MATERIALS LETTE.S ELSEVIER Materials Letters 40(1999)275-279 ww.elsevier. com/locate/mallet Ceramic green tape extrusion for laminated object manufacturing Yumin Zhang, Xiaodong He, Jiecai Han, Shanyi Du Center for Composite Materials, Harbin Institute of Technology, Harbin 150001, China Received 29 October 1998; received in revised form 16 February 1999, accepted 30 March 1999 Abstract Al,O3 and Sic green tapes with 0. 2 mm thickness used for LOM (laminated object manufacturing) were prepared from a 75 wt. ceramic suspension in a LdPe based organic vehicle followed by extrusion. Rheological characterization of the umina and Sic suspensions were studied. TG-DTA analysis was carried out in air and microstructures were examined by SEM. @1999 Elsevier Science B.v. All rights reserved Keywords: Extrusion, Ceramic tape; Laminated object manufacturing (LOM); Composites 1. Introduction plex shape can be formed from ceramic green tape After removal of the binder and sintering. a ceramic LOM (laminated object manufacturing), a new part with a complex shape will be obtained [4-6] forming technique, is a kind of rapid prototyping and Tape casting and extrusion are two major methods manufacturing technique. RP&M (Rapid Prototyp- for fabricating ceramic green tape [7]. The present ing and Manufacturing) changes the traditional re- work was to prepare Al, O, and Sic green tape with move method to anadd method RP&M combines 0. 2 mm thickness used for LOM. The organic vehi- CAD, laser, photochemistry and polymer techniques cle was LdPe LOM processes begin with a conventional 3-D CAD file that is converted to a standard format for manu- facturing(*. STL file) and sliced into thin cross sections by a separate computer program. The routes 2. Experimental procedure of scanning designed according to these slices are sed to control the movement of platform and laser scanning. Laser beam cut tapes of different material slice-by-slice, then add them to form components 2.1. Preparation of ceramic green tape required shape [1-3] Technical ceramic components can be fabricated The 2 um alumina powders(Shenyang First OM Ceramic green tape is necessary for LOM. Grinding Wheel Factory) were mixed with LDPE By LOM technique, ceramic green part with com- grains(Beijing Yanshan Oil Chemical Engineering) in the weight ratio 75: 25. Mixing, granulation and tape extrusion were performed using a Haake-RC90 Corresponding author ystem twin screw extruder. The product was an 00167-577X/99/ssee front matter o 1999 Elsevier Science B.V. All rights reserved Pl:S0167-577X(99)000890
September 1999 Materials Letters 40 1999 275–279 Ž . www.elsevier.comrlocatermatlet Ceramic green tape extrusion for laminated object manufacturing Yumin Zhang ), Xiaodong He, Jiecai Han, Shanyi Du Center for Composite Materials, Harbin Institute of Technology, Harbin 150001, China Received 29 October 1998; received in revised form 16 February 1999; accepted 30 March 1999 Abstract Al O and SiC green tapes with 0.2 mm thickness used for LOM laminated object manufacturing were prepared from a Ž . 2 3 75 wt.% ceramic suspension in a LDPE based organic vehicle followed by extrusion. Rheological characterization of the alumina and SiC suspensions were studied. TG-DTA analysis was carried out in air and microstructures were examined by SEM. q 1999 Elsevier Science B.V. All rights reserved. Keywords: Extrusion; Ceramic tape; Laminated object manufacturing LOM ; Composites Ž . 