Metal Casting FAQ

Metal Castings: Frequently Asked Questions

Qingdao Tian Hua Yi He Foundry answers to many of the most commonly-asked questions related to casting steel and iron products.

Q: What is the definition of casting?
A: In the metal casting industry, there are two distinct meanings:

  1. Casting refers to the process of creating a metal part (using cast iron or cast steel) by pouring liquid into a mold or die to form a solid shape. Once the part cools and solidifies, it is ejected or broken out of the mold.
       There are several casting techniques used that offer varying degrees of quality, precision, and economics. The three most common in the industry are sand casting, die casting, and investment casting.

  2. Casting terms can be used reciprocally. After the metal casting process is completed, the finished object is universally referred to as a "casting".

Q: What is a metal casting?
A: Any metal casting process begins with an actual design of the part desired. A cast steel foundry uses these designs and specifications to create a 3D dimensional model that will represent the mold’s “pattern” or “die”. The pattern is the actual shape of the object to be cast inside the mold’s “cavity”. As liquid metal enters the cavity, it fills the pattern shape or void inside the mold to form the final casting. After a period of cooling and solidification, the solid metal casting is removed from the mold.There are variations to the metal casting depending on the type of casting process used.

 

Q: What kind of metal is used in castings?
A: Any metal that can be melted can be cast.Cast steel foundry can accommodate different combinations of alloys and metals depending on the desired object’s structural and performance qualities. Throughout the industry, iron and steel represent the most common metals used today. In order to categorize metals, they are often referred to as Ferrous Metals and Nonferrous Metals.

Ferrous Metals: Metals which contain iron.

Examples of Ferrous Metals

  • Cast Iron, Gray Iron, Ductile Iron, Malleable Iron, Cast Steel (ASTM A27 Cast Steel is a commonly used cast steel), Compacted Graphite Iron, Stainless Steel, & Manganese Steel.

Nonferrous Metals: Metals which do not contain iron.

Example of Nonferrous Metals

  • Aluminum, Copper Alloy, Brass, Bronze, Zinc, Magnesium, Carbon & Low Alloy Titanium, Corrosion Resistant Nickel, Heat Resistant Cobalt, Manganese and Tin.

Q: What are common uses for castings?
A: Throughout the globe, metal casting represents a major sector for more than 90% of all manufactured goods and capital equipment. Whether it is for heavy machinery or consumer goods, metal casting is used for a variety of applications. Engineered components in capital equipment require castings. Farm equipment, railroads, ships, oil and gas extraction, water processing, and mining cannot operate effectively without precision metal casted parts.

In the consumer industry, items that we rely on everyday exist because of cast steel foundries. Cars, trucks, air conditioners, refrigerators, lawn mowers, weight lifting, and many moreutilize cast parts to maintain their operations. Even the very production lines that create consumer products likely require casted parts.

Q: How are castings made?
A: Since there are several commonly used casting processes, each will offer an advantage depending on the requirements:

  • Sand Casting: Sand casting is considered the most common and can accommodate a wide range of object sizes. The three dimensional replica or “pattern” of the required object is held within a mold surrounded by compressed sand and binder additives which are used to form the final shape of the desired part. After the impression of the pattern is formed, the pattern is removed from the mold. Metal is poured into the runner system of the mold’s cavity. Once solidified, the sand and metal are separated, and the feeding system (ingates, runners and risers) are parted from the raw casting. The casting is then cleaned, heat treated (as or if necessary) and finished prior to shipping. The sand is often reused with some post-production cleaning, screening and/or re-mixing with new additives; this sand is quite often recycled when it is no longer usable within the foundry sand system. Casting designs may also require hollow internal features or holes. In this case, a core is placed inside the mold cavity to replace the volume of that hole and prevent metal from entering. Once solidified, the mold is broken and the core is removed from the part prior to finishing operations.

  • Die Casting: For complex engineered shapes which require dimensional accuracy and precision, die casting is the most common approach. The molds are referred to as “dies”. The dies are precision machined steel molds capable of withstanding high pressure and temperature. Typically, die castings are made from nonferrous metals although water-cooled ferrous metal dies are possible. Forcing molten metal into a steel die results in several advantages. It allows for finer surface quality, higher dimensional accuracy, and improved part detail. Die casting is especially advantageous for small or medium sized parts requiring mold reusability and consistency.

  • Investment Casting: Otherwise known as “lost wax process”, investment casting has existed for at least 5000 years. In ancient times, beeswax was used to form patterns. Still used by cast steel foundries worldwide, investment castings often eliminate the need for machining a steel casting. The actual mold is created by making an impression pattern with wax. The process typically uses wax; although foam can also be used. The wax pattern is placed in a ceramic slurry which coats the pattern and forms a skin that surrounds its surface area. The pattern is then heated so the wax melts away leaving a cavity that can be filled with metal for final casting.Investment casting offers several benefits. This casting method produces objects with intricately smooth surface contours and which may not require extensive finishing.

Q: What are the differences between wrought iron vs. cast iron?
A: The primary difference between wrought iron vs. cast iron  involves the process in which the desired shape was achieved. Wrought iron is standard/stock metal that has been heated and then worked with tools to produce its shape and form. Cast iron is melted and poured into a mold to give it the desired look, shape, and surface qualities (casting).

The next difference involves the purity of the metal which affects the overall strength and “workability” of the product. Cast iron’s strength is affected by the addition and removal of chemical agents which effect its purity. The more impurities removed from cast iron, the easier it is to work with and result in a stronger or more durable end product.

In terms of its properties, cast iron as not as pure as wrought iron but, with molds, it can be used to create more accurate parts. In the early nineteenth century, wrought iron work was an individual craft or trade but during the industrial revolution, the development of more efficient casting processes made it less expensive to mass produce metal goods.

A subset of cast iron, known as "ductile cast iron" was invented in the 1940’s. It is less brittle than cast iron and offered a higher degree of manipulation in terms of flexibility and elasticity than traditional cast iron.

Q: What is the difference between a foundry and casting?
A: A foundry is a place where metal castings are produced. A casting is the process of pouring liquid metal into the hollow cavity of a mold to form a desired shape upon solidification.