Micro-manufacturing Techniques Research Articles

Micro ball-end milling—an emerging manufacturing technology for micro-feature patterns

The demand for complex micro-feature-based miniaturised products has grown over the last few decades due to their higher utility in many fields such as micro-fluidic devices, biomedical devices, orthopaedic implants, automotive industries, aerospace industries, etc. To fulfil the growing demand of these micro-feature-based products, several micromanufacturing techniques have been developed over the years. Micro-end milling is considered to be one of the favourable types among these techniques due to its higher flexibility and applicability over a wide range of materials. This technique is even more prominent when ball-end mill is used as a cutting tool due to its additional ability of finishing complicated surfaces and producing various 3D micro-textured surfaces. The present article provides an inclusive review of the tool fabrication, cutting mechanism, performance analysis, modelling and simulation and industrial applications of micro ball-end milling process. Furthermore, comments on future research scope have been emphasised in the direction of micro ball-end milling of different materials and their applications for producing new products with micro-features.

Modular and reconfigurable desktop microfactory for high precision manufacturing

Sub-millimeter scale devices are developing rapidly taking smaller, smarter, and more precise forms. This is achieved thanks to advancements in micro-manufacturing tools and techniques. For micro-production, a miniaturization of the machinery is a prominent idea that has numerous benefits in terms of material usage, precision, transportation, modularity, and reconfigurability. In this paper, a modular and reconfigurable desktop microfactory for high precision machining and assembly of sub-millimeter scale mechanical parts is presented and experimentally validated. The proposed system is built based on important functional and performance requirements, including miniaturization, high precision operation, modular and reconfigurable design, parallel processing capability, ease of installation, and transportation. The miniature factory consists of five mini processing units; two parallel kinematic robots for manipulation, the laser micro-machining system, the camera system for detection and inspection, and the rotational conveyor system for micro-part delivery. Different configurations of the system layout are proposed taking advantage of their modular design. Experiments are conducted to evaluate the system performance within a single process, like pick-place of a metallic ball with 3 mm diameter, laser machining of a half-millimeter size contour on the surface of the ball, and inspection and verification of the machined contour by means of microscopic camera. The results presented in this work demonstrate micrometer precision operation of the microfactory, showing high potential for manufacturing electro-mechanical devices with ease of readjustment of the microfactory layout.

Dynamic simulation of milling operations with small diameter milling cutters: effect of material heterogeneity on the cutting force model

Simulation of manufacturing processes (also called virtual manufacturing) is an important research topic in order to optimize the added value of the manufacturing chain. The mastering of these techniques allows companies to remain competitive on the market. Machining operations are very complex to simulate numerically due to the severe conditions undergone by the material (high strain, very high strain rates, high temperature,...). In addition, the rising need of micro-manufacturing techniques creates new challenges in numerical simulation. Indeed, some physical phenomena neglected for traditional machining simulation need to be taken into account for accurate simulation when the feedrate is fairly low (size effect, minimum chip thickness, material heterogeneity,...). New developments are thus needed to unlock the full benefits of these techniques. The aim of this paper is to enhance the classical mechanistic cutting force model for milling operations with small diameter tool by considering the effect of the heterogeneity of the material. The variability of the response during a test on fixed conditions (cutting tool, machined material and cutting parameters) is taken into account to develop a model whose parameters can evolve during a given operation. The statistical dispersion of cutting forces observed during experimental test is measured and modeled as a random perturbation of the force. The effects of this perturbation on the stability of milling operations are then demonstrated by means of numerical simulation.

The use of rapid prototyping techniques (RPT) to manufacture micro channels suitable for high operation pressures and μPIV

