A Systematic Approach for Developing 3D High-Quality PDMS Microfluidic Chips Based on Micromilling Technology

In recent years, there has been an increased interest in exploring the potential of micro-and mesoscale milling technologies for developing cost-effective microfluidic systems with high design flexibility and a rapid microfabrication process that does not require a cleanroom. Nevertheless, the number of current studies aiming to fully understand and establish the benefits of this technique in developing high-quality microsystems with simple integrability is still limited. In the first part of this study, we define a systematic and adaptable strategy for developing high-quality poly(methyl methacrylate) (PMMA)-based micromilled structures. A case study of the average surface roughness (Ra) minimization of a cuboid column is presented to better illustrate some of the developed strategies. In this example, the Ra of a cuboid column was reduced from 1.68 μm to 0.223 μm by implementing milling optimization and postprocessing steps. In the second part of this paper, new strategies for developing a 3D microsystem were introduced by using a specifically designed negative PMMA master mold for polydimethylsiloxane (PDMS) double-casting prototyping. The reported results in this study demonstrate the robustness of the proposed approach for developing microfluidic structures with high surface quality and structural integrability in a reasonable amount of time.

Generation of Reference Softgauges for Minimum Zone Fitting Algorithms: Case of Aspherical and Freeform Surfaces

Optical aspherical lenses with high surface quality are increasingly demanded in several applications in medicine, synchrotron, vision, etc. To reach the requested surface quality, most advanced manufacturing processes are used in closed chain with high precision measurement machines. The measured data are analysed with least squares (LS or L2-norm) or minimum zone (MZ) fitting (also Chebyshev fitting or L∞-norm) algorithms to extract the form error. Performing data fitting according to L∞-norm is more accurate and challenging than L2-norm, since it directly minimizes peak-to-valley (PV). In parallel, reference softgauges are used to assess the performance of the implemented MZ fitting algorithms, according to the F1 algorithm measurement standard, to guarantee their traceability, accuracy and robustness. Reference softgauges usually incorporate multiple parameters related to manufacturing processes, measurement errors, points distribution, etc., to be as close as possible to the real measured data. In this paper, a unique robust approach based on a non-vertex solution is mathematically formulated and implemented for generating reference softgauges for complex shapes. Afterwards, two implemented MZ fitting algorithms (HTR and EPF) were successfully tested on a number of generated reference pairs. The evaluation of their performance was carried out through two metrics: degree of difficulty and performance measure.

Machinability investigation of polymer/GNP nanocomposites in micro-milling

Nanoparticles such as graphene have been added to various polymer matrices to enhance the mechanical, thermal, and electrical properties of polymer materials that require complex designs on a microscopic scale. Micro-machining is used to process these nanocomposite materials to achieve high surface quality and dimensional accuracy while maintaining high productivity. In this study, a systematic micro-milling experiment was performed on polymer/graphene nanoplatelet (GNP) nanocomposites to advance knowledge of the micro-machinability of these materials. It evaluates the effect of the addition of 0.1wt% GNP nanoparticles on machined surface morphology, chip formation, cutting forces, and tool wear. It is found that the addition of GNP nanoparticles changes the slot edge formation mode from burring mode to chipping mode.

Process design of a novel combination of peel grinding and deep rolling

Grinding is mostly considered as a finishing operation by which a high surface quality is achieved. An increase in productivity is therefore limited by maintained surface properties such as the roughness or tensile residual stresses. Thus, a roughing operation is inevitable followed by a finishing operation, while both operations are separated, leading to larger cycle times and process costs. In this paper, a novel process combination is investigated in which the roughing is done by grinding and the finishing operation by deep rolling within one tool setup. In this way, both processes are conducted parallel within the primary processing time. The objective of this study is the knowledge of the characteristics of this process combination with regard to the workpiece surface integrity. Therefore, shafts are ground in peel grinding with varying grinding wheel types and process parameters and subsequently machined with deep rolling. The process combination is evaluated with regard to the process forces and the resulting surface properties. In addition, experiments using the process combination were conducted in order to investigate the transferability of the results towards the process combination. By this approach, it was found that the surface roughness was reduced up to 80% by deep rolling showing the potential of the process combination.

Electropolishing Parametric Optimization of Surface Quality for the Fabrication of a Titanium Microchannel Using the Taguchi Method

Titanium is widely used in biomedical components. As a promising advanced manufacturing process, electropolishing (EP) has advantages in polishing the machined surfaces of material that is hard and difficult to cut. This paper presents the fabrication of a titanium microchannel using the EP process. The Taguchi method was adopted to determine the optimal process parameters by which to obtain high surface quality using an L9 orthogonal array. The Pareto analysis of variance was utilized to analyze the three machining process parameters: applied voltage, concentration of ethanol in an electrolyte solution, and machining gap. In vitro experiments were conducted to investigate the fouling effect of blood on the microchannel. The result shows that an applied voltage of 20 V, an ethanol concentration of 20 vol.%, and a machining gap of 10 mm are the optimum machining parameters by which to enhance the surface quality of a titanium microchannel. Under the optimized machining parameters, the surface quality improved from 1.46 to 0.22 μm. Moreover, the adhesion of blood on the surface during the fouling experiment was significantly decreased, thus confirming the effectiveness of the proposed method.

