Investigation of focused ion beam induced damage in single crystal diamond tools

In this work, transmission electron microscope (TEM) measurements and molecular dynamics (MD) simulations were carried out to characterise the focused ion beam (FIB) induced damage layer in a single crystal diamond tool under different FIB processing voltages. The results obtained from the experiments and the simulations are in good agreement. The results indicate that during FIB processing cutting tools made of natural single crystal diamond, the energetic Ga+ collision will create an impulse-dependent damage layer at the irradiated surface. For the tested beam voltages in a typical FIB system (from 8 kV to 30 kV), the thicknesses of the damaged layers formed on a diamond tool surface increased from 11.5 nm to 27.6 nm. The dynamic damage process of FIB irradiation and ion-solid interactions physics leading to processing defects in FIB milling were emulated by MD simulations. The research findings from this study provide the in-depth understanding of the wear of nanoscale multi-tip diamond tools considering the FIB irradiation induced doping and defects during the tool fabrication process

Tips to Advance Business Writing Skills at EFL Classes (Through the Example of "Letter of Complaint")

Writing is a creative communicative skill to express thoughts. It is cognitively complex, requires much practice and is best learned through experience. Writing is one of the most challenging, time-consuming tasks in acquiring a foreign language. To improve students’ writing skills and accuracy, a teacher should encourage writing-thinking, provide instructions and examples of good writing in the target language, and give feedback focusing both on error correction (cohesion) and organization of writing (clarity, idea development, coherence). This paper explores difficulties of the development of business writing skills and gives recommendations on writing a letter of complaint at English as a foreign language classes

Development of the microbiological population in water miscible metal working fluids

The deterioration of metal working fluids (MWFs) due to the microbial colonization and degradation is a considerable economic factor in the metal working industry. Microorganisms (MO) are able to metabolize almost all components of MWFs and thus lead to a loss of its function by the reduction or depletion of additives. Microbial growth cannot be avoided completely, although various methods exist to reduce the bacterial load in MWFs. This paper presents a study on the colonization of MWFs by bacteria and fungi in an industrial environment. The cooling lubricants have been periodically examined based on biological and chemical methods. The level of the total bacterial load in the lubricant is considered as well as the composition of the species community and its development over the evaluation period. With regard to the increasing relevance of environment friendly processes, a conventional mineral oil based MWF has been compared to a product based on renewable resources

Experimentelle Messung ortsdifferenter Druckentwicklung an einem Kunstkopf bei supratentoriellen Raumforderungen

In der vorliegenden Arbeit wird die intrakranielle Druckentwicklung an einem Kunstkopf bei supratentoriellen Raumforderungen gemessen. Die Schädelkapsel, das Tentorium und die Falx werden aus Epoxyharz und Plexiglas nachgebildet. Zur Simulation der viskoelastischen Eigenschaften des Gehirns wird Gelatine als Hirnersatz verwendet. Durch zwei mit Wasser gefüllte Ballons soll das Ventrikelsystem volumengerecht dargestellt werden. Ein Gummiballon in der rechten Hemisphäre dient zur Simulation einer supratentoriellen Raumforderung, welcher mittels eines Perfusors mit Wasser gefüllt wird. Die Versuche zeigen keinen wesentlichen Druckunterschied zwischen der rechten und linken supratentoriellen Hemisphäre. Zwischen dem supratentoriellen und infratentoriellen Raum wird ein Druckgradient von bis zu 16 mmHg gemessen. An der Kante des Tentoriumschlitzes entsteht ein bis um 28 mmHg höherer Druck als im supratentoriellen Raum, im Vergleich zum infratentoriellen Raum liegt er bis zu 34 mmHg höher

Using Barkhausen Noise to Measure Coating Depth of Coated High-Speed Steel

Coated high-speed steel tools are widely used in machining processes as they offer an excellent tool life to cost ratio, but they quickly need replacing once the coated layer is worn away. It would be therefore useful to be able to measure the tool life remaining non-destructively and cheaply. To achieve this, the work presented here aims to measure the thickness of the coated layer of high-speed cutting tools by using Barkhausen noise (BHN) techniques. Coated high-speed steel specimens coated with two different materials (chromium nitride (CrN), titanium nitride (TiN)) were tested using a cost-effective measuring system developed for this study. Sensory features were extracted from the signal received from a pick-up coil and the signal features, Root mean square, peak count, and signal energy, were successfully correlated with the thickness of the coating layer on high-speed steel (HSS) specimens. The results suggest that the Barkhausen noise measuring system developed in this study can successfully indicate the different thickness of the coating layer on CrN/TiN coated HSS specimens

3D Finite Element Modelling of Cutting Forces in Drilling Fibre Metal Laminates and Experimental Hole Quality Analysis

Machining Glass fibre aluminium reinforced epoxy (GLARE) is cumbersome due to distinctively different mechanical and thermal properties of its constituents, which makes it challenging to achieve damage-free holes with the acceptable surface quality. The proposed work focuses on the study of the machinability of thin (~2.5 mm) GLARE laminate. Drilling trials were conducted to analyse the effect of feed rate and spindle speed on the cutting forces and hole quality. The resulting hole quality metrics (surface roughness, hole size, circularity error, burr formation and delamination) were assessed using surface profilometry and optical scanning techniques. A three dimensional (3D) finite-element (FE) model of drilling GLARE laminate was also developed using ABAQUS/Explicit to help understand the mechanism of drilling GLARE. The homogenised ply-level response of GLARE laminate was considered in the FE model to predict cutting forces in the drilling process

Synergistic approaches to ultra-precision high performance cutting

Diamond milling allows for the flexible production of optical and high precision parts, but suffers from poor setup and production speeds. This paper presents recent advances that aim towards achieving high performance (HPC) and high speed cutting (HSC) in ultra-precision machining. After a short introduction, the benefits of high speed cutting for both metals and brittle-hard materials are shown. Thereafter, novel mechatronic devices are presented that enable an automated balancing of the applied air bearing spindles and the application of multiple diamond tools on one tool holder and by thus, contribute to HPC. These developments are supplemented by a novel linear guiding system based on electromagnatic levitation that, along with a dedicated model-based control system, enables fast and precise movements of the machine tool. After presenting the recent developments in detail, their synergistic performance is assessed and an outlook to future developments is given. © 2020 The Author