MECHENG236 - Metal Manufacturing Flashcards
Types of metal casting
Sand mould casting
Shell mould casting
Investment casting
Die casting
Powder metallurgy
Forging
Extrusion
Difference between sand mould casting and shell mould casting:
Shell mould has tighter tolerances and a higher degree of dimensional stability
When to use sand mould casting:
Small quantities, small to large parts and complex geometries. Dimensional accuracy is not crucial, not exact size and weight. Possibly porosity is okay
When to use shell mould casting
Need higher dimensional accuracy than sand mould casting. Complex shapes with thin sections. Not for short runs
When to use investment casting
Extremely complex parts with good surface finish
Very thin sections can be produced
High dimensional accuracy
Small parts up to 35 kg
Complicated and relatively expensive
When to use die casting
High dimensional accuracy, smooth cast surface, thin walls
Want to prevent secondary machining operations
Rapid production rates
Only economical in very large quantities due to high tool cost
Limited to high fluidity metals
Some porosity may be present so not suitable for heat treatment or welding – softness must be acceptable
When to use powder metallurgy
Complex shapes
Minimal or no post processing
Parts have good specific properties
No wastage of metal powder
Only economical in large quantities
High raw material cost
Mechanical properties may be low
Possible density variation
Health and safety concerns
Types of forging
Drop forging – open die and closed die
When to use open die forging
Better fatigue resistance and strength
Reduces chance of error and/or holes Improves microstructure
Continuous grain flow Finer grain size
When to use closed die forging
Produces parts up to 25 tonnes
Produces near net shapes that require only a small amount of finishing
Economic for heavy production
Drop forging general characteristics:
Good for short to medium run lengths
Fine grain structure
Good longitudinal properties
High strength and good impact and fatigue resistance
Extrusion general characteristics
High production speed with good accuracy
Can require no additional finishing aside from being cut to length
Can produce complex cross sections not readily obtainable with other manufacturing methods
Types of extrusion
Based on method:
- Direct
- Indirect
- Impact
Based on temperature
- Hot
- Cold
Parts of extrusion machine:
Billet
Press cavity
Dummy block
Ram
Die
Die backer
Pros and Cons of direct extrusion
Advantages
No billet modification required
Can be used for both hot and cold extrusion
Simple tooling compared to other extrusion process
Disadvantages
High force requirement due to friction
Butt end left inside the cavity
The force required to push the ram changes as the punch moves
