Plastic Manufaturing Flashcards
(16 cards)
Vacuum forming
Plastic Vacuum forming is where a flat sheet of extruded plastic is heated until pliable, it is then allowed to shape by applying a vacuum. Once the forming has been cooled and hardened once again, you are able then to trim the part to the desired profile.
Injection moulding
Material granules for the part is fed via a hopper into a heated barrel, melted using heater bands and the frictional action of a reciprocating screw barrel. The plastic is then injection through a nozzle into a mould cavity where it cools and hardens to the configuration of the cavity. The mould tool is mounted on a moveable platen – when the part has solidified, the platen opens and the part is ejected out using ejector pins.
Blow moulding
Blow moulding is a technique used for the production of hollow plastic parts. Blow moulding can be based on extruding, injecting or stretching heated liquid mass into a mould. The material expands and takes the shape of the mould. Blow moulding is a technique to produce containers for liquids such as deepfrying oil.
Line bending
Line bending is a process used to bend thermoplastics in a straight line.
The line bending process involves heating a thermoplastic sheet over a strip heater until it becomes soft and then bending it to any desired angle.
The plastic sheet is then held still until it cools and stays in the bent shape.
Compression moulding
t is a method of molding in which the molding material, largely preheated, is first placed in an open, heated mold cavity. The mold is closed with a top force or plug member, pressure is applied to force the material into contact with all mold areas. Heat and pressure are maintained until the molding material has cured.
Extrusion
Manufacturing process in which a softened blank of a metal or plastic material is forced through a shaped metal piece or die to produce a continuous ribbon of plastic
Advantages of vacuum forming
The advantages of plastic vacuum forming is its flexibility,cost effectiveness and speed of production. Prototypes can be produced quickly and accurately to prove parts before full production tooling is required
Disadvantages of vacuum forming
Some bubbles can form from the air being pushed in. This will ruin the pieces look
Some clear parts can get dirty (i.e., defects or dirt from mold will transfer to parts)
Consistent wall thickness is not possible — very deep parts can create problems
Only one material can be formed at a time
Advantages of injection moulding
Allows for high production output rates
Can use inserts within the mold and fillers for added strength
Close tolerances on small intricate parts are possible
More than one material can be used at the same time when utilizing co-injection molding
Typically requires very little post-production work — ejected parts usually have a very finished look
Very little waste – all scrap can be reground to be reused
Full automation is possible
Lower cost-per-part compared to vacuum forming
Disadvantages of injection forming
Extremely high start-up costs
Requires a great deal of engineering time
Long time frames necessary to fabricate tooling, making time-to-market a major drawback
Advantages of blow moulding
Because of lower pressure, the mold costs in extrusion blow molding are lower as compared to injection molding and the machinery costs are low as well. Also, it’s easy to mold external threads.
Disadvantages of blow moulding
It is only limited to hollow parts and it is bad for the environment
Advantages of compression moulding
Parts are dimensionally to specification and made with specified materials
Short set-up times, allowing materials and colors to be changed quickly
Flexibility in mold design
Tools with multiple cavities can be made with less concern of balancing
Welding allows for tool modification
Faster mold manufacturing turnaround time
Parts with multiple undercuts can be manufactured
Mold tool cost is lower than injection
Cost of compression molding machines is low
Reduced molding process development time
Disadvantages of compression moulding
Slower part production rates
Can be difficult to control flash
Advantages of extrusion
Continuous High production volumes Low cost per pound Efficient melting Many types of raw materials Good mixing (compounding)
Disadvantages of extrusion
Limited complexity of parts
Uniform cross-sectional shape only
