Mechanical Micromachining Research Articles

Microneedle patch casting using a micromachined carbon master for enhanced drug delivery

For successful treatment of diseases, sufficient therapeutics must be provided to the body. Microneedle applications in therapeutic delivery and analytics sampling are restricted because of various issues, including smaller area for drug loading and analytics sampling. To achieve sufficient drug loading and analytics sampling and improve drug penetration while maintaining painless administration, patch-type microneedle arrays were designed and fabricated using polymer casting from a conical cavity mold. Microcavities were formed on a carbon plate via micromechanical machining. A porous polymer layer was coated on a microneedle patch (MNP). The pores of the porous polymer layer provided space and channels for drug delivery. A pH-sensitive polymer layer was employed to cap the porous polymer layer, which prevented drug leakage during storage and provided a stimulus drug release in response to body pH conditions. The drug can be delivered through holes connected to both sides of the patch. The drug release of the MNP was investigated in vitro and in vivo and showed conceptual proof that these MNs have the potential to enhance treatment protocols for various diseases with the flexibility of coating and therapeutic materials and offer significant scope for further variations and advancement.

Design of poly(vinyl pyrrolidone) and poly(ethylene glycol) microneedle arrays for delivering glycosaminoglycan, chondroitin sulfate, and hyaluronic acid

Osteoarthritis (OA) is a prevalent joint disorder characterized by cartilage and bone degradation. Medical therapies like glucosaminoglycan (GAG), chondroitin sulfate (CS), and hyaluronic acid (HA) aim to preserve joint function and reduce inflammation but may cause side effects when administered orally or via injection. Microneedle arrays (MNAs) offer a localized drug delivery method that reduces side effects. Thus, this study aims to demonstrate the feasibility of delivering GAG, CS, and HA using microneedles in vitro. An optimal needle geometry is crucial for the successful application of MNA. To address this, here we employ a multi-objective optimization framework using the non-dominated sorting genetic algorithm II (NSGA-II) to determine the ideal MNA design, focusing on preventing needle failure. Then, a three-step fabrication approach is followed to fabricate the MNAs. First, the master (male) molds are fabricated from poly(methyl methacrylate) using mechanical micromachining based on optimized needle geometry. Second, a micro-molding with Polydimethylsiloxane (PDMS) is used for the fabrication of production (female) molds. In the last step, the MNAs were fabricated by microcasting the hydrogels using the production molds. Light microscopy (LIMI) confirms the accuracy of the MNAs manufactured, and in vitro skin insertion tests demonstrate failure-free needle insertion. Subsequently, we confirmed the biocompatibility of MNAs by evaluating their impact on the L929 fibroblast cell line, human chondrocytes, and osteoblasts.

Machining technologies and structural models of microfluidic devices

In the past decades, microfluidic chips have been one of the hottest research topics in the “lab-on-a-chip” field. However, it is still a challenge for design the perfect microchannels with high functional integration, complex geometry, and high production efficiency. This review paper provides a comprehensive overview of microfluidic structural models and designs, manufacturing techniques, and bonding methods. The effect of three types of microfluidic channel structure models and their configuration parameters on the fluid behaviors of microfluidics was investigated. Surface-to-volume ratio of the flow channel is a critical parameter for determining the mixing and diffusion capabilities of the microfluidic devices (MDs). Thereafter, the main manufacturing techniques for microstructures were discussed, including etching, photolithography, soft lithography, molding, mechanical micro-machining, laser beam micromachining, printing, and 3D printing. We performed a statistical analysis to discuss the relative advantages and disadvantages of these manufacturing methods. In addition, the current bonding methods for MDs were also summarized, including thermal bonding, solution adhesive bonding, dry adhesive bonding, plasma bonding, and anodic bonding. a comparison of different bonding methods was presented to provide a reference to select a suitable bonding method for the assembly of microfluidic device. Finally, the tendencies and challenges of microchannel manufacturing were discussed, and the prospects were also provided.

