Development and Prototyping of a Ceramic Micro Turbine

W. Bauer1, M. Müller1, R. Knitter1, J. Oerding2, A. Albers2, J. Kotschenreuther3, J. Fleischer3

1 Forschungszentrum Karlsruhe, Institut für Materialforschung III (IMF III)PO Box 3640, 76021 Karlsruhe

+49-(0)7247-82 2990, werner.bauer@imf.fzk.de

2 Universität Karlsruhe (TH), Institut für Produktentwicklung (IPEK)3 Universität Karlsruhe (TH), Institut für Produktionstechnik (wbk)

Abstract

Within the framework of the Collaborative Research Center 499 (SFB 499) of the German ResearchFoundation (DFG), a zirconia micro turbine was chosen as a demonstrating tool to enhance the interaction of theparticipating workgroups. This case study describes the evolution of the demonstrator and experiences gainedwith the design and the manufacturing of a micro device. Although it was not the aim of this basic researchproject to develop a commercial product, the experiences can be useful for improving the performance of indus-trial product development processes for ceramic micro devices.

The various parts of the zirconia micro turbine were prepared by a Rapid Prototyping Process Chain(RPPC) that allows for a fast and inexpensive manufacturing of ceramic parts with details down to the micronrange. A first design concept was made to demonstrate mainly the shaping feasibility of the process in the microrange. However, some features affected the performance due to their low strength. Thus, a modified design wasoptimized for power output and durability. Models of the design parts were produced either in polymer by aRapid Prototyping method or as metallic models by micro machining. After some process optimizations, denseand homogenous ceramic micro parts could be replicated from the models. Currently, an assembling processtakes place, preparing the micro turbine for performance tests.

Keywords: micro component, prototyping, micro machining, LPIM, zirconia

Introduction

In 2000, the Collaborative Research Cen-ter 499 (Sonderforschungsbereich 499, SFB 499)“Development, production and quality control formolded micro components made of metallic andceramic materials” was established by the GermanResearch Foundation (Deutsche Forschungsge-meinschaft, DFG). Participating research institutesare from the University Karlsruhe (TH), the Uni-versity Freiburg and from the Research CenterKarlsruhe (Forschungszentrum Karlsruhe) [1]. It isthe aim of the SFB 499 to work out the scientificbasics for the development of a continuous andstable process chain for the mass production ofmolded micro components made of metallic andceramic materials. This includes the construction ofmicro components, the manufacturing and an at-tendant quality management. The core of the SFB499 consists in the production techniques of pow-der injection molding (PIM) that can be used forthe manufacturing of complex three-dimensionalmetallic or ceramic micro components, and themicro casting, exclusively used for metallic microcomponents.

A demonstrator system was defined to actas a link between the individual projects of theSFB. Although it was aspired to build a functioningsystem, one always has to bear in mind that it is notthe mission of the project to develop a commercialproduct with competitive costs and optimized func-tionality. The purpose of the demonstrator wasrather to represent a physical interface which al-lows to optimize the cross-linking between work-groups, to integrate a variety of manufacturingchallenges into a single system, and to demonstratethe problems which arise from assembling a com-plex system instead of manufacturing only individ-ual components. With the help of the demonstratorit was possible to detect restrictions and to crossfrontiers in the micro fabrication processes forceramics and for metals.

Various demonstrator systems were usedduring the runtime of the SFB. One of them is amicro turbine that drives a planetary gear set. Thispaper is focused only on the micro turbine section.It describes experiences which were gained withthe design and the manufacturing of the turbine

CICMT 2008

000246

components by a prototyping method and the as-sembly of the components to the device. Restric-tions and problems which were identified in themanufacturing and handling of a first design con-cept lead to a design evolution and to progresses inthe manufacturing processes.

