Callum is burned. The main function of

Callum Wheatley 789586

12-18-2017

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Abstract

 

                                                                                                              

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table of Contents
1.0        Introduction. 3
2.0        Engine cylinder head. 3
2.1        Overview.. 3
2.2        Primary forming
process- Sand casting. 3
2.2.1          Advantages and
disadvantages of sand casting. 4
2.2.2          Capabilities of
sand casting. 5
2.2.3          Costs of sand
casting. 5
2.3        Material 5
2.4        Alternative methods
for producing cylinder heads. 6
2.5        Why sand casting is
used for cylinder heads. 7
3.0        Engine Piston. 8
3.1        Overview.. 8
3.2        Primary forming
process- Closed Die forging (hot) 8
3.2.1          Advantages and
disadvantages. 8
3.2.2          Capabilities of
forging. 9
3.2.3          Costs of forging. 9
3.3        Material 9
3.4        Alternatives methods
to forging. 9
3.5        why forging is used
for car pistons. 9
4.0        Conclusion. 9
5.0        Bibliography. 9
6.0        Appendices. 10
7.0        Acknowledgements. 10
 

 

 

 

 

 

 

 

 

 

 

 

1.0 Introduction

Within this assignment I have been tasked to research into
two components of a single consumer product and the primary forming processes
used to manufacture the two parts. For this I have chosen my product to be a
car with the two parts being the engine cylinder head and the engine piston with
the primary forming processes being sand casting and forging respectively. I
will do further research into the specific characteristics, advantages and
disadvantages of each forming process and why they are the chosen method for
the given part over alternatives. From completion of this assignment I will develop
further knowledge on primary forming processes and be able to explain them in a
coherent way as well as understand why primary forming processes are used for
certain products.

2.0 Engine
cylinder head

 

2.1     
Overview

An engine cylinder
head is commonly located at the top of the engine block where It closes off the
top of the cylinder forming the combustion chamber where the fuel is burned. The
main function of the cylinder head is to help the head gasket to seal the
cylinders so that they can build enough compression for engine operation to
work efficiently. Also, the cylinder head contains lots of channels and
passageways which are used to stop the engine from overheating as they enable engine
coolant to pass through, allow air and fuel to the cylinder and let exhaust
fumes escape. (stein, n.d.)

Primary forming process- Sand
casting                            (Engine cylinder head,
2017)    

Sand casting is the
most widely used casting process due to the complexity of products that can be
made and the range of materials that can be used. The sand casting process
involves six main steps which are:

1.
Producing the mould- the first step of the process is to produce the mould
itself. A sand mould is formed by filling the two halves of the mould known as
the cope and drag with sand. The sand is packed around the pattern which is a
clone of the part you’re a trying to create. The pattern is removed leaving a
cavity in the shape of the part. Risers are also added into the mould to
prevent cavities forming from shrinkage. Risers avoid this by providing molten
metal space as it cools, so that the cavity forms in the riser rather than the
part.

2. Clamping- once you have produced a
mould it must be prepared before the casting can take place. The surface of the
cavity is lubricated to make it easier to remove the part. The two halves are
then positioned together securely inside the flask to avoid the loss of any
material.

3. Pouring- The desired metal is heated
to melting point and poured into the basin with a ladle where the material
passes through the runners to the cavity. Enough metal must be poured to fill
the whole cavity until it reaches the top of the open riser. The pouring
process has to be very fast as the material will begin to solidify.

4. Cooling- The molten metal will begin
solidifying once it enters the mould. The amount of time it takes for the
material to cool is calculated beforehand using the wall thickness and
temperatures used.

5. Removal- Once the metal has
solidified the part can be removed simply by breaking the mould and removing
the sand. This is often performed by a machine which shakes the sand and part
out of the flask. Any excess sand is then shot blasted from the part to create
a soother surface finish.

