Download - Thermoforming (MIT 2.008x Lecture Slides)
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ThermoformingMIT 2.008x
Prof. John Hart
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What thermoformed object(s) have you used already today?
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What is thermoforming (process definition)?à Forming a sheet (typically a thermoplastic) by applying heat then pressure against a mold.
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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.
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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
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Thermoforming:
2. Process and equipment basics
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Lego baseplates
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Lego baseplates
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Lego IM vs TF comparison
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The MIT 150 2.008 YoYo
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Thermoforming in the MIT shop
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Thermoforming in the MIT shop
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Thermoforming in the MIT shop
Heater (also one above)
Clamps
Die (custom)
Sheet
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What is different about this part?(hint: look at the surface features)
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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
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Thermoforming:
3. Polymer mechanics during thermoforming
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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
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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.
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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
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Demo: Stretching a thermoplastic
Heat
Heat
Pull
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Where is the strain greatest?
Figure 13.37 Fundamentals of Modern Manufacturing (4th Edition) by Groover. (c) John Wiley & Sons Inc. (2010).
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Where is the strain greatest?
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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
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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.
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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
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Thermoforming:
4. Rate limits and continuous processing
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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
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Radiative heating (infrared)
Images from: http://heraeus-thermal-solutions.com/media/en/webmedia_local/media/pdfs/ir_basics_and_technology2014.pdf
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0.2 mm thickness
Images from: http://heraeus-thermal-solutions.com/media/en/webmedia_local/media/pdfs/ir_basics_and_technology2014.pdf
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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]
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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
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Images from: http://heraeus-thermal-solutions.com/media/en/webmedia_local/media/pdfs/ir_basics_and_technology2014.pdf
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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
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Thermoforming:
5. Process window and design guidelines
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The thermoforming process window (P, T)
Figure 9.8 from Understanding Thermoforming by J.L Throne. (c) Hanser, 2008.
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Pressure and temperature ranges (for pressure-controlled forming)
Table 9.1 from Understanding Thermoforming (Second Edition) by J.L Throne. (c) Hanser, 2008.
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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
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Areal draw ratios
Figure 9.11 and Table 9.2 from Understanding Thermoforming (2nd Edition) by Throne. (c) Hanser, 2008.
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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
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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
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Positive versus negative mold
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Comparison of surface profilesPositive mold
Negative mold
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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
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Large TF tooling: car door panels
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Thermoforming:
6. Conclusion
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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
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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
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Thermoforming:
7. Other polymer Processes
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How were these parts made?
Image © Concept Sales Inc.
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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
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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)
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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)
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(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!
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How are trash bags made?
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Blown film extrusion
Figure 13.16, Groover, Fundamentals of Modern Manufacturing (4th Edition)
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Figure 13.16, Groover, Fundamentals of Modern Manufacturing (4th Edition)Picture: https://www.hosokawa-alpine.com/film-extrusion/blown-film-lines/
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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
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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
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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).
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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.
Stress-Strain vs. Temperature: Figure 9.6 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.
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References5 Process Window
Stress-Strain vs. Temperature: Figure 9.8 from "Understanding Thermoforming (2nd Edition)" by Throne. © Hanser, 2008.
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
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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
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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