Sand casting has been used in manufacturing industries for hundreds of years and is still one of the most common ways to make cast parts. Manufacturers like it because it can be used in many ways, is inexpensive, and can withstand high temperatures, among other things. In this guide, we’ll discuss sand casting and its process.
Table of Contents
What is Sand Casting
Sand casting, which is also called “sand molding casting,” is a process in which liquefied metal is poured into a sand mold, which has a hollow cavity of the required shape and is then allowed to harden.
It’s generally accepted that sand casting has a wide range of possible applications. Sand castings can use various metals to create castings of varying sizes and weights that have very complicated shapes. The most defining characteristic of sand casting is the use of sand as the molding media.
Sand casting is suitable for high-melting-point metals like steel, nickel, and titanium. This is the best casting method you can use with these components. For this reason, the automotive and aerospace industries have embraced technology as the standard for manufacturing low-cost, small-series components.
Leisheng Machinery is a Professional Sand Casting Manufacturer in China, founded in 1991. If you are looking for sand casting service for your projects, feel free to get quotations
The Process of Sand Casting
Sand casting is an easy process, but it still takes time, planning, and accuracy. Below are the detailed steps in the process of sand casting & video guidance.
Step1: Making the Pattern
In the process, a reusable pattern is used with the same details as the finished product. Patterns are always made bigger than the final part, so there is room for the part to expand or contract as it warms or cools. The shrinking that happens when a casting cools to room temperature is taken into account by the shrinkage allowance.
When a liquid metal turns into a solid, it loses some of its volumes. This is called liquid shrinkage. To make up for this, the mold has a riser that fills the casting with molten metal. Solid Shrinkage: A metal shrinks in size when it loses its solid state temperature. So that this is taken into account, shrinkage allowance is built into the patterns.
The machining allowance is for the extra material that will be cut away so the product can be finished. This process will get rid of the rough surface of the cast item. The machining allowance depends on the size, properties of the material, the accuracy of the finish, deformation, and method of machining. So that the pattern can be safely removed, all of the surfaces parallel to the direction of pattern removal are tapered slightly inward. It’s called “draft allowance.”
Step2: The Metal Delivery System – Incorporating the Sand and the Pattern in Gating System
The pattern also has metal channels that will feed the cast product design with the right gates and risers. This controls the flow of the metal and lets the gas out while pushing the inevitable thermal contraction in the right direction (other than the finished product itself).
Patterns can be made of expandable polystyrene (EPS), wood, synthetics, metal, and other materials, depending on how many are needed and how accurate they need to be. In other cases, like pipe fittings, the part must be hollow on the inside. When this happens, you need to make what are called “cores,” which are extra patterns.
Step3: Mold Creation
In this case, the sand is formed around the pattern as a refractory material. Sand is known to be stable at high temperatures. It is strong enough to support the molten metal weight during the casting process and is not affected by the metal, but fragile enough to be easily separated from the cast metal once it has cooled.
A mold can also be made by machining a cavity of the desired shape into a solid block of sand. During product development, the method is frequently used because it allows for easy management and implementation of design changes or eliminates the need to store or maintain a physical pattern for rarely used parts.
The mold is typically made up of the top (or “cope”) and the bottom (or “drag”). When the sand has hardened (the old-fashioned way, without machinery), the two halves are separated, and the design is removed. A refractory coating is applied to the mold to smooth out the surface and prevent damage from the turbulence when the metal is poured. After reassembling the pieces, a hole will be visible in the pattern’s shape.
Cores are an optional addition to molds that can be used to create channels or cavities inside the finished product.
Step4: Pouring the Liquefied Metal Into the Mold
Liquefied metal is then poured into the static mold. During this step, the risers and the finished part are defined as the molten metal that fills the cavity. The casting receives molten metal from the risers. Because they are supposed to solidify and cool last, any shrinkage and possible holes are more likely to happen in the riser than in the section that is supposed to be filled.
‘Tilt pouring’ can refer to several different techniques. It’s a method for making the metal poured into the casting without any turbulence. Reduced turbulence lessens the likelihood of oxide formation and casting defects.
With this method, you can make almost any kind of metal you can think of. Argon shielding is one method for preventing air from coming into contact with molten metal, which is necessary for materials that react strongly with oxygen.
Step5: Shakeout Process
Once the casting solidifies and cools, it contains the item that was wanted and the extra metal needed to make it. During a shakeout, the sand is broken up. A lot of the sand that was used to make the mold is collected, cleaned up, and used again
Step6: Final Operation
The gates, risers, and runners are cut out of the casting, and if needed, the casting is finished with grinding, sandblasting, or other methods to get it to the right size. Sand castings may need extra work to get them to their final sizes or tolerances.
Parts can be made more stable or have better qualities by being treated with heat. Testing that doesn’t hurt the object is another option. Some kinds of inspections are fluorescent penetrant, magnetic particle, x-ray, and others. Before shipping, finalizing sizes, alloy test results, and non-destructive testing (NDT) is done.
Types of Sand Used in Sand Casting
The following are the different types of sand used in casting:
Green Sand
As the name implies, it is sand or sandstone with a greenish color. It is composed of roughly 6% to 8% of water and around 18% to 30% of clay-coated silica sand. It is pliable, lightweight, and permeable, bonded by water and clay furnishing. ( for detailed green sand casting, please view “What is green sand casting” )
Pros
- Simple casting process.
- Readily available.
- Lower production costs.
- Higher production rate.
- Keep its form and impression under pressure.