6. Trimming-  Once you have retrieved the casting from the
mould the part you have produced will be joined to the runners and channels
that were used for the material to reach the cavity. This excess material is
cut away from the part leaving you with your desired product. The excess
material cut off can then be re-used in the process once again. (Sand moulding)

2.1.1    Advantages
and disadvantages of sand casting

Advantages

Disadvantages

You can produce parts with complex internal cavities which increases
the variety of products you can make

Low dimensional accuracy so casting is often made larger than
needed and machined down to its correct dimensions

Can produce complex external shapes which increases the
variety of products you can make

Poor surface finish casting must be made larger than needed
and machined to give a more desired finish quality

large parts can be produced which increases the variety of
products you can make

Secondary machining and tooling required which means you will
need extra equipment, use more energy and have higher labour costs

Low equipment and tool costs reducing the overall cost of the
process

Can have high porosity which increases the chances of cracking
to the part

Wide variety of material options increasing the variety of products
you can make

 

Excess material can be recycled reducing environmental effects
of the process

 

Short production times which gives the benefit of high
production speeds/short lead times for customers

 

 

(Sand Casting, n.d.)

 

 

 

2.1.2    Capabilities
of sand casting

 

Data

Value

Units

Production rates

1-60

Parts/hour

Machining allowances

1.5-6

mm

Draft angles

1-5

Degrees

Minimum section

Light alloys: 3, ferrous
alloys: 6

mm

Weight range

20g-400tonnes

 

Surface roughness

3.2-50

?m Ra

Material utilization

50-80

Percent

 

(Sand Casting, n.d.)

2.1.3    Costs
of sand casting

To be able to
perform the sand casting process there are many costs involved. Before you can
start anything, you must have any necessary tooling required for the process. This
involves the flasks to hold the mould in place, the ladle to pour the metal and
any machinery you may have to automate if required. The cost of flasks and a
ladle depends on the size of the part you are making, and cost of machinery
depends on whether you want to automate any parts of the process.

Material costs are
also another factor that must be considered when sand casting. This combines
the cost of the metal you are casting from as well as the cost of the mould and
core sand. The cost of the metal obviously depends on the size of the part and
the desired properties as different grades of metal have different prices. The
cost of the sand depends on the size of the mould and flask as well as what
type of sand you are using as there are many different types at different
costs.

Finally, you also
have production costs that are required for the process. This includes
manufacturing the pattern and mould, labour costs and energy costs. The cost
involved in producing the pattern and mould depends on the size and complexity
of the part you are producing as larger parts will use more material and more
complex parts will require more time and effort to produce increasing costs.
You also must factor in the labour costs involved for the workers who are
performing the process depending on the production rates. Energy costs are huge
with sand casting as extremely large amounts of energy are required to heat the
metal up to its melting point for it to be poured into the cast, this obviously
depends on what material is used for the part and what its melting point is.

(Sand Casting, n.d.)

2.2      Material

Cylinder heads in
automobiles are subjected to thermal strains, aggressive wear conditions, and
high fatigue stresses which is why it is key that the engineer selects the
correct material for the job. The main requirements of the material that are
needed to be suitable for use in an engine cylinder head are:

·        
Strength/weight ratio- The applied alloys
have to offer sufficient strength and hardness at room temperature for machining
and assembly as well as maintaining properties at elevated temperatures of up
to 250°C whilst also being as light as possible

·        
Thermal conductivity-  The alloy will have to have high thermal
conductivity to allow the heat from combustion to escape into the coolant quickly

·        
Surface quality- Smooth finishing
surfaces are required because of the constant gas flow for combustion as if
there were any rough patches or notches over time you will get cracks in the
part

·        
Fatigue strength-  Having a high fatigue strength if key as
engine cylinder heads are exposed to high-cycle fatigue (HCF) from combustion
cycles and to low-cycle fatigue (LCF) from thermal expansion and contraction
during start-up and stop of the engine

 (Aluminium
Automotive Manual, 2011)

Grey cast-iron
alloys were the popular choice in material in cylinder heads for many years due
to its cheapness compared to other metals like aluminium, castablility,
machinability, high corrosion resistance, rigidity, and hardness, as well as
its low thermal expansion. However cast-iron has the disadvantages of high
weight and low thermal conductivity when compared to alternatives. (cylinder head (automobile), n.d.) This then lead to the extensive use of aluminium alloys which left
cast iron only being used in applications where the internal stresses are much
higher in the cylinder head. This is because aluminium alloys are much lighter
and more conductive than cast-iron which makes aluminium alloys more suitable
for use in cylinder heads because it will help to keep the weight of the engine
down increasing performance of the vehicle and it will allow the heat from
combustion to escape into the coolant quicker which is the main purpose of the
part. (Galal,
2016)

Two of the most
common mixtures of aluminium alloy used in cylinder heads are:

·        
3.0% copper. 5% silicon, 0.5% manganese

·        
4.5% silicon, 0.5% manganese, 0.5% magnesium

The copper is used
in the mixture to improve the age hardening of the alloy while the silicon
increases abrasion resistance with the two working together to reduce the
thermal expansion of the material. By adding manganese or magnesium to the
alloy you increase the overall strength of the alloy. (cylinder head (automobile), n.d.)