Study on the Electrical and Geometrical Parameters of Micro Electrical Discharge Machining

Introduction: Micro-Electrical Discharge Machining (μEDM) is a technique for noncontact machining of conductive or semiconductor materials. It is mainly adapted to machining hard materials. Its principle is based on the creation of electrical discharges between the micro tool and the workpiece, which are immersed in a dielectric. Methods: Methods: It is a complementary process to mechanical or laser micromachining techniques or microelectronics (RIE, DRIE, LIGA). These methods can reach a resolution of 50 nm, but their main drawback is that they are mainly dedicated to silicon. The µEDM process depends on several physical, geometrical, and/or electrical parameters that need to be optimized in order to achieve a resolution lower than 5 µm in a reproducible way. The objective of this paper is to study the effect of the applied voltage VEE and the micro-tool diameter on the machining performances (removed volume, lateral gap, machining depth, and crater shape). Result: Result: The optimal parameters were used during drilling holes. An applied voltage of VEE = 50V was used as an optimal parameter. Conclusion: Concerning the diameter of the micro tool, we propose to use large diameter wires (Φ=250μm; Φ=125μm) during the roughing phase for machining complex structures and small diameter micro tools (Φ=80μm; Φ=40μm; Φ=20μm) during the finishing phase.

Modeling of laser-assisted micro-milling

The difficulties in the mechanical micro-machining process regarding the tool deflection, size effect and tool wear are much more pronounced than those in mechanical macro-machining. However, the role of mechanical micro-machining cannot be overestimated as an alternative against the non-traditional machining methods in manufacturing complex micro-parts with high dimensional and geometrical accuracies. Laser-Assisted Machining (LAM) can be used as a promising method by reducing the cutting forces and providing the possibility of increasing the Material Removal Rate (MRR) to enhance the productivity of mechanical micro-machining of difficult-to-cut material. Unlike common LAM, the parts are structured before machining using the ultra-short pulsed laser, followed by removing some parts of the material and consequently changing uncut chip thicknesses at the machining process. A model has been developed to understand how the structuring of the parts before micro-milling affects the uncut chip thicknesses at the micro-milling process. The model includes a variety of input parameters in terms of structure, tool, and process parameters to investigate this novel LAM comprehensively. Based on model results, the uncut chip thicknesses are reduced through the structuring of the part. The structure density was found as the most crucial parameter in uncut chip thickness reduction. The influence of structure density on cutting force reduction was also studied in the experiment. Workpieces made of titanium alloy (Ti6Al4V) were structured using a pico-second laser at different structure densities. The structured parts were machined at two feeds of 10 and 50 µm/tooth with a 35 m/min constant cutting speed. Structure density's role in reducing cutting force was also considerable. In addition, the contribution of different factors affecting cutting force reduction in this novel LAM process is discussed.

Tool-tip dynamics in micromachining with arbitrary tool geometries and the effect of spindle speed

Mechanical micromachining has become a leading approach to fabricating complex three-dimensional microscale features and miniature devices on a broad range of materials. To satisfy the accuracy and productivity demands of various micromachining applications, the tool-tip dynamics, i.e., the dynamic behavior of the tool-ultra high-speed spindle assembly as reflected at the cutting edges of a microtool, should be well-understood. However, existing techniques for predicting tool-tip dynamics pose strict limitations in frequency bandwidth and do not capture the effect of the spindle speed on tool-tip dynamics. In addition, those techniques cannot be applied broadly to predict tool tip dynamics for a myriad of microtool geometries. This paper presents a systematic approach to predicting the tool-tip dynamics accurately in micromachining when using ultra-high-speed (UHS) spindles and for arbitrary microtool geometries. The speed-dependent dynamics of the UHS spindle are obtained using an experimental approach. The dynamics of microtools are obtained analytically using the spectral Tchebychev technique, such that any microtool geometry can be modeled accurately and does not require new testing. The tool-tip dynamics are then predicted by combining (coupling) the spindle and microtool dynamics using a novel modal-Tchebychev domain coupling technique. This technique enabled accurate coupling/decoupling of substructure dynamics within a broad frequency bandwidth (up to 15 kHz) and at different spindle speeds (up to 120,000 rpm). Furthermore, an empirical model for the mode-splitting effect is derived to capture the effect of spindle speeds on tool-tip dynamics. The overall approach is demonstrated and experimentally validated on a UHS spindle with microtool blanks and micro endmills at operational speeds. We conclude that the presented methodology can be used to determine the tool-tip dynamics accurately.

