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"Vacuum in Research and Practice'n

I DryVacuum Pumps

! Coatings

f Surface Radicalson Polymers

I Nanotechnology @\TILEY-VCH

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AbsfroctEvery third patent regisffation in thearea of cutting tools submits a principalclaim concerning coating technologlaBut it is not only because of this thatcoating is one of the most importantdriving forces for the future of manuf-acturing engineering. It represents amajor influence on tool performanceand is improviflg it with giant steps

t1 l , [14].The following paper will not presentthe current state of today's coating-industry in the form of the commonreviews. It is a short composition ofimportant questions, problems andnews in the practice of coating. There-fore the stressed-out user should findthe time for answers to some of hisimportant questions.

I Do the cutting edges of preci-sion tools need speciol pre-lreolmenl before cooling?

For HSS tools, even simple de-burringis of major importance (figure 1).If coated without prior de-buffing, thecoated burr breaks on the lrst cut andthe tool edge continues its work uncoa-ted. This procedure yields only insigni-fi cantly better results.If the sharp cutting edges made of car-bide, cermet, ceramics and CBN (figure2), which are often charged with smallchjp\ and gears. are not well microstructured, big outbursts of completecutting parts are inevitable.The prevailing opinion is that mostof those cutting edges should berounded with a defined small radius.Consequently, these tools will also be

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Applicotion of Coqtings for ToolingQuo Vqdis 2OO5?

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able to "bite" at fine finishing withoutoutbursts.The table in figure 3 summarizes thecommon micro structuring methodsand their characteristics.In addition to the micro structuring ofcutting edges, some of these methods

F ig , l :Topping without ond with Micro Structuring (MS) for Cooting

F i g . 2 :Micro Strucluring of High Precision Tools- left: before Micro Structuring, right: ofter MicroStructuring

uncoar€d coargd c@ledwilrout lVlS 6lter lls

Mal..:X155CrMoV12 - [,18 - hole through - ao=zxdwz Hsco - vc=14 m/mln -sou.ce:iPL. Kasserand KMr.r Beriln

are also suitable for surface processingof cutting edge areas and flutes. Forexample, numerous well-known tool-makers brush or polish their high-per-formance thread formers both beforeand after the coating process:Before coating irregularities in the flutes

tool life; No. ol threads

2

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Fig. 3:lmportont Methodes for Micro Slrucluring (MS) for Cooiing

Fig. 4:Morkeishores ofCooting on HSS ondCorbide Tools

Aging in air at 70'C and 100% humidity

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and cuttingedge areas thatresulted fromgrinding are balanced. This allows themto sustain more pressure by the threadformer. The former edges become uni-formly roundeq which is an advantagefor the non-cutting procedure.After coating, droplets are removed,contributing to the better plastic flowof rhe formed work piece material.

2 Do AITiN cootings lose hord-ness during storqge?

Over the last few years, (Ti, Al) N-basedcoatings have achieved an increasinglylarger market share (figure .1).

Logically, the gains are higher forcarbide than HSS tools, because highstrength is far more important at hightemperatures and high cutting param-eters.In 2000 a publication from Japan [10]raised the suspicion that (Ti, AI) N-coat-ings would lose their hardness andstrength even without outer impactat room temperature. The suspicionwas not confirmed cleady, but doubtsremained (figure 5).

3 How con we breok fhrough thelimits of All iN-cootings?

It is a fact that the physical propertiesof AlTiN-coatings suddenly drop at anexcessive elevation of the alumiuurncontent (over abou( -0o6. f igure 6).These physical limits can be overcomebyI Adding more warm-resistanr alloyelements, such as chromium, )ttrium,silicon, creating AlCrN, TiAl\]I, TiAISiN-coatrngs orD By nanocomposite-stmctures, suchas (TiN)/ (SirNr, (TiAlN)/ (Si3N, or(AlCrN)/ (Si3Nr.

4 Will todoy's T|AIN-cootings bereploced by Ti-free coolings?

When it is not possible to increase theheat strength by adding more alumi-num in a TiAlN-coating, another metalinstead oftitanium v/ith a higher oxida-tion-resistance (like chromium) shouldbe used. This is howAlcrN-coatings arecreated (figure 7 t2l, [7], trll).Of course there are advantages anddisadvantages:Advantages:) Chromium is more heat resistant Lnantrtanlum.

