Manufacturing Technology - Part B Flashcards
What are the 5 types of permanent mold casting?
- Slush Casting
- Pressure casting
- Die casting
- Centrifugal casting
- Continuous casting
What is SLUSH casting and where is it used? how is thickness determined?
- Molten metal is poured into the metal mould.
- When desired thickness of solidified skin is
obtained - mould is inverted and remaining liquid metal
is poured out. - Mould halves are then opened.
- Casting is removed.
-hollow castings with thin walls
-decorative/ornamental objects
-Very common in theatre/film industry for
making latex/silicone props and costumes
-Thickness is a result of the cooling time, solidifies from the outside in
What is PRESSURE casting and where is it used?
What are the advantages & disadvantages?
-Molten metal is forced upward by
Gas pressure into a graphite or metal mould
-A vacuum removes gases and gives
the casting a lower porosity
-Pressure is maintained until the metal has
completely solidified in the mould
-Used for high quality casting of components, such as car wheels
Advantages)
-avoids rapid oxidation, solidifies from top down
Disadvantages)
-long cycle time
What is DIE casting and what are the two types?
how is it different from pressure casting?
-Molten metal is injected into a closed metal
die under high pressure
-Pressure is maintained during solidification
-Die is separated and casting ejected
- Hot chamber process
- Cold chamber process
-No vacuum present in die casting
What is the HOT chamber die casting? where is it used, what materials? what are the advantages?
- Significant difference is that metal is melted in a reservoir joined to the die, no transfer
- Dies are cooled by circulating water/oil through passageways in the die block
-zinc tin & lead based alloys (low melting point metals, Cornish metals..)
- No transfer process of the molten metal
- Fast cycling times
-Good strength
-Excellent dimensional precision and surface
finish
What is COLD chamber die casting? where is it used, what materials? what are the disadvantages?
-Metal is melted in a separate furnace and is
transported to the die casting machine
-Molten metal is fed into an unheated chamber
-A mechanical plunger forces the molten metal
into the die cavity where the metal solidifies
-Employed for die casting of materials that are
not suitable for hot chamber design (high melting point metals) e.g aluminium, magnesium and copper (shiny’s)
- Expensive dies
- Requires high production rate to justify the usage
- The need to transport molten metals
What is CENTRIFUGAL casting? what are the three types?
- Pour molten metal into rotating mould
- Utilises inertial force caused by rotation to distribute molten metal into mould cavities
- Metal is held against the mould wall by centrifugal force until it is solidified
1) True Centrifugal Casting
2) Semi-Centrifugal Casting
3) Centrifuging
what is TRUE Centrifugal Casting and where is it used?
- mold made of steel with refractory lining for longevity
- mold rotates as a barrel would
- used to create pipes with external geometries
- molten metal is distributed uniformly
-Pipes
what is Semi-centrifugal Casting?
- Used to cast parts with rotational symmetry
- the mold cavity rotates perpendicular to gravity
what is Centrifugal Casting and where is it used?
- similar to Semi-centrifugal casting only the molten metal is spun by a device that sprays it onto the mold
- Bushes, bearing housings etc, high precision cylindrical parts
What are the possible steps in the production of steel?
1) Recylced steel - An electric arc furnace is used (EAF) this melts steel and the molten steel is then rolled and continuosly cast
2) Blast furnace method - Iron is produced in a blast furnace, the molten iron then goes to a basic oxygen steel maker (BOS) where oxygen is added and the carbon content is altered; producing steel. The molten steel is then continuously cast
What are the possible faults in continuously casting steel? how is steel quality increased?
- prone to bubble entrapment which make the steel porous
- fluxes are added that can:
prevent oxidation, stop solidification of the surface
What are the benefits of using cutting fluids during machining? what is coolant made of?
- Allow for cutting speed to be increased
- Chips are removed
- extend tool life
-oil and water to lubricate & avoid rust
explain the different types of turning can be achieved using a lathe?
