Browsing by Subject "sintering"

Now showing 1 - 15 of 15

Binderless Jetting: Additive Manufacturing of Metal Parts via Jetting Nanoparticles
(University of Texas at Austin, 2017) Bai, Yun; Williams, Christopher B.
Binder Jetting AM has been used to fabricate metal parts by first jetting a binder into powder bed; the resulting green part is then thermally post-processed wherein the binder is removed and the metal particles are sintered. In this work, the authors replace conventionally-used polymeric binders with nanoparticle suspensions as a means for binding metal powder bed particles together. After being deposited into the powder particles’ interstices, the jetted nanoparticles are sintered at a low temperature via a heated powder bed to provide strength to the printed green part. Regions of the powder bed that do not receive the jetted nanoparticle suspension remain as loose powder as the sintering temperature of the nanoparticles is significantly lower than the larger powder bed particles. The concept of printing metal by jetting a nanoparticle binder made of the same material is demonstrated in the context of copper through printing copper parts with satisfactory green strength.
Development of a 3D Printing Method for Production of Dental Application
(University of Texas at Austin, 2013) Yang, Li; Zhang, Shanshan; Oliveira, Gustavo; Stucker, Brent
Traditionally, the manufacturing of dental restorations, including crowns, veneers and other structures made by ceramics, is a labor‐intensive and time consuming process. Additive manufacturing has the potential to significantly decrease the time and cost associated with this process. This work performed preliminary investigation for the feasibility of dental restoration parts printing using the ExOne M‐Lab system with a commercialized dental porcelain powder. The porcelain powders were characterized, and two measurements, including pre‐sintering and addition of flow agent, were taken in the attempt to improve the processability of the original powder feedstock. The results showed that while the addition of flow agent has more significant effects in improving the flowability of the powder used, the post sintered parts exhibit considerable shrinkage and residual porosity that necessitates further investigation.
Effect of Bimodal Powder Mixture on Powder Packing Density and Sintered Density in Binder Jetting of Metals
(University of Texas at Austin, 2015) Bai, Yun; Wagner, Grady; Williams, Christopher B.
The Binder Jetting Additive Manufacturing process provides an economical and scalable means of fabricating complex metal parts from a wide variety of materials. However, the performance metrics of the resulting sintered parts (e.g., thermal, electrical, and mechanical properties) are typically lower than traditionally manufactured counterparts due to challenges in achieving full theoretical density. This can be attributed to an imposed constraint on particle size and its deleterious effects on powder bed packing density and green part density. To address this issue, the authors explore the use of bimodal powder mixtures to improve the sintered density and material properties within the context of copper parts fabricated by Binder Jetting. The effectiveness of using bimodal powder mixtures in an effort to improve sintered density is studied in terms of particle size distribution and powder packing density.
An Investigation of Build Orientation on Shrinkage in Sintered Bioceramic Parts Fabricated by Vat Photopolymerization
(University of Texas at Austin, 2017) Aduba, Donald C. Jr.; Feller, Keyton D.; Williams, Christopher B.
In this work, a vat photopolymerization (VP) additive manufacturing process fabricated bioceramic cuboids at different build orientations to investigate their effects on post-sintering shrinkage and associated physical properties. A suspension of β-tricalcium phosphate (TCP) in Autodesk PR 57 commercial photopolymer resin and dimethyl sulfoxide (DMSO) solvent was used to shape green parts. Thermal treatment removed polymer from the green shape before sintering TCP at 1300 ◦C at 5 ◦C/min. Part morphology, dimensional shrinkage, and mass loss after sintering were evaluated. Part dimensions parallel to the build direction exhibited greater shrinkage compared to the other two dimensions. Mass loss was independent of build orientation. This paper is the first to investigate the relationship between build orientation and post-sintering shrinkage of bioceramic structures shaped by VP. In this work, an understanding of printing ceramic suspensions, and accounting for dimensional ceramic part shrinkage with respect to build orientation is gained to help guide print parameter selection to improve part fidelity and performance.
