Metal Casting ISAT 430. Module 5 Spring 2001ISAT 430 Dr. Ken Lewis 2 Metal Casting Casting is an ancient art More intricate shapes can be made by casting

Metal Casting

ISAT 430

Spring 2001 ISAT 430 Dr. Ken Lewis 2Module 5

Metal Casting Casting is an ancient art

More intricate shapes can be made by casting then by hammering

First metals cast were probably gold and copper. Cu melts at 1084° C Au melts at 1064° C

Egyptians were expert at investing or “lost wax” casting Allowed small intricate shapes to be cast.


Metal Casting2

Bronze casting

Made when people realized that copper tin alloys cast much easier than copper alone.

The Dark Ages (the fall of Rome {400 CE} until about 1400 CE)

All minds turned to finding and understanding the Spiritual nature of man

Bronze casting of bells became important Over time, they found the purity of the sound came from the

purity of the casting Size, shape, thickness, thinness Chemical composition.


Metal Casting3

Cannons First cannon was made by a monk!

Ghent, Belgium 1313 CE Made of bronze

The bore was part of the cast and was rough Very inaccurate Found that accuracy went up in proportion to the

smoothness of the bore Started machining the bore surface

This act today is called “boring” Hmmm.


Metal CASTING

Before we can discuss casting

We

Must first digress into

PHASE DIAGRAMS


Phase diagrams A phase diagram is a graphical representation of the

phases present and the ranges in composition, temperature, and pressure over which the phases are stable.

Remember: A phase is the part of a system which is chemically

and physically homogeneous throughout and is separable from other portions of the system by bounding surfaces


Phase diagrams2 –what is displayed Shows the phases present at difference compositions and

temperature under slow cooling or equilibrium conditions.

Indicates equilibrium solid solubility of one element (or compound) in another.

Indicates the temperature an alloy will start to solidify and the temperature range of solidification.

Indicates the temperature phases start to melt.

Equilibrium Conditions


Phase diagrams3 –what is displayed Keep in mind

Equilibrium phase diagrams are determined using slow cooling conditions.

In most cases equilibrium is approached but never fully attained.

Equilibrium Conditions


Phase diagram of pure water Water can exist as solid,

liquid or vapor. In the pressure-temperature

(PT) there exists a triple point at a P = 4.65 mm Hg and T = 0.0098°C. Here all three phases

coexist!


Phase diagram of pure water2

Liquid and vapor exist along the vaporization line

Solid and liquid exist along the freezing line.

These lines are two phase equilibrium lines.


Binary Phase Diagram Cu – Ni is one of the simplest cases. Composition is plotted on the x – axis Temperature is plotted on the y - axis


Copper – Nickel Alloy System Solid solution throughout the

entire composition range. Anywhere below the

solidus line the alloy is a solid solution

Anywhere above the liquidus line the alloy is a liquid solution.

Between the liquidus and solidus lines the metal is a mixture of solid and liquid phases.


Determination of the Chemical Composition of Phases and Their Relative Amounts in a Mixture

Draw a horizontal tie line. If we start with 60% B

At temperature V The solid will be 80%

B, 20% A The liquid will be

26% B, 74% A When the melt is

complete, the liquid will be all 60% B.


Change in the Microstructure of Cu-40 wt.%Ni Alloy During Equilibrium Solidification


Amount of a phase present Inverse lever rule

CSL phase present =

CS + CL

CLS phase present =

CS + CL


Important Metals Ferrous Non – ferrous

Aluminum & its alloys Magnesium & its alloys Nickel & its alloys Titanium & its alloys Zinc & its alloys Lead & Tin Refractory metals Precious metals

Super alloys


Ferrous Metals -based on ironIron

Symbol: Fe

Atomic Number: 26

Specific gravity: 7.87

Crystal structure: BCC

Tm: 2801°F (1539°C)

Modulus of Elasticity E: 30 x 106 lb/in2

Ores: Hematite (Fe2O3)

Applications: Construction, machinery, automotive, railways, etc.


Ferrous metals Two major groups

Steel Cast iron


Iron - Carbon also called ferrite also called austenite called delta iron Fe3C is called cementite

Not an alloy


Iron - Carbon

Percent Carbon Material

<0.008 Iron

0.008 – 1.6 Steels

1.6 – 2.1 Semi steels

2.1 -- ~4 - 5 Cast irons



Expendable Mold Processes

Sand Casting

Investment (“Lost wax”) Casting


Sand Casting Mold is made of green sand (“Green” means that it is

not fired or melted in a furnace) Can withstand the temperatures and pressures of

molten steel. Basic ingredients

SiO2 silica sand A binder clay


Sand Casting Mold is made of green sand (“Green” means that it is

not fired or melted in a furnace) Basic properties

Ability to withstand high temperatures Ability to retain shape under the action of metal flow Permeability

Able to pass gases and vapors developed during casting Collapsibility

Allows the mold to be broken up and separated from the casting.


