Characterisation of beech wood pulp towards sustainable rapid prototyping

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sustainable rapid prototyping

Julien Gardan, Lionel Roucoules

To cite this version:

Julien Gardan, Lionel Roucoules. Characterisation of beech wood pulp towards sustainable rapid prototyping. International Journal of Rapid Manufacturing, 2011, 2 (4), pp.215-233.

�10.1504/IJRAPIDM.2011.044700�. �hal-00867975�

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Julien GARDAN, Lionel ROUCOULES - Characterisation of beech wood pulp towards sustainable rapid prototyping - International Journal of Rapid Manufacturing - Vol. 2, n°4, p.215-233 - 2011

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susta inab le rap id prototyp ing Ju l ien Gardan*

Mechan ica l Eng ineer ing and Techno logy , 4 P l Henr i Manceau – 08390 , Marqu igny , France E-ma i l : con tac t@az tech- innova t ion .com

*Correspond ing au thor

L ione l Roucou les

A r ts e t Mé t iers Par isTech , CNRS , LSIS ,

2 cours des A r ts e t Mé t iers–13617 A ix-en-Provence , France E-ma i l : l ione l .roucou les@ensam .eu

Abstract: Wood has severa l advan tages tha t are transferab le to var ious der iva tes a l low ing the in troduc t ion of a sus ta inab le ma ter ia l in to the produc t l ifecyc le . The ob jec t ive of th is paper is to app ly a des ign for manufac tur ing approach based on wood f lour rap id pro to typ ing , wh i le assoc ia t ing the requ iremen ts of the ‘mass cus tom isa t ion’ in the imp lemen ta t ion of a cus tom ised produc t . New co l labora t ive sof tware a l lows consumers to be invo lved in the des ign process . Pro to typ ing processes a l low d irec t manufac tur ing of produc ts .

Keywords: mass cus tom isa t ion ; co l labora t ive produc t des ign ; des ign for manufac tur ing ; DOE ; des ign of exper imen ts ; mod if ied s tarch ; rap id pro to typ ing ; user co-crea t ion ; wood f lour .

Reference to th is paper shou ld be made as fo l lows : Gardan , J . and Roucou les , L . (2011) ‘Charac ter isa t ion of beech wood pu lp towards sus ta inab le rap id pro to typ ing’ , In t . J . Rap id Manu fac tur ing, Vo l . 2 , No . 4 , pp .215–233 . B iograph ica l no tes: Ju l ien Gardan d id h is PhD on Eng ineer ing Sys tem a t the Un ivers i ty of Techno logy of T royes (UTT ) in France . He works w i th the Labora tory of Mechan ica l Sys tems and Concurren t Eng ineer ing (LASMIS) a t Char les De launey Ins t i tu te (ICD) . He founded the company Az tech . H is research in teres ts focus on new produc ts , produc t ion processes , wood ma ter ia l and indus tr ia l app l ica t ions .

L ione l Roucou les is a Professor a t A r ts e t Mé t iers Par isTech Ins i tu te (France)

in the Depar tmen t of Des ign , Indus tr ia l isa t ion , R isk and Dec is ion . He rece ived

h is PhD in 1999 work ing on co l labora t ive produc t mode l l ing . He has been

promo ted as Professor in 2008 . The con tex t of h is research , rea l ised in the LSIS

labora tory , is in tegra ted des ign and co l labora t ive IT p la tform in a g loba l PLM

v is ion . H is spec if ic in teres ts are produc t–process in terface and he proposed a

des ign for manufac tur ing syn thes is approach wh ich is now par t of a larger DFX

mode l l ing for v ir tua l pro to typ ing by leas t comm i tmen t suppor ted w i th MDE

p la tform .

1 Introduct ion

The marke t for ‘mass marke t produc t’ has evo lved in recen t years towards cus tom isab le produc ts . Th is marke t change has crea ted new of fer ings no t on ly based on ex is t ing marke ts any more , bu t a lso genera t ing new app l ica t ions . Th is new behav iour has somewha t changed the dec is ion dur ing the produc t des ign process :

To take in to accoun t the no t ion of sus ta inab le produc ts , promp t ing use of ma ter ia ls and processes compa t ib le w i th respec t of the env ironmen t throughou t the produc ts’

l ife .

To access the techno log ies , in des ign as we l l as in manufac tur ing , wh ich can be be t ter exp lo i ted for manufac ture of be t ter produc t adap ted to the marke t (more sca lab le cons ider ing cos t , qua l i ty and dead l ines) .

To make a good produc t is necessary to be compe t i t ive , bu t unfor tuna te ly no t enough ; one shou ld a lso make the r igh t produc t tha t means the produc t tha t f i ts to the users’ rea l needs and expec ta t ions (Sago t e t a l . , 2003) . Many doma ins (au tomo t ive doma in) then use des ign me thods focused on the user . I t is shown tha t the invo lvemen t of users and the ir percep t ions is cr i t ica l to the des ign (Bouchard e t a l . , 2009 ; Po irson e t a l . , 2007) . As the manufac turab i l i ty of the produc t is a lso cruc ia l , severa l in tr ins ic parame ters , re la ted to the manufac tur ing process , are added to the des ign process ( i .e . des ign for manufac tur ing approach) . The no t ion of ‘sus ta inab le’ produc ts is a lso an impor tan t concep t . I t leads to the use of ma ter ia ls and manufac tur ing processes compa t ib le w i th respec t of the env ironmen t throughou t the l ife t ime of the produc t . The env ironmen t of a produc t has an impac t on i ts l ife cyc le . Based on spec if ic l ife cyc le ana lyses (LCA ) , Trouy -Tr ibou lo t and Tr ibou lo t (2001) show tha t wood has obv ious advan tages and appears as an

‘env ironmen ta l ly respons ib le’ so lu t ion .