1. Introduction LOM laminated object manufacturing , a new Ž . forming technique, is a kind of rapid prototyping and manufacturing technique. RP&M Rapid Prototyp- Ž ing and Manufacturing changes the traditional ‘re- . move’ method to an ‘add’ method. RP&M combines CAD, laser, photochemistry and polymer techniques. LOM processes begin with a conventional 3-D CAD file that is converted to a standard format for manufacturing Ž . ).STL file and sliced into thin cross sections by a separate computer program. The routes of scanning designed according to these slices are used to control the movement of platform and laser scanning. Laser beam cut tapes of different materials slice-by-slice, then add them to form components with required shape 1–3 . w x Technical ceramic components can be fabricated by LOM. Ceramic green tape is necessary for LOM. By LOM technique, ceramic green part with com- ) Corresponding author plex shape can be formed from ceramic green tape. After removal of the binder and sintering, a ceramic part with a complex shape will be obtained 4–6 . w x Tape casting and extrusion are two major methods for fabricating ceramic green tape 7 . The present w x work was to prepare Al O and SiC green tape with 2 3 0.2 mm thickness used for LOM. The organic vehicle was LDPE. 2. Experimental procedure 2.1. Preparation of ceramic green tape The 2 mm alumina powders Shenyang First Ž Grinding Wheel Factory were mixed with LDPE . grains Beijing Yanshan Oil Chemical Engineering Ž . in the weight ratio 75:25. Mixing, granulation and tape extrusion were performed using a Haake-RC90 system twin screw extruder. The product was an 00167-577Xr99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. PII: S0167- 577X 99 00089-0 Ž
Y. Zhang et al/ Materials Letters 40(1999)275-279 Al O ∽0u0 一一 SHEAR RATE. 1/s DIAMETER um alumina green tape. SiC green tape was prepared by the same process. Grain size distribution of the are shown in Fig. 28 powders are shown in Fig. 1. Typical particle shapes SHEAR RATE. 1/s 2.2. Surry rheology Fig. 3. Shear stress(a)and apparent viscosity(b)as function of Rheological characterization of suspensions with shear rate with alumina content. (1)LDPE, (2)60 wt %Al2O3 (3)70wt%Al2O3,(4)80wt%Al2O3,(5)85wt%Al2O3 various alumina content was carried out using a Haake-RC90 system mixer at various shear rates logical characterization of ceramic suspensions are The effects of temperature and particle size on rheo- discussed below 98886628KV Fig. 2. SEM micrographs of ceramic powders; (a) Al,O, and (b)SiC
276 Y. Zhang et al.rMaterials Letters 40 1999 275–279 ( ) Fig. 1. Grain size distribution of powders. alumina green tape. SiC green tape was prepared by the same process. Grain size distribution of the powders are shown in Fig. 1. Typical particle shapes are shown in Fig. 2. 2.2. Slurry rheology Rheological characterization of suspensions with various alumina content was carried out using a Haake-RC90 system mixer at various shear rates. The effects of temperature and particle size on rheoFig. 3. Shear stress a and apparent viscosity b as function of Ž. Ž. shear rate with alumina content. 1 LDPE, 2 60 wt.% Al O , Ž. Ž. 2 3 Ž. Ž. Ž. 3 70 wt.% Al O , 4 80 wt.% Al O , 5 85 wt.% Al O . 23 23 23 logical characterization of ceramic suspensions are discussed below. Fig. 2. SEM micrographs of ceramic powders; a Al O and b SiC. Ž. Ž. 2 3
. Zhang et al/ Materials Letters 40(1999)275-279 2.3. Analysis of products TG-DTa analysis was carried out in air in orde TA to optimize the burn-out cycle. Microstructures were mined by scanning electron microscopy and mi 3. Results and discussion TEMPERATURE,℃ 3.1. Shurry rheology The rheological behavior of the slurries with vari ous Al,O, contents was similar. The flow curves (Fig. 3a)at 190 C showed a pseudo-plastic behavior The shear stress, T, increased with increasing shear DTA rate,y,, with an approximately linear relationship Fig. 5. Simultaneous TG-DTA analysis on green tape, up to 600.C:(a)Al,O, and(b)Sic between log(shear stress) and log(shear rate), im plying a power law relationship 4040404040650 TEMPERATURE. K where c and n are constants, and mapp the apparent viscosity. The apparent viscosity (mapp)can thus be a T (2) The apparent viscosities of various Al2O3con- taining materials content are shown in Fig. 3b. Re- gression of the experimental results with Eq.(1) showed that the exponent n decreased and c 1 creased with increasing Al,, content. In the ceramic green tape forming process, the ceramic content (i.e, Al,O, and SiC) should be as SHEAR RATE, 1/s high as possible. However, the ceramic content is increased, the shear stress increases. For the 2 um (b)with 75 wt% AL, 0, content and particle size: (a)2 um, (b-1) alumina powder, the green tape can be extruded and 2m,(b2)10μm,(b-3)40um continuous rolls can be formed which should be
