Post on 05-Apr-2018
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ABSTRACT
The main objective of this study is to gain knowledge on advanced materials and
processing technologies. There is always a trend to improve the existing material of a
component in order to meet their adequate requirements for future. In this study, the
material is selected for crankshaft using Cambridge Engineering Selector (CES) and
their manufacturing route is discussed. Moreover, an alternate material process is also
discussed.
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1. INTRODUCTION
In the initial part of the study, the functions, in-service conditions and material
characteristics of crankshaft were studied and the material for crankshaft was chosen
using CES. Now, the influence of the selected material in the production route, the
current manufacturing route which causes microstructural changes to the material and
how it affects the material properties described. In addition, an advanced alternate
material for crankshaft is chosen and its advantages, limitations and manufacturing
route are also discussed.
BASICS OF MANUFACTURING
Manufacturing is the process of transforming raw materials into finished products.
Manufacturing process may be classified into three major stages
Selecting the material
Primary processing
Secondary processing
Selecting the material
It is the first stage in the manufacturing process. It involves locating and extracting the
material or choosing the existing material which are already been found.
Primary processing
It involves converting the material resources into industrial stock, for example: fusing
silica sand with additives to obtain glass. The product of primary processing is readily
available in the market as cast and it does not undergo any further stages of
processing.
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Secondary processing
In this the industrial materials are converted into products. This process is done in
factories employing people and manufacturing machines. There are six secondary
processes, they are
Casting and molding
Forming
Separating
Conditioning
Assembling
Finishing
MANUFACURING PROCESS
Manufacturing process is a series of actions in making a product by changing the
shape, size or composition of materials. It involves designing, engineering, producing
and service processing. In the material processing, it produces geometrical changes or
changes in material properties or both. The examples of manufacturing processes are
forging, rolling, powder compaction, casting, turning etc.
CLASSIFICATION OF MATERIALS
Engineering materials can be widely classified into three groups based on their
relationships. The three groups are metallic materials, non-metallic materials and
composite materials. Composite materials are formed from two or more materials
forming a material with newer property. Metallic properties are further divided into
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ferrous and non-ferrous materials and the non-metallic properties are sub-divided into
polymers, ceramics and glasses.
Diagram 1: Classification of materials
MATERIALS
METALLIC MATERIALS COMPOSITE NON-METALLIC
FERROUSMETALS
NONFERRO
USMETALS
POLYMERS
THERMOPLASTICS
THERMOSETTING
PLASTICS
ELASTOMERS
CERAMICS
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PRODUCTION ROUTE
Based on the result obtained from CES by using the basic material selection criteria,
gray cast iron was chosen for its high compressive strength and thermal conductivity
and for its low thermal expansion. The suitable manufacturing process for this material
is casting.
Gray Cast Iron
Gray cast iron accounts to the highest tonnage among the cast irons. The major
composition of gray cast iron is in the range of 2.5 % to 4% carbon and 1% to 3%
silicon. The carbon content present makes the iron very fluid when its in a molten state
allowing it to cast into intricate shapes. The chemistry leads to the formation of graphite
flakes throughout the cast product. There are two advantages because of the presence
of graphite flakes in the cast; they are (1) good vibration damping, which is a desirable
quality for crankshafts (2) good internal lubrication, which is suitable during machining.
The casting of gray cast iron has relatively few shrinkage cavities and low porosity. The
various forms of gray cast iron are ferritic, pearlitic and martensitic. Gray cast iron
basically have low ductility and moderate strength but high thermal conductivity. The
elastic modulus of gray cast iron is lower than steel and nodular cast iron so its non-
linear, but they tend to increase with increase in graphite content. The microstructure of
gray cast iron is desirable so that the material could be easily machined.
JUSTIFICATION OF CURRENT MANUFACTURING ROUTE
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By using CES chart,the limits such as shape, physical attributes, process characteristics
and economic attributes were assigned and the values were mapped with the relative
cost index and the best shaping process for gray cast iron was found out.
Green sand casting is chosen as the best process for the manufacturing of crankshafts.
Graph 1: Process selection of crankshaft using CES
CASTING
Casting is a process in which the molten metal flows into a mold which then solidifies in
the shape of the mold cavity. It is one of the oldest shaping processes which are still
followed for making parts of complex shapes like crankshafts. Casting process can be
made to any metal which could be heated to the liquid state. Few casting methods are
well suited to mass production.
Casting includes both casting of ingots and casting of shapes. The term ingot describes
that the casting undergoes subsequent reshaping by processes like rolling or forging.
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And shape casting involves the production of more complex geometries which is likely
to be as the final shape of the product.
