16 Rubber & Plastics News • January 27, 2003 www.rubbernews.com

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Technical

Fig. 1. A shot of the existing design.

Software aids design of rubber automotive partsExecutive summary

Special purpose seal software is helping to reduce the time needed to design rub-ber and plastic automotive components. In one example, Nicholas Plastics Inc. ofAllendale, Mich., considerably reduced the product development cycle of a thermo-plastic elastomer glass run channel for a midsize vehicle using a software packagethat simulates the operation of a seal on a computer, making it possible to quicklyevaluate design concepts and iteration to an optimal design. Geauga Co. reducedthe number of prototypes needed for a new dual-durometer bulb seal for car doorsto only two by performing most of the analysis and optimization in software.

By Jerry FiremanStructured Information

The engineer begins by modeling thegeometry of the seal and the surroundingcomponents in the computer-assisted de-sign system. That data are then importedinto EASi-SEAL from EASi EngineeringInc. of Madison Heights, Mich., as an IGESfile. The engineer supplies the programwith preliminary information, identifyingwhich component is the seal, then specify-ing parameters such as how far the sealshould be compressed and speed of the clo-sure. It also is necessary to specify materi-al data in the form of a stress-strain curve.The software stores material informationin a database, so once the properties of thismaterial are entered, they can be recalledfor future analyses. The analysis softwarealso allows the user to combine up to fivedifferent materials in the same seal.

Error checks on both material and geom-etry, such as whether all the required ma-terial data have been given or the closureimpinges on the seal, are performed by thesoftware automatically. Next, the softwaremeshes the seal, extrudes the geometry

into solids, applies boundary conditionsand material properties, and performs a fi-nite element analysis that takes both ma-terial and geometric non-linearities of theproblem into account. The analysis calcu-lates the closure force for the seal. Otheruseful output includes a frame-by-frameanimation showing the seal cross-sectionas it deforms. This is particularly helpful toseal designers because it provides a theo-retical understanding of seal performancethat normally can’t be obtained prior tophysical testing. The program providesother information as well, including com-pression load deflection curves, stress/strain contours and pressure distributions.

This information typically is used tomodify the original design, then the analy-

sis and modification process is repeateduntil the design is optimized. Because com-puter simulation is so much faster thanphysical testing, it usually is possible to in-vestigate how the performance is affectedby manufacturing variability. For exam-ple, engineers can run analyses at nominalvalues and at the worst-case values in thehigh and low directions. This provides in-sight into how the seal would perform inworst-case production scenarios, informa-tion that normally was not available in thepast because samples are run at nominalsize and shape. This information ultimate-ly helps the customer improve quality byalerting it to possible problems.

Applying a new materialRecently, Nicholas Plastics set out to de-

velop and produce a non-supported TPEglass run channel assembly designed toreplace current metal and EPDM assem-blies which meets the performance andquality requirements as designed by theluxury products group of a leading auto-mobile manufacturer. A glass run channelfits against the top of the moveable win-dows on a vehicle to provide a tight sealagainst air, noise or water entering the ve-hicle. The desire to switch from existingdesigns (Fig. 1) made of rubber and metalto TPE comes from the fact that TPE com-ponents offer a weight reduction of 15 to60 percent and also last considerablylonger because they do not harden withage like EPDM. TPE sealing components

also usually cost less overall because theydon’t require metal carriers and mechani-cal attachments so they typically can beproduced as a single molding that does notrequire assembly or painting.

Designing a seal with an entirely newmaterial is not a simple process. In orderto provide optimum sealing, existing sealsare designed to provide a mechanical ac-tion when the glass presses against theseal as the window is closed. The sealdrapes over and touches the glass on eachside in a process known as wink over. Thechallenge for engineers is designing a sealthat will provide exactly the right me-chanical action when the window closes.In the past, engineers would have createdsuch a design by creating an initial best-guess rough design. Then they wouldbuild a tool, produce a few parts and testthem. Inevitably, the initial design wouldnot work and engineers would then em-bark upon an extended process of chang-

ing the tool, running additional prototypesand testing the results. Ron Woltjer, de-sign group leader for Nicholas Plastics, es-timated that if this process had been fol-lowed, it would have taken about one yearto create a TPE glass run design that metthe customer’s requirements.

