Are there shape and intricacy restrictions in foundry processes?
Almost none, except for long and excessively thin shapes.
What are the weight range limitations in foundry processes?
Limited by the supply of molten metal and capacity of parts handling.
Can all types of alloys be cast in foundry processes?
Yes, virtually all types, especially beneficial for hard or tough alloys with poor machinability.
How does the cost of foundry patterns compare to alternative processes?
Foundry patterns are generally more cost-effective, with design changes easier in early production stages.
What are negative aspects of foundry operations?
The casting leads to a solidification structure with the inclusion of defects
the durface roughness is comperatively very high
The dimensional tolerances are low (=bad)
What are the principle operations in casting?
Melting
Secondary metallurgy
Casting
Extraction
What are the typical melting operations in foundry alloys?
Arc
Induction
Crucible
Cupola
What are the most typical foundry alloys?
Cast iron
Steels
Copper based alloys
Aluminium alloys
Magnesium alloys
Zinc alloys
Nickel alloys
Which furnaces are used for Steel casting?
Electric arc furnace
Induction furnace
Which furnaces are used for cast iron casting?
Cupola furnace
Rotary kiln furnace
Which furnaces are used for Aluminium casting?
Which furnace is used for supperalloy casting?
Vacuum induction furnace
What is the principle of the induction furnace?
The metal charge is heated by an alternating electromagnetic field, which induces an induction current
What is the principle of a rotary kiln furnace?
The rotary kiln furnace is a furnace for small and medium foundries which is rotated. The metal is heated by the gases that are passed through it.
On what does the metal fluidity depend?
Viscosity
temperature
chem. composition
What is the concept of super heat?
"superheat" refers to the temperature difference between the actual temperature of a molten metal or alloy and its liquidus temperature
What are the effects of surface tension on fluidity?
oxide films on the surface of the molten metal increase surface tension and therefore fluidity
high surface tenssion of the metal reduces flluidity
Which mould properties influence the fluidity?
Thermal properties
diffusivity
Evaporation of surface from the water
surface roughness
Use of reactive coatings
Resistance given by entrapped air
What are the steps in a sand casting process?
Mold creation and metal melting
Pouring into mold
Solidification and cooling
shakeout and removal of risers and gate
Cleaning and finishing
What are the main components of a sand casting setup?
Pattern, core, flask (cope and drag), and gating system.
How is a core used in sand casting?
A core is used to create internal cavities and complex shapes within the casting.
What are common materials used for making patterns?
Wood, metal, and plastics.
What does the castig modulus M define?
The Volume to casting flow ratio V/S
The casting flow S is defined by the Volume per time and speed (V/(t*v))
The casting modulus helps determine if a casting will solidify without defects, shrinkage, porosity or hot tearing.
How is the casting modulus applied to determine the right feeding properties?
Calculate the casting modulus of each part
each part can feed the adjacent one if Mn>1,1 Mn+1
Feeders need to be used if Mn>1,25 Mn+1
What is the typical composition of casting sand?
silica sand 83%
Binder 8.5 % (clay, betonite)
Additives 5% (carbon powder)
Water 3.5%
What are the advantages of shell mould casting compared to sand casting?
higher cooling rate
better liquid fluidity
better precision
good surface finish
What are the advantages and disadvantages of ceramic mould casting?
high dimensional accuracy
expensive
Name 5 permanent mould casting processes.
shell mould casting
low pressure casting
die casting
squeeze casting
semisolid metal forming
For which number of parts is a shell mould casting economical for which material?
5000 for steel casting
20000 for cast iron casting
25000 parts for CU alloy
100000 parts for Al alloy
What are the characteristics for die casting?
metallic mould
high cooling rates
tight tolerances
uniform properties
high productivity
non ferrous alloys
Which alloys are used in the cold chamber process?
Al, Mg, Cu
How many castings can be fabricated per hour in the cold chamber process?
20-200
What is the cold chamber process cylce?
Die preperation (cleaning, lubrication)
Chamber pre-fill
Cavity fill low pressure
Cavity fill high pressure
Dwelling for solidification
Die opening and ejection
plunger return
What are the characteristics of squeeze casting?
near net shape
no porosity
fine microstructure
mechanical properties similar to forging
automated process
What is the squeeze casting process limited by?
the die pressure resitance
What is the prinziple of the semi solid metal forming?
the metal is casted in between T solidus and T liquidus
What are the advantages of semisolid forging/forming?
homogenous microstructure
laminar filling of the cavities => lower gas entrapment
casting as well as wrought alloys can be used
low shrinkage in solidification
process suitable for composite materials
Name two expendable-mould, expendable pattern casting processes.
Lost Foam Process
Investment casting
What are the characteristics of lost foam casting?
Lamina metal flow
rapid cooling
polystyrene pattern
What are the characteristics of investment casting?
pattern fabricated out of wax, which is melted out
What is charged for the production of wrought aluminium alloys?
scrap
pure Aluminum
alloying metals (Zn, Mg, Sn)
Master alloys
What are the most common Aluminium oven types?
induction furnace
What are the steps in aluminuium casting?
melting furnace
melt treatment
Direct chill casting
Homogenization
Homogenization semis
semi finished part
final manufactoring
What is the effect of homogenization?
The treatment is carried out to improve workability, eliminate microsegregation, dissolove precipitates.
What are the purposes and materials for fluxing?
fluxes are introduced to the molten bath to improve the final product.
fluxing is salt based: NaCL, NaF, AlCl
how is the flux injected into the melt?
rotary flux injection system
introduction by spinning rotor, which leads to shearing of the salts
TAC process
introduction through a carrier gas that spreads the AlF3 powder through a rotary system.
conducted while metal is on way to casthouse
What are degassing methods?
gas treatments
inert gas (argon, nitrogen)
reactive gas (Chlorine based)
vacuum treatment
How does the inert gas degassing work?
The hydrogen diffuses into the inert gas bubbles.
What are the reasons for grain refinement?
increased mechanical properties
improved castability
better results from heat treatment
better machineability and plastic deformation
What are the methods of grain refining?
stirring (electromagnetic, ultrasound or gas)
refining additions (Ti alloys, salts, B, Zr)
Why does a high eutectic content lead to better fluidity?
Lower liquidus temperature and no “mushy zone”
What are the positive and negative aspects of adding Silicon to a aluminium cast alloy?
better fluidity cause of eutectic
high resistance to corrosion
good weldability
low thermal expansion
poor mechanical properties
poor machineability (brittleness and coarse microstructure)
How is filtration conducted?
filter cake
filtered out particles start filtering themselfs
depth filtration (most commonly used)
long path of filtering
higher possibility of filtering inclusions out
What materials are filters made out of?
metal or fiberglass meshes
Bonded ceramic particle filters of either AL2O3 or SiO2
Ceramic foam filters
coating of polyurethane with ceramic slurry and firing out
materials: Zr, Al, Cr2O3
Last changeda year ago