Building betterblueprints'Design for manufacturability' is critical to making micro medical devices

By William Leventon

When it comes to tolerances, you can getwhat you want if you're wiI1ing to pay for it.

ous manufacturers ofmicro medical devices useto enhance production.

Molding and machiningWhen designing microparts for molding or

machining, one effective way to improve themanufacturing process is to eliminate sharp

corners wherever possible."Especially with the part sizes we're making,

90· angles can be very tough to deal with:' saidStu Kaplan, president of Makuta Technics Inc.,a micromolding firm in Shelbyville, Ind. So indiscussions with designers, "we see if there's achance to put a radius on that sharp corner:'he said.

If medical designers can accept a 0.002"

" 'I 7J1en designing medical parts with micro­VV scale dimensions, engineers have more

on their plates than the difficult job of makingsure the parts function as intended. They mustalso ensure that manufacturers of the tiny partscan do their job. What's more, they should dowhatever they can to simplify the manufacturer'sjob as much as possible.

Design for manufac­turability at the micro­scale must account forthe requirements andlimitations ofdifferent manufacturing processes.But smart practitioners ofDFM go beyond theconsideration of what's possible for a certainmanufacturing technique. While staying withinthe limits of acceptable risk and medical designpractices, they also try to minimize manufac­turing problems, which can slash productiontime and costs.

Following are examples of DFM tactics vari-

micromanufacluring.com I 41

OEMs concerned about design for manufacturabiIityshould involve parts makers in the design process.

Additive DFMIn addition to molding and machining,

micro medical parts can be made usingadditive techniques developed to allowcost-effective manufacturing ofcomplexdesigns that would be extremely diffi­cult-if not impossible-to produce usingconventional processes.

EoPlex Technologies Inc., RedwoodCity, Calif., mass-produces complex, min­iature components via its High VolumePrint Forming process. Ultrathin layers ofvarious materials are laid down. Sintering

with a microscope, Empire will pass onthe job.

In injection molding, gates allow plas­tic to flow into the mold, but they alsoleave scars on the surfaces of tiny parts.Designers must determine where theycan allow gates-that is, where scars leftby gates won't interfere with part assem­bly or function.

"Gate location is a very big thing:' EIJisaid. "But most designers don't even con­sider how you're going to get plastic intothe mold and what that scar is going tobe like:'

Another important factor not consid­ered by some medical component design­ers is assembly, according to Jankoski,who often suggests that designs includecarriers, the strips of material that fa­cilitate the handling of tiny parts dur­ing assembly operations. For example, astamped part could sit on a carrier stripwith several pilot holes in it. Pins wouldbe inserted into the pilot holes in orderto accurately orient the part for assembly,Jankoski explained.

he said, "we try to get them to understandthat these measurements have to be madeat my shop and their shop-and we bothhave to get the same answer:'

The company has tried to persuadesome designers to loosen the tolerancesa bit. But if the designer insists on some­thing so tight that it can't be measured

Micro Medical Ttchn%glcs

Micro Medical used the metal-injection­molding process to produce thisimplantable device in one step. The device'sO.OOS"-radius tip required no sharpening.

safely reduced, thereby shortening thehole through that wall and reducing thestress on the pin used to make the hole.

In addition to dimensions, medicaldesigners concerned about the bottomline should take a hard look at tolerances.When it comes to tolerances, "you can getwhat you want ifyou're willing to pay forit;' said Pierre Paroz, CEO of AmericanMicro Products Inc., a machining firm inBatavia, Ohio. "But ifyou go from 0.0003"to 0.0002" total tolerance, that's a 50 per­cent difference, so your costs can go upa lot"-perhaps as much as 30 percent,depending on the machining process.

When Neal EUi sees a design with anextremely tight tolerance, his first ques­tion isn't, "Why is it so tight?" but rather,"How are you going to measure it?" Insome cases, designers are specifying di­mensions with tolerances that can't berepeatably measured by commonly usedinstruments, according to Elli, presidentof Empire Precision Plastics, a Rochester,N.Y., micromolder. When this happens,

Building better blueprints continuedor 0.003" radius, Micro Medical Tech­nologies, Somerset, N.J., can often useits metal-injection-molding process toproduce tips. But if designers insist onsomething that's needle-point sharp, thecompany will have to turn to a second­ary microgrinding operation that couldadd 50 cents to the price of parts that sellfor about $1 or $1.50, according to FrankJankoski, the firm's director of technicalservices.

In many cases, Jankoski added, cus­tomers specify radiuses that are so smallthat tooling can't be effiCiently fabricatedusing standard processes such as wireEDMing. The size of the EDM wire limitshow small radiuses can be made.

"Whenever we see a radius under0.003", we'll need to use a very expen­sive manufacturing process to fabricatethe tooling;' Jankoski said. For example,grinding can do the job, but it can alsodrive tooling costs up about 50 percent,he noted.

Before beginning such a costly process,Jankoski often checks with the designer tomake sure it's absolutely necessary. "We'llgo back and ask them if they really needthose really small radiuses, or if there's adifferent way we can achieve the samefunctional requirement:'

In other cases, designs include featureswith depths measured in microns andlengths measured in millimeters. Main­taining extremely small depths over rel­atively long distances is a tall order formolders, said Kaplan, who suggested thatdesigners break up such features into twoor more pieces to facilitate the manufac­turing process.

Kaplan also worries about medicalpart designs that include long holes withsmall diameters. This can cause problemsin the molding process, where pins areused to make holes. Ifa design calls for ahole 800~ long and 20~ in diameter,"the strength of the pin would be a con­cern;' he said.

