Browsing by Subject "SLA"

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Accuracy of Stereolithography Parts: Mechanism and Modes of Distortion for a "Letter-H" Diagnostic Part
(1995) Pang, Thomas H.; Guertin, Michelle D.; Nguyen, Hop D.
Rapid Prototyping and Manufacturing (RP&M) users need to compare the accuracy of various commercially available RP&M materials and processes. A good diagnostic test for both material and the fabrication process involves a 4-inch long "letter-H" diagnostic part. This diagnostic part, known as "H-4", was developed to measure the inherent dimensional characteristics ofvarious RP&M build materials. It is also less dependent on the calibration status of particular RP&M machines, and is excellent for the purpose of generating simple but meaningful accuracy information, which can be used to further understand the mechanism and the modes of distortion in RP&M materials. H-4 parts were prepared and built in Stereolithography Apparatus (SLA) using Ciba-Geigy epoxy based resins SL 5170 and SL 5180, and results were compared to acrylate based SL 5149. Experimental data involving the magnitude, mechanism, and the modes of distortion for these three resins are analyzed in this paper.
An Adaptive Control Architecture for Freeform Fabrication
(1996) Boudreaux, J.C.
Advances in Stereolithography Accuracy
(1991) Jacobs, Paul F.; Richter, Jan
It has been almost four years since the SLA - 1 ushered in the new technology of StereoLithography, and about 2\ years since 3D Systems introduced the SLA-250. Since then, nearly 300 systems have been installed worldwide and are currently providing benefits in a range of applications which might well be summarized by the term "Rapid Prototyping and Manufacturing" or "RPM". During the past year the accuracy of parts built with stereoLithography has benefitted significantly from nine important technological advances. The research and development efforts which formed the foundation for this progress originated within the Process, Chemistry and Software departments of 3D Systems. The following is a listing, and brief description, of the key features of each of these advances.
Build Style Decision Support for Stereolithography
(1997) McClurkin, Joel E.; Rosen, David W.
When building parts in a stereolithography apparatus (SLA), the user is faced with many decisions regarding how the part will be built. The quality of the build can be controlled by the user via changing one of several build style variables, including part orientation, cross sectional layer thickness, and laser hatch density. A user will probably have preferences for the part build (Le., accuracy or speed), but may not understand how to vary the build style variables to produce the desired results. A method based on response surface methodology and multi-objective decision support is described in this paper for relating build goals to three build style variables, and the use ofthese relationships in providing decision support for building a part on a SLA. The method is applied to the build style of a circuit breaker handle.
Ceramic Stereolithography for Investment Casting and Biomedical Applications
(1995) Griffith, Michelle L.; Chu, Tien.Min; Wagner, Warren; Halloran, John W.
Ceramic green bodies can be created using stereolithography methods by using an ultraviolet curable suspension of ceramic powders in place of the usual resin -a "ceramic resin". Weare developing ceramic resins from hydryoxyapatite ceramics, to enable custom made ceramic implants by SLA, and from silica and alumina, to enable metal casting molds by SLA. We demonstrate SLA ofsilica, a model refractory for metal casting molds, and SLA of alumina, which present the rheological behavior and UV curing properties of several "ceramic resins", and discuss silica parts made on an SLA-250.