Manufacturability and surface characterisation of polymeric microfluidic devices for biomedical applications

Generally, machining of polymeric microfluidic devices is a one-step manufacturing process. It is economical compared to lithography and can be used for batch production and rapid prototyping. However, surface properties are modified during machining due to the viscoelasticity property of polymers and the mechanical nature of fractures. In this present work, the manufacturing capability of the mechanical micromachining process of polymers has been explored. Surface characteristics like surface roughness, surface energy, and burr formation are investigated. Surface quality is chosen as a contributing factor for defining the manufacturing capability as it is one of the significant factors influencing the physics of fluid flow in microchannels. In the present work, several manufacturing methods, such as 3D printing, hot embossing, photolithography, and mechanical micromachining, were considered. The surface energy of various surfaces machined using the abovementioned methods is evaluated and compared. It has been observed that mechanical micromachining is the most suitable methods as they have less wettability with lower surface energy. Further investigations are carried out by machining microfluidic devices using polymethylmethacrylate (PMMA) and polycarbonate (PC) materials, as they are extensively used in biomedical applications. Surface roughness was measured on the PMMA and PC surfaces after milling. The surface roughness values and surface energies are used for evaluating the suitability of the machining process to fabricate microfluidic devices. Microfluidic devices with serpentine channels were machined on PMMA with a depth of 50 µm and width of 200 µm for evaluating inertial focusing in the channels. These devices were further evaluated for blood cell separation at different dilution rates. It is observed that PMMA is the preferable choice for fabricating microfluidic devices using mechanical micro-milling.

Burr removal from high-aspect-ratio micro-pillars using ultrasonic-assisted abrasive micro-deburring

The demand for high-aspect-ratio microstructures is ever increasing in the fields of microelectromechanical systems, biomedicine, aerospace, telecommunication, and heat transfer. Mechanical micromachining processes have a distinct advantage over lithography-based processes for machining complex three-dimensional microstructures on a variety of materials with high accuracy and surface finish. But the tool-based micromachining operations face inherent issues in the form of excessive burr formation, which needs to be addressed by post-machining burr removal operations. In this study, an ultrasonic-assisted abrasive micro-deburring process employing a probe sonotrode and abrasive particles has been investigated for deburring high-aspect-ratio micro-pillars machined on aluminium 6061 and copper. Deburring of micromilled pillars of aspect ratio 5:1 has been achieved while maintaining pillar integrity. The mechanism of deburring has been observed to be mainly by the impact of the abrasive particles with a minor role played by liquid cavitation. Burr reduction as high as 88.75% for Al 6061 and 90.1% for copper has been achieved in a short processing time of 10 s. This is a significantly faster process than other ultrasonic cavitation-based deburring processes described in literature (deburring time ranging from 60 min to a few hours). With proper control of the process parameters like stand-off distance and power, burr removal has been achieved while maintaining the integrity of the micro-pillars. Pure water cavitation has also been studied for comparison, which has resulted in a burr removal by 51.5% and 53.1% for Al 6061 and copper, respectively. Upon proper selection of the process parameters, this process can be a viable alternative to existing deburring methods in terms of minimal processing time and structure damage.

Experimental investigations on micro-EDM milling of niobium carbide-nickel based cermet using statistical and empirical techniques

Niobium Carbide (NbC) based cermet is a relatively less explored wear resistant material which has potential applications in moulds for ceramic injection moulding as well as cutting tool inserts. The NbC-Ni based cermets exhibit similar hardness as WC-Co cemented carbide but show better wear resistance and chemical stability against iron or steel. The demand for Ni bonded NbC cermets is forecasted to increase due to the rising cost of Co in conventional WC-Co cemented carbides. This poses additional challenges for existing mechanical micromachining processes such as frequent tool failure, higher tool wear and poor surface quality. Therefore, electrically conductive sintered NbC matrix cermets with a Ni binder have been developed which makes it suitable to machine them using electro discharge machining (EDM) and electrochemical machining (ECM) operations.This work presents experimental investigations using micro-EDM milling operation on NbC-Ni workpieces. A combination of empirical and statistical studies is employed to determine the suitable processing window for this material. The empirical study involves microstructural analysis and surface topography characterization using scanning electron microscopy (SEM) and confocal microscopy, respectively. The microstructural features such as micro-cracks, micro-cavities, micro-voids and micro-globules are identified and related to the major material removal mode of melting/vaporization. The statistical study involves parameter optimization and process monitoring. Material removal rate (MRR) of 0.091 mm3/min and tool wear rate (TWR) of 0.048 mm3/min can be achieved to its optimality and tracking the change in sparks frequency, shorts frequency and feed-rate enables to detect the suddenly accumulated debris. In this way, this holistic approach has been demonstrated to achieve an improvement in understanding and optimizing the machining process for novel NbC matrix cermet using micro-EDM technology.