The bus iness purpose of Az tech company (France – Champagne-A rdenne) is to prov ide on demand cus tom ised produc ts for the ‘genera l pub l ic’ w i th a produc t ion of un i t ob jec ts . As the reproduc ib i l i ty of produc ts needs spec if ic too ls , A rdu innova has chosen pro to typ ing manufac tur ing process techno log ies .

Th is paper d iscusses the in tegra t ion of na tura l ma ter ia ls in exper imen ta t ion of beech wood pu lp through two processes of pro to typ ing for manufac tur ing recons t i tu ted wood produc ts : 3D pr in t ing and so l id f reeform fabr ica t ion (SFF) .

2 Object ives and research approach

Th is paper proposes to in tegra te the consumer in crea t ing persona l ob jec t through an in terne t-based por ta l ca l led CREAFAB . Th is too l wou ld a l low the user to cons ider i ts purpose and to manufac ture the produc t accord ing to i ts reques t . The research work is then based on three s teps : the trans la t ion of consumer persona l requ iremen ts , the spec if ica t ion of web-based sof tware to f i t the des ign me thodo logy and the manufac turab i l i ty of the cus tom ised produc t in rap id pro to typ ing in tegra t ing a der iva t ive of wood .

Au thors se t up a scenar io to def ine the genera l approach . Th is scenar io shows the

d if feren t s teps wh ich enab le to ob ta in a cus tom ised produc t in recons t i tu ted wood

(cf . F igure 1) . I t a lso a l lowed us to loca te the sc ien t if ic and techno log ic issues to ach ieve

the ob jec t ives .

F igure 1 I l lus tra t ive research scenar io (see on l ine vers ion for co lours)

Dur ing the g loba l research work , au thors d iscussed areas of research such as the cus tom isab le produc ts towards new produc t , the user-cen tred des ign and the rap id pro to typ ing . Th is paper w i l l on ly presen t the resu l ts to unders tand ing the behav iour and produc t–process re la t ion in the con tex t of rap id pro to typ ing based on wood f lour .

3 Natura l ma ter ia ls used 3 .1 Wood f lour

Wood is a b iodegradab le organ ic ma ter ia l wh ich is more or less long- term re ins ta ted in the na tura l carbon cyc le . The cyc le ana lys is (LCA ) revea ls the g loba l s treng ths of the ma ter ia l . LCA takes in to accoun t the env ironmen ta l impac t of the subsequen t s tages of the wood l ife prepara t ion and ex trac t ion , process ing , transpor ta t ion , ins ta l la t ion , performance usage and recyc l ing . Informa t ion on the l ife cyc le of wood is s t i l l new and d ispersed (Trouy-Tr ibou lo t and Tr ibou lo t , 2001) , bu t Trouy-Tr ibou lo t and Tr ibou lo t (2001) can men t ion a few advan tages :

Opera t ion is less po l lu t ing than the ex trac t ion of o ther ma ter ia ls . The transpor t does no t invo lve any r isk and i ts supp ly is c loser . I t requ ires less energy and less wa ter than o ther ma ter ia ls .

The exp lo i ta t ion of under-produc ts of wood is in deve lopmen t , and wood energy is neu tra l in CO

produc t ion .

Wood takes par t in the reduc t ion of carbon d iox ide em iss ions as an a l terna t ive to non-

renewab le ma ter ia ls , the la t ter lead ing to energy cos ts and nega t ive impac ts tha t are hard

to be sus ta ined by our ecosys tem . The l ife cyc le of wood inc ludes cer ta in compounds tha t

invo lve a l l ma ter ia ls us ing wood ma ter ia l processed as ma in base , such as p lywood ,

par t ic le board , f ibre , e tc . The in teres t of these produc ts is based on the ir econom ic ,

techn ica l and commerc ia l asse ts . The s truc tura l d ifferences tha t can be found in one

essence , lead to a cer ta in amoun t of qua l i t ies and cr i ter ia for var iab le use . The f ibrous

na ture of wood s trong ly inf luences how i t is used (M i l ler , 1999) . Any ma ter ia l tha t has

l i t t le va lue wh ich can be recyc led is co l lec ted , crushed , shredded , f iber ised and may

resul t in recond i t ioned wood ma ter ia ls such as the wood f lour , w i th or w i thou t the add i t ion of b inder to advan tageous ly g ive paper , cardboard , f ibreboa rd or par t ic les (P lassa t , 1994) . The t imber has a very compe t i t ive sa le pr ice compared to so l id wood a l though the mechan ica l performances are lower . The ir techn ica l and econom ic va lues of fer s ign if ican t oppor tun i t ies for indus try sec tors of cons truc t ion , layou t and furn i ture incorpora t ing recogn ised decora t ive techn iques . The appearance and aes the t ics of wood is undoub ted ly an advan tage for th is ma ter ia l . W i th the in tegra t ion of f lour as ma in e lemen t in a process l ike pro to typ ing , i t wou ld be poss ib le to ob ta in a homogeneous and iso trop ic ma ter ia l , un l ike so l id wood . I ts h igh sens i t iv i ty to hum id i ty forced to l im i t the use of such ma ter ia l . In the ir exper imen ts , au thors use beech f lour w i th two d ifferen t gra in s izes de ta i led in Tab le 1 : L IGNOCEL HB 120 and ARBOCEL HW 630 .

