IN THIS ISSUE - s3.amazonaws.coms3.amazonaws.com/rdcms-spe/files/production/public/FileDownloads/... · Fall 2010 Page 2 SPE Injection Molding Division IMD Leadership DIVISION OFFICERS

Fall 2010 Page 1 SPE Injection Molding Division

Molding ViewsMolding ViewsMolding ViewsMolding ViewsMolding ViewsBrought to you by the Injection Molding Division

of the Society of Plastics Engineers

Disclaimer: The editorial content published in this newsletter is the sole responsibility of the authors. The Injection Molding Division publishes thiscontent for the use and benefit of its members, but is not responsible for the accuracy or validity of editorial content contributed by various sources.

No. 83, Fall 2010

The Effect of Impact and Other Rapid

Loading Mechanisms on Plastics Webinar

December 8, 2010 – 11:00am - 12:00pm

ARAB PLASTJanuary 8-11, 2011 – Dubai, United Arab Emirates

Introduction to Bioplastics Series Webinar

January 19-20, 2010 – 11:00am - 12:00pm

PLASTIVISION INDIA 2011January 20-24, 2011 – Mumbai, India

ASIATECFebruary 15-17, 2011 – Tokyo, Japan

MOLDING 2011March 7-9, 2011 – San Diego, CA, USA

SPE ANTEC 2011May 1-5, 2011 – Boston, MA, USA

AUSPLAS 2011May 24-27, 2011 – Melbourne, Australia

INTERPLASSeptember 27-29, 2011 – Birmingham, UK

SPE EUROTEC 2011November 14-15, 2011 – Barcelona, Spain

http://www.4spe.org/conferences-and-events • http://www.polymer-age.co.uk/x/events.html

IN THIS ISSUE:

Industry Events Calendar 1

IMD Leadership 2

Student Activities Report 2

Ask The Expert: Injection Molding 3

Ask The Expert: Hot Runner Systems 4

Feature Article 7

What You Need To Know About In-Mold

Decorating and Labeling

Feature Article 11

Focus on Precision (ICM Focus)

Featured Technology 16

The Evolution of Grafilm® Ultra

Feature Article 18

Playing With Light (ICM Focus)

Featured Technology 24

Does Early Retirement Make (Financial)

Sense for Unscrewing Molds

IMD Best Paper Finalist 26

Methodology for Evaluating Warpage

Sensitivity of Plastic Materials

New IMD Members 34

New IMD Companies 35

New IMD Countries 35

Membership Application 36

Sponsors in this Issue 37

Publisher’s Message 37

Sponsorship Opportunities 37

UPCOMING EVENTS:


IMD Leadership

DIVISION OFFICERS

IMD ChairLee Filbert, [email protected]

Chair-ElectJan Stevens, [email protected]

Past Chair, Alt. TreasurerDave Karpinski, [email protected]

Executive Committee Liason,Nominations ChairHoa Pham, Wash. Penn [email protected]

Secretary, StudentActivities ChairWalt Smith, Xaloy, [email protected]

Technical DirectorPeter [email protected]

TreasurerJim [email protected]

BOARD OF DIRECTORS

Awards Chair

Communications Chair,Website ChairAdam KramschusterUniv. of Wisconsin–[email protected]

Councilor, Reception ChairJack Dispenza, Ideal [email protected]

Education ChairPat Gorton, [email protected]

Engineer of the Year AwardKishor Mehta, Plascon [email protected]

Historian, Fellows &Honored Service AwardsLarry SchmidtLR Schmidt [email protected]

Membership ChairNick Fountas, [email protected]

TPC 2010Jan Stevens, [email protected]

TPC 2011Susan Montgomery, [email protected]

Board MemberErik Foltz, The Madison [email protected]

Board MemberBrad Johnson, Penn State [email protected]

Board MemberRaymond McKee, [email protected]

Board MemberLih-Sheng (Tom) TurngUniv. of Wisconsin–[email protected]

Board MemberMichael Uhrain, [email protected]

Emeritus Board MemberDon AllenPhillips [email protected]

Emeritus Board MemberLarry CosmaPerformance [email protected]

Emeritus Board MemberMal MurthyDoss [email protected]

Emeritus Board MemberJim [email protected]

CONTRIBUTORS

Publication: Editor/Publisher, SponsorshipChris LaceyUniv. of Wisconsin–[email protected]

IMD Leadership

Chair’s MessageStudent Activities

Student Activities ReportBy Walter S. Smith

The Injection Molding Division (IMD) offers an annual $3000 scholarship to a graduate orundergraduate student. Applicants must have experience in the injection molding industry, such as coursestaken, research conducted, or jobs held. The scholarship is awarded through the SPE foundation. JasonMcNulty from the University of Wisconsin–Stout was awarded the 2010–2011 IMD Scholarship (image onright).

The IMD sponsors the Injection Molding Reception at ANTEC, and will continue to do so for ANTEC2011. Students always heavily attend this event. This is another opportunity for students to network andmeet professionals in their chosen career paths. The IMD also works closely with local SPE sections andstudent chapters to provide various activities such as plant tours, IMD speakers, and scholarships.

The Society of Plastics Engineers (SPE) Foundation 2011–2012 Scholarship brochure/application is available for interestedstudents who will be attending college in the 2011–2012 school year. General foundation scholarships range up to $4000/year.Specific scholarships requiring specific knowledge or background can range up to $7000/year. The SPE Foundation gives outover $60,000 annually in scholarships.

SPE, along with sponsorship from SPE sections and divisions, will sponsor the 16th annual “Wonders of Plastics” essaycontest. This contest, which is open to all junior high and high school students, will require that an essay be written and sub-mitted to a local SPE section. The essay must be sponsored by a teacher and meet certain requirements. The winning entry at theSection level will be published in the Section newsletter and forwarded to SPE Headquarters for judging at the internationallevel. The student who wins the international competition will receive $1000 and a plaque. His or her school will also receive$1000 for their educational programming.

The Society of Plastics Engineers offers membership to over 120 student chapters. Learn, network, and prepare for yourfuture with the help of SPE. Get involved in an existing SPE chapter or start your own! For more information on what it takes tostart a student chapter, or to find out what SPE can do for your plastics program, contact Tricia McKnight at [email protected].

I strongly recommend that all students get involved. I promise you, it will be worth your time and effort.


Ask The Experts

Injection Molding Questions

Bob Dealey, owner andpresident of Dealey’s MoldEngineering, Inc. answers yourquestions about injection mold-ing. Bob has over 30 years ofexperience in plastics injection-molding design, tooling, andprocessing. Email Bob here:[email protected]

QuestionWhere can I locate tolerances and speci-

fications for injection molding screws and barrelsand their fit to each other?

AnswerI recommend the injection molding machine

manufacturer as the most authoritative source forany specifications. Their specifications list theacceptable tolerances when new. The secondsource, and most unbiased, is from the Society ofthe Plastics Industry (SPI).

I do not have an SPI standard in my library.However, a number of years ago I researched thisinformation as an expert witness and have retainedsome of the information. This information could bea used as a guide to get you started until you obtainthe SPI standard.

The tolerance on the barrel bore diameter isdependent upon both the nominal diameter of thebore and the length of the barrel. The table belowprovides the information that I have.

Barrel Diameter

Secondly, you must be concerned about thestraightness of the bore (see the table below).

Screw Diameter

The flight and bearing diameter tolerance is +0.000/–0.002 for screw diameters of up to 6.000 and +0.000/–0.004 for screw diameters over 6.000 inches.

www.xaloy.com


Ask The Experts -cont-

Hot Runner Questions

Terry Schwenk, owner andpresident of Process & DesignTechnologies, LLC, answers yourhot runner questions. Terry hasover 34 years of experience in theplastics industry, and more than22 years in hot runner technol-ogy specifically. Email Terry at:[email protected]

Question:What application(s) would you suggest the use

of an insulated runner system as opposed to atypical internally/externally heated system?

Answer:Insulated runner systems were the first type of

runnerless system to help thermal plastic injectionmolders reduce material waste and minimize theamount of regrind material used in the end product(see Figure 1).

Insulated runner systems had no heaters. They relied solely on the hot material from the molding machine andthe material's poor thermal properties to remain molten.

The answer to the above question will be twofold. I will address it from an economical and as well as atechnical perspective. Historically, hot runner systems were driven by economics. The insulated runner, an earlyform of the hot runner system, was incorporated into the tooling to reduce cold runner waste. The added cost toincorporate it in the tool was minimal. In several cases, it was less expensive than a three plate mold. This still holdstrue today. An insulated runner system is also less expensive then a full hot runner system. Thus, there is still is a realcost advantage of incorporating an insulated runnerless system.

www.incoe.com



The question to use or not use an insulated runnersystem is more of a technical challenge. The economicbenefits are fairly obvious. The technical benefits are inits simplicity. However, this type of runnerless systemrequires fast cycle times since the molten material onlygets its heat from the next injection cycle to stay molten.In the event that the cycle is interrupted or too long, themolten area will solidify and prevent another cycle. Therunner then needs to be removed and the injection cycle

process restarted (see Figure 2). This can result in a lot of down time if it occurs too often. Another challengeincludes sizing the gate to the cycle being run in order to keep the gate open for the next cycle without having toobig of a gate resulting in a secondary trimming process.

