Machining Micro Research Articles

A study of electrode compensation model improvement in micro-electrical discharge machining milling based on large monolayer thickness

Micro-electrical discharge machining (EDM) milling with a simple-shaped electrode is an effective machining method to fabricate three-dimensional micro parts and micro structures. However, the serious electrode wear occurring in the machining process significantly deteriorates the geometrical accuracy of the products. Since the electrode wear in micro-EDM milling is inevitable and hard to model accurately, it is difficult to conduct effective electrode compensation. To enhance the machining quality and efficiency of micro-EDM milling, a large layer thickness milling method is introduced and the improved electrode compensation model for large monolayer thickness milling is proposed based on modification of the conventional compensation model. First of all, proper machining parameters are obtained from processing tests without compensation. The wear law of the micro-electrode is then investigated and the conventional electrode compensation model is modified taking into consideration the changes of electrode shape during machining. Moreover, a new relative volume wear ratio measurement method is also presented through material composition analysis and the improved compensation model based on large monolayer thickness is finally established. Experiments demonstrate that the improved electrode compensation model can achieve accuracy when machining micro structures with large monolayer thickness and this method is an effective way to ensure the quality of micro products. Meanwhile, the use of large monolayer thickness in micro-EDM milling can enhance the machining efficiency significantly.

A mechanical micro molecular mass sensor.

One of the bio-sensing mechanisms is mechanical. Rather than measuring shift in resonance frequency, we adopt to measure the change in spring constant due to adsorption, as one of the fundamental sensing mechanism. This study explains determination of spring constant of a surface functionalized micro machined micro cantilever, which resonates in a trapezoidal cavity-on Silicon <100> wafer, with the resonating frequency of 7000 cycles per second. This thin-flimsy-oxide micro-cantilever has a typical shape, and the tip of the micro-cantilever is dip-coated with chemically and biologically active material. The change in mass, due to adsorption, is detected by measuring the change in spring constant. The Force-Distance spectroscopy is used to detect the change in spring constant. The experimental results, show that the mechanical sensing scheme used, permit this surface functionalized micro machined micro cantilever to be used as a molecular mass sensor. The mechanical spring behaviour of a micro-cantilever, a micro-mechanical device can be used to develop ultra-tech micro-mechanical system using computer interface.

Micro machining of pre-sintered ceramic green body

Ceramic materials are widely used in industrial products because of their excellent properties such as resistance to erosion, high temperature and wear. Those properties pose difficulty in processing ceramic materials to desired shapes and dimensions, especially in micro machining of ceramics using micro tools because of the low mechanical strength of tiny tools and the extreme hardness of ceramics. The machining of ceramic green body may be a solution to the problem. However, the low strength of ceramic green body results in low machining accuracy such as damage at the edges of micro features. In this paper, the pre-sintering of ceramic materials was used to enhance the material strength, and hence to improve the machining accuracy. Microstructures of pre-sintered ceramic green bodies at different temperatures were observed and analyzed. The mechanical strength of pre-sintered ceramics was measured. It was confirmed that the mechanical strength of ceramics increased with an increase of pre-sintering temperature. There was no obvious shrinkage after pre-sintering at below 850 °C. The edge damage of machined micro features was reduced significantly. The tool wear increased with the increase of pre-sintering temperature. Finally, a 3D micro feature was machined and the fully sintering shrinkage was compensated accurately.

A Method of Machining Micro Hole and Micro Cavity in Ceramics

For machining micro hole and micro cavity in ceramics, a manufacturing methods based on green machining have been systematically researched. The micro tool was prepared on-machine by micro electrical discharge machining (EDM). The tool size for micro hole drilling was determined based on extensive experimental results of the sintering shrinkage ratio and the gap caused by the removed ceramics particles between the tool and the workpiece to achieve the desired hole diameter. The tool path design was based on the tool size, the shrinkage ratio and the gap which is different from that in micro hole drilling. Micro holes with diameter of 100μm and micro cavities with upper surface size of 500μm×500μm was machined in ceramics successfully by this method. The final size error was controlled less than 2.25% in micro hole drilling and less than 2% in micro cavity generation.

