INVESTMENT CASTINGS 1

CONTENTS- 1.Defination 2.History 2.Brief process 3.Process video 4.An example of turbine rotor 5.Need of investment castings. 6.Comparision of investment castings and sand castings 7.Advantages 8.Disadvantages 9.Applications in India 10.Conclusions 2

HISTORY The history of lost-wax casting dates back thousands of years. Its earliest use was for idols, ornaments and jewellery In the 1940s, World War II increased the demand for precision net shape manufacturing and specialized alloys leading to investment casting boom. 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. 3

DEFINITION Investment Casting (Lost Wax Process) A pattern made of wax is coated with a refractory material and then metal is poured. "Investment" comes from a less familiar definition of "invest" "to cover completely," which refers to coating of refractory material around wax pattern It is a precision casting process ,capable of producing castings of high accuracy and intricate detail. 4

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FUTHER PROCESSES 1.Separation of individual components with high speed cutter. 2.Shot blasting 3.Grinding for gate removal and thick edges removal.May be manual or automatic. 4.Final product.

Investment Casting a Turbine Rotor Kalpakjian/Howmet Corp Wax pattern of turbine rotor Cut-away of ceramic mold applied over over wax pattern Cut-away showing wax melted out of mold. (Metal then poured into mold.) Finished turbine rotor, near-net shape 7

WHY INVESTMENT CASTINGS? Design Flexibility:Investment casting produces near net shaped configurations, offering designers and engineers freedom of design in a wide range of alloys. Wide Choice Of Alloys:Various Ferrous and Non Ferrous metals are routinely cast.   Eliminate Tooling Setup:By offering near net shaped configuration ,fixturing costs are substantially reduced or eliminated. rd continued

COMPARISON OF SAND AND INVESTMENT CASTINGS QUALITY Sand casting Tolerance (0.7~2 mm) and defects are affected by shrinkage Generally have a rough grainy surface Investment casting Tolerance (0.08~0.2 mm) Good to excellent surface detail possible due to fine slurry

FLEXIBILITY Sand casting Investment casting High degree of shape complexity (limited by pattern) Investment casting Ceramic and wax cores allow complex internal configuration but costs increase significantly

ADVANTAGES Parts of great complexity and intricacy can be cast. Close dimensional control and good surface finish. Wax can usually be recovered for reuse. Additional machining is not normally required this is a net shape process. Weight is reduced to some extent. 11

DISADVANTAGES Many processing steps are required . Relatively expensive process. Not suitable for simple parts. 12

APPLICATIONS IN INDIA 12-18 large size foundries • 390 investment casting units (12000 MT) 12-18 large size foundries grown by 30%n last 3 years 210 investment casting units exporting product • Product profile Valves & Pumps 50% Automobiles 30% Armaments 10% Industrial & Decorative Hardware 5% Electronics, Medical, Machine tools, 5% Turbine, Railway, Textile, Material Handling Equipment 13

CONCLUSIONS Investment casting may be termed as “lost-wax casting” Investment casting is practical for prototype and low-volume production applications. In less than two weeks, prototype castings in numerous alloys are ready for testing,evaluation or use. Although it is an expensive process,it produces quality casting. CONTINUED

In many cases weight is reduced by more than 50% percent thus inputing more raw material usage and increasing the overall productivity of the unit. Unlimited design freedom since draft angles, cores, parting lines, etc., are irrelevant.Very complicated products can be manufactured which are almost impossible by casting process,welding etc. Patterns and molds are expendable

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