Sand casting is a metal forming process in which a mold is formed from a 3-dimensional pattern of sand. Molten metal is poured into the mold cavity, and the sand shell is removed after the metal components have cooled and hardened. Some secondary machining processes may be required after casting to improve product accuracy.
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Sand casting is excellent for small production runs. It also offers a great deal of versatility in final product design. There are two types of sand which might be used in the sand casting process, either resin sand or green sand. This article looks at when to select the resin sand casting process.
In resin sand casting, quartz sand is mixed with a resin material. The sand component has very high quartz levels, a very high melting point in the range of ° Celsius, and extremely high hardness levels. The grain shape and surface smoothness of the sand are also important factors. These combined characteristics make raw sand well suited for casting purposes.
A chemical reaction created by the resin serves to bind and stiffen the quartz sand, resulting in quite solid, hard, and strong molds. The resin sand can be used to create the entire mold or just a part of the mold. The final mold can create a wide variety of shapes, configurations and sizes. Typical products made with resin sand castings include cylinder blocks, cylinder heads, hydraulic valve bodies, hardware, electrical contact parts, pulleys, gearbox parts, and landing gear components.
Engineers and product specifiers work with foundry specialists to determine which type of sand casting process is best for their specific application. Key factors to take into consideration include:
Resin sand casting offers the capability of making complex parts in smaller production runs in a very cost-effective manner; however, longer production timeframes might be required. Foundries also have to keep an eye on the cost of the resin, as prices may fluctuate due to global economic factors. Benefits which can be realized from this process, as compared to other casting methods, include:
Sand casting is a type of metal casting manufacturing technique that involves the use of sand to create a mold. Molten metal is poured into the mold to create the final product. This manufacturing process is used to create metal products in a wide range of shapes and sizes.
The sand cast molding process includes several steps. The sand casting process starts with the creation of a mold pattern and a gate system. Each pattern requires a new mold designed to the exact size and shape of the intended part. The setup also requires a two-part casting flask, referred to as cope and drag.
The mold pattern is placed in sand and the gate system is set up with a series of tunnels, a pouring cup, and a sprue. After packing sand around the pattern, the pattern is removed, leaving a mold cavity.
Metal is then heated to a high temperature, turning the metal into a liquid state also known as molten metal. The temperature needed to melt the metal depends on the alloy. Some metal takes longer to heat.
The molten metal is poured into the mold cavity. After the metal is poured into the mold, the metal starts to cool and solidify. To remove the part, the sand mold is separated along a parting line. During this process, the mold cavities are destroyed. However, the mold pattern is typically reusable.
Sand casting involves several components:
These components work together in the sand casting process to create the cavity into which molten metal is poured, solidified, and cooled to form the final cast part.
Using sand to cast metal is the oldest metal casting method and one of the most versatile. The earliest recorded use of sand casting is from around .
It wasn't until the high demand for automobiles and machines that the sand casting process would become fully automated. This increase in demand also led to technological advances in sand casting including increased molding speed and improved strength of the molds.
Image above: A clevis manufactured via sand casting.
Sand molded castings are cost-effective but may not be the best manufacturing process for every product or part. Key things to consider are quantity, budget, production timeline, shape, dimensional accuracy, tolerances, and surface finish.
The main advantages of this casting process include:
One of the most attractive features is that it has the lowest initial setup cost. The process is also easier to modify and reduces the cost of changes to the sand casting mold.
Due to these features, this method of casting is ideal for the fabrication of low- to medium-volume production runs, prototype castings, and the conversion of welded components to castings.
Green sand casting is a type of sand casting that refers to a method involving moist sand for forming the molds.
The sand used for this process is not literally green in color. It is called 'green' due to the moisture but is usually silica sand.
The moisture comes from the clay that is added to the sand. Combining bentonite clay and sand provides a stronger mold as the moisture helps the sand stick together. The sand remains uncured and 'green' when the molten metal is poured into the mold.
Air set casting (no-bake casting) and resin sand molding are two other common casting processes. With air set casting, chemical binders are used to bond the molding sand. Heat is not needed for this process.
Using green sand provides cost reductions compared to other casting processes. However, each process has its advantages. For example, the air set casting method allows for a better surface finish and greater consistency compared to green sand. It is also more costly.
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Resin sand molding involves a mixture of quartz sand and resin. The mixture creates a hard mold and requires no heating.
As with air set casting, resin casting increases costs and production time compared to green sand casting. However, it also produces fewer defects and a smoother finish.
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 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.
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.
When evaluating investment casting services, one major advantage is that they are typically much finer in surface finish compared to sand castings. The smoother finish in investment casting results from the precision molds, while the nature of the sand mold in sand casting often leaves a more textured surface. However, this can also be refined for sand castings with secondary machining methods.
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.
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.
Image above: Commercial stove burner manufactured via the sand casting process.
We offer a variety of sand casting methods and materials to suit your project, including:
Along with these processes, we offer a complete metallurgical analysis. With our state-of-the-art foundry, we can prepare metals for analysis to help reduce casting defects and process inefficiencies.
Our solutions also allow for the use of a wide range of materials including stainless steel, alloy steel, iron, aluminum, magnesium, brass, bronze, and copper. Our equipment includes magma solidification software to reduce or eliminate porosity. We also utilize a coreless induction melting furnace to increase productivity.
Image above: A sand casted and machined product finished with a rust preventing paint. Manufactured by The Federal Group.
Our foundry capabilities have a wide range from 1 lb to 30,000 lbs per piece. Different materials and methods can be used to achieve the ideal result for your casting products:
Castings are made using sand molds formed containing water and organic bonding compounds (typically clay).
Castings are made with resin sand, which is a mixture of quartz sand and resin. Also known as a hard mold, the resin sand becomes very hard and solid after mixing and burning.
This sand casting process involves the use of chemical binders to bond the molding sand at room temperature. Heating is not necessary for this process.
Various metal material can be used for sand casting depending on the application and desired properties of the final product. We use the following materials in our sand castings:
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:
Contact us to discuss your requirements of resin sand casting services. Our experienced sales team can help you identify the options that best suit your needs.