ANALYSIS OF SHRINKAGE DEFECT AND EFFECTIVE YIELD IMPROVEMENT OF CASTING

Abstract

Casting is the process of producing a determined shape by melting solid metal into liquid form,
pouring it into a mould cavity and letting it solidify into the desired shape. Casting is the primary manufacturing
process hence its application is found in many fields which includes manufacturing of turbine blades, boilers, IC
engine cylinder block, piston head, connecting rod, machine tools etc. Mass production of products can be done
by casting process, a large number of products in a single mold or in other cases by reusing the mold. There are
different types of casting process they are sand casting, low pressure die casting, high pressure die casting,
gravity die casting, centrifugal casting, investment casting, full mold casting and semi solid casting. A casting
that does not fulfil the requirements of a customer like dimensions, machinability, surface finish etc. is an
unacceptable one. It either becomes scrap or it has to be repaired. Defects that occur in castings may be of
overall shape defects, surface defects, internal defects and structural defects. The overall shape defect includes
oversize, distortion and misruns. The surface defect includes scabs. Internal defect includes shrinkage, pores,
sub surface holes and cracks. The structural defect includes undesirable micro structural constituents, excess
inclusion level and oversized eutectic grains or cells. This work concentrates on the shrinkage defect which
comes under internal liquid surface defects. This shrinkage defect is due to the cause of improper gating system
design, improper composition control and solid sections of high modulus (volume / surface area) in the
casting. The shrinkage can be reduced firstly by redesigning the gating system which is predominant and easily
accessible one. It is proposed to design a new gating system. Secondly the shrinkage defect can be reduced by
changing the chemical composition and thirdly by bringing down the pouring temperature. The gating system is
designed and analysed by SOLIDcast. Results were validated by implementing the designed gating system in the
foundry. The composition is changed by increasing the carbon percentage in the grey cast iron. The addition of
Barium (Ba) based inoculation and the effect of the chemical composition change in the hardness and tensile
strength are studied. The improvement in the effective yield and casting yield is achieved by reducing the
shrinkage defect and pouring weight.