Y. Zhang et al.rMaterials Letters 40 1999 275–279 ( ) 277 2.3. Analysis of products TG-DTA analysis was carried out in air in order to optimize the burn-out cycle. Microstructures were examined by scanning electron microscopy and microanalysis. 3. Results and discussion 3.1. Slurry rheology The rheological behavior of the slurries with various Al O contents was similar. The flow curves 2 3 Ž . Fig. 3a at 1908C showed a pseudo-plastic behavior. The shear stress, t , increased with increasing shear rate, gX , with an approximately linear relationship Fig. 4. Shear stress as function of temperature a and particle size Ž . Ž. Ž. Ž . b with 75 wt.% Al O content and particle size; a 2 2 3 mm, b-1 2 mm, b-2 10 Ž. Ž. mm, b-3 40 mm. Fig. 5. Simultaneous TG-DTA analysis on green tape, up to 6008C; a Al O and b SiC. Ž. Ž. 2 3 between log shear stress and log shear rate , im- Ž .Ž. plying a power law relationship tscgX n sh gX app Ž . 1 where c and n are constants, and h the apparent app viscosity. The apparent viscosity Ž . h can thus be app expressed as follows h strgX scgX ny1 app Ž . 2 The apparent viscosities of various Al O con- 2 3 taining materials content are shown in Fig. 3b. Regression of the experimental results with Eq. 1Ž . showed that the exponent n decreased and c increased with increasing Al O content. 2 3 In the ceramic green tape forming process, the ceramic content i.e., Al O and SiC should be as Ž . 2 3 high as possible. However, the ceramic content is increased, the shear stress increases. For the 2 mm alumina powder, the green tape can be extruded and continuous rolls can be formed which should be
Y. Zhang et al/ Materials Letters 40(1999)275-279 98887829KV 98987128K Fig. 6. Microstructural features of surface of tapes; (a)Al,2O, and(b) Sic strong enough to survive the feed mechanism when SEM(Fig. 6) showed that the particles were dis- the Al, O, content was 75 wt %(42 vol %) For the tributed in the LDPE matrix uniformly and remained 5 um SiC powder is used, the optimum content was their shapes 75 wt %(47 vol %) Fig. 4a showed that as the The final green tapes are continuous and can be mperature was reduced the shear stress increased rolled up and rolled out. However, the cracks will but with no sharp transition. At 190-210C, the appear on the tapes surface when strain is big enough green tape can be extruded The final green tapes for LOM had been used to The effect of particle size is shown in Fig. 4b. make samples With the same ceramic content, the shear stress increased slightly when the particle size was re- 4. Conclusion 3.2. Thermal analysis and micro-structure analysis The results showed that Al,O3 and SiC green tapes with 0.2 mm thickness used for LOM can be TG-DTA analyses (as shown in Fig. 5)were fabricated by extrusion For 2 um alumina powder, carried out in air. During the 245-375"C treatment, green tapes can be extruded when the Al, O, content there were three major exothermic peaks in the Dt was 75 wt %(42 vol %) For 5 um SiC powder, the curve of Al, O3-LDPE and weight lost rapidly be- Sic content was 75 wt%(47 vol %) The critical cause of the oxidation and decomposition of binder rature regime for burnout was 245-375C fo In the 421-500C, there were three major exother LDPE421-500°Cfor nic peaks in the Dta curve of SiC-LDPE. There oI the maximum heating rate in the proces was a small endothermic peak in both curves at 95c binder removal because of the melting of the binder. the critical mperature regime for burnout was 245-375C for AL2O3-LDPE, 421-500C for SIC-LDPE, which References controls the maximum heating rate in the process of removing of the binder [1] K.A. Don et al., Proceedings of the 1997 2 1st Annual Confer Microstructures were examined by scanning elec- ence on Composites Advanced Ceramics, Materials, and on microscopy and microanalysis Examination by Structures-B 18(1997)113
