Advances in Silicon Resonant Pressure Transducers

AbstractThis paper presents a MEMS Resonant Pressure Transducers (RPT) that is produced using a flexible fabrication route to allow pressure ranges from 1bar to 700bar in fully oil isolated hermetic packages without compromising sensor performance. The fabrication method makes use of silicon fusion bonding (SFB) and deep reactive ion etching (DRIE) to build up a three-layer die, with the middle layer consisting of a strain sensitive resonator. The key aspects of the fabrication process and sensor design that make this possible are presented, along with data showing long-term stability of better than 100ppm drift per year

Erosion resistance of laser clad Ti-6Al-4V/WC composite for waterjet tooling

AbstractIn waterjet operations, milled surfaces are left with some undesirable dimensional artefacts, thus the use of abrasion resistant mask has been proposed to improve the surface quality of machined components. In this study, the erosion performance of laser clad Ti-6Al-4V/WC composite coating subjected to plain water jet (PWJ) and abrasive water jet (AWJ) impacts to evaluate its potentials for use as waterjet impact resistant mask material and coating on components was investigated. Results showed that composite with 76wt.% WC composition subjected to PWJ and AWJ impacts offered resistance to erosion up to 13 and 8 times that of wrought Ti-6Al-4V respectively. Scanning electron microscopy (SEM) examination of the eroded composite surfaces showed that the erosion mechanism under PWJ impacts is based on the formation of erosion pits, tunnels and deep cavities especially in the interface between the WC particles and the composite matrix owing to lateral outflow jetting and hydraulic penetration. Composite suffered ploughing of the composite matrix, lateral cracking and chipping of embedded WC particles and WC pull-out under AWJ impacts. The composite performance is attributed to the embedded WC particles and the uniformly distributed nano-sized reaction products (TiC and W) reinforcing the ductile β-Ti composite matrix, with its mean hardness enhanced to 6.1GPa. The capability of the Ti-6Al-4V/WC composite coating was demonstrated by effective replication of a pattern on a composite mask to an aluminium plate subjected to selective milling by PWJ with an overall depth of 344μm. Thus, composite cladding for tooling purpose would make it possible to enhance the lifetime of jigs and fixtures and promote rapid machining using the water jet technique

Functionally graded Ni-Ti microstructures synthesised in process by direct laser metal deposition

The fabrication of biomedical devices using Ni-Ti compositions is limited to conventional techniques and the use of near equiatomic pre-alloyed Ni and Ti powders. In this study, functionally graded walls and cylinder built by concurrent feeding of Ni powder and commercially pure (CP) Ti wire using direct laser metal deposition technique are presented. The built structures consist of CP Ti wire-deposited layers and Ni-Ti layers of varying Ni composition. The microstructures of the built Ni-Ti structures including phase identification, phase compositions and area fractions of the phases present at various processing parameters were determined using a combination of scanning electron microscopy/ energy dispersive X-ray spectroscopy, X-ray diffractometry and image processing software. Vickers microhardness test was conducted on the deposited structures. It was found that the Ni-Ti layers comprise of NiTi and NiTi2 phases. The area fraction of the NiTi phase increases, whereas NiTi2 decreases with increasing the Ni powder feed rate. Ni-Ti layers with higher area fractions of NiTi2 phase are found to be harder with a maximum of 513 HV0.3 found in this study. The micro-hardness of Ni-Ti layers is, by at least a factor of 1.5, higher than the CP Ti wire laser-deposited layers

Surface finishing of intricate metal mould structures by large-area electron beam irradiation

The advancement of polymer moulding tools is increasingly focused on imparting not only form but also surface texture for functionality to the surfaces of parts that are created. Furthermore, the increasing demand for inexpensive and higher quality micro-components means that tools for replication processes must take advantage of advanced manufacturing techniques. Tools created by processes such as micro-investment casting, as in this case, may often suffer from excessive surface roughness, malformed edges and general deformation. This results in higher de-moulding forces and a reduction in fidelity of moulded parts to design intent. In this study, large-area electron beam irradiation (EB) is shown to be an effective technique for improving these metrics. For the first time, large population, high aspect ratio micro-features are subject to this process and the mechanisms of smoothing and key enhancement phenomena are demonstrated. The possibility of including EB irradiation in an integrated process chain for arriving at net shape is also discussed. Surfaces of protruding features are shown to have surface roughness reduced significantly from 126 to 22 nm Ra value, with bottom substrate also similarly improving from 150 to 27 nm Ra. Bottoms of recessed features are also observed to have much improved surface finishes. ‘Doming’ of tops of column features is also demonstrated, further enhancing form. These features would be far too fragile to be polished by any other mechanical method

Surface improvement of laser clad Ti-6Al-4V using plain waterjet and pulsed electron beam irradiation

© 2014 The Authors. Laser cladding is a flexible process which can be used to enhance the lifetime of components and repair them when worn. This is especially relevant where components are highly valued, and therefore costly to replace. To date, the surface finish achievable by laser cladding is poor and is characterised by ridges which correspond to the individual beads associated with the process. Increasingly laser cladding is being applied to conformal surfaces which are difficult to process by conventional grinding procedures which may also be ineffective because of discontinuous clad regions. There is therefore a need for a freeform approach which is capable of introducing specific surface finishes to complex components. Hence, in this study, a process chain incorporating plain water jet (PWJ) followed by a pulsed electron beam irradiation was used for the surface modification of laser clad surfaces of Ti-6Al-4V. Initially the surface was characterised by large recesses with peak-trough heights of 200 ± 18 μm and waviness of 49 μm. Upon processing employing water head pressure of 345 MPa impinging the clad surface at an angle 90°, 250 mm/min jet traverse speed, 3 mm stand-off distance and 0.25 mm milling overlap with 2 passes, it was possible to eliminate the peak-trough profile by milling to a depth of 480 ± 10 μm. A flat surface characterised by a surface waviness of 14.9 μm, 12.6 μm Ra and 44 μm straightness was achieved. PWJ milled surfaces were characterised by deep cavities, stepped fractured surfaces, cracks and sub-surface tunnels, however, with application of pulsed electron beam irradiation, most of these surface features were eliminated with a relatively smooth surface produced with 6.2 μm Ra finish

High precision self-alignment using liquid surface tension for additively manufactured micro components

This paper was accepted for publication in the journal Precision Engineering and the definitive published version is available at http://dx.doi.org/10.1016/j.precisioneng.2014.12.004Self-assembly of components using liquid surface tension is an attractive alternative to traditional robotic pick-and-place as it offers high assembly accuracy for coarse initial part placement. One of the key requirements of this method is the containment of the liquid within a designated binding site. This paper looks to expand the applications of self-assembly and investigates the use of topographical structures applied to 3D printed micro components for self-assembly using liquid surface tension. An analysis of the effect of edge geometry on liquid contact angle was conducted. A range of binding sites were produced with varying edge geometries, 45-135°, and for a variety of site shapes and sizes, 0.4 - 1 mm in diameter, and 0.5 x 0.5 – 1 x 1 mm square. Liquid water droplets were applied to the structures and contact angles measured. Significant increases in contact angle were observed, up to 158°, compared to 70° for droplets on planar surfaces, demonstrating the ability of these binding sites to successfully pin the triple contact line at the boundary. Three challenging self-assembly cases were examined, 1) linear initial component misplacement >0.5 mm, 2) angular misplacement of components, 3) 2 misplacement of droplet. Across all three assembly cases the lowest misalignments in final component position, as well as highest repeatability, were observed for structures with actual edge geometries <90° (excluding 45° nominal), where the mean magnitude of misalignment was found to be 31 μm with 14 μm standard deviation