Metal Casting and Forming
ALL manufacturing starts here!
What is Metal Casting?
• When liquid metal is poured into a mold, then
solidifies and takes the form of the mold.
• Iron, steel, aluminum, brass, bronze,
magnesium, and zinc are all metals that can
be casted.
Patterns
• Part to be made
• Allow for shrinkage (1-2%)
– Cast iron 1/8” per foot
– Steel 1/4” per foot
– Aluminum 5/32” per foot
• Metal, plastics, or wood
• Single or multiple pieces
Pattern removed from mold
Patterns cont.
• Draft to allow removal from the mold (2-3*)
• Commonly oversized for machinability
Ice cube trays have draft angles.
Castings
• Castings: Parts made using casting process
• Molds or Patterns used to make castings can
be made of one or more pieces.
Foundry
• A factory specializing in metal casting.
• Dirty, hot, loud hard but rewarding work
• Modern Foundry Video
Different Casting Processes
1. Green Sand Casting
2. Permanent & Die Casting
3. Investment (Wax & Foam)
4. Continuous
5. Centrifugal
Sand Casting
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Pattern is formed into a sand cast.
Liquid metal is poured into the sand cast.
A sand cast is a ONE time use casting
Mold is destroyed to remove casting/part
Sand Casting
• Produce castings of virtually any size and weight.
• Common for prototyping & low volume production.
Sand Mold
• Section view of mold showing spru, runner and
gating system, risers (feeders), cores and pattern
draft.
Permanent Mold Casting
• Mold is made of iron or steel
• Molds are good for multiple uses
• Used when poring large quantities of identical parts
Permanent Mold Casting
Advantages: Consistent, Precise, tighter tolerances
Disadvantages: very expensive to produce molds
Permanent Die Casting
• Similar to permanent mold casting except that
the metal is forced into the mold under pressure
• Large quantity production.
Investment Casting (Lost Wax)
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Over 1,000 year old technology
Pattern is made of wax.
A ceramic shell is built around the wax pattern.
Wax pattern is melted out of the shell.
Molten metal is poured into the shell.
Investment Casting Video
Investment Casting Video 2
Investment Casting (Lost Foam)
Styrofoam pattern is coated with a refractory
material and dry sand is compacted around pattern.
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Metal is poured
onto the foam &
instantly vaporized.
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No draft required
Continuous Casting
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Used to make large steel fixtures (iron plates, beams)
Metal is melted in hopper & gravity fed
Metal taken as needed
Unused metal recycled into hopper
Centrifugal Casting
• Used to produce objects
with large holes such as cast
iron drain pipe
• Mold is spun ~ 1000 RPM
• Impurities gravitate to the
inside surface
• Impurities machined off
Modern Foundry Processes
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Engineering
Mold Making
Melting
Checking Gas Levels
Pouring
Shakeout
Degating
Heat Treating
Surface Cleaning
Finishing
Secondary Machining
Quality Control
Engineering
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The best castings start with precise engineering
CAD software: concept to prototyping
Maximize production, minimize production cost
Maximize efficiency, consistency
Minimize waste
Design Engineering Video
Producing the Mold
• Fine sand is compressed tightly around pattern
• Course sand used as fill
Producing the Mold
Melting Metal
• Solid metal is placed into crucible (melting pot)
Ceramic bowl that that withstands extreme temps.
• Crucible is placed in furnace
• Slowly heated until metal is liquefied
• Poured into mold.
Melting Temperatures
• LEAD
• ALUMINUM
• BRASS
• COPPER
• STEEL
700*F
1200*F
1500*F
2000*F
2500*F
• Aluminum is typically poured at 1350*F
Checking Gas Levels
• Gas levels: specific to alloy & pattern complexity
• Quality Control: sample is taken and density is measured
• Porosity: Air pockets formed in metal
High gas levels
• Low viscosity
• More porosity
• Weaker casting
Low gas levels
• More viscous
• Less porosity
• Stronger casting
Altering Gas Levels
Too High
Too Low
• Argon or nitrogen is • Potatoes are added
bubbled into metal • Adds gas to metal
• Introduced at the
• New sample taken
bottom
• Bubbles rise and
catch hydrogen
• Bubbles rise to top
Pouring
• Metal is poured into mold to solidify
• Some molds require 4-5 pours
• 1-2% shrinkage common
Automatic Die Casting Machine
• Computerized casting machine that prevents fluctuations
in metal
• Mold is rolled into machine
• Metal is casted beneath via low pressure
• Provides consistency for difficult molds
Shakeout
• Solidified metal component is then removed
from its mold via shaking or tumbling
• Frees the casting from the sand
• Runners and gates are still attached
• Allows sand to be reclaimed and reused
• Lowers foundry production cost
• Old days sand went to landfill!
