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Cutting costs and
time with DFMA
Applying Design For Manufac turing and Assem bly
methodologies in early stages of produ ct design can redu ce th e
nu mber of par ts in a produ ct and thus redu ce cos ts.
By Steven Ashley, Associate Editor
I \ I R \ I yL\R v .'\( ;U .
S
D o u ul.r-,
Co u u ucrcia l Ai rcr.i f Co. ill
Lon g Bc.u-h. Calif". LUI ' 0 111(.'
vimul .u io n -, of th eir tit-si gn .m d
m.umt.u-nmng opera tions [0 determ ine wh .i t lin n 's t ill' costs o f ;I i l"li nn co nstru cti o n . T hL' CUlll p ,llly
di ' l()\,l'n ,d th.ir the costs o f .rsscmbl v. f.tbric.uiou. qua lirv ;\ " SU L llI Cl' ,
and 1'\"l.' 11 ovcrhc.rd-e-invc nto rv k,'1;' ]..;. tr.ukin g. and purch.i-iug-e-al l
dep end 011 the p .Ub co un t.
ROll Suit er. gl.' lI L'r;l 1 1ll.1I1.lg l'r to r
aircr.ui 'y,rL' 1I1' .utd in tcrior dt', ign
.it I )Oll gl.l "', .urd <cvcra l col leaguewere g in:1l the tack of findin g o u t
wh.u cou ld b e d one to cn r r h c
p.ur - co unt of ' 0 1111;' of th e com p.tny', pmducrv. Thev lined up ca ndid .uc, fo r prod u ct rvdcvicn .ui d
av-cm blcd m n ltid ic-ipl iu .rrv d e ,i~1l
tl..' ,I111 \ th .it in clud ed dcvign l' 1l ~ i­
n vvrv . m.uiufacr urin g l' llg illl' l·r,.
-ho p Ilo o r mech anics. and <nppli - The integr ati on of Boothr oyd Dewhurst's DFA software with Parametri c Technology's Pro/EN GINEER enables
cr n -p rc-cur.ui vcs. ;h \\'l·11 .1' <pv- a user to build a conceptual design as a three -dimensional solid model while simultaneously creati ng a DFA
structure chart complete with part names and dimensions.
ciali src ill prod u ct io n ' lIp po n,
wav," Su it er c.ud. " A n,llyz ing eve r-y p.nt .m d o peration ill
m.unr.riu.rbilirv, and n -lt.ihi lu v,
;1 b,l,i c ,l,,",l..'lllh ly IIl.1h·, th e rc.un ri goroll\l y confront th e
Te.u n mc m lu-rv were t.rug hr I k \i gn f o r I\ LlIluflCtli r i ll g
co mplexi ty o f ,I d l'\i gn .m d w o rk to ,i lll p l i t~ · it."
.urd A" l' l11bl y (I )F.\ lA) tt' l"i lll iq Ul'\-,lIl ex act ing d c-i gu T Ilt' rc-uh - of th e D Ollgl.l, I )r~ lA proj ect were imp rcvrev ie w me tho d t h.u id en tifi c-, th e o p tima l p ut d t'\i glL
m .ncri .il- choice..m d .I"l· mhly an d tab r ic.m o n opcr.uionsivc. Sui ter <ud . O ne ' lI CCI..'''"' ' to ry \ \ ',1\ th e rcd evign of the
D ill ,IiI' d o o r ,I\\l'mhly 011 th e ~ II )- 11. th e t"l Hllp,lIly" ,\{ II 1to p rodt u -c .m e tfi ci vn t .1I1 d rovr -c tfc crive produ c t.
vc.tt .urlinc r. Th e origi nal r.un .rir doo r ,1'\l'l1lh ly. ,1 p ,l "",,l g l'
" \\';ll king th ro ugh th e cx ivtinu lk'ig n in .1 n' ry \ pl..·citlc
th ro ugh w h ich outsid e- ,IiI' cuter- the c lhin ', .ur co nd itio nproced ure pro mpted throu gh out hy rhe I) F.\I A m ethod o lngy. l'\T ry bo dy star te d loo king .u th e dl..', igm ill ,I 111..' \\
ing -vsrctu. \\"" .t lon g-sen'illg d l'\igll bor rowed trot u the
D ouglas DC- IO airli ner. With 2 172 part s. the co m p lex
do o r unit was co nsidered difficult to install and ad just.