The co-emergence of Spanish as a second language and individual differences : a dynamical systems theory perspective
(2012-05) Lyle, Cory Jackson; Koike, Dale April; Salaberry, Maximo; Nishida, Chiyo; Blyth, Carl; Streeck, Jürgen
Dynamical Systems Theory (DST) (De Bot, Lowie, & Vespoor 2007; Larsen-Freeman 1997, 2007; Larsen-Freeman & Cameron 2008; Dörnyei 2009; and van Lier 2000) represents a scientific paradigm shift derived from the fields of physics, engineering and theoretical mathematics that attempts to solve real-world scenarios that do not respond to scientific reductionism, otherwise known as ‘analysis’. The purpose of this dissertation is to (re)frame foreign language learning/use as a dynamical process that that involves interplay among what Dörnyei (2009) terms the language, the agent and the environment. More specifically, this dissertation presents a quasi-experimental, psycholinguistic study that looks at the interface between language (in this case the talk that resulted from NS-NNS interactions) and agent (as defined by a set of personal traits, or Individual Differences [IDs], including motivation, attitudes, personality and aptitude) in order to answer the research question: Do IDs vary in conjunction with language learning/use, and if so, how? Eight tutored Spanish learners were followed over the course of 16 weeks during which time they participated in 8 chat sessions with a native Spanish-speaker. Their ID profiles were measured immediately before and after each session and sessions with significant pre- to post-session ID shifts were analyzed to determine to what extent such shifts correlated with certain types of talk and/or think-aloud sequences. Results indicated that all participants’ pre- and post-interactional ID profiles fluctuated measurably and significantly, even within the span of a single interaction. Moreover, those sessions with significantly positive ID shifts were qualitatively different in terms of language-related episodes (LREs), conversation management/pragmatic markers, and metacognition from those with significantly negative ID shifts. Other unexpected findings revealed, for example, that LREs (especially NS-initiated LREs) negatively impacted motivations and attitudes and, therefore, the language-learning process itself. Taken together, the results of this study indicate that the agent’s IDs and their (inter)language co-emerge; that is to say, they evolve simultaneously and in response to one another. Moreover, this study suggests that DST can indeed be quasi-experimentally applied to the study of SLA, thus necessitating further development in DST-oriented methodologies and research questions.
Cost model for commercially-available additive manufacturing machines
(2021-05-11) Martin Cardenas, Oscar A.; Seepersad, Carolyn
Cost models for individual commercial processes have been developed for additive manufacturing machines in the past; however, software and detailed information about the machines for cost modeling tend to be privatized within the industry. The addition of the Center for Additive Manufacturing and Design Innovation to The Walker Department of Mechanical Engineering at The University of Texas at Austin expanded the additive manufacturing facility to include the EOS M280 DMLS, 3D Systems HiS/HiQ Vanguard SLS, 3D Systems SLA 5000, and the Stratasys J750 Digital Anatomy Printer additive machines. To provide quotes for parts and obtain build-specific information for the aforementioned processes, an open-source software program is developed along with the cost models for each individual process to speed up the required calculations and provide an interface for the operator of the center to experiment with different build parameters. The design of each cost model for all four additive manufacturing processes explores assumptions that define the variables used by the open-source software program to perform calculations. The software program includes an interface for the operator to input part and build parameters to obtain desired outputs. Additionally, the software program includes underlying spreadsheets for the operator to make future edits and keep track of quotes. As part of the cost model for the DMLS, SLS, and SLA machines, a part build time estimation experiment is developed to aid the accuracy of machine related cost calculations. Experimental parts are designed and created to record data and develop an equation for the total build time of a desired part for a given process. The results of this experiment are verified with known machine-generated data to validate the accuracy of the results. Additionally, a case study is performed with an experimental build to verify the results of the cost models when compared to Stratasys’ web quoting tool to validate the behavior of the total cost per part estimation for a given process. Due to implications related to the COVID-19 pandemic and the 2021 Texas snowstorm, delays limited the data gathering from the center. Therefore, future adjustments to experimental data are discussed to further improve the cost model’s accuracy. Furthermore, as more knowledge of these processes is gathered by the center over time, adjustment to values in the cost model will be necessary
Describing and analyzing English as a Lingua Franca
(2012-12) Dunlap, Katie J.; Horwitz, Elaine Kolker, 1950-; Sardegna, Veronica G
Researchers are becoming increasingly interested in responding to the effects of the English language’s viability as a Lingua Franca. English as a Lingua Franca (ELF) is being used predominantly in communication from one non-native speaker to another, and descriptive studies are just beginning to emerge (Dewey 2007; Jenkins, 2000; Seidlhofer, 2004). This report offers a theoretical overview showing ELF’s increasing relevance, and reviews empirical studies that have investigated how ELF is manifesting in the field of language education. These empirical studies are gaining significant traction, specifically in relation to descriptive linguistics, sociolinguistics, and applied linguistics (House, 2003; Mauranen, 2003). In order to investigate a formal description of ELF, recent empirical work is reviewed after two seminal articles were published that helped gain viability into ELF as a distinct research area (i.e. Seidlhofer, 2001; Mauranen, 2003). Such reviews of empirical studies through the use of corpora are not meant to distinguish ELF as a distinct variety of English, but to simply allow for a deep description of how ELF is being used currently. Also discussed are the developments to English language pedagogy and directions for future research as ELF scholars begin to re-conceptualize what is meant by language context and communication in ELF.
