Unit 9 - Working with Metals

Question 1

Plating

Answer 1

plating can be done using PVD (Physical vapour deposition) and provides a thermal barrier

material is cleaned thoroughly
- protective layer
- applied through a vacuum

Question 2

Hard soldering

Answer 2

• wire the joint together with soft iron binding wire
• Paint’ the joint with Flux
• small drops of solder are palced along the joint
• the solder is gently heated so the flux dries out and the metal is not damaged
• heat in then increased

Question 3

Plasma cutting

Answer 3

• used for thicker metal plates
• uses a negative electrode and a positive workpiece
• particularly high temperatures
• can be done manually or with CNC
• uses a gas shield
• electric arc is send through the gas and intensified

Question 4

Flame cutting

Answer 4

focused oxy-acetylene gas
- inaccurate cutting
- leaves messy edges and dripping molten lava

Question 5

Turning

Answer 5

Metal is wasted using a centre lathe (often made from HSS)
Can be mass or batch produced
CNC lathes can either use multi-tool heads which automatically change tools

tool heads
- facing - drilling - taper turning - parting
- knurling - parallel turning

Question 6

Brazing

Answer 6

• uses an oxy-acetylene flame
• lower temperature than welding, so the joint isn’t as strong
• can be used in dissimilar metals

Question 7

Bending

Answer 7

• press brake
• the metal sheet is clamped and the punch lowers to bend the metal

Question 8

Powder coating

Answer 8

• The product is statically charged
• sprayed with the powdered paint
• The product is then baked to allow the polymer to melt and bond to the metal

Question 9

Dip coating

Answer 9

The metal product is heated to 230’ and dipped into the fluid polymer powder
- Warm air blows to melt the polymer and bonds the solution together
- left to cool and solidify

• tool handles and sports equipment

Question 10

Electroplating

Answer 10

• using a more visually pleasing metal to coat a cheaper one
• also provides a protective layer
• negative electrode is electroplated
• positive electrode is the coating metal
• The electrolyte solution is also made from the coating metal

Question 11

Cellulose paint

Answer 11

• dries quickly
• high levels of VOCs
• requires multiple layers of paint
• base must be degreased and prepared to ensure a high quality finish

Question 12

Milling

Answer 12

traditional milling cuts on two axis’ X,Y
advanced milling can cut on three axes’ XYZ to allow for more accuracy and dimension
can be done manually or via CNC
slots and holes can be machined with specific cutters

Question 13

Laser cutting

Answer 13

Laser cutting uses a direct and intense laser to cut the metal
- Compressed air removes the excess molten metal
- The fine laser allows for high levels of accuracy
- can only be used on sheet metal

Question 14

Riveting

Answer 14

• semi-permanent
• metal fasteners than join sheet or plate metal

cold rivets
- two components, a set and a snap end
- the snap is shaped under pressure
- requires access to both sides of the metal

pop riveting
- uses a pop-rivet gun
- only needs access to one side
- applies pressure which splays the inserted end and creates a rounded head

Question 15

Oxy-acetylene welding

Answer 15

used for low-carbon steel
uses oxygen and acetylene to produce a flame
- Separate filler or welding rod
- does not require a power source

Question 16

Spot welding

Answer 16

• doesn’t use a filler metal
• uses heat and pressure instead
• Workpieces are held together under pressure
• The process is limited by the size of the project and whether it can fit within the machine

Question 17

TIG welding

Answer 17

• uses a tungsten electrode (non-consumable) and a separate filler material, which allows for a more customisable amount of filler to be used
• An inert gas shield is used to prevent oxidation
• used for stainless steel, aluminium and copper alloys

Requires a constant electricity source

Question 18

Mig welding

Answer 18

• uses a consumable electrode
• inert gas shield to prevent oxidation
• The consumable electrode is beaded and melts between the two metals, connecting them
• can join dissimilar materials

requires a constant electricity source

Question 19

Pewter casting

Answer 19

used for small projects and jewellery
since it has a low melting point

raw materials are melted and heated up
poured into the mould
left to dry

Question 20

Investment casting

Answer 20

used to produce awkwardly shaped products and dental/medical devices

a wax mould is created
The wax mould is coated in ceramic
the wax is melted, leaving a hollow profile
The hollow profile can be filled with molten metal