278 Y. Zhang et al.rMaterials Letters 40 1999 275–279 ( ) Fig. 6. Microstructural features of surface of tapes; a Al O and b SiC. Ž. Ž. 2 3 strong enough to survive the feed mechanism when the Al O content was 75 wt.% 42 vol.% . For the Ž . 2 3 5 mm SiC powder is used, the optimum content was 75 wt.% 47 vol.% . Fig. 4a showed that as the Ž . temperature was reduced the shear stress increased but with no sharp transition. At 190–2108C, the green tape can be extruded. The effect of particle size is shown in Fig. 4b. With the same ceramic content, the shear stress increased slightly when the particle size was reduced. 3.2. Thermal analysis and micro-structure analysis TG-DTA analyses as shown in Fig. 5 were Ž . carried out in air. During the 245–3758C treatment, there were three major exothermic peaks in the DTA curve of Al O -LDPE and weight lost rapidly be- 2 3 cause of the oxidation and decomposition of binder. In the 421–5008C, there were three major exothermic peaks in the DTA curve of SiC-LDPE. There was a small endothermic peak in both curves at 958C because of the melting of the binder. The critical temperature regime for burnout was 245–3758C for Al O -LDPE, 421–500 2 3 8C for SiC-LDPE, which controls the maximum heating rate in the process of removing of the binder. Microstructures were examined by scanning electron microscopy and microanalysis. Examination by SEM Fig. 6 showed that the particles were dis- Ž . tributed in the LDPE matrix uniformly and remained their shapes. The final green tapes are continuous and can be rolled up and rolled out. However, the cracks will appear on the tapes surface when strain is big enough. The final green tapes for LOM had been used to make samples. 4. Conclusion The results showed that Al O and SiC green 2 3 tapes with 0.2 mm thickness used for LOM can be fabricated by extrusion. For 2 mm alumina powder, green tapes can be extruded when the Al O content 2 3 was 75 wt.% 42 vol.% . For 5 Ž . mm SiC powder, the SiC content was 75 wt.% 47 vol.% . The critical Ž . temperature regime for burnout was 245–3758C for Al O -LDPE, 421–500 2 3 8C for SiC-LDPE, which control the maximum heating rate in the process of binder removal. References w x 1 K.A. Don et al., Proceedings of the 1997 21st Annual Conference on Composites Advanced Ceramics, Materials, and Structures-B 18 1997 113. Ž
. Zhang et al/ Materials Letters 40(1999)275-279 [2]KA. Don et al., Evolving technologies for the competitive [5] C. Griffin et al. The American Ceramic Society Bulletin 73 dge, Proceedings of the 1997 42nd International SAMPE (1994)109 Symposium and Exhibition 42(1997)764 [6] J.D. Cawley et al., The American Ceramic Society Bulletin 75 3. A. Don et al., Proceedings of the 41st International SAMPE (1996)60. Symposium and Exhibition, Part 1(of 2)41(1996)220 7 L. Esposito et al., British Ceramic Transactions 94(1995)230 [4] E.A. Griffin et al., The American Ceramic Society Bulletin 75 (1996)65
Y. Zhang et al.rMaterials Letters 40 1999 275–279 ( ) 279 w x 2 K.A. Don et al., Evolving technologies for the competitive edge, Proceedings of the 1997 42nd International SAMPE Symposium and Exhibition 42 1997 764. Ž . w x 3 K.A. Don et al., Proceedings of the 41st International SAMPE Symposium and Exhibition, Part 1 of 2 41 1996 220. Ž.Ž . w x 4 E.A. Griffin et al., The American Ceramic Society Bulletin 75 Ž . 1996 65. w x 5 C. Griffin et al., The American Ceramic Society Bulletin 73 Ž . 1994 109. w x 6 J.D. Cawley et al., The American Ceramic Society Bulletin 75 Ž . 1996 60. w x 7 L. Esposito et al., British Ceramic Transactions 94 1995 230. Ž