Aluminium Investment Casting

Aluminium Investment Casting also called lost-wax casting, is one of the oldest known metal forming techniques. From 5,000 years ago, when bees wax formed the pattern, to today’s high-technology waxes, refractory materials and specialist alloys, the castings allow the production of components with accuracy, repeatability, versatility and integrity.

The process offers repeatable production of net shape components from a variety of metals and high-performance alloys. It is generally used for small castings, but has produced complete aircraft door frames, with steel castings of up to 300 kg and aluminium castings of up to 30 kg. It is generally more expensive than die casting or sand casting, but can produce complicated shapes that require little rework.
Investment casting dates back thousands of years. Its earliest use was for idols, ornaments and jewellery, using natural beeswax for patterns, clay for the moulds and manually operated bellows for stoking furnaces. Examples have been found in Egypt's tombs of Tutankhamun (1333 – 1324 BC), in Mesopotamia, Mexico, and the Benin civilization in Africa where the process produced detailed artwork of copper, bronze and gold.

The earliest known text that describes the investment casting process (Schedula Diversarum Artium) was written around 1100 A.D. by Theophilus Presbyter, a monk who described various manufacturing processes, including the recipe for parchment and the lost-wax process. This book was used by sculptor and goldsmith Benvenuto Cellini (1500 - 1571), who detailed in his autobiography the investment casting process he used for the Perseus and the Head of Medusa sculpture that stands in the Loggia dei Lanzi in Florence, Italy.

The investment casting process came into use as a modern industrial process in late 19th century, when dentists began using it to make crowns and inlays, as described by Dr. D. Philbrook of Council Bluffs, Iowa in 1897. Its use was accelerated by Dr. William H. Taggart of Chicago, whose 1907 paper described his development of a technique. He also formulated a wax pattern compound of excellent properties, developed an investment material, and invented an air-pressure casting machine.

In the 1940s, World War II increased the demand for precision net shape manufacturing and specialized alloys that could not be shaped by traditional methods, or that required too much machining. Industry turned to investment casting. After the war, its use spread to many commercial and industrial applications that used complex metal parts.

Modern investment casting techniques stem from the development in the United Kingdom of a shell process using wax patterns known as the Investment X Process. This method resolved the problem of wax removal by enveloping a completed and dried shell in a vapor degreaser. The vapor permeated the shell to dissolve and melt the wax. This process has been evolved over years into the current process of melting out the virgin wax in an autoclave.