Design and Technology A Level

• Riveting


  Used to join sheet metal or plates and are made up of a head at one end and a shaft/tail at other end.Rivet shaft inserted into hole through both pieces, head of rivet is dome shaped and sticks out. Set tool placed over head and end of shaft is then hammered over to squeeze the two pieces together.Example used are in tools such as trowel fastenings.
• Soldering


  similar to brazing but only used for lightweight applications and thin gauge metal. Commonly used on electronics, joining ring seams and joining precious metals e.g. gold and silver.Uses a filler metal of lower melting point than metal being joined, typically alloys of tin and copper and are heated by gas/air torch or even a handheld soldering iron.Metal must be very clean and important there are no gaps between areas being joined.

  
• Brazing


  the process of joining metal with a filler rod that melts at a temperature below the metal being joined. Produces a weaker bond than welding but is still useful for prototyping and joining thin gauge low carbon steel tubes and bars e.g. steel framework for furniture.Material to be joined is cleaned and degreased and the two pieces are then clamped together. Flux is then applied to prevent joint from oxidising and the joint is then heated using Oxy-Acetylene or gas at 850 oC. Brazing rod applied to joint area.

  
• Oxy-Acetylene Weldings

  Used to weld low carbon steel sheet, tube or plate where arc welding processes are not available. Almost obsolete due to MIG and TIG welding but useful for quick repairs or in the absence of a power supply.Uses a mixture of Oxygen and Acetylene stores in seperate containers and hoses. Gases are mixed at the blow torch and intensity can be adjusted by changing mixture at the valves.
• TIG Welding


  Used to weld metals like stainless steel and non ferrous metals like aluminium. Same electric arc welding process to MIG but electrode made from tungsten and does not melt. Separate filler rod used. Same gas shield of argon or helium used to prevent oxidation in weld area.Allows for greater control by operator and stronger welds created but it is slower than MIG.Examples include stainless steel ladders and exhausts.

  
• MIG Welding

  Fabrication method used to weld thin gauge metal, usually medium carbon steel or aluminium. It is suitable for thin gauge metal as heat generated is localised to small area and wont burn through. Can be used for one-off and mass production e.g. joining car panels.Uses electric arc to create heat to melt the join area. A wire electrode of the same material that is fed through the gun also melts in the arc and fills gap between the two pieces.Uses inert gas like CO2 or argon to form flux shield to remove oxygen from the weld area that could cause oxidation.

  
• Low temperature Pewter Casting


  Mould and runner made from MDF, Plywood or High Density Modelling foam which can be laser cut using CAD. Mould joined together and molten pewter poured in, cooled and then mould is removed.
• Investment Casting


  Used to cast intricate or awkward shapes such as jewellery. Exact Replica made of product and runner using wax and then dipped in refractory clay and fired in a kiln until hard. During this time the wax melts away, leaving a hollow mould. Molten metal poured in and allowed to cool. Clay broken off and runner cut off.
• High Pressure Die Casting


  Produces cast items quickly and in high volumes. Hydraulic plunger forces molten metal through goose neck into the die. Due to the high pressure, all the mould is filled to very high quality.
• Gravity Die Casting


  involves melting a metal and pouring it into the mould using gravity. Involves a runner and riser to pour metal in and indicate when it is full.

  
• Sandcasting


  Typically used for one-off or batch productions as the moulds are single use and very labour intensive. Used for drain covers, bollards etc, doesn't give high quality finish due to grainy texture of sand.Pattern made from wood which is replica of product to be cast and is placed in bottom of box called 'drag'. Drag filled with sand which is packed and levelled. Drag turned over and second box called cope is added and wooden stakes added also. Sand packed in around cope and then pattern and stakes removed to form runner and riser and connecting channels cut to join these to the mould cavity. Small depression cut away to form pouring basin around runner. Molten metal poured in, allowed to cool and removed and runners cut off.