Design of the micro turbine demonstrator

Designing micro parts is very much differ-ent from macroscopic design tasks. From the mac-roscopic point of view, the detailed design is usu-ally one of the last steps. The design of micro partsdeals from the beginning with the question what ispossible with available manufacturing methods.Even more than in other design tasks the limitationand restrictions for the design possibilities comefrom downstream process steps [2,3]. Therefore, itis important to stay in close contact to the otherprocess disciplines and to start testing and simulat-ing very early. First concepts are needed to validatethe details in the design of the parts.

Fig. 1: Exploded assembly drawing of the microturbine demonstrator device consisting ofperforated plate, rotor, nozzle plate and agear wheel with integrated axis.

Design guidelines that might support thedevelopment process of the fluidic components of aturbine are generally known for large systems, butit is not certain that they will be valid for the as-pired size range. For that reason the design ismainly based on experience gained in the macrorange. Another aspect that influences the design isthe specific purpose of the demonstrator. The inte-gration of demanding features was necessary toreveal manufacturing limits and to demonstratedeficits in the practicability of assembling strate-gies.

Fig. 1 shows a design scheme with thedemonstrator components. The system consists of aperforated plate with media inlets and outlets, the

rotor, nozzle plate and a gear wheel for power out-put. All rotating components should be fixed on acentral axis. An outer diameter of 4 mm was in-tended for the final, air-driven system.

Two concepts of the demonstrator deviceare presented. In concept 1 especially the microdimensions of the rotor wings and nozzle channelswere challenging for the molding process. Rotor,gear wheel and axis, which have been manufac-tured separately, were designed for assembly bypress fit. In concept 2 the assembling effort wasreduced by the combination of gear wheel and axisand by a form fit connection of the rotor. Addition-ally, the rotor wings were enlarged in width andheight for improved strength and for higher torqueoutput. In this case the high aspect ratios (ratio ofheight/depth to width) of the rotor wings and noz-zle channels were found to be a challenge.

Ceramic injection molding

Ceramic injection molding (CIM) has es-tablished itself as a standard process for the manu-facturing of complex micro patterned ceramicparts. On the equipment side, the process is basedon machines similar to those used in conventionalinjection molding which, however, had to be exten-sively modified and upgraded in terms of tool de-sign and process control, to accommodate the spe-cific requirements of micro devices and feedstockproperties [4]. There are two variants of ceramicsinjection molding, the widely used high-pressureinjection molding (HPIM) process [5] and the lesscommon low-pressure injection molding (LPIM)process. While the potential of high-pressure injec-tion molding lies in cost-effective mass production,low-pressure injection molding is predestined forthe fast manufacture of small production lots [6,7].One reason for the positioning of HPIM for massproduction are the high costs associated with themanufacturing of the molds. This makes the proc-ess only profitable when a large number of parts ismolded. On the other side, LPIM can work withsimple and inexpensive molds and is even eco-nomical for small series. Both variants complementone another in an ideal manner and cover the entirerange from one-off prototype to mass production.

A central objective of SFB 499 is the de-velopment of a processing technique adapted to themanufacturing of middle and large series. There-fore, HPIM takes up a central position in the pro-ject. On the other side, the demonstrator systemconsists of a large number of individual parts.Manufacturing the complete demonstrator byHPIM would produce large costs for the requiredmolds. Thus, it was decided to limit the applicationof HPIM to the molding of specific parts, mainlyfor the planetary gear set, and to establish a proto-typing project based on LPIM for the other parts,including the manufacturing of the complete microturbine.

CICMT 2008

000247

Prototyping of ceramic micro parts

During the last 20 years a variety of dif-ferent Rapid Prototyping (RP) or Solid FreeformFabrication (SFF) methods for the fast productionof models and prototypes were developed in themacro world. They are mainly generative methods,like stereolithography or laser sintering, enablingthe production of three-dimensional parts directlyfrom the 3-D CAD data. Originally developed forpolymer materials, meanwhile, numerous methodsalso exist for the production of large ceramic mod-els [8,9].

