Product Design (Metals)

Overview of Metal Materials

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Metal Examples

Non Ferrous – Metals that contain very little or no iron (e.g. copper, brass and bronze).

Ferrous – Magnetic metals which are predominantly composed of iron (e.g. Cast iron, Stainless Steel)

Alloy – Metals composed of one or more metals or non-metals for more enhanced properties are called alloys (e.g. Solder - lead and tin, Brass - copper and zinc)

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Work Hardening & Heat Treating Metals

Work Hardening – When a metal is worked by rolling, bending, hammering or drawing it becomes harder

Annealing – To relieve the hardness the metal is heated & allowed to cool slowly

Hardening – When medium & high carbon steel is heated & quenched in water it becomes harder but a little brittle

Tempering – This reduces the brittleness and makes the metal tougher 

Normalising – This involves heating a steel component to a specific temperature, “soaking” it in the flame and then allowing to slowly air cool. This allows the crystalline structure to become uniform

Case hardening – The surface of mild steel can be hardened by heating and then placed in a bed of carbon powder. Carbon is absorbed which hardens the surface.

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Manufacturing in Metals

CNC Laser Cutters & Plasma Cutters –

- Laser cutters can be programmed to cut out a wide variety of holes, slots & profile shapes in thick metal sheets. Laser cuts are very fine & smooth so there is little waste and very consistent quality 

- Plasma cutting uses an electric arc to generate heat energy plus compressed air or argon gas to blast through thick metal. Fine, smooth cuts are produced.

Press Forming 

- Press forming uses a punch & die of toughened die-steel to press the sheet metal into a 3-D shape

- Dies on press machines can be changed so different products can be made

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Embossing –

- This creates 3-D decorative patterns on the metal

Deep drawing –

- To make the elongated shape for a fizzy drink can the metal blank disc is stretched through a series of hard metal rings. So the metal is continually stretched.


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Metal Spinning

- A flat metal disc fixed to a former & both are spun  

- The disc is formed into a cylindrical shape by pressing a tool up against the metal as they spin at speed. 

- The disc gradually takes up the shape of the mandrel.

- Steel, stainless steel, aluminium, copper & brass can be spun 

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- Like polymers metals can be heated to known melting temperatures 

- When molten the liquid metal can be poured into a shaped mould 

- When allowed to cool the metal hardens & is removed from the mould

- The metal has taken up the shape of the mould

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Sand casting

- A pattern is made from wood, metal or a polymer. Sometimes the mould is split

- Each half of the pattern is put on a base board & half  a mould box is placed over

- Damp sand is rammed around the pattern

- The 2 halves of the mould box are placed together

- Molten metal is poured into the “runner” until it comes out of the “riser”

- When the metal has cooled & solidified the casting is removed from the casting box and cleaned up.

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Advantages & Disadvantages of Sand Casting

Advantages of Sand casting –

- Complex 3-D shapes can be made 

- Cores can be used to produce hollow shapes  

- Appropriate for small runs 

- Can be automated for longer runs

Disadvantages of Sand casting –

- Machining is necessary because of the poor surface finish 

- Not as accurate as other methods of casting 

- Slow process so has a low output rate suitable only for small production runs

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Die Casting

- The process is similar to sand casting except the shape of the die(mould) is machined out of  alloy steel. 

- The metals cast usually have low melting points like aluminium 660°C, magnesium 650°C & zinc 850°C

There are 2 types of die casting: 

- Gravity Die Casting 

- Pressure Die Casting

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Gravity Die Casting

- Molten metal is poured into the pouring basin 

- Gravity forces it to all parts of the die 

- The outside of the die is heated to ensure even cooling

- Fluxes prevent the metal oxidising as it is being cast

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Pressure Die Casting

- The process is similar to injection moulding polymers

- The molten metal is forced into all parts of the die by the pressure of a hydraulic ram

- Simpler dies need lower pressure

- The dies are water cooled for rapid cooling

- Ejector pins push the casting out of the die

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Advantages of Die Casting over Sand Casting

- The surface finish of the casting is as smooth as the die’s surface 

- The final shape & size are as accurate as the die. 

- Because the casting is cooled rapidly the material tends to be better quality

- Rapid cooling (<1 second /cycle) is suitable for large scale production covering the cost of the dies so a profit is made

- Low melting alloys need less heat to melt resulting in lower energy costs

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Investment casting

This is an extremely ancient method of casting used for small scale production 

- An wax pattern is moulded

- A runner & riser are added & it is sprayed with clay 

- Fired in a kiln bakes the clay & removes the wax

- Molten metal is poured into the now hollow mould

- After cooling the clay mould is smashed off

- The casting is then heat treated & cleaned 

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Forging Metals

- Hot metals can be forged either by hand or by machine 

- Hot metal is much more malleable than cold metal & needs less energy to shape it 

- Basic processes are carried out with hammers, anvils, swages & punches

- Processes involve bending, twisting, punching, scrolling, drifting, drawing down & drop forging

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Drop Forging

- Drop forging involves exerting very large forces onto a hot metal blank, forcing it into the shape of a metal die

- The component being forged will pass through a number of dies, progressively altering the shape of the blank at each stage 

- Large numbers of the same product can be manufactured in this way

There are 2 types of drop forging:

Closed Die Forging

This is where a hot billet of metal is forged inside an enclosed die which is split into 2 halves

Open Die Forging

This is where the 2 halves of the die are open so that longer forgings can be manufactured

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Structure of Metals

Drawings of Structures - 

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