• The technique of INVESTMENT CASTING is both one of the oldest and most advanced of the metallurgical arts.• Yet, the root of this technology, the cire perdue or “lost wax” method dates back to at least the fourth millennium B.C. and was originated in China.• The investment casting technique was ignored by modern industry until the twentieth century, when it was “rediscovered” by the dental profession, in Italy. Dr. William H. Taggart of Chicago published his research in 1907.• In today’s world, investment castings touch all of our lives. When we fly on an airplane, drive an automobile, play golf, we are using investment castings.
• Investment casting is used to describe a group of processes in which molds are produced from liquid refractory slurries.• The term investment refers to a cloak or special covering apparel. Cloak is a refractory mold which surrounds the pre- coated wax pattern.• The investment casting processes are of two types; Using Expendable Pattern. Using Permanent Pattern.
•The steps involved in casting process are shown in the following SLIDE :-
• Dies used for pattern making can be made by either “machining” cavities in two or more block of steels or by “casting” a low melting point alloy around a master pattern. Master pattern Sand mould Plaster Low melting point alloy Master die
• Wax patterns are produced using these master dies using Wax-injection machines. Wax at 150-170 F is injected into the die at a pressure of 7-70 kg/sq.cm.
• The types of wax used are:- STRAIGHT WAX(non-filled), FILLED WAX(30% of filler), and EMULSIFIED WAX (by air/water).• The wax patterns assembly is dipped into a refractory slurry. The slurry contains a “Filler material” (eg. 325-mesh silica flour) and “Binder material” (eg. Ethyl silicate solution. Then it is sprinkled with 40-50 AFS silica sand is then dried for 2-4 hours.• The pre-coated wax pattern is then, invested in the mold. Invest molds can be formed either by “solid molding” or “shell molding”.
• In solid molding, a ceramic slurry is allowed to pour over the wax pattern assembly and is left for hardening. The slurry consists of sand(91.2%) + water(33.8%) + primary calcium phosphate(6.5%) + MgO(2.3%) + 300-mesh.• In shell molding, continuous periodic dipping of the wax pattern assembly in a ceramic a slurry powder is done.• This refractory shell produced, is then de-waxed using overheated steam in boiler-claves (temp.- 160-170 C),• The wax obtained in de-waxing is then recycled.
Wax Patterns Wax Recycling
• Once the wax the molding is de-waxed then, molds are pre -heated to about 1900 F, and the metal is then poured into the molding . The pouring of metal can be done in three ways: under gravity, under direct air pressure(0.35-0.7 kg/sq.cm) under centrifugal force.• After the molten metal is solidified, the “castings” are removed from the mould. Following FINISHING OPERATIONS are carried out; casting cut-off from gating system. casting surface cleaning. casting heat treatment.• Finally, the casting is inspected for quality inspection.
Methods of pouringa) Under gravityb) Vaccum pouring
• Agricultural equipment, Automobiles and their components, Baling and strapping equipment, Cameras, Construction hardware and equipment, Dentistry and dental tools, Prosthetics, Computer hardware, Electrical equipment, and radar.• Guns and armament, Hand tools, Machine tool components, Aircraft engines, air frames, fuel systems, Aerospace, missiles, ground support systems.• Material handling equipment, Oil well drilling and auxiliary equipment, Components for compressor and pneumatic equipment.• Sports gear and recreational equipment, Textile machinery parts, Valves and flow control equipment, Components for
• Excellent details along with close tolerances (+0.003 or -0.003 mm per mm) are obtainable.• Excellent surface finish is a major advantage of this process (1500-2250 miro-mm root mean square).• This is a high precision casting technique, hence, near net shapes; very near to the finished component is produced.•There are no metallurgical limitations for investment casting. Difficult to machine metals are best shaped by this process.• The process is extremely versatile; almost any intricate shapes, thin walls(as thin as 0.75mm) and tiny delicate components can be cast.
• Pattern is expendable. Size limitation of components to be cast• Process is relatively slow. Use of core make the process more difficult.
Casing of tank control system – Boeing 777-APU duct- Al-alloy Part Ti-alloyPart of helicopter V-22 – Surgical implants(knee & hip joints)- Ti-alloy Ti6Al4V alloys, Co-Cr-Mo alloys
• LATEST TRENDS IN INVESTMENT CASTING TECHNOLOGY, by, Dr. Ing. Milan Horáček (PhD Brno University of Technology, CZ)• A TEXTBOOK OF FOUNDRY TECHNOLOGY, by, O.P. Gupta NOTE :- The picture used in 2nd slide is the famous “PERSEUS AND THE HEAD OF MEDUSA”, which was created by Benvenuto Cellini, using the lost wax process