MACHINABILITY COMPARISON OF CASTING METHODS

Stiff competition from local and global markets has made many manufact uring firms reduce lead time through the introduction of concurrent en gineering principles. Often the existing products and processes are re designed to reduce lead time. The motivation for the present work is b ased on changing the casting method to reduce machining allowance, the reby reducing machining time. Before such a change is implemented in a mass-production foundry, its influence on the machinability of the ma terials must be thoroughly investigated and understood. This paper dea ls specifically with comparing the machinability of cast iron produced by the green-sand-casting process (which by its inherent nature neces sitates a machining allowance of 6-8 mm), with respect to the machinab ility of cast iron produced by the encapsulated-sand-casting process ( which enables the machining allowance to be reduced to 3-4 mm), Severa l tests, including chemistry, microstructure, microhardness, milling p ower, drilling force, torque, and drill-bit wear tests have been condu cted to compare the cast irons. Two-level factorial design of experime nts has been used to develop predictive models for the power consumed in milling and the axial force and torque in drilling. Within the enve lope of cutting parameters investigated, the predictor model equations for power, force, and torque are found to approximate the actual resp onse to with 90.9%, 99.3% and 98.5% accuracy, respectively, for green- sand castings, and 93.4%, 97.7% and 98.6% accuracy for encapsulated-sa nd castings. All the experimental tests and the statistical models for power, force and torque are compared, no significant difference being found between the machinability of green-sand cast iron and encapsula ted-sand cast iron.