The Effects of Pre-Alloyed Steels Powder Compositions on Build Quality in Direct Metal Laser Re-Melting

Mechanical Engineerin

Some aspects of the injection moulding of alumina and other engineering ceramics

The literature concerning the injection moulding of engineering ceramics has been reviewed. This indicated that a number of claims had been made for the successful use of different organic binders during moulding and their removal prior to sintering. However, many of the claims were not supported by detailed/exact eScperimental evidence as to powder-binder compositions, moulding conditions, moulded properties, debinding times/cycles, or details of the structure and properties of the solid ceramic bodies produced. From the available information it was clear that there were few systematic and scientific investigations concerning the understanding of each stage of the injection moulding process. The present research programme has been carried out in two phases as follows. The first phase was concerned with the reinvestigation and re-evaluation of binder systems claimed to be successful for the injection moulding of alumina ceramics. The binders re-investigated included the thermoplastic-based binders such as polystyrene, polyacetal and atactic polypropylene and the water-based methylcellulose (Rivers) binder system. Alumina was chosen as the main powder to be investigated due to its simple handling and, highest applications amongst ceramic materials and on the basis that there is incomplete published work for almost every step of the injection moulding process. During the first stage of this work the optimum properties such as powder-binder compositions, mixing and moulding conditions, debinding properties, green and sintered densities provided by each binder system were determined. The results of these investigations showed that all the previous (re-evaluated) binder systems had major limitations and disadvantages. These included low volume loading (64 % maximum) of the alumina powder resulting in rather low sintered densities (96 % maximum-of theoretical density) and very long debinding times in the case of the thermoplastic-based binders. it ry low alumina volume loading (55 % maximum resulting in a 94 % . sintered theoretical density) and long moulding cycle time (- 5 min) along with adhesion and distortion problems during demoulding occurred in the case of the water-based methylcellulose binder system. Further work did not appear worthwhile. The newly developed binder systems have been used with a number of other powders such as zirconia, silicon nitride, silicon carbide, tungsten carbide-6 weight % cobalt and iron-2 weight % nickel, to establish- whether injection moulding is feasible. Optimum properties such as powder volume loadings, mixing, moulding, demoulding, moulded densities, debinding and some sintered density results showed that these new binder systems can also be used successfully for the injection moulding of other ceramic and metallic powders, although a fuller evaluation of the properties such as optimum sintered densities and mechanical properties is required

A Novel Algorithm for Human Fall Detection using Height, Velocity and Position of the Subject from Depth Maps

Human fall detection systems play an important role in our daily life, because falls are the main obstacle for elderly people to live independently and it is also a major health concern due to aging population. Different approaches are used to develop human fall detection systems for elderly and people with special needs. The three basic approaches include some sort of wearable devices, ambient based devices or non-invasive vision-based devices using live cameras. Most of such systems are either based on wearable or ambient sensor which is very often rejected by users due to the high false alarm and difficulties in carrying them during their daily life activities. This paper proposes a fall detection system based on the height, velocity and position of the subject using depth information from Microsoft Kinect sensor. Classification of human fall from other activities of daily life is accomplished using height and velocity of the subject extracted from the depth information. Finally position of the subject is identified for fall confirmation. From the experimental results, the proposed system was able to achieve an average accuracy of 94.81% with sensitivity of 100% and specificity of 93.33%

Fourth-Order Butterworth Active Bandpass Filter Design for Single-Sided Magnetic Particle Imaging Scanner

This paper describes the design and simulation of a fourth-order Butterworth active bandpass filter designed for single-sided magnetic particle imaging (MPI) scanner. Bandpass filters (BPF) are used in MPI scanner set-up to attenuate the harmonic distortions generated by the power amplifier before passing the purely sinusoidal signal to the excitation (Drive) coils. The BPF is designed based on the excitation frequency of 22.8 kHz, having Butterworth response, and realized using Sallen-Key topology by cascading one second-order highpass filter and one second-order lowpass filter, with values of the passive components calculated using the coefficient matching method. MATLAB and NI Multisim software are used to simulate the filter, and the results are compared. The magnitude response obtained using MATLAB have monotonic amplitude response in the pass and stopband, and maximally flat with small ripples in the passband than the NI Multisim implementation, while NI Multisimimplementation has better roll-off than MATLAB implementation