Yet the Rapid Prototyping of micro partsis still limited with regard to accuracy and materialsvariety. Extremely fine details have only been real-ized with stereolithographic methods which allowthe manufacturing of polymer parts with a resolu-tion of a few micrometers [10]. The principle feasi-bility of expanding RP methods to the manufactur-ing of small ceramic parts was already demon-strated on a lab scale for stereolithography or inkjet printing [11,12], but difficulties in the prepara-tion of suited dispersions limited the applicabilityto a few materials only, and the missing availabilityof commercial equipment prevents a wider prolif-eration of the technique.

The current restrictions of RP methods inthe micro range can be overcome by a Rapid Proto-typing Process Chain (RPPC), where a primarymodel is first manufactured from a polymer ormetal material and then replicated into the re-quested ceramic material by low-pressure injectionmolding (Fig. 2) [13,14]. Micro stereolithographyis particularly suited for the fabrication of a micropatterned polymer model. Furthermore, primarymodels can also be produced by micromechanicalmachining of polymers or metals which is de-scribed later in this paper. The second step of theprocess chain is the fabrication of a mold suited forLPIM.

Fig. 2: Schematic representation of a Rapid Proto-typing Process Chain (RPPC) for the pro-duction of ceramic parts.

Using molds from silicone rubber hasproven to be advantageous for several reasons.Such molds can simply be produced by casting theprimary model into a two-component silicone rub-ber. Cross linking of the material only lasts a fewhours till the model can be extracted and the moldcan be used. Silicone rubber is characterized by anexcellent reproduction ability of the finest struc-tures; even details in the sub-micrometer range arereplicated. The elasticity of the silicone rubber isnot only favorable for the extraction of the primarymodel but also for the subsequent removing of thesoft green body. This makes it possible to demoldalso fragile details and vertical walls with highsurface roughness, as they are often characteristicfor RP methods. Even undercuts can be removedwithout a complex tool design due to the compli-ancy of the material. However, this compliancymakes some demands on the control of the LPIMprocess. To avoid discrepancies in the dimensionsof the part, it must be guaranteed that the moldingprocess ends in a stress-free state. Deformationsmay also occur due to the weight of the green body,but this problem is usually negligibly for microparts. Another challenge is the high thermal expan-sion of the silicone rubber. For the production ofprecise parts there are high demands with respect totemperature control during hardening the siliconerubber as well as during the shaping process. Sili-cone rubber molds can withstand a large number ofmoldings, as long as the mechanical loads remainin a moderate frame. According to experience, aminimum batch of some 100 parts can be manufac-tured by a single mold.

Prototyping of the micro turbine (concept 1)

Zirconia (ZrO2) is proposed as the mostpromising ceramic material for micro components.It offers a fine microstructure and excellent me-chanical properties. Additionally, for micro partsthe high costs of the material only play a minorrole. For the micro turbine the widespread zirconiaTZ-3YS-E powder from TOSOH (Japan) was used.The starting powder has a mean particle size of lessthan 400 nm and a BET surface of 6-7 m2/g. Thepowder was dispersed at a solid content of52 vol.% in the commercial binder system SiliplastLP65 by Zschimmer & Schwarz (Lahnstein, Ger-many). The binder already contains dispersants andother additives, thus, no additional organics arerequired. Melting temperature of the binder is lo-cated at app. 65°C. For the preparation of the LPIMfeedstock a heatable dissolver mixer (VMA Geetz-mann, Reichshof, Germany) was used, resulting ina viscosity of 17 Pas (at 85°C and a shear rate of100 s-1).

Polymer models for the concept 1 of themicro turbine were mainly manufactured by the so-called RMPD® method, developed by microTEC(Duisburg, Germany) [16]. This company has a

CICMT 2008

000248

large experience in the prototyping of polymermicro parts down to the micro range. In the RMPDtechnique thin layers of photocurable acrylic orepoxy resins are exposed via a mask. By stackingthe layers, a three-dimensional micro part isformed. The layer thickness can be reduced downto a few micrometers resulting in very smoothvertical surfaces (Fig. 3), but for reasons of timeand effort usually a layer thickness of 25 or 50 µmis preferred. Lateral resolution is in the range ofsome micrometers.