- Straight turning
- Form turning
- Facing / Parting
- Boring
- Thread cutting
- Knurling
- Drilling
- Straight turning - cut in just the z direction x constant
- Taper turning - cut in the z & x direction
- Form turning - A specific tool is used that cuts a profile of the final shape
- Facing / Parting - The end of a work-piece is flattened off
- Boring - internal features are cute using an ‘L’ shaped tool
- Thread cutting - Produces external or internal threads in a work-piece
- Knurling - regularly shaped roughness is achieved on the surface of a component
- Drilling - the drill bit is kept stationary whilst the work piece is rotated
What are the advantages of using non-traditional methods of machining?
-No chips produced
-Complex geometries can be achieved
-Delicate components can be machined (brittle)
achieves a high surface finish
What are the four branches of Non-traditional machining?
- Chemical machining
- Electro-chemical machining
- Mechanical methods (water jet & abrasive flow)
- Thermal machining
what is CHEMICAL machining and what are its advantages & disadvantages?
-Material is removed from a work-piece by selectively
exposing it to a chemical reagent or etch-ant
-the material is masked using masking agents or photo-resist backing
-etch rate is proportional to chemical concentration
advantages)
-Induces no stress in the material
-Thin section (e.g. honey comb) can be machined as no
mechanical forces are involved
disadvantages)
- Very slow process
- Dangerous chemicals
what is ELECTRO-CHEMICAL machining and what are its advantages & disadvantages?
- It is a de-plating process where the tool is the cathode and the work-piece is the anode
- electrolyte is pumped through a hole in the tool
- metal ions are removed from the work-piece and washed away
- work-piece takes the form of a negative of the tool
advantages)
- Well suited for machining complex shapes
- materials that cannot withstand high machining forces
- No tool wear developed
- No thermal damage
Disadvantages)
- Costly
- Not environmentally friendly
what is WATER JET CUTTING (WJC) and what are its advantages & disadvantages?
-Water is ejected from a nozzle orifice at high pressure
(up to 400 MPa)
-This produces a jet velocity greater than the speed of
sound
-Small nozzle opening produces a
very narrow width of cut
advantages)
-The ability to cut materials without burning or
crushing
- Inexpensive
Disadvantages) -Loud process -Not suitable for brittle materials -It is not a powerful process therefore limited to cutting thin sheets
what is ABRASIVE WATER JET CUTTING (AWC), where is it used? what are its advantages & disadvantages?
- Just like water jet cutting only an abrasive is added, this allows for a stronger cutting method
- Used in aeronautical industry for cutting composite materials as they do not de-laminate
advantages)
-Can cut thicker stronger materials
Disadvantages)
-Costly & the abrasive can damage the tool
what is ABRASIVE FLOW MACHINING, where is it used?
-The workpiece is mounted in the machine and pistons
drive the abrasive fluid back and forth through it.
-used in the finishing of internal geometries of parts with complicated shapes
What are the 4 types of thermal machining?
Electrical Discharge Machining (EDM)
Particle Beam Machining (PBM)
Laser Beam Machining (LBM)
Plasma Arc Cutting (PAC)
What is Electrical Discharge Machining (EDM)? wwhat are the two types of EDM & how do they work? what are the applications?
- The electrode & work-piece are suspended in a dielectric fluid.
- The dielectric fluid allows for a spark to cross between the electrode and the workpiece
- Spark erosion
1) Ram EDM
- The electrode is a die in the shape of the negative of the cavity made from graphite, copper, copper-tungsten alloy
- By feeding the die into the workpiece, the shape of the die is machined into the workpiece
2) Wire EDM
- wire works similar to a band saw, only the cutting is caused by the spark erosion
Applications)
- Dies & punches (hardened materials)
- High precision parts
What is Particle Beam Machining (PBM)? what are its advantages & disadvantages?
- Uses a beam of high-energy electrons focused on a workpiece to melt and vaporise it
- thew electrons are produced by heating a tungsten filament
- Similar to EDM only there is no solution between the tool and workpiece
advantages)
-minimal thermal damage
Disadvantages)
Harmful X-rays produced