The lost-wax process is still used in statuary casing today and employs the same basic methods, although advantage is taken of modern aids. The lost-wax process was adapted by dentist during the late nineteenth century to produce accurate castings, often in gold, for fillings, crowns and bridges to individual requirements. The metal was cast by centrifugal techniques, which assisted good reproduction of fine detail.
The continued development of the process during the early years of the twentieth century laid the foundations of the engineering process as it is known today. The need to produce accurate dental castings led to the study of factors affecting pattern and mold stability and to the solidification and contraction characteristics of a number of metals and alloys. Many techniques were introduced to obtain dimensional accuracy of the casting; particular attention was given to the mold and mold materials and a number of ingenious casting devices were developed to try to counteract expansion and contraction effects. One of the more notable developments in this field was the introduction during the early 1930’s of a compensating investment material. The fact that at least four hundred patents covering the process were granted during the period 1900 to 1940 gives an indication of the interest in investment casting.
No serious effort was made to produce industrial castings by the investment casting process until the late 1930s, when it was realized that cobalt base alloy, which had been developed by the Austenal Laboratories for surgical implant work, possessed highly desirable properties at elevated temperatures. Certain components for aero-engine turbo-chargers operated under rigorous conditions and conventional alloys were found to be less than satisfactory for these applications. The cobalt-base alloy was suitable for the operating conditions but was very difficult to machine or work. There was an obvious need to develop “cast-to-size” process to produce components in this alloy and investment casting was the inevitable choice. The potential of the process was soon appreciated and industrial techniques were rapidly developed to serve the specialized requirements of the aero-engine industry.
Most early investment foundries were tied to aircraft companies or in government establishments, but a number of commercial foundries were set up to produce aircraft quality castings. Investment casting markets gradually expanded into the field of commercial castings, and soon the engineering industry was utilizing castings produced from a wide range of ferrous, nonferrous and light alloys. The industry has developed over the years and serves a very varied market from golf club heads to turbine blades. Castings are produced in a variety of alloys in weights ranging from a few grams to many hundreds of pounds. The process is versatile and competes very effectively with other manufacturing processes, often producing a better component at less cost.