Purpose – This paper aims to present a new methodology to manufacture micro-channels suitable for high operating pressures and micro particle image velocimetry (μPIV) measurements using a rapid-prototyping high-resolution 3D printer. This methodology can fabricate channels down to 250 μm and withstand pressures of up to 5 ± 0.2 MPa. The manufacturing times are much shorter than in soft lithography processes. Design/methodology/approach – The novel manufacturing method developed takes advantage of the recently improved resolution in 3D printers to manufacture an rapid prototyping technique part that contains the hose connections and a micro-channel useful for microfluidics. A method to assemble one wall of the micro-channel using UV curable glue with a glass slide is presented – an operation required to prepare the channel for μPIV measurements. Once built, the micro-channel has been evaluated when working under pressure and the grease flow behavior in it has been measured using μPIV. Furthermore, the minimum achievable channels have been defined using a confocal microscopy study. Findings – This technique is much faster than previous micro-manufacturing techniques where different steps were needed to obtain the micro-machined parts. However, due to current 3D printers ' resolutions (around 50 μm) and according to the experimental results, channels smaller than 250-μm2 cross-section should not be used to characterize fluid flow behaviors, as inaccuracies in the channel boundaries can deeply affect the fluid flow behavior. Practical implications – The present methodology is developed due to the need to validate micro-channels using μPIV to lubricate critical components (bearings and gears) in wind turbines. Originality/value – This novel micro-manufacturing technique overcomes current techniques, as it requires less manufacturing steps and therefore it is faster and with less associated costs to manufacture micro-channels down to 250-μm2 cross-section that can withstand pressures higher than 5 MPa that can be used to characterize microfluidic flow behavior using μPIV.

Proposal of In-process Measurement for Micro-stereolithography Using Surface Plasmon Resonance

There is strong demand for the development of micro-manufacturing techniques to realize three-dimensional micro-structures. One of the important techniques is micro-stereolithography, which solidifies photopolymer resin using optical energy. Regarding the manufacturing accuracy of micro-stereolithography, structural errors should be improved; however, they are influenced by optical conditions, the material conditions of resins, and so on. Because dimensions and shapes can be evaluated only after completing all of the manufacturing processes, in-process measurement is useful for improving manufacturing accuracy. The solidified photopolymer resin changes its refractive index as little as 0.04, compared with the case before solidification. In this study, the surface plasmon resonance (SPR) is proposed to measure minute changes of the refractive index. The condition required to excite SPR is highly sensitive to both the refractive index of environmental materials and the thickness of (and materials used in) the plasmonic substrate. In this paper, the novel method and fundamental properties are discussed.

Hybrid Fabrication of Stainless Steel Channels for Microfluidic Application

This research develops a hybrid micromanufacturing technique by combining micromilling and electrochemical micropolishing to fabricate extremely smooth surface finish, high aspect ratio, and complex microchannel patterns. Milling with coated and uncoated ball-end micromills in minimum quantity lubrication is used to remove most materials to define a channel pattern. The milled channels are then electrochemically polished to required finish. A theoretical model accurately predicts surface finish in meso-scale milling, but not in micro-scale milling due to size effect. Electrochemical polishing using an acid-based electrolyte is applied to repeatedly produce stainless steel microchannels with average surface finish of 100 nm when measuring across grain boundaries and 10 nm within a single grain.

A microscale pulsatile flow device for dynamic cross-slot rheometry

The design of micropumps received full attention since micromanufacturing and microfluidics techniques have become part of the engineering toolbox. The focus of most studies has been on the efficiency of these pumps: maximal net (mean) flow at minimal input power.We introduce a pulsatile micropump system, that is designed to dynamically perfuse a cross-slot micro-rheometer. To characterize complex materials dynamically, unsteady (oscillating and pulsating) flows with a frequency range of 0.1–20Hz at amplitudes of 10–100nl/s are required. Hence, in our study the priority concerning micropumps shifts from efficiency to the ability to produce well-defined flow pulses.For this purpose, an oscillatory micropump, based on a deflecting diaphragm, is designed and tested. By periodically deflecting a steel plate into a rigid fluidic chamber using a voice coil, an oscillatory flow is produced. Plate deflection is governed by bending, such that the stroke volume is proportional to the current through the voice coil. The oscillatory flow is superimposed to the steady flow of a syringe pump. The pump system obtained is characterized by micro particle image velocimetry (μ-PIV) measurements using fluorescence microscopy.The results show that the superposition of the mean flow of the syringe pump and an oscillatory flow of the diaphragm pump, is valid. A linear scaling of flow amplitude with frequency and driving voltage is found for frequencies up to 4Hz, after which excessive damping takes place. The causes for this behavior are identified and explain the results well. With this information, amplitude scaling for sinusoidal flow waves of different frequencies can be performed. In conclusion, with the present system, pulsatile flow with a well-defined waveform and a dynamic range up to 16Hz, can be created in an open-loop driven fashion.

