Intro 1 Flashcards
Primary
Secondary
Tertiary
Industry examples
Primary: exploit natural resources e.g. agriculture/mining
Secondary: take primary outputs and convert to consumer/capital goods
Tertiary: service sector and the economy
What’s a capital good
Goods purchased by companies to make other goods/ provide services e.g aircraft computers, diggers
How are product variety and production quantity related when comparing typical factories?
There’s an inverse correlation between product variety and quantity. High variety = low production
How does a shaping process differ from a surface processing operation?
Shaping changes the bulk shape of a material whereas surface processing operations only augment the surface properties
What are two subclasses of assembly processes?
Permanent joining processes including: welding brazing soldering and adhesives
Mechanical fastening: threaded fasteners and permanent fastening methods
Advantages of shape casting processes
Can:
- make complex shapes
- make parts to net shape or near net shape
- make very larger parts
- be suitable for mass production
- be done on any metal that can be heated to its liquid state
Limitations and disadvantages of casting
Porosity, poor dimensional accuracy and surface finish for some casting processes, safety hazards to humans when processing hot molten metals, environmental problems.
Two basic mold types that distinguish casting processes:
Expendable molds: more complicated geometries possible
Permanent molds: mold is more expensive but higher dimensional tolerance and higher manufacturing rates, simpler geometry
Three contraction sources in a metal casting after pouring:
- liquid contraction
- contraction during phase change from liquid to solid
- thermal contraction of solidified casting during cooling to room temperature
Which die casting machines usually have a higher production rate, cold chamber or hot chamber?
Hot die casting. Molten metal chamber allows for rapid material injection. In cold die casting this has to be done manually
Describe the microstructure of a cast part in terms of grain size and explain why the mechanical properties of the surface might differ from the bulk
Smaller surface grains as cooling rates are faster than the bulk where the grains are bigger. Surface can be more brittle than ductile centre because of grain size.
Describe the stages of investment casting:
- Wax patterns are produced
- Patterns are attached to a sprue to form a pattern tree
- Pattern tree is coated with a thin layer of refractory material
- Full mold is formed by covering coated tree with refractory material to make it rigid
- Mold is held in an inverted position and heated to melt the wax and permit drips out of cavity
- Mold preheated to allow contaminant elimination and allows liquid metal to flow easily into the detailed cavity. Metal poured and solidifies.
- Mold is broken away from the finished casting. Parts are separated from the sprue.
Why should corners be avoided in castings?
They are a source of stress concentrations and may cause hot tearing and cracks in the casting. Generous fillets should be designed on inside corners and sharp edges should be blended
Why are draft angles needed in some cast parts?
Sections that project into the mold should have a draft. In expendable mold casting, the purpose is to aid removal of the pattern from the mold. In permanent, purpose is to remove part from mold. 1’ for sand casting, 2-3’ for permanent
Give 2 reasons to make mold slightly larger than final thing
Compensate for shrinkage
Allow for machining
