Robert A. Malloy
`
`or Injection Molding
`
`i
`
`An Introduction
`
`5
`
`. W ' 11
`
`| MANSER
`
`EVERLIGHT ELECTRONICS CO., LTD. ET AL.
`Exhibit 1018
`
`

`

`SPE Books from Hanser Publishers
`Bernhardt, Computer Aided Engineering for Injection Molding
`Brostow/Corneliussen, Failure of Plastics
`Chan, Polymer Surface Modification and Characterization
`Charrier, Polymeric Materials and Processing-Plastics, Elastomers and
`Composites
`Ehrig, Plastics Recycling
`Gordon, Total Quality Process Control for Injection Molding
`Gordon/Shaw, Computer Programs for Rheologists
`Gruenwald, Plastics; How Structure Determines Properties
`Macosko, Fundamentals of Computer Aided Engineering in Injection
`Molding
`Malloy, Plastic Part Design for Injection Molding
`Matsuoka, Relaxation Phenomena in Polymers
`Menges/Mohren, How to Make Injection Molds
`Michaeli, Extrusion Dies for Plastics and Rubber
`O'Brien, Applications of Computer Modeling for Extrusion and Other
`Continuous Polymer Processes
`Progelhof/Throne, Polymer Engineering Principles
`Rauwendaa!, Polymer Extrusion
`Saechtling, International Plastics Handbook for the Technologist, Engineer
`and User
`Stoeckhert, Mold-Making Handbook for the Plastics Engineer
`Throne, Thermoforming
`Tucker, Fundamentals of Computer Modeling for Polymer Processing
`Ulrich, Introduction to Industrial Polymers
`Wright, Molded Thermosets: A Handbook for Plastics Engineers, Molders
`and Designers
`
`EVERLIGHT ELECTRONICS CO., LTD. ET AL.
`Exhibit 1018
`
`

`

`Robert A. Malloy
`
`Plastic Part Design for
`Injection Molding
`
`An Introduction
`
`With 427 Illustrations
`
`Hanser Publishers, Munich Vienna New York
`
`Hanser/Gardner Publications, Inc., Cincinnati
`
`EVERLIGHT ELECTRONICS CO., LTD. ET AL.
`Exhibit 1018
`
`

`

`The Author:
`Prof. Robert A. Malloy, Department of Plastics Engineering, University of Massachusetts,
`Lowell, MA 01854, USA
`
`Distributed in the USA and in Canada by
`Hanser/Gardner Publications, Inc.
`6600 Clough Pike, Cincinnati, Ohio 45244-4090, USA
`Fax: +1 (513) 527-8950
`
`Distributed in all other countries by
`Carl Hanser Verlag
`Postfach 86 04 20, 81631 Munchen, Germany
`Fax: +49 (89) 98 48 09
`
`I
`
`The use of general descriptive names, trademarks, etc., in this publication, even if the
`former are not especially identified, is not to be taken as a sign that such names, as
`understood by the Trade Marks and Merchandise Marks Act, may accordingly be used
`freely by anyone.
`
`While the advice and information in this book are believed to be true and accurate at the
`date of going to press, neither the author nor the editors nor the publisher can accept any
`legal responsibility for any errors or omissions that may be made. The publisher makes no
`warranty, express or implied, with respect to the material contained herein.
`
`Library of Congress Cataloging-in-Publication Data
`Malloy, Robert A.
`Plastic part design for injection molding : an introduction /
`Robert A. Malloy
`p. cm.
`Includes index.
`ISBN 1-56990-129-5
`1. Injection molding plastics. 2. Machine parts.
`3. Engineering design.
`I. Title.
`TP11 50.M35 1994
`668.4'12-dc20
`
`94-4213
`
`Die Deutsche Bibliothek - CIP-Einheitsaufnahme
`Malloy, Robert A.:
`Plastic part design for injection molding ; an introduction /
`Robert A. Malloy. - Munich ; Vienna ; New York : Hanser,
`1994
`ISBN 3-446-15956-8 (Munchen ...)
`ISBN 1-56990-129-5 (New York ...)
`
`All rights reserved. No part of this book may be reproduced or transmitted in any form or
`by any means, electronic or mechanical, including photocopying or by any information
`storage and retrieval system, without permission in writing from the publisher.
`
`© Carl Hanser Verlag, Munich Vienna New York, 1994
`Camera-ready copy prepared by the author.
`Printed and bound in Germany by Schoder Druck GmbH & Co. KG, Gersthofen
`
`EVERLIGHT ELECTRONICS CO., LTD. ET AL.
`Exhibit 1018
`
`