Effects of Electrolyte Flushing and Surface State on Electropolishing TB2 Titanium Alloy

TB2 titanium alloys are widely used in the aerospace industry. A high surface quality is required for the performance and fatigue life of titanium alloy parts. Electropolishing is useful for thin metal plates owing to its good processability and conformability. In this study, electrolyte flushing was proposed for electropolishing a large surface and a NaCl-containing ethylene glycol electrolyte was adopted. Three different mechanical grindings were employed for pretreatment, and the ideal surface quality was obtained with a rubber grinding head. Therefore, in the process of electropolishing a large surface, electrolyte flushing is superior to stirring because its flow field is even and controllable. The effects of the main processing parameters (voltage, flow rate, and process time) on the surface roughness and morphology were studied. Finally, a mirror-like surface with a surface roughness of 10.5 nm was obtained after flushing electropolishing for 30 min under a voltage of 25 V and a flow rate of 0.84 m/s.

Physical Modeling of Semi-continuous Casting for Developing an Industrial Technology of Producing Ingots From New Deformable Aluminum Alloys

A physical model of a semi-continuous casting unit (SCCU) has been manufactured and tested, designed to develop a technology for casting flat and cylindrical ingots from experimental aluminum alloys for subsequent metal forming. The SCCU includes two induction melting furnaces with a tilting mechanism, a rotary mixer, a metal path system, a vertical casting machine, a jib crane, water supply, power supply, monitoring and control systems. SCCU testing was carried out on six heats of alloy 1580 of the Al-Mg system with the addition of scandium. In the first three ingots the scandium content was 0.05% (wt.). In the second series of three heats ingots with 0.075% (wt.) scandium were cast. The ingots had a high surface quality, did not have casting defects, and there were no inclusions of primary intermetallic compounds Al3(Sc, Zr) in the structure of the ingots. The bottom and runner parts of the ingots were cut off, all faces were milled and subjected to homogenization annealing in a two-stage mode: the first heating at 350 °C, 3 h, the second heating for 1 h to 425 °C, 4 h. Then the billets were hot rolled from 40 to 5 mm, annealed at 380 °C, 1 h, rolled at room temperature to a thickness of 1 mm and annealed at 350 °C, 3 h. After that, tensile mechanical properties were tested. The results of modeling ingot casting were tested in industrial conditions when casting a large ingot with a cross section of 2100×500 mm. A template was cut from the ingot with the dimensions of a billet for rolling, as that obtained from an experimental ingot cast at the SCCU. The billet was subjected to hot and cold rolling according to the conditions used for rolling the experimental ingot. At the same time the modes of heat treatment of sheet semi-finished products were also repeated. The mechanical properties of sheets of alloy 1580 rolled from experimental and industrial ingots practically did not differ. This proves the reliability of casting modes for ingots obtained at the SCCU and tested for casting industrial ingots.

High-Temperature Corrosion of APS- and HVOF-Coated Nickel-Based Super Alloy under Air Oxidation and Melted Salt Domains

Various thermal spraying approaches, such as air/atmospheric plasma spraying (APS) and high-velocity oxy-fuel (HVOF) spraying, are widely employed by plants owing to their flexibility, low costs and the high surface quality of the manufactured product. This study focuses on the corrosion behavior of a Ni superalloy coated with powder Cr3C2-25NiCr through APS and HVOF at 950 °C under air oxidation and Na2SO4 + 0.6V2O5 molten salt environments (MSE). The results show that HVOF-deposited Ni superalloys have higher hardness and bond strength than the respective APS coating. The thermo-gravimetric probe reveals that the Ni superalloys exposed to an oxidizing air environment has a minor mass gain compared to those under the MSE domain for both non-coated and coated samples, in line with the parabola curvature rate oxidizing law. The Ni superalloys show good corrosion resistance but poor oxidation resistance in APS-deposited Ni superalloys under the MSE. HVOF-coated Ni superalloys in both environments exhibit better corrosion resistance and lower mass gain than APS-coated superalloys. The excellent coating characteristics of HVOF-coated Ni superalloys lead to their better high-temperature corrosion performance than APS.

Machining Characteristics of Electrochemical Polishing Using Ultrasonic Vibration for Nanoscale High Surface Quality

This study demonstrates a method to improve the surface quality by adding artificial vibration to the electrolyte in electrochemical polishing (ECP, electropolishing). ECP is a typical non-contact surface polishing process that has been used to improve surface quality without leaving any of the mechanical scratch marks that can arise when applying mechanical processes. ECP can polish work material via electrochemical dissolution between the surfaces of an anode and a cathode, and irregular defects are generated on the surface by impurities and bubbles generated during machining. This study confirms that our novel ECP method yields improved results over conventional ECP based on experiments using vibration electrochemical polishing (VECP) with ultrasonic vibrations. VECP minimizes nanoscale surface defects, improves surface roughness, makes it possible to quickly remove materials at nanoscale by increasing the material removal rate (MRR). Under high current density, where the electrochemical relatively reaction is active, value of the current is increased when ultrasonic vibration is added. The localized roughness of the work material was measured by atomic force microscopy (AFM) according to various electrical conditions. In addition, we also compared the overall surface quality and productivity to those obtained by conventional ECP.