1. Processes Used to Form Plastic Materials
Chapter 15

2. Plastic stock comes in many forms to accommodate different processes
sheets, pellets, powder, granules, rods
Produce near-net-shape parts
Shrinkage must be considered with plastic
Little to no scrap
Thermoplastic scrap can be reused

3. Compression Molding Cold compression molding
Used with thermoplastics and thermosets
Usually thermosets
Done hot and cold
Cold compression molding
The material is placed between the mold halves
Mold is closed
Part remains in mold and is transferred to an oven for curing
Hot press compression molding
Plastic mixture of resin, reinforcement and fillers placed in mold
Heated between 225°F and 325°F
Closed with pressure from 100 psi to 2000 psi
Curing happens in the mold, takes from seconds to 5 min
Molds are constructed with heating and cooling vents

5. Injection Molding High volume production, most widely used
Used with thermoplastics and thermosets
Primarily thermoplastics
Measured amount of liquid plastic forced into a heated mold
Called a shot
Molds are often cooled by water running through lines in the mold
Parts cool in seconds
Molding machines are rated by the amount of plastic (in ounces) that they can inject in one shot

7. Rotational Molding or Rotomolding
Makes hollow parts
Small to very large parts
Plastic is placed in molds
Molds are heated, then rotated until cool enough that the plastic has hardened
No need for inner core
Less expensive tooling

9. Blow Molding Thin and medium walled hollow products
Can be a fast process
Starts with a pre formed parison
Hollow tube of heat-softened plastic
Parison is positioned between two mold halves
One end is clamped shut, air tube is placed in other end
Air blown into parison, pushing it out against the mold

10. Injection Blow Molding
Hybrid process
Combines injection molding and blow molding
Two step process
Parison is formed by injection molding
Parison encircles the mandrel
Parison is moved to blowing station
Placed in another mold, formed to final shape

11. Thermoforming
Heating plastic to it’s softening point and forcing it over the contours of a one piece mold
Many different forms of thermoforming

12. Vacuum Forming Plastic sheet is heated
Vacuum is applied under the sheet drawing it down against a mold