Experimental and Analytical Investigation of Workpiece Thermal Load During External Cylindrical Grinding

AbstractThis paper focuses on the correlation between process quantities of an external cylindrical grinding process (heat partition factor ɛ, specific grinding energy partition uw transported to the workpiece, specific grinding power Pc″) and resulting surface and subsurface properties of the ground workpiece. In order to identify this correlation, experimental investigations were carried out and the maximum contact zone temperature Tmax was measured by using a grinding wheel-integrated temperature measurement system. The resulting surface layer properties are linked with the process quantities by means of the regression analysis combined with analytical considerations using the moving heat source theory. The results may contribute to predict resulting surface and subsurface properties of ground workpieces without detailed prior knowledge about thermal and mechanical loads caused by the grinding process

Influence of Different Machining Conditions on the Subsurface Properties of Drilled TiAl6V4

AbstractHigh thermomechanical loads in drilling of titanium alloys often cause significant alterations of the subsurface properties which are mostly connected to a degradation of the fatigue life of high dynamically loaded components. In the present study different drilling processes (conventional-, orbital- and vibration drilling), lubrication conditions (dry, MQL) and states of tool wear have been investigated regarding their influence on the subsurface properties of TiAl6V4. It was found that tensile residual stresses and increased hardness (result of severe plastic deformation) can be avoided if the process temperature and chip extraction are controlled

Experimental and Numerical Analysis of the Surface Integrity resulting from Outer-Diameter Grind-Hardening

AbstractBesides conventional heat treatment operations, an innovative approach for surface hardening is the grind-hardening process. During this process the dissipated heat from grinding is used for a martensitic phase transformation in the subsurface region of machined components. Additionally, compressive residual stresses are induced in the grindhardened surface layer. However, for the implementation of grind-hardening into industrial production extensive experimental tests are required to achieve iterative results of hardening depth. This paper focuses on the identification of parameter sets for a sufficient grind-hardening in outer-diameter grinding. On the one hand, grinding tests were conducted supported by metallographic investigations; on the other hand, a finite-element-based model was used to predict the surface integrity resulting from grind-hardening

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

Influence of Additives in Metalworking Fluids on the Wear Resistance of Steels

AbstractTheability of metalworking fluids (MWF) to cool and lubricate the contact zone between tool and workpiece is strongly dependent on the surface-active substances such as extreme pressure additives (EP) and passive extreme pressure additive (PEP) as well as the chemical surface properties of steel.Low alloyed steels and stainless steels were examined with a wear resistance test by applying MWF with defined varied concentrations of additivesfeaturing different properties e.g. regarding activity and molecular structure.The wear resistance was assessed and correlated with the chemical properties of the metals. Synergistic and antagonistic effects were obtained and will be discussed. The results gained from the experiments, clearly indicate, why the amount of the additives is less decisive for wear resistance than the relative ratio of polar and unpolar EP/PEP-additives.The optimal result furthermore depends on the chemical properties of the considered surfaces

Novel end-fly-cutting-servo system for deterministic generation of hierarchical micro–nanostructures

This paper reports on the diamond cutting based generation of hierarchical micro-nanostructures, which are conventionally difficult for both mechanical and non-mechanical methods to achieve. A novel end-fly-cutting-servo (EFCS) system, with four-axis servo motions that combine the concepts of fast/slow tool servo and endface fly-cutting, is proposed and investigated. In the EFCS system, an intricately shaped primary surface is generated by material removal, while the desired secondary nanostructures are simultaneously constructed using residual tool marks by actively controlling tool loci. The potential of the EFCS system is demonstrated firstly by fabricating a nanostructured F-theta freeform surface and a nanostructured micro-aspheric array

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