Several casting methods exist for producing the machine parts required for industrial manufacturing processes, including sand and investment casting . Here, we will explore some key similarities and differences between the two.
Metalworkers widely use sand casting technology because it is suitable for casting steel, iron, brass, and most nonferrous alloys—as well as for final products that weigh anywhere from less than a pound to thousands of pounds. The sand casting process begins with creating a sand mold. In a traditional foundry, after making the desired pattern or model of the final product from hardwood, urethane, or foam, sand is compacted around it to form the mold. In order to maintain its shape, the sand is initially treated with a bonding agent known as binder, which improves adhesion between its particles. The pattern is then removed by splitting the sand mold apart into two or more sections. These sections are then bound to receive the molten metal through a delivery system referred to as the gating system. After the metal sufficiently cools and solidifies, the final product is recovered by removing the sand through a shake-out process.
Some key benefits of sand casting are outlined below:
Also known as lost wax casting, investment casting technology is reliable for complex and detailed components. Metalworkers use it to create a final product with a near-net shape, leading to lesser material, machining, and labor costs compared to other forms of metal casting.
The investment casting method begins with molding wax into the desired cast and coating it with refractory material, such as ceramic. Applying heat melts out the wax, leaving an empty shell with the void to be filled shaped in the geometry desired. Molten metal is then introduced into this pre-heated shell. As soon as it suitably cools and solidifies, it is recovered by shattering the shell.
Some major advantages of employing investment casting include:
Both investment and sand casting have experienced significant improvements over the years—geared at minimizing the quantity of metal used and reducing extensive finishing and machining requirements. Although they are similar in some ways, some notable differences exist between them.
A few similarities between both casting methods include:
There are some fundamental differences between investment and sand casting, including:
The molding cycle for sand casting is short, while the investment casting process takes longer.
The final product from sand casting is usually rough depending on the sand used. Other defects include clip sand, sand wash, and gas holes. Meanwhile, products from investment casting are significantly smoother.
Materials needed for investment casting, such as paraffin wax, sodium silicate, etc., cost more than those required for sand casting (sand, binder, etc.). Sand casting is relatively cheaper.
Metalworkers can achieve more complex designs with investment casting, while sand casting may require extra tapering and machining to achieve the desired geometry. Sand casting patterns are more cost effective and require much less time to modify than the tooling required to manufacture investment castings, if design changes are required during a production run.
With the high dimensional tolerance of investment casting (CT 4-6), finished parts can have thin walls, while finished parts from sand casting have a minimum wall thickness of 3 to 5mm because of their lower-dimensional tolerance (CT 10-13).
The adaptability of sand casting is broad, and as a result, it can be used for a wide range of castings, including ductile iron, grey iron, steel, aluminum, etc. Although investment casting can be used for other metallurgies, they are generally suitable for steel castings.
Since investment casting can ensure consistency, it is suitable for mass production. Sand casting, however, cannot promise such consistency. Hence, mass-producing finished parts are more challenging using sand casting methods.
Knowing the appropriate method requires you to put some factors into perspective. Different materials are well suited for different products. Therefore, you must know the materials suitable for your product since it can help you determine the better-suited casting method. You must also consider the possibility of mass production and that each casting method requires different cycle times to inform your decision. Additionally, the overall casting cost must be considered. Ultimately, it is up to you to select the method which overall casting benefits for your project or application.
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