Thermoforming Flashcards
Thermoforming involves heating a plastic sheet and then using a _____________to form it over or into a mold
pressure difference
Thermoforming is a relatively new process (since ______) and is often used for__________, but also be used to make durable products.
WWII, packaging
Thermoforming offers relatively ______ product-specific investments with a large range of texturing and finishing options and production volumes (from _______to ______________)
low, one-offs hundreds of millions
In this Thermoforming method, material is formed over the mold
Positive Forming
In this thermoforming method the material is formed into the mold.
Negative Forming
In this Thermoforming method, a partial vacuum draws the material to the mold
Vacuum Forming
In this Thermoforming method, a higher pressure forces the material to the mold
Pressure Forming
In this Thermoforming method, sheets below 2.5 mm thick are exclusively used
Thin-gauge forming
In this Thermoforming method, sheets above 2.5 mm thick are used
Heavy-gauge forming
Steps of Thermoforming:
1.
2.
3.
4.
5.
Heating the material, Forming, Cooling, De-Molding, Edge trimming
In Thermoforming, heating the material and Cooling take up ________% of cycle time
80-90
While being heated, the material in Thermoforming is typically
stretched _____________
Biaxially
Heating can be done with _____________, ceramic, electric or gas heaters
infrared
In Thermoforming, ________ heating is sometimes
applied to heat certain areas of the sheet
more than others
Differential
In thermoforming, the hot sheet is _______ on all sides into an airtight box and material is forced around (or into) the mold with a pressure differential. ____________ are then placed in the mold to vent the air beneath the product
clamped, small holes
How long does the forming step take?
Fractions of a second
Thinner products can be formed _______ than thicker products
Faster
When plastics get stretched too fast it is called _________. This restricts how fast the forming process can be done.
Yielding
_________ Formed products are thinnest at their edges
Positive
_________ Formed products are thickest at their edges
Negative
________________can only be done on the side of the
product that makes contact with the mold
Texture/Embossing
Multi-cavity molds can only be used with ___________ forming
Negative
Cooling time depends on ___________, ___________, ______________
Material type, thickness and initial temperature
______________ molds cool products more slowly while _______________ molds can have water cooling to cool products much faster
Wooden, aluminum
To ease removal of part, negative ______________ are often added to forces the part out of contact with _______ of the mold by applying force in only one direction
draft angles, all sides
____________ is the removal of the material that
does not end up in the final product
Edge Trimming
For thin-gauge products edge trimming is done by simple
______________ but for heavy-gauge products, edge trimming is often done with a saw or _____________
cutting, CNC router
Heating is typically done with electrically powered
________ heaters for thin-gauge sheets and more
robust ________ heaters for heavy-gauge sheets
Infrared, ceramic
In high volume production, heating is typically
done from ______________
Both sides
Heating time is roughly proportional to
__________________
Sheet thickness squared
Cooling time increases with ____________ and can be reduced somewhat by using ____________ pressures and spraying water mist onto the part
thickness, higher
In ______________, a sheet of plastic is
clamped, heated and blown up into the
desired shape (usually a dome) and then
cooled in air
Free Blowing
In Free blowing, __________ mold is used, so cycle times
are ___________ (usually a few minutes) and form-freedom is very limited
No, longer
In Standard Thermoforming, a heated plastic sheet is forced _____ or _____ a mold
over, into
Standard Thermoforming offers large form freedom, but part wall thickness and its distribution is difficult to control, so molds cannot be too _____ or ______
deep, complex
Standard Thermoforming part sizes can span a wide range.
Production volumes can range from ________ to _______ and cycle times range from a few _______ to a few _________
one off, millions, second, minutes
_________________ is like standard thermoforming except the sheet is first stretched by blowing it ______ from the mold
Pre-Stretch Thermoforming, Away
Pre-stretch Thermoforming generates a more ______________ thickness distribution which allows for more complex and ____________ molds, but adds complexity and time to the process
Homogeneous, deeper
_______________ Thermoforming is similar to pre-stretch thermoforming, except sheet is blown against a cold plug.
Plug-Assisted
In Plug-Assisted forming, the portion of the sheet that contacts the plug stays relatively ____________, while the hotter portions thin out. This gives better control over part thicknesses and is good for products that require _________ thickness tolerances
Thick, tight
______________________ Thermoforming is a relatively ______ method where two sheets are heated and formed in their respective molds
Twin-Sheet
In Twin-sheet thermoforming, the two parts are pressed together before the material is fully ___________ which allows for the manufacturing of __________ parts
cooled, hollow