Surface Finish of Ball-End Milled Microchannels

This study develops a hybrid micromanufacturing technique to fabricate extremely smooth surface finish, high aspect ratio, and complex microchannel patterns. Milling with coat and uncoated ball-end micromills in minimum quantity lubrication (MQL) is used to remove most materials to define a channel pattern. The milled channels are then electrochemically polished to required finish. Assessment of the fabricated microchannels is performed with optical microscopy, scanning electron microscopy, atomic force microscopy, and white-light interferometry. Theoretical models were derived for surface finish of ball-end milling. The predicted surface finish data agree with experimental data in mesoscale milling, but the calculated data are lower than microscale milling data due to size effects. Built-up-edges, being detrimental in micromilling, can be reduced with optimal coating and milling in MQL. When micromilling and then electrochemical polishing of 304, 316L stainless steels and NiTi alloy, this hybrid technique can repeatedly produce microchannels with average surface finish in the range of 100–300 nm.

An impact excitation system for repeatable, high-bandwidth modal testing of miniature structures

Recent advances in various micro-manufacturing techniques have enabled utilization of miniature devices in numerous applications. However, testing, modeling, and predicting performance of these structures still poses various challenges. Experimental modal analysis techniques have been widely used to obtain the dynamic characteristics of structures; however, having very high natural frequencies, small vibration amplitudes, and high compliance, miniature structures require additional care during modal testing. Although recent developments in sensor technology enabled to obtain accurate high frequency vibration measurements during modal testing of miniature structures, excitation of miniature structures without any damage and within high frequency range in a reproducible manner is still being investigated. This paper presents design, development, and performance evaluation of a custom-made impact excitation system that enables repeatable, high bandwidth, single-hit impacts, and controllable impact force for modal testing of miniature structures. The system is equipped with a miniature force sensor attached to a custom designed flexure and an automated release mechanism driven by an electromagnet. The excitation bandwidth and the impact force exerted to the test structure can be controlled through control parameters: initial displacement given to the flexure and gap between the impact tip and the test surface.

Hydrophobic property of hierarchical polymer surfaces fabricated by precision tooling machine

Abstract Poly(methylmethacrylate) surfaces were patterned with micropillars and micro-micro hierarchical structures. Patterning was achieved by applying direct fabrication on polymer surfaces. The micro-manufacturing method has many advantages of precise control of dimensions, low cost, and short process time compared to other micro-manufacturing techniques of polymers. Fabricated structures were controlled accurately to <10% of the error range. Patterned micro-micro hierarchical polymer structures indicated a contact angle >130° without additional coatings. Furthermore, fabricated structures show good durability in terms of contamination and mechanical robustness for 2 months.

Design and fabrication of a three-dimensional microfluidic device for blood separation using micro-injection moulding

Micro-manufacturing is a fast developing area due to the increasing demand for components and systems of high precision and small dimensions. A number of challenges are yet to be overcome before the full potential of such techniques is realised. Examples of such challenges include limitations in component geometry, material selection and suitability for mass production. Some micro-manufacturing techniques are still at early development stages, while other techniques are at higher stage of manufacturing readiness level but require adaptation in part design or manufacturing procedure to overcome such limitations. This article presents a case study, where the design of a micro-scale, biomedical device is adapted for functionality and manufacturability by a high-volume micro-fabrication technique. Investigations are described towards a disposable three-dimensional, polymer-based device for the separation of blood cells and plasma. The importance of attempting a three-dimensional device design and fabrication route was to take advantage of the high-throughput per unit volume that such systems can, in principle, allow. The importance of a micro-moulding fabrication route was to allow such blood-containing devices to be cheaply manufactured for disposability. Initial device tests showed separation efficiency up to approximately 80% with diluted blood samples. The produced prototype indicated that the process flow was suitable for high-volume fabrication of three-dimensional microfluidics.

