expendable mold Flashcards
What are the 6 expendable mold processes?
- Shell molding
- Vacuum molding
- Expanded polystyrene- mold casting
- Investment casting
- Plaster mold casting
- Ceramic mold casting
Is a casting process in which the mold is a thin shell (typically 9mm or 3/8 in) made of sand held together by a thermosetting binder
Shell molding
What is shell molding?
Is a casting process in which the mold is a thin shell (typically 9mm or 3/8 in) made of sand held together by a thermosetting binder
It was developed in Germany during the early 1940s.
Shell molding
What are the advantages of shell molding?
- shell mold cavity is smoother than a conventional green sand mold.
- better surface finish (finishes of 2.5 micrometers)
- good dimension accuracy (tolerance of +-0.25 mm)
- collapsibility is sufficient
- thin wall thickness and complex castings
- less manpower and molding skill requirement
- mass production
What are the disadvantages of shell molding?
- more expensive metal pattern than green sand mold
- high production costs and casting prices
- size and weight limitation (less than 20 lb)
Examples of the application of shell molding.
gears, valve bodies, brushings, and camshafts
Vacuum molding is also called as ____________.
V- process
It was developed in Japan around 1970.
Vacuum molding
It uses a sand mold held together by a vacuum pressure rather than by a chemical binder.
Vacuum molding
What is vacuum molding?
It uses a sand mold held together by a vacuum pressure rather than by a chemical binder.
What are the advantages of vacuum molding?
- sand is readily recovered
- does not need extensive mechanical reconditioning
- moisture-related defects are absent
- surface quality
- dimensional accuracy
- unlimited pattern life
- design quality
What are the disadvantages of vacuum molding?
- relatively slow
- not readily adaptable to mechanization
It uses a mold of sand packed around a polystyrene foam pattern that vaporizes when the molten metal is poured into the mold.
Expanded polystyrene mold-casting
What is expanded polystyrene mold casting?
It uses a mold of sand packed around a polystyrene foam pattern that vaporizes when the molten metal is poured into the mold.
The process and variations of it are known by other names, including _____________.
*lost- foam process
*lost- pattern process
*evaporative- foam process
*full- mold process
In EPM, the foam pattern includes ________.
sprue, risers, and gating systems, also internal cores
In EPM, the form patter excludes _______.
draft, parting lines
In EPM, the pattern is usually coated with _______. Why?
refractory compound: to provide a smoother surface on the pattern and to improve its high-temperature resistance.
What are the advantages of EPM casting?
- the pattern needs not to be removed from the mold
- molding sand can be reused
- complex shapes without the use of cores
- no parting line
- good surface finish, high dimensional accuracy
- low-cost production
- process is relatively simple and straightforward
What are the disadvantages of EPM casting?
- a new pattern is needed for every casting
- pattern density
- low strength, and susceptible to damage
- econ justification is highly dependent on the cost of producing products
This uses a pattern made of wax which is coated with a refractory material to make the mold. After which, the wax is melted away prior to pouring the molten metal.
Investment casting
What is investment casting?
This uses a pattern made of wax which is coated with a refractory material to make the mold. After which, the wax is melted away prior to pouring the molten metal.
In investment casting, the word ‘investment’ comes from the word ‘invest’ which means ______________.
to cover completely; this refers to the coating of the refractory material around the wax pattern.