Fabrication of Fuel Cells with High Power Density Using Micro Electrical Discharge Machining Milling

Light and thin bipolar plates are essential in increasing the power density of a fuel cell. To construct high-aspect-ratio micro flow channels in such plates is, however, a big challenge. This study reports on machining micro flow channels in metallic bipolar plates using micro electrical discharge machining milling (micro EDMM) with a tungsten carbide electrode. We successfully machined metallic bipolar plates with 500μm channel and rib widths, height of 600μm in a reaction area of 20mm × 20mm, on 1mm thick of SUS316L stainless steel. The optimal operating parameters were explored and discussed. The performance of resulting fuel cell (Metallic-FC) was compared with a commercial available fuel cell composed of graphite bipolar plates (Graphite-FC). The high temperature of Metallic-FC increases its electrochemical reaction rate and consequently yields higher power density (723 mWcm-2) then that of Graphite-FC (687.3 mWcm-2)

Study on a Novel Adaptive Force Control Table Employed for Rotary Ultrasonic Drilling

A novel adaptive force control table for rotary ultrasonic machine tool was developed for processing micro holes. The adaptive force control table, a mechanical balancing device by which the load can be adaptively adjusted without numerical control was adopted as an attachment in an ultrasonic machine tool. To verify the performance, micro holes were drilled on SiC workpiece. The drilling force, tool wear and profiles of these machined micro holes were investigated. According to the experimental results, it is confirmed that the newly developed table attached on the ultrasonic machine tool is an economical and efficient approach for machining micro holes on hard and brittle materials.

Research on Micro Gear Design for WEDM

WEDM (Wire Electrical Discharge Machining) is an effective method for machining micro gears. In this paper, aiming at WEDM characteristics, the gear design method is discussed. Based on gear meshing theory, the gear tooth profiles are generated. Mesh interference and wire path for WEDM algorithms are presented. Micro gear CAD/CAM software is developed whose functions include gear modeling, interference judgment and wire path generation. Finally a pair of micro gears is manufactured to verify the work in this paper. With the above method, the constraints on some gear parameters can be eliminated and the micro gear design is made more flexible.

Influence of surface condition on wear behavior of μPIM mould inserts made of tool steel and cemented carbide

Mould inserts made of low alloyed tool steel and cemented carbide were tested using a laboratory tribometer simulating micro powder injection moulding (μPIM) to characterize the influence of surface condition due to different machining (micro milling or electrical discharge machining) and finishing (ultrasonic wet peening or abrasive micro peening) processes on wear in contact with ceramic feedstocks of different composition. Results show that abrasive micro peening is a suitable finishing process to ensure an excellent wear resistance of EDM processed mould inserts made from ultrafine cemented carbide even in contact with alumina feedstock of high abrasiveness. Ultrasonic wet peening on the other hand allows effective deburring and smoothing of relatively soft steel surfaces after micro milling.

3396 Micro hole processing using Electro-Chemical Discharge Machining

Recently, micro holes processing on glass were focused on the chemical and the biological filed. The authors focused on the Electro-Chemical Discharge Machining (ECDM) to machine the micro holes for glass, and developed the ECDM device for machining micro holes on glass. This paper reports about the feedback circuit for machining-stop and the two-step machining which were developed to reduce the smallest diameter of the micro hole. Additionally, the tool electrode with diameter of 20μm was produced. As a result, the smallest diameter of the micro hole, 12μm in diameter was achieved.

A Reclaiming Process for Solar Cell Silicon Wafer Surfaces

The low yield of epoxy film and Si3N4 thin-film deposition is an important factor in semiconductor production. A new design system using a set of three lamination-shaped electrodes as a machining tool and micro electro-removal as a precision reclaiming process of the Si3N4 layer and epoxy film removal from silicon wafers of solar cells surface is presented. In the current experiment, the combination of the small thickness of the anode and cathodes corresponds to a higher removal rate for the thin films. The combination of the short length of the anode and cathodes combined with enough electric power produces fast electroremoval. A combination of the small edge radius of the anode and cathodes corresponds to a higher removal rate. A higher feed rate of silicon wafers of solar cells combined with enough electric power produces fast removal. A precise engineering technology constructed a clean production approach for the removal of surface microstructure layers from silicon wafers is to develop a mass production system for recycling defective or discarded silicon wafers from solar cells that can reduce pollution and lower cost.

