Sand casting is one of the most common forms of metal casting and accounts for a large majority of cast prototypes in weight. During the sand casting process, a metal is heated to the point that it melts and the chemical composition can be modified. Once the material becomes a liquid property, the molten metal is poured into a sand mold that has been shaped to the desired specifications of the prototype being manufactured.
Like other forms of casting, the advantages and disadvantages of the casting type are semi-dependent on the knowledge that the designer has, as well as the care that they use to complete the process. Before any casting project is completed, it is important to carefully weigh the functional needs of the part that is to be cast, as well as how the particular casting method will help to achieve those results.
When working with sand casting, it is important for the designer to consider eight key elements of the casting process to avoid common engineering mistakes. Those key elements are:
- Draft Angle - The draft angle is the angle that is applied to all vertical faces of the design to aid in removing the product from the sand mold cleanly and easily. This angle will be different from project to project, meaning that it is important to find an experienced foundry to sand cast your prototype.
- Parting Line - A parting line is exactly what it sounds like — a line that separates the draft angles that change direction. The parting line is an important consideration in sand casting because it can drastically affect the price of the cast.
- Undercuts and Cores - Undercuts are the part of the sand cast that prevents the design from being removed during the mold making stage. The use of loose core sand pieces can increase the cost and timeline of production — meaning that an early parting line should be used to prevent undercuts.
- Cross Sections - Also known as uniform wall thickness, cross sections are support sections for the cast that are usually preferred to be thicker, but they can be infeasible, as larger masses of molten material will take longer to cool and harden.
- Wall Thickness - Wall thickness is an important consideration in sand casting because an improper volume to surface area ratio can cause cavities and integral failures in the mold.
- Corners and Angles - Corners and angles are cooling characteristics of the sand cast that have a major influence on the quality of the finished prototype. Sharp angles can cause localized heat spots that can degrade the overall quality of the casted prototype.
- Junction Design - Junction design refers to the places where two different parts of the cast meet at an angle. There are five junction types (L, X, V, Y, & X-T) and they should be carefully placed to minimize the risk of shrinkage and tears in the cooling cast.
- Casting Allowances - Casting allowances is the size that metal will shrink when it is solidifying. Each material will shrink differently, so it is important to consider what metal is being used in the casting process before engineering the sand mold.