Thermoforming Troubleshooting

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Transcript of Thermoforming Troubleshooting

Update on Troubleshooting in Thermoforming

Natamai Subramanian Muralisrinivasan

Smithers Rapra Update

Update on Troubleshooting in ThermoformingNatamai Subramanian Muralisrinivasan

iSmithers A Smithers Group CompanyShawbury, Shrewsbury, Shropshire, SY4 4NR, United Kingdom Telephone: +44 (0)1939 250383 Fax: +44 (0)1939 251118 http://www.iSmithers.net

First Published in 2010 by

iSmithersShawbury, Shrewsbury, Shropshire, SY4 4NR, UK

2010, Smithers Rapra

All rights reserved. Except as permitted under current legislation no part of this publication may be photocopied, reproduced or distributed in any form or by any means or stored in a database or retrieval system, without the prior permission from the copyright holder.

A catalogue record for this book is available from the British Library.

Every effort has been made to contact copyright holders of any material reproduced within the text and the authors and publishers apologise if any have been overlooked.

ISBN: 978-1-84735-137-1 eISBN: 978-1-84735-470-9

Typeset by Integra Software Services Pvt. Ltd. Printed and bound by Lightning Source Inc.

C1. 2. 2.1

ontents

Preface ..........................................................................................v Introduction ......................................................................... 1 Plastic Sheet, Sheet Materials, Physical Properties and Plastics an Overview .................................. 5 Thermoforming Materials Physical Properties ...................................................... 8

2.1.1 2.1.2 2.1.3 2.1.4 2.1.5 2.1.6 2.1.7 2.1.8 2.1.9

Acrylonitrile-butadiene-styrene (ABS) ..........8 Polyvinyl Chloride (PVC) ..........................10 Low-Density Polyethylene (LDPE).............12 High-Density Polyethylene (HDPE) ...........13 Polypropylene (PP) ....................................14 Polystyrene (PS) .........................................16 Expanded Polystyrene (EPS) (Foam) ..........18 Polyethylene Terephthalate (PET) ..............19 Polymethylmethacrylate (PMMA)/ Acrylic .......................................................20

2.1.10 Polyetheretherketone (PEEK).....................21 2.1.11 Polycarbonate (PC)....................................22 2.1.12 Thermoplastic Olen (TPO) ......................23 2.1.13 Polyphenylene Oxide (PPO) ......................23 2.1.14 Thermoplastic Elastomers .........................24 2.1.15 Biodegradable Polymer ..............................24 2.1.16 Cyclic-olen Copolymer (COC) ................25i

Update on Troubleshooting in Thermoforming

2.1.17 Polyacetal (POM) ......................................26 2.1.18 Composites................................................263. Machine Specications Effect of Parameters .................... 35 3.1 Methods of Vacuum Forming ................................... 39

3.1.1 3.1.2 3.1.3 3.1.4 3.1.5 3.1.6 3.1.7 3.1.8 3.1.9

Straight Vacuum Forming ..........................39 Vacuum (Thermo) Forming .......................39 Pressure Forming .......................................41 Plug-assist Pressure Forming......................42 Plug-assist Vacuum Forming ......................42 Pressure-bubble Plug-assist Vacuum Forming .......................................46 Free Forming .............................................46 Matched-die Forming ................................46 Drape Forming ..........................................48

3.2

3.1.10 Vacuum Snap-back Forming Process ......................................................49 Effect of Parameters .................................................. 51 3.2.1 3.2.2 3.2.3 3.2.4 3.2.5 3.2.6 3.2.7 3.2.8 3.2.9 Raw Material (Plastic Sheets) ....................51 Moulds ......................................................53 Vacuum .....................................................56 Vacuum Holes ...........................................56 Plug ...........................................................57 Sheet Temperature .....................................57 Heaters ......................................................58 Daylight ....................................................59 Process Parameters ....................................60

4.

