An official website of the United States government
Abstract Functionally graded surfaces — surfaces with properties that are engineered to have spatial variations — have numerous applications such as micropumps, auto-mixers, and flow control for lab-on-chip devices. Manufacturing of functionally graded surfaces is an increasingly important topic of research. This study investigates the feasibility of creating a functionally graded surface during channeling of borosilicate glass by the electrochemical discharge machining (ECDM) process. The ability to create surface roughness gradients in microchannels during the machining process was demonstrated by modifying the input voltage, tool feed rate, and tool rotation speed. Microchannels with graded surface roughness having Ra values ranging from 0.35 to 4.07 μm were successfully machined on borosilicate glass by ECDM. Surface profiles were obtained via a stylus profilometer, and roughness values were calculated after detrending and applying a Gaussian filter. To demonstrate the process versatility, micro channels with increasing and decreasing Ra values were machined, one increasing from 1.43 μm to 4.07 μm, another decreasing from 3.29 μm to 1.10 μm. To demonstrate the process repeatability, a micro channel with similar surface roughness on both ends and a lower Ra value in the center was created. In this channel, the Ra value at the start is 0.35 μm, reducing to 0.24 μm, then rising again to 0.38 μm in the final section.
more »
« less
Non-contact micromachining by a dynamic feed rate controlled electrochemical discharge machining process
Electrochemical discharge machining (ECDM) is an emerging micromachining method to drill advanced non-conductive materials such as Hexagonal boron nitride (hBN). Physical contact of micro tools with work material could cause machining inaccuracies, excessive tool wear, and even tool breakage. In this study, a control system based on monitoring the force generated by the ECDM gas film has been developed to achieve non-contact machining of ECDM by dynamically adjusting the tool feed rate. The accuracy of the control system was verified by accelerometer and Fast Fourier Transformation (FFT) data. In the modules, it was found that a non-contact machining process requires the FFT amplitude to be lower than 42 V for a 1200 rpm tool rotation. The experimental results show consistent micro-holes with an average diameter of 650 µm and less than 20 µm error in the overcut achieved using this control system.
more »
« less
- Award ID(s):
- 1833112
- PAR ID:
- 10432359
- Date Published:
- Journal Name:
- Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture
- ISSN:
- 0954-4054
- Page Range / eLocation ID:
- 095440542211476
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
null (Ed.)Abstract This paper presents a novel thickness profile measuring system that measures double-sided thin pipe wall surfaces in a non-contact, continuous, cosine error-free, and fast manner. The surface metrology tool path was developed to align the displacement sensors always normal to the double-sided surfaces to remove cosine error. A pair of capacitive-type sensors that were placed on the rotary and linear axes simultaneously scans the inner and outer surfaces of thin walls. Because the rotational error of the rotary axis can severely affect the accuracy in thickness profile measurement, such error was initially characterized by a reversal method. It was compensated for along the rotational direction while measuring the measurement target. Two measurement targets (circular and elliptical metal pipe-type thin walls) were prepared to validate the developed measurement method and system. Not only inner and outer surface profiles but also thin-wall thickness profiles were measured simultaneously. Based on the output data, the circularity and wall thickness variation were calculated. The thickness profile results showed a good agreement with those obtained by a contact-type micrometer (1-µm resolution) at every 6-deg interval. The uncertainty budget for this measuring system with metrology tool path planning was estimated at approximately 1.4 µm.more » « less
-
Tool-chip contact stresses are of major interest in developing a basic understanding of the mechanics of machining. The interfacial and sliding conditions along the tool-chip contact in machining differ significantly from that of conventional, lightly loaded, tribological contacts in two major aspects — the occurrence of plastic flow (in the chip) at the sliding interface and intimate nature of the contact where apparent and real contact areas are the same. In this study, we present an experimental method for direct measurement of the tool-chip contact stresses. This involves the use of sapphire as a cutting tool coupled with digital photoelasticity to obtain full-field principal stress difference (isochromatics) and principal stress directions (isoclinics). This enables direct full-field characterization of the tool-chip contact stresses, as well as stresses within the cutting tool, at a micron-scale resolution not achieved previously. Our results show that the shear stress exhibits a maximum at a small distance from the tool tip, while the normal stress decreases monotonically with increasing distance from the tool tip. The maximum shear stress shows a good correlation with the shear flow stress of the material that is being machined. We also briefly discuss applications of the method to derive the stress distribution at the tool flank face and quantify frictional dissipation at both the contacts — tool-chip contact and flank-machined surface contact.more » « less
-
Micromachining of glass has gained importance due to numerous applications of glass in microfluidics, optics, electronics, and biotechnology industry. Electrochemical discharge machining (ECDM) is an emerging nontraditional process which has the potential for micromachining of glass with minimal surface damages. Material removal during the machining of glass by ECDM involves thermal machining by electrical discharges between the tool and the gas film. The energy of these discharges is influenced by the gas film characteristics and affects the machining results. In this study, a combined approach of finite element simulation and experimentation is used to study the ECDM process to understand the impact of gas film characteristics on the overcut in machining. The multiphase simulation setup incorporates a combined electrochemical system of glass and electrolyte. The changes in the gas film characteristics due to the variations in the level of electrolyte and the corresponding changes in the overcut are studied. It was observed that the gas film thickness increased with an increase in the level of electrolyte and the gas film stability showed an opposite trend. This resulted in an increase in the overcut in the machining with the increase in the level of electrolyte. This trend observed in the simulation was validated with experimentation.more » « less
-
null (Ed.)Tool wear in machining is generally observed as early and late stage tool wear. During early stage tool wear, the tool is rapidly worn during a break-in period, followed by a stable region of tool wear. After machining more material, the tool reaches late stage tool wear. At this point, tool wear becomes unstable; tool failure occurs quickly or it may take some time. Therefore, late stage tool wear represents a bifurcation point, making it difficult to predict tool wear past this point. Tool wear is well known to be stochastically influenced. Due to this effect, it is difficult to perform studies on late stage tool wear since machining tools will be affected differently up to this point, introducing unknown variables. A novel method is presented in this research which utilized artificial wear to reach late stage tool wear. This method, termed contrived tool wear, may be capable of reducing the stochastic tool wear that occurs during early stage tool wear. As an initial investigation, machining tool inserts were worn by taking several passes over a grinding wheel with the tool rotating in reverse. Several parameters were tested in attempt to match the natural worn state as close as possible. Subsequent to artificial wear, the inserts were used to machine IN718. The presented method of contrived wear was found to be a good approach, but could not sufficiently replicate the tool wear typically produced in IN718 machining. Future work should aim at implementing a multi-axis approach to enable grinding at various angles to the rake face of the insert.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1177/09544054221147611
