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MCHE 3920 Final > Thermoforming > Flashcards

Thermoforming Flashcards

1
Q

Thermoforming involves heating a plastic sheet and then using a _____________to form it over or into a mold

A

pressure difference

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2
Q

Thermoforming is a relatively new process (since ______) and is often used for__________, but also be used to make durable products.

A

WWII, packaging

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3
Q

Thermoforming offers relatively ______ product-specific investments with a large range of texturing and finishing options and production volumes (from _______to ______________)

A

low, one-offs hundreds of millions

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4
Q

In this Thermoforming method, material is formed over the mold

A

Positive Forming

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5
Q

In this thermoforming method the material is formed into the mold.

A

Negative Forming

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6
Q

In this Thermoforming method, a partial vacuum draws the material to the mold

A

Vacuum Forming

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7
Q

In this Thermoforming method, a higher pressure forces the material to the mold

A

Pressure Forming

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8
Q

In this Thermoforming method, sheets below 2.5 mm thick are exclusively used

A

Thin-gauge forming

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9
Q

In this Thermoforming method, sheets above 2.5 mm thick are used

A

Heavy-gauge forming

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10
Q

Steps of Thermoforming:
1.
2.
3.
4.
5.

A

Heating the material, Forming, Cooling, De-Molding, Edge trimming

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11
Q

In Thermoforming, heating the material and Cooling take up ________% of cycle time

A

80-90

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12
Q

While being heated, the material in Thermoforming is typically
stretched _____________

A

Biaxially

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13
Q

Heating can be done with _____________, ceramic, electric or gas heaters

A

infrared

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14
Q

In Thermoforming, ________ heating is sometimes
applied to heat certain areas of the sheet
more than others

A

Differential

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15
Q

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

A

clamped, small holes

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16
Q

How long does the forming step take?

A

Fractions of a second

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17
Q

Thinner products can be formed _______ than thicker products

A

Faster

18
Q

When plastics get stretched too fast it is called _________. This restricts how fast the forming process can be done.

A

Yielding

19
Q

_________ Formed products are thinnest at their edges

A

Positive

20
Q

_________ Formed products are thickest at their edges

A

Negative

21
Q

________________can only be done on the side of the
product that makes contact with the mold

A

Texture/Embossing

22
Q

Multi-cavity molds can only be used with ___________ forming

A

Negative

23
Q

Cooling time depends on ___________, ___________, ______________

A

Material type, thickness and initial temperature

24
Q

______________ molds cool products more slowly while _______________ molds can have water cooling to cool products much faster

A

Wooden, aluminum

25
Q

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

A

draft angles, all sides

26
Q

____________ is the removal of the material that
does not end up in the final product

A

Edge Trimming

27
Q

For thin-gauge products edge trimming is done by simple
______________ but for heavy-gauge products, edge trimming is often done with a saw or _____________

A

cutting, CNC router

28
Q

Heating is typically done with electrically powered
________ heaters for thin-gauge sheets and more
robust ________ heaters for heavy-gauge sheets

A

Infrared, ceramic

29
Q

In high volume production, heating is typically
done from ______________

A

Both sides

30
Q

Heating time is roughly proportional to
__________________

A

Sheet thickness squared

31
Q

Cooling time increases with ____________ and can be reduced somewhat by using ____________ pressures and spraying water mist onto the part

A

thickness, higher

32
Q

In ______________, a sheet of plastic is
clamped, heated and blown up into the
desired shape (usually a dome) and then
cooled in air

A

Free Blowing

33
Q

In Free blowing, __________ mold is used, so cycle times
are ___________ (usually a few minutes) and form-freedom is very limited

A

No, longer

34
Q

In Standard Thermoforming, a heated plastic sheet is forced _____ or _____ a mold

A

over, into

35
Q

Standard Thermoforming offers large form freedom, but part wall thickness and its distribution is difficult to control, so molds cannot be too _____ or ______

A

deep, complex

36
Q

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 _________

A

one off, millions, second, minutes

37
Q

_________________ is like standard thermoforming except the sheet is first stretched by blowing it ______ from the mold

A

Pre-Stretch Thermoforming, Away

38
Q

Pre-stretch Thermoforming generates a more ______________ thickness distribution which allows for more complex and ____________ molds, but adds complexity and time to the process

A

Homogeneous, deeper

39
Q

_______________ Thermoforming is similar to pre-stretch thermoforming, except sheet is blown against a cold plug.

A

Plug-Assisted

40
Q

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

A

Thick, tight

41
Q

______________________ Thermoforming is a relatively ______ method where two sheets are heated and formed in their respective molds

A

Twin-Sheet

42
Q

In Twin-sheet thermoforming, the two parts are pressed together before the material is fully ___________ which allows for the manufacturing of __________ parts

A

cooled, hollow

MCHE 3920 Final (10 decks)

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