The lifetime and stability of reference electrodes is critical for the long-term reliability of electrochemical sensing technologies. In this work, we demonstrate that the operational lifespan of a ...reference electrode (RE) is heavily influenced by the length of the filling solution. A mathematical solution, based on 1D, Fickian diffusion between the RE filling solution and an infinite volume test solution, predicts that doubling the length of the filling solution channel will quadruple the lifespan of the RE. In comparison, halving the diffusion coefficient of the filling solution (e.g., by changing the material) only increases the RE lifetime by 20–25%. The quadratic dependence of the filling solution length on lifetime was experimentally observed by monitoring the open-circuit potentials of RE's composed of an Ag/AgCl couple and agar-gel filling solutions (agar + 1.0 M KCl) inside glass capillaries of different lengths. The 1 cm RE remained stable for 6 h, whereas a 10 cm RE was stable for approximately 18 days (430 h). Lastly, we demonstrate that 3D printed and CNC (computer numerical control) machined RE housings with long and narrow filling solution channels can be used to produce small REs with enhanced lifetimes. Reference electrodes prepared this way were low-cost, small, and more stable than a typical commercial reference electrode design. A 4 cm long, 3D printed RE housing with 3 mL of agar gel filling solution provided over 6 months of potential stability, outlasting a conventional RE design with double the amount of reference solution volume.
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This paper presents the first comprehensive investigation on the effects of cryogenic cooling using liquid nitrogen on surface integrity of Ti–6Al–4V titanium alloy workpiece in end milling ...operations. Titanium is classified as a notoriously difficult-to-machine material, where its machining is characterised by poor surface integrity and short tool life. Increasing productivity, whilst meeting surface integrity requirements for aerospace and medical titanium-based components has always been a challenge in machining operations. Cryogenic machining using super cold liquid nitrogen at −197°C is a method to facilitate heat dissipation from the cutting zone and reduce the chemical affinity of workpiece and cutting tool materials and therefore improving machinability. Since milling is one of the major machining operations for aerospace components, this study is concentrated on cryogenic milling. The effects of cryogenic cooling on surface integrity are compared to conventional dry and flood cooling in end milling Ti–6Al–4V titanium alloy. A series of machining experiments were conducted at various combinations of cutting parameters. Surface roughness and microscopic surface integrity were investigated and subsurface microhardness was measured for each sample. The analysis indicated that cryogenic cooling has resulted in up to 39% and 31% lower surface roughness when compared to dry and flood cooling methods, respectively. Furthermore, microscopic surface defects were significantly reduced as a result of cryogenic. The investigations indicated that cryogenic cooling considerably improves surface integrity in end milling of Ti–6Al–4V.
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Computer numerical control (CNC) carving is a widely used method of industrial subtractive manufacturing of wood, plastics, and metal products. However, there have been no previous ...reports of applying this approach to manufacture medicines. In this work, the novel method of tablet production using CNC carving is introduced for the first time. This report provides a proof-of-concept for applying subtractive manufacturing as an alternative to formative (powder compression) and additive (3D printing) manufacturing for the on-demand production of solid dosage forms. This exemplar manufacturing approach was employed to produce patient-specific hydrocortisone (HC) tablets for the treatment of children with congenital adrenal hyperplasia. A specially made drug-polymer cast based on polyethene glycol (PEG 6,000) and hydroxypropyl cellulose was produced using thermal casting. The cast was used as a workpiece and digitally carved using a small-scale 3-dimensional (3D) CNC carving. To establish the ability of this new approach to provide an accurate dose of HC, four different sizes of CNC carved tablet were manufactured to achieve HC doses of 2.5, 5, 7.5 and 10 mg with a relative standard deviation of the tablet weight in the range of 3.69–4.79%. In addition, batches of 2.5 and 5 mg HC tablets met the British Pharmacopeia standards for weight uniformity. Thermal analysis and X-ray powder diffraction indicated that the model drug was in amorphous form. In addition, HPLC analysis indicated a level of purity of 96.5 ± 1.1% of HC. In addition, the process yielded mechanically strong cylindrical tablets with tensile strength ranging from 0.49 to 1.6 MPa and friability values of <1%, whilst maintaining an aesthetic look. In vitro, HC release from the CNC-carved tablets was slower with larger tablet sizes and higher binder contents. This is the first report on applying CNC carving in the pharmaceutical context of producing solid dosage forms. The work showed the potential of this technology as an alternative method for the on-demand manufacturing of patient-specific dosage forms.