The insulated runnerless system is also limited with regard to the type of materials that functions well with it. Forthe most part, it is limited to amorphous materials because of their large heat range which minimizes prematuresolidification. Semi-crystalline resins solidify too quickly, making it difficult to keep the gates open long enough forthe next shot. To address this issue, modified insulated runnerless systems (see Figure 3) were developed. While

www.processdesigntech.com


Faster Mold Validation Using PRIAMUS Process Control Systems

Instantaneous material shear stress and shear

rate information

Automatic and accurate valve gate control for LSR molds

Proven process optimization

methods and hands‐on training

Automatic and effortless

process control

With Priamus control

Without Priamus control

the system still had an insulated runner, the addition of a heated probe inthe gate area gave processors better control over gate solidification. Thisconfiguration was more forgiving to cycle interruptions than a fully insulatedrunnerless system. It also opened up the process window, enablingprocessors to work with some semi-crystalline base resins.

Often the rule of thumb with regard to whether or not to use an insulatedrunnerless system is to have 100% of the insulated runnerless systemevacuated with every shot. Thus, part sizes need to be fairly large in orderto successfully use this type of runnerless system. Small parts or shot sizes

won't generate enough heat to keep the system operating. Cleaning amodified insulated runnerless system requires the same procedure assplitting the plates to remove the runner (see Figure 4). And of course thecost of a modified insulated runnerless system is more because of theheated probes and the temperature controller.

In summary, there is still a place for these low cost runnerless systemsprovided you fully understand some of their challenges and limitations.

Get Involved

Want to be an Author?

We are always looking for informative and educational articles on avariety of topics pertinent to the injection molding industry. When you attenda molding event such as a conference, exhibit, or trade show, you can shareyour experience with thousands of fellow IMD members. We feature an“On The Road” column to provide members with an opportunity tocontribute to the IMD community. New column ideas are also welcome. Ifthere’s something you’d like to see in this publication, we’d like to hearfrom you. Please email Heidi Jensen ([email protected]).


www.priamus.com


Feature Article

What You Need to Know About In-Mold Decorating and LabelingBy Al Hoeschele and Mike Ruminski, Originally published in Designfax

Applications for in-mold decorating and labeling(IMD/IML) with pre-printed film inserts continue to ex-pand since technological improvements have made it anoption for three-dimensional products with complexsurfaces. IMD/IML cuts costs and boosts quality in usesfrom automobile interior components with compoundcurves to contoured control panels on appliances and ina wide variety of consumer products. Consumer appli-cations include almost all electronic devices, medicaldevices, sports equipment, and toys to name a few.

IMD/IML is an effective alternative to hot stamping,heat transfers, pad printing, flexographic printing, directprinting, or pressure sensitive labels. It is ideal for partswith complex curves because the insert is formed to theshape of the finished product. It also has an advantagewith applications that require consistently registeredgraphics, optically clear windows, or conductive entitiessuch as RFID, antennas, and capacitive touch screens.

By integrating the graphics and conductive featuresinto the molding process, secondary operations are elimi-nated and scrap is typically greatly reduced. With pre-printed inserts in different solid colors, users may alsoavoid the need to purchase pre-colored resins. Altogether,cost savings from 5% to 40% can be realized. Insertmolding can also be considered a green process sincethe molded component is recyclable when using similarstock to injection molding resin (for example, polycarbo-nate stock to polycarbonate resin). This is especially truefor components which formally included pressure sensi-tive labels.

IMD/IML Process: Print, Form, Cut, and Mold

'Untouchable' Second SurfaceThe in-mold process begins with a screen or other

process-printed plastic sheet. Graphics can be printedon either the first or second surface of the insert's film.The "first" surface will be on the outside of the finishedpart. The "second" surface is where the insert's printedimage is viewed through the transparent film the imageis printed on. In this case, the molding resin bonds directlyto the image and the surrounding film. The transparentfilm allows the use of clear or tinted windows in theinsert. Using second-surface printing tremendously in-creases abrasion, scratch, chemical, and UV resistanceby encapsulating the graphics between the film and themolding resin.

After printing, and in many cases forming operations,the insert is die-cut to fit the mold. The die-cutting processcan be automated depending upon the size of the part,the application, and the production volume. The insertcan then be used as a flat or 3D overlay. Three dimen-sional forming involves the use of one of the followingforming methods: vacuum, thermo, hydro, pressure, orcombinations thereof. Proprietary elastic ink and coatingsystems have been developed to withstand the rigors offorming and molding.

In the molding process, the decorated insert is placedinto the cavity or onto the core of an injection mold thathas been designed for in-mold decorating. The desiredmolding resin is shot behind or over the insert, bondingits surface to the decorated insert and forming an integralfinished part.

Insert in Molding Tool


Feature Article -cont-

The durability, particularly of second-surface insertdecoration, is well beyond that of other decoratingmethods because the graphics on the insert are perma-nently embedded in the product and never exposed tothe surrounding environment. Second-surface printedIMD/IML constructions accomplish better durability forabrasion and chemical resistance based upon the sub-strate selected in the application. This contrasts with me-thods such as labeling or direct printing, in which theinks and coatings are directly exposed to various chemi-cals, dirt, human or mechanical handling, UV light, andother potential damage.

The in-mold process often produces significantly lessscrap than other methods such as adhesive labels becausethe decorated insert is shaped to fit precisely into themold so the position or registration of the graphic is highlyconsistent and permanent. During or after secondaryoperations, labels sometimes shift on a part or collectdust at their edges, making them difficult to clean. IMD/IML eliminates those concerns because the decorationis fixed on or in the part and there are no edges. IMD/IML creates a seamless appearance over 95% of the

total surface area of the molded component when theprinted construction ends within the body of the plastichousing. Thus, there are no exposed edges to trap dirtand delaminate from the plastic housing. This also enablesthe components to be cleaned with a wide variety ofchemicals depending on the resistance of the insert filmchosen. Component cleaning is particularly important inmedical applications where many antibacterial andantiviral cleaning solutions are used.

Typical IMD/IML Second-Surface Construction

www.autodesk.com



Matching Up the MaterialsThe most appropriate sheet or film materials for

printed inserts are those with higher surface energy thatwill allow stronger and more consistent ink bonding. Theseinclude polycarbonate, PET, acrylic, ABS, PVC, and PS.However, success with some lower surface energy ma-terials, as well as those that are self-lubricating, is limiteddue to interfilm adhesion issues. With proper pretreatment,PP and PE have also been successfully used in the in-mold process.

The most common molding resins used are poly-carbonate, PET, SAN, PC/ABS, PVC, nylons, ABS, PS,acrylic, PP, and PE. In general, the insert and backingresins do not have to be identical, but they must becompatible. If they are not, then a special heat-activatedadhesive must be used to ensure inter-coat adhesion.

IMD/IML does have its challenges and limitations.It is less cost-effective if the decorated area is a smallportion of the decorated surface. Up-front design consid-erations are of paramount importance for the process,including printing, forming tool, cutting tool, and injection

molding tool design. In particular, graphic locations mayneed to be printed distorted before the forming operationto allow the graphics to move into register during theforming process. While not recommended, some existingtools can be modified for IMD/IML. However, newtooling is almost always recommended.

With the correct design, film selection, and engineer-ing, IMD/IML can become your process of choice inmany applications. This process allows for cost effective-ness and a wide variety of aesthetic and functionaldesigns. In addition, in-mold decoration increases theability to recycle many components, thus reducing the

possibility of post consumer waste and stress on landfills.

Article Contributor: Serigraph is a full-service print-ing, in-mold decorating and custom graphics company,specializing in decorative, functional, and brand identitysolutions for consumer and industrial products, point ofpurchase, and promotions. The company offers a widerange of value-added services to global customers across

a variety of markets. Visit www.serigraph.com.


www.engelglobal.com/na


Feature Article

Focus on Precisionby Dipl.-Ing Michael Stricker, Dr. Georg Pillwein, and Dipl.-Ing Josef Giessauf

Injection Molding Optical Components

With above–average growth rates, optical tech-nologies can be considered as setting the pace for the21st century. However, the challenges when injectionmolding optical parts frequently differ from thoseencountered when injection molding conventional parts.In the face of international competition, the focus isshifting increasingly to innovative processing techniques.

Optical technologies are considered one of the mostpromising fields of the future. The opportunities for theplastics industry are to be found in the automatedproduction of high quality optical components in largequantities. Injection molding of such components posesgreater challenges than conventional injection molding,specifically with regard to the accuracy of surfacereplication and the level of molded-in stresses. In addi-tion, it is not unusual to have wall thicknesses as much asten times greater than those typically encountered ininjection molding. When it comes to producing high-qualityoptical parts in a cost effective manner, the conventionalinjection molding process quickly reaches its limits. Forthis reason, existing special processes undergo continualrefinement and new approaches to processing areintroduced:

· Injection compression molding is well-suited toproduce molded parts with high replicationaccuracy and low molded-in stresses.

