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.
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.
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-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.
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;
reproducibility of castings within close dimensional limits;
production of castings in high melting point alloys;
high standards of metallurgical quality;
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