Product Design (Metals)
Overview of Metal Materials
- Created by: Luke Bisset
- Created on: 09-04-12 17:22
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)
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.
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
Continued...
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.
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
Casting
- 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
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.
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
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
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
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
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
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
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
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
Structure of Metals
Drawings of Structures -
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