Micro assembly injection moulding

Injection moulding is established as one of the most common manufacturing processes of thermoplastics due to its high degree of automation and the short cycle times. Micro injection moulding is a rapidly growing technology that allows for the efficient production of very complex micro parts in high series. The “Market Analysis for Microsystems II 2002–2005” of the Nexus Task Force anticipates a yearly growth in the field of micro system technology of about 20% (Wechsung et al. 2002). This study identifies in addition to the continuous miniaturization the growing use of polymers in micro systems (Schneider et al. 2001). No other material group offers this wide range of material properties and permits to choose processing parameters and application properties according to necessities (Gächter 2000). While the production processes of micro technical components are mainly controllable, the assembly of these components to hybrid micro systems is a bottleneck to the industrial large scale production. The assembly itself represents a large fraction of the added product value and gains in importance with growing complexity and miniaturization of the systems.     

Abstracts

Ohne Zusammenfassung

---

Abstracts

     

Cognitive load and instructionally supported learning with provided and learner-generated visualizations

This study investigated, whether learning from science texts can be enhanced by providing learners with different forms of visualizations (pictures) in addition to text. One-hundred-two 9th and 10th graders read a computer-based text on chemical processes of washing and answered questions on cognitive load (mental effort, perceived difficulty) and comprehension (retention, transfer, drawing). Instruction varied according to a 2 × 2-factorial design with ‘learner-generated pictures’ (yes, no) and ‘provided pictures’ (yes, no) as factors. Results indicate positive main effects of provided pictures on all three comprehension measures and negative main effects on both cognitive load measures. Additional analyses revealed a mediation effect of perceived difficulty on retention and transfer, that is learning with provided pictures decreased cognitive load and enhanced comprehension. Furthermore, results show a positive main effect of learner-generated pictures on drawing and mental effort, but no mediation effect. Taken together, computer-based learning with provided pictures enhances comprehension as it seems to promote active processing while reducing extraneous cognitive processing. Learners, generating pictures, however, seem to have less cognitive resources available for essential and generative processing, resulting in reduced comprehension. These results are in line with cognitive load theory, cognitive theories of multimedia learning, and generative theories of learning.     

Advances in micro assembly injection moulding for use in medical systems

In micro systems technology, the process of micro assembly injection moulding is used for the generation of hybrid micro systems. With this process, more functions are integrated in less space. In the field of medical technology, miniaturisation also means new methods of treatment with fewer side effects on the patient. New cures are developed by the miniaturisation of medical instruments, such as keyhole surgery. For detailed investigations a specific demonstration was developed to display the potential of micro assembly injection moulding in medical science. This part consists of a carbon-fibre reinforced PEEK puncture needle, which incorporates three lumens. The selected materials allow use of the needle during magnetic resonance imaging. In order to attach additional equipment a plastic connector needs to be overmoulded on the needle. The investigations focus on the injection moulding process by characterising the influences of temperature, moulding parameters and material combinations on the resulting bond strength between needle and connector.     

Book Reviews

Ohne Zusammenfassung

---

Book Reviews

     

Investigation of Epoxide Curing Reactions by Differential Scanning Calorimetry – Formal Kinetic Evaluation

A differential scanning calorimeter measures the heat flow rates between sample and device as function of time and temperature. The increasing power of both computerisation and evaluation software enables the fast and reliable kinetic evaluation of a reacting system. This is the basis for valid predictions of the reaction behaviour even for very complicated time/temperature conditions, including systems with partial diffusion control. Both non‐isothermal and isothermal reaction modes are possible in DSC and have particular advantages and disadvantages. In each case, the simultaneous kinetic evaluation of non‐isothermal and isothermal measurements is not only possible but absolutely necessary to avoid wrong conclusions. Considering the objectives of a practitioner, the kinetic analysis is sufficiently simple, relatively fast, flexible enough and particularly valuable for versatile predictions, when using a formal kinetic model. This is shown for three examples of epoxide curing. Of course, the formal kinetic model is never the one‐to‐one reflection of the true reaction mechanism.     

Drawing as a generative activity and drawing as a prognostic activity.

In this study, 9th-grade students (N = 196) with a mean age of 14.7 years read a scientific text explaining the chemical process of doing laundry with soap and water and then took 3 tests. Students who were instructed to generate drawings during learning scored higher than students who only read on subsequent tests of transfer (d = 0.91), retention (d = 0.87), and drawing (d = 2.00). For students who were instructed to generate drawings during learning, those who generated high-accuracy drawings (according to a median split) scored higher than students who generated low-accuracy drawings on subsequent tests of transfer (d = 0.99), retention (d = 0.79), and drawing (d = 1.87); furthermore, drawing-accuracy scores during learning correlated with learning-outcome scores on transfer (r = .57), retention (r = .50), and drawing (r = .82). Results suggest that drawing can serve as a generative activity and as a prognostic activity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Learning with hypermedia: The influence of representational formats and different levels of learner control on performance and learning behavior

In this paper, two experiments on the use of hypermedia environments for learning about probability theory are reported. In Experiment 1a it was tested whether multimedia design principles (multimedia principle, modality principle, redundancy principle) are valid in hypermedia environments, despite the fact that hypermedia offers more learner control than multimedia. The results showed only little evidence for this validity, although the hypermedia environment entailed only a rather low level of learner control. In Experiment 1b it was investigated how learner control affects performance and how its possible impact is moderated by learners’ prior knowledge. A high level of learner control positively affected the effectiveness of instruction only with regard to intuitive knowledge, but was at the same time accompanied by large increases in learning time, thereby rendering the instruction inefficient. Unexpectedly, effects of learner control were not moderated by students’ prior knowledge. The results imply that the idea to use multimedia design principles for hypermedia learning is too simple and that the benefits and drawbacks of learner control depend heavily on learning objectives and time constraints.