16 - Metal processes

Question 1

3 groups for metal processes

Answer 1

• Forming
• Resditribution
• Wastage

Question 2

Metal processes - forming

Answer 2

Are processes in which no material is removed, but materials are deformed to produce required shapes

Question 3

Metal processes - redistribution

Answer 3

Are processes where the material is changed from one form to another without loss of material e.g liquid metal poured into a mould to take a solid shape

Question 4

Metal processes - wastage

Answer 4

Are processes that cut away material to leave the desired shape

Question 5

Types of forming (7)

Answer 5

• Press forming
• Spinning
• Cupping and deep drawing
• Drop forging
• Wrought iron forging
• Bending
• Rolling

Question 6

Types of redistribution

Answer 6

• Sand casting
• Gravity die casting
• Prssure die casting (hot & cold chamber)
• Investment casting
• Low temperature pewter casting

Question 7

Types of wastage (4)

Answer 7

• Milling
• Flame cutting
• Plasma cutting
• Laser cutting

Question 8

Press forming:

• stock form
• products

Answer 8

• Sheet
• Metal seats, car body panels, boxes and containers

Question 9

Press forming process (4)

Answer 9

• Sheet metal is clamped over a die of the product that will determine the final shape of the pressing
• A hydraulic press pushes the die into the sheet metal cutting blades may be included to punch holes into the sheet and trim the excess from the edges
• The hydraulic die is lowered and the pressed sheet components is removed
• The sheet may be placed into further press forming machines for additional pressing, where the shape is complex

Question 10

Spinning:

• stock form
• products

Answer 10

• Sheet
• Body of stainless steel kettles, saucepans, metal light shades

Question 11

Spinning process (6)

Answer 11

• A former called a ‘mandrel’ is put into the chuck. The sheet metal blank is held in place between the mandrel and tail stock

• The roller tool is moved into the blank and is rotated with the mandrel. This starts to stretch the metal over the mandrel
• The roller tool is moved along the mandrel as pressure is maintained against the rotating blank
• The roller tool is moved to the end of the mandrel, while still maintaining contact with the blank finishing the shape of the product
• The finished product is removed from the mandrel
• Excess material is trimmed off following the spirring process

Question 12

Cupping and deep drawing:

• stock form
• products

Answer 12

• sheet (round blank)
• tube-like shapes such as fire extinguishers, aerosol cans, drink cans

Question 13

Cupping and deep drawing process (3)

Answer 13

• The pressing blank is clamped over a deep drawing die using a prssure pad or clamping ring known as a retainer
• A hydraulic press moves the deep drawing punch to be in contact with the blank. It then pushes the blank into the die cavity to make a cup shape
• The ‘cup’ is then pressed further down through the deep drawing die to make the desired tube shape

Question 14

Drop forging:

• stock form
• products

Answer 14

• Billet
• Spanner’s, pliers and screwdriver shafts

Question 15

Drop forging process (5)

Answer 15

• A die is made from cast tool steel is secured from the top of an anvil
• A ram is also equipped with a die that resembles a mould
• The metal ‘billet’ to be forged is heated to above its recrystallisation temperature stopping the product from work hardening as it cools which would make it brittle
• Using tongs, the heated billet is placed by an operator into the anvil die, and the hydraulic ram is brought down with force making the hot billet spread around the shape of the die
• The ram is lifted and the complete product is removed for cooling and finishing

Question 16

Wrought iron forging:

• stock form
• products

Answer 16

• Bar
• Decorative metalwork such as gate scrolls, decorative fencing

Question 17

Wrought iron forging process (2)

Answer 17

• The wrought iron is heated in a gas or coke-fired forged
• It is then shaped by holding it with tongs, hammering it over an anvil or using other tools such as scroll formers or twisting bars

Question 18

Key features of wrought iron forging (3)

Answer 18

• Uses wrought iron (carbon content less than 0.08%)
• Can be hand or hydraulic press process
• Suitable for one-off or small-batch production

Question 19

Bending:

• stock form
• products

Answer 19

• Sheet or plate
• Seams on metal edges, bending sheets for product casting or housings
• mainly used for large scale batches in industry

Question 20

Bending process (3)

Answer 20

• Clamp the stock metal between a matching punch and die
• A hydraulic, pneumatic or mechanical brake holds the metal sheet or plate and lowers the punch to bend the material to shape
• Modern press brakes use a back gauge to accurately position the piece of metal, so that the brake bends the metal in the correct place

Question 21

Rolling:

• stock form
• products

Question 22

Key features of rolling (3)

Answer 22

• Hot rolling metal results in uniform mechanical properties, no deformation or stresses
• Surface is usually coated with carbon deposits which must be removed using acid pickling
• Cold rolling results in a material that has a tighter tolerance and better surface finish

Question 23

Sand casting:

• stock form
• products (7)