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Aging in nitrogen at 300"C and 1 bar

0 25 s0 75 100 125 i50 "o zo ao 60 eo

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F i g . 5 :Hordness Chonge o{ oging of AIT|N-Cootings. left: oging in nitrogen ot 300 'C ond Iright: oging in oir ot 70 'C ond 100 % humidily

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Fi9. 6:Feotures of (Ti,Al)-bosed Cootings Depend-ing on Al-Conients

D Cr based coatings normally have evenbetter adhesion than Ti-based ones.D With AlCrN, coating thickness can behigher than with AlTiN.Disadvantages:D The Cr-targets are much more expen-sive (up to 8 times) than Ti-taryets> With the same Al-content, AICrN coa-tings are softer rhan AITiN coatingsD Today, CrN can hardly be de-coatedfrom carbidesA genuinely new alternative for dre bre-akthrough ofphysical limits with AITiN-coatlngs afe nanocomposlte coanngs,which are more heat-resistant thanCrAlN-coatings and can be producedmore economically

5 Why ore nonocomposites thelruly new kind of cootings?

By depositing very different kinds ofmaterials, the components (like Ti, CfAl in the first group, and Si in the other)are not mixed completely, and 2 phasesare created. The nanocrystalline TiA.[N-or AlcrN-grains become embedded inan amorphous SLN4-MatrLx, which canbest be noticed on the structure withhigher silicon content (figure 8 [7]).The beach analogy [8] of figure 9 offersa good illustration for the hardnessincreases made possible by nanocom-posrte-structures.

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F i g . 8 :NonocomposileStruciures (nc-AICrN)/(o-Sl.Nr)Cooiings (nACO")with dif ferent si-Con-tenT

a C@ling cotainins hcp A N,!.pe ri6eo AlN/S3Nrrtultibysj A liMsihl'Ji-sadient

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Usually, the foot sinks in dry sand. Inwet sand, the foot does not silp q1 nq1 Fig. 9:

as fur, because the space between san6 Hordness Increosing by Nonocomposiie Slruclure

grains is f i l led with \ ater. The surfacehas a higher resistance, so it is harder composites (figure 10 [12]): Thanks to the high hardness, the enor-In addition to the higher hardness, D At about 200 - 3oo'C later than with mous heat-resistance and the rough-nanocomposite coatings show their AlTiN-coatings and ness of the silicon "binder", coatingsmosr important advantage in dre > At about 100'C later than with AlCrN. with a nanocomposite structure canenormous improvement of heat resis- There are even indications that the stand their ground not only againsttance. The spinodale segregation and hardness loss at 1200'C is caused by PvD-coatings, but even againsr rhickthe resulting loss of hardness tend to the cobalt diffi.rsion of the carbide and C\rD-coatings (figure 11).appear much later than with non'nano- not by the nanocomposite coating.

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6 How cdn nonocomposites bedeposited in on industriol ondeconomicol woy?

) To avoid expensive alloyed targets(TiAt, AlCr) and to make segregationpossible, much cheaper and "pure"

cathodes (Ti, Cr, Al, AlSi) have to beinstallable next to each other.D Highly ionized plasma with a highintensive magnetic field has to be built-lnD This requires a fast, moveable ARC-Spot.L These requirements are met bythe L4RC@-method. (LARC@: t-{teralRotating ARc-Cathodes; figure 12 [3],[131) .The water-cooled cathodes rotate, Themagnetic field is created by permanentmagnets and coils, and is steered ver-tically and radiall)a Because of the fastrelative movement, low-melting targetmaterials (like pure Al or AlSi) can beused insread of expensive alloys (likeN25%tti75%, N50./.1'ti50%, N67%/'1i33%, Ct33oÄ/N67% etc.). After depo-sition from the target, Al and Si have tobe separated ("segregarion"). The sili-con does not enter the metallic stage;instead, the nanocrystallines (like TiAINor ÄlCrN) becom€ embedded in theamorphous matrix (like Si3N4). Thefast ARC-spot permirs a highly inrensi-ve magnetic field, without burning thetargets. (V/hereas drere is a high dangerfor planar targets.) The originatingnanocomposite structure shows smallcrystalline sizes, no "gaps" between thenanocrystallines, sha-rp interface limitsand therefore a high hardness. Thegenerated conb structure stops cracksat grain boarders [7].The constant erosion all around makesoptimum use of the target material.Depending on the thicknesses and onthe structures (mono-, gradient-, nano-or multilayer) of the required coatings,up to 200 batches can be deposited byone target pair The cathodes should belonger than the coatable heighr, achiev-ing an excellent coating thickness dis-tribution in the chamber.