Fig. 3: SEM micrograph of a polymer gear wheelwith smooth surfaces, made by the RMPDprocess.

For the manufacturing of the molds a two-component silicone rubber NEUKASIL®RTV 20with a shore A-hardness 50 from AltropolKunststoff GmbH (Stockelsdorf, Germany) wasused. At a temperature of 40°C cross-linking tookplace within six hours, enabling the manufacturingof additional molds within short time.

The molding of the micro parts was per-formed in a piston-driven injection molding ma-chine GC-MPIM-2-MA-X from GOCERAM Ltd.(Sweden). With this machine it was possible towork at injection pressures as low as 0.1 to0.3 MPa to prevent distortion of the compliantsilicone mold. A feedstock temperature of 95°Cand mold temperature of app. 40°C was used. Priorto injection, the air was removed from the mold toprevent incomplete filling by entrapped gas. De-molding was performed manually. The process ispromoted when the micro parts are molded on abase plate. This supports the mold-filling as theplate creates an additional heat storage and thusreduces the risk of premature freezing of the feed-stock. Additionally it works as a support to facili-tate the demolding of the fragile micro parts. Theplate was removed by grinding before sinteringtook place. For that purpose the micro parts wererecast with wax or paraffin to protect them duringmachining. The wax is simply removed by meltingat the beginning of the debinding process.

Standard debinding procedures were per-formed up to 500°C at a rate of less than 1°C/minand dwell times at 150°C and 240°C. For sinteringa 3°C/min ramp up to 1450°C was used. For thethermal treatment, the micro parts were placed onan alumina substrate which could be heated up to1450°C, thus it was not necessary to transfer thesensible parts to another support after debinding.

Fig. 4: SEM micrograph of the turbine axis. Thelayer structure of the polymer model isreplicated in the sintered zirconia part.

Examples of sintered micro parts areshown in Fig. 4-6. All structural details of the tur-bine design could be manufactured with the de-scribed method. The high precision of the replica-tion process is evidenced by a complete replicationof the layer characteristic of the polymer modelsinto the ceramic micro parts (Fig. 4). However, at acloser look surface defects are revealed arisingfrom insufficient feedstock homogeneity. Powderagglomerates were not destroyed during feedstockpreparation, leading to a rough and porous surface.Direct measuring of the sintering density was notfeasible with sufficient accuracy due to the lowweight of the micro parts but could be performedwith parts where the base plate was not removed.The result was a mean sintering density of97% th. d. (at a theoretical density of 6.10 g/cm3)confirming the remaining porosity.

The precision of the micro parts is exem-plarily demonstrated by the sintered gear wheelpart. The axis diameter (di), the addendum circlediameter (da) and the height (h) of the parts aregiven in table 1. All values were measured on adozen samples with an optical microscope.

Table 1: Measurements of sintered ZrO2 microgear wheels

Mean / µm Standard deviation / µmdi 491 5da 1158 6h 155 17

CICMT 2008

000249

With the exception of the height a preci-sion of better than 10 µm can be obtained by LPIMwith silicone molds. Comparable values wereachieved for the precision of the other components.For all samples, the relative precision seems tobecome lower for the small features. This is mainlydue to the error of measurement, that was identifiedto be in the range of 3-4 µm for the used measur-ing equipment, but for still smaller features it willbe caused also by the grain size of the sinteredceramic (400-500 µm). The lower precision of theheight of the gear wheel has another reason. Itresults from the grinding of the base plate that wasperformed manually without precise process con-trol.

All components were produced with ahigh yield of more than 90 %. The only exceptionis the rotor part (Fig. 5). Here problems arose fromthe susceptibility of the wings with a cross-sectionof only 150 x 80 µm. During demolding, grindingof the base plate and other handling steps wingsbroke away easily. This reduced the yield of thispart to less than 20 %.

