Manufacturing Techniques Flashcards
Name 2 single use/disposable casting techniques
sand casting
investment casting
Name some casting defects
Liquid metals containing gas cause porous end products
metal can contain oxides
misruns/cold shuts - when metal solidifies before mould is full
Why is sand casting used
low cost
versatile
small upper limit in terms of size and weight
can cast complex shapes
short lead time
mould is cheap to make from wax, wood or plastic pattern
Common problems in sand casting
erosion - metal can be poured in too fast and sand can end up in the cast
penetrations - if molten material is too viscous it can flow into voids of the mould
rough surface and relatively high levels or porosity an low dimensional accuracy
applications of sand casting and main material used
cylinder heads
landing gear
mainly used with alloys
batch size of investment casting
10-10,000
benefits of investment casting
good surface finish
can produce complex shapes
no parting line
can be used with almost any metal
drawbacks of investment casting
expensive pattern and mould
high labour costs
size limitations
high lead time
single use
slurry build up in moulds
Name 4 permanent casting methods
pressure casting
slush casting
die casting
centrifuge casting
pressure casting advantages, drawbacks and minimum batch size
clean finish, no oxidation
expensive, long set up time
minimum batch size of 1000
slush casting benefits and drawbacks
hollow cast, good external detail
wall thickness can vary
what are the 2 types of die casting
hot chamber - lower melting point, non-corrosive metals
cold chamber - metal is melted separately, high melting point & corrosive alloys
die casting advantages, drawbacks and minimum batch size
fast cycle times, thin sections
expensive equipment, small components produced (under 10kg)
minimum batch size of 10,000
2 types of centrifugal casting
true centrifugal and semi centrifugal
continuous casting advantages and drawbacks
very high volume
very basic shapes
only uses steel
post processing required since shapes are so basic
continuous casting shapes
bloom
billet
rounds
why are fluxes added to moulds
protect steel from oxidation
defects of continuous casting
longitudinal crack
sub-surface cracks
thermal shrinking
sticker breakouts
common applications of powder metallurgy
oil impregnated bearings
cutting tools
metal filters
common powder metallurgy materials
iron, copper, tin, nickel, titanium
limitations of powder metallurgy
typically lower strength
restricted to relatively small, light parts
expensive equipment
what is extrusion used to manufacture
railings, sliding doors, window frames, tubing, brackets, gears, hangers
materials used for extrusion
copper, aluminium, steel and lead
defects of extrusion
cracking
centre cracking
piping
what is punching used for
improve edge quality or create holes in sheet metal
bending applications
car bodies, paper clips
what is spring back
the material trying to return to its original shape so will straighten a bit once it has been bent
what shapes are made with extrusion
pipes, rods, pellets
thermoplastic mould temperature
90
thermoset mould temperature
200
welding process
permanent joining of two materials, usually by coalescence - bonding of the molecules of both metals
what are tac welds used for
small welds to hold the join at the same angle before a full weld is carried out
what is the fusion zone
the area that has been melted and solidified
what is the heat affected zone
next to the fusion zone where there are changes in the microstructure but doesn’t melt
forms of flux
powder, paste, coated filler rod
flux function
produces gas shield, chemically cleans base metal and removes oxides, removes slag
advantages of welding
extremely strong joint
distributed force
light weight joint
limitations of welding
high energy requirements
limited to certain metals
similar metals must be used
permanent joints
residual stresses and distorsion
HAZ
expensive
most common resistance welding process
resistance spot welding
resistance welding advantages and limitations
no electrons required, no flux, easy and fast
complex and expensive equipment, electrode wear
resistance welding applications
sheet metal fabrications, automotive body assembly
diffusion welding advantages and application
can join different metals
titanium welding in aerospace
brazing filler metal melting point
> 450 degrees celcius
does brazing require a flux
yes - to prevent oxidation and clean base metal
how is filler metal drawn into gap
capillary action - uniform gap and clean surfaces
why is a welding agent used
reduce surface tension of the molten filler metal
enables it to spread across the surface of the base metal
what is the most common material used for sheet metal forming
low carbon steel
brazing disadvantages
not suitable for high temperature operating conditions
not as strong as welding (but still strong)
more sustainable to corrosion
tighter part tolerance required to promote capillary action
how can you improve brazing joint strength
increase the contact area
what is the filler metal melting temperature
<450 degrees celcius
advantages, disadvantages and applications of soldering
cheap, quick, no HAZ, no distortion
limited joint strength, low temp applications
electronics, plumbing, automotive radiators
name mechanical fasteners
stapling
seaming
crimping
snap in fasteners
advantages and considerations of mechanical fasteners
easy to manufacture, easy to assemble and disassemble, movable joints, low cost
temporary joint, what materials are being joined, weight limitations, cost, appearance, dimensions
adhesives industries
aerospace, automotive, home appliances, building products
adhesive advantages and limitations
strong sealed bonds, distributed loads, thin components, low temperatures >200, no distortion, corrosion resistant
limited range of temps, long bonding time, surface prep vital
what is subtractive manufacturing
parts made by removing material by chipping away from a bulk
additive manufacturing
parts made from small building blocks e.g. inkjet printing
advantages and disadvantages of additive manufacturing
more efficient energy use, waste reduced, huge design freedom
slow production, expensive
inkjet printing advantages and disadvantages
stencil can be reused, stencil defines final print
contamination from earlier prints, incomplete ink transfer, one ink at a time
what is the rake angle
angle of the cutting tool to the vertical
what is the relief angle
the angle of the cutting tool to the horizontal
up milling description
feed direction is traveling in the opposite direction to the tool direction
advantages and disadvantages of up milling
backlash isn’t an issue
surface finish is impared, suited for older machines
down milling advantages
better surface finish, better for modern machines
which teeth go into a material first when broaching
roughing teeth then finishing teeth
abrasive machining advantages and applications
high dimensional accuracy, excellent surface finish, can be applied to hard, brittle materials
ball bearings, pistons, valves, gears
most common abrasive machining process
grinding
what material does honing use
abrasive stones
what material does lapping use
leather