The effects of speaking anxiety on foreign language learning
(2009-12) Park, Sae Mee, 1985-; Horwitz, Elaine Kolker, 1950-; Palmer, Deborah K.
The purpose of this paper is to examine in depth and to synthesize the literature on foreign language anxiety, with specific focus on speaking anxiety. This paper reviews the development of the foreign language anxiety construct and extensive research on its relationship with other domains of second language acquisition, including specific language skills and language learning processes. Review of the literature has confirmed that foreign language anxiety plays a significant role in learners’ performance and achievement. However, there are still many areas that need further research and clarification. Variables such as individual differences still cloud the relationship between anxiety and achievement, thus suggesting that further research should be conducted in order to clarify the effects of foreign language anxiety and should strive to alleviate learners’ anxiety in the language classroom.
ESL students’ interaction in Second Life : task-based synchronous computer-mediated communication
(2010-05) Jee, Min Jung 1977-; Schallert, Diane L.
The purpose of the present study was to explore ESL students’ interactions in task-based synchronous computer-mediated communication (SCMC) in Second Life, a virtual environment by which users can interact through representational figures. I investigated Low-Intermediate and High-Intermediate ESL students’ interaction patterns before, during, and after three kinds of tasks, a Jigsaw task, a Decision-making task, and a Discussion task. The findings were that the Low and High-Intermediate ESL students engaged in several forms of interaction during the pre- and post-task periods in Second Life, such as checking their voice chat function, checking members, moving their avatars, and closings. These activities pointed to the nature of Second Life voice chat interaction as preconditions for further conversation, and for closing their conversation. Official task period activities revealed factors for task success, such as a leader, a structured way of approaching a task, no technical problem, and establishing a sense of telepresence (Schroeder, 2002) before the task. Concerning negotiation of meaning, the High-Intermediate students made more negotiation during the Decision-making tasks than the Jigsaw tasks, caused mainly by lexical meanings. The wrong answer team and the incomplete team engaged in more negotiations than the correct answer team and the complete team. However, the Low-Intermediate students in the complete team made more negotiations of meaning than the incomplete team. Both levels of students had fewer negotiations during the Discussion task than in the Jigsaw and Decision-making tasks, and they used comprehension checks, confirmation checks, and clarification requests as strategies for negotiation, overwhelmingly focused on meaning rather than form. The students played with their avatars more often during the Discussion task session than during the Jigsaw or Decision-making tasks, and their use of avatars seemed simply to be for fun, although another way explaining what students were doing is to recognize that they were also exploring the affordances of Second Life. Generally, the Low-Intermediate students had a positive attitude toward their learning experience in Second Life, whereas the High-Intermediate students expressed a more neutral view of their experience in Second Life.
Fabrication of Parts Containing Small Features using Stereolithography
(1996) Partanen, Jouni P.
The StereoLithography (SL) process has benefited from many advances in the last four to five years. These include new resins with reduced shrinkage and curl distortion, enhanced software, and improved scanning techniques. One can produce highly accurate parts for most dimensions within a few mils of the design value as shown in numerous accuracy and benchmarking studies. SLA systems use a laser beam focused to a spot size of 200 -250 ~m. This limits the range of applications where SL can provide accurate models to parts which do not contain very small features i. e. wall thickness values less than about 300 ~m. Industries that manufacture products involving components with small features include electronics and medical. In this presentation we describe an extension of the SL technology to applications involving small features. This capability is achieved by reducing the laser focal spot size in an SLA-250 to 75 ~m. The technological principle behind the spot size reduction is described in the presentation, together with process issues and applications ofthe technology.