Direct Selective Laser Sintering of Tool Steel Powders to High Density: Part B -The Effect on Microstructural Evolution

This paper describes recent progress on the Direct Selective Laser Sintering of M2 [Fe6W-5Mo-4Cr-2V-0.8C] high speed steel (HSS) and H13 [Fe-5Cr-1V-1Si-1.5Mo-0.4C] tool steel powders. Part B will focus on the microstructural evolution of laser scanned powder beds. It has been found that H13 powders are more amenable to Direct Selective Laser Sintering than M2 powders. Densities up to 90% are possible with H13 powder compared with 70% for M2. The relationship between alloy composition, microstructure, post-scanned density and scan conditions will be discussed for single track, single layer and multi-layer constructions.The research reported in this paper is a joint project between the Universities of Bradford, Leeds and Liverpool, funded by the UK Engineering and Physical Sciences Research Council under Grant Number GR/R32222.Mechanical Engineerin

Direct Selective Laser Sintering of Tool Steel Powders to High Density: Part A - Effects of Laser Beam Width and Scan Strategy

This paper describes progress on the Direct Selective Laser Sintering of M2 and H13 tool steel powders, comparing this with previous and further observations on stainless steel powders. The distinguishing feature is the melting of single tracks and layers in deep powder beds. The paper focuses on changing characteristics of the melt pool (mass, volume, aspect ratio, stability) and laser-powder interactivity as the laser beam width, power and scan speed change. It also compares the melt pool of neighbouring tracks during single layer construction. Simulations from a computer model to predict melt pool shape and dimension show reasonable agreement with experimental results at low scan speeds (0.5mm/s). But unexpected increases in melt depth above 1.0mm/s have been observed, suggesting higher values and more variability in laser absorptivity than expected, even approaching 1.0 for the CO2 laser radiation used in this work.Mechanical Engineerin

Electrocardiograph (ECG) circuit design and software-based processing using LabVIEW

The efficiency and acquisition of a clean (diagnosable) ECG signal dependent upon the proper selection of electronic components and the techniques used for noise elimination. Given that the human body and the lead cables act as antennas, hence picking up noises from the surroundings, thus a major part in the design of an ECG device is to apply various techniques for noise reduction at the early stage of the transmission and processing of the signal. This paper, therefore, covers the design and development of a Single Chanel 3-Lead Electrocardiograph and a Software-based processing environment. Main design characteristics include reduction of common mode voltages, good protection for the patient, use of the ECG device for both monitoring and automatic extraction (measurements) of the ECG components by the software. The hardware consisted of a lead selection stage for the user to select the bipolar lead for recording, a pre-amplification stage for amplifying the differential potentials while rejecting common mode voltages, an electrical isolation stage from three filtering stages with different bandwidths for noise attenuation, a power line interference reduction stage and a final amplification stage. A program in LabVIEW was developed to further improve the quality of the ECG signal, extract all its features and automatically calculate the main ECG output waveforms. The program had two main sections: The filtering section for removing power line interference, wideband noises and baseline wandering, and the analysis section for automatically extracting and measuring all the features of the ECG in real time. A Front Panel Environment was, therefore, developed for the user interface. The present system produced ECG tracings without the influence of noise/artefacts and provided accurate detection and measurement of all the components of the ECG signal