  
• Flexible Manufacturing Systems (FMS)


  A production method that is designed to easily adapt to changes in the type and quantity of the product being manufactured. E.g. new dies
• Computer Integrated Manufacturing (CIM)


  A process that allows all stakeholders involved in product to get involved with its development
• Cons of CAD

  Problems if system crashesTakes time to learnHigh cost of softwareTraditional skills may become obsolete
• Pros of CAD

  Designs can be communicated electronicallyProducts can be manufactured directly from CAD designsReduces product lead timeEnables testing to before manufacturing beginsDesigns can be easily and quickly changed
• Cons of CAM

  High cost of machinery and operator trainingPuts labourers out of workRequires skilled techniciansRequires regular maintenance, production stops
• Pros of CAM

  Can be fully automatedSaves time and labour costExtremely accurateEnables large number of identical parts to be manufacturedProductivity increased, less downtime
• Cons of Robotics in Manufacturing

  Poor mobility and flexibilityLimited degree of freedom, humans more efficient at other tasksHigh set up costsRemoves need for jobs
• Pros of Robotics in Manufacturing

  Carry out mundane boring tasksCarry out physically demanding tasksWork in hazardous areasHigh levels of accuracy, consistently and quicklyWorks for long periods of time
• Telematics


  Allows manufacturer to track production from parts through through to assembly and dispatchE.g. when a car company receives an order the order info is transferred into black box which follows car along production line and informs assembly workers of what part is needed to be fitted to the car to reflect customers order
• Master Production Schedule (MPS)


  a plan used to determine how many products will be made in a given time period
• Sequencing


  Once parts or materials arrive at factory, they must go to individual work cell at right time. All controlled by computer
• Kanbans (Card Signal)


  Barcode system used to inform manufacturer the type of part or quantity held within container. Barcode scanned as soon as part is used and automatically reordered
• Tensile Testing


  test piece placed in tensometer machine and clamped at each end. Once clamp fixed and other moves on worm gear mechanism. Test piece stretched, the load and distance travelled are plotted to give info on elastic limit, yield point and breaking point.
• Non Destructive Testing Methods

  Ultrasonic testing, X ray testing, electrical and thermal conductivity
• Vickers Hardness Test


  Consists of a diamond indenter and a light load to produce an indentation on the subject under testing. The depth of indentation is converted into the hardness value of the object.It is regarded as one of the easiest impact tests.

  
• Brinell Hardness Test

  used to determine the hardness of castings and forgings whose grain structure is too coarse for accurate Rockwell or Vickers testing.A predetermined force is applied to the spherical indenter diameter and held for a predetermined time period, and then removed.The indentation is measured across two or more diameters and then averaged to get the indentation diameter . Using this indentation size the Brinell Hardness Number is found

  
• Izod Test (Toughness)


  Measures a material's resistance to impact from a swinging pendulum. A suitable test piece is struck with a striker, mounted at the end of a pendulum. The test piece is clamped vertically with the notch cut into it, facing the striker. The striker swings downwards impacting the test piece at the bottom of its swing. Amount of force required to snap material is measured and the tougher the material, the more force required to snap/bend it

  
• What does the Rockwell number represent

  Difference in depth between major and minor load applied
• Rockwell Hardness Test

  Diamond indenter makes indent into test piece to determine its hardness. First a minor load is applied and a zero reference position is found. The major load is applied for a specified time period beyond the zero point. Major load released to minor load and Rockwell number established

  
• fusibility


  The ability of a material to change into a liquid or molten state when heated to its melting point
• mallebability


  ability to withstand deformation by compression without cracking, rises with temperature
• tensile strength


  The ability of a material to withstand pulling forces.
• toughness


  ability to absorb impact forces without fracture
• hardness


  ability to resist abrasive wear like scratching or cutting
• compressive strength


  the ability to withstand being crushed or shortened by pushing forces
• Issues with Mining


  Water pollution occurs due to heavy metals and acid that drain from minesAir pollution from machinery, trucks and diesel generators which emit CO2, Sulphur Dioxide and moreExtraction of Alumina from Bauxite leaves behind Bauxite Refinery Residue which is highly toxic and water polluting Copper sulphate and zinc mines impact nearby farmland, aquifers, fish wildlife and habitatTin mining leads to many deaths of workers in LIC's
• Annealing


  A heat treatment process that changes the physical and sometimes chemical properties of a material to increase ductility and reduce the hardness to make it more workable.Requires the material above its recrystallization temperature for a set amount of time before cooling.
• How does work hardening work?

  As stresses are exerted, the crystals slip against each other and the more they tend to place obstacles in the way of further slippage
• Work Hardening


  Work Hardening refers to an increase in hardness of a metal induced deliberately or accidentally, by hammering, rolling, drawing, or other physical processes. Strength will decrease with initial deformations, strength begins to increase with continuous deformationsoccurs because of dislocation movements and dislocation generation within the crystal structure of the material