What is the Sand Casting Process?

The sand casting process requires the following equipment and products ingots or scrap metal, metal melting furnace, a wood or metal pattern, casting sand and a sand mold box. 

1. The first step is in the process is placing the wood or metal pattern, which replicates your metal part and design, into metal or wooden box.
2. The second step is inserting sand and ramming the sand around the mold/pattern in the flask (metal frame) or wood box to form the part cavity.
3. Step 3 is withdrawing the mold from the flask or box, leaving behind a cavity in the sand.
4. The molds are normally made in two halves: an upper portion (the cope) and a lower portion (the drag).  Once these two molds are placed on top of each other, they form the complete cavity into which molten metal is poured through a spruce or runner (hole into the cavity). The boundary between cope and drag is known as the parting line.  A spruce or pouring hole and riser or vent hole, is part of the sand mold and this can be part of the pattern or it is made manually after the two sand mold halves are placed together. These are generally referred to as a spruce/runner and the riser that allows gas to escape from the cavity while pouring molten metal fills the cavity and comes out of the riser.
5. The metal that has been melted in an electric induction or gas fired furnace to the required temperature is ladled or poured through the spruce or runner or feed hole and fills the sand cavity mold that was formed by the pattern. The gasses and air escape through the riser hole and once this hole is filled with molten metal. That indicates that the cavity is filled.
6. Once the metal has had time to solidify and cool, the sand is then removed mechanically or manually from the parts. The metal spruce or runners and risers are still part of the casting part and these are cut off with a cutting wheel or removed by a band saw or metal saw.  The castings are then cleaned by various methods such as shot blast to remove any residual sand and it also blends any imperfections or the parting line.

When Should You Use Sand Casting?

When should you choose sand castings? When you have a design for a metal part and your requirements are:

• Low tooling costs
• Low or high volume requirements
• Low part cost
• Quick delivery or turn around

Sand castings are a smart choice. 

What are the Advantages of Sand Casting?

• Sand castings impose few restrictions on product shape

The only significant exceptions are the draft angles that are always needed on flat surfaces oriented perpendicular to the parting line. With good patterns and tooling, the proper choice of molding sands and careful foundry practice, surprisingly intricate details can be reproduced in this manufacturing process.

• Dimensional control and consistency

Dimensional control and consistency in sand castings ranges from about ±0.030 to ±0.125” (± 0.8 to 3.2 mm) depending on the size and design of the parts being cast. Within this tolerance range, the more generous tolerances apply across the parting line.

• Surface finish ranges between approximately 300 and 500 gin (7.7 - 12.9 gm) rms

Various finishes can be applied and they are: Shot blast finish, painted, powder coated, plated (chrome and others), various special coatings such as Rilsan.

• Sand castings are relatively inexpensive compared to other manufacturing processes

The process is quite simple and most any metals can be used. Parts can be used as is or can be machined.

• Sand castings are acceptably precise and above all, highly versatile

This process can be applied to simple shapes as well as castings of considerable complexity, and it can be used with all metals such as cast and ductile irons, copper alloys, steel alloys, stainless alloys, and other complex metals.

• Sand castings also lend itself to low volume production or high volumes

How Common is Sand Casting?

Sand castings currently account for about 75% of U.S. copper alloys, cast or ductile iron, stainless as well as aluminum alloy foundry production.