Fig. 5: SEM micrograph of the zirconia rotor. Thecracks in the wings were introduced dur-ing SEM preparation.

The individual components were tested forassembling to build the complete turbine. It wasintended to fix the gear wheel and the rotor on theaxis by a press fit as it is common for macroscopicparts. However, the scattering of the diameters ledto an insufficient fit of the components. Rotor andgear wheel were usually either loose or broke dur-ing the assembly. For thin parts like the rotor eventhe overcoming of the wall roughness producedtensile stresses which were high enough to breakthe central ring. Due to this, the press fit could notbe used for the assembly of the micro turbine. Inaddition, suited rotors were fixed on the axis withglue and turned from the outside via the gearwheel. The vulnerability of the design was so highthat even a slight contact with the surrounding partscaused failure of the wings.

The described problems evidenced theneed to improve various processing steps. Besidesthe design also the feedstock properties and themachining was updated. These steps optimized theproperties and facilitated the handling of the microparts.

Improvement by process optimization

The properties of the zirconia feedstockcould be improved by using a different binder sys-tem. The use of a paraffin binder Type TerHell6403 (Sasol Wax, Hamburg, Germany) and ofHypermer® LP1 (Uniqema, Emmerich, Germany)as a dispersant were found to be effective. Thedispersant was added to the paraffin with anamount of 2 mg per square meter of the particlesurface. Although the viscosity of this binder sys-tem is higher (23 Pas at 85°C, shear rate of 100 s-1

and a solid content of 50 vol.%) the homogeneityof the feedstock is obviously improved as an en-hanced sintering density of more than 99.6 % oftheoretical density and a reduced surface roughnesswere obtained (Fig. 6). The linear sintering shrink-age was 20.6%.

Fig. 6: SEM micrograph of the zirconia rotorwithin the nozzle plate. The twisted shapeof the nozzle is caused by a distortion ofthe silicone mold during the filling withthe high viscous feedstock.

The viscosity of this feedstock is near theupper limit compatible with silicone molds. Al-though all structural details are replicated in thesintered micro part, deformations can already beseen at the channels in Fig. 6. During the filling ofthe mold the silicone walls for the 40 µm widechannel structure are already distorted by the in-creased shear stresses of the feedstock.

Another optimization of the process wasachieved by an adapted machining process. Asparts were often destroyed during the grinding ofthe base plate in the green state, the strength of theparts was increased by a pre-sintering step. Afterdebindering, the micro parts were annealed for 1 h

CICMT 2008

000250

at a temperature of 1080°C to induce the formationof sintering necks at the particles. Thereby thestrength of the parts was sufficiently increased toimprove the handling without significantly aggra-vating the machining. In particular, the yield of therotor parts was considerably increased by this pro-cedure.

Turbine design optimization (concept 2)

In concept 2 the design was optimized forbetter permanence and for higher torque output bya new rotor profile and by increasing the height ofthe rotor from 150 to 800 µm. Gear wheel and axisare now a single unit. Additionally, the connectionbetween rotor and axis was now designed as atriangular form fit junction.

Fig. 7: SEM micrograph of the zirconia rotor(concept 2). The polymer model was madeby the RMPD process.

Models for the concept 2 were manufac-tured either as polymer model by the RMPD® proc-ess or by micromachining of brass. A challenge ofthe new design was the increased height of theinternal features. With the layer based RMPD®

technique thick layers and an undulated verticalsurface were produced for this sample height(Fig. 7). This aspect aggravated the demolding ofthe nozzle plate and the axis/gear wheel componentdrastically. For that reason, a micromachiningmethod was chosen to produce these two compo-nents with smoother surfaces (Fig. 8).