Mechanistic modeling of cutting forces in high-speed microturning of titanium alloy with consideration of nose radius

Microturning is a micromechanical machining process used to produce microcylindrical or axially symmetrical parts. Microcylindrical parts are mainly used in microfluidic systems, intravenous micromotors, microsurgical applications, optical lens applications, and microinjection systems. The workpiece diameter is very small in microturning and therefore is greatly affected by the cutting forces. For this reason, it is important to predict the cutting forces when machining miniature parts. In this study, an analytical mechanistic model of microturning is used to predict the cutting forces considering the tool nose radius. In the semi-empirically developed mechanistic model, the tool radius was considered. A series of semi-orthogonal microturning cutting tests were carried out to determine the cutting and edge force coefficients. The mechanistic model was generalized depending on the cutting speed and depth of cut by performing multilinear regression analysis. In the study, the depth of cut (ap = 30–90 µm) and feed values (f = 0.5–20 µm/rev) were selected considering the nose radius and edge radius of the cutting tool. The experiments were carried out under high-cutting speeds (Vc = 150–500 m/min) and microcutting conditions. Ti6Al4V alloy was used as the workpiece material and the tests were carried out under dry cutting conditions. Validation tests for different cutting parameters were carried out to validate the accuracy of the developed mechanistic model. The results showed that the difference between the mechanistic model and the experimental data was a minimum of 3% and a maximum of 24%. The maximum difference between the experimental and the model usually occurs in forces in the tangential direction. It has been observed that the developed model gives accurate results even at a depth of cut smaller than the nose radius and at feed values smaller than the edge radius.

Hemi-ellipsoidal microlensed fiber based on polishing and polymer technology

This paper represents a development of a new advanced technology to fabricate and characterize micro-collimators with hemi-ellipsoidal microlenses at single-mode fibers outputs. The proposed method utilizes the controlled mechanical micromachining technique based on the variation of the speed of the fiber around its axis in both X and Y directions followed by the injection of a quantity of polydimethylsiloxane (PDMS) to form the hemi-ellipsoidal microlenses. The experimental results show that this technique allows to obtain a wide variety of ellipticity diameters ratios from 0.68 to 0.84. An elliptical ratio of radii of curvature Ry/Rx in a range of 0.51 at 0.86 is also obtained. In this investigation a mode field diameters MFD in an interval between 3.26 μm and 9.93 μm have been realized. The measurement results demonstrate that the proposed technology allows to fabricate hemi-ellipsoidal microlenses having an MFD ellipticity ratios of about 0.60 to 0.97 in near field promising for micro-collimator suitable to match an elliptical laser beam to the circular one of a fiber.

Multi-Characteristics Optimization in Micro-milling of Ti6Al4V Alloy

Nowadays, Ti6Al4V alloy is widely used to fabricate miniaturized prostheses, orthopedic and dental implants. Surface quality is an essential aspect of the implant parts owing to its effect on service life, which could be achieved through a proper selection of precise micromachining parameters. In this research, the mechanical micromachining of Ti6Al4V alloy has been performed, and optimized process parameters are considered for analysis. Surface roughness (Ra) of the machined microchannels, cutting force in the feed direction (Fy), cross-feed direction (Fx), and vibration on the top surface plate along the spindle axis (a z) have been taken as the response variables and were analyzed. The tests were accomplished at various rotational speed (N), feed per tooth (f z), axial depth of cut (a p), and cutter diameter (D) as machining parameters, each at three levels. The significant factors and their levels are identified using analysis of variance (ANOVA) and S/N ratios of response plot. According to the GRA test, N : 15000 rpm, fz : 0.2 µm/tooth, ap : 30 µm, and D : 200 µm are optimal parameters setting for better machinability of Ti6Al4V. ANOVA results indicated that feed rate is the most influential factor for lower cutting forces, surface roughness, and workpiece vibration. Fast Fourier transform (FFT) analysis depicts the stiffness of different micro end-mills significantly affect the machining performance like vibration amplitude during the micro-milling of Ti6Al4V alloy.

