Understanding Thermoforming

by Throne, James L.

• ISBN13: 9781569902769
• ISBN10: 1569902763
• Edition: 2nd
• Format: Paperback
• Copyright: 2008-04-01
• Publisher: Hanser Gardner Pubns

Summary

This book is a primer developed during many in-plant short courses and the basic thermoforming course sponsored by the University of Wisconsin-Milwaukee. It is designed for people who may not have extensive formal education.

Table of Contents

Introduction to Thermoforming
Brief History	1	(1)
General Markets	2	(1)
Terminology	3	(2)
The Competition to Thermoforming	5	(4)
Polymers and Plastics
Polymer Characterization	9	(3)
The Thermoforming Window	12	(1)
Thermal Properties	12	(3)
Heat Capacity	12	(2)
Thermal Conductivity	14	(1)
Density	15	(1)
Thermal Diffusivity	15	(1)
Infrared Energy Absorption	15	(2)
Thermoformable Polymers	17	(5)
Polystyrene [PS and Other Styrenics]	17	(1)
Polyvinyl Chloride [PVC, Vinyl, RPVC, FPVC]	18	(1)
Polymethyl Methacrylate [PMMA, Acrylic]	18	(1)
Cellulosics [Celluloses, CN, CAB, CAP]	19	(1)
Polycarbonate [PC]	19	(1)
Polyethylene Terephthalate [Polyester, APET, PETG, CPET]	19	(1)
Polyethylene [PE, HDPE, LDPE, LLDPE]	20	(1)
Polypropylene [PP, PP Copolymer]	21	(1)
Other Polymers	21	(1)
Multilayer Polymers	22	(1)
Filled Polymers	22	(1)
Reinforced Polymers	23	(1)
Foams	24	(3)
General Forming Concepts
Simple Heating and Stretching	27	(3)
Drape Forming	27	(1)
Vacuum Forming	27	(2)
Free Forming	29	(1)
Assisted Forming	30	(2)
Non-Uniform Heating	30	(1)
Pneumatic Preforming	31	(1)
Plug Assist	31	(1)
Pressure Forming	32	(2)
Twin-Sheet Forming	34	(1)
Contact Forming	35	(1)
Diaphragm Forming	36	(2)
Mechanical Forming	38	(3)
Machinery for the Forming Process
Thin-Gauge, Roll-Fed Machines	41	(6)
General Features	41	(1)
Sheet Take-Off	42	(1)
Pin-Chain and Pin-Chain-Rail	42	(1)
Oven	43	(1)
Press	44	(1)
Forming Assist Devices	44	(1)
Trim Means	45	(1)
In-Machine Stacking Means	46	(1)
Trim or Web Take-Up Station	46	(1)
Condition Monitors	46	(1)
Process Control	47	(1)
Heavy-Gauge Sheet Forming	47	(8)
Shuttle Press	49	(1)
Rotary Thermoformers	50	(1)
Sheet Handling	51	(1)
Sheet Clamp	51	(1)
Oven	52	(1)
Press	52	(1)
Plug-Assist Means	53	(1)
Pre-Stretching Means	53	(1)
Vacuum and Pressure	54	(1)
Process Monitoring and Control	55	(1)
Thin-Gauge Form, Fill and Seal Machines	55	(2)
Extrusion/Forming Lines	57	(1)
Matched Mold Forming Machines	58	(1)
Methods of Heating Sheet
Concepts in Heat Transfer	59	(3)
Conduction	59	(1)
Convection	60	(1)
Radiation	61	(1)
Common Heating Sources in Thermoforming	62	(1)
Convection or Hot Fluid Heating	63	(1)
Electric Heating	64	(3)
Round Heaters	64	(1)
Flat Heaters	65	(2)
Combustion Heating	67	(2)
Selecting the ``Correct'' Heater	69	(2)
A Comparison of Widely Used Heaters	71	(1)
Heating Cycle Times	71	(8)
Forming Temperature	71	(2)
The Nature of Energy Uptake	73	(1)
Polymer Characteristics	74	(1)
Geometry	74	(2)
One-Sided vs Two-Sided Heating	76	(1)
Heating Cycle Time Prediction	77	(1)
Equilibration	77	(2)
Sheet Stretching and Cooling
The Concepts of Modulus and Stiffness	79	(2)
The Concepts of Stress and Strain	81	(2)
Molding Area Diagram	82	(1)
Pneumatic Prestretching	83	(1)
How Sheet is Stretched Against a Mold Surface	83	(4)
Draw Ratios	85	(1)
The Utility of Draw Ratios	85	(1)
Input for Computer-Aided Design	86	(1)
Sag and Its Relationship to Temperature, Elasticity, and Viscosity	87	(2)
Cooling Against a Mold Surface	89	(1)
Heat Removal by Mold and Coolant	90	(1)
Forming Times	91	(2)
Trimming
General Trimming Concerns	93	(1)
Thin-Gauge Trimming	94	(5)
In-Place Trimming	94	(2)
In-Machine Trimming	96	(1)
In-Line Trimming	96	(2)
Other Ways of Trimming	98	(1)
Heavy-Gauge Trimming	99	(4)
In-Plane Trimmers	99	(1)
Non-Planar Trimmers	99	(1)
Milling Machines	100	(1)
Multi-Axis Routers	100	(1)
Cutter Design	101	(2)
Molds and Mold Design
Production Mold Materials	103	(1)
Prototype Mold Materials	104	(2)
Mold Design	106	(7)
Cooling	106	(1)
Venting	107	(1)
Undercuts	107	(1)
Mold Surface Texture	108	(1)
Textured Mold or Textured Sheet?	109	(1)
Plug Assist Materials and Designs	109	(1)
Other Mold Features	110	(1)
Molds for Twin-Sheet Forming	111	(2)
Part Design
Part Design Philosophy	113	(2)
Project Protocol	113	(1)
Should this Part Be Thermoformed?	114	(1)
Shrinkage, Draft, Thermal Expansion, and Dimensional Tolerance	115	(4)
Improving Dimensional Tolerance	118	(1)
Part Wall Thickness Prediction	119	(1)
Some Guidelines to Successful Part Design	120	(3)
Issues of Quality Control
Incoming Sheet Quality	123	(5)
The Extrusion Process--What a Thermoformer Needs to Know	123	(1)
The Purchase Order	124	(4)
Incoming Sheet Quality Evaluaiton	128	(1)
Production Monitoring	128	(5)
Measuring Temperature	128	(1)
Sheet Formability	129	(1)
Cutting Surfaces	130	(1)
Finished Part Performance	131	(2)
Set-Up, Maintenance, and Troubleshooting
Safety	133	(1)
Thermoforming Machine Set-Up	134	(2)
Mold Set-Up	136	(1)
Trim Set-Up	137	(1)
Maintenance	138	(2)
Troubleshooting	140	(3)
Glossary of Thermoforming Terms	143	(7)
Recommendations for Further Reading	150	(1)
Index	151