Forming processes

Question 1

Describe the properties of thermoplastics

Answer 1

A material which can be repeatedly reheated and reshaped, allowing it to be recycled after its initial use.
Thermoplastics have long linear chain molecules held by van der Walls forces

Question 2

Describe the properties of thermosetting plastics

Answer 2

A material which, when heated, undergoes a chemical change whereby the molecules form rigid cross-links. Thermosetting polymers cannot be reheated and reshaped, even at high temperatures

Question 3

Describe the injection moulding process

Answer 3

1. Thermoplastic granules are poured into the hopper
2. A motor rotates a screw threaded. This pulls the granules through the chamber and past the electric heaters
3. The heaters melt the polymer
4. When a sufficient charge of polymer has melted and formed at the end of the screw, the hydraulic ram forces the screw thread forward. This injects the polymer into the mould
5. The mould is water-cooled, which enables the molten polymer to harden quickly
6. The mould opens, and the ejector pins push the moulding out
7. Any excess polymer is trimmed off the moulding. Formers or jigs may be used to maintain the dimensional accuracy of the moulding while it cools and hardens completely

Question 4

What are the advantages of injection moulding?

Answer 4

High production rate - thousands of identical parts can be produced quickly, ideal for mass production
High precision and repeatability - each part is dimesionally accuracte and consistent
Complex shapes are possible - undercuts, threads, and hollow sections can be produced
Low labour costs - machines handles most of the work automatically
Low waste - excess polymer can often be recycled into the process

Question 5

What are the disadvantages of Injection moulding

Answer 5

High initial costs - expensive moulds and machines, so not economical for small batches
Long set-up time - designing and manufacturing the mould can be time-consuming
Limited to thermoplastics - most thermosets are not suitable
Complex mould changes - design modifications require new moulds

Question 6

Name two adhesives suitable for bonding cardboard packaging and explain one key difference between them.

Answer 6

PVA (Polyvinyl acetate) – a water-based adhesive that dries slowly, allowing some repositioning of the materials before setting.
Contact adhesive – a solvent-based adhesive that bonds instantly when the two coated surfaces touch.

Question 7

Describe the lamination process

Answer 7

Wood veneers or thin manufactured boards can be glued together and bent over a former, so that when dry form a thicker board in the shape of the former. While drying the laminates may be held in place with clamps, or more commonly, using a vacuum bag

Question 8

Describe the lamination process with a vacuum bag

Answer 8

With a vacuum bag, the former and veneers are placed under a polyethene sheet. The edges of the sheet are taped down to the table. A valve is fitted to the polymer sheet and a vacuum pump sucks out air, and the resulting pressures pills the laminates hard together.

Question 9

What is the purpose of steam bending?

Answer 9

With a combination of heat and steam, the strips of timber can be made pliable so that they can be shaped over a former

Question 10

Describe the steam bending process

Answer 10

The process involves putting the timber into a steam box, where the timber will absorb the steam.
The timber is then usually bemt over the former and clamped to it until it dries

Question 11

What are the advantages of steam bending

Answer 11

Strong curved components - the grain follows the curve, giving continuous-grain strength
Low waste - no material is cut away; timber is bent rather than removed, compared to lamination, as parts usually require trimming
Sustainable - minimal energy and non-adhesive are needed
Elegant curves - ideal for furniture and decorative shapes
Preserves natural timber appearance - no layering or laminated needed
Time efficient - steam bending is quicker the laminating, in waiting for glued layer to dry

Question 12

What are the disadvantages of steam bending

Answer 12

Requires specialist equipment, increasing setup costs and time
Labour-intensive process that needs skilled operators
Limited to certain types of wood - only timber with good elasticity (e.g. ash, oak, beech)
Risk of defects such as spring-back, splitting, or fractures if bent too tightly
Slow process because timber must be steamed for a long period and left to dry
Accuracy issues - can be difficult to achieve consistent, repeatable shapes for mass production