3/20/2006 56:032 Design for Manufacturing 1

Chapter 11

Metal-Casting Processes

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Manufacturing Processes Alternatives

Material Removal ProcessesForming ProcessesAssembly

And..Casting Processes

Similar to?

Examples?

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Metal Casting ProcessesThe process involves:

Pour molten metal into a mold patterned after the part to be manufacturedAllow it to solidifyRemove the part from the mold

Advantages of Metal Casting Processes:Produce part in single step (“near-net” shape)Produce large partsCan produce a wide variety of shapes and sizesComplex shapes are possibleInternal cavities are possible

Any Disadvantages?

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Examples of Cast ProductsNote how difficult it might get to produce these parts using other manufacturing processes

Fig. 11.1 aFig. 11.1 bFig. 11.1 cFig. 11.1 d

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Categories of Metal-Casting ProcessesExpendable Molds:

Typically made out of sand, plaster, ceramics and similar materialSuch material are refractory i.e., capable of withstanding high temperatures. After casting the mold is broken up to remove the casting

Permanent Molds: Made of metals that maintain their strength at high temperatures.Are used repeatedly Designed in such a way that the casting can be removed easily

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Categories of Metal-Casting ProcessesComposite Molds:

Made of two or more materials (sand, graphite, and metal) in order to combine the advantages of eachHave both permanent and expendable portions

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First: Expendable Mold CastingThere’s a variety of casting processes that use expendable molds.We will focus on discussing 2 of them in detail:

Sand CastingInvestment Casting

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Sand CastingProcess outline:

Place a pattern (having the shape of the desired casting) in sand to make an imprintIncorporate a gating systemRemove the pattern and filling the mold cavity with molten metal Allow the metal to cool until it solidifiesBreak away the sand metal Remove the casting

ExampleCan we make hollow parts or parts with internal cavities? How?

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Sand Casting (contd.) Sands

Silica sands (SiO2) is widely used as the mold materialHigh melting point

Factors affecting sand selectionFine round grains can be closely packedFine grained sand has lower permeabilityMold should have good collapsibility

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Sand Mold Terminology

Figure 11.3 Schematic illustration of a sand mold, showing various features.

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Finished Casting

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Sand Mold Preparation

(a) Mechanical drawing of part (b & c) Pattern Mounting(d) Core Production

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Sand Mold Preparation (Cont’d.)(e) Cores are pasted(f ) Assembly of the cope half of the mold(g) The flask is rammed with sand (h) The drag half is produced in a similar manner (i) The pattern , flask, and bottom board are inverted; and

the pattern is withdrawn

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Pattern Plate

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Pattern Considerations/AllowancesShrinkage Allowance (Why?)Machining Allowance (?)Draft Allowance (?)Round corners (?)

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Demonstration of the Draft Allowance

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Sand Cores

Figure 11.6 Examples of sand cores showing core prints and chaplets to support cores.

Cores are used for internal cavities and passagesRemoved from the finished part during shakeoutMust be strong, collapsible, permeable, heat resistantMade in a similar manner to mold making

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Investment Casting ProcessAnother common casting process with expendable molds.Also known as lost-wax process

The mold material and labor is costlyAdvantages

Suitable for high-melting-point alloys Good surface finishFew or no finishing operations thus reducing cost

Typical parts Mechanical components such as gears, cams, valves.Lately, titanium aircraft-engineParts up to 2500 lbs were successfully produced

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Investment Casting Process (Cont’d)

Figure 11.13 Schematic illustration of investment casting (lost-wax) process. Castings by this method can be made with very fine detail and from a variety of metals.

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Disadvantages of Metal CastingDepending on the casting process used, and specially for expendable mold casting processes discussed in this lecture:

Production rate can be slowFinished Casting usually needs finishing operations

Casting Defects

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Casting Defects and How to Avoid them

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Next TimePermanent Molds Casting ProcessesOther Technicalities in various casting processes

Casting Design Research

Process designProcess modelingProcess simulationOpportunities

Design for Manufacturing 2

Casting System Components

Design for Manufacturing 3

Casting System Components

Design for Manufacturing 4

Metalcasting Lead Time & Cost Reduction Project

Objectives:Define an integrated casting design environmentDetermine the capabilities of existing softwareConsider both expendable mold & permanent mold processes

Tasks:Complete surveys of software suppliers & usersDetermine current industrial practice with casting softwareEvaluate costs & benefits of casting design softwareDefine scenarios for foundry use of softwareDevelop functional design of an integrated casting design environment

Design for Manufacturing 5

Casting Process Design

Part orientationParting line locationGate(s) and riser(s) designPattern/mold designProcess simulation

Design for Manufacturing 6

Casting Design Environment

Shared Database • Part & mold geometry • Casting material properties • Mold material properties • Process types & characteristics

CAD System

Laser Scanning

CAE Applications

• Dynamics • Heat transfer • FEM • Design optimization

Performance Capability • Resource availability • Time estimation • Cost estimation

Activity Manager

CAM Applications

• CNC machining • Rapid prototyping

Process Simulation

• Fluid flow • Heat transfer • Solidification • Stress growth • Defects/Quality Criteria Functions

Pattern/mold Design • Parting line location • Allowances & draft • Rigging system • Tolerance specification • Shape constraints

Design for Manufacturing 7

Integrated Casting Design Software Environment

Design for Manufacturing 8

Casting Design Software Functions

Design for Manufacturing 9

Casting Model

Input Parameters• Part Geometry• Part Material• Tolerance & Finish• Production Requirements

Process Design• Casting Process• Parting Line Location• Gating & Risering

Model Output• Casting Geometry• Production Cost• Solidification Time• Stresses & Defects

Design for Manufacturing 10

Casting Process Simulation

Casting Simulation Using MAGMAsoft– XM35 Rotor•Part design•Simulation model•Simulation results•Redesign iterations

Design for Manufacturing 11

Continuous Casting Research

Continuous casting processWorkflow – production planningIPSCO Caster model – process planning

Design for Manufacturing 12

Continuous Casting Process

Design for Manufacturing 13

Continuous Casting Model

NeuralNetwork

ThicknessWidthCarbon%SuperheatCasting SpeedCooling Rate

Mean

StandardDeviation

Design for Manufacturing 14

Optimization Scheme

Design for Manufacturing 15

Questions & Answers