Robert A. Malloy
`
`
`
`Plastic Part Design for
`Injection Molding
`
`An Introduction
`
`With 42? Illustrations
`
`“9'5 and
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`fies-Lion
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`I Cher
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`rs: Engineer
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`ceasing
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`are. Molders
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`- q.
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`Hanser Publishers, Munich 1iiiienna New York
`
`HanseriGardner Publications. Inc., Cincinnati
`
`
`
`Ex. 2018
`3M Company, Merck & Co., Inc., and Merck Sharp & Dohme Corp., v. Aptar France SAS
`|PR2018—01055
`
`

`

`Prof. Fto bert A. Malloy. Department of Plastics Engineering. LJniyersity of Massachusetts,
`Lowell. MA D1354. USA
`
`Distributed in the USA and in Canada by
`Hansor Gardner Publications, Inc. ""
`5915 Ilit'elle'y Ave.
`Cincinnati. on assets. use
`Fax: +1 1513? 52? 3535!]
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`
`Distributed in all other countries by
`|L'Ielrl Hanaer 'lr’erlag
`Poetfacl‘i as M ED. $1631 Frluhchen. Germany
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`"Ths use of general descriptive names. trademarks. etc.. in this puhticsatipnr cash if the former
`are not capacially identified. is not to be taken as a sign that such namesr ss understood by the
`Trade Marks and Merchandise Marks Act. may aceordingty be used freely by anyone.
`
`WhilE' the advice and information in this book are bailey-ad to be true and accurate at the date
`0* fining ID PUP-SS. “Eilher lhe author not the editors nortlte publisher can accept any legal res-
`pd nsibility for any errors or omissions that may be made. The publisher makes nn warranty,
`express 0: impliedwith respects the material contained herein.
`
` The Author:
`
`Library of congress Cataloging-in-F'ublicatlon Data
`Malloy, Robert A.
`Plastic psrt design for injection molding : an introduction.r
`Robert It. I'u'lalloy
`p.
`cm.
`Includes index.
`ISBN I-EEBQCI-‘l 29-5
`
`1. Iniection molding plastics.
`3. Engineering design.
`I. Title.
`TP115D.M35
`19134
`633.4'12--de2{|
`
`94-11213
`
`2. Machine parts.
`
`Die Deutsche Elibliothek - CiP-Einheitsautnahme
`Mallory. Robert A.:
`Plastic part design for injection molding :sn introductron.r
`Robert A. Malloy. - Munich ; 1il'isn na; New 't'otlt : Hanser.
`15%
`
`ISBN 3-445-15353-8 [Munchen ...l|
`ISBN 1-5904 zs-s INew York ...l
`
`All rights reserved. No part of this book may he reproduced or transmitted in any form or by
`any means, electronic or mechanical, including photococying or by any information storage
`and retrieval ayelernr without permission in writing from the publisher.
`
`{cf-J {2er Hanser Herlag. Munich 1tilenna New York, 1994
`Earneraweady copy prepared by the author.
`Printed and tie-u nd in Germany by Schoder Druclt lEmbH E: Co. KG. Eersthofcn
`
`

`

`88
`
`Manufacturing Considerations for Injection Molded Parts
`
`2.6
`
`Part Ejection
`
`2.6.1
`
`Introduction
`
`In the final phase of the injection molding process, the mold opens and the part is ejected
`from the tool.
`Ideally, this ejection phase of the process is accomplished without
`imparting any damage or distortion to the molded part as it is stripped from the cavity or
`core. While it is generally the responsibility of the tool designer to design a suitable
`ejection system for a given part geometry, it is the part designer that establishes ease or
`difficulty associated With this stage of the plastic part manufacturing process. The plastic
`part must be designed with ejection considerations in mind. This can be done if the
`product designers work closely with (or consult with) the tool designer right from the
`early stages of product development, when the part begins to take shape. The tool
`designer can comment on specific ejection related concerns and possible part design
`changes. Plastic part design considerations that influence the ease of ejection and ejection
`related tooling costs include:
`
`. Draft angles or tapers
`- Surface finishes
`
`Esthetic requirements
`The presence of undercuts or holes
`Stationary or moving half ejection
`~ Parting line location
`
`Almost all of the features associated with a particular part geometry will have some
`impact on the ability to eject the part. Ejection systems for even a relatively simple plastic
`part can be expensive (in terms of tooling cost) if the part is not “designed for ejection”.
`
`‘6"
`
`2.6.2
`
`Draft Angles
`
`CavityDraft: Draft angles or tapers are generally used to facilitate ejection of any molded
`part that has a significant depth of draw. When parts are produced using the standard
`cavity and core configuration, the cavity is stationary while the core is attached to the
`moving platen. In most cases, the part tends to stay with the core when the mold opens
`since (i) material shrinkage causes a contact pressure and normal frictional forces between
`the part and the core, and (ii) material shrinkage through the wall thickness tends to pull
`the part away from the cavity wall.
`It should also be noted that the area of contact
`between the part and the cavity can be greater than that of the part and the core, however,
`contact pressures with the cavity are likely to be lower due to shrinkage through the wall
`thickness of the part. Draft angles are typically added to the cavity side of the tool to
`assist in releasing the part from the cavity when the mold opens at the end of the molding
`cycle. The draft also reduces the potential for scuffing or abrasion to the outer (cavity)
`sidewall surfaces of the part when the tool opens.
`
`Cavity draft angles reduce the effects of undercuts, eliminate sliding friCtion and part
`damage after the initial break away as the tool opens, and facilitate air movement to
`compensate for vacuum effects as the tool opens. Typical cavity draft angles range from
`a fraction of a degree to several degrees. The draft angle that is required varies with
`
`parameters such as depth of dr.
`roughness and material shrinkag
`special mold action, such as a spt
`the part as the mold opens.
`
`Cavity
`retainer
`
`retainer
`
`Figure 2. 81. Cavity draft angles are us
`core draft angles are added to facilitate It
`
`The split cavity action reduces m
`for the part sticking to the cavity. ‘
`scuffing due to sliding friction
`essentially large side actions, and
`slots and other undercut feature:
`
`costly than more conventional op
`and potentially flash, will be visib
`
`0
`
`Deep draw parts with “zero cavity drif—
`generally require more complex toolntg
`
`
`
`
`It is possible to produce I
`Figure 2.82.
`must be used to facilitate part release fro:
`
`
`
`