Investigation on PEEK Fabrication Using Mask-image-projection-based Stereolithography
(University of Texas at Austin, 2012) Deng, Dongping; Chen, Yong; Zhou, Chi
This paper presents the findings of an initial study of the fabrication of polyetheretherketone (PEEK) components based on the mask-image-projection-based Stereolithography (MIP-SL) process. PEEK is a semicrystalline thermoplastic with excellent mechanical and chemical resistance properties that are retained to high temperatures. It has been extensively used in the aerospace, automotive, biomedical, and chemical process industries. The fabrication process based on the MIP-SL includes both green-part fabrication and the sintering of fabricated green parts. In the green part fabrication, the challenges of recoating viscous composite slurry are discussed. A prototype system has been developed for the fabrication of green-parts with complex shapes and small features. Based on the fabricated green-parts, the challenges in the sintering process for achieving desired functionality are discussed. The test results on the sintered PEEK components have also been presented. Future work based on the study has been identified.
Material Issues in Layered Forming
(1993) Amon, Christina; Beuth, Jack; Kirchner, Helmut; Merz, Robert; Prinz, Fritz; Schmaltz, Kevin; Weiss, Lee
A brief overview of key issues in layered thermal processing is given. Incremental sintering and layered fusion ofpowder and molten droplets are discussed. The criteria for remelting the solid substrate are derivedfrom a one dimensional heat transfer model. Temperature gradients which occur during solidification and subsequent cooling. are responsible for the build up of internal stresses which can be estimated through establishing an elastic beam model. The difficulties as well as opportunities regarding the generation of multi-layer multi-material structures are also described in this article.
Measurement of the Thermal Conductivity of Powders by Two Different Methods
(1993) Sih, Samuel S.; Barlow, Joel W.
The thermal diffusivities and thermal conductivities of powders, especially PMMA-coated silicon carbide, at various temperatures, have been tested by two different dynamic methods, the water-bath method and the laser-heated method. The thermal conductivity data found by these two techniques are found to be consistent with each other.
Optimal Process Parameters for 3D Printing of Dental Porcelain Structures
(University of Texas at Austin, 2015) Miyanaji, Hadi; Zhang, Shanshan; Lassell, Austin; Zandinejad, Amir Ali; Yang, Li
Dental porcelain material is a typical glass ceramic material that is widely used in dental restoration applications. However, there still exists limited knowledge about the fabrication of this type of materials using binder jetting additive manufacturing process. There are several important factors such as saturation level, power level, drying time as well as spread speed, which would potentially affect the accuracy and strength of the printed parts before and after sintering. Therefore, in this research an extensive experimental study was performed to obtain the optimal process parameters for the dental porcelain materials fabricated via ExOne binder jetting system. The results also provide general printing guidelines for the fabrication of glass ceramic materials.
Process Integrated Production of WC-Co Tools with Local Cobalt Gradient Fabricated by Binder Jetting
(University of Texas at Austin, 2019) Lehmann, Maja; Zaeh, Michael F.
Producing complex shaped tungsten carbide cobalt (WC-Co) tools by classical technologies is difficult and often impossible due to their high hardness and brittle fracture behavior. Additive Manufacturing (AM) is a suitable technology for creating complex structures and simultaneously shortening expensive machining processes. Binder Jetting (BJ) is an innovative AM technology that offers several advantages over laser-based processes, for example low manufacturing costs and high build-up rates. Binders with nanoparticle additives have already proven to be effective in increasing the packing density of the powder bed and improving the sintering properties. Additionally, they offer the possibility of selectively changing the material composition in the part. This paper presents a concept for the use of nanoparticles to generate gradients in the green compact, which leads to a cobalt gradient in the part after sintering. The possibility of introducing particles locally into complex structures allows local modification of the material properties.
Selective Separation Sintering for Metallic Part Fabrication
(University of Texas at Austin, 2016) Khoshnevis, Behrokh; Zhang, Jing
Selective Separation Sintering (SSS) is a powder layer based additive manufacturing approach. In the printing process a dry powder of higher sintering temperature is deposited into the base material which makes up the part. The inserted powder defines the boundary of the part and separates the part from its surroundings. A post sintering of the part is carried out in the furnace where the base material is sintered and the inserted powder remain loose due to its higher sintering temperature. The part is separated from the surrounding redundant material along the loose inserted powder region. A stable deposition rate of S-powder is the key for generating parts of easy separation and smooth surface. Factors that affect the flow rate are analyzed and the analyzed results are implemented to stabilize the process. With the progress in powder deposition rate control, bronze parts have been fabricated which demonstrate good quality.
