Shell Molding




Shell molding

  • Shell molding, also known as shell-mold casting, is an expendable mold casting process that uses resin covered sand to form the mold. As compared to sand casting, this process has better dimensional accuracy, a higher productivity rate, and lower labour requirements. It is used for small to medium parts that require high precision.Shell moulding was developed as a manufacturing process during the mid-20th century in Germany. It was invented by German engineer Johannes Croning.
  • Shell mould casting is a metal casting process similar to sand casting, in that molten metal is poured into an expendable mould. However, in shell mould casting, the mould is a thin-walled shell created from applying a sand-resin mixture around a pattern.The pattern, a metal piece in the shape of the desired part, is reused to form multiple shell moulds. A reusable pattern allows for higher production rates, while the disposable moulds enable complex geometries to be cast.
  • Shell mould casting requires the use of a metal pattern, oven, sand-resin mixture, dump box, and molten metal.Shell mould casting allows the use of both ferrous and non-ferrous metals, most commonly using cast iron, carbon steel, alloy steel, stainless steel, aluminium alloys, and copper alloys. Typical parts are small-to-medium in size and require high accuracy, such as gear housings, cylinder heads, connecting rods, and lever arms.

Process Consists Of The Following Steps:

shell mold casting

Benefits of Shell Molding

Shell molding offers several benefits for companies, some of which include the following:

  • Ability to create complex shapes with extreme precision
  • Low labor requirements
  • Supports most metals, including iron, steel, aluminum, copper and alloys
  • Bubbling isn’t a problem since the mold is free of moisture
  • Can be scaled for mass production
shell molding
shell molding

How Shell Molding Is Performed ?

  • Although it requires minimal labor, shell molding is a somewhat complicated process that requires multiple steps. First, the sand is thoroughly mixed with resin, which acts as a binding agent. Next, the sand is poured into a heated mold — with the mold typically reaching temperatures of 400 to 700 degrees Fahrenheit. A heated mold is important because the heat triggers a reaction with the resin-covered sand. When the sand comes into contact with the hot mold, a shell is formed on the inner surface of the mold.
  • After the shell has been formed, any excess sand is removed from the mold and either discarded or saved for other applications. The shell is then removed from the mold, which typically occurs using ejector pins. The ejector pins are built into the mold itself, allowing companies to easily remove the newly created shell without damaging it.
shell molding

In Conclusion

  • Shell molding is a molding process invented by German engineer Johannes Croning in the mid-1900s. Like other molding processes, it relies on a mold to create a new object often of a base material. Shell molding is unique, however, because it uses resin-covered sand as a base material. When the sand is poured into the heated mold, it fills the mold cavity while reacting with the heat. This reaction causes some of the resin-covered sand to form a shell inside the mold, which is removed using ejector pins.
shell molding
shell molding

Shell molding Process

Advantages and Disadvantages


  • Shell molding can be completely automated for mass production.
  • The high productivity, low labor costs, good surface finishes, & precision of the process can more than pay for itself if it reduces machining costs.
  • There are few problems due to gases, because of the absence of moisture in the shell, and the little gas that is still present easily escapes through the thin shell. 
  • Complex shapes and fine details can be formed with very good surface finish, high production rate, low labor cost (if automated).
  • Low tooling cost, Little scrap generated.
  • Very large parts and complex shapes can be produced.
  • Many material options.
  • Low tooling and equipment cost.
  • Scrap can be recycled.
  • Short lead time possible.


  • The gating system must be part of the pattern because the entire mold is formed from the pattern, which can be expensive.
  • The resin for the sand is expensive, although not much is required because only a shell is being formed.
  • High equipment cost.
  • Poor material strength.
  • High porosity possible.
  • Secondary machining often required.
  • High labor cost if done manually.