1. Materials Used
2. Filament Production
Figure 2: Filament production line. The material is extruded on a controlled manner by the regulation of the extrusion speed and temperature. Afterwards, it is collected and driven by a conveyor belt and haul-off unit. The filament diameter is measured and if the values are within the desired range, the filament is spooled. To regulate the filament dimensions, the pulling and spooling speeds must be progressively adjusted. Please click here to view a larger version of this figure.
3. Additive Manufacturing of Green Components
Figure 3: Manufacturing process for metal-ceramic component with tower structure. Please click here to view a larger version of this figure.
Figure 4: Virtual print of a component with surrounding ooze-shield. Please click here to view a larger version of this figure.
4. Debinding and Sintering of Components
The best fitting results for stainless steel sintering behavior were obtained with an attrition milling time of 180 minutes and a planetary ball mill (PBM) milling time of 240 minutes. Figure 5 shows a SEM-image of the untreated powder (left), the deformed particles after the attrition milling (middle), and the chopped particles after the PBM milling step (right).
Figure 5: Untreated stainless steel <38 µm (D90) (left), stainless steel powder after attrition milling (middle), and stainless steel powder after PBM milling (right) Please click here to view a larger version of this figure.
The sintering behavior of the initial and milled steel powder are compared with the sintering behavior of the zirconia powder in Figure 6, all measured with an optical dilatometer.
Figure 6: Dilatometric curves of the zirconia powder (TZ-3Y-SE) and the stainless steel powder (17-4PH) in the initial state and after a high-energy milling treatment of the stainless steel powder. Please click here to view a larger version of this figure.
The improvement of the feedstock mechanical properties in the high shear compounding step was characterized for the zirconia feedstock. A feedstock produced in a single compounding step of 75 min in a roller rotors mixer (RM) was compared with the one produced by the method described in the protocol. Filaments were extruded using a high pressure capillary rheometer with a die of 1.75 mm diameter, a piston speed of 1 mm/s and a temperature of 190 °C. The filaments were collected with a conveyor belt and tested with a universal tensile testing machine. At least 5 repetitions were conducted per material. Figure 7 shows a comparison of both materials concerning the ultimate tensile strength (UTS), the elongation at UTS, and the secant modulus.
Figure 7: Influence of the compounding method in the mechanical properties of the zirconia feedstock. Feedstock was compounded in an internal roller mixer (RM) or in combination with a co-rotating twin screw step (TSE). The strength, flexibility and stiffness of filaments produced with a capillary rheometer were determined using the mean value and the correspondent standard deviation of the ultimate tensile strength (UTS), the elongation at UTS and the secant modulus, respectively. Please click here to view a larger version of this figure.
In Figure 8, the diameter values obtained during the production of the filaments made of zirconia (left) and stainless steel (right) feedstocks are presented. The diameter of the extruded filament was recorded during the production process via single-screw extrusion. For the zirconia filaments, a good control of the dimensions could be achieved with a mean diameter of 1.75 mm and a standard deviation of 0.02 mm. For the filaments containing the modified stainless steel powder, a higher variability of the average filament diameter was observed. A possible reason for this could be an inhomogeneous particle distribution within the feedstock resulting from the platelet-like shape of the metallic particles (Figure 5). In this case, a higher number of measurement points were found outside the desired range of 1.75 mm ± 0.05 mm, and the mean diameter value was 1.74 mm with a standard variation of 0.03 mm. For both types of filaments, the ovality values were considerably smaller than the 0.1 mm limit.
Figure 8: Histograms of the filament diameter for the studied materials. Please click here to view a larger version of this figure.
Figure 9 shows the suitable metal and zirconia filaments to manufacture green sandwich structures with the composition steel-zirconia-steel (left) as well as zirconia-steel-zirconia (right).
Figure 9: Green steel-zirconia-steel (left) and zirconia-steel-zirconia components (right) additively manufactured by FFF. Please click here to view a larger version of this figure.
Due to the similar binder system of both materials, it is possible to fuse certain layers to a monolithic composite part. A larger round shaped part with sharp transitions is shown in Figure 10.
Figure 10: Structure with sharp transitions between Zirconia and stainless steel. Please click here to view a larger version of this figure.
Figure 11 shows other green single- and multi-material components that were further processed. Figure 12 shows a pure zirconia sample on the left side, The middle shows a pure stainless steel sample, and finally a sintered and well joined steel-ceramic composite is pictured on the right side.
Figure 11: Green test samples manufactured by FFF; top: zirconia-steel-composites with stainless steel on top; middle: stainless steel; bottom: zirconia. Grid box 5 mm. Please click here to view a larger version of this figure.
Figure 12: Sintered zirconia sample (left), sintered stainless steel sample (middle), and sintered zirconia-stainless steel-composite (right). All scales in mm. Please click here to view a larger version of this figure.
In Figure 13, a typical structure of FFF-components with crotches (or sub-perimeter) between two deposited filaments is shown, which resulted from an ordinary slicing (tool path) and the continuous way of material deposition.
Figure 13: Typical structure of FFF-components resulting from slicing and continuous material deposition. Please click here to view a larger version of this figure.
By raising the extrusion multiplier in the slicing software, which leads to a higher volume deposition, the sub-perimeter can be reduced as well as by adapting the tool paths. Nevertheless, due to the high content of particles in the filaments, it is evident that the deposition behavior differs from ordinary printing of thermoplastics. Therefore, a software modification to close such defects is desirable.
After solvent debinding, thermal debinding and subsequent sintering, all the different samples showed no significant deformation or bloating. The sintered pure zirconia and stainless steel FFF specimens have a good geometrical stability both with and without compressive load and they do not buckle. The total mass loss was 14.8-14.9%, indicating complete debinding.
