IET 365 - EXAM #2 || with 100% Errorless Answers.
Injection Molding correct answers A molding procedure in which a heat-softened plastic is
forced from a cylinder into a relatively cool cavity giving the item the desired shape
Types of injection molders correct answers -reciprocating screw
-plunger/piston/ram
Reciprocating screw zones correct answers 1. feed
2. transition (compression) (most melting occurs here)
3. metering
Shot size correct answers the amount of plastic that can be put into a mold in one cycle
Fill time (injection time) correct answers time it takes to displace the air in the mold cavity with
plastic
Pack time correct answers time required to maintain enough pressure to fill out the part and to
achieve gate freeze
Cooling/dwell time (freeze time) correct answers time required to maintain enough pressure to
cool/set enough for safe removal from mold cavity
Dead time correct answers time required to open the mold, remove the molded part, and close the
mold
mold design correct answers -sprue
-runner
-gate
-cavity
-knock-out pin
-alignment pin
What type(s) of plastic is used for injection molding? correct answers thermoplastics and
thermosets
Advantages of injection molding correct answers -high output rates
-fillers/inserts may be used
-small, complex parts with close dimensional tolerances can be molded
-more than one material may be injection molded (coinjection molding)
-parts require little to no finishing
-thermoplastic scraps may be ground and reused
-self-skinning structural foams may be molded (reaction injection molding)
-process may be slightly automated
Disadvantages of injection molding correct answers -competition is keen
, -high mold cost (multiple cavity molds)
-high equipment costs
-quality may be affected by workmanship, process control, and other variables
Sprue correct answers as long as the A plate is thick, plastic travels from the nozzle through the
sprue and then to the runners in order to fill the part
Runner correct answers Long channels that connect the sprue to the cavity of the mold (before
the gate)
Gate correct answers thin area between the runners and the mold cavity, allows for easy breakage
of parts
Knockout pins correct answers circular pins found in 1/2 of the mold (ejector half) that push the
part out of the mold
Alignment pin correct answers devices that maintain proper alignment of core/cavity as the mold
closes
How do I increase productivity and decrease cycle time for injection molding? correct answers -
pre-heat molds/post-cool molds
-use multi-cavity molds
-use aluminum molds or a cooling system
-use CAD/CAM for faster mold design times and better quality molds
-gas-assisted injection molding
Injection molding product examples correct answers -gears
-helmets
-batteries
-safety glasses
-toothbrushes
-eating utensils
Compression molding correct answers a technique in which a molding compound is places in an
open mold cavity, the mold is closed, and then heat and pressure is applied until the material has
cooled and cured (PRESSURE OR FORCE MUST BE PRESENT TO BE CLASSIFIED AS A
MOLDING PROCESS)
How does compression molding work? correct answers General rule of thumb for pressure: 2900
psi for plastic products up to 1" thick. for every extra inch, add 725 psi. Use vented molds when
possible
What kind of plastic(s) is used for compression molding? correct answers Thermosets
Advantages of compression molding correct answers -little waste
-low tooling costs
Injection Molding correct answers A molding procedure in which a heat-softened plastic is
forced from a cylinder into a relatively cool cavity giving the item the desired shape
Types of injection molders correct answers -reciprocating screw
-plunger/piston/ram
Reciprocating screw zones correct answers 1. feed
2. transition (compression) (most melting occurs here)
3. metering
Shot size correct answers the amount of plastic that can be put into a mold in one cycle
Fill time (injection time) correct answers time it takes to displace the air in the mold cavity with
plastic
Pack time correct answers time required to maintain enough pressure to fill out the part and to
achieve gate freeze
Cooling/dwell time (freeze time) correct answers time required to maintain enough pressure to
cool/set enough for safe removal from mold cavity
Dead time correct answers time required to open the mold, remove the molded part, and close the
mold
mold design correct answers -sprue
-runner
-gate
-cavity
-knock-out pin
-alignment pin
What type(s) of plastic is used for injection molding? correct answers thermoplastics and
thermosets
Advantages of injection molding correct answers -high output rates
-fillers/inserts may be used
-small, complex parts with close dimensional tolerances can be molded
-more than one material may be injection molded (coinjection molding)
-parts require little to no finishing
-thermoplastic scraps may be ground and reused
-self-skinning structural foams may be molded (reaction injection molding)
-process may be slightly automated
Disadvantages of injection molding correct answers -competition is keen
, -high mold cost (multiple cavity molds)
-high equipment costs
-quality may be affected by workmanship, process control, and other variables
Sprue correct answers as long as the A plate is thick, plastic travels from the nozzle through the
sprue and then to the runners in order to fill the part
Runner correct answers Long channels that connect the sprue to the cavity of the mold (before
the gate)
Gate correct answers thin area between the runners and the mold cavity, allows for easy breakage
of parts
Knockout pins correct answers circular pins found in 1/2 of the mold (ejector half) that push the
part out of the mold
Alignment pin correct answers devices that maintain proper alignment of core/cavity as the mold
closes
How do I increase productivity and decrease cycle time for injection molding? correct answers -
pre-heat molds/post-cool molds
-use multi-cavity molds
-use aluminum molds or a cooling system
-use CAD/CAM for faster mold design times and better quality molds
-gas-assisted injection molding
Injection molding product examples correct answers -gears
-helmets
-batteries
-safety glasses
-toothbrushes
-eating utensils
Compression molding correct answers a technique in which a molding compound is places in an
open mold cavity, the mold is closed, and then heat and pressure is applied until the material has
cooled and cured (PRESSURE OR FORCE MUST BE PRESENT TO BE CLASSIFIED AS A
MOLDING PROCESS)
How does compression molding work? correct answers General rule of thumb for pressure: 2900
psi for plastic products up to 1" thick. for every extra inch, add 725 psi. Use vented molds when
possible
What kind of plastic(s) is used for compression molding? correct answers Thermosets
Advantages of compression molding correct answers -little waste
-low tooling costs