`

`1.3 Structure-Property Relationships
`
`3
`
`The "degree of crystal I inity" (i.e. the relative percentage of crystalline vs. amorphous
`in the material) is influenced by both the chemical structure of the polymer and by
`areas
`the manufacturing / processing conditions; particularly the rate at which the molten
`polymer cools. Processing variables that reduce the rate of cooling will generally
`increase the degree of crystallinity. Polymers such as polyethylene, polypropylene, and
`the polyamides (nylons) are examples of semi-crystalline polymers.
`Liquid Crystalline Thermoplastics: Like semi-crystalline thermoplastics, liquid crystalline
`thermoplastics (LCPs) have ordered domain-type chain arrangements in the solid state.
`However, unlike conventional semi-crystalline polymers, liquid crystalline polymers also
`exhibit ordered (rather than random) molecular arrangements in the melt state. These
`unique materials are characterized by their stiff, rod like molecules that form the parallel
`arrays or domains. LCPs offer a number of processing and performance advantages
`including low mell viscosity, low mold shrinkage, chemical resistance, stiffness, creep
`resistance and overall dimensional stabilily [2J.
`
`1.2
`
`Thermosetting Plastic Materials
`
`Thermosetting polymers (or thermosets) are polymers that chemically react during
`processing to form a cross-linked polymer chain network as shown in Figure 1.2. The
`chemical reaction is irreversible. Unlike thernioplaslics, thennosets are not directly
`recyclable. Because there is a chemical reaction involved in thermoset molding, a number
`of additional reaction related process variables enter into processing. Thermoset materials
`(as a group) can be difficult to work with and require special molding equipment/
`practices, however, the materials do offer some outstanding properties. The cross-linked
`chain network characteristic of thermosetting polymers leads to properties such as
`excellent creep resistance, dimensional stability and chemical resistance. However, the
`difficulties encountered when processing thermosetting polymers, along with their lack of
`recyclability, limits their use in most applications. Examples of thermosetting polymers
`include phenolics, epoxies, unsaturated polyesters, and a variety of elastomeric materials.
`
`1.3
`
`Structure-Property Relationships
`
`The properties of a plastic material formulation can literally be "tailored" to meet the
`requirements of almost any specific end-use application. The properties of different
`plastic material formulations (or grades) will vary due to (i) differences in its chemical
`composition and (ii) differences in the additives incorporated into the material
`formulation. The chemical compositions of the different plastic materials can vary in
`many ways including;
`
`• Structure of the repeat unit
`• Homopolymer or copolymer
`• Average molecular weight
`• Molecular weight distribution
`• Linear vs. branched vs. crosslinked
`
`i
`
`EVERLIGHT ELECTRONICS CO., LTD. ET AL.
`Exhibit 1018
`
`