Simpl ifyi ng th e ram air door asse mbly des ign u sing
D H"l A techniqu es took abo u t two week s. T he effort led
to a 36 pe rc e nt re du c tio n in th e n um ber of p;uts (to
13H3), a 34 perce nt decrea se in the numbe r of assembly
o peratio ns (fro m 40 3H to 2()49 ). and th e elim inatio n of
107 po unds, a significant mass red uctio n in an air plane.
M or eove r, th e new ly reco nstituted door un it design w as
signific antly more reliable and easier to ma int ain . " T here
are fewer parrs to wear our," Suiter said. " Eve n th e uni t's
fu ncti on has improved ."
TYP I CAL RESULTS
The suc cess o f Do uglas Com m ercial Aircraft in applying
DFM A practices to its designs is not unusual . Accordi ng
to a su rve y of D FM A users co n d uc ted by Bo o t h ro yd
D ew h u rst Inc. (BDI) in Wa kefiel d, R .I. , the fo re mo st
developer of D FMA strategies and software, typi cal results
arc a 51 perce nt reductio n in part s co u nt , a 37 percent
decrease in parts cost, SO percen t faster tim e-to-market , a
()H perce nt imp ro vem en t in qu alit y and rel iabi lity, a (12
percent drop in assembly tim e, and a 57 perce n t red uctio n ill n u uu fact ur ing cycle tim e.
O ther u se rs have achieved sim ila r result s. " In mo st
cases, we end up with from 30 to HO pe rcellt fewer parrs
an d fro m th ree to five m ore funct ions than pr ev io u sly.
depending on th e product ," said Sandy M un ro, principal
in M u n ro & Asso c. ln c., a prod u ct -desig n consu lting
fi r m in Troy, M ich ., an d anot her lead er ill im plem enti ng
I) F!'vlA techniqu es.
I)FMA, said Peter D ew hurst. dir ector of g radua te studie s in manufact uring e nginee r ing at th e U n iversit y o f
R h od e l sla n d in K i n g st on a n d a p rin ci p al in BD !.
"makes o ne lo o k cr itically at the structu re of producr sthe relatio nsh ip betwee n parts, th e nu mber of par ts. th e
sec uring m ethods- and try to design the assem bly co ntent out of it w hile the de sign is still fl exible."
Th ough the division is so mewh at arb itrary, DFMA is
generally split int o D esign Fo r Assembly (DFA) and D esign For M anufa ct uring (D FM). In DFA. the key to 100\'er
cost and im proving reliability is to prod uc e designs with
fe wer parr s. T he DFA approa ch also sugges ts w hen it is
appropriate to design ori enting and insert ion fe atures into
th e part. In gelle ral, DFA focu ses OIl parrs co nsolidatio n,
to p-dow n (gravity-ass iste d) assem bly, and co nce pt-s tage
design review th ro ugh team co nsensus. DFM , 011 the ot her hand , co m pares the lise of selec te d mater -ials and m anufactu ri ng pro cesses fo r th e parts of an asse m bly, determ in es th e cos t im pact of those mat eri als and processes,
and fi nds the most efficie nt use of th e com po nen t design.
DI~ A and DFM evaluate a design by ro ug hly estim ating
th e re so urce s and e ffor t ne ed ed to b uild th e prod uct
based o n ind ustr y average estim ates . Ikwh ur st said . T his
kind of "sc o rekcc ping" allows di rect com pariso n among
designs. Fo r ex am ple, red ucing the number of parts may
sim plif)' the entire assembly, but co m bining several fuu crio ns ill on e co m po ne n t co u ld result in a co m plicate d
part th at is pro hibitively expe nsive to manufa ctu re. M o re
typi cally, howe ver, the cost o f prod ucing extra feat ures o n
o ne part is m uc h less th an th at o f p ut ting th ose featu res
o n separate parrs. T hus, DI:MA allow s for diffe rent design
scenarios. By see ing the result s up from , D ewh u rst said,
o ne can ge t th e m ost out of each m ater ial and pro cess.
