Thermoforming

Question 1

What is Thermoforming?

Answer 1

Heating a plastic sheet and using pressure difference to form it over or onto a mold

Question 2

Process Types

Answer 2

Positive Forming
Negative Forming
Vacuum Forming
Pressure Forming
Thin-Gauge
Heavy-Gaue

Question 3

Positive Forming

Answer 3

Material is formed over the mold

Greatest stress on Surface
Greatest deformation on edge – thinner edge

Question 4

Negative forming

Answer 4

A material is formed into the mold

Greatest stress on edge
Greatest deformation on bottom – thicker edge

Question 5

Vaccum Forming

Answer 5

Vacuum draws a material into/onto the mold

Question 6

Pressure Forming

Answer 6

Higher pressure forces the material to mold

Question 7

Thin & thick-gauge

Answer 7

Thin: sheets below 2.5 mm thick

Thick: sheets above 2.5 mm thick

Question 8

Steps(5)

Answer 8

1.Heating material
2. Forming
3. Cooling
4. De-molding
5. edge trimming

heating and cooling take up 90% of cycle time

Question 9

Heating

Answer 9

While heated material is stretched biaxially to create film

Question 10

Forming

Answer 10

Clamped on all sides in airtight box
forced around (or into) mold

Question 11

Cooling

Answer 11

Cooling time depends on material type, thickness, and initial temp

Question 12

Edge Trimming

Answer 12

Thin-gauge: simple cutting
Thick-gauge: Saw or CNC router

Question 13

Methods

Answer 13

1.Free-blowing

2.Standard Thermoforming

3.Pre-stretch thermoforming

4.Plug-assisted Thermoforming

5.Twin Sheet Thermoforming

Question 14

Conservation of Volume

Answer 14

V_in = V_out
L_o * W_o * t_o = A_s * t_f

L_o: intimal length
W_o: initial width
t_o: initial thickness
A_s: Surface Area
t_f: final thickness
V: volume