Journal of Materials Processing Technology Volume

Được đăng lên bởi Thiện Nguyễn Minh
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Journal of Materials Processing Technology 182 (2007) 615–623
Effect of evaporative pattern casting process parameters on the
surface roughness of Al–7% Si alloy castings
Sudhir Kumar
, Pradeep Kumar, H.S. Shan
Mechanical & Industrial Engineering Department, Indian Institute of Technology Roorkee, Roorkee 247667, Uttaranchal, India
Received 14 December 2005; received in revised form 16 August 2006; accepted 11 September 2006
Evaporative pattern casting (EPC) process has drawn great attention from both academia and industry in recent years. The expandable polystyrene
(EPS) pattern is a key feature of EPC process which is buried in unbonded sand and replaced by molten metal. This paper investigates the effect
of process parameters like degree of vacuum, pouring temperature, grainfiness number, amplitude of vibration and time of vibration on the
surface roughness of Al–7% Si alloy castings in EPC process. In order to evaluate the effect of selected process parameters, the response surface
methodology (RSM) is used to formulate a mathematical model which correlates the independent process parameters with the desired surface
roughness. The central composite rotatable design has been used to conduct the experiments. The analysis of results indicates that the surface
roughness increases with increase in degree of vacuum, pouring temperature. Whereas, it has an inverse relationship with grainfiness number,
amplitude of vibration and time of vibration.
© 2006 Published by Elsevier B.V.
Keywords: EPC process; Process parameters; Surface roughness; Response surface methodology (RSM)
1. Introduction
Evaporative pattern casting (EPC) process offers several
advantages over conventional sand casting processes, such as
simplified production techniques, and reduces environmen-
tal waste due to binder emissions and sand disposal. The
process is well-suited for castings with complex geometries,
tight tolerances, and smooth surface finish requirements. When
the castings are designed to fully exploit these advantages,
cleaning and machining times are dramatically reduced if not
completely eliminated. Therefore, the EPC process is viewed
as a value-added process rather than a substitute for sand
In EPC process, pattern is usually made of expandable
polystyrene (EPS). The use of a polystyrene pattern increases
dimensional accuracy, and gives improved casting quality, com-
pared to conventional casting [1]. Barron indicates that smooth
surface of the pattern can be obtained by use of small, light
weight polystyrenebeads and thin walled low density pattern [2].
Corresponding author. Tel.: +91 9412420113.
E-mail addresses: s
k tomar02@yahoo.com,
kumardme@iitr.ernet.in (S. Kumar).
In this process, the sand mold contains no binder and moisture
and hence the refractoriness of the mold is entirely dependent
upon the molding sand [3]. The sand without binder leads to
a defective casting due to sand falling problem. An attempt is
made to bind the EPC mold by creating vacuum in the mold
while mold is sealed from the both end by polyethylene film
[4]. Any type of molding sand can be used for the process as
long as the sand resists the temperature of the molten metal
being poured [3]. Silica sand, zircon sand, olivine sand and
chromites can be used as molding sand. Due to high degree
of sand reclamination in EPC process, expensive sands such as
zircon or chromites can be used [5]. The strength of the mold
is determined by frictional resistance between the sand grains.
The strength of the mold is higher with angular grains, although
rounded grains provide a higher bulk density [6,7]. The density
of free flowing sand can be increased by vibration. Leighton
Buzzard sand compacted by vibration was found to have a den-
sity 12.5% greater than for unvibrated sand or resin bonded sand
which had been lightly rammed [8]. Bennett et al. have studied
various gating arrangements for the different aluminum castings
to determine the pyrolysis defects. Pyrolysis defects with foam
sprue were found to be greater compared to untapered hollow
ceramic sprue. Multiple gates also had little effect on reducing
defects. When the pattern was oriented vertically, top gating was
0924-0136/$ – see front matter © 2006 Published by Elsevier B.V.
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