· Multilayer injection molding can be used toincrease replication accuracy. With thick-walledparts, it is further possible to reduce cycle time.

· Variotherm mold temperature control is notlimited to improving the quality of replication ofmicro- or nano-structured surfaces.

Table 1 is an aid to deciding which process is the mostappropriate for your application. Individual processes arediscussed in greater detail in the following sections.

Injection Compression Molding: Well-EstablishedProcess, Modern Machine Technology

The injection-compression molding process has beenused for several decades to successfully mold opticalcomponents. In this process, the plastic melt is injectedinto an oversized cavity and is subsequently compressedby moving mold elements during a compression phase.

For molded parts with a large flow length/wall-thickness ratio, partial filling of the greatly oversizedcavity takes place first. In this case, the shape is notformed until the compression phase; reduced mold fillingpressure and consequently lower molded-in stresses arethe result. For thick-walled parts, it is useful to fill thecavity during the injection phase and use the compres-sion stroke to compensate for shrinkage. Compared toconventional injection molding, this process improves themolded-in stress level and replication accuracy.

Depending on the geometry of the molded part,compression may take place over the entire surface oronly over segments of the surface. To prevent the plasticsmelt from flowing into the parting line, sealing framesare often used to enclose the cavity. The necessarysealing force can be applied by spring elements orhydraulic cylinders (see figure below). Shut-off nozzlesor slides must be installed as a blocking mechanism toprevent the melt from flowing back into the injection unit.These should be positioned as close to the cavity aspossible to minimize movement of the melt and themolded-in stresses produced as a result.

In addition to mold design, the machine and controlsare essential factors in the successful production of opticalparts. Because of its similarity to the injection and holdingpressure phases, a newcomer quickly becomes familiarwith the injection compression software. In the case ofthe all-electric “e-motion” series by Engel Austria GmbH(Schwertberg, Austria), the operator interface is organizedinto the following steps: speed-controlled compressiontransfer, cavity-pressure or force-controlled compression,and position control (isochoric cooling) corresponding tothe typical process sequence.

Schematic of possible mold concepts in which the com-pression stroke is executed by the clamping unit. Left:Compression over entire surface, spring-loaded sealingframe. Right: Compression over a segment of the surface,hydraulically actuated sealing frame.



During the speed-controlled compression phase, the cavity is filled volumetrically and the melt is compressed.The operator can trigger transfer via either position, time, compression force or cavity pressure, with the compressionforce or cavity pressure profile being variable as required by the application. While the part continues to cool to thede-molding temperature, the molded-in stress level is determined primarily by the pressure gradients present and theextent of material movement. A high level of molded-in stresses adversely affects the optical characteristics oflenses, among other things, and can cause cracks to form in subsequently applied coatings.

Isochoric cooling prevents material movement and helps to reduce the molded-in stress level. The compressiongap—and therefore the volume of the cavity—is kept constant. For this reason, a position sensor is attached to themold and used for position control.

The Accuracy of Electric Injection Molding Machines

Surface replication accuracy requirements are especially high for optical components. Dimensional tolerances ofless than ± 20 μm are quite common. For this reason, all relevant machine movements must be highly accurate andrepeatable. All-electric injection molding machines are well suited for production of precision optical components,since the position sensors in the servo motors permit very high positioning accuracy in conjunction with the kinematicsof the toggle mechanism. In the course of trials to investigate repeatability, the compression gap was observed priorto the start of injection with the aid of an inductive position sensor. In the all-electric “e-motion” Series of injectionmolding machines, the variation of the gap was less than 5 μm.

In addition to its high repeatability of extremely accurate positioning, this machine line is characterized by the highdynamics of the clamping unit. These dynamics can be utilized, for instance, for thin-wall molded parts with a micro-

www.ultrapurge.com



Table 1: Aid to decision-making for processors--benefits and drawbacks of selected processing techniques comparedto conventional injection molding.

structured surface by first forming the structure through an abrupt increase in compression force and subsequentlyachieving a low molded-in stress level.

Better Replication with Variotherm Temperature Control

With variotherm mold temperature control, the surface of the cavity is heated prior to each injection cycle andthen cooled again. Compared to conventional mold temperature control, this produces a higher contact temperaturebetween the plastic and cavity wall that delays solidification of the melt. Depending on the geometry and surface ofthe molded part, this makes it possible to improve different characteristics (Table 1). In addition to fluid-basedvariotherm mold temperature control systems using water, steam, or oil, additional methods such as induction, infraredradiation, or electric resistance heating are available. Cooling generally takes place with water.

Variotherm mold temperature control permits the establishment of independent temperatures that have beenoptimized for the respective process step. During the cooling phase, the water supply temperature can be considerablylower than is normally the case with conventional mold temperature control. This makes it possible to reduce thecooling time when producing thick-walled optical parts.

In a simulation of temperature profiles to mold an 11 mm thick LED lens from PMMA with both conventionaland variotherm temperature control, a constant supply temperature of 75°C was assumed in one case, while thetemperature was varied between 125 and 25°C in the other case. In this example, the cycle time savings was 15%.



The benefits of variotherm temperature control areobvious: it improves molded part quality and can, undercertain circumstances, shorten the cycle time. Withregard to drawbacks, the relatively high investment, de-pending on the type of temperature control, and increasedenergy consumption have to be mentioned.

Improving Quality by Layers

Multi-layer injection molding—or overmolding—is aprocess still relatively new to the field of injection moldingoptical parts, which can help improve the quality of thick-

walled lenses. The processinvolves molding of a sub-strate first, and then subse-quently overmolding one ormore layers of the samematerial onto it. A machinewith a rotary table or a moldwith an indexing plate is

generally needed; a physical transfer is also possible.The major benefit of the process is that the overmoldingstep can correct or compensate for sink marks or otherflaws in the surface of the substrate. An obvious surfaceflaw was created on a lens for demonstration proposes(see inset). This lens was then overmolded with a 2 mmthick layer of plastic to show that this process can correcteven severe flaws or defects on the substrate surface.

The often-discussed question of the possible cycletime savings associated with multi-layer molding cannotbe given a generally valid answer. The potential savingsdepend largely on the part geometry, the ratio betweenthe layer thicknesses, and mold temperature conditions.

When using a rotary table, the general constraint isthat the time required for the individual steps should beas close to identical as possible. Since the substrate is incontact with both sides of the mold, while subsequentmolded layers are cooled largely from only one side, theconclusion drawn is that subsequent layers should beapproximately half as thick as the first layer. In the caseof two layers, the relationship between the layerthicknesses should be 2/3 to 1/3; in the case of threelayers, 2/4 to ¼ to ¼, etc. These relationships applyexactly only for a flat plate, but can be taken as a rule ofthumb for layer thicknesses with simple part geometries.

Ideally, each station of the rotary table should haveindependent mold temperature control. Care must betaken to ensure that the outer surfaces essential to theoptical function are temperature-controlled to satisfyquality requirements. For the inner surfaces, the supplytemperature can be lowered to reduce the cooling time.

To obtain useful information about the cooling time,a thermal simulation based on the actual part geometry

is required. Simulations were conducted under variousconstraints for a 30 mm thick, plano-convex polycarbo-nate lens. These simulations compared 1-, 2-, and 3-layermolding processes, with two variations for the three-layerapproach: The three layers can be molded in succession,or an initial substrate can be overmolded on both sidessimultaneously. It is assumed in the simulation that theinner surfaces are cooled more intensely (60 instead of90°C). Compared to molding a single-layer lens, thevarious approaches to overmolding multiple layers inconjunction with appropriate temperature control shortenthe cooling time (see figure below).

Overall, the multi-layer molding process can not onlyimprove surface quality considerably, but reduce thecooling time as well. This is mainly the case when theinner layers are cooled more intensely. For the lensinvestigated here, the possible cooling time reductionamounted to as much as 35%. The processor must, ofcourse, take the additional investment costs for the morecomplex equipment (rotary table, indexing plate, etc.)into consideration when investigating the economicviability of any particular approach.

Beneficial Process Combination

The variety of requirements that a plastic opticalcomponent must satisfy may require a combination ofseveral processes. A structured optical component thatpermits glare-free office illumination may, because of itshigh flow length/wall thickness ratio, require the use ofinjection compression molding on the one hand, while onthe other, the precision needed for the angles of the micro-pyramids can be achieved only with variotherm moldtem-perature control. This combination of processes hasbeen successfully brought to actual part production.

The outcome was positive and should encourageinjection molders: the examples presented in this articleshow that improved quality and economics are indeedcompatible with one another where optical parts areconcerned.


www.industramark.com


Durable Products – The Evolution of Grafilm® Ultraby David M. Coughlin

In today’s environment, manufacturers are constantly seeking ways to effectively brand and market their newproducts. These goods come in many shapes and sizes, requiring a variety of labeling technologies to effectivelymark the product and withstand the environment that the product faces during its life. Product labeling comes intwo distinct categories: functional (warning and informational) and decorative (brand recognition and graphics).