How high school learners of Spanish respond to a flipped classroom : an analysis of performance & involvement
(2018-06-25) Abels, Jared P.; Horwitz, Elaine Kolker, 1950-; Schallert, Diane; Kelm, Orlando; Murphy, Melissa
Although many studies have examined “flipped classrooms” (essentially the inversion of presentational and practice learning spaces, Bergman & Sams, 2012; Bledsoe 2015; Bretzman, 2013; Lockwood & Folse, 2014; Pasisis, 2014; Plunkett & Beckerman, 2014), few have examined flipping foreign language classes and even fewer have examined the practice in high schools (Huang & Hong, 2016; Hao 2016). In addition, although a large number of blogs, teacher forums and online help pages address flipped language classrooms, few empirical studies have appeared in peer-reviewed journals. Consequently, the efficacy of the flipped classroom approach in the foreign language high-school classroom has not been adequately assessed. The purpose of this study was to better understand learning interactions and outcomes of secondary Spanish 2 students within a flipped classroom environment. The nine -week action research project assessed the flipped classroom approach for two high-school Spanish classes. The study investigated the process of learning second year Spanish at a private high school through a collection of questionnaires, teaching artifacts, and assessment data. Involvement with the flipped materials and student performance on daily quizzes proved to explain most of the variation in grades and other outcome measures. Data analysis showed students to be classified into four groups: high-performance high-involvement, low-performance high-involvement, high-performance low-involvement, and low-performance low-involvement. The study found that effective learners reported a range of learning strategies which they used to select the best methods to practice the target language concepts. A variety of learning strategies in addition to efficient choice of time and investment corresponded with increased performance in the Spanish class. The flipped classroom was an effective approach to teaching Spanish for secondary students in this study. The study also found that some learners needed support in selecting learning strategies, managing time, and remaining accountable. Teachers who want to implement flipped high school Spanish classrooms should pay attention to individual student involvement and performance for this approach to achieve maximal effect.
Key components in a successful Arabic immersion program for high school students : a case study
(2010-05) Milliman, Britten Moya Jo; Al-Batal, Mahmoud; Schulte-Nafeh, Martha
As more second-language acquisition research is published about the optimal age to begin foreign language instruction, and the best methods for teaching foreign languages, many colleges and universities are seeking to create intensive immersion programs which would prepare prospective students for the rigors of their language programs and serve as a productive language-learning environment. One such program, the Middlebury-Monterey Language Academy, is based on the highly successful summer language schools model. This research isolates the components which would help create successful, intensive Arabic immersion programs. Specifically, this thesis asks: How can an institution create a successful Arabic immersion learning environment for high school students? To answer this question, this thesis reviews current literature in the field of Second Language Acquisition (SLA), includes personal observations about the program and analyzes responses to surveys administered to two groups of stakeholders, namely students, and teachers/resident assistants. After the descriptive section, the thesis proposes a curricular framework which encompasses the main components of the curriculum (including goals, teacher and learner training, instructional materials, and native versus target language use). This framework is presented as a model to help teachers and other administrators as they try to set up new Arabic programs for high school students.
Material and Process Parameters that Affect Accuracy in Stereolithography
(1993) Chartoff, Richard P.; Flach, Lawrance; Weissman, Peter
Experimental real time linear shrinkage rate measurements simulating stereolithography are used in an analysis of shrinkage during line drawing in stereolithography. While the amount of shrinkage depends on the polymerization kinetics, shrinkage kinetics and overall degree of cure, it also depends on the length of time to draw a line of plastic. A line drawn slowly will exhibit less apparent shrinkage than one drawn very quickly because much of the shrinkage is compensated for as the line is drawn. The data also indicates that a typical stereolithography resin in the green state may shrink to only 65% of its maximum, thus retaining considerable potential for shrinkage during post-cure. This infonnation can be used to predict the amount of shrinkage to be expected under certain exposure conditions and to fonnulate overall strategies to reduce shrinkage and subsequent warpage that causes shape distortion.
Methods and procedures for a long-term additive manufacturing metrology study
(2023-04-20) Hornung, Skylar Laura; Seepersad, Carolyn; Crawford, Richard H.