Preparation and electrochemical application of an AgNW/graphene/SU‐8 composite conductive photoresist

AbstractPhotoresists play an increasingly important role in industrial fields like micro‐electro mechanical systems, micromachining, and chip packaging. However, the traditional one‐component photoresist is insulated, and additional steps are required to make it conductive, which complicates the process and limits its application. In order to solve the problem, we establish a one‐step strategy to build conductive composite photoresist. Herein, graphene (GR) and silver nanowire (AgNW) are doped into SU‐8 photoresist to fabricate a photo‐patternable conductive composite. The composite photoresist is employed to make micro‐patterns on an ITO electrode using photolithography, followed by electrochemical reduction of copper nanoparticles (CuNPs) to produce a nonenzymatic sensing coating. Experimental results prove that the response current of the obtained sensor is linearly related to the concentration of hydrogen peroxide in the range of 1–25 mM. The sensitivity and detection limit of the sensor are 41.8 μA mM−1 cm−2 and 9 μM, respectively. Moreover, excellent sensing performance including anti‐interference, repeatability, and stability demonstrates the potential application of CuNPs/AgNW/GR/SU‐8 composite material in electrochemical sensing.

An experimental investigation on tool wear behaviour of uncoated and coated micro-tools in micro-milling of graphene-reinforced polymer nanocomposites

Nanomaterials such as graphene have been added to various matrices to enhance mechanical, thermal and electrical properties for various applications requiring intricate designs at the micro-scale. At this scale, mechanical micro-machining is utilised as post-processing to achieve high surface quality and dimensional accuracy while still maintaining high productivity. Therefore, in this study, the machinability of polymer nanocomposites in micro-scale (micro-machinability) is investigated. Graphene (0.3 wt%)-reinforced epoxy nanocomposites were fabricated using traditional solution mixing and moulding. The samples were then subjected to micro-milling at various cutting speeds using three different micro-tools, including uncoated, diamond and diamond-like carbon (DLC) tools. Mechanical and thermal properties of nanocomposite were also used to support the discussions. The result indicates that the DLC-coated tool shows better performance than the other tools for less tool wear, improved surface quality and less cutting forces.

Micro milling process modeling: a review

The trend towards miniature manufacturing in high technological fields like bioengineering, electronics and aerospace has increased dramatically over the last decade. Many methods of micro manufacturing have been researched and applied to manufacture small scale components. Among these manufacturing methods micro-mechanical machining methods have shown themselves to be attractive alternatives. Micro milling is one of the most frequently used micro-mechanical machining method with high potential for the precise manufacturing of complex parts. The aim of this work is to present the principal aspects related to micro milling technology, with emphasis on process modeling and quality of the finished product. A general view on process modeling starting from chip thickness models up to tool and workpiece machining induced distortion models is depicted. Specifically, different modeling techniques related to modeling of micro milling process are evaluated and important aspects that authors revealed during their research are presented. Finally, implications are discussed and suggestions for future research are presented.

Electrical stimulation of the mechanical micromachining process

Electrical stimulation of the mechanical micromachining process

Nozzle scaling effects for the thermohydraulic performance of microjet impingement cooling with distributed returns

