Evaporative-pattern casting

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Evaporative-pattern casting is a type of casting process that uses a pattern made from a material that will evaporate when the molten metal is poured into the molding cavity. The most common evaporative-pattern material used is polystyrene foam. [1]

Contents

The two major evaporative-pattern casting processes are: [1]

The main difference is that lost-foam casting uses an unbonded sand and full-mold casting uses a bonded sand (or green sand). Because this difference is quite small there is much overlap in the terminology. Non-proprietary terms that have been used to describe these processes include: cavityless casting, [2] evaporative foam casting, foam vaporization casting, lost pattern casting, the castral process, and expanded polystyrene molding. [3] [4] Proprietary terms included Styro-cast, [5] Foam Cast, [6] Replicast, [7] Policast. [4] and Lost Foam Sintered Shell (LFSS) [8]

History

The first patent for an evaporative-pattern casting process was filed in April 1956, by Harold F. Shroyer. He patented the use of foam patterns embedded in traditional green sand for metal casting. In his patent, a pattern was machined from a block of expanded polystyrene (EPS), and supported by bonded sand during pouring. This process is now known as the full mold process. [9] [10]

In 1964, M.C. Flemmings used unbonded sand for the process. The first North American foundry to use evaporative-pattern casting was the Robinson Foundry at Alexander City, Alabama. General Motors' first product using these processes was the 4.3 L, V-6 diesel cylinder head, which were made in 1981 at Massena, New York. [11]

A study found in 1997 that evaporative-pattern casting processes accounted for approximately 140,000 tons of aluminium casting in the United States. The same survey forecast that evaporative-pattern casting processes would account for 29% of the aluminium, and 14% of the ferrous casting markets by 2010. [12] [13]

Related Research Articles

Casting (metalworking) Pouring liquid metal into a mold

In metalworking and jewelry making, casting is a process in which a liquid metal is delivered into a mold that contains a negative impression of the intended shape. The metal is poured into the mold through a hollow channel called a sprue. The metal and mold are then cooled, and the metal part is extracted. Casting is most often used for making complex shapes that would be difficult or uneconomical to make by other methods.

Sand casting Metal casting process using sand as the mold material

Sand casting, also known as sand molded casting, is a metal casting process characterized by using sand as the mold material. The term "sand casting" can also refer to an object produced via the sand casting process. Sand castings are produced in specialized factories called foundries. Over 60% of all metal castings are produced via sand casting process.

Cope and drag

In foundry work, the terms cope and drag refer respectively to the top and bottom parts of a two-part casting flask, used in sand casting. The flask is a wood or metal frame, which contains the molding sand, providing support to the sand as the metal is poured into the mold. In flaskless molding, the same terms are used, cope for the top or upper piece and drag for the bottom or lower piece.

Lost-foam casting Type of evaporative-pattern casting process

Lost-foam casting (LFC) is a type of evaporative-pattern casting process that is similar to investment casting except foam is used for the pattern instead of wax. This process takes advantage of the low boiling point of polymer foams to simplify the investment casting process by removing the need to melt the wax out of the mold.

Metal injection molding

Metal injection molding (MIM) is a metalworking process in which finely-powdered metal is mixed with binder material to create a "feedstock" that is then shaped and solidified using injection molding. The molding process allows high volume, complex parts to be shaped in a single step. After molding, the part undergoes conditioning operations to remove the binder (debinding) and densify the powders. Finished products are small components used in many industries and applications.

Foundry

A foundry is a factory that produces metal castings. Metals are cast into shapes by melting them into a liquid, pouring the metal into a mold, and removing the mold material after the metal has solidified as it cools. The most common metals processed are aluminium and cast iron. However, other metals, such as bronze, brass, steel, magnesium, and zinc, are also used to produce castings in foundries. In this process, parts of desired shapes and sizes can be formed.

This article is a list of terms commonly used in the practice of metalworking – the science, art, industry, and craft of shaping metal.

Investment casting industrial process based on lost-wax casting

Investment casting is an industrial process based on lost-wax casting, one of the oldest known metal-forming techniques. The term "lost-wax casting" can also refer to modern investment casting processes.

Pattern (casting)

In casting, a pattern is a replica of the object to be cast, used to prepare the cavity into which molten material will be poured during the casting process.

A chill is an object used to promote solidification in a specific portion of a metal casting mold. Normally the metal in the mould cools at a certain rate relative to thickness of the casting. When the geometry of the molding cavity prevents directional solidification from occurring naturally, a chill can be strategically placed to help promote it. There are two types of chills: internal and external chills.

