Cold Isostatic Pressing Process Research Articles

Enhanced density and microstructural integrity of binder jetting manufactured ceramics through cold isostatic pressing

Binder jetting (BJ) is a type of additive manufacturing (AM) process that enables fabrication of complex zirconia (ZrO2) ceramic components. However, there are significant challenges in fabricating ceramic parts with high relative density and superior performance. In this study, cold isostatic pressing (CIP) process was integrated into BJ, successfully producing high-performance ZrO2 ceramics. Comprehensive study was conducted on ZrO2 granules, binder, and their interactions. In addition, effects of CIP process on relative density and mechanical properties of sintered samples were investigated. Results indicate that CIP process significantly enhances green body density and reduces spacing between particles, thereby facilitating subsequent densification during ceramic sintering. Moreover, debinding followed by CIP treatment yields superior mechanical properties compared to the methods where CIP was performed prior to debinding, as it prevents defect formation during debinding. Subsequently, differences in performance between ZrO2 ceramics treated with and without CIP were compared at various sintering temperatures. After sintering at 1400 °C, relative density and flexural strength of ZrO2 ceramics reached 98.75 ± 0.19 % and 1047.80 ± 88.45 MPa, representing significant improvements of 53.24 % and 100-fold increase compared to those without CIP treatment, respectively. These findings indicate that proposed method is highly promising for fabrication of high-density and high-performance ZrO2 components.

Computational analysis and experimental calibration of cold isostatic compaction of Mg-SiC nanocomposite powders

The consolidation process and density distribution of Mg-SiC nanocomposite powder were studied using computational finite element modeling (FEM) and experimental approaches. Cold isostatic pressing (CIP) was employed for producing fully dense Mg-SiC nanocomposites with a homogeneous distribution of SiC nanoparticles. The elastoplastic modified Drucker-Prager Cap (DPC) model was applied to predict SiC nanoparticle density distribution effects on the milled powder compressibility after the CIP. The FEM results revealed that increasing SiC nanoparticles from 1% (M1Sn) to 10% (M10Sn) volume leads to harder compressibility, increasing the maximum equivalent pressure stress value 717.2 to 737.1 MPa, and decreasing the relative density value 94.63% to 88.67%. The maximum element volume (EVOL) for pure Mg (MM), M1Sn, and M10Sn powders was estimated as 21.69, 20.13, and 15, respectively. The model is validated by comparing finite element simulations with experimental results of relatve density and reduction of volume under 700 MPa cold isostatic pressure for MM, M1Sn, and M10Sn powders. The finite element modeling results of samples after the CIP process were consistent with the experimental results. These results indicate the effectiveness of the modified DPC model and confirmed compaction behavior and relative density of Mg-SiC nanocomposite powders.

Cold Isostatic Pressing to Improve the Mechanical Performance of Additively Manufactured Metallic Components.

Additive manufacturing is becoming a technique with great prospects for the production of components with new designs or shapes that are difficult to obtain by conventional manufacturing methods. One of the most promising techniques for printing metallic components is binder jetting, due to its time efficiency and its ability to generate complex parts. In this process, a liquid binding agent is selectively deposited to adhere the powder particles of the printing material. Once the metallic piece is generated, it undergoes a subsequent process of curing and sintering to increase its density (hot isostatic pressing). In this work, we propose subjecting the manufactured component to an additional post-processing treatment involving the application of a high hydrostatic pressure (5000 bar) at room temperature. This post-processing technique, so-called cold isostatic pressing (CIP), is shown to increase the yield load and the maximum carrying capacity of an additively manufactured AISI 316L stainless steel. The mechanical properties, with and without CIP processing, are estimated by means of the small punch test, a suitable experimental technique to assess the mechanical response of small samples. In addition, we investigate the porosity and microstructure of the material according to the orientations of layer deposition during the manufacturing process. Our observations reveal a homogeneous distribution independent of these orientations, evidencing thus an isotropic behaviour of the material.