Tab le 1 Beech f lours

Name S truc ture Gra in s ize ( m) Dens i ty (g L

)

HB 120 F ibrous 40–120 140–200

HW 630 F ibrous 20–40 200–300

3 .2 Mod i f ied s tarch

Au thors a lso focused on na t ive s tarches and mod if ied s tarches to s tudy the ir behav iour through research in the sc ien t if ic commun i ty . Th is ma ter ie l cou ld indeed be used for rap id manufac tur ing techn iques as prev ious ly in troduced . Such processes opera te a t a tempera ture be low 40°C for the 3D pr in ter and a t room tempera ture for the depos i t ion mode l l ing process .

S tarch is the ma in carbohydra te reserve subs tance of h igher p lan ts . I t represen ts a s ign if ican t mass f rac t ion in a large number of agr icu l tura l commod i t ies such as cerea ls (30–70%) , tubers (60–90%) and vege tab les (25–50%) . In presence of wa ter a t a tempera ture of 50–70°C , depend ing on the se lec ted s tarch , v iscos i ty appears on the s tarches . Af ter coo l ing , the na t ive s tarches , as ma ize or whea t s tarch and po ta to s tarch , transform w i th a rap id recrys ta l l isa t ion of po lymers (amy lose and amy lopec t in) ca l led s tarch re trograda t ion (Bours ier , 2005) .

There are var ious mod if ied s tarches tha t improve the ir behav iour . The chem ica l ly mod if ied s tarches deve lop the ir v iscos i ty and the ir b ind ing proper ty a t low tempera ture or a t norma l cook ing tempera tures in env ironmen ts where wa ter ava i lab i l i ty is l im i ted . Th is ca tegory ga thers those mod if ied s tarches ob ta ined by reac t ion of hydroxy l groups of s tarch w i th monofunc t iona l agen ts to in troduce subs t i tu t ion groups . The purpose of th is type of trea tmen t is to s tab i l ise the amy lose aga ins t the re trograda t ion and preven t in termo lecu lar assoc ia t ion of amy lopec t in f rac t ions . The in troduc t ion of es ter or e ther groups in the s tarch mo lecu le can s tab i l ise the v iscos i ty , espec ia l ly a t low tempera tures (Banks and Greenwood , 1975) .

The ex tra produc ts of the reac t ion mus t then be removed by wash ing to ob ta in a

comp le te ly b iodegradab le s tarch . No te tha t s tarch is sens i t ive to hum id i ty and i ts

mechan ica l proper t ies decrease w i th increas ing mo is ture . For examp le , po ta to s tarch is

used in indus try to manufac ture g lue wa l lpaper , b iodegradab le by e ther if ica t ion

(descr ibed in Tab le 2) . The in troduc t ion of new hydroxy la ted func t ions prov ides a

mo is ture leve l equ iva len t or super ior to tha t of na t ive s tarch . The chem ica ls are no longer presen t in the f ina l mod if ied produc t , i t is comp le te ly b iodegradab le . However , i t shou ld be no ted tha t the charac ter of the s tarch as a na tura l subs tance decreases w i th increas ing e ther if ica t ion .

Tab le 2 Mod if ied s tarch

Name Chem is try Food manu fac ture

E ther s tarch Hydroxypropy l s tarch E 1440

4 Rap id pro totyp ing ana lyses

4 .1 Se lec t ion o f the manu fac tur ing process

To increase produc t iv i ty , indus tr ies have a t temp ted to app ly more compu ter ised au toma t ion in manufac tur ing . Among the la tes t techno log ies tha t have emerged over the pas t two decades , rap id pro to typ ing techno log ies a lso known as SFF , desk top manufac tur ing or layer manufac tur ing techno log ies (Chua e t a l . , 2010) prov ide a grea t advan tage to prov ide d irec t manufac tured par ts .

4 .1 .1 3D pr in t ing

Au thors , in the ir labora tory , had access to a 3D pr in ter , the ZCorp 510 , wh ich by defau l t uses a powder made f rom gypsum and a b inder d is tr ibu ted by ZCorpora t ion . De ta i ls of the compounds used are usua l ly secre t wh ich w i l l no t fac i l i ta te the in terpre ta t ion .

Tha t techn ique is a m ix ture of pro jec t ion of b inder and s in ter ing . A pr in t head inc lud ing severa l nozz les , to en ab le co lour pr in t ing , throws drop le ts of b inder over a tray of powdered ma ter ia l . B inder pene tra tes the agg lomera tes and the powder becomes r ig id . Pos t-process ing-based g lue is necessary to ob ta in suff ic ien t mechan ica l s treng th .

The cho ice is based on a mach ine wh ich a l lows us an easy access to trays con ta in ing powder and pr in t ing sys tem cons t i tu ted con ta iners , cana ls and s tandard type Hew le t t Packard pr in t heads .

4 .1 .2 Depos i t ion mode l l ing

SFF has the po ten t ia l to revo lu t ion ise manufac tur ing , even to a l low ind iv idua ls to inven t , cus tom ise and manufac ture prof i tab le goods a t homes . The open-source Fab@Home pro jec t has been crea ted to promo te SFF techno logy by p lac ing i t in the hands of hobby is ts , inven tors and ar t is ts in a form wh ich is s imp le , cheap and w i thou t res tr ic t ions on exper imen ta t ion (Ma lone and L ipson , 2007) .

