Material Processing

Question 1

What is material processing?

Answer 1

The application of physical and chemical processes to alter the geometry, properties and appearance of a starting material to make parts or products for a given application.
–> transformation of materials into items of greater value.

Question 2

Polymer processing: dependent factors

Answer 2

• Thermoset or thermoplastic (recyclable)
• If thermoplastic, the softening temperature (processes often conducted at elevated temps)
• –> Tg for amorphous thermoplastics
• –> Tm for crystalline thermoplastics
• Atmospheric stability
• Geometry and size

Question 3

Polymer processing techniques

Answer 3

• COMPRESSION MOULDING (temp activated thermosets): the pressing of a deformable material charge between the two halves of a heated mould, and its transformation into a solid product under the effect of the elevated mould temperature.
• TRANSFER MOULDING (temp activated thermosets): a softened temperature-activated material is transferred through a narrow gate into the closed cavity of a heated mould, where it cures to a solid state.
• INJECTION MOULDING (thermoplastics): known amount of polymer (usually pellets) loaded into feed hopper, pushed by hydraulic ram to become pressurised in heating chamber and released into mould.
• EXTRUSION: continuously shaping a fluid polymer through the orifice of a suitable tool (die), and subsequently solidifying it into a product (extrudate of constant cross section) by blowers, water spray or both.
• FUSED DEPOSITION MODELLING (FDM) (thermoplastic): Filament is fed from a large spool through a moving, heated printer extruder head, and is deposited on the growing work. The print head is moved under computer control to define the printed shape.
• STEREOLITHOGRAPHY (more complex geometries): a technique or process for creating three-dimensional objects, in which a computer-controlled moving laser beam is used to build up the required structure, layer by layer, from a liquid polymer that hardens on contact with laser light.

Question 4

Additive vs subtractive manufacturing techniques

Answer 4

• Additive manufacturing is a process that adds successive layers of material to create an object, often referred to as 3D printing.
• Rather than adding layers, subtractive manufacturing involves removing sections of a material by machining or cutting it away.

Question 5

Metal processing techniques

Answer 5

• CASTING: The production of a metallic component by casting of the molten metal into a mould. Sand, continuous, die, investment.
• FORGING: the shaping of metals using localised compressive force (manual or mechanical).
• ROLLING: the cheapest and most efficient method of reducing the cross-sectional area of a metal section. Commonly used for producing flat products. The rollers are used to shape the product and by rolling, redistribution of any impurities reduce the effect of any segregation present in the original ingot.
• EXTRUSION: A ram is driven with pressure to force the metal through a hard steel mould.