Micro milling enables the manufacturingof metal models with accurate geometrical toler-ances in the range of a few microns and smoothsurfaces with an attainable roughness as low as a Rz

of 0.3 µm [17-19]. Brass was selected as workpiece material, featuring a very good machinabilitywhile still being quite wear resistant.

Fig. 8: SEM micrograph of the zirconia axis/gearwheel combination (concept 2). The modelwas fabricated by micro milling of brass.

The most complex part of the turbine wasthe nozzle plate with thin slots and a high aspectratio in order to guarantee the proper functioning ofthis fluidic part. The width should be as small aspossible while maintaining a total depth of1000 µm (corresponding to 800 µm after sintering).

Smallest available tool diameters in micromilling with a sufficient reproducibility rate are30 µm wide. However, these tools currently onlyallow machining of aspect ratios of up to three. Toreach the desired depth a 100 µm tool had to beused with a flute length of 1 mm and therefore anaspect ratio of 10. The process parameters em-ployed with this tool were 24.000 rpm, a feed pertooth of 2 µm and an axial feed of 2 µm.

For smaller nozzles, EDM (Electro dis-charge machining) had to be used as an additionalmachining step. Therefore, the complete geometryhas been machined by milling except for the nar-row slots. Subsequently this work piece wasclamped to a Micro-EDM machine tool by Sarix(SX 100). Round electrodes with a diametersmaller than 10 µm could be produced by WEDG(Wire electro discharge grinding), but the electrodewear is very high resulting in uneven surfaces(slopes) at the bottom of the work piece. In a sec-ond approach small feeler gauges, commerciallyavailable as electrodes with a thickness of 30 µm,were successfully employed. The used processparameters were: pulse frequency 180 kHz, pulsewidth 2 µm, gap 70 V, pulse peak 100 A, idle volt-age 90 V.

In first tests, the total slot width includesthe width of the electrode and the process imma-nent gap on all sides and accumulates to 63 µm anda depth of 800 µm (Fig. 9). Further test showed thatthe desired depth of 1 mm could easily be reacheddemonstrating the potential of EDM to producehigh aspect ratios.

CICMT 2008

000251

Fig. 9: SEM micrograph of 63 µm test slots madeby EDM in brass.

Due to the smooth vertical surfaces of themicromachined model the zirconia nozzle plateswith 100 µm slots could be demolded from thesilicone molds without problems. After sintering aslot width of approximately 80 µm is achieved(Fig. 10). The preparations for the manufacturingof the brass model with 63 µm slots are still run-ning. If the demolding step works for this sample, aslot width of 50 µm at a depth of 800 µm is ex-pected for the sintered nozzle plate.

Fig. 10: Optical micrograph of the sintered zirco-nia nozzle plate (concept 2). Width ofnozzle channels is app. 80 µm at a depthof 800 µm.

Outlook

It is obvious that an operative and reliablesystem will only emerge if it is possible to manu-facture all components with tight tolerances. This isnot only a prerequisite for the proper assembling ofthe parts on the axis but also obligatory with re-spect to the long-term behavior of the device. Theoutstanding assembling and operating tests willindicate whether the obtained status is alreadyadequate for turbine applications.

Also intended are performance tests whichmeasure the power output of the device as the tur-bine must provide sufficient torque to move thesubsequent planetary gear drive. Results will bepublished in a following paper.

Acknowledgement

The authors thank the German ResearchFoundation (Deutsche Forschungsgemeinschaft)for the support of the works in the scope of theCollaborative Research Center (Sonderforschungs-bereich) 499.

References

[1] D. Spath, T. Barrho, M. Knoll, “Mikrourformen– der SFB 499”, wt Werkstatttechnik online, Vol.93, No. 3, pp. 136-140, 2003 (in German).

[2] A. Albers, T. Deigendesch, J. Marz, “Micro-specific design flow for tool-based microtechnolo-gies”, Microsystem Technologies, Vol. 13, No. 3-4pp. 305-310, 2007.