Sand casting is the widely used casting process. Sand casting is also called as sand-
mold casting. It is nothing but pouring the molten metal into a sand mold and allowing it
to solidify and then breaking the sand mold to obtain the casting. The casting can be
then checked to improve its metallurgical properties. As the mold is been broken to
obtain the casting, a new sand mold has to be made for each part that is produced.
Diagram 2: Steps in the production sequence in sand casting
Core
making (if
Pattern
making
Preparation
of sand
Melting
(Raw
Mold
making
PouringSolidifica
tion and
cooling
Removal
of sand
mold
Cleaning
and
inspectio
Finishe
casting
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SAND MOLDS
Sand molds are classified as green-sand , dry-sand, or skin-dried molds.
Green-sand molds
Green-sand molds are a mixture of sand, clay and water. The word green refers to that
the mold contains moisture content in it. Green-sand molds have required strength for
most of the applications, good permeability, good collapsibility and good reusability.
This is the least expensive one of all the other molds and it is the widely used one. But
these sand molds have even few problems like the moisture in the sand can cause
defects in some castings, depending on the metal and geometry of the part.
Dry-sand mold
A dry-sand mold is made by using organic materials rather than clay, and this mold is
baked in an oven at a high temperature. Baking the mold in oven strengthens the mold
and hardens the cavity surface. Therefore it attains better dimensional control than
green-sand mold. Dry-sand molding is more expensive.
Skin-dried mold
In a skin-dried mold ,the advantages of a dry-sand mold is slightly achieved by drying
the surface of a green-sand mold to a depth of 10-25 mm at the mold cavity surface,
using heating lamps or other means. Special bonding materials can be added to the
mixture to strengthen the cavity surface.
MICROSTRUCTURE
Gray cast iron contains two microstructure constituents causing hard spots, which
aggravate machinists. The two constituents are iron carbides and iron phosphides. The
figure shows the typical microstructural arrangement of iron carbide and iron
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phosphides. Iron carbide is commonly called as steadite. Its a constituent of the
eutectic phases between iron and carbon. As it is eutectic they take a long time to
solidify. And in case of iron phosphide, a eutectic phase is developed between iron and
phosphorous.
A tertiary iron-carbon-phosphorus eutectic is found in the microstructure when these two
eutectics are combined. The tertiary eutectic formed has a still lower melting point when
compared to the individual eutectics.
As these eutectics take a longer time to solidify it is present in the form of liquid
surrounded by solid in the microstructure of gray cast iron. And this could flow from thin
sections to thick sections forming microscopic shrinkage voids in the thin sections. The
microscopic shrinkage voids are similar to those of the carbide and steadite
constituents.
Microstructure of gray cast iron
The resistance to wear of gray cast irons depends on the microstructures, increasing
the amount of graphite and ferrite reduces the resistance to wear.
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Due to the effect of graphite flakes on crack initiation, the fatigue strength of gray cast
iron is lower.
The composite structure of gray cast irons and the bonding structure of graphite makes
it as the one of the best damping metal.
ALTERNATE MATERIAL
As the demand increased by automotive industries, the need for alternate materials for
the manufacturing of various parts of the system has widely increased nowadays. This
led to the development of innovative combinations like composite materials. Composite
materials are made up of two or more distinct phases having very good properties which
are different from those of the constituent materials. The majority of these materials ate
metal matrix composites (MMC) .In these metallic matrices are reinforced with high
strength and modulus phases like oxides, nitrides and carbides. The usage of the matrix
metal carbides has greater advantages like positive modifications in the strength and
structure and improvement in physical properties of the material.Normally matrix metal
composites are processed by stir casting and infiltration.
In recent times, aluminium matrix composites are attaining higher importance because
of its low cost and added advantages like their isotropic properties. It has high strength,
specific modulus and good wear resistance than other composites. They are more
specific for their isotropic mechanical properties. Depending on the chemical
composition of the al-matrix it offers a wide variety of mechanical properties. Normally
they are reinforced by Al2O3, SiC and C.
TYPES OF ALUMINIUM MATRIX COMPOSITES
Depending on the type of reinforcement, the aluminium matrix composites can be
classified into four types
Particle-reinforced AMCs
Short fibre-reinforced AMCs
Continuous fibre-reinforced AMCs
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Mono filament-reinforced AMCs
PARTICLE-REINFORCED AMCs
These composites contain ceramic reinforcements. Ceramic reinforcements are
basically oxides or carbides. These are used for structural and wear resistance
applications. They are generally manufactured by solid state or liquid state processes.
These are less expensive when compared to other processes and even the mechanical
properties are lower than them.
SHORT FIBRE-REINFORCED AMCs
Short fibre-reinforced AMCs is the first and the famous one to be developed and used in
pistons. The mechanical properties are better than that of particle or short fibre
reinforced composites. The characteristics are similar to that of continuous fibre and
particle reinforced AMCs
CONTINUOUS FIBRE-REINFORCED AMCs
In continuous fibre-reinforced AMCs the reinforcements are in the form of continuous
fibres. The fibres can be parallel to the production of the composite. These composites
are produced by pressure infiltration route.
