MMET 281 EXAM II QUESTIONS AND
ANSWERS ALL CORRECT
What are some applications of thermoforming? - Answer- ice cube trays, drawers, toys,
containers, food packaging
What is draw ratio? - Answer- -maximum cavity depth to minimum span across the top
opening
-USUALLY LESS THAN 1
What is the most versatile and widely used thermoforming process? - Answer- straight
vacuum thermoforming
Describe plug-assist vacuum forming - Answer- sheet is heated and positioned over the
mold cavity, heated plug pushes down into mold cavity, vacuum engaged and plug
removed (can also be used with pressure instead of vacuum)
What are the advantages of plug assist vacuum forming? - Answer- -reduces non-
uniform thinning
-allows for deeper drawing
-allows for better control of wall thickness
What are the disadvantages of plug-assist vacuum forming? - Answer- -requires close
temperature control
-equipment is more complex than straight vacuum forming
Describe Pressure Bubble Plug Assist Vacuum Forming - Answer- sheet is heated and
sealed across mold cavity, air is introduced to blow the sheet upward and thin material,
heated plug forces material into cavity, vacuum engaged
What is pressure bubble plug assist vacuum forming used for? - Answer- -deep
thermoforming
-controlled air pressure stretches the material to a predetermined thickness
Describe vacuum snap-back forming. - Answer- heated plastic is sealed over top of
vacuum box, vacuum pulls the heated sheer into a box, plug is lowered, vacuum drawn
through it, and vacuum beneath the sheet is realeased (two vacuum process)
, What are the applications of vacuum snap-back forming? - Answer- making those little
snap things for assemblies and such
Describe matched-mold forming. - Answer- part is clamped over female die and heated,
male die is pressed down
Describe twin sheet forming. - Answer- two sheets are simultaneously heated between
2 molds, on reaching Tg, the two molds move together, forming is achieved by high
pressure and/or vacuum
Describe free forming. - Answer- air pressure blows hot plastic to form a smooth bubble-
shape object
What is free forming used for? - Answer- aircraft canopies
What are the two basic parts than an injection molding machine consists of? - Answer-
injection unit and clamping unit
What is the compression ratio in injection molding? - Answer- flight depth in the feed
zone to flight depth in the metering zone
What is shot size? - Answer- maximum amount of material machine will inject per cycle
What do you want shot size to be? - Answer- very close to the gross part size to prevent
thermal degradation of material
What is clamp tonnage? - Answer- the maximum force the machine can apply
What do you want the clamp tonnage to be in injection molding? - Answer- greater than
pressure of material times the cross-sectional area
What materials can be used in injection molding? - Answer- most thermoplastics and
some thermosets
What does the tooling look like in injection molding? - Answer- because of high
pressures, steel tooling is preferable; aluminum may be used for low volumes and
prototyping
What does the cost of injection molding look like? - Answer- offers lowest prices per
piece but equipment and tooling prices are generally the highest
Name two processes used to put a coating on a wire. - Answer- extrusion coating and
calendar coating
What process is used to place coatings on tool handles? - Answer- dip coating
ANSWERS ALL CORRECT
What are some applications of thermoforming? - Answer- ice cube trays, drawers, toys,
containers, food packaging
What is draw ratio? - Answer- -maximum cavity depth to minimum span across the top
opening
-USUALLY LESS THAN 1
What is the most versatile and widely used thermoforming process? - Answer- straight
vacuum thermoforming
Describe plug-assist vacuum forming - Answer- sheet is heated and positioned over the
mold cavity, heated plug pushes down into mold cavity, vacuum engaged and plug
removed (can also be used with pressure instead of vacuum)
What are the advantages of plug assist vacuum forming? - Answer- -reduces non-
uniform thinning
-allows for deeper drawing
-allows for better control of wall thickness
What are the disadvantages of plug-assist vacuum forming? - Answer- -requires close
temperature control
-equipment is more complex than straight vacuum forming
Describe Pressure Bubble Plug Assist Vacuum Forming - Answer- sheet is heated and
sealed across mold cavity, air is introduced to blow the sheet upward and thin material,
heated plug forces material into cavity, vacuum engaged
What is pressure bubble plug assist vacuum forming used for? - Answer- -deep
thermoforming
-controlled air pressure stretches the material to a predetermined thickness
Describe vacuum snap-back forming. - Answer- heated plastic is sealed over top of
vacuum box, vacuum pulls the heated sheer into a box, plug is lowered, vacuum drawn
through it, and vacuum beneath the sheet is realeased (two vacuum process)
, What are the applications of vacuum snap-back forming? - Answer- making those little
snap things for assemblies and such
Describe matched-mold forming. - Answer- part is clamped over female die and heated,
male die is pressed down
Describe twin sheet forming. - Answer- two sheets are simultaneously heated between
2 molds, on reaching Tg, the two molds move together, forming is achieved by high
pressure and/or vacuum
Describe free forming. - Answer- air pressure blows hot plastic to form a smooth bubble-
shape object
What is free forming used for? - Answer- aircraft canopies
What are the two basic parts than an injection molding machine consists of? - Answer-
injection unit and clamping unit
What is the compression ratio in injection molding? - Answer- flight depth in the feed
zone to flight depth in the metering zone
What is shot size? - Answer- maximum amount of material machine will inject per cycle
What do you want shot size to be? - Answer- very close to the gross part size to prevent
thermal degradation of material
What is clamp tonnage? - Answer- the maximum force the machine can apply
What do you want the clamp tonnage to be in injection molding? - Answer- greater than
pressure of material times the cross-sectional area
What materials can be used in injection molding? - Answer- most thermoplastics and
some thermosets
What does the tooling look like in injection molding? - Answer- because of high
pressures, steel tooling is preferable; aluminum may be used for low volumes and
prototyping
What does the cost of injection molding look like? - Answer- offers lowest prices per
piece but equipment and tooling prices are generally the highest
Name two processes used to put a coating on a wire. - Answer- extrusion coating and
calendar coating
What process is used to place coatings on tool handles? - Answer- dip coating
