Number Of Process Cycles Research Articles

A review on magnetically assisted abrasive flow machining and abrasive material type

The development of fine surface finish with no defects is still a significant challenge for the present industry and the finishing operation in the manufacturing of the precision components is the major problem. It is difficult rather impossible to polish/finish the difficult-to-reach surfaces, internal surfaces, and complex geometries by existing finishing methods. Abrasive flow machining (AFM) is a well-established advanced finishing process that can meet the required finishing requirements. However, the main disadvantages of this process are the surface integrity with low surface finish and high machining times. Magnetically Assisted Abrasive flow machining (MAAFM) is one of the non-conventional machining techniques that can successfully handle these problems. This process was developed in the early 2000s as a technique for deburring, polishing, and radiusing tough to reach surfaces like complicated configurations and edges/boundaries by flowing a magnetic abrasive polymeric medium across them. Magnetic flux density (MFD), extrusion pressure, flow volume, abrasive type, grit size, number of process cycles, medium, and workpiece configuration are the principal machining parameters that control the surface finish characteristics. The medium extruded forward and backward between two vertically opposed hydraulic cylinders across transit created by the workpiece and tooling. Abrasion of workpiece takes place wherever the medium proceeds across the highly confining transit. The major elements of the MAAFM process are the machine, tooling, and the magnetic abrasives containing media. MAAFM has a wide scope of uses in industries including automotive, aviation, precision dies, medicinal, electronics. This article represents a review of current advancements in the area of the MAAFM process and the type of magnetic abrasive particles (MAPs) used.

Investigation of the joinability of single- and multi-layered AA6014 sheets produced by accumulative roll bonding in the shear-clinching process

Accumulative roll bonding belongs to the severe plastic deformation processes and is suitable for producing multi-layered as well as high-strength sheets through repeated rolling. After four accumulative roll bonding-cycles, the strength of the investigated AA6014-T4 alloy is elevated due to strain and fine grain hardening by 170% in yield strength and by 37% in ultimate tensile strength. This is accompanied by a significant decrease in material ductility which is disadvantageous for joining processes based on forming operations. Shear-clinching, however, can be used to join high-strength and low-ductile materials on the die side. Thus, it is a promising method for the mechanical joining of accumulative roll bonding components. The multi-layered and more brittle material is located on the die side whereas the single-layered base material with higher ductility is positioned on the punch side. At present, there is no scientific knowledge how the multi-layered material behaves in the shear-clinching process. Since the material is cut in the process, delamination effects could occur at the interfaces produced via accumulative roll bonding. Additionally, the investigation aims at the influence of the accumulative roll bonding process on the properties of the joints. They are expected to depend on the number of process cycles and thus on the change of mechanical properties of the multi-layered material. The bond strength of the shear-clinched joints is determined by shear and tensile tests. The areas of material failure are analysed via metallographic methods. From the failure behaviour and load-bearing capacity it is determined which number of accumulative roll bonding cycles is ideal for joining multi-layered sheets via shear-clinching.

Optimization to the parameters of abrasive flow machining by Taguchi method

This project summarizes the study of the parameters (Number of process cycles, Extrusion pressure and Abrasive concentration) and experimented variation used in Abrasive flow machining (AFM) for the surface finishing process and its optimization using Taguchi method. Abrasive flow machining (AFM) process is a most suitable non-conventional finishing process of internal passages of IC engine vehicles .Workpiece were machined by making all possible arrangements of these parameters on 3 levels which resulted into total of 27 workpiece which were machined to find the optimum value of parameters. Finally the results were verified using Taguchi method to find the optimum value of parameters. It has been found through the experiment that the optimum result is obtained when ‘Number of cycles is equal to 6, Extrusion pressure is 15 bars and Abrasive concentration is 100gm’, which shows that the percentage difference in surface roughness after machining is 26.42%. The result obtained shows that Taguchi designs recognize that not all the factors that causes variability can be controlled. These non-controllable factors are called noise factors. Taguchi designs try to identify controllable factors that can minimize the effects of noise factors.

ALD Growth Behavior of High-K Nanolayers on Various Substrates Characterized by X-Ray Spectrometry in Gracing Incidence Geometry

Thin films of high-k material are becoming more and more used for semiconductor devices. A further shrinking of the devices requires also a further reduction of the high-k film thickness. With this reduction of the high-k thickness down to just a few nanometers two technical challenges have to be addressed. The first one is the ALD process for the deposition of the high-k material. Usually the ALD process can be well controlled by tuning the number of process cycles. But it is theoretically predicted [1] that the growth-per-cycle of the first cycles can be different than the steady growth-per-cycle which is obtained for high cycle numbers. This effect is caused by a not fully covered initial surface during the first cycles. Only when the deposited material forms a closed surface and the surface probabilities are the same for each following cycle the deposition rate will be constant. The second challenge is that the electrical properties of thin films with a thickness of a few nanometers are significantly determined by the quality of the interface between the film and the substrate.

Preparation of Nano-Coenzyme Q10 by Water Jet Comminution

Nanoparticles usually prepared through chemical synthetic method. In our study, nanoCoenzyme Q10 was prepared by water jet comminution process. The results were characterized with scanning electron microscope (SEM) and the color change of the water solution. The color becomes lighter when the particles have a smaller size. The effect of comminution is related to the number of process cycles. nanoCoenzyme Q10 water solution (particle size less than 50nm) was obtained through water jet comminution at 50Mpa with five cycles. This new method not only solves the problem of physical comminution collection, but also gives an effective way to prepare natural nanoparticles.

