Machine Tools With Metal Foams Neugebauer, R.; Hipke, T.
Advanced engineering materials,
September, 2006, Letnik:
8, Številka:
9
Journal Article, Conference Proceeding
Recenzirano
Machine tool construction calls for subassemblies with reduced weight while retaining excellent dynamic properties. Modern frame components do always meet required static stiffness but often display ...oscillation problems due to low component wall thicknesses. Breaking down solid steel structure into wide‐area sandwich designs such as steel‐aluminum foam‐steel panels results in good static properties to be combined with excellent properties since these sandwiches have 30 to 40 times the flexural strength. This is due to their major geometrical moment of inertia in relation to adequate‐mass steel sheet metals. In addition, the foam core dampens oscillations. Studies on foamed steel sections indicate that 2 to 3 times higher damping is likely in relation to unfoamed steel sections. These benefits were the motivation for the Chemnitz Metal Foam Center to accelerate development of extremely large‐format sandwiches with dimensions of 1,500 × 1,000 mm2.
Today's machine tool construction calls for a extreme light weight construction with excellent dynamic properties. Modern frame components achieve this with metal foam components. They are breaking down solid steel structure into wide‐area sandwich designs such as steel‐aluminum foam‐steel panels. Newest developments show the way from prototype manufacturing to a real serial production of machine tool components.
The main goal in manufacturing is to minimize production time, cost, energy and resources while maintaining or even improving performance. The main influence on process efficiency in metal cutting ...can be related to the machining parameters, while performance also depends on the material behavior such as strain rate, machining temperature and cutting forces. In the past, industry was searching for higher efficiency mainly by using higher production rates, achieved with higher cutting conditions. However, during the last decade the production process chain has been controlled more and more by the near-net-shape of semi-finished components and the use of high performance processes. This paper presents established and new applications of process modifications, substitutions, optimizations as well as the use of hybrid processes. In high performance cutting (HPC) additional elements play an important role, for example tool design and tool material, wear and tool life, coolant strategies, including dry cutting, MQL, cryogenic and high pressure flushing as well as the machine tool properties. Furthermore, this paper presents and discusses examples of the influence of process parameters in turning, milling, drilling, grinding and impact cutting under HPC conditions on the energy and resources efficiency in the automotive, aerospace, dies and moulds, micromachining and heavy duty industries.
This paper describes a new method and its results in the roll-forming of gears that has significantly surpassed the conventional limits known till now. The method describes the rolling process and an ...alternative pitch design of forming tools. A model was created to analyze rolling processes which determined that in contrast to flat rolling tools, round tools need additional kinematic compensation during diameter-related variable pitch forming processes. This presented method shows up to a 50% improvement in pitch accuracy and the ability to roll high teeth gears (up to 10
mm in height and a tooth-height-coefficient larger than 2).
We examined the association between the percentage of students with disabilities (SWD) in general education teachers’ classes and their likelihood of turnover, investigating potential internal and ...external resources (certification, experience, preparation, classroom management, and working conditions) as moderators and disaggregating types of teacher mobility. Before accounting for other variables, the percentage of SWD, and the percentage of students with most specific disabilities, in teachers’ classes were positively associated with moving within and moving between districts. These associations were not significant after accounting for student, teacher, and school characteristics. We identified a negative association between leaving teaching in the state and the percentage of SWD in teachers’ classes, even after accounting for other variables. Dual-certification and instructional leadership moderated some of these associations. Results suggest that future research is needed to identify the supports teachers have access to when they teach higher percentages of SWD.
Although item response theory (IRT) models such as the bifactor, two-tier, and between-item-dimensionality IRT models have been devised to confirm complex dimensional structures in educational and ...psychological data, they can be challenging to use in practice. The reason is that these models are multidimensional IRT (MIRT) models and thus are highly parameterized, making them only suitable for data provided by large samples. Unfortunately, many educational and psychological studies are conducted on a small scale, leaving the researchers without the necessary MIRT models to confirm the hypothesized structures in their data. To address the lack of modeling options for these researchers, we present a general Bayesian MIRT model based on adaptive informative priors. Simulations demonstrated that our MIRT model could be used to confirm a two-tier structure (with two general and six specific dimensions), a bifactor structure (with one general and six specific dimensions), and a between-item six-dimensional structure in rating scale data representing sample sizes as small as 100. Although our goal was to provide a general MIRT model suitable for smaller samples, the simulations further revealed that our model was applicable to larger samples. We also analyzed real data from 121 individuals to illustrate that the findings of our simulations are relevant to real situations.