Previous research studies showed that bare die liquid multi-jet impingement coolers with locally distributed outlets using silicon processing, mechanical micromachining, and additive manufacturing technology can achieve high cooling efficiency for high power electronic applications. The nozzle density is a crucial factor for thermal performance as well as for selecting the required fabrication technology. However, general design guidelines for the optimal nozzle density and cavity height are still missing in literature. In this paper, the impact of nozzle density on direct multi-jet impingement jet cooling is investigated using experiments and numerical modeling for an N×N nozzle array. The general scaling analysis with experimentally validated models is investigated based on three independent design parameters: nozzle density (N2/A), nozzle diameter (di) and cavity height (H). The objective is to find the optimal design parameters and to study the scaling trends. The experimental studies show that a very good thermal performance for the 8 × 8 jet array cooler with 1 × 1 mm2 cooling cells has be achieved as low as 0.13 cm2-K/W for a flow rate of 1000 ml/min. The best cooler design, expressed as the cooler with the highest COP value, can be achieved in the middle range of the nozzle density between 30 and 300nozzles per cm2 for the constant flow rate consideration. Comparisons in terms of constant cooler flow rate or constant pumping power will result in different optimal design parameter values.

Role of PVD coating on wear and surface integrity during environment-friendly micro-drilling of Ni-based superalloy

Owing to its capability to significantly mitigate the detrimental effects of flood cooling, minimum quantity lubrication (MQL) has emerged as a potential cooling technique for environment-friendly machining. Although coated cutting tools are widely used in the industry, the role of surface coating on micro tools during mechanical micro-machining is relatively unknown. The current research work seeks to explore the mechanism of physical vapour deposition (PVD)-based TiAlN coating during micro-drilling of a Ni-based superalloy (Incoloy 825). MQL was employed considering potential of tool coating to minimize the usage of cutting fluid. Results indicated increase in edge radius due to coating hindered the performance of coated micro-drill while machining with very low feed (1 μm/rev). This was attributed to ‘size effect’. However, elevation of feed, cutting speed and also machining duration (number of holes drilled) was found to be effective for TiAlN coated micro-drill. Thrust force, oversize error and deformed layer thickness along with hole periphery could be satisfactorily reduced under elevated machining condition. Similarly, improvement in resistance to wear of TiAlN coated micro-drill was evident after drilling 58 number of holes. Overall, a reduction in average flank wear up to 43% was observed for coated micro-drill after 168 number of holes when compared to uncoated micro-drill. Therefore, it is recommended to carefully work out a machining condition conducive for successfully utilizing coated micro-drill in machining of Ni-based superalloy.

Generation and categories of solitons in various mode-locked fiber lasers

Optical solitons generated from fiber lasers have been extensively investigated for their good stability, narrow pulse width and high peak power, which play an indispensable role in many fields such as mechanical micromachining, optical microscope, imaging technology, optical soliton communication and so on. In this review, we summarize the development of soliton fiber laser, and the current application of soliton pulses. There are many different kinds of mode-locking technologies to generate solitons, such as actively mode-locked fiber lasers, passively mode-locked fiber lasers and hybrid mode-locked fiber lasers. During the long-term research of solitons, various types of solitons have been gradually realized under different group velocity dispersion (GVD) conditions in passively mode-locked fiber lasers, such as conventional solitons (CSs) (GVD < 0), dispersion-managed solitons (DMSs) (GVD≈0), self-similar solitons (GVD ≥ 0), dissipative solitons (DSs) (GVD > 0). And in order to apply solitons to more fields, soliton amplification and compression technologies are widely used to improve the performance of solitons, such as chirped pulse amplification (CPA) technology, self-similar soliton amplification technology, large-mode area (LMA) fiber, etc. Finally, the development prospect of soliton in the future is prospected.

Prediction of cutting force in micro-end-milling by a combination of analytical and FEM method

Mechanical micro-machining, in general, and micro-end-milling, in particular, has become a very good technique for fabricating 3D micro-features in a variety of materials. To optimize and control the process, prediction of the cutting force accurately is very important. In this work, a force prediction model is developed by a combination of analytical method and finite element (FE) simulations. The model predicts the cutting force components for micro-end-milling process successfully which is compared with experimental force signal obtained by using Al2024-T3 and AISI 4340 as workpiece materials. The predicted and experimental cutting forces are in very good agreement for both the amplitude and trend of the cutting force. The percentage deviation of the predicted force from the experimental force values for both feed force ( Fx) and transverse force ( Fy) is around 15% (except one case) for Al2024-T3. For the AISI 4340 material, the percentage deviation for Fx is around 25% and for Fy is approximately 10%. The methodology followed here is general in nature and it can be applied to any other machining process as well.