Accord ing to De Rosnay (2006) , por tab le 3D pr in ters w i l l be ava i lab le on marke t

wh ich f inds the ir app l ica t ions a t homes , garages and sma l l workshops . He in troduces th is

techno logy l ike the m icro-fac tory cus tom ised (MFC) . De Rosnay (2006) pred ic ts a

democra t isa t ion of MFC around 2020 . Techn ica l and sk i l ls d iff icu l t ies are h idden in tha t

pr inc ip le bu t the process is descr ibed in the l i tera ture .

J. Gardan and L . Roucou les

The me thod is based on the ex trus ion of ma ter ia l in the form of pas te (s i l icone , choco la te , pas try dough , e tc .) . One or more need les , gu ided by three d ig i ta l axes , lay down a f i lamen t . The f i lamen t does no t so l id ify immed ia te ly . The s tra ta of the ob jec t are cons truc ted by s tack ing a spec if ic track connec ted w i th a free open-source (we can f ind the same type of sof tware on the RepRap (Se l ls e t a l . , 2010)) . The sy r inge connec ted to a p lunger depos i ts i ts f i lamen t in a hor izon ta l p lane , then the p la tform is lowered to s tar t the nex t cyc le . Th is approach cou ld a l low us to make a wood pu lp to form some ob jec ts .

5 F irs t manu fac tur ing exper iments by 3D pr inter us ing wood f lour 5 .1 In troduc t ion

Ma in ob jec t ive of shap ing is to ge t aes the t ica l par ts and to ob ta in mechan ica l proper t ies correspond ing to the produc t spec if ica t ions . Therefore , th is paper now presen ts the exper imen ta l resu l ts to assess the mechan ica l performances and the shape .

5 .2 Manu fac tur ing-dr iven exper imen ta t ion

In us ing the ZCorp 510 pr in ter , au thors were ab le to incorpora te the f lour Beech HB 120 in the pr in ter and rea l ise the pre l im inary tes ts w i th the b inder of the mach ine (ZB58 transparen t) . Au thors assume the hypo thes is tha t the b inder of the mach ine is no t as ef fec t ive on wood f lour . The f irs t tes t p iece ended up w i th very f r iab le p ieces in pr in ter ou tpu t (cf . F igure 2) .

A pos t- trea tmen t was therefore cons idered by d ipp ing the ob ta ined par t in indus tr ia l wax . The par t is no t rea l ly immerged bu t jus t la id on the wax . The wax then r ises up by cap i l lary ac t ion (cf . F igure 3) .

The par t is in tac t on the top surface , bu t i ts base is degraded by the soak ing suppor t . Never the less , i t can be manua l ly man ipu la ted af ter harden ing as expec ted .

F igure 2 Cond i t ion of par ts af ter fabr ica t ion (see on l ine vers ion for co lours)

F igure 3 Tens i le tes t on a spec imen soaked in an indus tr ia l wax (see on l ine vers ion for co lours)

5 .3 Charac ter isa t ion o f the wax-based ma ter ia l

To assess the behav iours of the ob ta in par t w i th respec t to spec if ica t ions , severa l tes ts have been done to mechan ica l ly and d imens iona l ly charac ter ise our ma ter ia l .

5 .3 .1 Mechan ica l s tra in assessmen t

Tes t p ieces to measure the tens i le s treng th of the ma ter ia l have been rea l ised (cf . F igure 4) . The tes ts were performed us ing s tandard spec imens and w i th exper imen ta l cond i t ions g iven on Tab le 3 .

A t f irs t , au thors rea l ised spec imens us ing the manufac tur ing exp lora tory process as prev ious ly descr ibed : ten spec imens in f lour spruce by 3D pr in t ing by the b l inder ZB 58 . Then au thors have d ipped the p ieces in a ba th of pa lm wax .

5 .3 .2 Resu l ts and ana lys is

Tens i le tes ts have resu l ted in usab le da ta . They are summar ised in Tab le 4 .

F igure 4 Spec imen ou tpu t pr in ter ( in fa ir) and pos t- trea tmen t spec imen ( in dark) (see on l ine

vers ion for co lours)

J. Gardan and L . Roucou les Tab le 3 Exper imen ta l cond i t ions

Cap tor 10 daN

Tens i le s treng th 0 .1 N Ves t ing per iod 50 ms D isp lacemen t 50 mm mn

Spec imen d imens ion x = 10 .3 mm / y = 76 mm / z = 5 .5 mm

Tab le 4 Summed up tes ts

Tens i le tes t Tes t 1 Tes t 2 Tes t 3

R

(MPa) 0 .97 1 .51 1 .26

Modu lus E (MPa) 667 728 707

Au thors can observe on the tens i le curves , the e las t ic modu lus and the rup ture l im i t of the spec imens . The three curves are s ign if ican t ly d if feren t and show tha t the ma ter ia l’s charac ter is t ic is very d ispersed . Au thors f irs t assume tha t the sensor is no t sens i t ive enough to measure a ma ter ia l as f rag i le . Then , the ma ter ia l seems to fa l l be tween the jaws of trac t ion mach ine . A lso resu l ts can be d ispersed and g ive us ins igh t in to the behav iour of the ma ter ia l in tens ion . I ts tens i le s treng th is low (be tween 0 .97 and 1 .51 MPa) .

5 .4 D imens iona l var ia t ions and geome tr ic d is tor t ions

Deforma t ions are v is ib le on tes t p ieces af ter coo l ing the wax . The harden ing of the wax ma tr ix imp l ies a w i thdrawa l , wh ich leads to d imens iona l var ia t ions and geome tr ic d is tor t ions due to surface tens ion . Au thors used a coord ina te measur ing mach ine (CMM) to measure these d is tor t ions . By us ing rec tangu lar tes t p iece (as shown on F igure 4) , au thors can de term ine var ious charac ter is t ics (cf . Tab les 5 and 6) .