Question 21

Sand casting

Answer 21

A two-part mould is created from ‘green sand’
liquid metal is poured into the mould and left to cool
the sand is then removed and the final piece is produced
messy finish - more industrial uses such as engines
all materials used can be repurposed

Question 22

Forging

Answer 22

molten metal is forced into shapes under great pressure so it retains its original grain structure

used to make pliers and screw drivers

Question 23

Cupping and deep drawing

Answer 23

A punch is used to shape the metal and pushes the sheet into the die to produce a tube-like profile
the punchs’ rounded corners help to stretch and push the metal without tearing

deep drawing - depth is greater than the width
cupping - width is greater than the depth

Question 24

Spinning

Answer 24

used to form sheet metal with radial symmetry
uses a mandrel and stock to shape the metal
can be identified by the parallel lines of the product

Question 25

Press forming

Answer 25

used to cold shape sheet metal Often used in mass production low carbon steel and aluminium uses pressure to force the metal into the mould Dies are made from hardened die steel

Question 26

Electrical conductivity testing

Answer 26

A multimeter is used; the lower the resistance, the better the conductivity Four-point probe tests are used in industry as they measure current and voltage

Question 27

Galvanising

Answer 27

Coats ferrous metals with zinc to provide a protective layer The zinc then produces zinc carbonate, which is resistant to corrosion can be done through electroplating or zinc coating (dipping)

Question 28

Anodising

Answer 28

done on aluminium produces an aluminium oxide finish anodising becomes apart of the metal, so it will not chip or flake off placed in an acidic electrolyte solution

Question 29

Zinc dipping

Answer 29

caustic cleaning - rinsing = pickling - rinsing Then the component is dipped into the molten zinc, producing a thicker layer than electroplating The metal is then cooled, cleaned and inspected

Question 30

Acrylic paint finish

Answer 30

water based, so no VOCs requires more specialsied equipment than cellulose paint and takes longer to cure can be used for bikes and window frames

Question 31

Stock forms of metals

Answer 31

sheet - up to 3mm thick bar structural beams plate - over 3mm thick

Question 32

Sealants

Answer 32

provide an additional barrier by preventing air or fluids from passing through metal joints often polymer based can help prevent corrosion

Question 33

Preservatives

Answer 33

can be temporary or long-term used in moulds to prevent buildup Preservatives are often oil-based to add lubrication and prevent static charge and build-up

Question 34

Soft soldering

Answer 34

lower melting point metals used in plumbing and electronics Metal is cleaned to remove any grease or contaminants Flux can be added to prevent surface oxidation A soldering iron is used to apply the metal left to cool and checked

Question 35

Die casting

Answer 35

used with lower melting point metals molten metal is fed into a die using gravity or pressure ejector pin helps with the release used for engine components

Question 36

Annealing

Answer 36

relieves the stresses of metals and makes them easier to work with difference - annealing is cooled more slowly ferrous metals - cherry red and slowly cooled

Question 37

Cathodic protection

Answer 37

A sacrificial metal is used to coat another metal to control the corrosion - Zinc is often used as it will corrode instead of the metal underneath (often iron or steel) Often used on boats or oil rigs

Question 38

Normalising

Answer 38

a form of annealing for ferrous metals to remove internal stresses and strengthen the metal heated to 700 - 900 and 'soaked' at that temperature before air cooling

Question 39

Tempering

Answer 39

done after the metal has been hardened medium to high carbon steel heated to a critical temperature, which is calculated based on the colour of the metal oxide layer air cooled

Question 40

Case hardening

Answer 40

hardens the exterior layer of low-carbon steel The steel is carburised (dipped in carbon powder) and heated

Question 41

Hardening

Answer 41

Helps to harden steel heated to a red heat and cooled quickly by quenching used for blades