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F ig , 10 :NonocomposileSlrr.,rclure shifts Spin-odol Segregolion tohigher Temperotures

F ig . l 2 :ARC-Guiding ondTorget Erosion withPlonor ond Roiot ingCylindricol Cothodes

F ig . l 3 ;Hordness of Nono-composrTe lnc-TiAIN)/(o-SlrNr) withNonoloyer Siructore

0 2 4 6 8 1 0reaming djstance, m

Hlsh-Perfomance Reamer RRo1 HM - d=11.5mmvc- 80 m/r ,n, f - 0,4 mm,re!

Sourcer Beck, Wlnterlingen, Germany

constant erosion on rotating cylihdricrl cathode

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200 400 600 800 1000 1200anneallng tempeEturer I"Cl

Tool Life Comparison at Drillingof Carbon Fibred Sandwich Meterial

F i g . 1 l :Nonocomposiies in Comporsion wilh Conventionol CVD- ond PVD-Cootings; left : Tool l i feComporsion Dri i l ing of Corbon Fibred Sondwich Moteriol; r ight: Diometer Degreosing ofthe Holes ot HSC-Reominq in Cost lron

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Tools: solid carbide drilis - d=l0-12 mm

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7 Whof ore lhe most imporlonlodvontoges of rololing cothodes

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Industrial production of nanocompo-sites with non-alloyed, cost-effectivetafgers.

b :Optimal coating adhesion through \rIR-TUAI, SHUTTER@The magnetic field is rotated by 180"towards the back. The ARC is ignitedat the back to clean the targets beforethe main coating process and to depo-sit any rough particles to the rear wall.After that, the ARC is turned towardsthe tools without switching off In thisway rhe duration of the ion erching issignificantly shonened and the coatingis deposited with pure metallic targets.

c :"wide" Targets with high durabilityAt equal space requirement, the rota-ting cylindrical cathode is n-times widerthan a planar target.

d :Smooth coatings through reduction ofARC-dropletswith rotating cathodes, the spot move-ment is fast and constant. It resultsfrom the addition of the target-rotationand the venical oscillation of the widemagnetic field (figure 12). with thesupport of VIIITUAL SHUTTER@ dro-plets from the beginning of the coatingprocess are "sprayed" to the back wall,after v/hich the fast ARC-spot move-ment is able to produce very smoothcoatrngs.

e :Ability to produce nanolayers due tothe cathode pair wirh minimum dis-tance, enabling exact control of thelayer period (figure 1l).

ftFreely programmable coating srochio-metryWith the use of non-alloyed cathodes,the ideal coating structure (figure 14)can be realized [7]:) The adhesion layer is supposed toshow a Young-Modulus comparable tothe substrate's.D The middle of the coating is supposed

0 500 1000 1500 2000

m llmg d|6täncet LI [m]

F ig . l 4 :Free ProgromobleStochiometry d^epos-ited with LARC--To rgets from Pure Tiond ALS|

F ig . l 5 rHord Mil l ing withAITiN ond Nono-composite Cooiings

F ig . l 6 :Hordness of AlCr-bosed CoolingsDepending on theCr-Conlent

the silicon content to 10%, the tool lifeis increased nearly to double (fig. 15

[ 7 ] , t 111 ) .By using pure (non-alloyed) targets,I-ARC@ technology allows the deposi-tion of freely programmable nanocom-posite structures (currently with Ti, Al,Cq Zr, and Si). The comparison ofhard-ness tendencies between the nanocrys-talline AICfN and the nanocomposite(nC-AICTN) i (a-SLN, proves again thatnanocomposite strttctures show essen-tial advantages against the conventionalcoating compositions (figure 16).