By definition, a durable good is a product that does not wear out quickly, typically with a useful life of threeyears or more. Durable products are often exposed to harsh conditions, such as prolonged exposure to sunlight,exposure to gasoline and other solvents, and abrasion that occurs during normal product use. Product labelingmust withstand these harsh conditions for the life of the product in order to protect the consumer from potentialhazards and promote the brand. For plastic components and products, the latest in in-mold labeling technologyoffers manufacturers of durable products an alternative to pressure sensitive labels: Grafilm® Ultra.

Durable product labels are subjected to various industry-standard tests to determine resistance to abrasions,solvents, sunlight, and other harsh conditions (see table below).

Functional Decorative

Featured Technology


Traditional in-mold labeling tech-nology utilizes varnishes and hardcoats that are prone to cracking andpeeling in durable product environ-ments. By incorporating proprietaryover-laminate construction, GrafilmUltra improves abrasion resistancewhile protecting against light fadingand failure caused by condensation.The illustration below shows theconstruction of Grafilm Ultra.

Grafilm Ultra, which marries thelatest in over-laminate technology withpatented Grafilm® micro-porousfilm, bonds to a wide variety of ther-moplastic materials. Because of themicro-porous nature of the Grafilmbase, the bond is permanent and thelabel is non-removable. There is noadhesive to fail, and the label cannotbe removed by the consumer withoutdefacing the plastic surface. Further-more, the durable over-laminate pro-tects the ink surface from various environments that durable labels face today.

Grafilm® Ultra offers an alternative to pressure sensitive labeling for durable products and offers superiorperformance for functional and decorative labels that last the life of the product. It is the latest in in-mold technology,designed specifically with the needs of durable product manufacturers in mind.

About the Author

Dave Coughlin is the Director of Operations for Industramark™, a Standard Register business unit.Coughlin joined Standard Register in 2004 and has previously held the positions of production manager,assistant plant manager, plant manager, and senior manager of Operational Excellence. He holds a bachelorof science in chemical engineering from Cleveland State University.

Featured Tech. -cont-

www.dme.net


Reprinted with permission from Kunststoffe International 6/2010

Feature Article

















Featured Technology

Does Early RetirementMake (Financial) Sensefor Unscrewing Molds?

By Alan Hickok and David Helenius

A case can now be made, both on financialreturn and technical advantages, for retiring anexisting unscrewing mold in favor of one with acollapsible core.

Unscrewing molds are usually built for many yearsof production, as they are considered a long-terminvestment for the production of millions of parts. Theseare among the most complex of all injection molds,and they require the highest amount of expertise bothto build and maintain.

Though many leading mold builders have evolvedtheir standards over the years, in general, there arestill maintenance issues such as broken rollers, dama-ged racks, water and oil leaks, dropped racks, and soforth. Add to that common part quality issues such asscuffing, ovality, flash, and grease contamination, andit’s no wonder that companies often look to a “jump-thread” approach to eliminate the issues of unscrewingmolds, or they explore collapsible cores as an alterna-tive.

Recently there’s been an evolution of thestandardization of the collapsible core approach. Thismethod is now justifying handing a pink slip to anexisting unscrewing mold—even one capable of runningfor the required years ahead—in favor of a new, fullymechanical, collapsible core tool.

A Radical Move?

Shelving or gutting an existing, functioning moldmay seem like a radical move in these conservative,cost-conscious times, but it’s exactly the desire for moreprofits that’s driving people to do the math. One cancalculate the return on rebuilding a tool, or at least onsalvaging the cavity half and rebuilding the core half,in order to gain returns that outweigh the capitalexpenditure.

For example, Mold-Rite Plastics Inc. (Plattsburgh,NY) builds and runs molds for its proprietary line ofcaps and closures. Recently it took a look at the futureof two tools with 20 years of service that still had yearsof production ahead. Rather than simply keeping thetools going indefinitely, they did the math and wereable to isolate the savings of converting to mechanical,dovetail-style collapsible cores developed by RoehrTool Corp. (Hudson, MA).

The goal for this project was to replace the existingmolds with new technology in order to gain tooling withsimpler operation, less maintenance, and shorter cycletimes. Phil Titherington, senior design engineer andtoolroom manager at Mold-Rite, learned about the DTSeries Collapsible Core from Roehr just as he wasbeginning to explore his options for replacing a 12-cavitytool to mold a 38-mm cap and a 24-cavity tool to mold a24-mm cap.

“I was looking at collapsible core options fromvarious suppliers, but when I heard about the DT Series,I sent Roehr drawings for the two projects,” explainsTitherington. “Technical support was excellent, as wewere provided info with the first mold so that we wouldlearn proper handling, disassembly, and assembly of thecores, as well as installation of the cores into the moldbase. By the time we built the second tool, everythingwent very smoothly without the need for assistance.”

The new standard product developed by Roehrconverts what would have been a complex tool to anopen/shut mold. Titherington also emphasizes the easeof mold setup, removability of the cores while the moldis in the press, and ease of maintenance. A final deter-mining factor was greaseless operation. “It’s a cleanerprocess, making it a lot less susceptible to contamination,

www.procomps.com


which is a chief concern for us on the production floor,”he says.

Calculating the savings, Mold-Rite confirms thatinvestment in new tooling using DT Core technology wasthe right move.

Maintenance Goals Surpassed

Mack Molding (Arlington, VT) recently had theopportunity to quote the replacement of two four-cavityunscrewing molds used to manufacture PVC seal nuts,roughly 1.25 and 2 inches in diameter. The older molds,which were run by another molding company, had ahistory of excessive downtime, an issue attributed to theirunscrewing cores.

Before quoting the project, Mack knew any main-tenance costs incurred within the first million cycleswould be their burden, as the OEM customer would notbe held responsible. Mack was apprehensive about build-ing the new molds using the same unscrewing methods,as the same maintenance issues could arise with the newtooling.

Rather than using flexing-steel-style collapsiblecores, stainless steel was required due to molding PVC,and Roehr was able to provide this with its DT Cores.This approach gave Mack engineers the confidence theyneeded to introduce new designs to the customer formore robust and reliable tools, and reduced exposure toextensive mold maintenance expense.

Mack selected Carlson Tool & Mfg Corp. (Cedar-burg, WI) to build the new tools, and the moldmakerfound them to be “very simple molds to design becausethey didn’t have a complex unscrewing system,” saysBrian Wagner, engineering manager at Carlson Tool. “Thesimplicity was also apparent in the mold building process.We were excited to be involved in a project that didn’thave unscrewing but gave us such a great outcome.”

Eliminating the gears, racks, and the cylinder super-structure of an unscrewing mold resulted in the use of asmaller mold base and fewer moving parts. A final reviewshowed notable gains in mold efficiency and productivityover traditional unscrewing methods.

“The OEM customer verified that part quality wasmuch improved and more consistent, thus requiring lessdestructive testing,” states Jeff White, senior accountmanager at Mack Molding. “Ease of maintenance wasalso a selling point. Because of how they are constructed,the DT Cores can even withstand welding for repairs orrevisions.”

“From a production standpoint, we have been ableto mold complex internal threads very efficiently as aresult of the collapsible cores,” says Gene Birmingham,manufacturing manager at Mack’s Cavendish, VT facil-ity. “Eliminating complex unscrewing mechanisms andadditional sequencing saves time and helps us meet ourcustomer’s production schedule.”

“The simple fact is that the math works,” states DavidFowler, president of Windspeed Inc. (St. Thomas, ON).“Cycle time is reduced and maintenance cost is lowered.”Fowler is a seasoned toolmaker with 40 years of exper-ience, and is now a consultant specializing in tool andpart design. “I’ve worked with clients using collapsiblecore technology for many years. The benefits of a simplermold design, faster sequence, and less stress on the partitself results in increased profits for the molder.”

Roehr says this new approach also allows for remov-ing the entire core stack while the mold is in the press—impossible with rack and gear systems. This factoralone—eliminating an unscheduled mold pull andincreasing cavity utilization—can drive the decision toretire an existing unscrewing tool.

About the Authors

Alan Hickok is Midwest and OEM sales managerwith mold component supplier Progressive Com-ponents. David Helenius is engineering manager atsister company Roehr Tool.

Featured Technology -cont-


IMD Best Paper

Methodology for Evaluating Warpage Sensitivityof Plastic Materials

Brian A. Young, Penn State Erie, the Behrend College. Erie, PAJohn P. Beaumont, Penn State Erie, the Behrend College. Erie, PA

Zachary T. Stefanik, Penn State Erie, the Behrend College. Erie, PA

Abstract

This paper presents research related to the deve-lopment of a methodology for evaluating the sensitivityof a given plastic material to warpage. The methodologyrates a material’s sensitivity to warpage from each ofthree different criteria: thermal, orientation, and process.The study found that two test geometries could be usedto determine the three warp indices. For the materialstested, on average, orientation-induced warpage was morethan double that of process-induced warpage. Fiber rein-forcements and part thickness had a significant influenceon all three of the warp indices.

