花瓶组合件的数控加工工艺

设计了一款花瓶组合件,分析了花瓶组合件的工艺特点,制定合理的工艺流程,采用分体设计、整体加工等手段,有效解决了刀具干涉、零件变形、振动及表面粗糙度不易保证等问题,采取了一系列工艺措施,保证了零件的加工质量,为今后加工该类产品提供了经验借鉴。     

钻削刀具及其工艺新进展

通过实物照片,介绍了几种新型钻削刀具及其实施工艺。包括采用一把钻头实现钻、扩非定尺寸加工及沉孔加工、深孔加工的多工序复合刀具,加工深孔和微小孔用的特种刀具等,并介绍了刀具涂层技术的新进展。这些新型刀具和工艺的应用对提高生产效率和质量,降低制造成本有着实际意义。     

拉瓦尔超音速小孔径喷嘴孔板的建模与加工

通过在Master CAM中使用内嵌语言处理高次方程曲线的方法实现了拉瓦尔超音速小孔径喷管曲面模型的构建,并从装夹定位方案、刀具选用和成型刀具的设计制造等方面,探索了小孔径曲面加工精度保证的工艺装备要素。实践表明,其方法和措施切实可行。     

工艺系统的受力变形对工件形状误差的影响

在机械加工过程中,由相应的机床、刀具、夹具以及被加工工件共同构成的一个闲环系统,称之为机械加工工艺系统,简称工艺系统。工艺系统的组成及其特性对机械加工过程、加工质量、加工效率、加工成本有直接影响。本丈以工艺系统受力变形对工件形状误差影响为例进行分析。     

浅谈数控加工工艺分析的一般步骤与方法

程序编制人员在进行工艺分析时,要有机床说明书、编程手册、切削用量表,标准工具,夹具手册等资料,根据被加工工件的材料、轮廓形状、加工精度等选用合适的机床,制定加工方案,确定零件的加工顺序,各工序所用刀具,夹具和切削用量等。此外,编程人员应不断总结、积累工艺分析方面的实际经验,编写出高质量的数控加工程序。     

干式硬态车削用PCBN刀具的研制实践

采用粉末冶金法试制干式硬态车削用PCBN刀具,并对该刀具的使用性能效果和磨损情况进行分析。结果表明：PCBN刀具制造工艺简单,成型质量好;该类刀具用于HRC〉60硬质钢的干式车削过程平稳,刀具磨损小,所加工的工件质量符合要求;该刀具磨损原因主要是氧化磨损和粘结磨损共同作用的结果。     

数控车床端面螺纹加工程序的优化

通过对端面螺纹数控车床加工方法对比、刀具选用、数控程序编辑指令选择、程序对比分析、加工工艺设计等优化,可以达到简化程序以及工艺合理的目的,从而大幅度提高机床的加工效率。     

高速切削技术中刀具选用问题探讨

高速切削技术是20世纪90年代迅速走向实际应用的先进加工技术,高速切削刀具的选用是实现高速切削加工的关键技术之一。生产实践证明,高速切削刀具必须具备可靠的安全性和高的耐用度。文章从刀具材料、刀具结构、刀杆结构、刀具动平衡几个方面介绍了高速切削技术中刀具的选用。     

试分析车床切削速度的合理选用

车床切削加工过程中,要提高生产效率,就要合理选择切削速度,根据加工材料、工艺要求、工件大小、刀具材料和车床的性能等因素合理选用,在保证顺利加工的同时,尽可能选用最快的切削速度来提高生产效率。     

数控车床凹弧加工中刀具的选择

通过对在数控车床上进行凹弧曲面加工的剖析,提出了一种根据凹弧尺寸要求,合理选择加工刀具的方法,从而避免因缺少依据而进行猜测或凭借加工经验选择刀具,防止造成刀具损坏和影响工件的加工质量。     

德国"双元制"职业教育模式探微

"双元制"模式是德国职业教育的主体和核心,是最独到、最有特色的内容,也是德国职业教育获得成功的关键。它具有法制性、实用性、社会性、公平性、选拔性和先进性等特点。探索德国"双元制"模式,可为我国职业教育的改革和发展提供可资借鉴的经验和理论指导。     

略论法律推理与逻辑推理

逻辑推理和法律推理的关系十分密切,法律推理是逻辑推理的一般方法在法律领域中广泛、综合的运用,逻辑推理是法律推理重要的理性工具之一。法律推理中的逻辑推理形式必须是有效的,有效的逻辑推理可以消解裁判中的任意性,避免谬误,帮助获得正当的裁判结论。     

Science Teachers’ Perceived Benefits of an Out‐of‐school Enrichment Programme: Identity needs and university affordances

Science enrichment programmes housed outside traditional school settings offer unique opportunities to access and use authentic scientific tools and practices, especially for urban students whose school science experiences often lack resources. Yet opportunities to access these tools and practices are realized only when science teachers value them sufficiently to take advantage of them. This study examines how eight urban secondary science teachers evaluated a specific out‐of‐school science enrichment programme—a one‐year partnership with a local university science outreach centre, which culminated in a half‐day laboratory experience for their students. Teachers’ perceptions were captured through interviews and surveys. Findings indicate that these teachers came to identify and value many of the potential benefits for out‐of‐school enrichment programmes reported in the literature as well as some additional ones. The teachers’ also showed a shift over time with respect to their perceptions of the value of the out‐of‐school experience, moving from an initial focus on increasing test scores toward a greater appreciation for its impact on students’ motivation and identity development. The study offers insight into secondary science students’ and teachers’ identity needs, and what universities can offer to address them.     