2.3      Alternative
methods for producing cylinder heads

A) low retail
value, high volume

An alternative
method that may be used to sand casting for low value, high volume is pressure die
casting. Die casting consists of injecting molten metal under high pressure
into a steel mould called a die. The process is used to make large volumes of
zinc, aluminium and magnesium parts in complex shapes such as cylinder heads. The
cost of castings is relatively low with high much higher volumes and production
rates than sand casting.

B) medium value,
medium volume

Another forming
process that could be used to manufacture cylinder heads at medium value and
medium volume is investment casting. Investment casting is a process in which a
mould is made around a wax pattern that is burned away when the molten material
is poured in. investment casting is suitable at medium value and medium volume
rates because the process has such great versatility in both as you can use
rapid or precision investment casting methods or in the middle for medium,
medium.

C) high value,
low volume

One forming process
that could be used in high value low volume cylinder head production would be
ceramic mould casting (Swift,
2003). The
process is suitable for high value, low volume because It is a process that use
ceramics as the mould material which are often expendable. Also, ceramic mould
casting is relatively expensive but can achieve a good surface finish and
dimensional accuracy.

(Metal
casting processes, 2006)

2.4      Why
sand casting is used for cylinder heads

 

3.0 Connecting
rods

 

3.1     
Overview

The connecting rod is one of the most important parts of a
car engine as it is part of the system that creates energy for a car to move.
Connecting rods are used to join the crankshaft to the piston so that as the
crankshaft turns the connecting rods drive the pistons up and down which is
where the “four stroke” process intake, compression, combustion, exhaust takes
place.

3.2     
Primary forming process- Hot forging

Forging has been one
of the most common methods for the manufacture of car connecting rods for many
years due to the ability to create a variety of different shapes from a number
of materials with the process. The desired material is first heated up to
around 75% of its melting point which loosens the crystalline structure of the
metal to reduce the flow stress and reduce the amount of energy that will be
required to deform the material. The reason hot forging is used over cold is
because temperatures are required in order avoid strain hardening during
deformation. The hot material is then placed either manually or autonomously
into the cavity before the press/hammer comes down and forces the material into
the shape of the cavity. The press is sometimes heated as well as the material
at the same temperature to reduce temperature loss of the material while the
pressing takes place.  Once the material
has been pressed into shape the part is the removed and left to cool.

(What is
hot forging, n.d.)

3.2.1   
Advantages and disadvantages

Advantages

Disadvantages

High fatigue resistance which is key for a connecting rod as it will
constantly be moving at typically up to 6000 revolutions per minute

Energy and cost of heating the material to its deformation point is
high

Good strength from the grain structure alignment

The initial tooling costs of hot forging are massive mainly the hammer/press

You can use a wide variety of material, so you can produce a large
range of parts

Parts must be monitored closely as they cool to avoid warping

Good surface finish

Shape limitation when compared to casting processes where complex products
can be made

Less machining required afterwards than casting processes

Die wear is significant

Good material utilization

Lead times are typically weeks

 

 

3.2.2   
Capabilities of forging

Data

Value

Units

Production rates

1-300

Parts/hour

Machining allowances

0.8-6

mm

Draft angles

5-10

Degrees

Minimum section

3

mm

Weight range

10g -250Kg

 

Surface roughness

1.6-25

?m Ra

 

3.2.3   
Costs of forging

To be able to perform closed die forging there are many
costs involved. The initial tooling cost for this process is huge and is the
most expensive. You must buy/manufacture your two dies in the shape of the
product you want to produce. These dies are also likely to wear significantly
so you will need to replace them often. You Must also consider the cost of the
hammer/press that is used to force the material into shape. This can be huge
depending on the materials used and the size of the part.

You must also consider material costs which will vary
completely depending on the properties you require the part to have as
different grades of metal come at different prices.

The post forging processes that are required can greatly
increase the overall cost of the process as heat treatment is typically
required to achieve the material properties that you require. Also surface
treatment and machining maybe required afterwards which can be costly.