Shakeout Machine
Degating
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Spru, runners, gates, and risers are removed
Torches, bandsaws, ceramic cutoff blades, sledge hammers
Specialized knockoff machinery used if design permits
Gating system (sprue, runner, gate) may equal 50% of a poor.
– Gating components must be remelted as salvage.
– Important economic consideration
Heat Treating
• Part baked in large oven at a controlled
temperature and time interval
• Changes molecular grain for more strength
• Heat Treated part is then quenched in bath
– Adds strength to casting
• Not all parts are
heat treated
Surface Cleaning
• Casting is blasted with tiny steel bb’s
• Removes any sand or debris
• May be used to achieve a particular rough finish
Finishing
• The final step in the process usually involves grinding
and sanding
• Achieve dimensional accuracies, shape & finish.
• These steps are done prior to any final machining.
Quality Control
• CNC equipment for precision gauging
• Parts are x-rayed for imperfections
(Internal cracks, Porosity)
X-Ray Photograph
X-Ray Machine
Secondary Machining
• Parts are machined using precise CNC
equipment.
• Some foundries machine parts in house &
some sub-contract machine shops
• Secondary Machining Video
Tooling Up
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Flask
Molding Board
Bottom Board
Rammer
Riddle
Trowel
Slick
Sprue Pin
Riser Pin
Lance Pyrometer
• Tool used to identify molten metal
temperature.
• Different types of metal poor better at
different temperatures.
• Aluminum – 1450*F
Ingots
• Ingot: a solid piece of metal that has been
formed into a particular shape (such as a
brick) so that it is easy to handle or stored
Flask & Boards
• Flask
– Cope - top
– Drag – bottom
• Boards
– Molding Board – used on drag when being
rammed
– Bottom Board – placed on top of drag when
flipping the mold, supports the bottom of the
mold.
Sand Charactoristics
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Sand grit is determined just like sand paper
Fine sand will give a smooth finish
Rough sand will give a rough finish
Sand is 6% moisture – don’t let it dry out
Shovel – Used to mix & move sand
Riddle find sand around mold!
Sand allows gas to escape to
Slick, Sprue Pin, Riser Pin
• Slick – Another tool used to flatten face of the mold.
• Sprue Pin – Tapered wood or metal pin used to form
sprue hole
• Riser Pin – Wood or metal pin used to form overflow
Vent Wire, Molder’s Bellow, Bulb
Sponge
• Vent Wire - Small holes in mold to allow for gas escape.
• Bellow - Tool used to blow excess sand from the mold cavity
• Bulb Sponge – Smoothens the edges of the pattern to prevent loose
sand from entering mold.
Sprue, Riser, & Gate Cutters
• Same purpose as pins but used after the sand
has been rammed/packed.
• Tapered shank allows us to cut & extrude.
Parting Compound
• Sprinkled around pattern for easy mold
extraction
• Baby powder or fine gritt sand may be used
Hot Tips
• Finish molding before you starting the furnace!
– Safety & Attention to detail
• Keep sand covered or in a sealed container when not
in use!
• Avoid melting aluminum cans!
– Cans are coated with vinyl for protection
– Best results are obtained from clean metal
• DO NOT stir molten metal, this adds gas!
• Always skim slag before pouring!
Safety
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PPE: GLASSES, FACE SHIELD, SPATS, COAT, GLOVES!
ALWAYS PRE-HEAT METAL !
NEVER ADD LIQUID OR MOISTURE!
PLACE HOT CASTINGS IN A SAFE PLACE!
NEVER SET CRUCIABLE ON CONCRETE!
NEVER LOOK DIRECTLY OVER MELTING POT!
KEEP AREA CLEAN!
DON’T RUSH!
ALWAYS POUR WITH A PARTNER!
AVOID MOLDING NEAR EDGES OF FLASK!
NEVER LEAVE THE ROOM!
INSTRUCTOR MUST BE PRESENT!
A look at Local Foundries
• Eck Industries
– http://www.eckindustries.com/
• Wisconsin Aluminum Foundry
– http://www.wafco.com/drysand.htm
• Bremer Manufacturing
– http://www.bremermfg.com/