Introduction

The successful development of injection moldedplastic parts presents a significant challenge to bothdesigners and manufacturers. Of particular challengeis the production of a plastic part to a specified size andshape. At the core of the problem is the complex inter-action of material, process, part design, and tool designto the shrinkage and warpage of a molded part. Thoughmethods have been developed for characterizing theshrinkage of plastics, including ASTM D955, nothingexists to characterize a material’s sensitivity to warpage.

This paper is the first part of an ongoing study thatevaluates a method for determining the relative sensitivityof a plastic material to warp. The method characterizeswarpage sensitivity into three criteria: orientation-induced,thermal-induced, and process-induced warpage. This in-formation should provide valuable assistance to part de-signers, mold designers, and molders, as well as part costestimators.

Theory and Background

Understanding part warpage requires one to recognizethe complex interaction between material, part design,mold design, and process and their combined effect on thepart. These interactions are some of the most complexof all manufacturing methods. In an attempt to developa warp index one must first establish a fundamentalunderstanding of the factors that influence part warp-age. A test then must be designed that evaluates thematerial’s warpage potential relative to factors that have

the most value to the successful development of the plasticpart. It is also important that the test not be overly complexand expensive to conduct. In doing this, it should berecognized that not all factors affecting warpage can becaptured.

Essentially, warpage results from variations inshrinkage within the same part and the ability of thematerial and part’s structure to resist the resultant stresses.These variations in shrinkage can occur on one side of apart’s wall versus the other side, from one direction acrossa wall versus another, and from one region of a part versusanother region. Some of the more common issuesrecognized to influence these shrinkage variations thatcause warpage include variations in mold cooling (sideto side or region to region), variations in wall thickness,and filling pattern as established by gate location andpart geometry. The amount of the actual warpage within agiven part will be dependant on the magnitude of theresidual stresses developed from the differential shrink-ages and the structural ability of the part geometry andmaterial’s modulus to resist them.

The test method introduced here focuses on isolatingthe effects of thermal variations and flow pattern. Thermaleffects are most important to the mold designer andcapture not only issues related to mold cooling but alsosome aspects of the material’s sensitivity to warp fromwall thickness variations. Flow patterns establish thedirection of orientation for both the polymer and anyasymmetrically shaped additive. Orientation can have adramatic effect on part warpage and is important tounderstand when establishing gating locations in a mold.

As warpage results from variations in shrinkage, afoundation in understanding shrinkage is presented here.Shrinkage of thermoplastics can be characterized into twobroad classifications: volumetric and linearized.

Volumetric Shrinkage:

Volumetric shrinkage in a plastic part is most directlyinfluenced by temperature and pressure as demon-strated in a P-V-T graph (see Figure 1). Temperatureeffects can be attributed to thermal contractions whichoccur in all polymers, and to crystallization which occurs insemi-crystalline polymers. In the absence of any externalforces, this shrinkage will be isotropic. Pressure effects


IMD Best Paper -cont-

are due to the compressibility of the melt. However, from

a molding standpoint, pressure effects are related to thepacking or hold phase of the molding cycle. Here amolder is actually feeding in additional material tocompensate for the thermal contraction and crystallization

contraction that is happening in the polymer.To characterize a material’s sensitivity to warpage,

the test procedure must include provisions for variationsin temperature and pressure within the same part atthe same time. One method of evaluating the effects oftemperature is to vary the mold’s temperature from oneside of a part’s surface to the other. The warmer halfwill go through more thermal contractions than thecooler side. The side to side differences in thermal con-traction will be compounded with a semi-crystalline ma-terial as the differences in cooling rate will affect thedegree of crystallization and therefore its relative shrink-age.

A simple 25 mm by 127 mm plaque of constant wallthickness was selected for this study to characterizewarpage due to thermal variations. The part is fed by a25 mm wide fan gate feeding the part from one of the25 mm wide edges. This part geometry and gatingwill result in near ideal linear flow thereby avoiding thedevelopment of orientation-induced stresses. If thisparts is molded across the x-z parting plane of a mold,and its top surface (positive y direction) is warmerthan its bottom surface (negative y direction), higher thermalcontraction and crystallization on the top surface willcreate stress that will warp the edges of the part upwardinto the shape of a smile (see Figure 2).

Figure 1: Characteristic PVT graph of a semi-crystallinematerial.

Linearized Shrinkage:

Linearized shrinkage results from shear and ex-tensional forces that act on a flowing polymer and itsadditives. These forces occur during both the fill andcompensation (packing) phase of a molding cycle.These forces cause the polymer to be oriented in thedirection of the principle strain. This orientation in the polymeris an unnatural high energy state from which the materialwants to relax. The resultant entropic elasticity will causethe material to shrink differently dependant on the directionand magnitude of the orientation. It is more common thata neat polymer will have higher shrinkages in the directionof the polymer orientation. However this is not alwaysthe case. If the polymer contains an additive with ahigh aspect ratio, such as glass fiber, the particle willbecome oriented in the same direction as the polymer.These oriented additives can have a significant effecton the resultant shrinkage. Not only will they nearlyalways cause a polymer to shrink more in the transverseto orientation direction, but they will result in much moredramatic anisotropic shrinkage characteristics than a neatpolymer. Where as anisotropic shrinkages of neat ma-terials are rarely more than 1.2:1, anisotropic shrink-ages in glass-fiber-filled materials have been reportedto be as high as 18:1 (1).

Shear forces act to orient a polymer in the direction ofthe flow. Figure 3 illustrates the characteristic shearstress and shear rate distribution across a flow channel.Note that shear affects are highest near the flow channelwall and drop to zero in the middle of the channel.

Figure 2: Example warpage in a plaque exhibiting linear flow.

Figure 3: Characteristic shear stress and shear rate distribu-tion across a flow channel.


With pure linear flow that would result in a fan-gatedrectangular flat plaque, except at the flow front wherethere are only shear stresses acting on the polymer. Theseshear stresses are unidirectional along the length of thepart. Therefore polymer and filler orientation will onlybe in the length direction of the part. The magnitude ofpolymer orientation will vary through the thickness as aresult of the diminishing shear stress and the longer, slow-er cooling rate. The magnitude of the polymer orientationwill also vary with the magnitude of the shear stresswhich is influenced primarily by wall thickness, but alsomelt temperature and fill speed.

In addition to shear forces, extensional forces willact to orient a polymer and any additives. Extensionalforces result in a tensile strain on the material and willexist in both diverging and converging flow geometries.In a converging geometry, extensional forces will act toorient the polymer in the direction of the flow. In a diverg-ing geometry they will act to orient the polymer transverseto the flow (2).

To characterize a material’s potential to warp fromorientation, a half disk was chosen. Gating the flat partmid way along the straight edge of the half disk will resultin a pure radial flow pattern. This radial flow patterncreates 180 degrees of variation in shear induced orien-tation and maximizes the melts diverging extensional floweffect on the orientation.

Warpage Potential:

As stated earlier, warpage of a plastic part resultsfrom variations in shrinkage that create a residual stressand the inability of the material and the part’s structureto resist these stresses. If there were no variations inshrinkage, there would be no stress and therefore nowarpage. The variations in shrinkage must also createstrains that create conflict within a given part in order tocreate a stress. For example, in a pure linear flow that wouldbe approximated by flow across a long flat plaque, mole-cular orientation would be unidirectional along the lengthof the part. Here there is maximum potential for shrinkagedifference in flow versus transverse to the flow direction.Despite this situation where maximum potential aniso-tropic shrinkage would exist, the shrinkage variations areat 90 degrees to each other and thereby are not in conflict.Therefore, despite the extreme variation in shrinkage,orientation-induced warpage is minimized.

In addition to the development of varying strains andstresses within a part, the part’s actual warpage will alsobe influenced by the rigidity of the material and the part’sstructure. As a high modulus material will resist deflection

more than a low modulus material, so will the high modulusmaterial warp less from the residual stresses developedfrom variations in shrinkage.

The final component to warpage is the part’s struc-ture. A flat part provides little rigidity when contrasted tostructural shapes such as I beams, domes, and cylinders.This is a part design property and is independent of thematerial’s property that is being characterized in thispaper. Test samples are flat in order to minimize theirpotential to resist warpage.

Test Geometries, Gating, and Runners:

As stated earlier, two basic shapes were selectedfor this test. Each of these was molded in two differentwall thicknesses. For the purpose of characterizing amaterial’s potential for warpage, a flat rectangular plaqueand a flat half disk were chosen. The 25 mm x 100 mmflat plaque is gated along one edge with a fan gate. Thisprovides for a near ideal linear flow. As discussed earlier,this part should not warp as a result of orientationaleffects. Therefore, the part provides for the isolation ofthermal effects on shrinkage by cooling one side different-ly than the other (top versus bottom cooling). Sampleswere molded at 1 mm and 3 mm wall thicknesses.