With the help of LARc@-technology thedisadvantages of the A-[CrN-coating canbe reduced:

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350

300

250

2aa

150

100

50

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to build up the hardness like a spring,guarantee the suspension, and absorbcracks to make interrupted cuttingpossible.> For the surface of the coating, thehardness, the wear resistance, and theoxidation resistance should be impro-ved.|> A lubricating coating with a low fric-tion-coefftcient should prevent built-upedges.

8 Whot olloy contenfs ore opfi-mol for nonocoolings?

At hard milling, nanocomposite coa-tings (TiAlN)/ (Si3N, achieve cleadybetter results than conventional AITiNlayers at just 6% silicon. By increasing

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depih (nm)

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Fig . l7 :MoDeC !r: Modulor Dedicoied Cooting

'Ihe hardness is again over 40 GP,r.) Due to the lo$- (5%) Cr content:D the use of the expensive Cr-target canbe minimized andI Thc coating can bc stripped fromtungsten carbide.> The deposition of thick layers (7, oreven up to 10 pm) is possible with thehelp of the Cr content and thereforethe AlCr-basecl coatings will be prefer-fed for application on HSS hobs, moldand dies.

9 Whol is fhe r ight mochinesize?

Currentl)'. -t:rilor-made coatings area lmost cx r lu . , i re l r p roducet l fo r ma jorclients" [2] in job coating. Therefore,modern coatinla units have to beconstructcd small enough so that thisis also affordable lbr small and mcdi-um enterpriscs ('SMES"). [14]. $/hilethis is not the onl,v argument for smallmachincs. ir ma1'easily be the mostimportantiI New coatings do not replace TiAINand Co. immediately. The dcmand forn : rn , ,s t ruc tL l r rd (oJ t tngs \ \ i l l g ros inthe next couple of _years, which makesit possible to use bigger machines.I In smaller machines there is no needto coat completel_v different parts toge-ther. Smallcr batches can also be per-lbrmed in an economical way.D Several small coating machines are

not less productive than a big machine.lhey are much more flexible and makebetter delivery times possible.D Once coaters have created the infra-structure lbr small-scale coating tech-nology. \(rl ing up getr much easicrthanks to the rotating cathodes.D The modular upgrading in widrh (norin height) is the correct way. becausethat way the same cathodes can be usedmodulady (figure 17):

Central cathodes enhance separationby factor 3, to satisfi' the requests ofcoating centers for an extremely pro-ductive coating of larger batches.b .Single cathodes at one side can takeover special tasks, like deposition ofa special adhesion layer or a DLC ropcoating. The central cathode pair pro-duces the nanocomposite coating.

In this configuration even the use ofplanar cathodes is suitable to producesimpler coatings.d.The horizontal usage possibilities showimpressivcly the high flexibility of rora-tion-s,vmmetrical cathodes. Vith thisarrangement, it is possible to have aconstant coating thickness for flat-lyingparts like sarv bands and forming-tools.

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l0 Job Goofing or Integrolion intoOwn Production?

SMES, e.g. mold and die makers. needdedicated high performance coatingsfor tq/o critical production steps atleast.D for cutting tools (free form end mills,drills, taps etc.) to machine the harde,ned form pieces and- for the moulds and dies themselves artheir application for injecrion molding,prcssing, punching, stamping.

The large coatings centers serve theSMES more slowly than rheir large keycostumers and normally \rrith standardcoatings only. Due to this rhe SMESloose thcir rn o imponanr adr antages:D the capability for fast delivery andI the flexibility to offer dedicated solu-tions adapted to the applicarion of themoulds even in small series.The real solution to these handicaps forthc SMES can be the integration of thecoating into their production line onlv

References:[1] Bellmann, B.: Herd and soft coatings

Hand book, Emuge, Laufa. d. Pegnirz, willbe published in 2004

[ 2 ] D . ' m m . H r E ( l i r u r r : u e r k z e u g - D o p i n g :

eine Umfrage unter fuhrenden Beschich-

Vrerksrarr und Betrieb, Hanser Verlag,München. 3/2001, p.10,19

l3l Holubar, ll a. o.: Success of nanostruc-tured coatings prepared by novel ARC-technolos', E'MRS Spring Meeting.Srrasbourg, Mai/200.i

