Heather Almond

Technical comparison of micro-electrodischarge machining, microdrilling, and copper vapor laser machining for the fabrication of ink jet nozzles

Ink jet nozzles require accurate definition and smooth surface finish to promote laminar flow of ink and prevent turbulence. We have fabricated ink jet nozzles by three different fabrication ttechniques to evaluate the characteristics of each technique and assess the differences between them. Scanning electron micrographs illustrate the differences between the three types of nozzle produced and these have been quantified where possible. The machining times for these fabrication processes are also compared.

Modelling and prototyping the conceptual design of 3D CMM micro-probe

This paper details the prototyping of a novel three axial micro probe based on utilisation of piezoelectric sensors and actuators for true three dimensional metrology and measurements at micro- and nanometre scale. Computational mechanics is used first to model and simulate the performance of the conceptual design of the micro-probe. Piezoelectric analysis is conducted to understand performance of three different materials - silicon, glassy carbon, and nickel - and the effect of load parameters (amplitude, frequency, phase angle) on the magnitude of vibrations. Simulations are also used to compare several design options for layout of the lead zirconium titanate (PZT) sensors and to identify the most feasible from fabrication point of view design. The material options for the realisation of the device have been also tested. Direct laser machining was selected as the primary means of production. It is found that a Yb MOPA based fiber laser was capable of providing the necessary precision on glassy carbon (GC), although machining trials on Si and Ni were less successful due to residual thermal effects.To provide the active and sensing elements on the flexures of the probe, PZT thick films are developed and deposited at low temperatures (Lt720 degC) allowing a high quality functional ceramic to be directly integrated with selected materials. Characterisation of the materials has shown that the film has a homogenous and small pore microstructure.

Typical Metrology of Micro-Hole Arrays Made in Stainless Steel Foils by Two-Stage Micro-EDM

Abstract Two-stage micro-EDM utilises one machine to fabricate electrodes and a second machine to manufacture holes. The diameter and taper of a hole are dependent on the accuracy of the electrode fabrication which has now been quantified. The accuracy of hole positioning has also been measured using commercial equipment in a novel application. The surface roughness and uniformity of the internal surfaces of the holes (typically 50 μm in diameter) have been examined using a novel method not involving cross-sectioning. Random surface microcracks appear to be metallurgy-dependent, not process related.

Positional accuracy study of a micro-EDM machine

Micro-electrodischarge machining is used to machine small features such as holes, cavities and slots with high aspect ratios in electrically-conductive materials for various applications including medical implants, printing devices, dies and spray nozzles. In this study, the positional accuracy of a micro-EDM machine was assessed while simulating the machining of an array of holes. The measurement involved the use of a diffraction grid plate and non-contact scanning head. This enabled various conclusions to be drawn as to the relative deviations experienced when machining small features such as (phi) 50 micrometers holes.

Testing of a LIGA-microspectrometer for monitoring dissolved nickel concentration when etching nickel and its alloys in aqueous ferric chloride solutions

In the photochemical machining of micro-parts from nickel-containing alloys, a solution of ferric chloride is used as the etchant. As the alloy is dissolved into solution, the concentration of dissolved nickel will increase to a point where the surface finish of the etched parts will be affected adversely and become rougher. To control part quality and reduce the number of defective parts, it is therefore necessary to monitor the build-up of nickel ions on-line. A miniature, commercial microspectrometer has been evaluated for its suitability to monitor the nickel concentration. The microspectrometer has been shown to be cost-effective and is capable of measuring the concentration of nickel ions to /spl plusmn/1 g/l.

Airborne sand and dust soiling of solar collecting mirrors

The reflectance of solar collecting mirrors can be significantly reduced by sand and dust soiling, particularly in arid environments. Larger airborne sand and dust particles can also cause damage by erosion, again reducing reflectance. This work describes investigations of the airborne particle size, shape, and composition in three arid locations that are considered suitable for CSP plants, namely in Iran, Libya, and Algeria. Sand and dust has been collected at heights between 0.5 to 2.0m by a variety of techniques, but are shown not to be representative of the particle size found either in ground dust and sand, or on the solar collecting mirror facets themselves. The possible reasons for this are proposed, most notably that larger particles may rebound from the mirror surface. The implications for mirror cleaning and collector facet erosion are discussed.The reflectance of solar collecting mirrors can be significantly reduced by sand and dust soiling, particularly in arid environments. Larger airborne sand and dust particles can also cause damage by erosion, again reducing reflectance. This work describes investigations of the airborne particle size, shape, and composition in three arid locations that are considered suitable for CSP plants, namely in Iran, Libya, and Algeria. Sand and dust has been collected at heights between 0.5 to 2.0m by a variety of techniques, but are shown not to be representative of the particle size found either in ground dust and sand, or on the solar collecting mirror facets themselves. The possible reasons for this are proposed, most notably that larger particles may rebound from the mirror surface. The implications for mirror cleaning and collector facet erosion are discussed.

