Flatness optimization of micro-injection moulded parts: The case of a PMMA microfluidic component

Micro-injection moulding (µ-IM) has attracted a lot of interest because of its potential for the production of low-cost, miniaturized parts in high-volume. Applications of this technology are, amongst others, microfluidic components for lab-on-a-chip devices and micro-optical components. In both cases, the control of the part flatness is a key aspect to maintaining the component's functionality. The objective of this work is to determine the factors affecting the flatness of a polymer part manufactured by µ-IM and to control the manufacturing process with the aim of minimizing the in-process part deformation. As a case study, a PMMA microfluidic substrate with overall dimensions of 10 mm diameter and 1 mm thickness was investigated by designing a µ-IM experiment having flatness as the experimental response. The part flatness was measured using a micro-coordinate measuring machine. Finite elements analysis was also carried out to study the optimal ejection pin configuration. The results of this work show that the control of the µ-IM process conditions can improve the flatness of the polymer part up to about 15 µm. Part flatness as low as 4 µm can be achieved by modifying the design of the ejection system according to suggested guideline

DESIGN AND MICROFABRICATION OF EDGE-LIT OPTICAL LIGHT CURTAINS

Plastic optical light guides can be used for a variety of interior and exterior vehicle light curtains such as cabin illuminators and automotive tail lights. The edge-lit wave guide is an optically transparent substrate coupled with one or more energy efficient light emitting diodes (LEDs). The light rays from the source travel through the substrate based on the principle of total internal reflection. If a surface of the optical wave guide is patterned with optical microstructures then the light rays will scatter and refract throughout the medium, primarily exiting opposite to the patterned surface. Uniform illumination over this active surface region is a function of the individual optical microstructure\u27s shape and the spatial distribution of the microstructures. The goal of this research is to investigate the light dispersion characteristics in both smooth and micro-patterned optically transparent substrates, and utilize optical simulation software to develop viable design approaches for fabricating small and medium sized light curtains. The study first identifies an appropriate optical microstructure (i.e. cylindrical indentations) that can be reliably imprinted on the surface of an optically transparent polymethyl-methacrylate (PMMA) substrate using a multi-axis micromilling machine. The optical simulation software Light Tools is then used to determine the most appropriate microstructure radius and spatial positioning of elements for uniform light distribution. The key design and fabrication parameters for near optimal performance are summarized and used to establish the process plan for the high-speed precision micromilling operations. Experiments are performed on several 100 mm x 100 mm x 6 mm polymer light guide panels (LGPs) including a customized design with a hexagonal arrangement of microstructures. Both interior and boundary regions of the sample LGPs are investigated for intensity distribution, optical transmission efficiency, and light loss. Although the experiments involve relatively small flat PMMA LGPs, the optical design and microfabrication methods can be readily extended to larger surface areas or curved optically transparent polymer substrates for contoured light curtains

A study on the mouldability of POM microdetails in moulding blocks using micromanufacturing technologies

The integration of micro fabrication and micro-moulding techniques contributed to the massifica-tion of microsystems in several domains of activity at feasible costs. In this study the mouldability of microdetails generated by microEDM, micromilling and laser milling in microinjection moulding blocks is assessed. For that purpose, a polyacetal for precision microparts is used to evaluate how mi-crofeatures are replicated in microinjection mould-ing. The mouldings were produced in a instru-mented micromould with two interchangeable moulding blocks, enabling the test of various mould inserts. The processing conditions were simulated with the Moldex3D commercial software. Despite the commercial success of microinjection moulding, the process involves microscale phe-nomena that make the polymer flow different from the conventional flow at the macro scale. The mi-croinjection tests and the simulation allowed the gathering of knowledge to incorporate on mathe-matical models and simulation software, enabling the filling simulations at this scale being more ac-curate. Further to the assessment of the microde-tails mouldability, the surface replication and finish-ing of the mouldings were analysed by optical and SEM microscopy.Fundação para a Ciência e a Tecnologia (FCT) - SFRH/BD/36982/200

Micromachining

To present their work in the field of micromachining, researchers from distant parts of the world have joined their efforts and contributed their ideas according to their interest and engagement. Their articles will give you the opportunity to understand the concepts of micromachining of advanced materials. Surface texturing using pico- and femto-second laser micromachining is presented, as well as the silicon-based micromachining process for flexible electronics. You can learn about the CMOS compatible wet bulk micromachining process for MEMS applications and the physical process and plasma parameters in a radio frequency hybrid plasma system for thin-film production with ion assistance. Last but not least, study on the specific coefficient in the micromachining process and multiscale simulation of influence of surface defects on nanoindentation using quasi-continuum method provides us with an insight in modelling and the simulation of micromachining processes. The editors hope that this book will allow both professionals and readers not involved in the immediate field to understand and enjoy the topic

