Metal casting is a fabrication process that involves flowing molten metal into a custom-designed mold that contains a negative impression of the desired part or product. After the metal cools and solidifies within the mold, it maintains the shape and size of the mold design.
In the following article, we provide an overview of the metal casting process, outlining the different methods available, materials employed, and factors to consider when planning a project.
Types of Metal Casting Methods
Metal casting methods can be classified into one of two groups: expendable and reusable molds. Below we describe the difference between the two and provide process examples.
Metal Casting Processes Using Expendable Molds
Expendable molds are single-use molds destroyed during casting operations. Some of the casting methods that employ them include:
- Investment casting: Investment casting—also referred to as lost-wax casting—utilizes ceramic molds made forming ceramic material over injection-molded wax patterns. By the end of the casting process, both the wax pattern and ceramic mold are destroyed to form the casting.
- Sand casting: Sand casting is one of the most commonly used metal casting method. It uses tightly packed sand to form a mold, which is later shaken apart to remove the finished casting.
- Plaster mold casting: Plaster mold casting is similar to sand casting. However, it uses plaster of Paris—rather than sand—to create a mold for the casting.
Metal Casting Processes Using Reusable Molds
In contrast to expendable molds, reusable molds are designed and constructed to be used across multiple production runs. Some of the cast methods that employ them include:
- Gravity casting: Gravity casting processes rely on gravity to funnel molten metal from the vessel or ladle to the mold. Examples include permanent mold, semi-permanent mold, slush, and continuous casting.
- Permanent and semi-permanent mold casting: The permanent mold casting process employs molds made from durable metals with higher melting points than the casting material. They are simple and often thicker than the molds used in other casting methods. The semi-permanent casting process uses permanent metal molds with expendable sand cores to create parts and products with more complex internal designs.
- Continuous casting: The continuous casting process involves feeding molten metal into a water-cooled die to create a continuous strip or rod. After the casting has solidified, it is cut into specified lengths with a rounded saw.
- Pressure casting: Pressure casting processes use forces other than gravity—such as pneumatic pressure, vacuums, or centrifugal force—to add material to the mold. Examples include die casting, centrifugal casting, and vacuum casting.
- Die casting: The die casting process utilizes an injection system to force the molten metal into the mold under high pressure.
- Centrifugal casting: The centrifugal casting process involves rotating the mold at high speeds while material is added and cooled. The centrifugal force generated distributes the material evenly against the walls of the cavity.
- Vacuum casting: The vacuum casting process uses a vacuum to pull molten metal into the mold.
Common Casting Materials
The metal casting process accommodates a wide range of metals. Essentially, if the metal can be melted, it can be cast. Some of the most common materials used in casting operations include:
- Aluminum and aluminum-based alloys
- Stainless Steel
- Copper and copper-based alloys
- Tool steel
Which Metal Casting Method Is Right for My Needs?
As there are many metal casting methods available—each offering unique benefits and limitations—it can be difficult to determine which one is right for a particular production project. Some of the factors to consider when deciding which method to use include:
- Construction materials: What materials are you using to make your casting?
- Production requirements: How many units are required in this run, and is this a one-off or recurring order?
- Surface finish: What finish are you looking for in the final piece?
- Tolerance range: What dimensional tolerances do you require?
- Minimum wall thickness required
- Machining requirements: How much machining will the cast part be subjected to post-production?
- Tooling costs: What is the budget for tooling costs?
Metal Casting Solutions From Mardek
If you’re looking for a metal casting partner, turn to the experts at Mardek. Our extensive partner network of reputable overseas manufacturers allows us to fulfill a wide range of metal casting needs, from small and delicate pieces to large and heavy assemblies. We offer the following metal casting services:
- Die casting
- Investment casting
- Permanent mold casting
- Sand casting
In addition to our metal casting capabilities, we also provide other fabrication and finishing services to facilitate the delivery of complete cast parts and products. These services include precision machining, heat treating, assembly, anodizing, plating, polishing, powder coating, and painting.