A flat half disk is used for the orientation and processinduced warp studies. The half disk has a 63.5 mm radiuswith a 127 mm straight edge. The half disk part is edgegated midway along its straight edge. This shape andgate location provides for a nearly pure radial flow result-ing in contrasting shear and extensionally inducedorientation effects. Additionally, these effects will varyalong the flow length. Near the gate, shear forces willclearly be more dominate over extensional forces. Asflow diverges from the gate region, shear rates continuallydecrease and allow extensional forces to play a greaterrole in the polymer orientation. In a case where trans-verse to flow orientation is dominate, as would happenwith a fiber-filled material, the part would tend to warpin a bowl shape. If the flow direction shrinkage is dominatethe part will tend to twist while it attempts to decreaseits radial length relative relative to its circumferentiallength. Parts were molded with a 1 mm and 2 mm wallthickness. The variations in wall thickness will also providea contrast of shear stress effects. The thinner part willaccentuate shear induced orientation.

Both the fan and common edge gate are lapped tominimize potential for jetting. The gates are 1.6 and 3.2mm, respectively. The runners are parabolic, having a1.6 mm radius, 3.2 mm depth, and 10 degree draft perside.




Materials

The following four materials were selected fortesting: neat polypropylene, 25 % talc-filled polypropylene,30% glass-fiber-filled polypropylene, and neat ABS.

The neat ABS and polypropylene were selectedto contrast the behavior of a low shrinkage, amorphousmaterial with a high shrinkage, semi-crystalline material.The talc and glass fiber were evaluated to contrast the impactof a filler with a high aspect ratio (glass fiber) and a fillerwithout a high aspect ratio (talc).

Procedure

Two part geometries described earlier were usedfor this study. The thermal warp studies utilized a 25 by127 mm flat strip. Samples were run at two thicknesses, 1mm and 3 mm. The orientation warp samples utilized theflat half disk. Parts were molded in 1 and 2 mm thicknesses.

An optimum process was established for each of thematerials, part geometries, and wall thicknesses (sixteentotal). The optimum process utilized a two stage process todetermine injection speed and VP (velocity/position)switchover (3). Pack pressure was 2/3 between thepressure at just fill and the pressure when the parts beganto flash. Pack time was gate freeze plus three seconds.Twelve samples were collected for each of the sixteencombinations. These were then suspended from theirrunner on a string in midair so that there were no exteriorstorage influences on part warpage. After the parts wereconditioned for 72 hours, they were measured to deter-mine the warpage.

Thermal warp samples were molded using theoptimum process described above; however, side to sidemold temperatures were varied according to Table 1. Highand low temperatures were targeted to be around +/- 19C of the optimum process mold temperatures. Twelvesamples were saved for each of the four new mold temp-erature variations for each of the materials at the twodifferent part thicknesses (total of 32 additional runs).The parts were suspended in midair for 72 hours andthen measured for warpage.

After the two-stage process was established, a sixfactor Taguchi analysis was performed on each of the

sixteen combinations of material, geometry, and wallthickness (four materials, each molded with the two testgeometries and two wall thicknesses). The process vari-ables used in the Taguchi analysis were based aroundthe optimum process and included melt temperature, cycletime, packing pressure, injection velocity, mold temper-ature, and storage method. For each of the 128 runs (16combinations of material, geometry, and wall thicknesstimes the eight runs required for the Taguchi analysis),twelve parts were collected. The storage method for theTaguchi method consisted of a high value designated byhanging the molded parts from a string to isolate the partsfrom any factors that could influence the cooling andshrinkage and a low value which consisted of laying themolded parts ejector face up on a metal table for a periodof an hour before being stored in bulk fashion. After theparts were conditioned for 72 hours, each sample wasmeasured to determine the warpage.

Part warpage was measured with an optical com-parator. Thermal warp test samples were placed on athree post test fixture. The three posts were the sameheight and consisted of 3 mm diameter pins having a 1.5mm radiused tip. The three mounting posts provided aplatform on which the samples would not rock and pro-vided clear vision for inspection. Warpage was measuredas the maximum warpage relative to the tops of the pins(see Figure 4).

Orientation warp test samples were placed on a secondthree post test fixture. The fixture was similar to the

Table 1: Matrix of mold temperature variation used to evaluatesensitivity to thermal variations.

Figure 4: Linear flow test fixture used for measuring thermal-induced warpage.

thermal warp test fixture except that the third support postwas placed as shown in Figure 5. Warpage was measur-edby first positioning the sample such that the two highestvertical positions on the part were along the same hori-zontal plane. Warpage was then determined by taking thedifference between this plane and the lowest point on thewarped part and then subtracting the wall thickness.



Warp Index:

A warp index (WI) was determined rather thanproviding a measured warpage. The WI establishes avalue that factors in part size. It is then multiplied by 100in order to express the unit/unit as a percentage. Thepercentage expression provides a value that is inde-pendent of units and increases the scale of the final value.

Figure 5: Radial flow test fixture used to measure orienta-tional and process-induced warpage.

A separate WI value was established for thermalsensitivity, orientation sensitivity, and process sensitivity.Warp index values are provided for both wall thicknesses.

Results

The results of the warp studies are summarized inTables 2 and 3. Table 2 contains the results for the thermalstudies and Table 3 contains the results of both theorientation and process warp studies. Within the tables,the four test materials are identified. From left to right inTable 2, the low and high thermal warpage is shown.The Delta column is the difference between the low andhigh thermal warpage and then the calculated warp indexis given. The low and high thermal warpage are theaverage values found from the two contrasting moldtemperature conditions shown in rows 4 and 5 in Table1. These are the two most extreme contrasting variationsin mold temperature. Thermal warp index (WIT) is cal-culated as:

Table 3 provides data for both orientation and pro-cess induced warpage. Again each material is identi-fied. Each material has two rows of data. Range desig-nates the range of warpage that was measured foreach of the eight runs within the Taguchi analysis (firsttwo columns) followed by a Delta column which is thedifference between this range. The Opt row is the averagewarpage found in the samples run at the optimum pro-cess. The orientation warp index (WIO ) is found as:

The process warp index is based on the Delta columnand is calculated as:

The thermal studies found that all four of the thinnersamples were more sensitive to warpage than the thickersamples. The thin sample had a WI ranging from 0.08to 1.48 whereas the thicker samples ranged from 0.04to 1.08. The average WI of all of the thicker sampleswas 0.61% of the thinner samples. The ABS was theleast sensitive to thermal warpage where the WI of the thinand thick samples averaged less than 6% of the average ofthe neat PP. The talc-filled samples averaged about 10%higher than the neat PP, and the glass-filled PP was onlyabout 12% of the neat PP.

For the orientation-induced warp studies it was foundthat all of the thin polypropylene samples were muchmore prone to warpage than the thicker samples. Hereorientation induced warpage ranged from 0.26 to 4.82whereas the thicker samples ranged from only 0.16to 1.08. The average orientation-induced WI of all ofthe thicker samples was less than 23% of the thinnersamples. By far the most sensitive material to orientationwas the glass-fiber-filled material with a WI of 4.82.This was almost three times more sensitive than the neatand talc-filled PP. The ABS showed very little sensitivityto orientation in both the thin and thick samples whereWI was only 0.04 and 0.06, respectively.

For the process-induced WI it was also found thatthe thin samples were again much more sensitive towarpage than the thick samples. With the PP thedifferences averaged over 300%. The thin samplesprocess-induced WI ranged from 1.96 to 2.54 whereasthe thicker samples ranged from 0.18 to 1.02. The thin ABSsamples also had a higher WI than the thick samples but


both the WI value and the difference in values was fairlylow. The average ABS WI was only about 20% of theaverage of all of the PP samples.

A summary of the relationship of material, partthickness, and the three warp indices can be seen inFigure 6.

Discussion

The three warp criteria evaluated here each provideunique information relative to the performance of a givenmaterial. This could not be achieved with a single test.Each piece––thermal, orientation, and process sensitivity––provides value that can be used to help avoid, diagnose,and troubleshoot warpage-related problems.

The warp index establishes a relative scale factor-ing in warpage and part size. This helps scale the warp-age as a large part would be expected to warp morethan a small part. Multiplying the ratio of warp to partdimension by 100 gives a percentage which is inde-pendent of units (SI or English units will provide thesame results). In this study, the thermal-induced WI isin the range of 0.04 to 1.48 whereas the orientation-induced WI showed much more variation, ranging from0.04 to 4.82. The process-induced WI ranged from 0.18to 2.0.

The two part geometries used for this study allow forthe separation of thermal- and orientation-inducedwarpage. The 25 mm by 127 mm fan-gated strip providesfor a pure linear flow pattern that minimizes orientation as acontributing factor in the warpage. The edge-gated 67.5

Figure 6: Contrast of warp index based on thermal, orienta-tion, and process effects.

Figure 7: Contrast of process-induced warp index showingthe thin radial flow geometry having the most influence.

mm radius half disk results in a contrasting pure radialflow pattern. This causes extreme variations in shear andextensional effects, thereby maximizing orientation-induced warp. This is particularly true with thin radialflow samples where shear-induced orientation is mostacute.

