Systematic Variation Of Process Parameters Research Articles

Melt Electrowriting of Isomalt for High‐Resolution Templating of Embedded Microchannels

AbstractFabrication of microchannels using 3D printing of sugars as fugitive material is explored in different fields, including microfluidics. However, establishing reproducible methods for the controlled production of sugar structures with sub‐100 μm dimensions remains a challenge. This study pioneers the processing of sugars by melt electrowriting (MEW) enabling the fabrication of structures with so far unprecedented resolution from Isomalt. Based on a systematic variation of process parameters, fibers with diameters down to 20 μm can be fabricated. The flexibility in the adjustment of fiber diameter by on‐demand alteration of MEW parameters enables generating constructs with perfusable channels within polydimethylsiloxane molds. These channels have a diameter that can be adjusted from 30 to 200 μm in a single design. Taken together, the experiments show that MEW strongly benefits from the thermal and physical stability of Isomalt, providing a robust platform for the fabrication of small‐diameter embedded microchannel systems.

Improving single-step scCO2 dyeing of wood by DMSO-induced micro-swelling

Supercritical dyeing of wood is a smart green technology. Beyond being of interest to wood industry, it could help to preserve tropical forests and decrease the environmental pollution from overseas shipping. However, scCO2 dyeing is still in its infancies. This paper demonstrates at the example of three major European hardwood species and the dye Naphthazarin that the uptake of colorants can be improved if scCO2 is complemented with small amounts of DMSO. The latter triggers micro-swelling of wood, thereby improving dye penetration. Systematic variation of process parameters revealed that optimal colouration is reached at 20.0 MPa and 85 °C. Colour gradients as observed in the interior of halved specimen were evaluated by two methods. While the Euclidean distance ΔE (CIELAB) represents relative colour change only, a recently proposed scanning densitometric approach translates colour depth into absolute dye surface concentration. Morphological investigations conceal this study investigating the impact of selected process conditions.

In situ selective laser gas nitriding for composite TiN/Ti-6Al-4V fabrication via laser powder bed fusion

Laser-assisted gas nitriding of selective Ti-6Al-4 V surfaces has been achieved during laser powder bed fusion fabrication by exchanging the argon build gas environment with nitrogen. Systematic variation of processing parameters allowed microdendritic TiN surface coatings to be formed having thicknesses ranging from a few tens of microns to several hundred microns, with TiN dendrite microstructure volume fractions ranging from 0.6 to 0.75; and corresponding Vickers microindentation hardness values ranging from ∼ 7.5 GPa–9.5 GPa. Embedded TiN hard layers ranging from 50 μm to 150 μm thick were also fabricated in the laser-beam additively manufactured Ti-6Al-4 V alloy producing prototype, hybrid, planar composites having alternating, ductile Ti-6Al-4 V layers with a hardness of ∼ 4.5 GPa and a stiff, TiN layer with a hardness of ∼8.5 GPa. The results demonstrate prospects for fabricating novel, additively manufactured components having selective, hard, wear and corrosion resistant coatings along with periodic, planar or complex metal matrix composite regimes exhibiting superior toughness and related mechanical properties.

Novel approaches in zero taper, fast drilling of thick metallic parts by ultra-short pulse laser

Use of high average power, high repetition rate, ultra-short pulse lasers jointly with trepanning head (enabling both beam rotation and inclination) has been shown to be an effective tool to obtain holes with high machining quality, zero or even negative taper, aspect ratio as high as > 10 and high throughput. Nevertheless, in standard operating conditions (focal length 50 mm – 100 mm, spot size of 20–30 μm, and pulse energy comprised between some tens and hundred μJ), this technological approach shows its limitations when material thickness is higher than nearly 1 mm. Here a novel approach is proposed consisting of a top-down, hybrid (sequence of trepanning, drilling and trepanning) drilling process. By systematic variation of process parameters (beam inclination angle, focus re- positioning, etc.) this approach has been optimized to drill zero tapering holes in stainless steel 316 L having a thickness varying from 0.9 mm to 2 mm. An analysis of the impact induced by each process step on the hole evolution (both geometry and ablated volume) has been carried out and in particular the role it plays on the hole shape evolution the dust generated by the material ablation before to be evacuated, has been highlighted. Importantly, a zero-tapering hole with aspect ratio of 10 was obtained in a 2 mm thick sample with a processing time of 32 s. Finally, an analysis of the thermal effects on the internal part of the holes was carried out by SEM micrograph and here reported.

Layerwise monitoring of electron beam melting via backscatter electron detection

PurposeThe purpose of this study is the introduction and validation of a new technique for process monitoring during electron beam melting (EBM).Design/methodology/approachIn this study, a backscatter electron detector inside the building chamber is used for image acquisition during EBM process. By systematic variation of process parameters, the ability of displaying different topographies, especially pores, is investigated. The results are evaluated in terms of porosity and compared with optical microscopy and X-ray computed tomography.FindingsThe method is capable of detecting major flaws (e.g. pores) and gives information about the quality of the resulting component.Originality/valueImage acquisition by evaluating backscatter electrons during EBM process is a new approach in process monitoring which avoids disadvantages restricting previously investigated techniques.

