INTRODUCTION: events to produce casting parts. First event includes

INTRODUCTION:

Metal parts with simple to intricate shape
complexity and thick to thin walls can be cheaply produced by green sand
casting process. Casting can have wide range from a small amount of grams to
several hundred tons and can produce in job to mass production.  Sand casting is the most extensively used
process for both ferrous and non-ferrous metals and accounts for around 90% of
all castings produced. In sand casting process, everything can be recycled
except electricity and manpower. In general, 
 foundry  industries involves three group of events to
produce casting parts. First event includes sand preparation, core making, creation
and assembly of mold. Second event involves furnace charging, metal melting,
holding, metal treatment, pouring liquid metal into moulds, which are then left
to cool. Third event involves shakeout, cleaning, fettling, shot-blasting and
inspection. These parts are used in automobile, 
aerospace, railways, shipping, medical devices, automobiles, sanitary,
electrical machineries, home appliances ,art object ,chemical, biomedical and
other critical applications.

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Gray cast irons exhibit high resistance to
wear and seizure, excellent vibration damping capacity, excellent
machinability, high thermal conductivity, high fluidity and low cast. More than
50% castings have been produced by various grades of cast iron. They are
required to be free of defects and possess the desired range of sustainability
where they are used. In practice, this is a big challenge, since there are
large number of parameters and their interactions related to process and alloy
composition. Their values modify for each casting component and their effect on
quality is not very well understood. A large number of castings are therefore
rejected, repaired or recycled, leading to wastage of production resources.

A survey of 20 sand
casting (SC) foundries located in Kolhapur cluster in Western India was first
carried out to understand their capabilities and quality issues. Survey
indicated that majority of defective castings produced in foundries have
suffered from major defects such as shrinkage, blow holes and sand inclusions.
It was observed that a large proportion that is 50 %  to 70% of the defective castings produced in a
iron foundries, have two, three or four types of defects occurring
contributed  major proportion of total
rejection and remaining all types of defects occurring contributed minor
proportion of total rejection. At one side remedies applied for one specific type
of defect have control the specific defect but some remedies of controlled  specific defect can fervor other types of defects
and at other side large number of parameters related design, process, material
and geometry. Such type of scenario commonly observed in foundries.

  Casting 
 defects   in
foundries contributes directly to customer concerns about reliability, quality
characteristics and prompt delivery. Controlling of defects   depends on understanding its sources and
causes. Identified sources and causes grouped under design and process
categories and analyzed independently one after another to ensure significant
improvements in product quality, component performance, design reliability and
quick delivery. This can be achieved if casting defects in castings can be
minimized or eliminated with the help of systematic sequential approach which
leads proper identification, selection and optimization of parameters related
to design and actual process of production of casting components.

       
Foundry engineers and researchers have contributed significantly to find
parameters responsible for individual defect and optimized parameter values to
reduce individual defect. This is not sufficient for controlling overall
rejection. Also, several different models were evolved to predict casting defects
such as Artificial Neural Network (ANN) and Multivariate Regression (MVR) needed
a large amount of data related to casting process parameters, alloy composition
and occurrence of defects for training and collected from SC foundries. The
main limitation of ANN is that the relationship between inputs and outputs
cannot be readily explained in technical terms. The individual techniques were found to have specific restrictions that
prevent their widespread use in foundry industry. The rationale for the
present research would be

Ø  It
was observed that a large proportion that is 50 %  to 70% of the defective castings produced in
a iron foundries, have two, three or four types of defects occurring
contributed  major proportion of total
rejection and remaining all types of defects occurring contributed minor
proportion of total rejection.

Ø  Aim
of foundrymen   to produce defect fee
casting with higher yield.

Ø  In
small and medium scale foundries, it is found that casting product development
based on trial and error approach hence more time for product development.

Ø  Less
focus on grouping of parameters to minimize the multiple defects.

Ø  Major
quality metrics of sand  castings
component include dimensional reliability (with

respect to designed part), internal and
external soundness (Internal porosity).

This leads the
necessity to,

Ø  A
systematic categorization of sand casting defects based on multiple attributes,
and implementation in a user-friendly environment.

Ø  Mainly
focused on multiple defects that is mostly occurred defects in sand casting
process.

Ø  Identification
and selection of parameters causing major casting defects such as shrinkage,
sand inclusions and blow holes.

Ø  Feeding
related parameters such as feeder size, neck size, feeder efficiency and feeder
yield  grouped in first group and optimized
feeder and neck size to obtain shrinkage porosity free casting supported by
simulation.

Ø  Melting
and sand related parameters such as pouring temperature, permeability, mould
hardness, green compressive strength and moisture content grouped in second
group and optimized to minimize major casting defects such as shrinkage,
blowholes and  sand inclusions.

Ø  Determination
of significant parameters and their specific values to avoid the occurrence of
defects.

The
proposed research developed iterative process approach based on modulus of last
freezing section and obtained empirical relationship to find feeder diameters,
feeder efficiency and feeder yield to minimize shrinkage porosity development in
casting component supported by simulation. After confirmation of simulation results,
the sequential two stage optimization has been implemented to obtain optimal
set of melting, chemical and sand parameters to minimize major casting defects
such as shrinkage, blowholes and sand inclusions with the help of grey relation
analysis approach.

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