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Precisiewerk Zierikzee BV

HISTORY OF THE LOST WAX PRODUCTION PROCESS

The basic technique of investment casting, under its traditional name of lost wax (or cire perdue), has been know for well over 6000 years. The exact origin of the proces is unknown. Table 1 shows the estimated ages of lost wax objects, plotted according to the area where they were manufactured or recovered. Archeological investigations have indicated Mesopotamia, around 3000-4000 BC, as the location of a civilised society of city states posessing the skills in engineering and metallurgy, including the knowledge and the means to produce a range of gold, silver and copper artefacts made by lost wax casting.

 

Thailand/South-East-Azia

Another candidate location for the original use of the technique is Thailand/South East Asia, where it is believed that metallurgical activities were carried out by local tribes rather than by urban populations. There is evidence that elaborate bronze artefacts were made by the lost wax method as early as 4500 BC in South East Asia.

The Chinese were using the technique from 2000 BC onwards and the Egyptians from around 1400 BC. An archeological excavation in 1972 of a first century BC Iron Age factory, was particulary interesting, since it provided one of the few examples where clay-based investment moulds were recovered. Over 7000 fragments were found, for leaded bronze harnesses and chariot fittings.

 

 

So is is clear that knowledge of the investment casting process was widely dispersed in the ancient world and was practised in China, South East Asia, Mesopotamia, Egypt, Greece, Italy and Northern Europe, and possibly elsewhere as well.

During the next 1000 years there are isolated references to the process. One remarkable example, dating from 11th century AD or earlier, is Shiva, the Lord of the Dance, 96cm high bronze figure surrounded by a circle representing the cycle of creation, destruction and birth. This investment casting was produced by the Chola dynasty in India, and emphasies their cult of the god-king; the statue is unsurpassed in technical skaill and delicacy of design.

Tabel 1: Geschatte leeftijden van verloren wasmodel voorwerpen.

Aztecs

Well before Columbus set sail, the Aztecs in Mexico and the aboriginal Quimbaya goldsmiths in the Cauca Valley, Colombia, were familiar with the process, producing remarkable hollow gold castings.
At about the same time (the 13th century AD) investment casting was the chosen production method for a number of bronze tomb effigies for kings and queens; examples of these are the effigies of king Henry III and Queen Eleanor in Westminster Abbey.

It may be noted that the 14th and 15th centuries represented the flowering of lost wax bronze casting in mid western Nigeria, particularly in Benin, the capital of the Bini region of the country. Probably introduced into the area from the nearby Ife region some centuries before, the techniques became very sophisticated, but were restricted in use to artefacts for the royal household.

Early castings were produced from a wide range of patterns. Archealogical finds indicate that production of identical wax patterns was achieved by the use of dies of carvable stone, cast bronze and carved wood. It is possible that the bronze dies were also used to cast lead by the gravity die process.

The Quimbaya workers probably mass produced patterns for ornamental castings by pressing sheet wax on to the carved surface of stone matrices. In regions as far apart as Africa, India, and South and Central America, it was traditional to build elaborate patterns from wax thread and wire; the wires were wound round a clay or clay/charcoal core, either to cover it wholly or as an open network.

 

West Afrikaanse Strijder
West-Afrikan warrior, bronze,
near 1800 AC

Highest artistic expression

Lost wax casting reached possibly its highest artistic expression in Renaissance Italy. Benvenuto Cellini produced many masterpieces by the process, one of the most outstanding being a bronze statue of Perseus holding the head of Medusa. Cellini has left a detailed description of the process, both in treatise of 1568 and in his autobiografie, claiming to have learnt about the casting method from a descrition by the monk Theophilus Presbyter

Other written evidence of investment casting has come down from about the same time, when Varrinee Krickes of Prague describes the use of the lost wax method to produce bronze gun barrels. In 1538, Vannocio Biringuccio, head of the Papal foundry and a contemporary of Leonardo da Vinci, wrote in his Pirotechnia:

There are likewise moulds for large statues wich, if one desires to make them of bronze, are first made of wax according to the ordinary procedure.
This procedure involved creating an original model or sculpture in wax, which was subsequently polished and embellished by its creator. Each item was a unique work of art; the image was then coated with a milky slurry of plaster, building up successive layers until a strong shell completely eveloped the wax. After melting out the residual wax, molten metal was poured into the void, which after removal of the plaster shell left a perfect duplicate of the original pattern form, complete even to undercuts and folds.

Bronzen beeld van Perseus

The modern lostwax industry

By the 1930s investment casting ranked as a usefull specialised casting method, but with little relevance to mainstream engineering. It was the requirements of the Second World War that changed this situation and laid the foundations of the modern investment casting industry. An urgent demand for finished components could not be met by the capacity of the machine tool industry and attention turned to investment casting to produce precision components for armament and aircraft parts. The pace of development accelerated with the introduction of the aircraft gas turbine, where designers, seeking increased efficiency by the use of higher operating temperatures, were attracted to investment casting to form the refractory alloys specified (or developed) for turbine blades.

To meet this challenge, the traditional process had to address four new requirements;

  1. reproducibility of castings within close dimensional limits;
  2. production of castings in high melting point alloys;
  3. high standards of metallurgical quality;
  4. cost savings over parts produced by alternative manufacturing techniques.
It was the solution to these problems that laid the foundation of the modern investment casting industry.
The introduction of the jet engine for civil aviation after the war proved to be a real opportunity for investment casting and strengthened the links between it and high quality, critical component manufacture.

Expansion continued through the 1950s, with a growing list of applications and the beginning of a general commercial market. The range of metals and alloys cast became more diverse, with steel, superalloy and non-ferrous (copper and especially aluminium alloy) markets being established.

The wider scope of the process was facilitated by the introduction, from the mid-fifties, of the ceramic shell proces of mould production in place of the original block mould technique; this gave more versatility to the process and allowed much larger parts to also be cast.