Sand Casting Mold Mold is made in a box called a

‘draft’. Bottom part is called the ‘drag’ Top part is called the ‘cope’. The pattern is made of wood,

plastic or metal Sand cores determine the shape

of external cavities Must be stronger than the sand

of the primary mold Must support buoyancy forces


The Part The iron casting to be made

in the process Note internal holes


The Mold1

Bottom half of the pattern is on the mold board Surrounded by the

bottom or drag half of the flask

May be made by hand or by a jolt machine

Notice the pattern is solid with no holes.


The Mold2

Molding Sand is added Tamped or rammed in

multiple layers Need even density so there

is no preferential metal movement.

Tamp


The Mold3

After bottom half of mold is filled Top half of pattern is put

in place Top half of the flask is

installed More sand is added and

tamped in place.


The Mold4

Section through the mold

The pattern is still in place

The sprue hole has been formed for the entrance of the molten metal.


The Mold5

The cope and drag halves of the mold are separated.

The pattern is removed

The gate channel is cut from the sprue to the mold cavity


The Mold6 – the core of bonded sand This is the core of the part

It will form the holes in the casting.

This is the core that must withstand the buoyancy forces.

It is carefully placed in the mold.


The Mold7 – the finished touch After placing the core in the

mold It is closed and clamped The molten metal is

poured into the mold.

The metal cools The mold is opened and the

part is removed. Finishing means removal

of the channel, etc.


Some Impressive Castings


V8 cylinder block


Six wheel motor truck frame

DieselLocomotive


1.5 m Stainless Steel Propeller

MaritimeUse


107 m3 Shovel Shoes38 shoes per

assembly

4 assemblies pershovel

Total cast weight333 tons


Most Impressive!

BUDDHAat the Po Lin Monastery

on Lantau Island


His head isone

piece



Investment Casting Also known as the “lost wax” process

First used during the period 4000 – 3000 BCE Medieval Italy

Cellini’s golden rings (with miniature sculptures on them)

The pattern (exactly as the part will look) is made of wax or plastic Made by injecting molten wax into a metal die in the

shape of the pattern


Investment Casting1

The pattern is first made of Wood Metal Plastic

Material is whatever will allow the craftsman to create the detail desired.

The pattern is made into a mold.

The mold is injected with wax which reproduces the pattern.


Investment Casting2

Once the wax cools, the pattern is retrieved.

The pattern is usually both temperature and touch sensitive.


Investment Casting3

The master mold makes many patterns.

These are assembled onto a casting “TREE”

The TREE is ready then to receive the outer coatings


Investment Casting4

Slurry coating This is a slurry made of

fine silica and binders Water Ethyl silicate

Coating is dried Process is repeated again

and again to build up the mold.

SlurryA watery mixture of insoluble matter

Here: silica, H2O and additives


Investment Casting5

The coating is applied again and again The first coatings are

fine grained silica or other refractory material

Almost a powder Provides a smooth

surface to the final casting.

The coating material used is coarser and coarser Building up the strength

of the mold.


Investment Casting6

Finally we get the completed mold

There is a common sprue in the middle

The mold is free standing and somewhat delicate

It is still full of wax.


Investment Casting7

The one piece mold is held in air and heated to 90° -- 175°C The wax flows out Takes about 12 hours

The wax can be recycled The mold is then fired to

650° -- 1050°C to drive off water Burn off residual wax


Investment Casting8

The mold is inverted and placed in a support vessel.

The mold is preheated to a high enough temperature eliminates residual

contaminants. The liquid metal flows

more easily. The liquid metal/alloy is

poured


Investment Casting9

Shakeout The system is cooled The mold is broken away

The mold is destroyed.


Investment Casting10

The finished product.


Investment Casting Example


Investment Casting -- Advantages Cast great complexity and intricacy Close dimensional control

Tolerances of ±0.003 in (±0.076 mm) Good surface finish The wax can be recovered This is a net shape process


Investment Casting Possibilities - Constraints

Parts are usually small in size Finished products up to around 75 lbs.

Many steps, so relatively expensive. Amenable for most alloy and metal systems

Noble metals Steels Stainless steels Super alloys

Documents

Metal Casting ISAT 430. Module 5 Spring 2001ISAT 430 Dr. Ken Lewis 2 Metal Casting Casting is an ancient art More intricate shapes can be made by casting