T he m ethodology, said D avid M eeker. pr in cip al eng ineer at the Systems Business Technology unit o f D igital
Eq u ipment Corp. in M ayna rd . M ass.. m akes the team
physically and syste m atically walk throu gh th e d esign
and talk about its adv an tages and sho rt co m in gs, w hi ch
co m pe ls clear decisio ns o n rradc- otl s. " It also f()f(..' es yo u
to keep go od design reco rds, w hich are useful dow n th e
line." M eeker adde d. By th e en d o f a D FMA pro cess. a
step- by-s te p descriptio n o f th e ag ree d- upo n m auu fa ctu ring and assem bly process has been wr itt en dow n .
BEYOND KEEPING IT SIMPLE
Wh en co m pute r- aide d design (CAl )) technology was devclopcd . D ew hurst said . design enginee rs acq uired powertul q uantitative an alyti ca l to ols that provid ed the basis
for making a j udgem ent of a design 's perfo r mance. " Un til
I)FMA came aro und, manufact urin g engin eers did n't have
sim ilar q uantitative tools. The qu alitative evaluat io ns the
ma nufa cn ui ng engine ers had to o ff er ill ;lllY discu ssio ns
di dn 't carry mu ch w ei ght wh en th e d esign ers had rea l
numbers fro m CAD upon whi ch to base th eir decision s."
" M anu fac tu r in g te c h n ol o g y h as impro ved over t h e
years, but no t necessar ily in th e mi nd of the de sign eng ineer, wh o is typi cally used to ap plyin g th e ' Kee p It Sim ple. Stupid' ap proa ch ," said Mel H unter. corporate m anager of co st improvem en t at Em erson Electr ic C o. in St.
Louis, Mo. " H oweve r, more co m plica te d pa rt s capa ble
of fulfil ling several functions usually m ean using a d ifferent ma nu factur ing pro ccss. Df MA allows o ne to estimate
th e cost ramifi cat ions of that cho ice ."
DFMA is a way to get away fro m tradition al pro d uct design pr actic es, in which deep- seated habit s 0 11 th e part of
rh e design engine ers lead to seq ue nt ial eng inee ring . creat io n of single- fuuc n o n parts with ma llY fasreu ers. and
th e iteratio n of multiple pro d uctio n models. It also helps
avo id the in teror g.uu zation al and int erdi scipl inar y pro blem s that ofi eu plag ue new prod uct tea ms.
T he techn iq ue has gained popula rity as a benchmarking
tool becau se it helps define the design and nunufa crurm g
cap .rbilirics of compcri rors and their cost- to - nu rkct -e nn-v
tar get s, as we ll as pro vidin g com pa r-iso ns to co m pe titors '
pro d uct s, M eek er said. But D FM A call go eve n b eyo nd
those tasks, D ew hurst said. " We realized it was a co uuu unicnti on tool tor te.uu work iug. Ha ving arisen at the same
time as th e movem ent toward co nc u rre nt e ng inee ring.
DFMA provi des a focu , for th e d iff ere nt organi zat io nal
cultu res repr esented by the team members."
Thou g h th ere a re seve ra l d iffer in g va ri e ri e s of th e
DFMA m cr hodologv, th e ge ne ral co ncep t be hind all o f
th em o riginated in Britain in th e late 1970s, wh en manu fac t u r in g re sear c h ers w ere in vest iga ting \vays to rcdesign produ cts so th ey co uld be easily assem bled by ;1tI rotuat ed eq u ipme nt . Soon it was realized that this work
was lead ing to 'a set o f guidelines that wo u ld point prod:>.HT llAN IC A I I'. N C I :-.JU ' R I N C
",I AR C II 1' )'1 .:; 7 5
u c t design e rs tow ard d esign s tha t wo uld b e easier to
build ill ge neral. But w he n Br-i tish industry failed to support th e new research , th e co nce pt ende d up bein g appli ed initially in th e U nite d Sta te s. UDI introduced its
first Il FA so ftware in l Y81 in respons e to requests from
earlv practitioners, incl uding electrical co nnecto r- ma ker
AJ\l P Iuc.. Di gital Equipment C orp.. G en eral Electric
Co rp.. We\ ting ho use Electric C o .. and X erox Corp.
