manufacturing technology- metal casting

8/9/2019 Manufacturing Technology- Metal Casting

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Metal Casting

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Lesson Outcomes

By the end of this lessons, students should be able toexplain:

1. The generic metal casting process

2. The sand casting process and example products3. The inestment casting process and example

products

!. The die casting process and example products



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The metal casting process

The casting process generally inoles:

1. "ouring molten metal into a mold

patterned after the part to be manufactured

2. #llo$ing the metal to cool and solidify

3. %emoing the solid part from the mold

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Types of molds'asting processes can be classified by the type of mold used:

( )xpendable molds * #fter the casting has solidified, mold is bro+en to remoe the

casting

* Typically made of sand, plaster, ceramics( "ermanent molds

* sed repeatedly -not bro+en after solidification

* /ade of metals

( 'omposite molds * 'onsists of permanent and expendable portions

* /ade of t$o or more different materials -eg: sand, graphite, metal



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Oerie$

Shell mold Good dimensional accuracy

and surface finish; high

production rate.

Part size limited; expensive

patterns and equipment required.

sand Most metals cast with no limit

to size; complex shapes

Patterns have low strength and

can be costly for low quantities

Plaster mold Intricate shapes; gooddimensional accuracy and

finish; low porosity.

Limited to nonferrous metals;limited size and volume of

production; mold making time

relatively long.

Ceramic mold Intricate shapes; close

tolerance parts; good surface

finish.

Limited size.

Investment Intricate shapes; excellent

surface finish and accuracy;

almost any metal cast.

Part size limited; expensive

patterns, molds, and labor.

Permanent mold Good surface finish and

dimensional accuracy; low

orosit hi h roduction rate.

High mold cost; limited shape

and intricacy; not suitable for

hi h-meltin - oint metals.

"rocess #dantages Limitations



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)xamples

(a) (b)

-a The "olaroid "'42555 digital camera $ith a #671 die4cast,high purity magnesium case. -b T$o4piece "olaroid camera casemade by the hot4chamber die casting process. Source: 'ourtesy of"olaroid 'orporation and 'hicago 8hite /etal 'asting, 9nc.



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and 'asting

( /ost common type of casting

( The mold is made of sand

( There are t$o types of sand used:

* ;aturally bonding

* ynthetic

( )xample products: machine bases,

propellers, impellers, etc.



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and casting: # typical sand mold



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and 'asting: and mold features

1.


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and casting: /old "atterns

# typical metal match4plate pattern used in sand casting. Taper on patterns for ease of remoal

from the sand mold.

(sed to shape the sand mixture into the shape of the casting

(sed repeatedly to ma+e sand molds

('an be made of $ood, plastic or metal

('oated $ith parting agent to ease remoal of mold from pattern



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and casting: teps

Outline of production steps in a typical sand4casting operation.



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9nestment casting

( )xample products: components for office

e>uipment, gears, cams, ales, etc.



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9nestment 'asting: teps

chematicillustration ofinestmentcasting, -lost4$ax process.'astings by thismethod can bemade $ith eryfine detail andfrom a ariety ofmetals. Source:teel


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1. /old is normally made of metal

2. "attern is then made by in@ecting $ax or plastic into mold

3. # series of patterns can be assembled into a pattern tree!. The pattern tree is then dipped into a slurry -eg: fine silica

and binders

&. tucco coating is applied repeatedly to increase thic+ness,forming a one4piece mold

0. The one4piece mold is dried and heated to melt out the $ax-original pattern.

. The one4piece mold is heated further to remoe $ater and burn off any remaining $ax.

. /olten metal is poured into the one4piece mold. #fter

solidification, the one4piece mold is bro+en up and thecasting is remoed.

9nestment 'asting: teps



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ie 'asting( 9n permanent4mold casting, t$o hales of a mold are made

from materials that resist erosion and thermal fatigue suchas cast iron, steel and graphite.

( The die casting process: * # piston traps a olume of molten metal

* "iston then forces molten metal into the die caity through anoAAle

* /etal is held under pressure -up to 3& /"a until it solidifies.

* The part is then e@ected by an e@ector mechanism

* The die is normally cooled using circulating $ater or oil

( )xample products: * )ngine bloc+s, hand tools, motor housings



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ot4chamber die4casting

Heated chamber



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'old4chamber die casting



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ie 'asting 'aities

=arious types of caities in a die4casting die. Source: 'ourtesy of #merican ie'asting 9nstitute.

'h b i



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ot 'hamber ie

'asting /achine

-b

-b 554ton hot4chamber die4casting machine, #/ 55& -made in Cermanyin 177. This is the largest hot4chamber machine in the $orld and costsabout D1.2& million.



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ummary

( /etal casting inoles pouring molten metal into amold, allo$ing the metal to solidify and remoingthe part from the mold

( 'asting processes can be classified as permanentmold and expendable mold processes

( )ach process is suitable for manufacturing a particular class of products.

manufacturing technology- metal casting

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