Casting Flashcards
Typical Products of Casting
Engine blocks, hub caps, dies and molds, railroad wheels, transmission body car
what kind of material
ferrous (iron, steel) and non ferrous (aluminium, etc)
advantages of casting
- complex part geomitry
- very large parts
- any metal that can be brang in a liquid state
some: mass production and net shaping possible
disadvantages casting
- limitations on mechanical properties
- porosity
- safety hazards
-environmental problems
Sand casting: - poor dimensional accuracy
- poor surface finish
Casting Process
A process in which metals are melted and poured into a die (mold) and solidified
Foundry
Place where Casting takes place
Foundrymen
Workers
Types of Casting
Expandable Molds:
- permanent pattern
- expandable pattern
Permanent molds
Sand Casting
Sand: permeable (needed for air), collapsible (casted product shouldnt stick to sand), strength, reusable, thermal stability (high temp.)
Process Sand Casting
Pattern + Sand = Mold
Liquid metall –> Mold –> solidifies
Parts of Sand Mold
Flask: Supports the mold, consist of cope (top) and drag (bottom)
Pourin Basin: molten metal is poured here
Blind Risers: Supply of additional metal, when solidified metal shrinks
Cores: When you need a hollow part –> inserts
Patterns
- Patterns
- -> Used to mold the sand mixture into the shape of the casting and may be made of wood, plastic or metal
- One piece (solid) patterns (easiest)
- split pattern (higher production rate than the others)
- match plate pattern
- cope and drag pattern
Sand cores
Placed in the interior of the mold to form the interior surfaces of the part
- Core prints: recesses added to the pattern that locate and support the core, provide vents for gases
- Chaplets: Metal supports to prevent core from shifting
Mold Making
90% sand, 3% water
7% clay, resins or other binders
Compaction
- Hand ramming
- Pneumatic pressure
- Mechanical jolting action
- Mechanical slinging action
Sand Casting Application
high/low product vol.
all liquid metals
size: very small to very large
other casting processes
- shell molding process
- ceramic mold process
- lost foam casting
- investment casting ( similar to lost foam casting)
- hot chamber die casting
- cold chamber die casting
Difference Hot & cold chamber die casting
Hot chamber casting: Shot chamber is beeing heated with molten metal in the mold
Cold chamber casting: shot chamber is not heated, molten metal comes seperately in the chamber, injection system is not part of molten metal
Production Rate die casting
- higher production rate about 200 pieces /hour
Dies for Die casting
- ejector pin push parts out when mold opens
- made of steel
- multiple or single cavity
Die Casting general
- no net shaping process (flash has to be removed)
- machines are larges compared to casting because of higher forces and complex mechanical engineering systems
- cooled with oil/water
- cannot be used with molten steel because die is made out of it and would start to melt as well
advantages of die casting
-Mold can be reused
-Economical for high production quantities
-Tight tolerances can be achieved (+/- 0.003” for small
parts)
-Good surface finish
-Thin sections are possible (~0.020”)
-Due to rapid cooling: Finer grain structure; stronger
castings
Investment casting application
- all types of metal
- normally small parts
- expensive production process