The metal-ceramic samples showed a good macroscopic adhesion of both materials. The mass loss after the sintering of the composites was found to be 14.1-14.4%, which also indicates a full debinding. Further analysis and process adjustments will follow. The electron microscope characterization of the composites is intended to provide insight into the quality of the composite. The desired formation of the composite has taken place successfully as shown in Figure 14.
Figure 14: SEM Image of microstructure in the metal-ceramic interface showing the material joint. Please click here to view a larger version of this figure.
The results show that a promising approach to manufacture metal-ceramic composites using FFF generating electrical conductive and electrical isolating properties into one component. Furthermore, the implementation of ceramic parts into metallic environments becomes possible due to the good material bond and weldability of the stainless steel. Within the EU, project heating devices were manufactured by FFF containing an electrical conductive path made of stainless steel in a non-conductive ZrO2 matrix. Figure 15 shows the sintered samples. These multi-material components must be analyzed and tested in the future.
Figure 15: Sintered heating elements made of zirconia and stainless steel Please click here to view a larger version of this figure.
Figure 16 and Figure 17 show the new print head with two FFF-printing heads and two T3DP-printing heads as CAD-model (Figure 16) as well as implemented in the FFF device (Figure 17). One challenge is controlling of the output for both systems. For the micro dispensing units, the output is controlled by the frequency of a piezo-driven piston instead of the stepper motors speed for the belt drives within the FFF-printing heads. The interaction of both devices must be tested in the future.
Figure 16: CAD model of new print head with two FFF-printing heads and two T3DP-printing heads. Please click here to view a larger version of this figure.
Figure 17: Image of new print head with two FFF-printing heads and one T3DP-printing head (left). Please click here to view a larger version of this figure.
Zirconia | TZ-3YS-E | Tosoh, Europe B.V. | |
Stainless steel | UNS17400 -38 µm | Sandvik Osprey Ltd. | |
Table of Devices and Software | |||
slicing software | Simplify 3D | Simplify 3D, USA | |
roller rotors mixer | Plasti-Corder PL2000 | Brabender GmbH & Co. KG, Germany | |
3D printer | model Ceram | HAGE, Austria | |
cutting mill | SM200 | Retsch Gmbh Germany | |
corotating extruder | ZSE 18 HP-48D | Leistrutz Extrusionstechnik GmbH, Germany | |
laser measurementdevice | Diagnostic Laser 2010 | SIKORA AG, Germany | |
capillary rheometer | Rheograph 2002 | Göttfert Werkstoff-Prüfmaschinen GmbH, Germany | |
single screw extruder | FT-E20T-MP-IS | Dr. Collin GmbH, Germany | |
tungsten furnace | Hochtemperatur-Wolframofen WOHV 250/300-1900V | MUT Advanced Heating GmbH | |
debinding furnace | Retorten-Entbinderungsofen RRO 280 / 300-900V | MUT Advanced Heating GmbH | |
attrition mill | PE 1.4 | Erich NETZSCH GmbH & Co. Holding KG, Germany | |
PBM (planetary ball mill) | PM 400 | Retsch Gmbh, Germany |
Technical ceramics are widely used for industrial and research applications, as well as for consumer goods. Today, the demand for complex geometries with diverse customization options and favorable production methods is increasing continuously. With fused filament fabrication (FFF), it is possible to produce large and complex components quickly with high material efficiency. In FFF, a continuous thermoplastic filament is melted in a heated nozzle and deposited below. The computer-controlled print head is moved in order to build up the desired shape layer by layer. Investigations regarding printing of metals or ceramics are increasing more and more in research and industry. This study focuses on additive manufacturing (AM) with a multi-material approach to combine a metal (stainless steel) with a technical ceramic (zirconia: ZrO2). Combining these materials offers a broad variety of applications due to their different electrical and mechanical properties. The paper shows the main issues in preparation of the material and feedstock, device development, and printing of these composites.
Technical ceramics are widely used for industrial and research applications, as well as for consumer goods. Today, the demand for complex geometries with diverse customization options and favorable production methods is increasing continuously. With fused filament fabrication (FFF), it is possible to produce large and complex components quickly with high material efficiency. In FFF, a continuous thermoplastic filament is melted in a heated nozzle and deposited below. The computer-controlled print head is moved in order to build up the desired shape layer by layer. Investigations regarding printing of metals or ceramics are increasing more and more in research and industry. This study focuses on additive manufacturing (AM) with a multi-material approach to combine a metal (stainless steel) with a technical ceramic (zirconia: ZrO2). Combining these materials offers a broad variety of applications due to their different electrical and mechanical properties. The paper shows the main issues in preparation of the material and feedstock, device development, and printing of these composites.
Technical ceramics are widely used for industrial and research applications, as well as for consumer goods. Today, the demand for complex geometries with diverse customization options and favorable production methods is increasing continuously. With fused filament fabrication (FFF), it is possible to produce large and complex components quickly with high material efficiency. In FFF, a continuous thermoplastic filament is melted in a heated nozzle and deposited below. The computer-controlled print head is moved in order to build up the desired shape layer by layer. Investigations regarding printing of metals or ceramics are increasing more and more in research and industry. This study focuses on additive manufacturing (AM) with a multi-material approach to combine a metal (stainless steel) with a technical ceramic (zirconia: ZrO2). Combining these materials offers a broad variety of applications due to their different electrical and mechanical properties. The paper shows the main issues in preparation of the material and feedstock, device development, and printing of these composites.