`

`'0: core surface. The coating has
`‘ for es for a variety of polymers
`nlypropylene [92].
`
`:15 such as ejector pins, blades,
`molding.
`It is generally the
`mien system for a particular part
`ize .hat the ejection components
`aims. The part designer should
`iabl= for ejection placement for
`I I
`raiding shown in Figure 2.94,
`6.
`[I
`
`
`
`
`
`
`
`Vice—55 marks on the molding and must
`
`eject the part with ejector pins
`5 enough. Ejector tabs can also
`,4. :owever, the tabs require an
`
`Ejection mold is not a stand alone
`I ejection are closely related to
`rations. Consider once again the
`me half of a clamshell appliance
`writ}- mold, the simplest way to
`Eduard cavity/ core set up (i.e.
`[ding machine while the core is
`
`
`
`2.6 Part Ejection 99
`
`attached to the moving or force platen of the molding machine). It is generally preferred
`to have the part stay with the moving half of the mold so that the molding machine’s
`knockout system can be utilized to activate the molds ejector system. However, if the
`outer surface of the part is an appearance surface, sprue gating into the top exterior
`surface is esthetically unacceptable. As an alternative, the part could be gated on the
`underside , however, because parts tend to stay with the core (they shrink onto the core)
`and the ejector marks must be hidden, the tool must then be designed with ejection
`provisions on the stationary side of the tool. While this can be accomplished, it is not
`standard practice, and will result in additional tooling costs. The designer should
`recognize that there are other possible options or alternatives to stationary side ejection in
`this case. For example, the conventional cavity and core set up could be used with a
`cavity side sprue gate was used, if the sprue gate vestage was covered up using a label or
`logo.
`
`2.6.5 Undercuts and Holes
`
`Ideally, a plastic part should be designed so that it can be ejected from the mold without
`any special mold actions. Special mold movements such as side action, side coring,
`angle pins, collapsible cores, unscrewing mechanisms and the like should be avoided
`whenever possible. These special mold actions can be expensive to tool, add to mold
`maintenance, may interfere with the molds cooling layout, and may ultimately add to the
`overall cycle time for part production. While it may not be possible to eliminate special
`mold movements, their use should be limited whenever possible. If side actions must be
`used, movement in a direction perpendicular to the mold opening direction is preferred.
`Actions at oblique angles should be avoided whenever possible. As an example, the hole
`in the sidewall of the part shown in Figure 2.95 would require side action to pull the
`small core pin (that produces the hole) from the hole before the part can be released from
`the cavity as the mold opens. The side action, and added tooling cost, could be
`eliminated if the part is designed with consideration towards ejection. For example, the
`hole could be replaced by a slot in the line of draw, and as a result, no special side actions
`or core pulls are required.
`
`
`
`
`/' Molded slots:
`no special mold
`t
`actions required
`
`Mold
`Molded hole:
`movement
`
`
`requires side action
`
`
`
`Internal cantilever snap:
`no special mold action
`
`required when slot is added
`
`Internal cantilever snap:
`
`blind-requires use of lifter
`
`‘
`
`Figure 2.95. Whenever possible, part features such as holes or cantilever snap beams should be “designed
`for ejection”. For example, changing a hole in a part sidewall to a slot will eliminate the tooling costs
`and maintenance problems associated with side action.
`
`
`
`