Low-profile and wearable energy harvester based on plucked piezoelectric cantilevers

The Pizzicato Energy Harvester (EH) introduced the technique of frequency up-conversion to piezoelectric EHs wearable on the lateral side of the knee-joint. The operation principle is to pluck the piezoelectric bimorphs with plectra so that they produce electrical energy during the ensuing mechanical vibrations. The device presented in this work is, in some ways, an evolution of the earlier Pizzicato: it is a significantly more compact and lighter device; the central hub holds 16 piezoelectric bimorphs shaped as trapezoids, which permits a sleek design and potentially increased energy output for the same bimorph area. Plectra were formed by Photochemical Machining of a 100-μm-thick steel sheet. To avoid the risk of short-circuiting, the plectra were electrically passivated by sputtering a 100 nm layer of ZrO2. Bench tests with the steel plectra showed a very large energy generation. Polyimide plectra were also manufactured with a cutting plotter from a 125μm-thick film. Besides bench tests, a volunteer wore the device while walking on flat ground or climbing stairs, with a measured energy output of approximately 0.8 mJ per step. Whereas most of the tests were performed by the traditional method of discharging the rectified output from the EH onto a resistive load, tests were performed also with a circuit offering a stabilised 3.3 V supply. The circuit produced a stable 0.1 mA supply during running gait with kapton plectra.

The Causes and Prevention of Smut on Etched AISI 300 Stainless Steels

Abstract During the fabrication of stainless steel parts by photochemical machining (PCM), a seemingly random occurrence of a partially-adherent, brown/black deposit, known as smut, can occur. This quality problem has plagued the PCM industry for over 30 years. In the past, the problem has been attributed to “poor etch-quality” stainless steel. However, an extensive investigation by the authors, comprising some 7 person-years of effort, has established that while the metallurgy of the stainless steel has some influence on the formation of smut, by far the most important factor is the condition of the ferric chloride etchant used for etching the parts. The influences of etchant concentration, free hydrochloric acid content, temperature, atmosphere and hydrodynamic flow have now been assessed quantitatively for the first time. The investigation has led to the development of a theory outlining the causes of smut formation, thus providing solutions for its prevention.

Influence of materials selection and quality on ink jet nozzles fabricated by micro-electrodischarge machining

Ink jet nozzles require accurate definition and smooth surface finish to promote laminar flow of ink and prevent turbulence. Recent investigations into micro-electro discharge machining of nozzles in thin stainless steel have shown that surface finish is dependent not only on machining parameters but also on material selection and quality. Defects within the material such as cracks, aligned to the direction of rolling, are a source of random defects within nozzles after machining. They can cause severe problems by acting as sites for ink-flow perturbation and corrosion and thereby cause defective printing. Evaluation of material quality at the microscopic level prior to machining is therefore recommended to avoid a waster of machining-time on sub-standard material and the resultant low yield of acceptable nozzles. Image analysis of a range of materials has shown that some materials examined contained relatively few defects.

Structure zone diagram and particle incorporation of nickel brush plated composite coatings

This work studies the deposition of aluminium-incorporated nickel coatings by brush electroplating, focusing on the electroplating setup and processing parameters. The setup was optimised in order to increase the volume of particle incorporation. The optimised design focused on increasing the plating solution flow to avoid sedimentation, and as a result the particle transport experienced a three-fold increase when compared with the traditional setup. The influence of bath load, current density and the brush material used was investigated. Both current density and brush material have a significant impact on the morphology and composition of the coatings. Higher current densities and non-abrasive brushes produce rough, particle-rich samples. Different combinations of these two parameters influence the surface characteristics differently, as illustrated in a Structure Zone Diagram. Finally, surfaces featuring crevices and peaks incorporate between 3.5 and 20 times more particles than smoother coatings. The presence of such features has been quantified using average surface roughness Ra and Abbott-Firestone curves. The combination of optimised setup and rough surface increased the particle content of the composite to 28 at.%.