Ductile-Regime Machining of Glass Using the Micromilling Process

Glass is a homogeneous material with amorphous crystal structure that is produced through the rapid cooling of its molten state below the glass transition temperature. Glass exhibits many excellent mechanical and physical properties, and it is widely used in automotive, communications, optics, electronics, architectural, and biomedical industries. For certain applications such as DNA microarrays, glass components with microfeatures are typically produced using a combination of photolithography and etching processes, which is generally time consuming and can involve hazardous chemicals. It would be ideal to fabricate some glass devices through mechanical micromachining for some rapid prototyping applications of glass-based devices, but the brittle nature of glass makes machining difficult. The machined surface is usually fractured and requires additional finishing processes that are costly and time consuming. Fortunately, it is found that the glass can be machined in a ductile regime under certain controlled cutting conditions. Machining in the ductile regime can produce continuous cutting chips. For micromilling to be used in the manufacturing of glass-based devices, further machining research is required to find optimum cutting configurations to produce high quality micro-scale features. It is known that the cutting regime transition from brittle to ductile cutting regimes is attributed to the effect of pressure and temperature in the cutting zone. The transition has also been correlated to the undeformed chip thickness. However, the mechanism behind ductile regime machining still cannot be fully explained. In this study, the effect of tilt angle on cutting regime transition has been studied in micromilling crown glass with a micro-ball end mill. Straight glass grooves were machined in a water bath by varying the tool tilt angle and feed rate, and the resulting surface was characterized using a scanning electron microscope and a profilometer to investigate the cutting regime transition. In characterizing the cutting regimes in glass micromilling, rubbing, ductile machining, and brittle machining regimes are hypothesized according to the undeformed chip thickness. In addition, mechanistic stress and temperature models are used in conjunction with experimental data to predict the stress and temperature information in glass micromilling in order to provide insight into why ductile machining happens. For the conditions investigated in this study, a 45¡ tool tilt angle was found to produce the highest ductile machining-related feed rate, 0.32 mm/min, and the best surface finish (less than 60 nm Ra) for feed rates less than 0.32 mm/min. The specific cutting energy relationship is determined based on the experimental force data and the effective undeformed chip thickness, which is derived based on the surface roughness measurements. The predicted stresses indicate that the 45¡ tilt angle easily leads to ductile cutting by increasing the glass fracture toughness while comparing with the performance under the other tilt angles (0¡, 15¡, 30¡, 60¡). The temperature rise is estimated negligible under the investigated micromilling conditions. This study offers a better understanding in optimizing the glass micromilling process, and it is expected that the occurrence of the glass ductile-brittle cutting regime transition will be elucidated based on the advances in glass material properties understanding and milling process modeling

Characterization of machine tools and measurement system for micromilling

Technological progress has led to increased demand for small components with tiny features, which cannot be achieved through conventional machining. Industrial application of processes based on microcutting is limited by some issues concerning the geometrical scale. The process performance is significantly affected by milling machine, tool holder, tool, workpiece material microstructure, workpiece fixtures, and process parameters. At present, an ultimate micromachining assessment procedure is not available. This study aims to propose and conduct an experiment on a testing procedure for micromilling. The set up to be implemented and the output to be considered are defined and described. Three major stages are identified: estimation of the effective bandwidth of the load cell–tool holder system, the milling machine natural frequency measurement, and micromilling test execution. The entire procedure is performed, and its robustness is demonstrated. Keywords: Micromilling, Machine tool performance test, Tool run-out, Force analysis, Modal analysi

Development of the UMAC-based control system with application to 5-axis ultraprecision micromilling machines

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.Increasing demands from end users in the fields of optics, defence, automotive, medical, aerospace, etc. for high precision 3D miniaturized components and microstructures from a range of materials have driven the development in micro and nano machining and changed the manufacturing realm. Conventional manufacturing processes such as chemical etching and LIGA are found unfavourable or limited due to production time required and have led mechanical micro machining to grow further. Mechanical micro machining is an ideal method to produce high accuracy micro components and micro milling is the most flexible enabling process and is thus able to generate a wider variety of complex micro components and microstructures. Ultraprecision micromilling machine tools are required so as to meet the accuracy, surface finish and geometrical complexity of components and parts. Typical manufacturing requirements are high dimensional accuracy being better than 1 micron, flatness and roundness better than 50 nm and surface finish ranging between 10 and 50 nm. Manufacture of high precision components and parts require very intricate material removal procedure. There are five key components that include machine tools, cutting tools, material properties, operation variables and environmental conditions, which constitute in manufacturing high quality components and parts. End users assess the performance of a machine tool based on the dimensional accuracy and surface quality of machined parts including the machining time. In this thesis, the emphasis is on the design and development of a control system for a 5-axis bench-type ultraprecision micromilling machine- Ultra-Mill. On the one hand, the developed control system is able to offer high motion and positioning accuracy, dynamic stiffness and thermal stability for motion control, which are essential for achieving the machining accuracy and surface finish desired. On the other hand, the control system is able to undertake in-process inspection and condition monitoring of the machine tool and process. The control of multi-axis precision machines with high-speed and high-accuracy motions and positioning are desirable to manufacture components with high accuracy and complex features to increase productivity and maintain machine stability, etc. The development of the control system has focused on fast, accurate and robust positioning requirements at the machine system design stage. Apart from the mechanical design, the performance of the entire precision systems is greatly dependent on diverse electrical and electronics subsystems, controllers, drive instruments, feedback devices, inspection and monitoring system and software. There are some variables that dynamically alter the system behaviour and sensitivity to disturbance that are not ignorable in the micro and nano machining realm. In this research, a structured framework has been developed and integrated to aid the design and development of the control system. The framework includes critically reviewing the state of the art of ultraprecision machining tools, understanding the control system technologies involved, highlighting the advantages and disadvantages of various control system methods for ultraprecision machines, understanding what is required by end-users and formulating what actually makes a machine tool be an ultraprecision machine particularly from the control system perspective. In the design and development stage, the possession of mechatronic know-how is essential as the design and development of the Ultra-Mill is a multidisciplinary field. Simulation and modelling tool such as Matlab/Simulink is used to model the most suitable control system design. The developed control system was validated through machining trials to observe the achievable accuracy, experiments and testing of subsystems individually (slide system, tooling system, monitoring system, etc.). This thesis has successfully demonstrated the design and development of the control system for a 5-axis ultraprecision machine tool- Ultra-Mill, with high performance characteristics, fast, accurate, precise, etc. for motion and positioning, high dynamic stiffness, robustness and thermal stability, whereby was provided and maintained by the control system