`

`12
`
`Introduction
`
`Good Thermal Insulation: Plastic materials also offer good thermal insulation. This is
`important in a variety of energy conservation appliealions. The reduced heal transfer
`rates give plastic products a warm feel, even when the temperature of the plastic object is
`cool. On the other hand, the low thermal conductivity can be a problem in dynamic
`applications such as gearing (where frictional heat is generated), or in applications such
`as computer enclosures (where electrical sources generate heat). Forced ventilation
`systems (e.g. fans) are often required for applications where natural conduction and
`convective heat transfer to the environment cannot keep pace with heal generation. When
`heat dissipation is a problem, designers must pay strict attention to both the surface area
`to volume ratio for the part and the material's thermal properties. Filled or reinforced
`thermoplastic material grades (composite materials) can offer significantly improved heat
`transfer capabilities.
`Flammable: Almost all plastic materials will burn to some degree or decompose when
`subject to combustion eonditions. A polymer such as polyethylene wil I ignite and bu rn
`readily, while a thermosetting phenolic will simply char. The flammability resistance of
`most plastic materials can be improved using flame retardant additive packages.
`Designers must be concerned with a number of issues with respect to flammability,
`including combustibility, dripping, and combustion by products, including the
`by-products of the additives.
`Poor Weather Resistance: Many plastic materials have poor long term weather resistance.
`While most materials are unaffected by the presence of moisture at low temperature (with
`the exception of the plasticizing effect for hygroscopic polymers), the combined effects of
`ultraviolet energy (from sunlight) and oxidation can lead to a deterioration in color,
`transparency, and other properties over time. This is a concern for the many long term,
`outdoor applications such as automotive, toys, sporting goods or building construction
`products. Some plastic materials such as acrylics have excellent inherent weather
`resistance, while others such as polypropylene require additional stabilization. The long
`term weather resistance of any polymer can be improved significantly using ultraviolet
`stabilizers and antioxidants as additives. In some cases, coatings are used to overcome
`the problems associated with long term aging.
`Relatively High Coefficient of Thermal Expansion: In general, plastic materials have
`relatively high coefficients of thermal expansion (CTE). This becomes a concern when
`plasties are used as a component of a larger product assembly containing metals, glass,
`ceramics or even another plastic material (having a different CTE value) due to the
`thermal expansion mismatch. The thermal expansion coefficients for plastic materials
`vary greatly from material to material. Materials such as filled or reinforced liquid crystal
`polymers have very low coefficients of linear thermal expansion, while a material such as
`an unfilled polyethylene, has a coefficient of linear thermal expansion that is an order of
`magnitude greater than that of steel. Designers must incorporate provisions to
`compensate for this thermal expansion mismatch into their product designs. The
`coefficient of linear thermal expansion for a polymer can be reduced significantly by
`adding inorganic fillers and reinforcements such as glass fiber (glass has a very low
`reinforced materials are used, anisotropic thermal
`CTE). However, when fiber
`expansion behavior can be observed due to fiber and molecular orientation effects. It
`should also be noted here that hygroscopic polymers, such as acetals or nylons, can also
`exhibit dimensional changes with changes in relative humidity due to its effect on the
`level of absorbed moisture within the polymer. A hygroscopic thermoplastic will tend to
`swell as the level of absorbed moisture increases.
`
`EVERLIGHT ELECTRONICS CO., LTD. ET AL.
`Exhibit 1018
`
`

`

`3.7 Thermal Properties of Plastic Materials
`
`171
`
`relation to glass transition. The DTUL test provides a measure of the temperature at
`which a polymer achieves a certain flexural modulus value (971 MPa at the 1.82 MPa
`outer fiber stress), but does not provide any indication as to the shape of the
`modulus-temperature curve for the polymer (i.e. it is a short term, single point test). As
`such, the DTUL test is suitable only for initial material screening and should not be used
`for final material selection and design [5,7].
`
`A variant of the DTUL test is the Vicat Softening Temperature Test. Unlike the bending
`test configuration associated with the DTUL test, the Vicat temperature test (apparatus
`shown in Figure 3.48) provides a measure of the temperature for which a lightly loaded
`flat pin penetrates a fixed distance into a test specimen. The object of the test is to
`provide a relative indication of the ability of a material to withstand short term contact
`with a heated object [6,7]. The test is also commonly used for process design purp
`oses
`(molding simulations) as a measure of the minimum temperature at which an injection
`molded part can be ejected from a mold. It is likely thai ejector pins, sleeves etc. would
`damage parts if the parts were ejected at temperatures above the Vicat temperature. Both
`Vicat and DTUL temperature values can also be used as a rough measure of the intrinsic
`resistance of a thermoplastic to distortion or warpage at elevated temperatures. The
`values are useful only as a guide since the tendency towards warpage is influenced by
`factors such as the degree of orientation, residual stress, loads, and part geometry [6].
`
`3.7.3 Coefficient of Linear Thermal Expansion
`Like most other materials, plastic materials expand when they are heated and contract
`when they are cooled (i.e. they have positive coefficients of thermal expansion).
`Compared to many other materials, plastic materials have relatively high thermal
`expansion coefficients, however, the values vary significantly from polymer to polymer.
`The volumetric change associated with a given change in temperature (or pressure) can be
`characterized using pressure - volume - temperature curves such as those shown in
`Figures 2.60 a & b. However, for part design purposes, it is the Coefficient of Linear
`Thermal Expansion (CLTE) that is most useful. CLTE values are more commonly
`measured directly (rather than extracted from pressure - volume - temperature data)
`because injection molded plastic parts may not exhibit isotropic behavior. The CLTE is
`defined as the ratio of the change in linear dimension to the original dimension per unit
`degree change in temperature. The CLTE has units of l^C (l/T) or cm/cm0C (in/in/T).
`Tile latter units are preferred because they implicitly indicate that the value is the linear
`CTE rather than area or volume CTE. The CLTE value for molded polymeric materials
`can vary significantly between the flow and cross flow directions, especially for fiber
`reinforced polymer grades. Oriented fibers restrict the dimensional changes (glass fibers
`foj- example have very low CLTE values) in the flow direction, while cross flow CLTE
`values can become greater since a certain volume change must take place. In addition,
`CLTE values do change with temperature and can be considered constants only over a
`small temperature range. Significant changes (increases) in the CLTE value occur when
`temperatures approach thermal transitions such as Tg or Tm. This is a particular
`concern
`for semi-crystalline polymers that are commonly used at temperatures that span their glass
`transition temperature.
`
`Typical Coefficient of Linear Thermal Expansion values are given for a variety of
`niaterials in Table 3.2 [6,7]. When designing parts that must assemble with another, it is
`io use materials that have similar CLTE values (i.e. avoid a CLTE mismatch). This
`
`f
`
`EVERLIGHT ELECTRONICS CO., LTD. ET AL.
`Exhibit 1018
`
`