[.i ] Jilek. M.. Moßtein. M. u. a.r A hard, \l€ar-rcsisimt aluminum nitride based coatngPatent proposal, 0.1.1052'11.3, EuropaenPatent Olice, München, 19.O1.2004

[51 ]Ialik, n: frendänderung imrnanentM.o.M. Letter, Sr.Gallen, 09.03.200!i

16l Mattox. D.: Handbook of Physical VaporDeposition (P\aD) Processing\villiam Andreq',4{oyes Publications, Nor-n'ich. 1998

[7] Morsrein. M., a.o.: Smart srructuring ofhigh performance nanocomposire coat,ings ICMCT4 88-2.3, Sxn Diego, Aprif2004

[8] Patscheider. J.: Nanocomposite bard coat-rngs rcr sear protectron

MRS Bulletin 28/3, 180 (2003)

l o t \ t r r e h l e . J . . P c r . p e k l i \ c n d e r . r h u e r z r rWirrschaftCredit Suisse Privare Banking, Zurich.8 . 1 2 . 2 0 0 3

[10] Suzuki, T., a. o.: Microsrructure andsecurd instabiliq ofthe (Tir l\lx) N,films

Journal of Materials Sciencc 35 (2000)1191-11.)9

o ,

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[11] Torp, B., x.o.: The first 2 years of experi-ence with industrial Applications depos-ited with rhe l-rlRc@,rechnologyICMCTF, G2-6, San Diego, ,{priv200'i

[12]Veprek, S. a. o.: Ävoiding the high'tem-perature decomposition and softening of(All-xTix)N coatings by the formation of

stable super h.ud nc'(Al1'xTix) N/a-Si3N.lNanocompositesMaterials Science and Engineering A 366(2OO1) 2O2-2O5

[13] Cselle, T., u. a.: Lr,RCr neue, industrielleBeschichtungstcchnologiewerkstatt und Betrieb, Hanser verlag,

Münchefl, Nr. 3, 2003

I14l Csellc, T.: Driving forces oftoday's manu-

facturing tcchnologyIndustrial Tooling, Southampton, Sept/2004

The R&D team:Olivier CoddetDr. Pavel HolubarDr. werner HuebenDr. Mojmir JilekAlexander MoschkoDr Marcus Morstein

AulhorTibor CSELLE (Ph.D., MSMM, MSME)CEo, Platit AG, Grenchen. SwiüerlandDr. Cselle studied two different disci-plines: machine tool engineering anddigital electronic. He worked for themachine tool industry in Switzcrlandand as a professor at dillirrent techni-cal colleges and universities in Hun-gary and Germany. His Ph.D. thesesled to his lecturing qualification. Heworked for the German tool manuläc-turer Guhring for 12 years, finally as

Dr. Milan RuzickaMichael SimaDr. Bo TbrpDr. Ondra zindulkaDr. Tibor Cselle

the head of research and development.As a consultant, he has been activein the Technical Advisory Councils ofthe European Union and for differentcompanies in Europe and in the USA.He was honored with differcnt innova-lion awards (e.9. Kistler and the Ameri-can Machinist). He is a pioneer of dryhigh speed machining, and leads sev-eral national and international researchprojects. Dr. Cselle has published over250 papers, patents, books and heldlectures in 25 countries.

(r\ \ \ ' \ ' r i l t t ' / i

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M r r r i l 50ver 110 PLATIT PVD coating units are in 0perat 0n w0rld wide.The r80 and tf00 rnodels feature the revolutionary LABC'techn0l0gy with rOtating cathodes. They are the tirst t0 allowdeposition of high performance nanocomp0site coatlngs suchas nACo@and nACBo" on an industria scale. 0f course, theyalso pr0duce traditional hard coatings l ike TiN, TiCN, TiAlCN,CrN, ZrN, and AlTiN.Check out our website f0r the coating c0mpass, which guidesy0u t0 the recommended c0atingf0ry0urapplicati0n.

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