Thermoforming (MIT 2.008x Lecture Slides)

2.008x

ThermoformingMIT 2.008x

Prof. John Hart

2.008x

What thermoformed object(s) have you used already today?

2.008x

What is thermoforming (process definition)?à Forming a sheet (typically a thermoplastic) by applying heat then pressure against a mold.

Figu

re 1

3.37

from

Fun

dam

enta

ls o

f Mod

ern

Man

ufac

turin

g (4

th E

ditio

n)" b

y G

roov

er. (

c) J

ohn

Wile

y &

Sons

Inc.

(201

0).

2.008x

Vacuum thermoforming(vacuum forming, vacuforming)

Excerpt from: https://www.youtube.com/watch?v=BqV_jsxD0UA

http://formech.com/product/508fs/

2.008xHow is thermoforming similar to injection molding?à Both use heat and pressure to shape thermoplastics.

How are thermoformed parts different from injection molded parts?à Thermoformed parts are typically thinner, and have less complex shapes then injection molded parts. à The dimensional quality (corners, edges) and tolerances of thermoformed parts are lower than injection molded parts.

2.008x

Agenda: Thermoforming

§ Basic equipment and process configurations

§ Polymer mechanics during thermoforming

§ Rate-limiting steps of thermoforming

§ The process window and design rules

§ Conclusion

Extra: Other polymer forming processes

2.008x

Thermoforming:

2. Process and equipment basics

2.008x

Lego baseplates

2.008x

Lego IM vs TF comparison

2.008x

The MIT 150 2.008 YoYo

2.008x

2.008x

Thermoforming in the MIT shop

2.008x

Thermoforming in the MIT shop

Heater (also one above)

Clamps

Die (custom)

Sheet

2.008x

2.008x

What is different about this part?(hint: look at the surface features)

2.008x

Figures 13.36, 13.39 from Fundamentals of Modern Manufacturing (4th Edition) by Groover. (c) John Wiley & Sons Inc. (2010)

Mechanical thermoforming

Pressure thermoforming Clamps

2.008x

2.008x

Thermoforming:

3. Polymer mechanics during thermoforming

2.008x

How does the polymer stress-strain curve change with temperature?à Recall from IM: Glass transition and softening

Figure 9.5 from Understanding Thermoforming (Second Edition) by J.L Throne. (c) Hanser, 2008.

Increasing temperature≈TgBreak

Yield

2.008x

Temperature-dependent modulus of thermoplasticà Recall from IM: Glass transition and softening

Figure 9.1 from Understanding Thermoforming (Second Edition) by J.L Throne. (c) Hanser, 2008.

2.008x

Implication: thermoformingtemperature range

Figure 9.6 from Understanding Thermoforming by J.L Throne. (c) Hanser, 2008.

“Not too hot, not too cold. Just right.”Increasing temperature

Forming range

2.008x

Demo: Stretching a thermoplastic

Heat

Heat

Pull

2.008x

Where is the strain greatest?

Figure 13.37 Fundamentals of Modern Manufacturing (4th Edition) by Groover. (c) John Wiley & Sons Inc. (2010).

2.008x

Where is the strain greatest?

2.008x

0.394 mm

0.423 mm

0.290 mm

R = 0.310 mm

R = 0.201 mm

0.199 mm

0.154 mm

0.164 mm

2.008x

Generally, areas that touch the mold last are thinnest

0.394 mm

0.423 mm

0.290 mm

R = 0.310 mm

R = 0.201 mm

0.199 mm

0.154 mm

0.164 mm

THICK AREAS

THIN CORNERS AND EDGES

The area that stretched the most to reach the bottom is the thinnest.

2.008x

Simulation of TF (ANSYS): predicts strain and thickness distribution

“For thermoforming a medical device package” from http://www.ansys.com/Industries/Materials+&+Chemical+Processing/Polymer+Processing/Thermoforming

(left) finite element mesh automatically refined to capture mold curvature details

(right) predicted thickness distribution

2.008x

Thermoforming:

4. Rate limits and continuous processing

2.008x

What limits the rate of thermoforming?