- It can be used in the casting of both ferrous and non-ferrous materials.
Cons
- More casting defects.
- Bad casting dimensions.
- Rough surface quality.
- Unstable casting quality.
Resin Sand
When you mix resin sand with water and heat it, you get a solid mold with a smooth surface. A solid mold means that there will be fewer bad castings, but it will cost more and take longer to make. Resin sand molds take longer to make than green sand molds because they need to be mixed and burned to make the right shape. Resin sand is much more expensive, and even though the resin can be used again and again, it needs to be replaced all the time. This adds to the cost of the process.
Pros
- Sand made from resin is easy to move around and packs down well. Using the above feature, you can change how long it takes to eject.
- After it gets hard, resin sand is very strong. This will make it less likely that the resin sand will change shape when it is cast.
- Less bad castings.
Cons
- Quite expensive.
- Slower production than green sand.
- When resin sand is cast and molded, it gives off an unpleasant smell.
Water Glass or Sodium Silicate
Sodium silicate is ideal in casting that requires a cavity. By passing CO2 through it, it is easy to change from a liquid to a solid. This dehydrates the sodium silicate. The water glass must be combined with other materials to remove the core during product breakdown. The core will be trapped in the casting if the mixture is incorrect.
Pros
- Even semi-skilled workers can handle the casting process using sodium silicate.
- It is very versatile.
- It can be used for long production.
- The effect of the distortion is minimal.
- It produces an impressive surface finish.
Cons
- It is expensive.
- It requires a very thorough mixing of the materials.
- Gathering the materials needed is not easy.
- Poor surface finish due to over-gassing.
- Without a sand reclamation plant, the sand can’t be used again.
Loam Sand
Loam sand is a type of molding sand that contains 50% of clay. It combines clay, sand, and water in equal quantity to produce a thin plastic paste. This type of sand is used in producing large casting
Pros
- It is recommended for small quantity production.
- Ideal for molding cylindrical, conical shapes, and domed like large bells, cylinders, etc.
- A strickle can replace expensive and time-consuming large patterns for the caster.
Cons
- It is not recommended for large quantity production.
- The process is used less often because it requires great technical skills.
The Benefits of Using Sand Casting
Can Be Produced in Ferrous or Non-Ferrous Alloy
Sand castings are easy to make in almost any ferrous or non-ferrous alloy. Melting and pouring super-alloys in a vacuum is done with some other casting methods but not with sand casting. Some materials can’t be “worked,” so they have to be cast instead.
Minimal Tooling Cost
Sand casting is a good choice for low-volume needs because the cost of tools is low. Patterns wear out, so the material chosen for the pattern (usually plastic, wood, or metal) depends on how often the part being made is expected to be used. Even though it may not be cheaper in the short term, machined (or “patternless”) molds may be a good idea for parts that are expected to be used less often over a longer period.
Flexible
Sand casting provides flexibility without compromising the level of detail that can be achieved, in contrast, to die casting, which restricts the design complexity achieved by fabricating from a block of flat sheet steel.
Versatile
Sand castings can be made to weigh anywhere from a few ounces to more than 200 tons. Cores can be used to put internal structures in place. Most shaped parts depend on the designer’s creativity. On the other hand, most sand castings will need at least some of their surfaces to be machined, either because of how the process works or because they need to fit with other parts.
Produces High Volume at Low Cost
Sand casting may be good for a one-off run because the cost of making the tools is often low. On the other hand, this process is used to make car parts, so it could also be used in high-volume applications. When choosing this casting process, other things, like design and tolerance, are often more important than quantity.
Fast
Compared to investment casting, the sand casting process may be faster. But, when figuring out total lead times, it’s important to consider processes like machining that may be needed after casting.
Stand With High Temperature
Casting sand can stand up to very high temperatures, making a sand casting one of the few ways to work with metals like steel, titanium, and nickel with very high melting points.
Simple Casting Process
The process involves simple steps creating a pattern, pouring the liquefied metal, allowing it to cool, and removing it from the cast. You will produce high-quality products that meet your requirements with suitable materials.
Can Capture Complex and Detailed Design
The force exerted by the flow of the molten metal into the cavities is extremely powerful, and it is this force that precisely captures the intricacy and detail of any given component.
Sand Casting Application
Sand casting is used in so many different ways that it is hard to keep track. It can be used to make almost any complex part because it can be cast in many different ways. This process is used to make almost every modern technology. Here is a list of just a few of the things that can be made with sand casting, which shows how many different things it can be used for
Sand casting is used to manufacture the following products:
- Agricultural machines
- Automobile parts
- Blowers/impellers
- Cams, bushing, and bearings
- Electronic equipment
- Engine blocks
- Gas/oil tanks
- Many kinds of pistons and valves
- Medical equipment
- Mining equipment
- Most hardware
- Screws, nuts, and gears
- And a lot more
Sand casting is not nearly as precise as investment casting, but it is a low-cost, simple way to make things that have been used for a long time and has proven to be an important part of modern manufacturing. If investment casting is too hard to do or you need big parts, you might want to add sand casting to your production line.
Sand Casting Services
Looking for a trusted manufacturer who can provide Sand Casting Services is very important for your metal parts. It’s only can effect your metal parts quality, but also the time needed.
Leisheng Machinery is a World Leading Sand Casting Foundry founded in 1991. Also an ISO9001:2015 certificated company. Providing a variety of sand casting methods and materials. If you are interested & need quotations, please feel free to contact us
