Material Processing

Describe two techniques that can be used to change the strength of a metal

• Alloying: mixing the metal with one or more metals / non-metals together to form a material with different properties

• Heat treatment: changing the temperature of a material over time to change its crystal structure and properties

• Work hardening: applying a physical force to plastically deform a metal or alloy changing its structure and properties

Describe two techniques that can be used to change the material properties of a polymer

• Blending: mixing two or more different polymers together

• Drawing: aligns polymer chains in the direction they are stretched and can increase strength

• Cross-linking: when strong covalent bonds are made between polymer chains

• Reinforcement: other solid components are placed in solid polymer

What is meant by ideal strength of a solid, and why do materials not reach their ideal strength?

• Ideal strength of a solid: the theoretical maximum stress a material can withstand without failure and is based on bond strength between the atoms

• Materials do not reach their ideal strength due to imperfections (non-crystallinity and defects) within the crystal structure

What happens to the ductility of a metal when a process is used to increase its strength and why?

• As strength of materials increase, their ductility generally decreases

• Most strengthening methods work to prevent structural dislocations within the material from moving

• If unable to move then material becomes more rigid and less ductile

Other than changing the mechanical properties of a metal, why else may you want to alloy it?

• To change electrical, thermal and optical properties of a metal

• To change how a material reacts to a certain environment, affecting susceptibility to different types of corrosion

• Change environmental and economic properties of a metal

Describe a shaping, joining and surface treatment process suitable for a metal

• Shaping: casting, forging, extruding, rolling and sheet forming

• Joining: adhesives, welding, fastening

• Surface treatment: precision machining, grinding, lapping, polishing

E.g. extruding is forcing a malleable metal or polymer through a die of fixed cross section so that the metal takes the form of the die

Why does an engineer have to consider processing when selecting a material?

• As certain materials can only be used in conjunction with certain processes, can only be formed into certain shapes

• Different processes have different costs so affects overall cost of selecting that material

Describe a shaping, joining and surface treatment process suitable for a polymer

• Shaping: blow moulding, injection moulding, compression moulding, rotational moulding

• Joining: adhesives, polymer welding, fasteners

• Surface treatment: precision machining and polising

E.g. injecting moulding is the process where the heated polymer is injected into a mould. as polymer cools, it takes desired shape of the mould.

What is casting? (to shape a metallic material)

• Process where metal is heated past its melting point and is liquid

• Cast into a die, has geometry of required component and allowed to cool and solidify to form the component

What is forging? (to shape a metallic material)

• Manufacturing process to shape a metal using localised compressive forces

• Blows caused by a hammer or die

What is extrusion? (to shape a metallic material)

• Process to create objects of a fixed cross-sectional profile

• A material is pushed through a die of desired cross-section