Process induced variations were reviewed for bothlinear and radial flow geometries. These were basedon the eight runs used for the six factor Taguchi analysis.The results are summarized in Figure 7. Here themaximum variations in warpage for each of the sixteenvariations of material, part geometry, and wall thicknessare contrasted. Process variations had a dominate effect inthe thin radial flow geometry with all of the materialsexcept the ABS. The PP materials were 300% to 400%more sensitive to process-induced warp in the thin radialflow geometry than either of the thin or thick linear flowgeometries. With ABS, there was relatively little variationregardless of part geometry or thickness.

Thermal and orientation warp index tests revealedthat the radial flow mold provided a geometry that wasmost affected by process variation. As a result, this partgeometry was used to evaluate the process warp index.Unlike the thermal and orientation warp index, the processwarp index must contrast a variety of processes to pro-vide a meaningful value. In order to minimize the cost ofdetermining WI, it is suggested that with futureapplications the process WI be based only on the thin ra-



dial flow geometry as it most sensitive to process vari-ations.

The neat PP was found to be from fifteen to nearlytwenty times more sensitive to thermal induced warp-age as the ABS. This can be expected as PP is a highershrinkage material and therefore has a higher potentialto warp. In addition, the PP has a lower modulus and istherefore more able to deflect as a result of a residualstress. The addition of glass fiber to the PP significantlyreduced its thermally induced warpage. This might beexpected as fiber reinforcement will both decreaseoverall shrinkage and provide more rigidity to thematerial. Both of these will reduce the opportunity forthe part to warp from thermally induced stresses. Asexpected, it was also found that the thinner samples warpedmore than the thick samples. This should occur due to themoment of inertia of the thinner part being less than thethicker part and thereby less able to resist the stressesdeveloped from differential cooling.

Orientation-induced warpage was most dramaticwith the fiber-filled PP. This was expected due to thesignificant anisotropic shrinkage that results from fiber-filled materials.

This study builds on the experience of previousstudies supervised by Beaumont (4-5) where the conceptof a warp index was explored. This study expands theexperimental base with significantly more variables,replaces the concept of a WI scale of 10 to 1, introducesa process WI, and improves on previous warp measure-ment methods.

One of the major challenges to developing a practicalwarp index is minimizing the cost in man hours andmachine time. This paper presents a portion of a moreextensive study that not only examines development of aWI but examines what data is needed and how to obtain itat the least cost. Future work makes use of Taguchiruns to help determine the most direct path to obtainingthe required test data.

Further studies will also expand on part thicknessissues. Though the thinner 1 mm samples provide desir-able information, some higher viscosity plastic materialsmay not be able to fill the mold cavities. Additional studiesalso need to further evaluate and streamline the methodof measuring the warped samples.

Interpreting Warp Index for Application:

The practical application of the WI values wouldcome from a mold designer, part designer, processor, andeven a cost estimator. The data summarized in Figure 6would indicate that a mold designer should be somewhatconcerned with providing uniform mold cooling, regard-

less of wall thickness, if molding a neat or talc-filledPP part. In contrast, the designer can be less concerned ifthe molded part were to be made from a fiber-filled PP orneat ABS. This may allow the designer to focus on otherdesign issues with the mold that might have otherwisebeen compromised. This could include improved ejection.

When determining gate placement in a thin walledpart to be molded with any of the PP materials, thedesigner should be cautious to select a location that willminimize the creation of radial flow patterns. Ideally thegate would be placed on one end of the part allowing thematerial to establish a more linear flow pattern. Thisshould be an acute concern if the part is to be molded withfiber-filled PP. Even a thicker walled part should be ofconcern with the fiber-filled PP. However, as with moldcooling, there should be much less of a concern withgating location if the part is to be molded with neatABS. This would allow the molder to focus on a gatinglocation that might be more strategically placed to addressissues such as weld line placement, gate blush, pressure tofill, and clamp tonnage.

Overall, there should be much less of a concern re-garding thermal- or orientation-induced warpage with theABS than with the other materials. In addition to the lowpotential of warp, as indicated by the low thermal- andorientation-induced WI, the higher relative process-induc-ed WI indicates that there should be a reasonable oppor-tunity to modify any nondesirable warpage through pro-cessing.

With all three PP materials it follows that whereorientation-induced warpage is high in the thin parts, theprocess sensitivity is also relatively high. Where orienta-tion-induced warpage is low in the thicker parts, processsensitivity is also low. Though this trend is consistent, itcan be seen that the process sensitivity with the fiber-filledPP does not come close to keeping pace with the orienta-tion-induced warpage.

Process-induced warpage may be found to be botha gift and a curse. A material whose process-inducedwarpage is high has a chance to influence warpage andthereby potentially correct a nondesirable warp. However,it is also an indicator that the part may drift in and out ofdimensional specifications with subtle changes in processthat may occur from day to day.

Conclusions

The concept of a warp index is explored that couldsignificantly improve the knowledge base provided todesigners and molders. This information would improvetheir ability to focus their design decisions on the mostcritical aspects of the mold.



Three warp criteria are evaluated and shown to provide uniquely different information that could not be capturedwith a single test. The three criteria are thermal, orientation, and process-induced warpage. In particular is the contrastin thermal, orientation, and process-induced warpage influences found in the glass-fiber-filled PP. In this case,sensitivity to warpage from flow-induced warpage is nearly 30 times higher than from a mold’s thermal variations and3 times higher than from process variations.

This study found that two simple part geometries could be used to determine three different warpageindices. A relatively simple and low cost method was used to measure the warpage.

Future studies will focus on how to streamline the process for determining the three warp indices. These studieswill include evaluating the Taguchi analysis results to determine what the most significant variables are and streamliningthe tests around these. A broader range of materials will be tested and application of the resultant WI data applied toactual industrial design and process applications.

References

1. J. A. Doolittle, “Effects of Glass Fibers on Shrinkage of Molded Parts,” ANTEC.2. J.P. Beaumont, R. Nagle, R. Sherman. “Successful Injection Molding,” pg. 35.3. J.P. Beaumont, “Runner and Gating Design Handbook,” 2nd Edition, Hanser Publishers, Chapter 15.3,

by B.G. Johnson.4. R. Seyler, A. Schenck, “Warpage Index Based On Cooling And Orientational Effects,” ANTEC 2003.5. M. McMeans, B. Bogdanski, and P. Bogdanski, “Warpage Index for Mold Designers and CAE Analysis,”

ANTEC 2001.



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New Members

Juan Jose AguirreSungjoon AhnNaci AlpuganEmmanuel P. AnchetaMike AndersonJohn R. AnselmiMark AppletonJohn ArgitisMansour AshtianiMark AtchisonSamy M. AwadJeff L. BakerJonathan BakerNancy BarrieMarty BellBrandon S. BellisAnurag BhatnagarLeslie E. BigottKlaus BindczusGregory S. BowesTrent BowlingJeremy BraatenJason BraithwaiteDouglas E. BreitenfeldJean-Francois BrousseauChad BrownBrent BrownRoberto Cesar BuiocchiPhillip A. BurnCraig E. CaldwellCarl CarlsonAntonio J. CarrilloJohnny CarrollJen-An Chang PhDFelix ChangJose ChavezSteven ChickoskyAlzir ChoquetJoanna ClarkRobert C. CollinsDuncan H. CooperTimothy F. CostiganBrian CoucheyPhil CoutureMartine CrispoEttore DaddiSavanna DaleyRachel DaleyLuis De JesusStanley S. De LeonGenis I. De TeraLindsey M. DelaneyJohn Denkler

Russ DibbleCurtis DillavouTravis DillavouGuillermo D. DobaranJoe DoughertyClifford E. DrakeTom ElkingtonIssac EmmanuelChristopher C. EschMark EthridgeCory J. FalconaPaul FletcherDustin FlockJames FlogausEmilio FloresHelene ForguesDonald P. FreierVincent GalloZiad GhannoumAlbert Lim How GheeLott GloverMorgan GolabowskiElizabeth GrimesMartin GroenKevin HagerSoebekti HambaliShane HarrisJerry HaskinChuck HeadrickCesar HernandezThomas R. HillCraig A. HuegelRishad IsmailRamesh S. IyerAaron JohnsonAchim KammerPaul KaneJames KegelmanIn KimDavid G. KinghornRoderick E. KleissAldo V. KremmelRoger KreseScott P. KuehnShivani S. KumarNeil LachapelleChris LandauerByung Hak LeeW. Douglas Lilac PhDRaul LlopisMehrdad Maddahali Sr.Jean-Christophe Magnan