Need for a new design tool“We needed to look for a faster and more

effective way to design the glass run chan-nel,” Woltjer said. “Of course, there aremany computer-aided engineer softwarepackages that make it possible to evaluatedesigns on a computer. The problem is thehigh deformations involved in seal opera-tion mean that the most expensive anddifficult-to-use non-linear finite elementanalysis software is required to analyzethem. The cost of purchasing such a pro-gram and hiring an analyst to run it is amajor commitment. Then we heard abouta new software package designed speciallyfor seal design that provides all of the ana-lytical tools required to evaluate a pro-posed seal design while providing a muchsimpler user interface and costing far lessthan general purpose programs with thesame capabilities.”

Simulation-based design Woltjer began by importing the initial

seal geometry, which was based on theexisting EPDM design, and entering thematerial properties for the Thermovin

TECHNICAL NOTEBOOKEdited by Harold Herzlichh

See Software, page 18

18 Rubber & Plastics News • January 27, 2003 www.rubbernews.com

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Fig. 2. A shot of the comparison plot.170-H8NC seal. The program performed anon-linear finite element analysis and pro-vided all the information needed to deter-mine seal performance, such as CLDcurves, seal deformation, stress/strain con-tours and contact pressure distributions. Astepwise animation of the seal cross-sec-tion provided an intuitive understandingof seal performance, which helped improvethe design through subsequent iterations.

The initial design did not provide the de-sired wink over effect so Woltjer mademodifications and then analyzed the per-formance (Fig. 2) of each one using thesoftware. Woltjer used the results of the

simulation to help identify the best possi-ble positions to locate hinge points, thinnerwall sections that are used to encouragethe seal to bend in one direction or anoth-er. After running a number of simulations,he iterated to a design that worked exactlylike the original EPDM design (Fig. 3).The design then was released for prototypebuilding. Testing showed the designworked exactly as predicted by the simula-

tion. Nicholas Plastics then installed theprototypes in a production vehicle to showthe auto maker how it functioned and itsaesthetics. “The automobile manufacturerwas very pleased with the fact that wewere able to produce a TPE glass run

channel that worked exactly the same asexisting steel and rubber parts in muchless time than they expected,” Woltjer said.

Geauga Co. produces a dual-durome-

ter bulb seal consisting of a bulb made ofa softer material and a harder rubber Uchannel that grips to the sheet metal ofSoftware

Continued from page 16See Software, page 20

Technical

20 Rubber & Plastics News • January 27, 2003 www.rubbernews.com

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Fig. 3. A shot of the optimized design.

the car. The purpose of having the softbulb is to permit closure without a greatdeal of effort but one that seals againstwater, outside materials or wind noise.Typically, the customer requests a cer-tain closure force and contact pressurefor a seal that Geauga must meet whenit makes the seal.

In the past, the design process for a bulbseal began with hand drawings showingthe product in place. After that, it was nec-essary to find the right combination of ma-terials so the seal would meet the cus-tomer’s specification for closure force andcontact pressure. This was done through a

lengthy build and test cycle and there wasno way to know how a seal would performuntil it was made. This required the pro-duction of an extrusion die that closelymatched the CAD drawing. Once the diewas ready, about 45 to 60 minutes wereneeded to set up extrusion lines and runthe product. If the die needed modification,that took from 15 minutes to severalhours. For a new seal, it usually took sev-

eral iterations to get the die right. Once theseal was produced, it was subjected to teststhat simulated the car door closing and cal-culated how much effort it took. This couldtake many hours, and anywhere from oneto 10 tests were needed to obtain a seal

with the right degree of closure force.This led the company to look into simu-

lating seal performance on a computer.Engineers used that information to modi-fy the original design, then repeated theanalysis and modification process untilthey got the closure force they needed.The company has so far used EASi-SEALin the design of five new products. For the

first few products, engineers verified theEASi-SEAL results against physical test-ing. They found an average correlation of91 percent. This high level of correlationwas maintained over many iterations asshown by comparing relative relation-ships in the different dimensions. Thishas given the company confidence in this

SoftwareContinued from page 18

Technical

See Software, page 22

22 Rubber & Plastics News • January 27, 2003 www.rubbernews.com

design approach and what it can offer tocustomers. Geauga now creates better ini-tial designs and needs significantly lesslead time to get to the final product.