Microstructure and mechanical properties of 3Y-TZP dental ceramics fabricated by selective laser sintering combined with cold isostatic pressing

Additive manufacturing (AM) technology is showing great potential in dental restorations. In this paper, 3Y-TZP ceramics which are widely used in the fabrication of dental restorations were fabricated by selective laser sintering (SLS) combined with cold isostatic pressing (CIP) technology, and the effect of sintering temperature on phase composition, microstructure and mechanical properties of 3Y-TZP ceramics was investigated. 3Y-TZP/MgO/Epoxy resin E12 composite powder with good flowability and homogeneity was prepared by mechanical mixing method. The SLSed samples were obtained with optimum parameters (laser power = 7 W, scanning speed = 2600 mm/s, hatch spacing = 0.15 mm and layer thickness = 0.09 mm). Then they were densified by CIP (280 MPa, 5 min) process and sintered to obtain 3Y-TZP ceramics. It was found that the sample had the highest flexural strength of 279.50 ± 10.50 MPa and the maximum relative density of 86.65 ± 0.20% when sintered at 1500 °C due to the appropriate grain size and phase composition. Finally, some all-ceramic dental restorations were successfully fabricated by this technology. This work provides a new way for the manufacture of individualized all-ceramic dental restorations.

Cold Isostatic-Pressured Silver Nanowire Electrodes for Flexible Organic Solar Cells via Room-Temperature Processes.

Transparent conducting electrodes (TCEs) are considered to be an essential structural component of flexible organic solar cells (FOSCs). Silver nanowire (AgNW) electrodes are widely used as TCEs owing to their excellent electrical and optical properties. The fabrication of AgNW electrodes has faced challenges in terms of forming large uniform interconnected networks so that high conductivity and reproducibility can be achieved. In this study, a simple method for creating an intimate contact between AgNWs that uses cold isostatic pressing (CIP) is demonstrated. This method increases the conductivity of the AgNW electrodes, which enables the fabrication of high-efficiency inverted FOSCs that have a power conversion efficiency of 8.75% on flexible polyethylene terephthalate with no short circuiting occurring as the CIP process minimizes the surface roughness of the AgNW electrode. This allows to achieve 100% manufacturing yield of FOSCs. Furthermore, these highly efficient FOSCs are proven to only be 2.4% less efficient even for an extreme bending radius of R ≈ 1.5 mm, compared with initial efficiency.

Mechanical and dielectric properties of SiCf/SiC composites fabricated by PIP combined with CIP process

2D KD-1 SiC fiber fabrics were employed to fabricate SiCf/SiC composites by an improved polymer infiltration and pyrolysis (PIP) process, combined with cold isostatic pressing (CIP). The effect of CIP process on the microstructure, mechanical and dielectric properties of SiCf/SiC composites was investigated. The infiltration efficiency was remarkably improved with the introduction of CIP process. Compared to vacuum infiltration, the CIP process can effectively increase the infiltrated precursor content and decrease the porosity resulting in a dense matrix. Thus SiCf/SiC composites with high density of 2.11gcm−3 and low porosity of 11.3% were obtained at 100MPa CIP pressure, together with an increase of the flexural strength of the composites from 89MPa to 213MPa. Real part (ε′) and the imaginary part (ε″) of complex permittivity of SiCf/SiC composites increase and vary from 11.7-i9.7 to 15.0-i12.8 when the CIP pressure reaches 100MPa.

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Although isostatic pressing is an effective method to densify low-molecular-weight organic semiconducting films (OSFs), the application for polymeric OSFs has never been examined. In the present study we optimized coating conditions of polymethylmethacrylate (PMMA) films and poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS) films coated on glass substrates by both drop-casting and spin-coating methods, and examined cold isostatic pressing (CIP) behavior of the films. The drop-cast and spin-coat PMMA films were effectively densified using the CIP process by factors of 56% and 63% respectively. Additionally the pressed drop-cast PMMA films were hardened by 5.7 times. However there was no change between the drop-cast PEDOT/PSS films before and after the CIP process in terms of film thickness and hardness, indicating the process didn’t effectively work to improve the density of the films.