In the B1 )1 approa ch (w hich is repr esen tative of others),
several qu estions arc asked about each part in a product
design : D o cs t he pa rt m ove w it h respec t to t he ot her
parts already asse m blc d? M ust th e part b e m ade from a
d ifferent mat er ial o r isolated from all th e other parts already a.. sembled? M ust th e part be separate from all ot he r
parts because assembl y or disassem bly wo uld ot he rw ise be
imp ossible? These qu estio ns lead th e reviewe rs to n -cvaluate each part and process th at has been specified.
" T he idea is to ge t away from piece-functional design
and move to ward syste m - func tio nal design . w h ich im pro vcs system efficien cy' Sandy M UIln> said . H is com pany 's I>FMA ap proach pro m o tes a ser-i es of "good design
pr incip les" related to DFMA: I . USt' team wo rk. 2 . M inimi ze th e number of part s. 3. Design so the assem bly can
proceed in a layered fa.. hion from above . -l. D esign mating
parts that are t'asy to insert and align . 5. Avoid expe nsive
fasteni ng operations. 6. 1k sign out hand ling problems-
After Dougla s Aircraft enginee rs redesigned the ex isting waste pipe and
wire harn ess bra cket on the MD·9Q airliner (left) using DFMA procedures.
the unit's part count droppe d from 15 to 3, assembly operations were cut
from 210 to 8, assembly time decreased from 46 min. to 3 min., weight
was reduced from 2.1 oz. to 0 .8 oz.• and tota l product cost was lowered
from $64 .01 to $4.74 (rightl.
7h
M AR Cil l'l'l~ M F.C H . .,NI CA L EN(;INF.F.RINC
go for bulk sto rage. 7. Design for " Po ke Yoke" o r erro rproof assembly H. Design th e p:uts to affix th em selves one
t o ano the r. <J . Sim p lify se rvici n g an d pack agin g . 10 .
Eliminate adjustm ents and ph ysical reorientation s.
GETT ING MANAGEME NT ON BOARD
IJcspite th e relative success of I)FMA it rem ains a woefitllv
uud cru sed tool. said consultant Rob C arr inge r. senior vice
president of the Georg e Group Inc. in Dallas. " By the time
th e lit-sign is in m an u factu ri ng, abo ut SO perc ent o f the
cost is locked in , but it's hard to tackle the root causes."
Althoug h everyo ne in product t' ngin eering is aware of
the ben efits o f DFMA, Bill Sprague . BDI's vice president
of implementati on services, said th at few h ave bo ug ht
int o th e full-fledged process changes it dem ands or lived
th rou gh it so th at th ey tr uly under stand its pot ential.
Em er son 's Iv1e1 H unr cr said th at unl ess m an agem ent is
educ ated about th e DFMA approa ch , and co m m itted to
the proj ect , it will fail. "They have to put th eir bacon on
th e line to ensure there is no co nfli ct between part s of
th e organiz at ion . Man ag e m c ur also h as to se t aside
eno ug h tim e for th is fu ndam e nt al cha nge to take place.
It do esn 't happ en instantly,"
Assembling and manag ing the int erdi sciplin ary produ ct
dcsign team is also no sm all o rde r. ""A lot of co m pan ies
just throw a bu nch a peo ple toge ther," M eek er said . " O f..
ten th ey don 't pull together and wo rk for th e co m m on
goa l, becau se man agem ent do esn't g ive th em eno ugh auth ority or co ntro l over w hat th cv are doi ng." H e adde d
tha t m anagem ent m ust also reward th e team as a w hole.
T hen the re are the pe rsonal dynam ics involved . All of
the team m em bers. M unro said, " have to adm it to th emselves that th ey cau'r do it all by th em selves. for team work
is the key to success. Using DFMA in a vacuum w ill yield
lim ited results because no one knows everything .'