The Effects of Nanoparticle Reinforcement on the Micromilling Process of A356/Al2O3 Nanocomposites

Abstract Improving scientific knowledge around the manufacturing of nanocomposites is key since their performance spreads across many applications, including those in meso/micro products. Powder metallurgy is a reliable process for producing these materials, but usually, machining postprocessing is required to achieve tight tolerances and quality requirements. When processing these materials, cutting force evolution determines the ability to control the microcutting operation toward the successful surface and part quality generation. This paper investigates cutting force and part quality generation during the micromilling of A356/Al2O3 aluminum nanocomposites produced via powder metallurgy. A set of micromilling experiments were carried out under various process parameters on nanocomposites with different nano-Al2O3 reinforcements (0–12.5 vol.%). The material’s ductility, internal porosity, and lack of interparticle bonding cause the cutting force generation to be irregular when nanoparticle reinforcements were absent or small. Reinforcement ratios higher than 2.5 vol.% strongly affect the cutting process by regularizing the milling force generation but lead to a proportionally increasing average force magnitudes. Hardening due to nano-reinforcement positively affects cutting mechanisms by reducing the plowing tendency of the cutting process, resulting in better surface quality. Therefore, a threshold on the nano-Al2O3 particles’ volumetric loadings enables an optimal design of these composite materials to support their micromachinability

Design of a microfabricated device for Ligase Detection Reaction (LDR)

The Ligase Detection Reaction (LDR) is a mutation detection technique used to identify point mutations in deoxyribonucleic acid (DNA). Developed by Francis Barany and associates at Cornell University it is used to find specific low abundant point mutations that may lead to colorectal cancer in the early stages of disease development. The research objective was to design and manufacture a microscale Ligase Detection Reaction (LDR) device in polycarbonate. The LDR module will be incorporated with other microdevices such as: Continuous Flow Polymerase Chain Reaction (CFRCR) and Capillary Electrophoresis (CE) in modular lab-on-a-chip technology. In making the microdevice, the duration of original reaction had to be scaled down from the current 2½ hours for 20 cycles for the macroscale reaction. It was found that an excess of primers in relation to PCR product was needed for efficient ligation. By changing the concentrations, volumes and time for the process the current time is down to 40 minutes for 20 cycles with indications that further time reductions are possible on the microscale. There are two mixing stages involved in the reaction. Micromixers were simulated in Fluent (v5.4, Lebanon, NH) and several test geometries selected for fabrication. Passive diffusion mixing was used based on obtaining high aspect ratios, 7 to 20. The mixers were made by SU-8 lithography, LIGA, laser ablation, and micromilling to characterize each fabrication method. It was found that LIGA was best for making the micromixers, but was the longest process. The micromixers are fabricated and tested using chemi-luminescence technique. For a successful reaction, temperatures of 0°C, 95°C and 65°C were needed. A stationary chamber was used for thermal cycling in which the sample sits while the temperature is cycled. Finite element analysis showed uniform temperatures in the rectangular 1.5μl chambers and that air slits can effectively separate the thermal cycle zone from the 0°C cooling zone and also isolate the mixing region. A test device was laid out and micromilled with the temperature zones maintained and fluid flow controlled. A commercial thin film heater and a thermoelectric module were used with PID controls to obtain the required process temperatures. Heating from 65°C to 95°C took 10 seconds, while cooling from 95°C to 65°C also took 10 seconds. The residence times at the required temperatures can be adapted to changes in the LDR