Plastic Production Methods

Vacuum Forming

• Uses plastic form, it is usd to make any different products from packaging, helmets, masks, toys and baths.

Line bending

• Simple process and uses a ***** heater to achieve a straight, small curved bends in acrylic
• As it cools it will retain its shape
• Low cost

Thermoforming

• New process is very similar to vacuum forming
• Thermoforming uses a female outer mould to help in the process which allows greater detailed products e.g lettering, symbols and sharp edges
• Low cost process
• Requires trimming after

Process:

1) Heated just above softening point

2) Held securely in a frame between the two mould halves

3) Then close and at the same time a vacuum is applied through the bottom mould

4) Upper mould ensures the required amount of detail is achieved

Injection Moulding

• Produce complex 3D items
• Mass production- thousands
• Equipment and moulds are very expensive

Example: Bowls, buckets, chairs, packaging and toys

Disadvantages:

• High set up costs
• Price of moulds can be expensive to produce

Injection moulding: Process

1) Plastic granules (colours and additives) pass from the feed hopper into the barrel

2) Rotating archimedean screw pushes plastic down the barrel by the motor and gearbox where it is melted by heaters

3) Injected into mould by the ram of the screw

4) Mould is cooled and then split allowing the ejector pins to release the component from the mould

Identifying injection moulding:

• Complex 3D shapes
• A computer mouse is good example, the covering is a complex shape with curves and fixings for screws

Extrusion

• Instead of injecting a mould the plastic is pushed through a die
• Continuous length of the product with the same cross section products like pipes, guttering, curtain rails and UPVC window frames
• Can only produce continuous cross sectional shapes

Process:

1) Thermoplastic powder placed in hopper where it falls into the archmedean screw

2) Heated and forced in the die

3) Exiting is cooled using a water jet and is then cut to the desired length

Blow Moulding

• Manufacure of bottles
• Hollow and have a narrow neck
• Quick process- do not have to be circle
• Moulds can be expensive
• Cant be too complex in design

Process:

1) Starts off extrusion of a preform tube

2) Passes into a split mould which closes sealing both ends

3) Hot air is blown into the tube pushing the plastic out to the sides of the mould

4) The mould then cools the polymer

5) The two halves open and the product is removed

Identifying blow moulding

• Hollow
• One end sealed
• Sprue mark- bottom of the products where plastic is introduced into the mould
• Seam line where mould halves joined

Rotational Moulding

• 3D hollow products e.g footballs, dolls, road cones and large storage tanks
• One piece mouldings
• Moulds tend to be cheaper
• Cheaper production runs

Disadvantage:

• Can only do hollow, sealed products

Process:

1) Number of arms which rotate continuously apart from beginning and end

2) Moulds open and exact measurement of powder is enetered and clamped tight

3) The mould is then rotated and is heated to melt the plastic

4) Cooled and seperated- final product

Compression moulding

Combination of heat, pressure and time is needed

Advantages:

• Start up costs are low
• Complex parts can be processed over long production runs
• No waste material due to it being calculated prior to moulding

Disadvantages:

• Have to make preforms
• Need to be of low complexity for compression moulding

Compression moulding process

1) A preform of the exact amount is placed beween the two halves of the mould

2) Mould is then heated so that the cross-links will form in the thermosetting material

3) Mould is then closed so that the material flows around the mould

4) Any excess material is pushed out of the mould and after set time the material has cured, this can be ejected when it is still warm

5) Repeat the process