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Moulding

11.2.1 Define sprue, flash, parison, die, draft angle and injection moulding.

Sprue
This is the passage through which a liquid material flows into a die, where it solidifies to form parts.
Flash
Excess material on a moulded part, forming a thin fan where two parts of the mould meet.
Parison
A short length of extruded pipe for use in blow moulding.
Die
A tool used in the manufacture of parts by moulding, forging, swaging or stamping processes.
Draft angle
The angle of taper, expressed in degrees (usually 5 to 7), given to the sides of the forging and the side walls of the die impression.
Injection moulding
The direct introduction of molten plastic under pressure into a die, which then cools rapidly, allowing the formed object to be released from the mould.

11.2.2 Explain how an injection-moulded product is made.

Diagrams must include the hopper, hydraulics, heaters, screw, sprue and mould.

11.2.3 Outline the advantages of injection moulding.

Consider initial capital investment, tooling, accuracy, quality control and quantity of product.
  • High initial capital investment however it is recouped quickly.
  • Quick re-tooling
  • Highly accurate
  • High Quality control - few errors
  • Can be volume produced 24/7

NB can be considered a clean technology

11.2.4 Discuss how standardised bottle caps have constrained bottle design, but have cut costs for manufacturers.

Bottle caps can be classed as standardised parts. Bottle tops are injection moulded, while bottles are normally made by blow moulding. It is financially beneficial for a blow moulding company to use off-the-shelf bottle tops instead of purchasing an injection moulding machine and new tooling.

11.2.5 Describe how a blow-moulded product is made.

Diagrams must include the extruder, parison, the mould and air inlet.

11.2.6 Explain how a rotational-moulded product is made.

Diagrams must include the mould, filling the mould, heater chamber, rotation and cooling chamber.
An animation

11.2.7 Explain how a compression-moulded product is made.

Diagrams must include the mould, pre-form, hydraulic press, finished part and flash material.

11.2.8 Discuss why some products have to be made using compression moulding.

Consider the heat the product must withstand, quantity and type of product to be made. Refer to thermosets.

The plate needs rigidity and resist heat

11.2.9 Describe how a vacuum-formed product is made.

Diagrams must include the vacuum chamber, former, platen, heater, air in and out.

11.2.10 Identify manufacturing methods suitable for thermoplastics and thermosets.

Thermoplastics: vacuum forming, blow moulding, injection moulding and rotational moulding. Thermosetting plastic: compression moulding.

References

Bulleted list and italicised paragraphs are excerpted from Design Technology: guide. Cardiff Wales, UK: International Baccalaureate Organization, 2007.

Images are clickable links to its location.

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Page last modified on September 19, 2012, at 02:21 AM