Solid Freeform Fabrication of Silicon Nitride Shapes by Selective Laser Reaction Sintering (SLRS)
(1995) Marcus, H.L.; Birmingham, B.R.
SelectiveLaser ReactionSinteringis a variation ofselective laser sintering (SLS) that incorporates anjn~situreaction underthe·scannedbeamtofabricate shapes from materials not directly accessible by traditional SLS. Thispaperclescribesaninvestigation into the production of silicon nitride (Si3N4) shapes by lasersinteringsiliconpowderinanammonia (NH3) atmosphere. The effect of gas pressure and the importance of gas/laserinteractionsarediscussed. Single and multiple layer shapes are fabricated. The material is analyzed by x~ray diffraction spectroscopy (XRDS) for phase content and scanning electron microscopy (SEM) for macrostructure. Data is presented that demonstrates conversion rates from silicon to silicon nitride on the order of 85%.
Statistical Process Control Application to Polymer Based SLS process
(University of Texas at Austin, 2016) Akande, S.O.; Dalgarno, K.W.; Munguia, J.; Pallari, J.
The quality of selective laser sintering (SLS) made parts is known to be influenced by process parameters and the quality of input material. In order to ensure consistency in part quality, there is a need to monitor the quality of parts made using the SLS machines. Benchmark specimens were designed and manufactured to track key quality characteristics of strength, bending stiffness, density and dimensional accuracy of parts made in multiple builds. Using data collected from the benchmark tests, correlation analysis and statistical process control (SPC) charts were established. SPC was found to be a useful tool that can provide SLS users with the mean of identifying possible changes in the process. Therefore, it can be used for process monitoring in SLS process to ensure consistency in part quality for long term production.
Support-Free Sintering of 3D Printed Binder Jet Copper and Stainless Steel Parts
(2022) Jangam, John Samuel Dilip; Anthony, Thomas; McKinnell, Jim; Pon, Ben; Piderman, Jake; Zhao, Lihua
Binder jet additive manufacturing involves selectively applying a binder, layer-by-layer, to produce green parts, followed by a high temperature sintering treatment. During sintering, green parts are inherently prone to undesired part distortion/sag in the unsupported regions. Traditional methods use 3D printed supports or machined ceramic setters to avoid the part distortion/sag during sintering. We introduce a shape-retaining-stimulus coating that will mitigate/eliminate the need of additional supports during sintering. Simply supported coper and stainless steel green parts of various thickness were evaluated for part distortion. Our experimental results demonstrate that a selective application of the shape-retaining-stimulus coating on 3D printed copper parts with a spanning up to 50 mm, and stainless steel parts spanning up to 33 mm can be sintered without auxiliary supports. Our shape-retaining-stimulus coating produces exceptional results, and the ease of removal makes it an attractive candidate.
Support-free sintering of 3D printed binder jet copper and stainless steel parts
(2022) Jangam, John Samuel Dilip; Anthony, Thomas; McKinnell, Jim; Pon, Ben; Piderman, Jake; Zhao, Lihua
Binder jet additive manufacturing involves selectively applying a binder, layer-by-layer, to produce green parts, followed by a high temperature sintering treatment. During sintering, green parts are inherently prone to undesired part distortion/sag in the unsupported regions. Traditional methods use 3D printed supports or machined ceramic setters to avoid the part distortion/sag during sintering. We introduce a shape-retaining-stimulus coating that will mitigate/eliminate the need of additional supports during sintering. Simply supported coper and stainless steel green parts of various thickness were evaluated for part distortion. Our experimental results demonstrate that a selective application of the shape-retaining-stimulus coating on 3D printed copper parts with a spanning up to 50 mm, and stainless steel parts spanning up to 33 mm can be sintered without auxiliary supports. Our shape-retaining-stimulus coating produces exceptional results, and the ease of removal makes it an attractive candidate.
A Three Dimensional Model for Selective Laser Sintering
(1991) Sun, Ming-shen M.