Collaborative Reasoning: Expanding Ways for Children to Talk and Think in School

This article presents a framework to help teachers facilitate small group discussions about stories children read. Collaborative reasoning discussions are intended to create a forum for children to listen to one another think out loud as they learn to engage in reasoned argumentation. Children use personal experiences and evidence from the stories to support their conclusions and consider each other's points of view. Excerpts from an ongoing study of 12 fourth-grade classrooms in rural, urban, and suburban settings are used to illustrate four characteristics of cognitive reasoning: (1) children's response to text; (2) children's use of text to consider multiple possibilities; (3) children's use of tools for persuading others; and (4) children's control of topic and turn-taking.     

Associations of epistemic beliefs in science and scientific reasoning in university students from Taiwan and India

The purpose of this study was to compare the associations of epistemic beliefs in science, performance of scientific reasoning in university students from Taiwan and India, and the relations with their science learning experiences. A total of 126 university students including 67 from Taiwan and 59 from India who had science and mathematics backgrounds were involved in the study. Students’ epistemic beliefs in science were assessed by the SEV questionnaire, while their reasoning performance and learning experiences were prompted by open-ended questions and survey items. Content analysis was performed to analyze their scientific reasoning, and correlation analysis, t tests and ANOVA were applied to reveal the associations between variables. The results showed that students from both countries differed in epistemic beliefs in the dimensions of certainty, development and justification. While few students from either country performed successfully in identifying genuine evidence and giving full rebuttals, Taiwanese participants seemed to demonstrate slightly better scientific reasoning. It was found that the Indian students were more balanced in receiving structured and engaged learning experiences. Varying associations for the students from the different countries were found between epistemic beliefs and scientific reasoning performance, and between epistemic beliefs and science learning experiences.     

Making sense of conceptual tools in student-generated cases: Student teachers' problem-solving processes

This article examines the way student teachers make sense of conceptual tools when writing cases. In order to understand the problem-solving process, an analysis of the interactions is conducted. The findings show that transforming practical experiences into theoretical reflection is not a straightforward matter. To be able to elaborate on the task it is crucial to make meaning of the tools. It is demonstrated that the institutional practices, rules and expectations must be explicit for the students. The overall aim is to demonstrate that activity theory can enhance our understanding of the interdependence between activity, task and mediating tools.     

Designing effective supports for causal reasoning

Causal reasoning represents one of the most basic and important cognitive processes that underpin all higher-order activities, such as conceptual understanding and problem solving. Hume called causality the “cement of the universe” [Hume (1739/2000). Causal reasoning is required for making predictions, drawing implications and inferences, and explaining phenomena. Causal relations are usually more complex than learners understand. In order to be able to understand and apply causal relationships, learners must be able to articulate numerous covariational attributes of causal relationships, including direction, valency, probability, duration, responsiveness, as well as mechanistic attributes, including process, conjunctions/disjunctions, and necessity/sufficiency. We describe different methods for supporting causal learning, including influence diagrams, simulations, questions, and different causal modeling tools, including expert systems, systems dynamics tools, and causal modeling tools. Extensive research is needed to validate and contrast these methods for supporting causal reasoning.     

路基基床表层级配碎石施工技术探索与实践

客运专线路基基床表层采用级配碎石作为填料,在我国铁路施工中是首次采用,其特点是技术新、工艺新、质量要求高,无成熟的经验可借鉴。以秦沈客运专线为依托,从配料选择、施工工艺和施工检测几个方面对级配碎石填料进行控制,形成独特的路基级配碎石施工技术。     

Four case studies,six years later: Developing system thinking skills in junior high school and sustaining them over time

This study examines the process by which system thinking perceptions develop within the context of a water cycle curriculum. Four junior high school students undergoing an especially designed inquiry‐based intervention were closely observed before, during, immediately after, and 6 years after completing a year long systems‐based learning program. The employed research tools included observations, semi‐structured interviews, and a number of “concept viewing” tools (drawings, concept maps, and repertory grids). Out of the data, four distinct “stories,” each presenting a different way of constructing hydro system mental models, are described. The paper's main conclusion is that students develop their systems mental models and remember the learned material based on learning patterns that tend to remain unchanged over time. Consequently, in order to facilitate efficient and lasting construction of students' system models, learning experiences should harness these, and especially the meta‐cognitive learning pattern, which holds special significance for constructing systems. © 2010 Wiley Periodicals, Inc. J Res Sci Teach 47: 1253–1280, 2010     

归纳推理中单调性和非单调性效应的实验研究

归纳推理研究中存在着一个非常重要的现象：前提数目的增加对归纳推理强度的影响，即单调性效应和非单调性效应。单调性效应和非单调性效应既是归纳推理理论模型的具体阐释，也是其理论基础和源泉。但是由于对归纳推理这个概念的界定不一以及归纳推理任务的选择标准不同，已有的许多研究并非标准的归纳推理研究，夹杂着其他如演绎推理、类比推理等心理成分，其研究结论值得商榷。采用标准的归纳推理任务研究结果表明，单调性效应与非单调性效应的出现同前提与结论之间的类属关系有关。