Improving the dielectric and piezoelectric properties of screen-printed Low temperature PZT/polymer composite using cold isostatic pressing

This paper reports an improvement in dielectric and piezoelectric properties of screen-printed PZT/polymer films for flexible electronics applications using Cold Isostatic Pressing (CIP). The investigation involved half and fully cured PZT/polymer composite pastes with weight ratio of 12:1 to investigate the effect of the CIP process on the piezoelectric and dielectric properties. It was observed that the highest dielectric and piezoelectric properties are achieved at pressures of 5 and 10 MPa for half and fully cured films respectively. The relative dielectric constants were 300 and 245 measured at 1 kHz for the half and fully cured samples. Using unoptimised poling conditions, the initial d33 values were 30 and 35 pC/N for the half and fully cured films, respectively. The fully cured sample was then poled using optimized conditions and demonstrated a d33 of approximately 44 pC/N which is an increase of 7% compared with non-CIP processed materials.

Indirect selective laser sintering of epoxy resin-Al2O3 ceramic powders combined with cold isostatic pressing

To fabricate Al2O3 ceramic components with complex shape, selective laser sintering (SLS) combined with cold isostatic pressing (CIP) process was used to consolidate Al2O3 powder with additive of epoxy resin E06 (ER06) and polyvinyl alcohol (PVA). The starting material preparation combined spray drying with mechanical mixing to formulate compound powder consisting of PVA (1.5wt%), ER06 (8wt%) and Al2O3 and provide a good fluidity for SLS. Experimental investigations were carried the shrinkage, relative density, bending strength of Al2O3-ER06 SLS specimens in order to optimize the laser sintering parameters. It was found that Al2O3-ER06 SLS specimens represented acceptable shrinkage, high density and bending strength when laser power, scanning speed, scanning space and layer thickness were, respectively, 21W, 1600mm/s, 100μm and 150μm. Following that, the SLS specimens were processed through CIP to eliminate the pores in green ceramics. Finally, the optimized SLS/CIP Al2O3 specimens were debinded, sintered to produce crack-free Al2O3 bodies. The final Al2O3 components achieved a relative high density of more than 92% after furnace sintering. The study shows a novel and promising approach to fabricate complex ceramic matrix and ceramic components via indirect SLS and CIP process.

Weibull distribution of the fracture strength of 99% alumina ceramic reshaped by cold isostatic pressing

The mechanical reliabilities of 99% alumina ceramics preformed by dry pressing using various pressures and reshaped by cold isostatic pressing (CIP) at 150MPa are investigated using the maximum likelihood method for the estimation of the Weibull parameters of the results. The results indicate that among the various values of dry pressing and sintering temperatures applied, a maximum Weibull modulus of 13.9974 and high reliability were attained for 75MPa dry pressing followed by subsequent 150MPa cold isostatic pressing (CIP) and a 1580°C sintering temperature. In addition, excessive preforming pressure caused dangerous flaws, called hardening defects, which were not repaired automatically by the CIP and sintering process, thus acting as a source of fracture and reducing the reliability of the specimen strength.

Numerical simulation of cold isostatic pressed alumina parts produced by selective laser sintering and part shape optimization

Cold isostatic pressing (CIP) combined with selective laser sintering (SLS) is a practical and effective process for producing complex ceramic components with high density. This paper focused on the numerical simulation of alumina SLSed components during CIP for near net shaping. The Drucker–Prager-Cap plasticity model was used to predict the densification behavior and deformation of the alumina/epoxy resin composite powders. CIP experiments were conducted to determine the required parameters for the model. The simulative final dimensions and densities agree well with the experimental results, with the relative error less than 1.7% in the forming plane. Structure optimization was made to the part and bag, which proves conducive to reducing distortion. The effects of the part fillet radius on shape accuracy were investigated, and the optimal fillet radius can be determined by simulation. Eventually, the alumina part reached its highest density of 94.5% through optimized CIP and sintering process.