Abstract Stent graft fixation in the vessel affects the success of endovascular aneurysm repair. Thereby the radial forces of the stent, which are dependent on several factors, play a significant ...role. In the presented work, a finite element sensitivity study was performed. The radial forces are 29% lower when using the hyperelastic approach for the vessel compared with linear elastic assumptions. Without the linear elastic modeled plaque, the difference increases to 35%. Modeling plaque with linear elastic material approach results in 8% higher forces than with a hyperelastic characteristic. The significant differences resulting from the investigated simplifications of the material lead to the conclusion that it is important to apply an anisotropic nonlinear approach for the vessel. The oversizing study shows that radial forces increase by 64% (0.54 N) when raising the oversize from 10 to 22%, and no further increase in force can be observed beyond these values (vessel diameter D = 12 mm). Starting from an oversize of 24%, the radial force steadily decreases. The findings of the investigation show that besides the oversizing the material properties, the ring design and the vessel characteristics have an influence on radial forces.
In the course of ongoing development of mechanical joining technologies, different technologies were developed in the last years, where often the necessary die as contrary die was substituted by a ...flat anvil. Using the example of dieless clinching, the full potential of such process alternatives is visible. If the tools, as the punch or the blank-holder are modified and the necessary die is substituted by a flat anvil, then several advantages for the process alternative — the dieless clinching — emerges. For example, it is possible to produce a one-sided flat connection, which is not producible with any other joining technology. Additionally it is possible to enlarge the application potential of mechanical joining technologies as for example semi-finished parts made of magnesium can be partially heated and directly joined without an increase in process time or a reduction in the process stability. The tool’s costs, the necessary tolerances and the tool wear are significantly reduced. The publication includes an overview over the state of the development and the application potential with practical examples of different process alternatives.
The current investigation addresses critiques about motivation terminology and instrumentation by examining together three commonly used reading motivation assessments in schools. This study explores ...the distinctiveness and redundancies of the constructs operationalized in these reading motivation assessments with 222 middle school students, using item response theory. Results support distinctions between constructs grounded in self-determination theory, social cognitive theory, and expectancy-value theory as well as conceptual overlap, among constructs associated with competence beliefs and social sources of motivation across different theoretical traditions. Educational benefits of multidimensional and unidimensional interpretations of reading motivation constructs covered in these instruments are discussed.
This study explores the disciplinary literacy perspectives of middle school students of color attending urban parochial schools and the reader subject positions they took up across content-area ...classrooms. Qualitative analysis of 19 student interviews and accompanying observations of subject-area classes revealed that students’ constructions of reading, circumscribed by classroom literacy activities, inhibited discipline-specific reading subject positions. In particular, this study highlights how teachers’ reading activities promoted reading as being about accomplishing a task rather than being apprenticed in ways of taking discipline-specific knowledge from text. When the boundaries between students’ home literacy experiences and school disciplinary literacy experiences were more contiguous, and when more meaningful, authentic literacy experiences were provided, students evidenced deeper disciplinary literacy engagement. Educational implications, including troubling disciplinary knowledge to open the disciplines to wider ways of knowing and learning for all learners, are discussed.
Due to decrease in the area of extensively managed, semi-natural grasslands, that contribute to high biodiversity level preservation, the conversion of highly productive meadows to extensively ...managed, species-rich grasslands is now regarded as an important task for nature conservation. The aim of this long-term study was to assess the significance of restoration measures for diversity and trophic structure of above-ground insect community. That study challenges some weaknesses of previous studies as it was conducted with the use of suction trap enabling quantitative analyses of the changes in most insect taxa, and in a long time-span (1992â2005) in a set of permanent plots. The study area was located in a subalpine zone in Bavaria, near Laufen (Germany). The restoration process was initiated in 1996 by a cessation of fertilization and reduction of number of mowing to 1â2 per year. The changes in insect density and diversity (number of families) were monitored in ten restored and two reference plots with the aid of a suction trap. The changes in the insect community recorded during 14 years support findings from other studies that response of insect community to restoration process is usually slow on average. The short-term comparison in 2004â2005 between the restored and reference plots show that the first ones were characterized by more diverse (in term of family number) insect communities (as a whole as well as in guilds of predatory and parasitic species). From the other side, the long-term trend analysis shows that since 1998â2000 insect diversity and abundance was declining. Also trophic structure is fluctuating without clearly defined trend. These findings are in line with the results of the analyses of taxonomic composition similarity. They did not support the expectations neither that difference between initial and current taxonomical composition in a restored plot increases in time (mainly because of incoming new species), nor that spatial heterogeneity of insect assemblages should increase. However, spatio-temporal insect interactions between sample plots (located close to each other), linked to high movement ability of many insect taxa, could mask the changes in insect community caused by restoration.
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