Early o n , it is useful to give the team structured tasks to
spark crearivirv and to ge t m embers used to working to get he r. " J)FMA pro vid es a nonthreat ening wa y to ge t
peopl e talkin g abo ut a design w itho ut feeling like others
arc e ncroachi ng o n the ir territor y," said J im 'Ib ut , dire ctor o f d esign e ug iuec ring at roy tu aker H ashr o Inc. in
Pawtu cket , R .I. , w hich has succe ssfu lly app lied J>FMA to
several products.
It is also esse nt ial to ge t hand s- on kn owl ed ge from
th ose o n th e sho p floor and fr o m inst allers [0 tr uly un dervtan d th e p robl em.. wi th th e exi sting design . M arry
design engineers say they had no idea ho w mu ch wo rk
p e opl e go throu gh t o put t h ci r produ ct s to geth er.
"When peopl e really und er stand th e other team m em ber s' requirem en ts. it removes most of rhe subj ectivity or
rivalry from the decisio n-making pro cess," Sprague said .
C on vinc in g reams to rely on the cost and cycle tim e esrimat cs for eac h design choice is also a problem . " N o bod y trust s what yo u say on face value : ' Munro said.
" T hey wan t to sec w he re th ose cost and tim e estim ates
co me from. The estimates have to have eno ug h credibility fo r peop le to buy into th e program . In fact. the ent ire
issue o f choosing m etr ics is important because di ff erent
kinds of scorekeeping lead to diflerenr result"."
Following a DFMA design review by Hasbro engineers, the ladder assembly
on the Tonka Talk n' Play Firetruck was redesigned in plastic, the number
of components was reduced fr om 33 to 5 , and assembly ti me dropped
from 198 to 22 sec.
T h ere is also so me di sp ut e ab o ut wh eth er everyt h ing
sho uld be boiled down co cycle tim es and mon ey. "I think
it's a big m istake to calibrate every thing in terms of do llars,"
said Mel H unt er, " beca use it allo ws peo ple to twe ak th e
figures to push the analysis in on e directio n o r ano ther."
Spr ague said that th ere is a need to calibrate the analysis
m et ho ds to th e spec ific activities of th e part icular o rganization and the ind ustry to mak e su re tha t th e ter m s me an
so me th ing to th em . Fo r ex am ple, in mo st D FJ\l A system s, th e ma nufactu r-ing eng ineer e m set up preferen ces
to fit th e o rgani zatio n 's syste m o r e nviro u m en t-c-t' th e
typc of tool s yOll use, th e d istan ce s yOli m o ve. and so
forth ," Spra gue said . In gene ral. th e er ro r associated with
th e cost and tim e estima tes is in the range of S to 10 perce nt, " Ifth ere is a discrep an cy, it's usually because ce rtain
aspect s o f th e process are being ignored." he said.
DESI GNIN G FOR CU STOMERS ' OPERATION S
T he next frontier for DFMA lllay be de signin g prod uct s
for effic ient use in the custo mer's manufactu ring op eration s, ac co rd ing to Pet er M ark s, ma n agin g d irect or o f
D esign Insight in Los Cntos, C alif. As pan of a survc y o f
th e best desig n an d m anu facturi ng pract ices, he fou nd
th at co m pa n ies like AM P were designing th eir connectors no t j ust for m an ufact ura bilirv in th eir own pla nts but
fo r co m patibility w ith th e custo m er's operations. Sim ilar
effo r ts, M arks said , we re taking place at Ko dak (fast photo labs, digital im agin g), G e neral Electr ic Aircraft Engin es (easie r integr atio n wi th airfram e d esigns), H arr is
(faste r p rint job ch an ge overs ). and Ke nn c m eral (o pt im ized tool select io n and mana gem ent ).
1\;10st cut -re nt DF M A pro grams are followed using so fiwa re devel o ped fo r the pro cess. "Software is cr uc ial to
en fo rcin g str uc tu re an d add ing rigo r to th e pr oj e ct ,"
Spragu e said , " T he re are to o man y var iables to keep in
yo ur head , and th e so ftware collec ts all th e data,"
n r:MA software is provided by UD!. Lucas Engin eering &Syst em s Ltd . in Sol ih ul l. U. K. (d istr ib u te d in N o rt h
Am eri ca by Mu nro }, and Sapphire I)esih:rtl System s Inc. in
Palo Alto, C alif. " Each syste m has the same mi ssion ," said
M eeker. " they j ust do it differently or to different degrees."
