A novel superplastic dieless drawing process of ceramic tubes
Introduction
Recently, a compact solid-oxide fuel cell (SOFC) was proposed for down-sizing and higher efficiency of the fuel cell with aim to innovate car driving system [1]. The compact SOFC consists of micro ceramic tubes expecting high performance (see Fig. 1) [2]. These tubes are required to accomplish further miniaturization. Mother ceramic tubes are manufactured through sintering after sharping processes such as powder paste extrusion, powder injection molding or press forming of powder to half tubes and bonding them to round tube. However, their size is not so small, therefore, an appropriate mass production process to reduce their size and make into micro ceramic tubes are required to extend the proposed SOFC.
Normally, the ceramics are not subjected to plastic forming due to hard and brittle characteristics. Meanwhile, the ceramics show superplastic deformation at the high temperature range from 1400 to 1700 °C, reported by Wakai et al. [3]. However, dies and tools cannot be practically safe in such high temperature. Therefore, the ceramics cannot be delivered, in general, to the practical plastic forming processes.
On the other hand, Weiss and Kot proposed the dieless drawing by introducing local heating of metal bars [4]. The authors proposed a superplastic dieless drawing for fabrication of microtubes and the effectiveness of the process was demonstrated for manufacturing superplastic metal tubes [5], [6], [7].
In this study, the authors intend to propose a novel superplastic dieless drawing for effective and expectable mass manufacturing of micro ceramic tubes SOFC used in fuel cell car. For this final goal, a superplastic dieless drawing apparatus with acetylene burner for obtaining ultra-high temperature over 1700 °C has already designed for 3Y-TZP tubes in our previous study [8]. The performance of designed apparatus such as load and temperature distribution measurements in the dieless drawing were evaluated. However, detailed deformation behaviour of zirconia ceramic tubes in the superplastic dieless drawing has not been clarified adequately.
In this paper, the fundamental deformation behaviour of zirconia ceramic tubes were investigated in the superplastic dieless drawing by using designed apparatus. Geometry of cross-section and surface roughness of drawn tubes and necessary drawing stress were made clear in a single pass drawing. The effectiveness of the proposed drawing method was verified. Furthermore, the possibility of manufacturing micro zirconia ceramic tube which could be applied to SOFC was demonstrated by applying the multi-pass drawing.
Section snippets
Basic formula of superplastic dieless drawing
The superplastic dieless drawing as shown in Fig. 2 was performed by a combination of local heating and drawing, that is tensile elongation. The local heating zone is fixed and the tube moves through the heating zone. Concurrently, the tube was subjected to tensile force and resulted elongation due to the difference in speed between drawing V1 and feeding V2. The reduction in area R is expressed by
based on the volume constancy law, where A1 and A2 are initial and deformed
Material and experimental procedure
In this study, as a representative superplastic ceramic, 3Y-TZP was employed and its tubes with outer and inner diameter of D = 6 mm and d = 4 mm were subjected to the experiment. Fig. 3 shows the schematic illustration of the proposed superplastic dieless drawing designed by authors [8]. As a heating source, an acetylene burner was introduced to obtain ultra-high temperature over 1500 °C. This heating method was effective for achieving superplastic deformation of 3Y-TZP tubes. The heating temperature
Fundamental features of superplastc dieless drawing
Fig. 4 shows the deformation features of 3Y-TZP tubes captured by a camera. The deformation mode changes from initial non-steady deformation to steady states deformation during drawing. There are the results obtained under the condition of V2 = 0.05 mm/s and reduction in area of 70.5%. As shown in the figures, the outer diameter of the tube is reducing gradually during non-steady stage (Fig. 4(b)). In the steady stage from Fig. 4(c) to (d) (final stage), the deformation zone becomes stable. Thus,
Conclusion
In this paper, fundamental deformation features of 3Y-TZP tubes for next generation SOFC in a novel dieless drawing process were investigated. The following results were obtained. (1) The reduction in area R and/or the outer diameter of drawn tubes is controlled by changing feeding and drawing speeds. (2) The smooth surface of drawn tubes can be obtained by introducing fine grained of mother tubes. (3) Extremely low tensile stress is enough for actual drawing. (4) High value of strain rate
Acknowledgement
This study was supported by JSPS KAKENHI Grant-in-Aid for Scientific Research (C) Grant number 24560888.
References (11)
- et al.
Fabrication of the Large Area Thin-film Solid Oxide Fuel Cells
CIRP Annals—Manufacturing Technology
(2014) - et al.
Study of Steam Electrolysis Using a Microtubular Ceramic Reactor
International Journal of Hydrogen Energy
(2009) - et al.
Design and Development of a Novel Load-control Dieless Rod Drawing System
CIRP Journal of Manufacturing Science and Technology
(2011) - et al.
Fabrication of Noncircular Multicore Microtubes by Superplastic Dieless Drawing Process
Journal of Materials Processing Technology
(2014) - et al.
On the Roughening of a Free Surface During Sheet Metal Forming
CIRP Annals—Manufacturing Technology
(1988)
Cited by (15)
Deformation behavior and mechanical anisotropy in ZrB<inf>2</inf>-based ceramic
2024, Ceramics InternationalEffect of microstructure on outer surface roughening of magnesium alloy tubes in die-less mandrel drawing
2022, Journal of Magnesium and AlloysCitation Excerpt :Furushima and Manabe reported that a reduction in the cross-sectional area of 50 % was obtained in a single pass of die-less drawing [22]. However, active thinning of the wall thickness is generally difficult in die-less drawing because the ratio of the wall thickness to the outer diameter is constant [23]. Recently, a die-less mandrel drawing, which can achieve active thinning of the wall thickness by suppressing the decrease in the inner diameter due to the mandrel, has been developed.
Continuous observation of twinning and dynamic recrystallization in ZM21 magnesium alloy tubes during locally heated dieless drawing
2022, Journal of Magnesium and AlloysLocally heat-assisted torsion forming of metal tubes for improvement of mechanical properties based on microstructure control
2020, CIRP AnnalsCitation Excerpt :However, it is very difficult to manufacture thin-walled pure aluminum microtubes because of size effect of grain size, friction and dies and tools manufacturing in micro-scale [4], and a new method of manufacturing thin-walled microtubes of pure aluminum for high-efficiency heat exchangers is required. In previous studies, Tiernan et al. [5] and the present authors discussed locally heat-assisted dieless drawing without using any dies and tools to manufacture metal microtubes, and magnesium alloy microtubes with low ductility were successfully manufactured by dieless drawing [6]. In addition, the authors developed an apparatus for locally heat-assisted torsion forming with the function of applying twisting (shear deformation) to a local heating zone in dieless drawing [7].
Flexibility in metal forming
2018, CIRP AnnalsCitation Excerpt :The main prerequisites of dieless drawing are localized heating and uniaxial tension. Localized reduction in an area is caused in the tension state by low flow stress at the locally heated part [44]. Dieless tube drawing offers flexibility to reduce the cross-sectional area of a tube only by adopting a drawing speed higher than the feeding speed without requiring dies or a mandrel.