Machining of Micro-Channels on Brittle Glass Using an Abrasive Slurry Jet

This paper presents a study of using an abrasive slurry jet for the machining of micro channels on brittle glasses. The machined surface morphology and channel dimensions are used to assess the technology. Surface morphology was found featuring with two types of wave patterns; one was along the channels with large wave lengths as a result of the jet deflection during the motion of nozzle, and the other was due to viscous flow that resulted in smooth surface eroded predominantly by ductile mode. The investigation showed that using higher jet pressure and higher particle concentration enables to create channels with higher depth, although these widened the channels and degraded the surface quality in some cases by inducing a larger number of pit fragments on the surface. With proper control of the operating parameters, this technology can be used for machining micro channels on brittle materials with high quality of surface finish.

Micro Machining of Three-Dimensional Microstructure with the Tiny-Grinding Wheel Based on the Electro-Magneto-Rheological Effect

Using the tiny-grinding wheel based on the synergistic effect of the electro-magneto- rheological (EMR) fluid, a novel method is presented to machine the three-dimensional (3D) microstructure of hard-brittle materials. Machining experiments of micro-groove were conducted to reveal the machining performances of the tiny-grinding wheel. Experimental results confirm the effectiveness and feasibility of the micro machining technique with the EMR effect-based tiny-grinding wheel. The shape of machined micro groove is found to be an inverted trapezoid, and the material removal mode of normal glass with the micro machining method is the plastic-removal mode. With the increase of the rotation speed of the tool, the material removal rate, width and depth of micro grooves increased first and decreased afterwards. The maximum removal rate, width and depth of micro groove occur at different speeds of the tool.

Fabrication of High-Aspect Ratio Micro Holes on Hard Brittle Materials -Study on Electrorheological Fluid-Assisted Micro Ultrasonic Machining-

Ultrasonic machining (USM) is an effective method for machining of hard brittle materials. In this process, the slurry is supplied to the gap between the workpiece and the ultrasonic vibrating tool, and the materials are removed by the impacts of the abrasive grains that are pressurized by an ultrasonic vibrating tool. The purpose of this research is to achieve precise and efficient microfabrication on hard brittle materials by USM. However, in the case of microfabrication, chipping which is generally observed around the edges of machined micro holes and grooves, deteriorates the machining accuracy. In addition, there is another problem in that the machining efficiency decreases with the progress of the machining. Electrorheological fluid-assisted USM has been proposed as a countermeasure to these problems. In the present study, the problems and countermeasures associated with the machining of high-aspect ratio micro holes in hard brittle materials by electrorheological fluid-assisted USM are investigated. By positioning an auxiliary electrode under the workpiece, it becomes possible to keep the electric field high even when the machining depth becomes large. As a result, high-precision and high-aspect ratio micro holes can be machined on hard brittle materials.

Study on the Influence Factors of Electrochemical Micromachining

There are many influence factors of electrochemical micromachining (EMM) development. So the characteristics of EMM technology were analyzed firstly. It was an effective method that the nanosecond pulses voltage was used in EMM, and the nanosecond pulses voltage was prepared to solve the problems of machining area, using small gap, and machining micro 3D structure. Its minimum pulse duration is 5ns, and its voltage, current, and duty ratio can be changed freely. Moreover, many experiments of EMM were carried into execution. After the phenomenon and results of the experiments were analyzed, the reformative project of experiment was put forward. The feasibility of the project and technique route was testified correctly by the nanosecond pulses voltage on the multifunction machine tool which was manufactured independently. After studying on the influences of EMM technology, the experiences of EMM process will be enriched and make EMM have a further development.