Optimal conditions of SU-8 mask for micro-abrasive jet machining of 3-D freeform brittle materials

Micro-abrasive jet machining (AJM), also called micro-blasting, is a mainstream machining process that uses abrasive particles for difficult-to-cut workpieces such as glass, carbides, and ceramics. During the micro-blasting process, non-machined areas are covered by a protective mask. Today, either mask fabrication practice or micro-blasting process is well suited and optimized for producing micro-features on planar workpieces. However, the demand for micro-features on three-dimensional (3-D) freeform substrates in micro electro-mechanical systems (MEMS) and lab-on-a-chip devices requires more refined non-planar micro-manufacturing techniques. We focused on devising an appropriate photoresist mask required by micro-AJM processes on the surface of a 3-D freeform workpiece. Fundamental erosion mechanisms based on SU-8 mask properties (hardness, surface roughness, and thickness) were investigated. The optimal conditions were found at an ultraviolet (UV) energy of 12.0752 μJ/μm, focus ratio of 4.8341, and hard baking time of 8.4974 min. Under these settings, the mask hardness and surface roughness were 25.04 HV and 1.14 μm, respectively. The reliability of the fabricated mask was verified through a micro-AJM process. With existing plant conditions, the engraved microfeature dimensions on the surface of a 3-D freeform workpiece were 535.3 μm (width) and 11.6 μm (depth).

Flying like a fly

When biologists unravelled the principles of insect flight, they inspired a generation of engineers to build on their aerodynamic feats. Thanks to a revolution in micro-manufacturing techniques, the first robotic fly now flies.

Effects of geometric parameters for superhydrophobicity of polymer surfaces fabricated by precision tooling machines

Effects of geometric parameters are regarded as indicating factors that affect super hydrophobic surfaces. Micro-sized pillar-type structures were prepared using a precision tooling machine that was able to fabricate various structures precisely on polymer surfaces. The tooling machine has many advantages of low cost, short processing time, and precise control of geometric parameters compared to other micro-manufacturing techniques of polymers such as injection molding, replica molding, and hot embossing. Hydrophobicity of the polymer affected by surface conditions and geometric properties is considered. Furthermore, to examine the effects of low surface energy, we coated the CF2-based fluoropolymer onto various pillar structures. The some of the coated surfaces show the superhydrophobicity with a water contact angle greater than 150°. The hydrophobic and oleophobic properties are regarded as verifying the transition of the energy state and the tendency of wetting behavior depending on the geometric parameters and low surface energy property.

Field-effect transistors with layer-by-layer self-assembled nanoparticle thin films as channel and gate dielectric

This letter reports the fabrication of inorganic field-effect transistors (FET) combing “bottom-up” layer-by-layer (LbL) nanoself-assembly and “top-down” micromanufacturing techniques. The self-assembled multilayer of In2O3 and SiO2 nanoparticles, patterned by photolithography and lift-off methods, serve as channels and insulating layers, respectively. This FET works at an accumulation mode, with a threshold voltage of −1.25V, a carrier mobility of 4.24×10−3cm2∕Vs, and an on/off current ratio of 102. Due to the simple, low-cost, and low-temperature features of the LbL nanoself-assembly technique that greatly eliminates expensive and complex facilities, this approach is particularly suitable for the very inexpensive FET fabrication.

A manufacturing technique for 3D polymer micro-venturi tube

Micro-shaping techniques have been realized for various applications. In this paper, a polymer micro-manufacturing technique is proposed to fabricate 3D micro-venturi tubes. Polymethylmethacrylate (PMMA) was dipped in methyl for 2 h to fully generate the physical–chemical change. The PMMA swelling appeared through the mass transfer effect. The swelling effect techniques used on various adhesives for attaching polycarbonate to PMMA are discussed. This polymer swelling process was implemented to form the 3D micro-venturi tube into a curved nozzle with the throat size successfully reduced to 100 μm. This paper presents an economical fabrication process for micro-venturi tubes for future analysis in micro-technologies.

Various replication techniques for manufacturing three-dimensional metal microstructures

In microsystem technology a large range of different 6materials will be available only after the necessary micromanufacturing techniques have been developed or adapted. Existing manufacturing techniques are structuring or shaping techniques producing three-dimensional microstructures out of silicon (silicon etching, silicon surface micromechanics), mostly unfilled plastics (lithographic techniques, injection molding, hot embossing, reaction molding) or a few pure metals or binary alloys (electroforming). The choice of materials for microcomponents is determined by the function and conditions of use of microsystems. Especially the range of metals is still restricted considerably because the only processes available are electroforming and thin-layer techniques. It is for these reasons that we are developing various processes for manufacturing three-dimensional metal microstructures. In addition to direct electroforming of injection molding lost plastic micromolds, these are a new microcasting process and Micro Metal Injection Molding (Micro MIM). Microstructures have already been molded from mold inserts made by micromechanical cutting or by the LIGA technique. The results achieved, and future prospects, are outlined below.