Permanent mold casting is a metal casting process that employs reusable molds, usually made from metal. The most common process uses gravity to fill the mold, however gas pressure or a vacuum are also used. A variation on the typical gravity casting process, called slush casting, produces hollow castings. Common casting metals are aluminium, magnesium, and copper alloys. Other materials include tin, zinc, and lead alloys and iron and steel are also cast in graphite molds.

Ceramic mold casting, also known ambiguously as ceramic molding, is a group of metal casting processes that use ceramics as the mold material. It is a combination of plaster mold casting and investment casting. There are two types of ceramic mold casting: the Shaw process and the Unicast process.

Full-mold casting

Full-mold casting is an evaporative-pattern casting process which is a combination of sand casting and lost-foam casting. It uses an expanded polystyrene foam pattern which is then surrounded by sand, much like sand casting. The metal is then poured directly into the mold, which vaporizes the foam upon contact.

Plaster mold casting is a metalworking casting process similar to sand casting except the molding material is plaster of Paris instead of sand. Like sand casting, plaster mold casting is an expendable mold process, however it can only be used with non-ferrous materials. It is used for castings as small as 30 g (1 oz) to as large as 7–10 kg (15–22 lb). Generally, the form takes less than a week to prepare. Production rates of 1–10 units/hr can be achieved with plaster molds.

Threading is the process of creating a screw thread. More screw threads are produced each year than any other machine element. There are many methods of generating threads, including subtractive methods ; deformative or transformative methods ; additive methods ; or combinations thereof.

Casting Manufacturing process in which a liquid is poured into a mold to solidify

Casting is a manufacturing process in which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process. Casting materials are usually metals or various time setting materials that cure after mixing two or more components together; examples are epoxy, concrete, plaster and clay. Casting is most often used for making complex shapes that would be otherwise difficult or uneconomical to make by other methods. Heavy equipment like machine tool beds, ships' propellers, etc. can be cast easily in the required size, rather than fabricating by joining several small pieces.

Shell moulding, also known as shell-mould 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 labor requirements. It is used for small to medium parts that require high precision. Shell molding was developed as a manufacturing process during the mid-20th century in Germany. It was invented by German engineer Johannes Croning. Shell mold casting is a metal casting process similar to sand casting, in that molten metal is poured into an expendable mold. However, in shell mold casting, the mold 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 molds. A reusable pattern allows for higher production rates, while the disposable molds enable complex geometries to be cast. Shell mold casting requires the use of a metal pattern, oven, sand-resin mixture, dump box, and molten metal.

A core is a device used in casting and moulding processes to produce internal cavities and reentrant angles. The core is normally a disposable item that is destroyed to get it out of the piece. They are most commonly used in sand casting, but are also used in die casting and injection moulding.

A casting defect is an undesired irregularity in a metal casting process. Some defects can be tolerated while others can be repaired, otherwise they must be eliminated. They are broken down into five main categories: gas porosity, shrinkage defects, mould material defects, pouring metal defects, and metallurgical defects.

References

  1. 1 2 Degarmo, Black & Kohser 2003 , p. 321.
  2. ↑ U.S. Patent 4,068,704 .
  3. ↑ American Society for Metals et al. 1991 , p. 229.
  4. 1 2 Totten, Funatani & Xie 2004 , p. 357.
  5. ↑ Styro-cast , retrieved 2009-03-29[ permanent dead link ].
  6. ↑ American Foam Cast , retrieved 2009-03-29.
  7. ↑ Replicast Process (CS) , retrieved 2009-03-29.
  8. ↑ "Metafore Castings Private Limited - Pioneers in Stainless Steel, Alloy Steel and SGI Castings through Lost Foam Sintered Shell Process in India". www.metaforecastings.com. Retrieved 2018-12-05.
  9. ↑ Donahue, Raymond; Anderson, Kevin, Lost Foam Casting, ASM International , retrieved 2010-04-06.
  10. ↑ U.S. Patent 2,830,343
  11. ↑ Biswanath, Mondal (2004), Proceedings of the National Conference on Investment Casting: NCIC 2003, Allied Publishers, ISBN   978-81-7764-659-7
  12. ↑ Bodine, Jack R. (1999-05-01), "From a monument to the Vega: the journey of the aluminum casting industry", Modern Casting: 13.
  13. ↑ Success through partnership: lost foam (PDF), September 1998, retrieved 2009-03-30.

Bibliography

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