§ Heating (à radiative transfer)§ Stretching (à viscoelasticity)§ Cooling (à contact with cold mold; see IM analysis)

Video: https://www.youtube.com/watch?v=YQ-s1BILiag

2.008x

Radiative heating (infrared)

Images from: http://heraeus-thermal-solutions.com/media/en/webmedia_local/media/pdfs/ir_basics_and_technology2014.pdf

2.008x

0.2 mm thickness


2.008x

Radiative heating of a plastic sheet

Lamp

Substrate (to be formed)

h = thickness [m]r = density [kg/m3]cp = specific heat [J/kg-K]a = total absorption coefficient of substrate [unitless]plamp = lamp power [W/m2]DT = temperature rise [K]

2.008x

Radiative heating of a plastic sheet

h = thickness [m]r = density [kg/m3]cp = specific heat [J/kg-K]a = total absorption coefficientof substrate [unitless]plamp = lamp power [W/m2]DT = temperature rise [K]

theat =ρhcpaplamp

ΔT

Lamp

Substrate (to be formed)

DT = 250 Kh = 1 mmr = 1200 kg/m3

cp = 1200 J/kg-K

2.008x


2.008x

A continuous TF + packaging system (Ulma)

Image from http://www.ulmapackaging.com/packaging-machines/thermoforming-and-blister/tfs-700Video: https://www.youtube.com/watch?v=qC5KFpNnR_4

2.008x

Thermoforming:

5. Process window and design guidelines

2.008x

The thermoforming process window (P, T)

Figure 9.8 from Understanding Thermoforming by J.L Throne. (c) Hanser, 2008.

2.008x

Pressure and temperature ranges (for pressure-controlled forming)

Table 9.1 from Understanding Thermoforming (Second Edition) by J.L Throne. (c) Hanser, 2008.

2.008x

Thermoforming strains

λ1/ λ2 = 1.28λ1 = 1.50

λ1/ λ2 = 1.87λ1 = 2.33

λ1/ λ2 = 4.01λ1 = 5.17

λ1/ λ2 = 4.73λ1 = 4.33

x1

x2

Draw ratio

L1

L2

L0

Biaxial stretch ratio

5 cm

8 cm

10 cm

~ 2.03

Note, that DR = 1 for the sheet material prior to forming

2.008x

Areal draw ratios

Figure 9.11 and Table 9.2 from Understanding Thermoforming (2nd Edition) by Throne. (c) Hanser, 2008.

2.008x

Additional TF design guidelines§ Avoid sharp corners in mold (R

~2*thickness) or greater.§ Use draft angle if possible.§ No undercuts (unless multi-part tooling)!

§ When you want to simplify mold making, sharp corners are OK but beware of tearing.

§ For thin plastic, areal draw ratios >2:1 require careful optimization and suffer non-uniformity.

Poor Design

Good DesignR = 2*t or greater

t

R

Draft angle: ¼°min for female tooling1°for male tooling

2.008x

Additional TF design guidelines

Higher temperature: still cannot draw deep teeth; non-uniformity results

Even higher temperature: tearing

§ Avoid sharp corners in mold (R ~2*thickness) or greater.

§ Use draft angle if possible.§ No undercuts (unless multi-part tooling)!

§ When you want to simplify mold making, sharp corners are OK but beware of tearing.

§ For thin plastic, areal draw ratios >2:1 require careful optimization and suffer non-uniformity.

Poor Design

Good DesignR = 2*t or greater

t

R

Draft angle: ¼°min for female tooling1°for male tooling

2.008x

Positive versus negative mold

2.008x

Comparison of surface profilesPositive mold

Negative mold

2.008x

Pre-stretching to reduce thicknessvariation

Figure 13.38 from Fundamentals of Modern Manufacturing (4th Edition) by Groover. (c) John Wiley & Sons Inc. (2010).https://www.youtube.com/watch?v=WJlXdb2zA0k

2.008x

Large TF tooling: car door panels

2.008x

Thermoforming:

6. Conclusion

2.008x

What’s new (and coming soon)?§ Bio-derived and biodegradable plastics§ Formable fiber materials§ Paper (complex product packaging)§ Carbon fiber (dream of auto industry)

For examples see:§ http://vegware.com§ http://www.billerudkorsnas.com/fibreform§ http://www.darpa.mil/program/tailorable-feedstock-and-forming

2.008x

Reflection: the big fourInjection Molding Thermoforming

Rate High Greater (parts/time)

Quality Good Less

Cost Low (at high volume) Less ($/part, especially at lower volume)

Flexibility Low (tooling cost high) Less: fewer shapesGreater: lower tooling cost

2.008x

Thermoforming:

7. Other polymer Processes

2.008x

Figure 19.1 from Kalpakjian and Schmid, Manufacturing Engineering & Technology (7th Edition)

Polymer processing overallTP = thermoplasticTS = thermosetE = elastomer

Plastic bottlesPlastic bagsà Same physics, different machine and product format

2.008x

Blow molding of plastic bottles

Images: http://designtekplastics.com/tips/injection-molding-vs-blow-molding/, http://dtresource.com/images/what-is-stretch-blow-molding-300x210.jpg, http://dongkong.en.ec21.com/500ml_water_bottle_blow_mold--4844865_4844892.html Figure 13.32 from Groover, Fundamentals of Modern Manufacturing (4th Edition)

2.008xMelt/Extruder

(Like an IM machine)

Rotating molds

§ 0.08 - 0.5 L containers (e.g., PP, HDPE)

§ Multimold wheel system (18-60 cavities)

§ Production rates of 7,500 -30,000 bottles per hour (500kg/h)!

Video of the machine: http://www.youtube.com/watch?v=u-eW2lrxrq0Diagram and data from http://www.wilmingtonmachinery.com/media/pdf/small_bottle_insert.pdf

Continuous process!

2.008x

How are trash bags made?

2.008x

Blown film extrusion

Figure 13.16, Groover, Fundamentals of Modern Manufacturing (4th Edition)

2.008x

Figure 13.16, Groover, Fundamentals of Modern Manufacturing (4th Edition)Picture: https://www.hosokawa-alpine.com/film-extrusion/blown-film-lines/

2.008x

Figure 13.16, Groover, Fundamentals of Modern Manufacturing (4th Edition)https://www.hosokawa-alpine.com/film-extrusion/blown-film-lines/https://images-na.ssl-images-amazon.com/images/I/61uTRra5KkL.jpg

2.008x

Rotational molding (‘Rotomolding’)

Fig. 19.15, Kalpakjian and Schmid, Manufacturing Engineering and TechnologyVideos: https://www.youtube.com/watch?v=M0_l269cPvQ, https://www.youtube.com/watch?v=b619f-0QhEs

2.008x

References1 Introduction

Photo of Lunch Tray © St. Louis County, Minnesota.

Photo of ATV by Vesa Minkkinen on Pixabay. This work is in the public domain.

Photo of Fruit Container by Vedat Zorluer on Pixabay. This work is in the public domain.

Photo of Refrigerator by US Consumer Product Safety Commission. This work is in the public domain.

Positive Mold Vacuum Thermoforming: Figure 13.37 from "Fundamentals of Modern Manufacturing (4th Edition)" by Groover. © Wiley (2010).

Image of Formech 508FS © Formech International Ltd. 2016. All Rights Reserved.

2 Process Equipment Basics

Positive Pressure Thermoforming: Figure 13.36 from "Fundamentals of Modern Manufacturing (4th Edition)" by Groover. © Wiley (2010).

Mechanical Thermoforming: Figure 13.39 from "Fundamentals of Modern Manufacturing (4th Edition)" by Groover. © Wiley (2010).

2.008x

References3 Polymer Mechanics

Stress-Strain vs. Temperature: Figure 9.5 from "Understanding Thermoforming (2nd Edition)" by Throne. © Hanser, 2008.

Elastic Modulus vs. Temperature: Figure 9.1 from "Understanding Thermoforming (2nd Edition)" by Throne. © Hanser, 2008.


