Recent advances in modelling of metal machining processes

Microinjection molding (µIM) appears to be one of the most efficient processes for the large-scale production of thermoplastic polymer microparts. The microinjection molding process is not just a scaling down of the conventional injection process; it requires a rethinking of each part of the process. This review proposes a comparative description of each step of the microinjection molding process (µIM) with conventional injection molding (IM). Micromolding machines have been developed since the 1990s and a comparison between the existing ones is made. The techniques used for the realization of mold inserts are presented, such as lithography process (LIGA), laser micromachining and micro electrical discharge machining (µEDM). Regarding the molding step, the variotherm equipment used for the temperature variation is presented and the problems to solve for each molding phase are listed. Throughout this review, the differences existing between µIM and conventional molding are highlighted.

https://iopscience.iop.org/article/10.1088/0960-1317/17/6/R02/pdf

Microinjection molding of thermoplastic polymers: a review

Micro and Nano Machining by Electro-Physical and Chemical Processes

Ever since the discovery of triboelectric nanogenerator (TENG) by Wang's group in January 2012, various breakthroughs have been achieved in the fundamental mechanisms of TENG as well as the demonstrated self-powered systems. TENG has shown many advantages in micro-scale energy harvesting for applications in sensors and portable devices. As a self-sufficient power source, TENG can be used in conjunction with electrochemical processes as self-powered electrochemistry without the use of external power source. This review mainly focuses on the updated progress in TENGs for both high performance energy conversion and self-powered electrochemical systems in application such as water splitting, sea water desalination, air pollution cleaning, degradation of organic pollutant, collecting of heavy metal ions and many more. The idea of performing electrochemistry without using an external power could be useful for large-scale application in environmental science.

Triboelectric Nanogenerators Driven Self-Powered Electrochemical Processes for Energy and Environmental Science

https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1275&context=mechengfacpub

Review of Electrochemical and Electrodischarge Machining

In this paper, electrochemical machining (ECM) for fabricating micro structures is presented. By applying ultra short pulses, dissolution of a workpiece can be restricted to the region very close to an electrode. Using this method, 3D micro structures were machined on stainless steel. Good surface quality of the structures was obtained in the low concentration electrolyte, 0.1 M H2SO4. In ECM, when the machining depth increases, structures taper. To reduce the taper, a disc-type electrode is introduced. By electrochemical milling, various 3D micro structures including a hemisphere with 60 µm diameter were fabricated.

https://iopscience.iop.org/article/10.1088/0960-1317/15/1/019/pdf

Micro electrochemical milling

Electro-chemical machining (ECM) has been rarely applied in micro machining because the electric field is not localized In this work, ultra short pulses with tens of nanosecond duration are used to localize dissolution area The effects of voltage, pulse duration, and pulse frequency on the localization distance were studied High quality micro hole with 8 μm diameter was drilled on 304 stainless steel foil with 20 μm thickness Localization distance can be manipulated by controlling the voltage and pulse duration, and various hole shapes were produced including stepped holes and taper free holes

Electro-chemical micro drilling using ultra short pulses

Plane surface generation mechanism in flat end milling is studied in this research. The bottom of a flat end mill has an end cutting edge angle that plays an important role in surface texture. Surface texture is produced by superposition of conical surfaces generated by the end cutting edge rotation. The machined surface is cut once again by the trailing cutting edge. This back cutting phenomenon is frequently observed on surfaces after finishing. Tool run-out and tool setting error including tool tilting and eccentricity between tool center and spindle rotation center are considered together with tool deflection caused by cutting forces. Tool deflection affects magnitude of back cutting and the surface form accuracy. As a result, the finished surface possesses peaks and valleys with form waviness. Surface topography parameters such as RMS deviation, skewness and kurtosis are used for evaluating the generated surface texture characteristics. Through a set of cutting tests, it is confirmed that the presented model predicts the surface texture and roughness parameters precisely including back cutting effect.

Roughness and texture generation on end milled surfaces

Tungsten carbide (WC) micro-shaft can be used as various micro-tools for MEMS because of its high rigidity and toughness. In this study, we performed fabrication experiments of the WC micro-shaft using electrochemical etching. H2SO4 solution was used as the electrolyte because it can dissolve tungsten and cobalt simultaneously. Optimal electrolyte concentration and applied voltage resulting in uniform shape, good surface quality, and high material removal rate (MRR) of a workpiece were experimentally selected. A straight micro-shaft with 5 μm diameter and 3 mm length was obtained by controlling the various machining parameters. Using the fabricated micro-shafts as tools, we machined a high quality micro-hole with 8 μm diameter and a micro-groove with 9 μm width in stainless steel 304 (304 SS).

Fabrication of WC micro-shaft by using electrochemical etching

In this research, an effective method for the form error prediction in side wall machining with a flat end mill is suggested. The form error is predicted directly from the tool deflection without surface generation by cutting edge locus with time simulation. The developed model can predict the surface form error accurately about 300 times faster than the previous method. Cutting forces and tool deflection are calculated considering tool geometry, tool setting error and machine tool stiffness. The characteristics and the difference of generated surface shape in up milling and down milling are discussed. The usefulness of the presented method is verified from a set of experiments under various cutting conditions generally used in die and mold manufacturing. This study contributes to real time surface shape estimation and cutting process planning for the improvement of form accuracy.

Shi Hyoung Ryu

Papers

Micro electrochemical milling

Electro-chemical micro drilling using ultra short pulses

Roughness and texture generation on end milled surfaces

Fabrication of WC micro-shaft by using electrochemical etching

The form error prediction in side wall machining considering tool deflection