topic 3- processes, techniques and specialist tools Flashcards
what are the 5 heat treatments for metals
- hardening
- tempering
- case hardening
- annealing
- normalising
what is hardening
-medium and high carbon steels are heated then held at a certain temperature for a given time
-then quenched in water oil or saltwater baths
- the process increases the hardness but also increases brittleness
what is tempering
- reduces some of the excess hardness and brittleness from a hardened metal
- increases the toughness and ductility
- metal is heated to below critical point for given time then slowly air cooled
- exact temp the metal is heated to will determine the amount of hardness removed
what is case hardening and what is the process
- hardens the surface of steel which have less than 0.4 percent carbon content
- outer surface has improved hardness and resistant to indentation
- inner core keeps it properties
PROCESS–
- carburising- changes the chemical composition of the surface of low carbon steel so it can absorb more carbon to incr surface hardness
- steel placed into ceramic box packed with carbon and is heated to 930-950 degrees
- carbon atoms diffuse into materials structure and build up on the surface
- depth of carbon layer determined by length of time material is exposed to carbon
- product is heated to 750 degrees and the quenches
- quenching seals hard surface case
what is annealing
the heating and slow cooling of work hardened metal to make it easier to work
- less brittle and more ductile
what is normalising
-used on low carbon steels to give the metal a fine grained structure
- material is heated to same temp as for hardening
- quickly quenched then left to cool
- makes the metal more ductile with increased toughness
what is alloying
- metal made from two or more metals or combining two elements of which one must be a metal
- alloy gives enhanced features and properties
-produced in either a furnace or in casting process - metals melted together in specific quantities and poured into bars or ingots
what is printing
-flexography and offset lithography use four colour process- cyan magenta yellow and key ( black)
-four colours are printed on top of each other in various quanitites
- colours must line up exactly to ensure non blurry image
what are the uses, advantages and disadvantages of offset lithography
- used for books, magazines, posters
- consistently high quality
- long life of printing plates
- expensive set up
what is Direct Printing
image transferred directly from the plate cylinder (or image carrier) to the paper eg gravure, flexography, screen printing and letterpress printing processes.
what is Indirect or offset printing –
image is transferred from the plate cylinder to the blanket cylinder and then on to paper eg offset lithography, which is the most widely used commercial printing process.
what is the process, uses, advantages and disadvantages of flexography
- uses fast drying water ink
- ink transferred to the roller then to the material via pressure from printing roller
- newspapers ,comic , carrier bags
- high print speed
- low maintenance
- cost of printing plates is high
- time consuming to change any alterations to the print content
what is the process, uses, advantages and disadvantages of screen printing
- screen has open areas for the ink to pass through
- diff screen required for each colour
- used for small print runs like t-shirts
- minimal set up cost
- slow process with high cost per product
what is the process, uses, advantages and disadvantages of gravure
- rotary printing process
- image engraved or etched onto rolling cylinder
- packaging, gift wrapping
- good print quality
- simple printing process
- lot economic for small runs
- expensive set up costs
what are the 4 printing techniques
- offset lithography
- flexography
- screen printing
- gravure
what is casting
- a process mainly for metals, involving heating metals into molten state then transferring to a mould
- there are 5 different casting techniques
what are the 5 casting techniques and what are pros and cons of them
- SAND:
labour intensive and not high quality surface finish
suitable for one off
-INVESTMENT:
wax patterns used which melt in contact with molten metal
high quality finish
-GRAVITY DIE
gravity helps metal flow into mould
used for thicker mold sections
suitable for large batch
-PRESSURE DIE
molten metal stored in chamber then forced into die
fast process
used for large batch
-PLASTER OF PARIS
low cost
only used for non ferrous metals
excellent surface finish
explain the process of sand casting
-sand is flattened down in the drag and the pattern is put into the sand as well as two sprue pins
- cope is then also filled with sand and pins removed to create vents
- molten metal poured in
what is resin casting
-a process for casting polymers
- involves pouring polymer into pre made mould then allowing the resin to set in shape
- mould can be gently vibrated to stop air bubbles
- most commonly used resins are acrylic, polyester and epoxy
- can be done at room temp
- moulds made from things like silicone rubber or MDF
- pigments can be added
what are the 5 processes of machining
milling/ routing
drilling
turning
stamping
pressing
what is routing
- makes small holes or channels in wood or metal
- slower process than routing
- can be linked to CNC manufacture
- CNC router
what is drilling
- rotating drill bit drills into static material such as wood, metal or polymer
- drill produces holes for items like dowels and screws
what is turning
- uses a lathe and can be used for wood or metal
- can be a cnc process
- material is rotated and a cutting tool is pressed against materials surface to remove excess material
- used to make things like chair legs
what is stamping
- sheet material is removed using CNC stamping procedure which stamps the material shape out of the sheet
- shearing action of upper tool and lower tool removes material
