PSI - Issue 71

Sameer S. Gajmal et al. / Procedia Structural Integrity 71 (2025) 430–437

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The casting die material for making the pin shaped castings is Graphite the properties of which are given in Table 2. Table 2. Characteristics of the graphite used in casting die Gajmal and Raut (2022) Grade MG1 Density (g/cm 3 ) 1.85 Grain Size (micron) 43 Compressive Strength (MPa) 81 Flexural Strength (MPa) 40 Coefficient of Thermal Expansion (mm/) 4.5×10 -6 Electrical Resistivity (μ.Ω.m) 9 Porosity (%) 13 Ash Content （ PPM ） 800/50/10 2.3 Die development In microwave-aided casting the die used needs to be microwave-compatible, where the microwaves are to be absorbed by the die material, which in turn raises the temperature and causes heating. Due to this, the charge will get heated and when the temperature goes beyond the melting point, it gets liquified. The microwave-absorbent materials are silicon carbide, graphite and alumina that provide a blend of thermal and electromagnetic properties. The die assembly is subjected to microwaves, and the molten metal is poured inside the die cavity for specimen preparation automatically and allowed to solidify with time inside the die cavity and later the pin is extracted. The base plate, split mould, pouring basin, and sprue cum gate with die assembly is shown in Figs. 2(a) and 2(b). Graphite being an excellent microwave absorber, the die facilitates quick heating and the charge melts in less time. The details of machining various components of the die are given in Table 3.

Fig. 2(a) Schematic if casting die assembly, and Fig. 2(b) Casting die assembly

Table 3. CNC machining operations used in die development Die Part Machining operations

CNC machine details

Facing, Plain Turning & internal Taper Turning

Pouring basin

Make: Galaxy Machinery Pvt. Ltd. Controller: Fanuc X & Z Axes: Servo Controlled

Sprue cum gate, Split mold, Base plate

Facing, Turning

2.4 Microwave aided pin casting process The castings were created using a microwave furnace (Make: CEM Corporation, USA; Model: Phoenix). The microwave furnace consists of three components namely microwave generator to produce the microwaves; wave guide to carry the waves and their manipulation is done by an applicator. The furnace maximum power at 240 V is 1.4 kW with heat chamber dimensions as 21 x 11.6 x 7.6 cm. The schematic representation of the microwave casting is shown in Fig. 3. The casting die inside the furnace, loaded with charge, is exposed at a power of 1.4 kW until the alloy melts at above 350 °C. The furnace is equipped with an infrared pyrometer having a temperature range of 350 to 1800 °C and least count of 1 °C to monitor the temperature.