3.3     
Material

The most common materials that are used in the hot forging
primary forming process are stainless steel, aluminium alloys, copper,
magnesium, titanium, nickel alloys and a range of steel alloys. This is because
the forgeability of these materials is good because they become more ductile
when they are heated which makes it easier to deform the material.

Generally, there are a few materials that are commonly used
in car connecting rods depending on the type of car. Steel alloys are the most
common material used in every day vehicles for their high durability so that
the part will last as long as possible. However, in high performance vehicles
aluminium alloys are used because they offer a much lower weight reducing the
overall weight of the car at the cost of the durability. Furthermore, Titanium alloys
are sometimes used although steel and aluminium are more common titanium can be
used if you are trying to get a balance between the weight and strength for
your car but titanium is more expensive.

3.4     
Alternatives methods to hot forging

(A)Low retail value, high volume

If you were to produce a car engine connecting rod at low
value in high volumes and alternative for hot forging would be high pressure
die casting. High pressure die casting involves forcing molten metal under high
pressure into a mould cavity. Pressure die casting is a fast, reliable and cost
efficient forming process for the manufacture of high volume metal components
such as connecting rods. (Pressure die casting, 2018)

(B) medium value, medium volume

To produce connecting rods on a medium value, medium volume
scale you could use the sand casting process. Sand casting is a process
involving the casting of molten metal in a cavity surrounded by sand as the
mould material. Sand casting can be used at medium, medium because the
production rates of the process range greatly as you can produce them at almost
any quantity. However, the higher your production rate the lower the quality so
a medium, medium can be achieved.

(C) high value, low volume

An alternative method to hot forging to produce connecting
rods for a high value, low volume ratio would be manual machining. Manual
machining is a very slow forming process and requires the most skill to
complete. However, if performed well can offer a highly accurate part but only
in low volumes because of the time it takes to complete.

(Metal casting processes, 2006)

3.5     
why forging is used for car pistons

 

4.0 Conclusion

 

5.0 Bibliography

Aluminium Automotive Manual. (2011). Retrieved january 17, 2018, from
https://www.european-aluminium.eu/media/1580/aam-applications-power-train-4-cylinder-head.pdf
cylinder head (automobile). (n.d.). Retrieved from what when how:
http://what-when-how.com/automobile/cylinder-head-automobile/
Engine cylinder head. (2017). Retrieved from Makino:
https://www.makino.com/resources/case-studies/Engine-Cylinder-Head-/473/
Galal, M. A. (2016). How its made-cylinder head
manufacture. Retrieved january 2018, 16, from

made, H. i. (2013, October 23). How enginer
pistons are made. Retrieved from How its made:

Metal casting processes. (2006). Retrieved from Engineers handbook :
http://www.engineershandbook.com/Tables/castchart.htm
Pressure die casting. (2018). Retrieved from The metal casting:
http://www.themetalcasting.com/pressure-die-casting.html
Sand Casting. (n.d.). Retrieved from custompart:
http://www.custompartnet.com/wu/SandCasting
Sand moulding. (n.d.). Retrieved from Metal Technology Group:
https://mtgbg.com/uploads/documents/page/2/Sand_Moulding.pdf
stein, a. (n.d.). Function of a cylinder head.
Retrieved january 2018, 16, from
https://itstillruns.com/function-cylinder-head-7163457.html
Swift, K. a. (2003). Process selection from
design to manufacture . Butterworth Heinmann.
What is a piston, and what does it do. (n.d.). Retrieved from Haynes:
https://haynes.com/en-gb/tips-tutorials/what-piston-and-what-does-it-do
What is hot forging. (n.d.). Retrieved from China Savvy:
https://www.chinasavvy.com/what-is-hot-forging
 
 
 

https://www.buyautoparts.com/howto/what_is_a_cylinder_head.htm

http://what-when-how.com/automobile/cylinder-head-automobile/ 

http://www.custompartnet.com/wu/SandCasting

http://www.chinasavvy.com/surface-finish-and-sand-types

https://www.chinasavvy.com/what-is-hot-forging

https://www.european-aluminium.eu/media/1580/aam-applications-power-train-4-cylinder-head.pdf

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.529.4877=rep1=pdf

6.0 Appendices

 

7.0 Acknowledgements