Surface integrity in finish hard turning of case-hardened steels

Highly stressed steel components, e.g., gears and bearing parts, are appropriate applications for hard turning. Therefore, the process effects on significant engineering properties of work materials have to be carefully analyzed. Roughness, residual stresses, and white layers as parts of surface integrity, are functions of the machining parameters and of the cuttability of the cutting edge, i.e. of the tool wear.The aim of this work was to study the influence of feed rate, cutting speed, and tool wear on the effects induced by hard turning on case-hardened 27MnCr5 gear conebrakes and to point out the technical limitations in mass production.     

Custom single-photon avalanche diode with integrated front-end for parallel photon timing applications

Emerged as a solid state alternative to photo multiplier tubes (PMTs), single-photon avalanche diodes (SPADs) are nowadays widely used in the field of single-photon timing applications. Custom technology SPADs assure remarkable performance, in particular a 10 counts/s dark count rate (DCR) at low temperature, a high photon detection efficiency (PDE) with a 50% peak at 550 nm and a 30 ps (full width at half maximum, FWHM) temporal resolution, even with large area devices, have been obtained. Over the past few years, the birth of novel techniques of analysis has led to the parallelization of the measurement systems and to a consequent increasing demand for the development of monolithic arrays of detectors. Unfortunately, the implementation of a multidimensional system is a challenging task from the electrical point of view; in particular, the avalanche current pick-up circuit, used to obtain the previously reported performance, has to be modified in order to enable high parallel temporal resolution, while minimizing the electrical crosstalk probability between channels. In the past, the problem has been solved by integrating the front-end electronics next to the photodetector, in order to reduce the parasitic capacitances and consequently the filtering action on the current signal of the SPAD, leading to an improvement of the timing jitter at higher threshold. This solution has been implemented by using standard complementary metal-oxide-semiconductor (CMOS) technologies, which, however, do not allow a complete control on the SPAD structure; for this reason the intrinsic performance of CMOS SPADs, such as DCR, PDE, and afterpulsing probability, are worse than those attainable with custom detectors. In this paper, we propose a pixel architecture, which enables the development of custom SPAD arrays in which every channel maintains the performance of the best single photodetector. The system relies on the integration of the timing signal pick-up circuit next to the photodiode, achieved by modifying the technological process flow used for the fabrication of the custom SPAD. The pixel is completed by an external standard CMOS active quenching circuit, which assures stable timing performance at quite high count rate (>1 MHz).     

Experience Management Wikis for Reflective Practice in Software Capstone Projects

Software engineering curriculum guidelines state that students should practice methods, techniques, and tools. A capstone project is one possibility to address this aim. A capstone project helps the students to increase their problem solving competencies, improve their social skills (e.g., communication skills), and gather practical experience. A crux of such projects is that students perform ldquoreflectiverdquo practice in order to learn from their experiences. The authors believe that experience gathering and reuse are effective techniques to stimulate reflective activities. An adapted free- and open-source Wiki-based system called software organization platform (SOP) is used to support students in managing their observations and experiences. The system can be used for experience exchange within the team and for experience reuse in forthcoming projects. The results of a case study show that standard Wiki functions improve communication and information sharing by means of explicit observation and experience documentation. A total of 183 documented observations and experiences at the end of the project provide a measure for the amount of reflection students have had during the capstone project. Still, the advantages of using Wikis will decrease when no technical adaptations of the Wiki to the learning objectives and to the software engineering tasks are made. Limitations of the case study, future evaluation steps, and planned developments of SOP will be provided in this paper.     

The effect of lubrication conditions on belt finishing

The belt finishing process is a recent manufacturing technique in the field of superfinishing of hard material. Belt finishing leads to an homogenous surface with a very smooth surface roughness and good bearing curve parameters. In this way, belt finishing can complement effectively hard turning, whose disability is the shifting of the surface quality due to tool flank wear. In order to study the effect and the interaction of lubrications conditions on belt finishing after hard turning, an experimental study is proposed. The interaction between lubrications conditions and belt feed and the effect on roughness parameters has been investigated. It was shown that minimum quantity lubrication with low belt feed is the best way to have the optimal roughness characteristics. Under these conditions, the process is not a basic belt finishing operation but a combination of belt finishing and lapping due to the presence of a slurry made of free abrasive grains, microchips and oil, in the contact. Additionally, it has been revealed that dry belt finishing is not suitable because of the rapid destruction of abrasive grains.     

Identification of a friction model—Application to the context of dry cutting of an AISI 1045 annealed steel with a TiN-coated carbide tool

The characterization of friction coefficients at the tool-chip-workpiece interface remains an issue. This paper aims to identify a friction model able to describe the friction coefficient at this interface during the dry cutting of an AISI1045 with TiN coated carbide tools. A new tribometer has been designed in order to reach relevant values of pressures and sliding velocities. This set-up is based on a modified pin-on-ring system. Additionally a numerical model simulating the frictional test has been associated in order to quantify average friction coefficients around the spherical pin, from the standard macroscopic data provided by the experimental system. A range of cutting speeds has been investigated. It has been shown that the friction coefficient is very much dependant on the sliding velocity. A new friction model has been identified based on the average local sliding velocity.     

Investigation of machining performance in high-pressure jet assisted turning of Inconel 718: An experimental study

This paper investigates the application of the high-pressure jet assistance (HPJA) in rough turning of Inconel 718 with coated carbide tools. The region of operability, which sets the boundaries of the process parameters, has been experimentally determined using the tool–material pair (TMP) methodology. The assessment of HPJA machining performance is based on response surface methodology (RSM), which integrates a design of experiment (DOE) and a regression modelling technique for fitting a model to experimental. This leads to a new insight into the influence of the cutting process on chip breakability, cutting forces, contact length, surface finish and tool temperature, which are the key machining performance measures.     

Interdigitated back‐contact heterojunction solar cell concept for liquid phase crystallized thin‐film silicon on glass

We present an interdigitated back‐contact silicon heterojunction system designed for liquid‐phase crystallized thin‐film (~10 µm) silicon on glass. The preparation of the interdigitated emitter (a‐Si:H(p)) and absorber (a‐Si:H(n)) contact layers relies on the etch selectivity of doped amorphous silicon layers in alkaline solutions. The etch rates of a‐Si:H(n) and a‐Si:H(p) in 0.6% NaOH were determined and interdigitated back‐contact silicon heterojunction solar cells with two different metallizations, namely Al and ITO/Ag electrodes, were evaluated regarding electrical and optical properties. An additional random pyramid texture on the back side provides short‐circuit current density (j_SC) of up to 30.3 mA/cm² using the ITO/Ag metallization. The maximum efficiency of 10.5% is mainly limited by a low of fill factor of 57%. However, the high j_SC, as well as V_OC values of 633 mV and pseudo‐fill factors of 77%, underline the high potential of this approach. Copyright © 2015 John Wiley & Sons, Ltd.     

GPUs Neutron Sensitivity Dependence on Data Type

Graphics Processing Units are very prone to be corrupted by neutrons. Experimental results obtained irradiating the GPU with high energy neutrons show that the input data type has a strong influence on the neutron-induced error-rate of the executed algorithms. Moreover, when operations are performed using floating-point data, the probabilities to be corrupted are very different for the mantissa, the exponent or the sign. We investigate the occurrences of errors in the different positions, evaluating the related effects on the result precision. The reported results and the architecture analysis demonstrate that under radiation, whenever possible, one should favor floating-point arithmetic, which is both more reliable and potentially easier to protect than the integer one.