Tab le 5 C ircu lar dev ia t ion syn thes is

Measure CMM Spec imen 1 Spec imen 2 Nom ina l va lue (mm ) Ø 37 .727 Ø 37 .727 Measured (mm ) Ø 37 .693 Ø 37 .314

Max (mm ) Ø 38 .133 Ø 37 .929

M in (mm ) Ø 37 .238 Ø 36 .942

Tab le 6 F la tness dev ia t ion syn thes is

Measure CMM Spec imen 1 Spec imen 2

Nom ina l va lue (mm ) 0 0

Measured (mm ) 0 .494 1 .037

Max (mm ) 0 .308 0 .507

M in (mm ) 0 .186 0 .530

5 .4 .1 Resu l ts and ana lys is

A l l th is informa t ion shows the geome try of par ts af ter coo l ing . However , au thors can observe v isua l ly curved p ieces on the ends (an effec t of warp ing) . The d iame ter of the c ircu lar opened ho le decreased and a s trong dev ia t ion of abou t 0 .034 mm for spec imen number 1 and 0 .414 m for spec imen number 2 . The represen ta t ions of ac t ions and deforma t ions show tha t the ho le is no t c ircu lar and deformed towards the ex trem i ty of the mode l . The f la tness of mode ls is a lso affec ted by coo l ing wax . The graph ica l in terpre ta t ion a l lows to eas i ly v iew the larger s tra ins presen t a t the ex trem i ty . The remova l of par ts af ter harden ing ind ica tes tha t the ir in terna l tens ions affec t the f ina l geome try . The da ta a l low us to in terpre t the mod if ica t ions to be cons idered ahead of the des ign for a ‘func t iona l geome try ’ .

5 .5 Case s tudy

In th is sec t ion , au thors presen t the app l ica t ion process by re ly ing on an ob jec t for the genera l pub l ic . Au thors de l ibera te ly chose a s imp le ob jec t because they recogn ise tha t ear ly in terpre ta t ions are of an exp lora tory na ture . They des igned a sco tch- tape suppor t (cf . F igure 5) accord ing to the process of des ign ing and manufac tur ing tha t au thors are ab le to imp lemen t .

The rea l isa t ion of the sco tch- tape suppor t fo l lowed the manufac tur ing process as a lready descr ibed . Af ter harden ing of the wax , au thors ge t a v isua l ly iden t if ied par t . The absorp t ion of the wax caused some a l tera t ions and pe l le ts of wax in the inner edges . The mode l is re la t ive ly br i t t le and the mas tery of the process is de l ica te , bu t these resu l ts are encourag ing for the exper imen ta l app l ica t ion .

Th is sec t ion of th is paper has a l lowed to observe the f irs t manufac tur ing so lu t ions proposed by the au thors and to de term ine i ts v iab i l i ty . Au thors a lso presen ted the research resu l ts based on the de term ina t ion of mechan ica l and geome tr ica l charac ter is t ics . Sec t ion 6 presen ts the second (SFF) manufac tur ing process tha t has been se lec ted as in teres t ing for wood form ing (cf . Sec t ion 4 .1) .

F igure 5 Sco tch- tape suppor t : compu ter-a ided des ign mode l and manufac tur ing process

(see on l ine vers ion for co lours)

J. Gardan and L . Roucou les

6 DOEs for process and product charac ter is t ics ident if ica t ion based on so l id free form manu factur ing process

6 .1 In troduc t ion from depos i t ion mode l l ing

To f ind a so lu t ion to prev ious l im i ta t ions of the f irs t manufac tur ing process (3D pr in t ing) , the au thors d iscuss a new manufac tur ing approach . S ince au thors do no t have the fab@home sys tem , they dec ided to k i t the manufac tur ing process . Au thors are therefore us ing open-source sof tware for the RepRap ( i .e . ‘ rep l ica t ion rap id’) tha t genera tes a f irs t f i le descr ib ing the f i lamen t tra jec tory f rom a s tereo l i thography mode l of the par t . Then au thors trans la ted th is spec if ic f i le in to G code app l icab le to a numer ica l con tro l (NC) mach ine . By adap t ing a sy r inge ins tead of an end m i l l , au thors cou ld rea l ise the manufac tur ing opera t ion . The app l ica t ion is done by manua l pressure on the syr inge to lodge a ‘wood pu lp’ .

The f irs t tes ts show tha t the au toma t ion of the f i lamen t depos i t does no t seem to be a techno log ica l lock . The ad jus tmen t of ex trus ion parame ters genera ted thanks the RepRap sof tware a l low to parame ter the NC mach ine for trace a mode l w i th the wood pu lp . Au thors can use th is manufac tur ing me thod to try to rea l ise wooden produc ts . The f irs t issue re l ies upon the pu lp’s cons is tency and no tab ly i ts rheo log ica l charac ter is t ics to ob ta in a f i lamen t tha t w i l l no t co l lapse dur ing the lay down . The second issue is to respond to geome tr ic and use cons tra in ts of the produc t af ter f i lamen t dry ing .

Au thors propose to imp lemen t a des ign of exper imen ts (DOE) focused on the w ire to ge t the bes t poss ib le depos i t in the manufac ture and on i ts geome tr ica l and mechan ica l charac ter is t ics af ter dry ing .