O ne no table recent develo pm ent Ius been th e int egra tion of UUI's D FA package in to Pro / EN(; IN EER from
Param e tr ic Techn o logy Corp, ill Walt ha m , Ma ss. Th e
integrnte d syste m allo ws feature d im e nsio ns and parts
lists bui lt into the solid model to be auto ma tically dow nloaded into DFA files. An enginee r can build a co nce ptual design as a th ree-d im ensio nal mo del and automa tically
creat e a Dr:A str ucture ch art , co m ple te with part s nam es
and dim en sions . ready fo r sim ultane o us design revi ew.
BI) I also o ffers DFM co st-esti m ating mod ules for several
manuf acturi ng processes, including ma chining. shee rme tal
wo rk ing. inject ion molding, powd er m et al fo rm ing. and
die casting, f o r exam ple. BDI recently released M achi nin g
for Windows. versio n 2, wh ich derives m ach ini ng tim es
and costs to r co nc ept-stage design s. Based o n eco no mic
mo dels of the pro cesses, these DFM tool s permit eng inee rs
to calcul ate the cost savings resultin g from easier assembly
versus the adde d co st o f more co m plicate d to oling an d
ot her process factor s for a mo re co mplex part.
A success fu l e xam p le of th ese DFM capabi liti es to o k
place ;1£ H asbro. T he largest toy co m pany in th e world is
using D[= J\.l A to identify design aud cos t imp ro vem ents at
th e w ry earli est co ncl'pt stages of design .
Toy ret ailers do no r wa nt to car ry inven tori es. said Ji m
To ur. " Be ca use tim ing is so critica l, till' em phasis is on
gett ing pro du cts shippe d o n sche d ule, DFMA is a big part
of th is move ment because it helps eliminate pro blem s ill
the de -bu g prod ucti o n sta rt - u p p ro ce ss by an alyzin g
part s co unts, asseil lbly tim es. and m ater ial cos ts before a
d esig n c o nce p t is lo cked in an d cha nges be com e too
tim e-consum ing to imple ment ,"
Co st wa s t h e c h all e nge for t h e Ton k a Tal k n ' Pla y
Pircn-uck , one of H ashro 's suc cesses o f the I<J<J3 Christm as seas o n , A fte r DFMA ana lysis. it be came clea r that
co sts co uld be red uced if th e traditio nally m et al firerruck
we re red esigned in plastic.
T he red esign invol ved m oving the ligh ts fro m th e front
cab to th e rear assembly, changing aesth etics, co m bining
so me part s, an d el im in atin g m any fast e ners. T h e bi g
ch ange, howe ver, was to th e ladder assem bly, explaine d
Ha sbro proj ect enginee r Pat Egan . The o r iginal ladd er
was co m posed. of a tota l of 33 parts and assemblies, w ith
an assembly tim e of 19R seco nds. T he redesigned ladd er
brought th e num ber of part s down to its th eore tical min innuu of o nly five. all pla stic. w ith all assembly tim e of
just 22 sec o nds, " It looks as n ice as th e m et al asse mble.
and it performs the sam e fu nction s," Ega» said . " Plu s. it 's
more reliable wh en subjecte d to abuse-testin g." In additio n , th e toy tru ck met its cost targets.
DH\;lA co nsul tan ts are typ ically brought in as a last reso rt , Sp ragu e said, wh en a co m p any w ants to up g rad e
prod u ct-devel op m en t capabilities to tig ht it s co m petition , o r wh en it has specific cos t obj ectives for a product
co nside red to be cr itical to the co m pany an d n r:M A is
th e onl y way to do it. T he "lu xury of ad versi ty," however, sho uld not be the pri m e reason to ad o pt n r:MA prac tices, Einstein on ce said th at " the best de sign is the simplest o ne th at wo rks." DFMA provid es the ch eapest way
to reach tha t go al. •