Book Cover: Denslow's "Three Bears" (1901) on read.gov: Library of Congress. This work is in the public domain.

Positive Mold Vacuum Thermoforming: Figure 13.37 from "Fundamentals of Modern Manufacturing (4th Edition)" by Groover. © Wiley (2010).

Image of ANSYS Simulation © 2016 ANSYS, Inc. All Rights Reserved.

4 Rate Limits

Videos of Thermoforming and Sealing Packaging © ULMA Packaging, S.Coop.

Images of Infrared Heating Process and Equipment © 2016 Heraeus Holding

Video of TFS 700 Thermoforming Machine © ULMA Packaging, S.Coop.

2.008x

References5 Process Window


Draw Ratio Diagram: Figure 9.11 from "Understanding Thermoforming (2nd Edition)" by Throne. © Hanser, 2008.

Draw Ratios: Table 9.2 from "Understanding Thermoforming (2nd Edition)" by Throne. © Hanser, 2008.

Video of Presuction © 2011-2015 EPW LLC

Thermoforming with Prestretch: Figure 13.38 from "Fundamentals of Modern Manufacturing (4th Edition)" by Groover. © Wiley (2010).

Image of Automotive Doors: © 2011-2015 EPW LLC

6 Conclusion

Image of Carbon Fiber Manufacturing © Hearst Communications, Inc.

Images of Paper Products © BillerudKorsnas AB

2.008x

References7 Bonus

Photo of Drinking Straws by User: Alexas_Fotos (Alexandra) via Pixabay CC0. This work is in the public domain.

Photo of Water Bottles by User: PublicDomainPictures via Pixabay CC0. This work is in the public domain.

Photo of Kayaks by User: vonpics via Pixabay CC0. This work is in the public domain.

Photo of Trash Bag by User: cocoparisienne (Anja) via Pixabay CC0. This work is in the public domain.

Photo of American Football by User: Hans (Hans Braxmeier) via Pixabay CC0. This work is in the public domain.

Photo of Disposable Cup by User: rodrigolourenco (Rodrigo Lourenço) via Pixabay CC0. This work is in the public domain.

Photo of Sprayer Tanks © Copyright 2016. Den Hartog Industries, Inc.

Polymer Processing Overview: Figure 19.1 from Title: Manufacturing Engineering & Technology (7th Edition); Authors: Serope Kalpakjian, Steven Schmid; © Prentice Hall; (2013);Blow Molding: Figure 13.32 from Title: Fundamentals of Modern Manufacturing; Author: Mikell P. Groover; Publisher: Wiley; 4 edition (2010); ISBN: 978-0470-467002

2.008x

ReferencesImage of Bottle Blow Mold: Copyright ©1997-2016 EC21 Inc. All Rights Reserved.

Photo of Injection Molded Parisons © Steven Daly. All Rights Reserved.

Photo of Blow Molded Bottles ©2015 Design-tek Tool and Plastics Inc.

Image of Blow Molding Machine © Wilmington Machinery.

Image of Blow Molding Machine in Operation © Wilmington Machinery.

Blow Film Extrusion: Figure 13.16 from Title: Fundamentals of Modern Manufacturing; Author: Mikell P. Groover; Publisher: Wiley; 4 edition (2010); ISBN: 978-0470-467002

Photo of Blow Film Extrusion Process © HOSOKAWA ALPINE Aktiengesellschaft. All Rights Reserved.

Images of Hefty Garbage Bags © 1996-2016, Amazon.com, Inc. or its affiliates

Rotomolding: Figure 19.15 from Title: Manufacturing Engineering & Technology (6th Edition); Authors: SeropeKalpakjian, Steven Schmid; Publisher: Prentice Hall; 6 edition (January, 2009); ISBN-13: 9780136081685

Video of Rotational Molding Machine © Reinhardt Rotomachines

Video of Unmolding Rotational Molded Tank © Reinhardt Rotomachines

Thermoforming (MIT 2.008x Lecture Slides)

Engineering

Transcript of Thermoforming (MIT 2.008x Lecture Slides)