Application of CIP processing and sol-gel surface coating to PZN-PZT piezoelectric ceramics for use as energy harvesters

Piezoelectric 0.2Pb(Zn 1/3Nb 2/3)O 3-0.8Pb(Zr 1/2Ti 1/2)O 3 (PZN-PZT) ceramics in disc form were fabricated and characterized for use as energy harvester devices. A powder mixture with an average particle size of about 1 μm with the addition of 0.5 wt% ZnO was used to obtain a high piezoelectric coefficient and low sintering temperature. A molding method, including cold isostatic pressing (CIP), was used to resolve the cracking and bending problems of thin ceramics during the high-temperature post-processing sintering step. A sol-gel surface coating was found to be very effective for ceramic discs with a very high piezoelectric constant d 33 of 536 pC/N. The results of this study could be applicable to small piezoelectric energy harvester devices.

Plastic forming simulations of cold isostatic pressing of selective laser sintered components

A combined method of selective laser sintering (SLS) and cold isostatic pressing (CIP) was applied to manufacturing metal parts rapidly. Finite element method was used to predict final dimensions and decrease cost. The simulations of CIP of selective laser sintered parts were carried out by Drucker-Prager-Cap constitutive model with ABAQUS computer program. The property of metal powder was measured by CIP experiments. The results show the rubber bag and the friction coefficient have little influence on results of simulations. The parts only have uniform shrinkage and have no obvious distortion in shape. The results of simulations show a good agreement with the experimental results and the calculated results, indicating that the Drucker-Prager-Cap model is an effective model to simulate CIP process. The simulations could give a useful direction to forming process of the CIP of selective laser sintered components.

Influence of Parameters of Cold Isostatic Pressing on TiO2Films for Flexible Dye-Sensitized Solar Cells

Cold Isostatic Pressing (CIP) is used to make TiO2working electrodes for flexible dye-sensitized solar cells (DSCs). Different CIP processes, varying pressures from 50 MPa to 200 MPa and holding time 1 s up to 600 s, are performed to study the effect of CIP on the resistivity of TiO2electrode thin films and the power conversion efficiency (PCE) of DSCs. The results show that the CIP process has significantly improved the PCE of DSC devices. Electrochemical impedance spectroscopy (EIS) analysis indicates a clear correlation between the PCE enhancement and the resistivity reduction in TiO2thin films after various CIP processes. Porosity reduction and localized joints formed between some TiO2nanoparticles due to the friction heat in the CIP process are believed to be responsible for the resistivity reduction of the TiO2working electrode thin films.

Densification of Porous Stainless-Steel SLS Components During Cold Isostatic Pressing

The process that combines selective laser sintering (SLS) and cold isostatic pressing (CIP) can manufacture nearly fully dense metal components with complex geometries. However, the SLS component will shrink to a significant extent during the CIP process. The modified cam-clay model was used to describe the constitutive equation of porous stainless-steel SLS components. The densification process of SLS porous components was simulated using the finite element method. The visual distributions of shape change, displacement, density, and stress were obtained, which showed that SLS components shrank with the same shape as the original design over the CIP process. In addition, a relative uniform density distribution appeared in cold isostatic pressed components. The experiment measurements displayed that the shrinkage rate of SLS components during the CIP process in height direction was a little higher than that on the forming plane due to the layer-by-layer manufacturing process of SLS. On the forming plane, the dimensional errors between simulations and experiments for the cuboid and the gear components are lower than 1% and 3%, respectively. However, the errors in height direction of the two components increase to the range of 6% and 9%.

Experimental based finite element simulation of cold isostatic pressing of metal powders

The present work addresses the various ingredients required for reliable finite element simulations of cold isostatic pressing (CIP) of metal powders. A plastic constitutive model for finite deformation is presented and implemented into an explicit finite element (FE) code. The FE implementation is verified so that numerical errors (both temporal and spatial errors) are kept under control. Thereafter, uniaxial die compaction experiments are performed required for determining the material parameters in the constitutive model. Subsequently they are applied for the simulation of a “complex” CIP process. The experimental observations of the complex CIP process were used to validate the overall method by comparing the FE results (final dimensions and average relative density) to the experimental observations. The numerical results (final dimensions and relative density) are in good agreement with the experimental observations.