Allan MalcolmJoseph A. MantiaYvan MarcouxRick A. MartinBrent MartzGrant MathisonBen J. MauloricoGreg McConougheyJoseph P. McFaddenRick McKeldinCrisg McKinnonJames N. McKirahanPankaj S. MehtaVivek K. MehtaMike MichalskiCharles MiddelaerDavid MillerTravis MinyardJoseph MitchellJorge Luiz MorillaAngelo S. MoronesoAmelie NormandeauLouis NotarianniMehdi OubahmaneJoby V. P.Douglas D. PagoriaHarry C. ParayKamran ParizadHyung-Pil ParkHoward PatzkowskyMark PeaseJoe A. PeckDarrin W. PelleyXie PengchengEric PetersonAbraham PineiraDan J. PlafcanGuy PlourdeJonathan D. PoelDonald Deane PopmaVarsha K. PrasadLucas PretteMichael PughRick QuinnDeepak RajkumarJoe RennerTherese RiestererGuntur RotuaBrandon C. RoyGene A, RuppFrancis SamsonEdgar Sanchez

Mark S. SankovitchJohan A. SchimmelWendelin SchmidtRandolph L. SchmittelKurt SchuepbachScot SchumacherJeffrey SenichDhaval V. ShahSeth R. ShepardRobert SherriffRon P. SherringPranav SinghJohn SkubonJonathan SmalleyClarence J. SmallsPhilip M. SmithSally Ann SpencerKhantapoat SrisathitChristo Stamboulides PhDLarry StantonMatthew K. SudakDnyaneshwar P. SuleDaniel m. SwantnerHaruo TagaXP TanJim TaylorKevin ThortsenJosh j. ThurkettleMichael d. TongJ. Stephen TrappRubens TraviTim UhrmeisterRicardo VallejosDick H. Van De WeteringMaricela VenturaRonald VitarelliMark VliemChris WardSharon WeinelJason WerginzMichael Richard WilliamsBob WilliamsRichard WilliamsMichael WilliamsMitch A. WillisStephen E. WilsonLei XieTom YorioMac ZafarAlexandre Magalhaes Zarzar


The IMD also welcomes 193 companies and organizations that haverecently expanded their membership in the Injection Molding Division

New Companies

The IMD also welcomes members and companies from these countries

ArgentinaAustraliaBrazilCanadaEgyptFranceGermanyHong Kong

IndiaIndonesiaIranItalyJapanKoreaMalaysiaMexico

NetherlandsNew ZealandPeoples Republic ofChinaPeruPhilippinesSpain

Sri LankaSwitzerlandTaiwanThailandTurkeyUnited KingdomU.S.A.

3M Co.ABA-PGTAegis Worldwide LLCAG Geophysical Products IncAir Vent Inc.Alcon LabsAlexandria Co. for Industrial

PackagesAMA PlasticsAmerichem Inc.AMWAY Corp.Aptar Food & BeverageArihant Gold Plast P LtdArkema Inc.Asahi Kasei PlasticsAstra PlasticsAutodeskAutotravi Borrachas e Plasticos

Ltda.Avon Products IncBarretteBaxter Healthcare Corp.Bayer MaterialScience Pvt.

Ltd.Beijing U. of Chemical Tech.Bel Art Products Inc.Bemis Manufacturing Co.Bender Plastics Inc.Boston Scientific Corp.Bowles Fluidics Corp.Business International Ltd.C&J Industries IncorporatedCBS Molds Co.Centro Español de PlásticosCereplast Inc.Chevron Phillips ChemicalChung Yuan Christian U.Corning IncCraig Caldwell ConsultingDelhi CollegeDelstar Inc.DuPont Co.EAS Mold and Die Change

Systems Inc.

Eastman Chemical Co.Efficient EngineeringElka Industries IncEmerson Industrial

AutomationEMS Grivory AmericaEngel MachineryEntegris Corp.Envirotech Molded ProductsEppendorf ManufacturingEthridge Plastics Inc.Farapolymer Co.FAST HoustonFerris State U.Ferro Specialty PlasticsFosta-Tek OpticsG&D consultingG&F Industries Inc.Global Packaging

Optimization LLCGM Consulting LLCGreat Lakes Media

TechnologyHalkey RobertsHusky Injection Molding

SystemsInstitute of Polymer

Materials and PlasticsEngineering

Interpower Corp.Inverness Medical

InternationalINVISTAIPL Inc.Iran PlastItem Industries Ltd.Johnson & Johnson Vision

Care Inc.Kangan InstituteKIS International SrlKleiss Gears Inc.Kohler Co.Kraiburg TPEKS Engineering GmbH

Kuka Produtos Infantis LtdaLavelleLighthouse for the Blind Inc.Linflex Plastics LtdLS MtronLS Polymer TechnologyM Holland Co.M. Vliem & Associates LLCMahanakorn U. of Tech.Martogg & CoMayfair Plastics Inc.McFadden CAE ServicesMecaplast do BrasilMerck Inc.Micro Plastics Inc.Milsi Plastics IncMitsui Plastics Inc.MMI Engineered SolutionsMoldworx LLCMXL Industries Inc.Natech Plastics Inc.Neaton Auto ProductsNorth Carolina A&TNypla Ind’l Ltd. of USANypro Inc.Odesa PolymerPacific Market InternationalPamolsaPandrol USAParkway ProductsPenn. State U.Pittsfield Plastics

EngineeringPlastic Injection MoldersPlasticos Tecnicos

MexicanosPlastiques Appalaches Inc.Pliant PlasticsPolaris IndustriesPOM WonderfulPrecise Mold & Engr. Inc.Priamus Systems

TechnologiesProgressive International

PT DynaplastPTI Engineered Plastics Inc.R&D Plastics LLCRich Products Corp.RTP Co.RWTH AachenSamsung Electronics Co. Ltd.SamtecSanchez Plastics Equip. LLCSchneider ElectricSeeley InternationalSeeley International Pty. Ltd.Servtech PlasticsShop Vac Corp.SiemensSign LettersSmaK Plastics Inc.SMC Ltd.Solegear Bioplastics Inc.Sonoco ProductsStarplex ScientificStone Plastics and Mfg., Inc.StormtechSuburban Plastics Inc.SugitySunbelt Plastics Inc.TakataTalbot Technologies Ltd.Teck See Plastic Group of

CompaniesTehcna Manufacturing IncThortsen MagneticsTicona PolymersToro Co.Total Petrochemicals USAU. Wisconsin-StoutValvic II LLCVenture Plastics Inc.Viking PlasticsVisteonWashington Penn PlasticsWhiteline Industries Colombo

(Pvt.) Ltd.Zirc Corp.


Membership Application

http://www.4spe.org/membership/membership-application


Chris LaceyPublisher

1513 University Ave.Madison, WI 53523T: 608-263-5963F: [email protected]

Dear Readers,

I hope you’ve enjoyedthe winter edition of the SPEIMD publication. With arti-cles on injection compressionmolding, as well as variousfeatured technologies, wehope this issue has been es-pecially informative.

As announced in thesummer edition, this is my lastissue as editor and publisher.I have greatly enjoyed work-ing with all of the IMD mem-

AUTODESK 8www.Autodesk.com

D-M-E 17www.DME.net

ENGEL 10www.EngelGlobal.com/na

INCOE 4www.Incoe.com

INDUSTRAMARK 15www.Industramark.com

PRIAMUS 6www.Priamus.com

PROCESS & DESIGN TECH. 5www.ProcessDesignTech.com

PROGRESSIVE COMPONENTS 24www.ProComps.com

ULTRA PURGE fromMOULDS PLUS INTERNATIONAL 12www.UltraPurge.com

XALOY 3www.Xaloy.com

Sponsors Publisher’s Message

Become A Sponsor Today

The Injection Molding Division publication is issued threetimes a year to more than 5000 members worldwide.

SPONSOR’S FEE SCHEDULE

1 page $3,300/yr.1/2 page $1,900/yr.1/3 page $1,260/yr.1/4 page $960/yr.1/10 page $350/yr.

ISSUE DEADLINES

Spring Issue: February 1, 2011

AD SIZE (W X H in inches)

1/10 page: business card1/4 page std: 3-3/8 by 4-7/81/4 page horiz.: 4-3/4 by 3-1/41/3 page square: 4-3/4 by 4-3/41/3 page vertical: 2-1/4 by 101/2 page horiz.: 7 by 4-7/81/2 page isl.: 4-3/4 by 7Full page: 7 by 10

For information please contact :

Heidi Jensen, 908-797-1968

[email protected]

Sponsorship Opportunities

bers, sponsors, and board members .

I am pleased to announce that Heidi Jensen willsucceed me as publisher. She has an extensivebackground in publishing for industry professionalsand is looking forward to working with InjectionMolding Division members and sponsors. You canreach Heidi at 908-797-1968 or via email [email protected].

As always, we invite you to take advantage ofour sponsorship opportunities. Our readership iscomposed of individuals just like YOU who areinvolved in all aspects of injection molding. It’s agreat way to reach your target audience!

www.autodesk.com

www.dme.net

www.engelglobal.com/na

www.incoe.com

www.industramark.com

www.priamus.com

www.processdesigntech.com

www.procomps.com

www.ultrapurge.com

www.xaloy.com

Documents

IN THIS ISSUE - s3.amazonaws.coms3.amazonaws.com/rdcms-spe/files/production/public/FileDownloads/... · Fall 2010 Page 2 SPE Injection Molding Division IMD Leadership DIVISION OFFICERS