Fabrication and characterizations of hydrogels for cartilage repair

YesArticular cartilage is a vascular tissue with limited repair capabilities, leaving an afflicted person in extreme pain. The tissue experiences numerous forces throughout its lifetime. This study focuses on development of a novel hydrogel composed of chitosan and β-glycerophosphate for articular cartilage repair. The aim of this study was to investigate the mechanical properties and swelling behaviour of a novel hydrogel composed of chitosan and β-glycerophosphate for cartilage repair. The mechanical properties were measured for compression forces. Mach-1 mechanical testing system was used to obtain storage and loss modulus for each hydrogel sample to achieve viscoelastic properties of fabricated hydrogels. Two swelling tests were carried out to compare water retaining capabilities of the samples. The hydrogel samples were made of five different concentrations of β-glycerophosphate cross-linked with chitosan. Each sample with different β-glycerophosphate concentration underwent sinusoidal compression forces at three different frequencies -0.1Hz, 0.316Hz and 1Hz. The result of mechanical testing was obtained as storage and loss modulus. Storage modulus represents the elastic component and loss modulus represents the viscosity of the samples. The results obtained for 1Hz were of interest because the knee experiences frequency of 1Hz during walking

Effect of TGF-β1 on water retention properties of healthy and osteoarthritic chondrocytes

YesArticular cartilage, a connective tissue, contains chondrocytes and glycosaminoglycans (GAGs) which aid in water retention, providing the tissue with its magnificent ability to prevent friction, withstand loads and absorb compressive shocks however, cartilage, does not have the ability to regenerate and repair. Osteoarthritis (OA) is a progressive degenerative disease, which includes reduction of cartilage thickness between two bones in a joint, causing painful bone-to-bone contact. OA affects over 8 million people in the UK alone. , and as the primary causes are unknown, available treatments including surgical and non-surgical techniques which only reduce the symptoms created by the disorder instead of providing a cure. This project focused on utilizing TGF-β1, a cytokine found in elevated amounts in healthy cartilage when compared to degraded cartilage, in order to observe the effects of the growth factor on both healthy and osteoarthritic chondrocytes. The healthy and the osteoarthritic chondrocytes were cultured in two different media (DMEM with and without TGF- β1) before utilizing the SpectraMax M2/M2e plate reader to observe and analyze the effect of TGF-β1 on water retention properties of cells. This has been achieved by quantifying the GAG content using DMMB dye. Results showed that although TGF-β1 did displayed an increase in glycosaminoglycan synthesis, the statistical increase was not vast enough for the alternative hypothesis to be accepted; further experimentation with TGF-β1, alongside other cytokines within the growth factor family is needed to perceive the true influence of the growth factor on un cured degenerative diseases. It was concluded that both the healthy and osteoarthritic cells treated with TGF-β1 absorbed considerably more DMMB in comparison to the cells, suggesting that TGF-β1 indeed works to aid in water retention. TGF-β1 is a key factor to be exploited when constructing treatments for osteoarthriti

Investigation of Pulse electric field effect on HeLa cells alignment properties on extracellular matrix protein patterned surface

YesCell behavior in terms of adhesion, orientation and guidance, on extracellular matrix (ECM) molecules including collagen, fibronectin and laminin can be examined using micro contact printing (MCP). These cell adhesion proteins can direct cellular adhesion, migration, differentiation and network formation in-vitro. This study investigates the effect of microcontact printed ECM protein, namely fibronectin, on alignment and morphology of HeLa cells cultured in-vitro. Fibronectin was stamped on plain glass cover slips to create patterns of 25μm, 50μm and 100μm width. However, HeLa cells seeded on 50μm induced the best alignment on fibronectin pattern (7.66° ±1.55SD). As a consequence of this, 50μm wide fibronectin pattern was used to see how fibronectin induced cell guidance of HeLa cells was influenced by 100μs and single pulse electric fields (PEF) of 1kV/cm. The results indicates that cells aligned more under pulse electric field exposure (2.33° ±1.52SD) on fibronectin pattern substrate. Thus, PEF usage on biological cells would appear to enhance cell surface attachment and cell guidance. Understanding this further may have applications in enhancing tissue graft generation and potentially wound repair.Ministry of Higher Education Malaysia and UTHM Tier 1 Research Grant (U865