•Face gears are cut in popular CNC milling machine tools.•The envelope of developable ruled surface is obtained explicitly.•An advanced geometry study is proposed to the tool path planning.•Tool ...paths are generated with the biggest allowable cutters.
Face gears can take advantages in different mechanisms, but the current manufacturing technology is inferior to satisfy the growing industry. CNC (computer numerical control) milling is a popular manufacturing way that could promote the applications of face gears. Generally, CNC milling can be implemented to a product with given CAD (computer-aided design) model by planning the tool paths in commercial CNC machining software. Unfortunately, there is no commercial software available to directly generate their CAD models with given design parameters. Hence, we propose a novel geometric analysis to bridge the gap between the CAD and CNC milling of face gears. First, a novel envelope approach, which calculates the envelope surface of the developable ruled surface as closed-form (explicit) result, is introduced to study the tooth surface geometry of face gears. It obtains the representation of face gear tooth surface as closed-form rather implicit one. Second, the 3D modeling and curvature analysis are implemented as the preparation of tool path planning. Third, a comprehensive algorithm is proposed to generate tool paths by choosing biggest allowable cutters without interference. The algorithm is verified by both simulation and experiment. The results show the validity of the proposed method.
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Novel cost effective, versatile, reconfigurable, reusable and easy to assemble glass capillary microfluidic devices were developed and used to generate micro/nano-materials with ...controlled size and morphology. The devices are composed of coaxial assemblies of glass capillaries held between two interchangeable plastic blocks fabricated from chemically inert polyoxymethylene copolymer using computer numerical control (CNC) machining. Three different blocks were combined and locked together using Lego® inspired stud-and-hole coupling system to achieve different flow configurations. The device allows a truly axisymmetric round capillary inside a round capillary geometry and self-alignment of capillaries. The synthesis of polyvinylpyrrolidone capped gold nanoparticles and liposomes of controlled size was demonstrated in the co-flow device by mixing the contents of two parallel laminar streams. The flow focusing device was used to generate piroxicam monohydrate crystals of controlled size (10–29 μm) by antisolvent crystallisation. Silver nanoparticles with tailored size (40–90 nm) were prepared in the three-phase device by merging silver nitrate and tannic acid/citrate streams inside droplets. The same device was used to prepare fluorescently labelled double emulsion droplets with controlled number of inner droplets. The droplet morphology was modified and tuned during operation by adjusting the distance between the inner capillaries. Water-in-oil emulsions consisted of Eudragit S100 solution at pH > 7 dispersed in Miglyol® 840 were prepared and gellified in situ over 6 h without fouling. The setup time of the novel devices was reduced from ∼30 min in manually made capillary devices to just several minutes.
The surface roughness is a crucial index that is commonly used in the machining process to evaluate the final product quality. This paper investigates the effect of different machining parameters on ...the surface roughness of the high-strength carbon fiber composite plate, manufactured by utilizing the vacuum infusion process, under dry end milling conditions. Besides, a hybrid intelligence approach consisting of artificial neural network (ANN) whose parameters are tuned by genetic algorithm (GA) is introduced for accurate estimation of surface roughness. To construct a database for the ANN, the experimental milling tests have been carried out according to the Taguchi optimization method with the design of a mixed orthogonal array L32 (21 × 42). The influence of the machining parameters such as cutting tools, feed rate, and spindle speed on surface roughness have been examined by using analysis of variance (ANOVA). The analyses reveal that the cutting tool and the feed rate are the most effective factors in the surface roughness of the composite material. It is also determined that the experiment with “A1B2C1” combination (TiAlN coated cutting tool, 5000 rpm spindle speed, and 250 mm/rev feed rate) gives the optimal result. The proposed hybrid ANN-GA algorithm provides a good prediction correlation ratio (R = 0.96177) indicating that the estimated and the measured surface roughness values are remarkably close to each other. The mean square error (MSE) specifying the accuracy and adequacy of the network model is obtained as 0.074 during the 33th iteration of the GA.
