Praaveen Materials 2

7/31/2019 Praaveen Materials 2

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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

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