Improving superconductivity and mechanical properties of Bi-2223/Ag-wire composite bulk by cold isostatic pressing

To improve superconductivity and mechanical properties of Bi-2223 sintered bulk, silver (Ag) wires of 0.4 mm in diameter were added to the bulk. The sample was sintered at 840/spl deg/C for 50 hours in air. After treatment with cold isostatic pressing (CIP), the sample was re-sintered. When twenty-four Ag wires were composed, the critical current density (J/sub c/) at 4.2 K and self-field increased from 1,200 A/cm/sup 2/ to 2,000 A/cm/sup 2/ with the CIP process. SEM observation results showed that high alignment and dense structures of Bi-2223 plate-like grains were formed around the interfacial region between the superconducting oxide and the metal Ag. The mechanical properties were measured by a three point bending test. The maximum bending stress of 60 MPa was obtained in the bulk without Ag wire, which was fractured separately. With the CIP process the maximum bending stress increased to 90 MPa for the composite. The composite did not fracture but only fine cracks were induced after the maximum bending stress.

Fluctuation conductivity analysis for Bi-2223 superconductors with different sintering time

In a Bi-based superconductor, the critical current J c increases in accordance with the length of the sintering time and further increase is attained by cold isostatic pressing (CIP). The temperature dependence of the resistivity in polycrystalline Bi-2223 superconductors with different sintering time ( t s) of 10–200 h was measured. In order to investigate the mechanism to improve J c, the excess conductivity caused by the thermal fluctuation above T c was analyzed using the Aslamazov–Larkin theory. It was found that the samples show a two-dimensional fluctuation in conductivity irrespective of t s, and that the amplitude of fluctuation increases with t s. The analysis indicates that the correlation length, which is inversely proportional to the amplitude, decreases with the length of t s. Therefore, it can be deduced that J c of the samples improves as the crystals become more uniformly aligned with increased t s, resulting in a shorter correlation length as confirmed by the SEM study. A similar result has been obtained for the samples with the CIP process.

Fundamental Properties of Monolithic Bentonite Buffer Material Formed by Cold Isostatic Pressing for High-Level Radioactive Waste Repository

AbstractThe methods of fabrication, handling, and emplacement of engineered barriers used in a deep geological repository for high level radioactive waste should be planned as simply as possible from the engineering and economic viewpoints. Therefore, a new concept of a monolithic buffer material around a waste package have been proposed instead of the conventional concept with the use of small blocks, which would decrease the cost for buffer material. The monolithic buffer material is composed of two parts of highly compacted bentonite, a cup type body and a cover. As the forming method of the monolithic buffer material, compaction by the cold isostatic pressing process (CIP) has been employed.In this study, monolithic bentonite bodies with the diameter of about 333 mm and the height of about 455 mm (corresponding to the approx. 1/5 scale for the Japanese reference concept) were made by the CIP of bentonite powder. The dry densities: pd of the bodies as a whole were measured and the small samples were cut from several locations to investigate the density distribution. The swelling pressure and hydraulic conductivity as function of the monolithic body density for CIP-formed specimens were also measured.High density ( ρd: 1.4–2.0 Mg/m3) and homogeneous monolithic bodies were formed by the CIP. The measured results of the swelling pressure (3–15 MPa) and hydraulic conductivity (0.5–1.4×10−3 m/s) of the specimens were almost the same as those for the uniaxial compacted bentonite in the literature. It is shown that the vacuum hoist system is an applicable the handling method for emplacement of the monolithic bentonite.

Cold isostatic pressing as a method for fabricating ceramic products with high physicomechanical properties

The experimental results published by the author and his co-workers in 24 earlier works and novel original data are analyzed. It is shown that the process of cold isostatic pressing (CIP) occurs with mechanical activation of the powder particles due to their self-deformation with a simultaneous self-compaction of the semiproduct. The CIP process of powders or traditionally shaped preforms is shown to elevate their density and activate the sintering processes but diminish their sintering temperature and increase the density, strength and crack resistance of the ceramics. The use of surface-active substances (SAS) in CIP is shown to elevate the level of the physicomechanical properties of the ceramics. The basic concepts of controlling the properties of ceramics by choosing the appropriate dispersity of the powder, the CIP pressure, the SAS, and the sintering regime are presented.