`

`The Design Process and Material Selection
`172
`can be difficult when parts contain both metal and plastic components, since plastic
`material CLTE can be an order of magnitude greater than that of steel. In many cases,
`fasteners themseives present problems since they are commonly produced from steel. The
`part designs developed for applications involving CLTE mismatches must incorporate
`features such as clearance holes or slots to accommodate the changes in dimensions over
`the entire range of temperature associated with the end-use application.
`
`Table 3.2. Typical Linear Coefficient of Thermal Expansion Values [7]
`
`Material
`type
`
`Typical CTE
`(10"5 cm/cmAC)
`
`Material
`type
`
`Typical CTE
`(10-5 cnycnv^C)
`
`0.6
`LCP (GFR)*
`0.3 - 0.7
`Glass
`1.1
`Steel
`1.4
`Concrete
`1.6
`Copper
`1.8
`Bronze
`1.8
`Brass
`2 . 2
`Aluminum
`Polyetherimide (GFR)* 1.5-3.2
`2.3
`Nylon (GFR)*
`2.5 - 7.5**
`TP Polyester (GFR)*
`2.5
`Magnesium
`2.0 - 4.0
`Polycarbonate (GFR)
`3.1
`Zinc
`* Typical glass fiber reinforced grade.
`** Highest CTE value for cross flow direction.
`
`ABS (GFR)*
`Polypropylene (GFR)*
`Polyphenylene sulfide
`Acetal (GFR)*
`Epoxy
`Polyetherimide
`Polycarbonate
`Acrylic
`ABS
`Nylon
`Acetal
`Polypropylene
`TP polyester
`Polyethylene
`
`3.1
`3.2
`3.6
`4.0
`5.4
`5.6
`6.5
`6.8
`7.2
`8.1
`8.5
`8.6
`12.4
`13- 17
`
`3.7.4 Aging at Elevated Temperatures
`
`Many plastic materials become brittle or discolored when exposed to high temperatures
`for extended periods of times. The changes in material properties that occur over lime ai
`elevated temperatures can be due to physical effects such as the loss of additives 1 e.g-
`plasticizer migration) or chemical changes such as oxidation. The thermal stability of a
`polymer is typically evaluated by placing a series of molded specimens in an oven held ai
`a specific temperature (typically a high temperature to accelerate the test) for an extended
`period of time. The samples are removed periodically for evaluation. Once a sample is
`removed from the oven, it is observed and tested for the desired physical, mechanical,
`electrical, optical, chemical, etc. property. The test results are then presented as a plot
`property (or property retention) as a function of time at the particular aging temper ,urCj
`This type of test provides a measure of thermal stability at the particular environmental
`conditions associated with the test.
`
`EVERLIGHT ELECTRONICS CO., LTD. ET AL.
`Exhibit 1018
`
`