Answer 23

• Molten metal from a billet
• Railway carriage wheels, wood working clamps, vices, motor housings, bollards, drain covers, post boxes

Question 24

Sand casting process (6)

Answer 24

1 - a ‘pattern’ is made, usually from wood which is a replica of the item that will be cast and is then placed into a drag. The drag is then filled with sand which is packed or rammed in tight around the pattern and levelled

2 - The drag is turned over and the cope is clamped into position over the top of the drag

3 - sand is packed into the cope a round the runner, riser and pattern. A small depression is made on the surface around the sprue to make a pouring basin

4 - the cope and drag are separated, and the stakes and patterns are carefully removed. Connecting channels are cut to join the sprue to the pattern cavity, and from this to the riser. The cope and drag are then re-assembled and the mould is ready for pouring to begin

5 - small metal spikes may be inserted and removed to make vent holes. These will allow gases from the casting process to escape

6 - The molten metal is poured into the pouring basin. It flows down the runner, into the cavity. When cavity is full, the molten metal flows up the riser, indicating to the worker that the cavity is full. Once cool, the sand is removed to reveal the casting

Question 25

Key features of sand casting (3)

Answer 25

* Labour-intensive process * Not a high-quality surface finish * Suitable for one-off or small-batch production

Question 26

Gravity die casting: - process - stock form - products

Answer 26

•

Question 27

Gravity die casting process (4)

Answer 27

* Involves melting the metal and then pouring it into the mould * This process relies on gravity to help the metal to flow through the mould * There is a runner and riser. The runner is used to poor the molten metal into the mould while the riser will indicate when the mould is full * Once the metal is cool, the mould is opened and the casting can be removed

Question 28

Key features of gravity die casting (2)

Answer 28

* Used for thicker mould sections * Used for very large-batch and mass production

Question 29

Pressure die casting (hot chamber): - process type - stock form - products

Answer 29

* Redistribution * Molten metal from a billet * Toy cars collectible figures, decorative door knobs and handles

Question 30

Pressure die casting process (4)

Answer 30

1 - The molten metal is stored in a chamber which is part of the high pressure die casting machine 2 - A pneumatic hydraulic plunger forces a 'shot' of molten through the 'goose neck' into the die 3 - Due to process using high pressure all of the mould is filled and it allows a fine detail to be moulded 4 - The process is fast as the molten metal is not stored seperately and then transported to the casting machine

Question 31

Key features of pressure die casting hot chamber (2)

Answer 31

* Fast process * Uses for very large batch and mass production

Question 32

Pressure die casting (cold chamber): - process type - stock form - products

Answer 32

* Redistribution * Molten metal from a billet * Toy cars, collectible figures, decorative door knobs and handles

Question 33

Pressure die casting (cold chamber) process (3)

Answer 33

* The molten metal is kept separately in a melting crucible * The molten metal is then ladled into the shot chamber, and a hydraulic ram forces the molten into the mould cavity * When the metal has hardened, the mould opens and ejector pins push the finished casting out

Question 34

Key features of pressure die casting (cold chamber)

Answer 34

Used for very large-batch and mass production

Question 35

Investment casting: - process - stock form - products

Answer 35

* Redistribution * Molten metal from a billet * Cast jewellery or collectable figures, hip replacement joints

Question 36

Investment casting process (6)

Answer 36

1 - An exact replica of the product to be cast is made using wax 2 - The wax pattern is dip coated with a refractory clay. It is then fired in a kiln to bake the clay hard. The wax is burned away, leaving a hollow clay 3 - molten is poured into the clay mould 4 - Once the metal has filled the mould, it is allowed to cool 5 - The clay mould is then broken away, revealing the casting 6 - The runner and any connecting channels are machined off

Question 37

Key features of Investment casting (3)

Answer 37

* Used for intricate or awkward shapes that would be difficult or impossible to Luke using any other casting process * High quality excellent finish * Wax patterns are cast from a master mould, repeatable quality process

Question 38

Low temperature pewter casting: - process type - stock form - products

Answer 38

* Redistribution * Molten metal from a billet * Jewellery, key fobs and decorative components

Question 39

Low temperature casting process (7)

Answer 39

1 - A mould is made from MDF, plywood or high density modelling foam. If made from MDF or plywood, the mould might be laser cut or cut with a fret saw. The mould will include a spruce or runner which will be used to pour the pewter into 2 - The mould is sandwiched between two pieces of MDF and clamped together. The top of the mould will be level with the top of the side pieces 3 - The pewter is melted in a ladle and then ladled into the sprue 4 - Once the casting is cooled, it is removed from the mould 5 - The sprue or riser is removed with a junior hacksaw 6 - The casting is then filed, and cleaned up using abrasive wet and dry paper 7 - The casting would then be polished

Question 40

Key features of low temperature pewter casting (3)

Answer 40

* Used for school or college projects * Can be used with simple MDF moulds * Suitable for one-off production or small batch