When customers ask for such holes,Kaplan discusses the situation with them.A review of the deSign might show thatthe thickness of a certain wall can be

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ature. When designers come to EoPlexwith bad material combinations, "we'llwork with them to see if there are alterna­tives that allow processing in a single heattreatment," he said. "Ifyou can find them,you've lowered the cost of the process~

Like the EoPlex process, the EFABtechnique offered by Microfabrica Inc.,Van Nuys, Calif., produces intricate metaldevices with extremely small features. Tocreate these devices, the process depositsa stack of thin metal layers that include

ated with molding and machining, theprocesses have their o\'{n DFM issues.For the EoPlex process, that list includeslimits on the choice of materials. Addi­tional processing can be done on a com­ponent produced by the technique, but"the lowest cost option is putting a partin the oven and taking it out finished andready for shipping;' Chait said.

Therefore, designers should choosematerials that can be processed togetherin a one-step co-fire at a certain temper-

foPlex TechnoIog.es

With Eo?lex Technologies' High VolumePrint Forming process, parts are fabricatedfrom ultrathin layers of material. Then theparts are sintered, which binds the layersand eliminates sacrificial material (top left,right). Parts can include as many as sevendifferent materials (bottom).

binds the deposited material into mono­lithic parts that can consist of hundreds oflayers and up to seven different materials.

"We give designers 3-D freedom thatother processes can't even approach;' saidEoPlex President Arthur Chait. As an ex­ample, he said to consider a channel thatwanders in a curving path through a partfor a fluidic device. According to Chait,such a channel wouldn't be suitable formachining processes, which are better atcutting features that run in straight linesand bend at right angles.

What about molding? A molderfaced with a complex channel designwould probably opt to mold the part intwo pieces that would then be joined to­gether. By contrast, he said, the EoPlextechnique can produce parts with wan­dering channels in a single process.

Though additive techniques can elimi­nate manufacturability problems associ-

micromanufacturing.com I 43

M_Etch holes must be designed into some parts made byMicrofabriea's EFAB process. The holes allow etehant toreach and remove sacrificial material within the part.

ContributorsAmerican Micro Products Inc.(800) 479-2193www.american-micro.com

Empire Precision Plastics(585) 454-4995www.empireprecision.com

EoPlex Technologies Inc.(650) 361 9070www.eoplex.com

Makuta Technics Inc.(317) 642-0001http://makuta.com

Microfabrica Inc.(818) 786-3322www.microfabrica.com

Micro Medical Technologies(732) 302-0800www.micromedicaltech.com

Building belter blueprints continuedstructural material, which forms the fea­tures of the device, and sacrificial mate­rial, which serves as "scaffolding" thatsupports the device during fabrication.When all the layers have been depos­ited, the sacrificial material is removedby an etching process, leaving the fin­ished device.

A thorough etching process dependson a hole configuration designed to allow

etchant to reach all the features and cor­ners of the device. A good etch-hole de­sign also ensures that hole sizes, shapesand locations don't have a significantimpact on part strength or functional­ity. For example, the size and numberof etch holes should be as small as pos­sible in areas with high stress concen­trations, noted vacit Arat, president ofMicrofabrica.

Another manufacturability concern isminimum feature size. Micro­fabrica recommends that de­sign features be at least 20~mwide for the EFAB process.However, EFAB can producefeatures as small as lO~m wideif the layer thickness is 5~m,

which is the process minimum."If designers want a 10~m

feature in an area that's25~m high, we can only do itif the layers are 5~m thick;'Arat explained. Instead of asingle 25~m layer, "they needfive 5~m layers on top of eachother to achieve what theywanf'

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Involving the manufacturerNo matter the process, contract man­

ufacturers are unanimous on one point:OEMs concerned about DFM shouldinvolve them in the design process. Insome cases, however, companies tryingto protect design secrets are reluctant toshare information with their manufac­turing partners.

"They don't necessarily know what youneed to know, so they give you as little in­formation as possible:' American MicroProduct's Paroz said. As a result, "you endup doing things three times to get themright because you didn't have the rightinformation upfronf'

As an example, Paroz cited a job wherethe client insisted that some miniatureparts with extremely thin walls be brazedtogether-without explaining why. "Thebrazing turned out to be a nightmare;' herecalled. After repeated and costly failuresto braze the components together, Ameri­can Micro finally convinced the client toswitch to laser welding. Paroz still doesn'tknow why the company insisted on braz­ing at the outset.

"If people would share more infor­mation with us, we could give themmanufacturing input based on our expe~

rience;' he said. When they don't, "theycan end up costing themselves a lot ofmonei'

DFM difficultiesEarly manufacturing input is crucial

in the medical industry, where designchanges to components that have al-

ready gone through the FDA approvalprocess can be both expensive and timeconsuming. Medical considerations alsohave an impact on what DFM changescan be made. For example, Elli pointedto situations where designers select ma­terials that aren't optimal for the moldingprocess, but more moldable alternativescan't be substituted because the selectedmaterials meet key biocompatibility orsterilization requirements.

In many cases, however, DFM changeshave no significant adverse impact ondesigns, according to Jankoski. "In thedesigner's mind, though, he's addinga bit of risk when he deviates from hisdesign. So the easiest thing for him todo is tighten up all the tolerances tominimize his risk. But what he doesn'trealize is that he's adding cost by mini­mizing risk:'

Manufacturing costs can be driven

up so much that a "perfect gem" is asunpalatable as a cheap part that doesn'tperform its intended function, ]ankoskinoted. "If the part is too expensive andcan't be sold, what good is it?" P

About the author:William Leventon isa New Jersey-basedfreelance writer.Telephone: (609)926-6447. E-mail:wleventon@Verizon.net.

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