engineering materials and processes lecture 5 – casting...
TRANSCRIPT
Engineering Materials and ProcessesLecture 5 – Casting Process
Casting iron in a sand mould:
Wikipedia
Casting
Engineering Materials and Processes
Reference Text Section
Higgins RA & Bolton, 2010. Materials for Engineers and Technicians, 5th ed, Butterworth Heinemann
Ch 5
This lecture follows exactly with Higgins Chapter 5.
Cooling a thick casting causes poor grain structure. Large ingots are a problem.
Grains in cast aluminium
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Engineering Materials and Processes
Ingot casting (Higgins 5.2)
Low Pressure Metal Casting (Higgins 5.3 Sand-casting)
Engineering Materials and Processes
VIDEOMetal casting: Sand MouldsScutt, Don. [Chadstone, Vic.] : Double D Technical Productions, c2004. DVD (29 min.)This program covers jobbing moulding, cold box moulding, pit moulding, rapid prototyping, investment casting, medium volume green sand moulding, automated cold box moulding, hot box moulding, high volume lost foam moulding, hunter process, disamatic.Mt Druitt College Library: DVD 671.252/METARecommended Viewing: All sections.
5.6 Investment-casting5.7 Full-mould process (Lost foam)
Porosity in Low Pressure
Porosity occurs because the casting shrinks on solidification. High pressure can fix this, but it makes the mould very expensive. Another way is to use a reservoir of molten metal that feeds more liquid as it solidifies.
In this low pressure casting, aluminium alloy was poured down the runner into the mould. The hollow in the top of the runner caused by liquid flowing from the runner into the mould as the casting solidified. As well as the hollow at the top, you can see some holes in the runner and one hole within the casting itself. The runners and risers will later be cut off and discarded.
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Engineering Materials and Processes
High Pressure Metal Die Casting(Higgins: 5.4 Die-casting)
Engineering Materials and Processes
VIDEOMetal casting: Die Casting Scutt, Don. [Chadstone, Vic.] : Double D Technical Productions, c2004. DVD (29 min.) This video shows six casting processes and outlines the advantages, limitations and areas of application of each process. Included are gravity casting high pressure hot chamber die casting, high pressure cold chamber die casting and squeeze casting. Mt Druitt College Library: DVD 671.253/METARecommended Viewing: All sections.
5.4.1 Pressure die-casting5.4.2 Gravity die-casting5.5 Centrifugal casting
(Higgins: 5.9 The choice of casting process)
Engineering Materials and Processes
In order of precision:
1. Investment-casting2. Die-casting3. Sand-casting4. Full-mould process
In order of melting point:
1. Investment-casting2. Sand-casting3. Die-casting
Metal Casting Processes
Engineering Materials and Processes
Wikipedia: Casting
(Higgins: 5.9 The choice of casting process)
Engineering Materials and Processes
The initial costs of mould and equipment are higher in the case of die-casting (B) than for sand-casting (A). Labour costs are higher for sand casting. The break-even value, i.e. the number of castings which must be made before the use of die-casting is justified, may be of the order of several thousands. Once the break-even value has been reached, the cost per die-casting becomes less than the cost per sand-casting.
Higgins Fig 5.8
Shrinkage AllowanceAtoms in a solid fit closer together than in a liquid, so shrinkage occurs.
A few substances expand when they solidify because they have a very loose packing arrangement. E.g. Water (ice), and Silicon.
Based on;http://www.calculatoredge.com
Metal Contraction (%)
Grey cast iron 0.7 to 1.05
White cast iron 2.1
Malleable iron 1.5
Steel 2.0
Brass 1.4
Alluminium 1.8
Aluminium alloys 1.3 to 1.6
Bronze 1.05 to 2.1
Magnesium 1.8
Zinc 2.5
Manganese steel 2.6
Engineering Materials and Processes
Design Study
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Engineering Materials and Processes
Learning Space > All Units > Engineering and Technology > T173_2> Manufacturing > PART 2. Casting:
2 Casting2.1 Introduction2.2 Properties for processing – casting2.3 Types of casting
2.3.1 Permanent pattern2.3.2 Permanent mould2.3.3 Expendable mould and pattern
2.4 Casting processes2.5 Casting metals2.6 Casting plastics2.7 Casting microstructure and defects2.8 Casting our gearwheel
Engineering Materials and Processes
Graphical comparison of materials properties.
Online Properties Resources.
Metal Grains and processing
DoITPoMS: Dissemination of IT for the Promotion of Materials Science
Wikipedia: Casting
GLOSSARYBinders Break EvenCharge Cope Core Draft Drag FeederFettlingFlash Gas Porosity GateGreen Sand Impurity
Engineering Materials and Processes
Castings Glossary
Inclusion Investment Casting Ladle Lost Foam Parting LinePattern RiserSand Casting Shrinkage Shrink Hole Sink MarksSlag SprueVacuum Casting
QUESTIONSMoodle XML: Some questions in 10107 Processing
1. Define all the glossary terms.2. List 2 advantages that casting offers over other manufacturing processes.3. List in a table the advantages/disadvantages of casting processes: Sand,
investment, gravity die and high pressure die. Include melting point, accuracy, setup costs, production costs, design limitations.
4. Sand casting pattern and sand mould costs $1900 and each part costs $50 in labour. Die casting mould (die) costs $25000 and per part is $10. Calculate the break-even quantity where die-casting becomes cheaper than sand casting.
5. Explain the following casting terms: Flash, porosity, feeder, runner, draft, ejectors, cores.
Engineering Materials and Processes