Fundamental experiments as benchmark problems for modeling ultrasonic micro-impact processes

Many ultrasonic processes are based on the mechanical contact of oscillating parts. Within ultrasonic machining (drilling, milling, grinding) micro impacts lead to abrasion at the processed workpiece and hopefully do not damage the tool. In ultrasonic motors ideally neither part gets worn. Thus the appropriate design of contact partners as well as their kinematics is a substantial task during the development of such devices. A first step to optimize contact mechanics is to understand their behavior and dependencies on parameter variations, such as vibration amplitude and pre-stress of the impacting parts. For a detailed understanding models validated with convincing experimental data from measurements are absolutely essential. This paper focuses on simple vibro-impact experiments which can be used as benchmark data for future models. The setup of the experiment and first experimental investigations are described in detail.

Key technologies in ultrasonic machining micro holes

In order to enhance the micro level and precision of micro holes machined by ultrasonic machining (USM), the key technologies for machining micro holes are studied, which in- dude high precise machine tool, USM unit, manufacturing technology of the micro tool and the choice of the geometric parameters. The dynamic stability of the tool is analyzed, which shows that the stability of compressive bar depends on not only the static pressure but also the ultrasonic amplitude. The Mathieu equation for discriminating the dynamic stability is derived. The criterion for calculating critical pressure and criti- cal length of the tool is obtained from simplifying the Mathieu equation, which can solve the problem of the tool's bend, breakage, and deteriorating the hole shape accuracy caused by the improper choice of tool length, static pressure and ultrasonic amplitude. The experiments of micro holes machining using micro-USM with work vibration are carried out, the experi- mental results show that the wear rate of the micro tool in- creases with the accretion of the feed rate and the amplitude. On the developed micro USM system, the micro hole with di- ameter of 13μm can be machined.

Micro-machining and micro-grinding with tools fabricated by micro electro-discharge machining

This paper provides an overview of several approaches to micro-machining by mechanical and electro-discharge means of material removal. Two steps are required in machining micro features. Firstly, a custom-shaped tool is created from suitable stock. In many cases, this is carried out using a small-scale version of wire Electro-Discharge Machining (EDM) in tool materials such as sintered PolyCrystalline Diamond (PCD) or tungsten carbide. Then the micro-tool can be used as a miniature end mill, drill or abrasive wheel. Each of these mechanical machining methods can be combined with EDM to achieve a customisable surface finish and feature accuracy. Trade-offs such as tool wear, Material Removal Rate (MRR) and machining time are discussed in this paper within the context of several examples.

Research on Multifunctional Micro Machining Equipment

To perform several micro-machining on same machine tool, a micro machining equipment was researched and developed. The equipment adopts some high and new technologies. It is equipped with high precision XYZ stage, a spindle with high rotation accuracy and variable rotation speed, a granite worktable, a block electro discharge grinding unit for machining micro rod, a ultrasonic vibration unit for workpiece vibrating, a high frequency pulse power supply for micro-ECM and a video microscopic system with high enlargement factor. The equipment can perform micro electro discharge machining (EDM), micro electrochemical machining (ECM), micro ultrasonic machining (USM) as well as their combination. It can also machine 3D microstructures. A series of experiments were carried out. Using micro-EDM, micro rods with the diameter of less than 5µm were ground on block electrode, micro holes and 3D microstructures were obtained. Shaped holes were machined by using combination of micro-EDM and micro-USM. A micro hole with the diameter of 100µm was machined via micro-ECM.

Modelling and Simulation of Micro EDM Process

In micro EDM, simple-shaped tools are being used to machine complex 3D micro features because of the cost and difficulty in fabricating multiple complex-shaped micro electrodes. However, the tool wear adversely affects the accuracy of machined micro features. Therefore, a theoretical model for surface profile generation which takes into account the effect of tool wear is needed. This paper presents such a model and a simplified simulation algorithm. The experimental results of micro and macro EDM generated surface profiles confirm the validity of the proposed mathematical model and the simulation algorithm.