6 .2 Pr inc ip les o f DOE approach

The me thod of DOE can bo th reduce the number of tes ts and s tudy a large number of fac tors , bu t a lso to de tec t poss ib le in terac t ions be tween fac tors . The s tudy of the inf luence of one fac tor a t a g iven leve l is done by compar ing the average responses ob ta ined a t th is leve l to the overa l l average (H inke lmann and Kemp thorne , 2008) . Accord ing to the def in i t ion of fu l l fac tor ia l , one has an answer for each comb ina t ion . 6 .3 App l ica t ion

Au thors chose to app ly th is me thod to d iscover the effec ts of the process and of the chosen ma ter ia l ( thanks to the f irs t exper iences p lan) on var ious predef ined geome tr ica l shapes w i thou t increas ing tes ts .

Our l i tera ture search has iden t if ied inf luen t ia l fac tors l ike h igh sens i t iv i ty of the ma ter ia ls to mo is ture (wood and s tarch) .

Ob jec t ive: To assess the var ious fac tors tha t makes up pu lp from i ts mechan ica l behav iour and rheo log ica l cr i ter ia .

Consequen t ly , the s tud ies are made on parame ters tha t have a s ign if ican t inf luence , name ly :

The gra in s izes of beech f lour : 40 and 120 μm .

The mass of beech f lour : 20 and 40 g .

The mass of e ther s tarch : 10 and 40 g .

The vo lume of dem inera l ised wa ter : 200 and 300 m l . 6 .4 Samp les for exper imen ts

Tes t p ieces a re samp les w i th non-cons tan t geome try (cf . F igure 6) . The s truc ture can vary f rom one spec imen to ano ther . Three samp les per dough type have been rea l ised and the average of every se t of resu l ts have been ca lcu la ted to avo id the d ispers ions .

F igure 6 Samp les geome try (see on l ine vers ion for co lours)

6 .5 Manu fac tur ing cond i t ions

Au thors produced the tes t manua l ly w i thou t NC mach ine . Techn ica l ly the f i l ing of the w ire is feas ib le , bu t the resources do no t perm i t to au toma te the descen t of the p lunger . Never the less , au thors assume the independency of tha t issue on the resu l ts .

Manufac tur ing parame ters of spec imens are : W ire d iame ter : 2 mm .

Tempera ture : 20°C . Hum id i ty : 55% RH .

Ma ter ia l : Beech f lour 20 and 120 μm (dec iduous) . 6 .6 Measures cond i t ions o f the mechan ica l proper t ies

The measuremen t of mechan ica l s tra in is performed on a mach ine for s tra in compress ion w i th a sensor 100 daN . The deforma t ion is measured on the in i t ia l leng th (L0%) ; the measure of s tress is MPa . The tes ts are conduc ted in an env ironmen t a t a tempera ture and hum id i ty of 42% RH.

6 .7 Rheo log ica l cr i ter ia cond i t ions

Au thors d id no t have too l to d irec t ly measure the rheo logy of the pu lp . Au thors then

app l ied the cr i ter ia of observa t ions to assess the w ire he ld : good behav iour : cr i ter ion

no . 1 ; med ium behav iour : cr i ter ion no. 2 ; worse behav iour : cr i ter ion no . 3 .

J. Gardan and L . Roucou les 6 .8 Prac t ica l me thod

The DOE is performed on a tens ion and compress ion mach ine us ing the cond i t ions men t ioned in Sec t ion 6 .6 . Au thors have a two- leve l p lan , w i th the s tudy of a l l the poss ib le b i la tera l in terac t ions per samp le type , wh ich corresponds to an L 16 tab le . The leve ls chosen are shown in Tab le 7 . The cond i t ions were chosen on bo th s ides of the tes t cond i t ions of reference presen ted in Sec t ion 6 .6 .

The cons truc t ion of the DOEs is shown in Tab le 8 . The spec if ied ou tcomes are the averages of measuremen ts performed in tens ion on a fam i ly of three iden t ica l spec imens . To summar ise , au thors have three ou tcomes : the max imum s tra in in MPa named A , the e las t ic i ty modu lus in MPa named B and the rheo log ica l cr i ter ia assessed dur ing the ex trus ion performed w i th a syr inge named C .

Tab le 7 Leve ls tab le

Fac tors Leve l 1 Leve l 2

E ther s tarch (g) 10 40

Beech f lour (g) 20 40

G ra in s ize (μm ) 40 120

Dem inera l ised wa ter (mL ) 200 300

Tab le 8 DOE cons truc t ion and resu l ts

No . E ther s tarch (g) Beech f lour (g) Wa ter (mL) Gra in s ize (μm) A (MPa) B (MPa) C

1 40 20 300 40 7 .30 719 .0 2

2 40 40 200 40 2 .69 289 .0 3

3 10 20 200 40 0 .16 21 .6 2

4 40 40 300 40 1 .01 113 .3 3

5 40 40 200 120 0 .53 65 .0 3

6 10 40 200 120 0 .31 45 .6 3

7 10 40 300 120 0 .01 2 .00 2

8 10 20 300 40 0 .29 39 .33 1

9 40 20 200 40 1 .11 98 .33 3

10 10 40 300 40 0 .01 2 .00 2

11 40 20 200 120 2 .49 274 .3 3

12 10 40 200 40 0 .41 64 .3 3

13 10 20 300 120 0 .00 0 .0 1

14 40 20 300 120 3 .81 332 .6 2

15 10 20 200 120 0 .30 52 .0 2

16 40 40 300 120 1 .17 160 .6 3

6 .9 S tudy e f fec ts

The re la t ive impor tance of a parame ter is es t ima ted us ing graphs l ike those in F igure 8 . The impor tance of the s lope on each parame ter g ives informa t ion on the impor tance of the inf luence of th is parame ter . The more the fac tor’s effec t is impor tan t , the s tronger the segmen t’s s lope is . I t was therefore a means of qu ick v isua l assessmen t on the same graph of the re la t ive inf luence of represen ta t ive fac tors de ta i led in F igure 7 .