[3] A. Albers, D. Metz, “Impact of the microstruc-ture on the strain of micro components”, Journal ofMicrosystem Technologies, Vol. 12, No. 7 pp. 685-690, 2006.

[4] V. Piotter, T. Benzler, T. Gietzelt, R. Ruprecht,J. Hausselt, “Micro powder injection molding”, Ad.Eng. Mat., Vol. 2, No. 10, pp. 639–642, 2000.

[5] V. Piotter, W. Bauer, T. Benzler, A. Emde,“Injection moulding of components for microsys-tems”, Microsystem Technologies, Vol. 7, No. 3,pp. 99–102, 2001.

[6] W. Bauer, J. Haußelt, L. Merz, M. Müller, G.Örlygsson; S. Rath, “Micro Ceramic InjectionMolding”, D. Löhe, J. Haußelt (Eds.), “AdvancedMicro and Nanosystems 3”, Wiley VCH, Wein-heim, pp. 325-356, 2005.

[7] W. Bauer, R. Knitter, G. Bartelt, A. Emde, D.Göhring, E. Hansjosten, “Replication techniquesfor ceramic microcomponents with high aspectratios”, Microsystem Technologies, Vol. 9, No. 1-2, pp. 81–86, 2002.

[8] J. G. Heinrich, “New Developments in the SolidFreeform Fabrication of Ceramic Components”,cfi/Ber. DKG, Vol. 76, No. 5, pp. 29-35, 1999.

[9] B. Y. Tay, J. R. Evans, M. J. Edirisinghe,“Solid freeform fabrication of ceramics” Interna-tional Materials Reviews, Vol. 48, No. 6, pp. 341-370, 2003.

[10] A. Bertsch, S. Jiguet, P. Berhard, P. Renaud,“Microstereolithography: A Review”, Mat. Res.Soc. Symp. Proc., Vol. 758, L.L.1.1-L.L.1.1-11,2003.

CICMT 2008

000252

[11] A. Bertsch, S. Jiguet, P. Renaud, “Microfabri-cation of ceramic components by microstereolitho-graphy” J. Micromech. Microeng., Vol. 14, pp.197-203, 2004.

[12] T. Wang, B. Derby, “In-Jet Printing and Sin-tering of PZT”, J. Am. Ceram. Soc., Vol. 88, No. 8,pp. 2053-2058, 2005.

[13] R. Knitter, W. Bauer, D. Göhring, J. Haußelt,“Manufacturing of Ceramic Microcomponents by aRapid Prototyping Process Chain”, Adv. Eng. Mat.,Vol. 3, No. 1-2, pp. 49-54, 2001.

[14] W. Bauer, R. Knitter, “Development of aRapid Prototyping Process Chain for the Produc-tion of Ceramic Microcomponents”, J. Mat. Sci.,Vol. 37, pp. 3127-3140, 2002.

[15] W. Bauer, R. Knitter, M. Müller, H.-J. Ritz-haupt-Kleissl, “Prototype Manufacturing of Ce-ramic Microparts”, Cfi/Ber. DKG, Vol. 83, No. 13,pp. 65-69, 2006.

[16] http://www.microtec-d.de

[17] H. Weule, V. Hüntrup, H. Tritschler “Micro-Cutting of Steel to Meet New Requirements inMiniaturization”, CIRP Annals, Vol. 50, pp. 61-64,2001.

[18] J. Hesselbach, A. Raatz, J. Wrege, H.Hermann, H. Weule, C. Buchholz, H. Tritschler,M. Knoll, J. Elsner, F. Klocke, M. Weck, J. Boden-hausen, A. von Klitzing, "International State of theart of micro production technology”, ProductionEngineering, Vol. XI/1, pp. 29-36, 2004.

[19] D. Dornfeld, S. Min, Y. Takeuchi, “RecentAdvances in Mechanical Micromachining”, Key-note in Annals of the CIRP, Vol. 55, No. 2, pp. 1-24, 2006.

CICMT 2008

000253