 1: Produce a Pattern
The pattern is used to create a cavity in the sand the size and shape of the part being cast.
Patterns are reused, unlike the sand mold itself. Inexpensive patterns can be made in wood or plastic, or for greater durability, aluminum. Patterns are often made in two pieces, each slightly larger than the part being cast to allow for shrinkage as the metal cools. Vertical walls of patterns have a slight angle or “draft” so the pattern can lift out without pulling sand away.
Step 2: Form Two Halves of the Cavity
One half pattern is placed in a box where sand is packed around it. The pattern is positioned so it can be lifted out afterward, which means the cavity only reproduces half of the pattern, and there can be no re-entrant features.
This process is repeated for the other half pattern. Additional inserts are added that will provide channels for the metal to flow into the cavity. The dimensions of this “gating system” determine how fast the cavity fills. Higher flow reduces the risk of nonfills, but at the cost of increased turbulence, which can cause casting defects.
The traditional sand casting process used “green” sand. This refers to it being damp, rather than the color. Green sand contains bentonite clay, which binds the grains together. Today, most sand casting is done with resin sand. This is sand that has been coated with a resin binder. It forms denser, stronger molds and more accurate cast parts.
Step 3: Insert the Cores
Cores take up space within the mold cavity that would otherwise be filled with metal. They are usually made from sand and are placed into the cavity before the top and bottom halves are joined.
Step 4: Assemble the Cope and Drag
The drag is the lower sand cavity, the cope is the upper piece containing the metal feeding channels. Together, the assembly is called a flask. Pins ensure good alignment between the two halves. The region in the cavity where the two sand surfaces meet will form a parting line on the cast part.
Step 5: Pour the Molten Metal
Metal flows into the cavity from a pouring basin on the top surface of the mold. As the cavity fills, metal rises up in a channel called the riser. This forms a reservoir that gets drawn back into the cavity to compensate for shrinkage.
Copper, bronze, brass and iron tend to pour and flow readily, but some other alloys are less fluid and some, like aluminum, can react with the sand. This is minimized by reducing exposure to air and adding fluxes to the molten metal.
Step 6: Demold and Knock-Out
After pouring, the metal is left to cool and solidify. On completion, the sand molds are removed from the flask and the cast parts knocked out. This also breaks up any cores incorporated into the mold.
The gating system and riser are then cut away, leaving metal castings that are ready for machining.
Sand Casting Applications
As we know that 70% of the metal castings are from the sand casting process, some of the commonly known sand casting products or parts that are manufactured through this process are pump bodies, bushes, pistons of air compressors, Impellers, engine crankcases & oil pans, gears, flywheels, and gas & oil tanks.
- Mining and Construction: Sand casting is utilized in the mining and construction industries to produce equipment components, such as crusher parts, dragline teeth, excavator buckets, and wear-resistant plates.
- Marine Industry: Sand casting is used in the marine sector to manufacture marine engine parts, propellers, boat fittings, and other components required for marine vessels.
- Railways: Sand casting is employed in the railway industry to produce components like railway wheels, brake system parts, and couplings.
- Agriculture and Farm Equipment: Sand casting is used to manufacture parts for agricultural machinery, including tractor components, plowshares, and irrigation system parts.
Difference Between Die Casting and Sand Casting
Die casting involves forcing molten metal into a mold under high pressure, producing intricate and precise shapes with smooth surfaces. In contrast, sand casting employs a mold made of compacted sand to create more complex shapes but with a slightly rougher finish.
| Aspects | Die Casting | Sand Casting |
| Process | Molten metal forced into a metal mold | Molten metal poured into a sand mold |
| Mold | Permanent mold made of steel or other | Temporary mold made of green sand or other |
| Complexity | Suitable for complex and intricate shapes | Better suited for simpler shapes and larger objects |
| Surface Finish | Excellent surface finish and dimensional accuracy | Rougher surface finish and less precise dimensional accuracy |
| Speed | High production rate | Lower production rate |
| Cost | Higher tooling and equipment costs | Lower tooling and equipment costs |
| Material | Wide range of metals, including aluminum, zinc, and copper alloys | Various metals, including iron, steel, and non-ferrous alloys |
| Size | Suitable for small to medium-sized objects | Suitable for small to large-sized objects |
| Tolerance | Tighter dimensional tolerances | More flexible dimensional tolerances |
| Automation | Highly automated process | Less automated process |
| Application | Commonly used in industries like automotive, aerospace, and electronics | Widely used in industries like foundries, art, and sculpture |
Advantages of Sand Casting
Due to its diversity compared to the other manufacturing methods, sand casting allows engineers the ability to build complicated parts from a limitless variety of metals and alloys. Here are some of the benefits of sand casting.
- Casted parts might be as small as a few milliliters and grams or as large as metres and many tonnes.
- No other method provides the same options to make intricate shapes as sand casting
- The cost of equipment and tooling is low compared to other manufacturing processes.
- The scrap produced can be recycled back to make another cast.
- It is adaptable and usable for a wide range of materials, from low- to high-melting-point metals.
Robust and Economical
The sand casting process is adaptable to a wide range of alloys, part dimensions, and production quantities. Surface finish is dictated by sand particle size, and accuracy is determined by pattern precision and the alignment between cope and drag.
Limitations of the process are the need for draft angles on vertical surfaces and the parting line at the meeting point between the two halves of the mold. However, for many metal parts, the cost advantages outweigh the expense of machining these features away.
Conclusion
In summary, sand casting stands out as one of the most versatile and widely used metal casting processes due to its simplicity, cost-effectiveness, and adaptability to various shapes and sizes. The six-step process—ranging from pattern making and mold preparation to pouring, cooling, and finishing—ensures that even complex designs can be realized with precision and efficiency. As industries continue to embrace advancements in materials and technology, sand casting will remain a fundamental technique, offering opportunities for innovation and improvement. By understanding and mastering this process, manufacturers can enhance production capabilities and deliver high-quality castings that meet demand.
References
- H. P. D. Kumar, “Fundamentals of Casting Manufacturing Processes,” Journal of Manufacturing Processes, vol. 19, no. 3, pp. 205-213, 2017.
- R. H. Perry, “Modern Casting: The Engineering of Metal Casting Technologies,” International Journal of Advanced Manufacturing Technology, vol. 94, no. 1-4, pp. 123-136, 2018.
- A. G. T. Rahman, “Materials and Process in Manufacturing,” Engineering Materials and Processes, Springer Nature, 2020.
- A. B. D. R. Smith, “An Overview of Sand Casting,” Casting Technology Review, vol. 32, no. 2, pp. 45-56, 2021.
- M. J. W. Hensley, “Optimization of Sand Casting Process for Efficiency and Quality,” Journal of Mechanical Engineering Science, vol. 235, no. 5, pp. 1107-1116, 2022.