F igure 7 G raph of ma in effec ts (see on l ine vers ion for co lours)

J . Gardan and L . R oucou les

Figure 8 Sy r inge se t o n t he compu ter numerica l co ntro l (see on l ine vers ion for co lours)

6 .10 S tudy in terac t ions

An in terac t ion be tween fac tors occurs when the mod if ica t ion of the response ob ta ined on m in imum leve l or on max imum leve l of a fac tor d iffers from the mod if ica t ion of the response on two iden t ica l leve ls of a second fac tor . In o ther words , the effec t of a fac tor depends on ano ther fac tor . You can use in terac t ion d iagrams to compare the re la t ive s treng th of the effec ts of d ifferen t fac tors .

6 .11 Op t im isa t ion

The responses op t im isa t ion func t ion searches a comb ina t ion of inpu t var iab les tha t jo in t ly op t im ises a se t of answers wh i le sa t isfy ing the requ ired cond i t ions for each response of the se t (Wu and Hamada , 2009) . To op t im ise the manufac tur ing cond i t ions of forms , ind iv idua l des irab i l i ty is def ined for each response . We mus t therefore increase our des ire to ob ta in the bes t poss ib le w ire p lace dur ing manufac ture wh i le ma in ta in ing a tens i le h igh s tress . We keep the goa ls wh i le max im is ing the responses .

The op t im isa t ion d iagram i l lus tra tes the effec t of each fac tor on the responses or compos i te des irab i l i ty . For the ind iv idua l des irab i l i ty , au thors se lec t a we igh t (be tween 0 .1 and 10) to def ine the impor tance of reach ing the targe t va lue . The compos i te des irab i l i ty is the we igh ted geome tr ic mean of ind iv idua l des irab i l i ty of d ifferen t answers . Tab le 9 summar ises the resu l ts and ‘bes t’ conf igura t ion to s imu l taneous ly max im ise the ou tcomes .

Tab le 9 Op t im isa t ion responses

Compos i te des irab i l i ty 0 .86 Max imum s tra in 3 .5 MPa W ire-he ld cr i ter ia 1 .35 G ra in s ize 40 μm E ther s tarch 40 g Beech f lour 24 .64 g

Wa ter 246 .46 mL

In th is s tudy , the compos i te des irab i l i ty (0 .86) is fa ir ly c lose to 1 , ind ica t ing tha t the se t t ings seem to ach ieve favourab le resu l ts for good pe rformances of the thread dur ing the manufac tur ing and i t responds to us ing fea tures .

6 .12 DOEs syn thes is

Mod if ied s tarch used is the mos t impor tan t fac tor affec t ing the tens i le s treng th of the ma ter ia l . The f lour beech f ibre s ize may affec t the res is tance in our se tup , con trary to wha t au thors though t . The s tarch needs enough wa ter and does no t need a h igh load of f lour to ach ieve i ts charac ter is t ics .

For ho ld ing the w ire on f i l ing , i t is more s tab le when the pu lp is made up of less wa ter and more f lour . S tarch is unden iab ly the invar ian t fac tor in our compos i t ion . Th is s tudy shows tha t in terac t ions of beech f lour and s tarch have a s trong respons ib i l i ty to ho ld the w ire in the presence of dem inera l ised wa ter . W i th the a im to improve our wood pu lp , au thors headed towards the responses op t im isa t ion to be c loser to the bes t of our terms of use and manufac ture .

6 .13 Shap ing o f the wood pu lp

In th is sec t ion , au thors presen t the shap ing app l ied to f i l ing of a w ire to wood pu lp . In subs t i tu t ing the end m i l l of NC mach ine by a sy r inge , au thors imp lemen t a sys tem for ex trud ing the wood pu lp . The p is ton is temporar i ly manua l ly ac t iva ted , bu t the ex trus ion is a func t ion a lready presen t in the sof tware (RepRap) . Au thors add an arm mu l t ip l ier to s imp ly ex trude the w ire (cf . F igure 8) .

From a process ing G code manufac tur ing us ing the RepRap sof tware , the G code is readab le for the NC mach ine (cf . F igure 9) . No te tha t the approach does take in to accoun t the pa th of the too l , espec ia l ly the s tra t if ica t ion . Au thors mus t press on the p is ton to ex trude the pu lp . Th is me thod invo lves a sem i-au toma t ic ex trus ion speed occas iona l ly random . However , the in i t ia l se tup is accura te enough to eva lua te the cons truc t ion of mode l (w ire d iame ter , th ickness of layers , e tc .) and manua l ly con tro l the f low of wood pu lp (scan speed) .

Af ter mak ing a t leas t ten p ieces , au thors observed some irregu lar i t ies in the ir geome tr ies . Dur ing the scan , the chang ing of d irec t ions of too l genera tes pro trus ions ma in ly due to poor con tro l of the manua l ly run ex trus ion . Never the less , the shape of the mode l corresponds to the in i t ia l geome try and the manufac tur ing process has func t ioned accord ing to the approach (cf . F igure 10) .

