Lost-foam casting

Patent

LFC originated on April 15, 1958, when H.F. Shroyer patented the use of foam patterns, imbedded 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".

The polystyrene foam pattern left in the sand is filled by the molten metal, precisely duplicating all of the features of the pattern. Like the lost wax process, a pattern must be produced for every casting made.

With the full mold process, the pattern is usually machined from an EPS block and is used to make a one-of-a kind casting. The "full mold process" was originally known as the "lost foam process".

In 1964, M.C. Flemmings used unbonded sand for the process. Flemming’s method is today known as "lost foam casting" (LFC). LFC is differentiated from full mold by the use of unbonded sand, as opposed to bonded sand that is used in the full mold process. Currently, more foundries in North America use the LFC process than the full mold process.

Foam casting techniques (both “full mold� and LFC) have been referred to by a variety of generic and proprietary names. Among these are “full mold�, “cavityless casting�, “lost foam�, “evaporative foam casting�, “evaporative pattern casting�, foam vaporization casting, Styrocast™, Foamcast™, and Policast™. The use of these terms has led to much confusion among design engineers, casting users, and casting producers.

Benefits

The advantages of LFC include:

* Flexibility of foam: Foam is easy to manipulate, carved and glued, due to its unique properties.

* Dimensional accuracy: The patterns are accurate representations of the desired casting, as compared to sand casting and there is no tool wear. There is also less finishing work required for an LFC casting, as there are no fins or parting lines.

* Elimination of cores: This allows for more complex casting designs, well-controlled wall thickness of castings, and no core-prints. This process also eliminates fins or shifts, core defects and sand mixing.

* Elimination of parting line: There is no draft and multiple levels of casting are possible. Proper gating and riser placement can be achieved, and there are no shifts or fins. Forms that are not typically possible with traditional cope and drag methods can be produced since the mold does not need to be parted to remove a pattern.

* Part consolidation: The flexibilty of LFC often allows for consolidating the parts into one integral component; other forming processes would require the production of one or more parts to be assembled.

* Lower cost: Because the process is very much simpler, as compared to traditional sand-casting methods, production cost is very much lower.

Public recognition of the benefits of LFC was made by General Motors in 1993. By 1998, LFC production had reached approximately 140,00 tons in the United States alone. And in 2005, it is forecast that LFC will account for 29% of the aluminum, and 14% of the ferrous casting markets.

Copyright 2008 - France BtoB from Wikipédia