Flashcards in Polymer Manufacturing Processes Deck (32):
Injection moulding is a manufacturing process in which a molten material is injected into a mould to shape a product
Injection Moulding Advantages (3)
Quick, low labour cost, high output
Blow molding is the process of forming a molten tube (parison or preform) of thermoplastic material and placing the parison or preform within a mold cavity and inflating the tube with compressed air, to take the shape of the cavity and cool the part before removing from the mold. Any hollow thermoplastic part can be blow molded.
Blow Moulded Items (4)
Industrial bulk containers
Car under hood parts
Extrusion Blow moulding stage 1
Plastic is melted and extruded into a hollow tube (parison)
Extrusion blow moulding stage 2
Mould closes and the parison is gripped in place
Extrusion blow moulding stage 3
Air is blown into the parison which then inflates it to the container, bottle, part etc.
Extrusion blow moulding stage 4
After the plastic has cooled the mold is broken and the part ejected
Extrusion blow moulding stage 5
Any excess material is removed from the mould be trimming with a knife
Why use blow moulding
To create a hollow plastic part which has thin walls
Injection blow moulding
In this process, The hot material, still on the core pin, is then indexed to the blow molding station where it is blown into a bottle and allowed to cool. The bottle is then indexed to the next station and ejected.
Injection blow moulding vs extrusion blow moulding
Injection blow moulding adds more physical detail like more precise detail in the neck and finish (threaded) area than extrusion blow molding.
Stretch blow moulding
Like injection blow moulding, the material is injected. It is then presented to the blow mold in a conditioned state, but before final blowing of the shape, the preform is stretched in length as well as radially.
Stretch blow moulding uses (2)
To create wide mouthed jars
Used to make speciality products where high production rates are not required
Blow moulding vs injection moulding similarities (2)
Both are high production
Create cost effective plastic parts and products
Blow moulding vs injection moulding differences (2)
parts made by injection molding and parts made by blow molding is that injection molding creates solid parts, while blow molding creates hollow parts.
Injection moulding makes rigid walls whereas blow moulding makes smooth walls for things like bottles
where a sheet of plastic is heated to a forming temperature, stretched onto a single-surface mold, and forced against the mold by a vacuum.
Vacuum forming stage 1
place the mold in the machine then lower it down into the machine to prepare it for its function.
Vacuum forming stage 2
place the material on the frame and then clamp omit down so it is locked in place and cannot move
Vacuum forming stage 3
place the heater over the thermo plastic for 30sec or any other specified time so it is springy and not rigid
Vacuum forming stage 4
remove the heater and pull the mold onto the plastic so it begins to take shape
Vacuum forming stage 5
Suck the air out from below the mold and plastic so the plastic fills the mold and takes shape
Vacuum forming stage 6
Lower down the platen then remove the clamps holding the plastic down
Vacuum forming stage 7
Remove the plastic from the frame which should be easier because of the rake angle in place on the mold an you have your finished product
Vacuum forming products (6)
• Baths & Shower Trays
• Yoghurt Pots
• Boat Hulls
• Machinery Guards
• Refrigerator Liners
• Sandwich Boxes
Disadvantages of injection moulding (3)
High initial tooling and machinery cost.
Part design restrictions.
Small runs of parts can be costly
Injection moulding stage 1
Clamping - the two halves of the mold must first be securely closed by the clamping unit. Each half of the mold is attached to the injection molding machine and one half is allowed to slide. The hydraulically powered clamping unit pushes the half’s together.
Injection moulding stage 2
Injection - The raw plastic material, usually in the form of pellets, is fed into the injection molding machine. During this process, the material is melted by heat and pressure. The molten plastic is then injected into the mold very quickly and the buildup of pressure packs and holds the material. The amount of material that is injected is referred to as the shot.
Injection moulding stage 3
Cooling - The molten plastic that is inside the mold begins to cool as soon as it makes contact with the interior mold surfaces. As the plastic cools, it will solidify into the shape of the desired part. However, during cooling some shrinkage of the part may occur. The packing of material in the injection stage allows additional material to flow into the mold and reduce the amount of visible shrinkage.
Injection moulding stage 4
Ejection - After sufficient time has passed, the cooled part may be ejected from the mold by the ejection system, which is attached to the rear half of the mold. When the mold is opened, a mechanism is used to push the part out of the mold. Once the part is ejected, the mold can be clamped shut for the next shot to be injected.
Injection moulding products (3)
Plastic bottle caps