Au thors d id no t observe any co l lapse of the shape . However , the ma ter ia l has s trong adhes ive power , wh ich requ ires a smoo th surface a l low ing us to take off the p iece af ter dry ing (cf . F igure 11) . Af ter 48 hr dry ing a t amb ien t tempera ture , au thors ge t a h igh ly d is tor ted p iece w i th a tendr i l led ef fec t . The irregu lar i t ies observed on the fresh p iece are accen tua ted . Af ter harden ing and sa l t ing of the wa ter con ten t in the ma ter ia l , the w ire d iame ter narrows f rom 2 to 1 mm .

Au thors observed the deforma t ion dur ing a spec if ied t ime . A t f irs t , au thors have a

fresh mode l tha t does no t co l lapse . Subsequen t ly , in terna l tens ions w i l l gradua l ly deform

the geome try . Par t of the w ire be ing in con tac t w i th the suppor t has s tuck on i t , wh i le the

res t of the surface tends towards the in ter ior of the mode l by crea t ing cav i t ies . The edges

have gradua l ly ben t to the hear t of the ma ter ia l . The mass of the p iece and i ts remova l of

ma ter ia l imp ly the deforma t ions through the geome try cen tre .

J . Gardan and L . R oucou les Figure 9 T ra jec tory mode l (see on l ine vers ion f or co lours)

F igure 10 Mode l af ter manufac tur ing (see on l ine vers ion for co lours)

F igure 11 Mode l af ter harden ing (see on l ine vers ion for co lours)

A t the ‘aes the t ic’ and surface cond i t ion of the mode l , reduc ing the d iame ter of the nozz le has improved the recovery of the layers . We do f ind more ho les or cav i t ies due to depos i t ion of sem i-au toma t ic w ire (cf . F igure 12) .

F igure 12 Decrease of w ire d iame ter (see on l ine vers ion for co lours)

6 .14 Syn thes is

In th is sec t ion , au thors exp lo i ted so lu t ions by depos i t ing a w ire wood pu lp . Au thors f irs t proposed a me thod app l ied on a NC mach ine . Then , they propose the exper imen ta l me thod wh ich a l lows ob ta in ing wood f i l ler to answer manufac tur ing cons tra in ts . The proposed approach a l lows spec ify ing profess iona l ru les spec if ic to the process . The mechan ica l resu l ts do no t exac t ly correspond to the da ta announced by the exper imen ta l p lan , bu t the overa l l resu l ts seem cons is ten t . When au thors v isua l ly compare the par ts produced a t the beg inn ing and a t the end of the pro jec t , i t is easy to observe the s truc tura l changes (co l lapse , respec t of the geome try ) and aes the t ic mode ls (ob jec t render ing) (cf . F igure 13) .

In add i t ion , the aes the t ics shou ld be improved to ach ieve the genera l pub l ic produc t expec ted . Oppor tun i t ies for improvemen t are poss ib le , such as reduc ing the d iame ter of the nozz le wh ich requ ires a mechan isa t ion of the p is ton and the es tab l ishmen t of a research phase deeper on the compos i t ion of the pu lp (s tudy the remova l through the harden ing , e tc .) .

F igure 13 Mode ls’ evo lu t ion (see on l ine vers ion for co lours)

J. Gardan and L . Roucou les

7 Conc lus ion and recommendat ions for fu ture work

Au thors proposed two approaches for mak ing ‘ob jec ts’ in recons t i tu ted wood . Au thors in troduced an app l ica t ion to use a f lour spruce f rom a 3D pr in ter invo lv ing a pos t- process ing , s tab i l is ing the p ieces tes ted . Au thors rea l ised a case s tudy us ing our des ign and manufac ture me thod . I t concerns a sco tch- tape suppor t , wh ich perfec t ly ma tches the consumers’ produc ts fam i ly . The impor tance of measur ing the roughness of the ma ter ia l to foresee the f r ic t ion of the ro l l ing is a l l the grea ter tha t i t w i l l app ly to our case s tudy . One of the goa ls is to au toma te the manufac tur ing process .

In a second app l ica t ion , au thors have subm i t ted an app l ica t ion invo lv ing a NC mach ine and a f i l ing sys tem of w ire . Th is depos i t uses a sy r inge and spec ia l ised sof tware in the genera t ion of the mode l . The approach is essen t ia l ly gu ided by exper imen ts us ing a DOE . The so lu t ions tha t ar ise f rom these app l ica t ions a l lowed us to tack le some sc ien t if ic and techn ica l issues . The invo lvemen t of a renewab le ma ter ia l opens up in teres t ing eco log ic and econom ic poss ib i l i t ies . However , a subsequen t phase wou ld be necessary to comp le te those app l ica t ions . A t the end of th is sec t ion , au thors can cons ider app l ica t ions to revea l the v iab i l i ty of the genera l approach , name ly :

The use and in tegra t ion of a wood de r iva t ive in rap id manufac tur ing . Ob ta in ing processes of shap ing and interpre ta t ion of the ir mechan ica l and geome tr ica l charac ter is t ics .

In the long term , au thors wan t to deve lop app l ica t ions re la ted to manufac tur ing by rap id pro to typ ing wooden par ts . Conv inced of the econom ic and eco log ica l po ten t ia l of process , severa l research pro jec ts are expec ted to lead to more re l iab le too ls . The prospec ts for th is work are numerous . They can focus on the user in terface , the me thod and ma ter ia l , the v ir tua l produc t deve lopmen t (mode l l ing , s imu la t ion , e tc .) and the manufac tur ing process s tudy .

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