Atomic layer deposition of hafnium silicate film for high mobility pentacene thin film transistor applications

The performance of pentacene thin film transistors (TFTs) was improved using a hafnium silicate (HfxSi1−xO2) thin film as a high-k dielectric layer. For growth of the HfxSi1−xO2 thin films, an atomic layer chemical vapor deposition (ALCVD) process was optimized using silicon alkoxide and hafnium amido as precursors. The self-limiting surface reactions of each precursor were observed, indicating the ALCVD growth characteristics. The film thickness linearly increased depending on the number of process cycles, with a remarkably high growth rate of 2.3 A per cycle. The chemical binding states, thermal stability and electrical characteristics of the films grown were investigated using XPS, XRD and capacitance–voltage and leakage current–voltage analysis. The pentacene TFTs fabricated with the ALCVD-grown Hf0.67Si0.33O2 dielectric layer were characterized and the results were compared to the pentacene TFTs using Al2O3 and SiO2 film as dielectric layers. The pentacene/Hf0.67Si0.33O2 TFT showed a three-fold and five-fold higher mobility than a pentacene/Al2O3 TFT and a pentacene/SiO2 TFT, respectively. With additional treatments to enhance the characteristics of the OTFT, pentacene/HfxSi1−xO2 TFTs have great potential as high mobility devices with low operational voltage.

Thermodynamic properties and interfacial layer characteristics of HfO2 thin films deposited by plasma-enhanced atomic layer deposition

The thermodynamic properties and interfacial characteristics of HfO2 thin films that were deposited by the direct plasma atomic layer deposition (DPALD) method are investigated. The as-deposited HfO2 films that were deposited by the DPALD method show crystallization of the HfO2 layers, which initiates at approximately the 35th cycle (about 2.8nm) of the DPALD process. Medium-energy ion scattering analysis reveals that the direct O2 plasma causes a compositional change in the interfacial layer as the process progresses. With an increase in the number of process cycles, the Si content decreases and the O content increases at that position, so that the HfO2-like Hf-silicate layer is formed on top of the interfacial layer. The enhanced physical reactivity of the oxygen ions in the direct plasma and the Hf-silicate layer may be the driving forces that accelerate the early crystallization of the HfO2 layer in the DPALD process in the as-deposited state.

ABRASIVE FLOW MACHINING WITH ADDITIONAL CENTRIFUGAL FORCE APPLIED TO THE MEDIA

Abrasive flow machining (AFM) is one of the important non-traditional metal finishing technologies which was introduced during the late 1960s. The process has found applications in a wide range of fields such as aerospace, defence, surgical and tool manufacturing industries. Recently, an effort has been made towards the performance improvement of this process by applying centrifugal force on the abrasive media with the use of a rotating centrifugal force generating (CFG) rod introduced in the workpiece passage. The results have been encouraging. The present paper discusses the results of changing the parameters like shape and rotational speed of CFG rod, extrusion pressure, number of process cycles and abrasive grit size. The results indicate that all the input variables have significant effect on the response parameters, which for the present study were taken as material removal and surface roughness. An analytical model is proposed for the velocity and the angle at which abrasive particles attack the workpiece surface in the process.

ZnO layers deposited by the ion layer gas reaction on Cu(In,Ga)(S,Se)2 thin film solar cell absorbers—impact of ‘damp‐heat’ conditions on the layer properties

AbstractCu(In,Ga)(S,Se)2 (‘CIGSSe’) based solar cells with a ZnO window extension layer (WEL) deposited by the ion layer gas reaction (ILGAR) reach competitive efficiencies compared to corresponding references with CdS buffer and lead to a simplified device structure. The WEL replaces not only the CdS buffer, but also the undoped part of the usually applied rf‐sputtered ZnO window bi‐layer. The long‐term stability of CIGSSe‐based solar modules is currently under investigation. In order to pass the respective stability tests, which include exposure to ‘damp‐heat’ (DH) conditions (85% relative humidity at 85(C) to accelerate possible aging effects, a good intrinsic material stability is required. In Reference1 it was revealed, that ILGAR‐ZnO contains a certain amount of meta‐stable hydroxide, which can be directly tuned by the ILGAR process parameters (number of process cycles and process temperature). In order to determine the ILGAR process parameters, which result in intrinsically stable WELs, ILGAR‐ZnO/CIGSSe test structures were investigated by means of scanning electron microscopy (SEM) and x‐ray photoelectron spectroscopy (XPS) before and after a DH‐test. It was found that, induced by the DH‐conditions, a continuous dehydration of the WELs together with a disintegration of the ILGAR‐ZnO layers takes place. This supports an earlier suggested mechanism of a DH‐induced degradation by a release of water at the most critical location in a solar cell, at the heterointerface between window and absorber. By a systematic variation of the ILGAR process parameters it was possible to reduce the hydroxide content in the ILGAR‐ZnO layers resulting in intrinsically more stable samples. Copyright © 2006 John Wiley & Sons, Ltd.