Metal processes

Ingot

starter material for metal processes – simple in shape intended for subsequent reshaping. - made via casting

shape casting

casting more complex geometries

casting advantages and process

pros:

applicable to any metal

can be used to produce any size component

process pts:

make the mould slightly bigger than necessary to allow for shrinkage

open mould exists but such limited geometry - closed mould better

actual process obv

types of mould

expendable - made of sand and thrown away after use - ALLOWS FOR MORE COMPLEX SHAPES

permanent mould - made of refactory or metal - quicker production because reusable

solidification time + riser

depends on both size and shape - SA to volume ratio.

chorinov eq:

n = exponent = 2 usually, given

Tts = solidification time

etc

RISER MUST HAVE A LARGER V to SA ratio IN ORDER TO STAY MOLTEN WHEN SHAPE COOLS SO THAT IT CAN FILL GAPS CAUSED BY SHRINKAGE.

shrinking stages

shrink whilst liquid cooling - can stick to mould .:. use lubricant

shrink whilst changing state

shrink whilst solid cooling

NOTE: you can get a cavity in the top centre area of the workpiece because it doesnt have much access to molten metal (below gravity pulls it down to fill gap.

names of sand casting parts

upper = cope

lower = drag

core = middle part to make internal shapes iin workpiece

outer box = flask

NOTE: parting line = line on workpiece showing mould meeting point.

How do you make the moulds for sand casting?

Use a pattern made of wood or plastic

what is the name of the path into the mould

Gating system

one key property of sand cast

porous sand allows trapped air to escape

investment casting advantages

complex shapes produces

high accuracy/low tolerance

wax used to make mould can be reshaped into new mould unlike sandcasting pattern!!!

investment casting processes

wax patterns made with master die

wax patterns attached to wax sprue

mould produced by covering wax moulds and sprue in refractory material

flip and melt wax leaving cavity inside

fill moulds through sprue with molten metal and let cool then remove cast and disconnect from metal sprue.

die casting info

moulds = dies

and its a permannet form of casting

two types:

hot chamber limited to low mp metals.

cold chamber for high mp metals.

hot chamber die casting

metal turned molten in an ATTACHED container

piston injects molten metal into die

cold chamber die casting

metal made molten in a disconnected container - hence piston and rest of machine arent under continous molten metal flooding which damage it over time hence its able to do higher tempos but less often.

same piston process

SLOWER cycles compared to hot chamber casting

casting restrictions

same as vacuum fdorming:

draft angle required

no sharp corners

cant be too thick

easier shapes = more castable

metal forming

involves plastic deformation to change the shape of metal work pieces - jig used to plastically deform it is also called a die!!

the 4 main bulk deformation processes:

Rolling = metal pushed through 2 opposing rollers to thin material

Forging = compress between two dies (like hammer hand held)

Extrusion = piston pushes through die to produce constant CSA.

Drawing = metal drawn/pulled through in order to reduce diammeter.

press working

term given to most processes involved with sheet forming

in press working what are the names of the parts of the machine

top = punch\

bottom = die

name of workpiece after press working

stampings

4 main press working processes

Bending

Drawing = shape of bowl

Shearing

cutting

main issue with bending and how to fix it

main issue with bending is slight elastic reformation once load removed. = springback. - can compensate for it though - either OVER BEND or BOTTOM it = squeeze at end of press to retain shape.
spring back eqaution = … where at = TOOL a = part

3 main shearing press working processes

shearing = straight line

blanking = cuts shape out of sheet - excess = sheet

punching = cuts hole out of sheet - excess = circle = slug

cut parts names

rollover = top of the cut surface = smoothest

Burnish = below rollover = relatively smooth

Fracture zone = where the fracture/cut actually properly occurred

Burr = bottom edge - sharp and rough.

2 main bending types

v bending = punched down into die

edge bending = canti-lever like force applied to bend about corner of die.

bending force equation

w = width

TS = tensile strength of metal

t = thickness

…

bend allowance equation

Ab = bend allowance

R = INSIDE BEND RADIUS

…

drawing process

rounded punch pushes down on sheet into cavity

this causes two bends but as the punch pushes further it causes the second bend to straighten out hence becoming the outer sufrace of the cylinder.

this straightening can cause a thinning of the material so be weary.

the workpiece can then be placed into another die for a new stage of drawing to make the cylinder thinner and so on.

joining vs assembly

joining = permanent connection

assembly = made for disassembly

types of welding joints

name of parts connected by welding

weldment

name of area on part to be joined

faying surface

welding pros and cons

pros:

strong

doesnt require shape alterations

cons:

labour intensive and hence expensive

dangerous

difficult to dissassemble

welding types

arc welding

resistance welding

oxyfuel gas welding

other

arc welding

utlising the heat of an electric arc between an electrode and workpiece to join two metals together

can add filler to strengthen

electric arc

discharge of electric current between a gap - flows through a plasma in the air

categories of arc welding electrodes

consumable = feeds in filler through electrode

e.g. MIG or stick

non-consumable = doesnt need filler but can be manually fed directly onto surface - if not just melts the two metals joining them due to heat from electric arc.

e.g. TIG

flux and inert gases purpose

both used to produce a cleaner and stronger weld/solder by:

preventing metal reaction with the air at high temperatures

removing oxide layer on workpiece

increase flow of filler metal

‘disappearing‘ once connection complete

stick welding

literal stick of metal and flux as the electrode that u put current through - cheap + not accurate

MIG metal inert..

consumable electrode - metal wire fed through and inert gas surrounds it. advantages = versatile but expensive

TIG

non- consumable tungsten electrode - NO SPLATTER and high quality welds but expensive

NOTE: no splatter because TIG u feed in filler metal or dont at all directly to surface, MIG its shot on from electrode through arc.

brazing and soldering

brazing = middle between weld and soldering

soldering = super low mps for metals (<450deg)

NOTE: no melting of the base metals occur only the filler metal melts unlike in welding.

used when heat of welding can damage components and high strength is not a necessity.

for welding and brazing diagonal cuts are hard to keep alligned in the process how do u fix this?

change from scarf = straight diagonal line

to

stepped = stair like = easier to keep in place

2 thigns to watch out for when brazing and or welding

clean surface before and after

gap size:

cant be too big - molten metal wont be able to flow between the two

or too small - filler metal must fit in gap

brazing types

furnace = automatic - much quicker but much more enrergy - just place filler between parts and conveyor belt loads into furnace

torch = manual - slower but less energy and more flexibility

soldering types

hand solder

wave soldering - mass production version = whole circuits placed over wavy basin of molten solder after being fluxed which sticks.

reflow soldering - mas production also = whole circuit placed with solder past stuck below it in the right places then put in oven and then let to cool.