•A comprehensive review (based on 168 papers) of free-form milling is presented.•The advances over a decade (2009–2020) are discussed in five sections.•Experimental, analytical, tool-path and ...inspection based studies are covered.•The literature is presented and compared concisely in tables and flowcharts.•The prominent findings/observations and scope for future studies are highlighted.
The advent of CNC machines resulted in the reduction of machining complexity through efficient programming and increased productivity. The free-form surface milling (FFSM) process comprises several applications in the aerospace and automobile industries that mainly concerned with accuracy of the finished part. Numerous studies were attempted over the years to understand the mechanism involved in FFSM, which reported and facilitated the advances in the overall process. The complex surface milling still poses challenges with continuous change in the tool-workpiece contact that leads to vary an effective tool radius, along with the active cutting speed and cutting forces during machining. Accordingly, the material removal mechanism changes from shearing to plowing (plastic deformation), and vice-versa, which determines the tool wear and overall part quality. This paper presents a review of the research work (a total of 168 papers) published over the past decade considering five main domains in the FFSM process, which leads to enhance accuracy, machinability, productivity, and machining economy. The experimental investigations highlighted the input-output correlations, parametric influence on various machining responses, while analytical models underline the principles and mechanics involved in the process and useful in predicting/estimating the responses. The tool-path generation leads to an efficient tool-path that minimizes the machining time and cost, enhancing the part surface quality, and the surface reconstruction includes an accurate representation of the machined surface in the FFSM. Finally, the part inspection process is implemented for effectively measuring and comparing the accuracy of the machined components is reported. The inclusive knowledge of all five elements of the FFSM process would facilitate a clear understanding of the overall process and useful in developing research objectives and future perspectives.
In this study, the effects of different cooling/lubrication strategies and cutting parameters during milling hybrid composites based on Al-4Gr, a new material, were investigated. The main matrix was ...formed by adding Gr at a constant rate (4%) to Al. Hybrid composites were fabricated by vacuum sintering by adding WC and Al2O3 in different ratios (2-4-8 wt.%). Environmentally friendly cryogenic liquid nitrogen (cryo-LN2) and minimum quantity lubrication (MQL) fluids were used as cooling and lubricating environment in the milling process. Three different cutting speeds (150, 225, 300 m/min), three different feed rates (0.150, 0.225, 0.300 mm/rev) and a single depth of cut (0.5 mm) were selected for milling. Surface roughness, flank wear, cutting temperature, and chip morphology were evaluated for different cooling/lubrication environments. As a result, the cryo-LN2 environment reduced the surface roughness, flank wear, and cutting temperature by 34.9%, 18.5%, and 69.5%, respectively, compared to the dry medium. Adhesion wear was reduced in MQL and cryo-LN2 environments. In addition, it was determined by the analysis of variance that the most effective factor among the response parameters was cooling/lubrication. The cooling/lubrication environment has an effect of 74%, 58%, and 94% on surface roughness, flank wear, and cutting temperature, respectively.
•Novel Al-4Gr hybrid composites were milled in dry, MQL, and cryo-LN2 environments.•Surface roughness, flank wear and cutting temperature results were evaluated in terms of cutting environments and parameters.•According to the Al-4Gr hybrid composite type, the most effective processing environment is cryo-LN2.•Experimental results analyzed with the help of ANOVA, and the most effective parameters were determined.
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