For more information, contact EASiEngineering by phone at 248-582-3800;fax at 248-582-8523; e-mail info@eas-iusa.com; or visit the company’s Website at www.easi.com.

SoftwareContinued from page 20

The authorJerry Fireman has a bachelor’s degree

in journalism from Wayne State Univer-sity and a master’s of business adminis-tration degree from the University ofMichigan. He worked four years as engi-neering editor for Valeron Corp., a cuttingtool manufacturer, and seven years forFrench & Rogers, a high-tech advertisingand public relations agency, last servingas vice president/account supervisor.

Fireman founded Structured Informa-tion in 1984 and has served as presidentever since. He has written more than6,000 articles for more than 1,500 tradejournals in 24 countries around theworld.

Fireman can be reached by phone at248-540-5610, Ext. 100, or e-mail jer-ry_fireman@strucinfo.com.

hazards including toxicity to the nervous system; damage tothe reproductive system, liver and kidneys; respiratory impair-ment; cancer; and dermatitis.

“The needless loss of lives and disease really becomes notonly a personal and national issue but also a global one,” Fine-frock said. “The saving of one life and the many health afflic-tions makes this development project very worthwhile.”

With 40 years of experience in the industry—37 in the rubbertank lining business—Finefrock and Blair Rubber received aU.S. patent on the solvent-free rubber lining adhesion systemfor tank linings in May 2002. Finefrock authored the patent andassigned it to Blair Rubber Co.

Finefrock will present his findings in a paper entitled “Solvent-Free Rubber Lining System” at the National Association of Corro-sion Engineers convention, scheduled for March 19 in San Diego.

Solvent-free rubber lining adhesion system development hasbeen Finefrock’s mission since that dreadful day in 1971, he said.He spent years in the laboratory experimenting with a non-flam-mable, non-toxic process, with the last three years dedicated tomaterial and process development in the lab, factory and field.

“It has been a slow progression, but this certainly is the mostimportant project I’ve ever been on,” Finefrock said.

The patented solvent-free adhesion system eliminates sol-vent emissions and allows the application of tank linings with-out the risks of flammability or toxicity that come from usingadhesives containing isopropanol, tack cement, toluene or oth-er potentially hazardous materials.

Finefrock combined non-solvent tie-gum, a two-coat rubber-to-metal adhesive, special seam closure solvent-free adhesives,a non-solvent chemical repair solution and cleaners to createthe final system.

While his main goal was to eliminate hazards, Finefrock had toconsider how his product would measure up to other systems thatuse adhesives and contain solvents. He said his adhesion systemis comparable in processability with only a slight increase in price.

A prototype tank car, holding 14,000 gallons of phosphoricacid, was chosen to test the solvent-free system and the owner re-ported no problems with the lining after one year, Finefrock said.

“And the people who have worked with the solvent-free ad-hesives say they feel more alert and are more efficient on thejob after using the system,” he said.

The rubber tank lining industry is examining and consider-ing the system, he said. But a comment made to Finefrock by alongtime worker in the rubber lining industry summed up theimportance of the invention.

“I had a father who came to me and said that he was gladthat his son, who is also a worker in the industry, wouldn’thave to work around the same materials that he had to 20years ago,” Finefrock said. “That meant a lot.”

RPN photo by Rachel Wenger

From left, Jim Finefrock, head of research and development,President Roger Turner and General Manager David Jentzschgather in Blair Rubber Co.’s laboratory to discuss the firm’ssolvent-free rubber lining system developed by Finefrock.

LiningContinued from page 1

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