processes, techniques and specialists tools Flashcards
what is heat treatment
how heating up a metal can change its properties
what is hardening
medium and high carbon steels are heated for a given time then quenched, increases hardness but also brittleness
what is tempering
reduces some of the hardness and brittleness from a hardened metal whilst increasing the toughness and ductility, metal is heated below the critical point then air cooled
what is case hardening
hardens surface of steels with less than 0.4% carbon content
case hardening process
steel is placed in ceramic box which is fill with carbon , heated to 950 degrees C, long the exposure to carbon thicker the layer of carbon, metal heated to 760 degrees C and quenched
what is annealing
the heating and slow cooling of work-hardened material to make it easier to work with, less brittle and more ductile
what is normalising
low carbon steel to give the metal a fine grained structure, material is heated to the same temperature for hardening then quenched and left to cool, increases brittleness and toughness
what are alloys
metal made of 2 or more metals, eg stainless steel
what is sand casting
cope is placed on the drag, mould made of sand, runner and riser, molten metal poured through the runner and when it comes up the riser you can tell there’s enough molten metal in it
labour intensive, low quality finish, suitable for one-off or batch production
eg clamps, train wheels
what is gravity die casting
a permanent mould casting process, where the molten metal is poured from a vessel or ladle into the mould, the molten metal is poured down the runner and when it comes up the riser you know the mould is full
lower melting point (aluminium), used for thicker moulding sections, suitable for large scale production
eg engine parts, door knobs
what is pressure casting
a process in which molten metal is forced under pressure into a securely locked metal die cavity, where it is held by a powerful press until the metal solidifies
lower melting point (aluminium), molten metal stored in chamber then forced into die, fast process, large scale production
eg toy cars, doorknobs
what is blow moulding
the forming of a hollow object by inflating or blowing a thermoplastic molten tube called a “parison” in the shape of a mould cavity, for making hollow thin walled components, high tooling costs, used for continuous production, eg shampoo bottles
advantages and disadvantages of blow moulding
adv- lower cost than other similar processes, one piece construction, automated
dis- only hollow parts, low strength, trimming is necessary, have to use thermoplastics
what is injection moulding
The molding machine heats the plastic until it is liquid. The nozzle of the injection molding machine then injects the melted plastic into the mold (injection pressure). The cavity of the mold is now filled with the plastic liquid. This will then cool down to form a solid product
eg TVs, calculators
adv and dis of injection moulding
adv- faster than similar processes, large scale construction, complex shapes are possible
dis- high initial costs, costly to run, some limitations to shape, moulds take time to make and are expensive
what is vacuum forming
heats a plastic sheet until it becomes pliable, stretches the material onto a mold, and then uses vacuum pressure to obtain the desired part geometry
eg trays, coffee cups
adv and dis of vacuum forming
adv- cost effective, excess plastic can be recycled, moulds are easy to create
dis- excess moisture can cause unwanted bubbles to form, limit to the angle on the mould
what is rotational moulding
A hollow mold is filled with powdered plastic resin. The mold begins rotating bi-axially and is transferred into an oven. The mold continues to rotate as the resin melts and coats the walls of the mold.
eg kayaks, traffic cones
adv and dis or rotational moulding
adv- most cost-effective for production volumes of less than 3,000 annually, uniform wall thickness, high stability
dis- few material options, high process durations
what is offset lithography (adv and dis)
- a method of mass-production printing in which the images on metal plates are transferred (offset) to rubber blankets or rollers and then to the print media
- adv- consistent high quality image, high volume print runs, long life of printing plates
- dis- expensive set up costs for small quantities
what is flexography (adv and dis)
- form of rotary printing in which ink is applied to various surfaces by means of flexible rubber (or other elastomeric) printing plates
- adv- high print speeds, suited for long runs, prints on large range of materials, low cost of equipment (least expensive printing process), low maintenance
- dis- cost of printing plates is high but can last for a long time, time consuming to change what is being printed
what is green printing (adv and dis)
- the process of transferring a stencilled design onto a flat surface using a mesh screen, ink and a squeegee
- adv- minimal setup costs due to ice of basic equipment
- dis- slow process, high cost per product
what is gravure (adv and dis)
- the paper is pulled between two rollers (impression roller and printing cylinder) where a doctoring blade takes off excess paint from the painting cylinder and so as the paper goes between these two rollers the paint gets printed on the paper
- adv- good print quality and speed, simple process
- dis- not economic for small runs, not good for fine text lettering, expensive set up costs
what is milling/routing
- milling makes small holes or channels in wood or metal
- milling is a slower process than routing but can be linked to CNC
- routing machines make slots or holes in wood and can be done by hand or with a CNC router