MONO FILAMENT-REINFORCED AMCs
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Mono filament-reinforced AMCs are usually of larger in diameter and are produced by
chemical vapor deposition. Directionality is the important aspect of these composites.
The reinforcement is done to strengthen the material by preventing matrix deformation.
Now for the manufacturing of crankshaft we are choosing Al-SiC because of its
high specific strength and stiffness, temperature resistance, low thermal
expansion co-efficient, wear resistance and thermal conductivity. The material
requirements for crankshaft are satisfied by this material.
ADVANTAGES OF ALUMINIUM MATRIX COMPOSITES
The major advantages of aluminium matrix composites are
The aluminium matrix composites have greater strength comparatively.
There is a tendency of the composite to provide improved stiffness.
The weight of the composite is reduced.
The temperature properties of the composites are higher.
The thermal expansion coefficient is possible to be controlled.
Enhanced thermal/heat management.
Electrical performance of the composites.
Wear resistance is high.
The mass could be controlled during reciprocating applications.
The damping abilities are high.
The processability of the composite is better.
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LIMITATIONS
Even if there are a plenty of advantages in using aluminium matrix composites, as this
is an innovative and distinct process it may have few limitations in the manufacture of
crankshafts. They are
The reuse of the composite materials is not possible.
Due to the light weight of the aluminium matrix composites the density properties
are quite low.
The cost of the composite is high.
The fabrication of aluminium matrix composite is tedious.
As new technologies are involved in this process it is immature.
The service experience of aluminium matrix composite crankshafts is limited.
MANUFACTURING OF CRANKSHAFT BY USING Al-SiC
By using CES chart , the properties of Al-SiC were taken as the limits and the desirable
manufacturing process was chosen based on the relative cost index. Hot closed die
forging is the best manufacturing process for making crankshafts.
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Graph 2: Process selection of crankshaft by using CES for advanced material
FORGING
Forging is a process in which the work is compressed between two dies using either
impact or pressure to form the part. It is one of the oldest metal forming process. It is
one of the most important processes to make high-strength components for automotive,
aerospace and other applications.
Forging is carried out in different ways. One way is to classify by its working
temperature. Most of the forging operations are hot which leads in decreasing strength
and increasing the ductility of the metal. On the other cold forging process increases the
strength of the metal.
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MANUFACTURING ROUTE FOR Al-SiC
Al-SiC is manufactured by hot closed die forging. In hot closed die forging a heated
blank is formed by means of a single compressive stroke by hammer or press using
closed dies. There are two dies in-between the work piece, the upper and the lower die.
Normally a succession of a dies is used to achieve the final or near final shape. Hot
forging could be performed when the temperature is higher than the the recrystallization
temperature. Hot forging leads to have components with good mechanical properties
and structural integrity due to the grain refinement, reduction in porosity and break up of
inclusions.
Hot closed die forging
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The process results in highly oriented grain flow and anisotropic mechanical properties
which can be aligned to give improved mechanical properties in the direction of principal
service stresses.
The process is capable of relatively tight tolerances. Closed die forgings may be
intricate but are limited in size. There is a number of variants which can be distinguished
mainly by how close-to-form the final product is. Variants include blocking, precision
forging, close-to-form forging and precise form forging.
CONCLUSION
In this report the manufacturing route of the material that is chosen by using CES chart
is justified and the process is explained. The microstructural changes in the material
during the manufacturing process areanalyzed and the change in the material
properties is indicated. Moreover an advanced material for the manufacturing of
crankshaft is selected and their advantages and limitations are discussed. The
manufacturing route of the advanced material is then justified by CES chart.
REFERECES
Groover, Mikell P. 2007 Fundamentals of Modern Manufacturing. 3 rd Ed.
United States of America: John Wiley & Sons, Inc.
Thompson, R. 2007 Manufacturing Processes for Design Professionals.
London: British Library Cataloguing-in-Publication data
Kalapakjian, Schmid, S. 2006 Manufacturing Engineering and Technology. 5 th Ed.
Singapore: Pearson Education South Asia Pvt Ltd.
MICHAEL F.ASHBY, 2011. Materials Selection in Mechanical Design. 4th Ed.
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Oxford,UK: The Boulevard
Journal of Minerals & Materials Characterization & Engineering.
[18-oct-2011] [Online]
http://www.imp.mtu.edu/jmmce/issue8-6/issue8-6P455-467.pdfhttp://www.imp.mtu.edu/jmmce/issue8-6/issue8-6P455-467.pdf