Most additive manufacturing metrology studies focus on individual prints to characterize or optimize a given process, but there is a lack of publicly available metrology data collected over a series of builds over time. Long-term metrology studies continually monitor the performance of a machine to track changes in the machine’s output. The goal of this study is to support future long-term metrology studies for direct metal laser sintering (DMLS), stereolithography (SLA), and material jetting (MJ) processes, each of which are used by The University of Texas at Austin’s Center for Additive Manufacturing and Design Innovation (CAMDI). This thesis proposes a new dimensional metrology artifact, a measurement fixture compatible with a coordinate measuring machine (CMM), a measurement program for the CMM, and a database. The proposed metrology artifact includes features that test dimensional and form accuracy for raised and embedded features with square and circular cross-sections. This artifact is small enough to unobtrusively fit into regular unrelated builds without consuming excessive material or extending build times. The accompanying measurement fixture holds each artifact in the same position on the CMM table to reduce user intervention in the CMM’s base alignment process, prevent the artifact from moving when prodded by the CMM’s contact probe, and allow easy artifact insertion and removal. The measurement program enables the fast, precise, and automatic measurement of each specimen. The database reports statistics for each characteristic measured. To explore the results in the database, the user supplies the date range of tests to include in the analysis and flags a test to compare to the historical data. The paper concludes with a small metrology study from multiple artifact copies printed in a single material on each of CAMDI’s machines to verify the utility of the artifact for each additive manufacturing process. The paper explores the database’s output to find each machine’s tendencies. The results indicate that the proposed artifact, fixture, measurement procedure, and database will be useful tools to monitor each machine in a future long-term metrology study.
Net Shape Composites Using SLA Tetracast Patterns
(1997) Gervasi, Vito R.
Net-shape composites have been a focus of Solid Freeform Fabrication (SFF) for a number of years. A new method to achieve net-shape composites uses hollow Stereolithography (SLA) TetraCast* patterns. The TetraCast* pattern is injected with a filler material consisting of a matrix (typically epoxy) and reinforcement fibers, flakes, andlor particles. Upon solidification ofthe injected matrix, the net-shape composite is achieved. Net-shape composites are ideal for custom manufacturing due to the virtually limitless geometry capabilities of SLA. Areas such as aerospace, medical, manufacturing, and others could someday benefit from this process. Research to date has shown this composite structure to follow the "rule ofmixtures." It has also been shown that heat-deflection, elasticmodulus, and tensile-strength can be enhanced andlor predicted in the composite material. Several areas of continuing research include: viscosity limitations, stair-step notch reduction, reinforcement combinations, shrinkage prediction, cooling methods, SLA skin removal, nextgeneration TetraCast* structures, wear-resistant coatings, process automation, and TetraCast* pattern fill methods.
Soft Tooling for Low Production Manufacturing of Large Structures
(1996) Lee, Cheol H.; Gaffney, Thomas M.; Thomas, Charles L.
A new technique for building large prototypes from layered substrate relies on a higher order construction algorithm to produce accurate prototypes from thick layers. The process is capable ofproducing a 4' by 8' by 20' object in less than two days. Using this technique to produce molds instead ofparts allows construction oflarge castings and composite structures. Example parts include composite airfoils, a 19 foot canoe, and a custom fairing for a racing car.
Solid Modeling and Stereolithography as a Solid Freeform Fabrication Technique at Texas Instruments Incorporated
(1990) Baumgardner, Owen; Blake, Paul
Over the past 25 years, the CAE/CAD/CAM industry has developed technological advances that have provided industrial users the ability to increase productivity and decrease the cycle time necessary for product development. These technologies include basic wireframe and surface design, specializedapplication software packages, finite element analysis, numerical control, solid modeling, and rapid prototyping. Each of these technologies plays a significant role in industry today. The Defense Systems & Electronics Group of Texas Instruments currently uses these technologies in the mechanical design engineering process. This paper discusses the two specific technologies of solid modeling and rapid prototyping (specifically stereolithography), including their advantages, benefits, and practical applications within the Texas Instruments Defense Systems & Electronics Group. This paper also discusses the use of stereolithography (SLA) rapid~prototype parts within the solid-mold investment~casting process.
Steel-Based Sprayed Metal Tooling
(1990) Fussell, P.S.; Weiss, L.E.
A strategy for building sprayed steel tooling by arc spray deposition is discussed in this paper. Depositing steel is crucial for moving sprayed metal toolingfrom prototype applications to superior prototype and production-quality tooling. Tooling is fabricated by spraying onto S\lbStra~S that define the tooling shell shape. In particular, two process issues are addressed: deposition of thick metal shells, and control of oxide content by atomization with inert gases.
Stereolithography Epoxy Resin Development: Accuracy and Dimensional Stability
(1993) Pang, Thomas H.