Problem Identication Classication Troubleshooting Flow Chart............................................ 67 4.1 Troubleshooting........................................................ 71

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Contents

4.1.1 4.1.2 4.1.3 4.1.4 4.1.5 4.1.6 4.1.7 4.1.8 4.1.9

Blisters or Bubbles .....................................71 Webbing or Bridging .................................73 Excessive Sheet Sag....................................74 Pinhole or Rupturing .................................75 Excessive Post Shrinkage ...........................76 Uneven Sag ................................................77 Part Sticks to Mould..................................77 Stretch Marks on Part ...............................78 Nipples on Mould Side of Thermoformed Part ...................................78

4.1.10 Pock Marks ...............................................79 4.1.11 Poor Wall Distribution ..............................80 4.1.12 Uneven Edges ............................................81 4.1.13 Tearing of Sheet When Forming ................82 4.1.14 Bad Denition at the Edges of the Forming Area ..................................83 4.1.15 Glossy Spots ..............................................84 4.1.16 Part Warpage .............................................85 4.1.17 Cracking in Corners ..................................86 4.1.18 Raised Corners ..........................................87 4.1.19 Surface Markings ......................................88 4.1.20 Parts in the Corners Too Thin ...................................................89 4.1.21 Folds, Webbing or Wrinkles ......................90 4.1.22 Part Deforms During De-moulding .............................................904.2

4.1.23 Poor Part Detail.........................................91 End-product Problems .............................................. 91 4.2.1 4.2.2 Migration of Additives ..............................91 Melt Failure During Thermoforming .........93

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Update on Troubleshooting in Thermoforming

4.2.3 4.2.4 4.2.55. 6.

Blue Coloured Dots ...................................93 Shrinkage ..................................................94 Sheet Pull-out ............................................94

Optimisation of the Production .......................................... 97 Case Studies ..................................................................... 103 6.1 6.2 6.3 Case Study 1 ........................................................... 104 Case Study 2 ........................................................... 106 Case Study 3 ........................................................... 107

7.

Conclusion ....................................................................... 109

Abbreviations ........................................................................... 113 Author Index............................................................................ 115 Subject Index............................................................................ 121

iv

P

reface

This book is written to serve as a general purpose source both for experienced plastics users and for those who are new to plastic processing. It should be of interest to non-designers and managers who need a general overview of the concepts and critical issues related to thermoforming. Although the book is not a guide to thermoforming, much of the troubleshooting is based upon forming criteria involved in the manufacturing and thermoforming of plastic parts. Most thermoforming books deal with specic topics. This book deals with issues common to all thermoforming thermoplastic resins, with associated troubleshooting methods. Tables, gures and other descriptive methods are used to help illustrate signicant troubleshooting differences. The book, which is divided into seven chapters, gives a thorough overview of troubleshooting in the thermoforming process and provides information for the experienced user of polymers who wishes to use thermoforming. Problems of surface quality in thermoforming are dealt with, and the complex interrelationship between the mould and the processing is recognised. The goal is to assist with the practical aspects of thermoforming, and the factors affecting the quality of thermoformed parts, such as the process, the machinery and the mould, are considered. Consideration is also given to the detection, classification and troubleshooting of defects. Case studies are included, the effects of thermoforming parameters are discussed and machine specications are examined.

v

Update on Troubleshooting in Thermoforming The book will serve both as a reference and as a how-to guide for those new to thermoforming processes. Information about every aspect of troubleshooting in the thermoforming process is provided in a reader-friendly form. The advantages of working with thermoplastics are discussed, and practical comments on processing are provided. The book begins with a general background overview and describes and reviews processing issues and conditions for the wide range of techniques used to optimise the processing. It is an indispensable resource for anyone working within the thermoforming industry. The book looks at different problems that can occur during thermoforming of extruded plastics, and how to solve them. An update on thermoforming troubleshooting, rather than a complete survey of the literature, is the main subject of the book. The main emphasis will be placed