Microstructure–fracture toughness correlation in an aircraft structural component alloy Ti–5Al–5V–5Mo–3Cr

Ti–5Al–5V–5Mo–3Cr alloy is a relatively new alloy developed for aircraft structural application where fracture toughness is an important property of consideration. A systematic variation of processing parameters has been carried out to generate different beta annealed microstructures, in terms of their dimensions in this alloy. Quantitative measurements of microstructural features have been carried out using stereological procedures. Different length scales of features have been correlated with the fracture toughness in order to optimize the processing parameters to develop desired microstructure that results in improved fracture toughness. The change in fracture mode associated with different microstructures has been investigated using fractographic analysis.

Influence of Impact Angle and Gas Temperature on Mechanical Properties of Titanium Cold Spray Deposits

Titanium coatings have a high potential for various applications and can be produced in high quality by cold spraying. In this contribution, the two major challenges are addressed: (i) optimizing mechanical properties by systematic variation of process parameters, and (ii) evaluating the influence of the spray angle with respect to complex geometries. High deposition efficiencies of more than 95% can be obtained and the coatings show very low porosities as well as high tensile strength of over 450 MPa by using nitrogen as process gas. The influence of process conditions on the mechanical properties is discussed on the basis of single impact morphologies, coating microstructures, tubular coating tensile, as well as shear tests.

Characteristics of indium zinc oxide thin films prepared by direct current magnetron sputtering for flexible solar cells

The In 2O 3–ZnO (IZO) thin films were prepared on polyethylene terephthalate substrate at room temperature by direct current (dc) magnetron sputtering. The properties of IZO thin films were studied in terms of O 2 concentration and deposition parameters. As the O 2 concentration in O 2/Ar gas increased, the transmittances of the films were increased up to 90% and the resistivities were decreased. The systematic variation of process parameters including dc power, gas pressure and target-to-substrate distance was performed to examine the properties of the deposited films. It was disclosed that there was an optimum O 2 concentration for high transmittance and low resistivity. With decrease in dc power and gas pressure and increase in target-to-substrate distance, the IZO films with high transmittance and low resistivity were obtained. The observation of the IZO films by atomic force microscopy indicated that the microstructure and surface morphology of the films were responsible for the transmittance. It was demonstrated that IZO films with a resistivity of 5.1×10 −4 Ω cm and an optical transmission of 90% in the visible spectrum could be prepared at room temperature on flexible substrates.

Laser assisted Friction Stir Welding of drawable steel-aluminium tailored hybrids

Steel aluminium Tailor Welded Hybrids are still mentioned to be difficult to be joint as intermetallic phases appear during melting welding techniques. These phases are the reason for failure of the joint during loading or forming. As conventional friction stir welding, a solid phase welding technology, is not feasible to join steel and aluminium, laser assistance for preheating the steel sheet is adapted in order to enhance the weldability as well as the welding feed and to reduce the wear at the tool. Tensile tests are performed to achieve mechanical properties of joints, which were welded by systematic variation of process parameters. Finally deep drawing tests are conducted to demonstrate the formability of laser assisted friction stir welded steel aluminium joints.

Strong, high-yield and low-temperature thermocompression silicon wafer-level bonding with gold

A systematic variation of process parameters for wafer-level thermocompression bonding with gold is presented for the first time. The process was optimized for high bond strength and high bond yield. In addition, the impact of the process temperature was investigated. A bond strength of 10.7 ± 4.5 MPa and a bond yield of 89% was achieved when bonding a wafer pair at 298 °C applying 4 MPa pressure for 45 min. A total of ten wafer pairs were bonded in a custom-built bonding tool and tested to establish the optimal process parameters. The bonded interface was found to be strong and dense enough for MEMS applications. The bonds were characterized using pull tests, transmission electron microscopy (TEM) and energy dispersive x-ray spectroscopy (EDS). The TEM inspections indicated that it is possible to form hermetic seals by using the presented bonding method.

Microstructure and residual stresses of a plasma-nitrided M2 tool steel

Abstract Nitriding leads to improved tribological and corrosive properties of iron-alloy components. In order to study the effect of plasma-nitriding parameters on the structure of the compound layer and diffusion zone, a systematic variation of process parameters, temperature and process gas atmosphere has been carried out. Metallographic inspection, X-ray diffraction and glow discharge optical spectroscopy analysis were used in the investigation. The results revealed that, depending on the amount of nitrogen in the gas atmosphere, nitrided layers with and without a compound layer can be generated in the surface of M2 tool steel for temperatures ranging from 350 to 500°C. For plasma nitriding in 5 vol.% nitrogen and 95 vol.% hydrogen, no compact compound layer was formed. The gas mixture of 76 vol.% nitrogen resulted in compound layer formation for all temperatures from 350 to 500°C. X-ray phase analysis indicated an almost 100% ϵ-(carbo)nitride phase, but the existence of the γ′-(carbo)nitride could not be excluded completely from the X-ray phase diagrams. After corrections had been made according to the nitrogen gradient, high compressive surface residual stresses were measured in the diffusion zone and were found to increase with temperature. After a qualitative correction for chemical composition gradients, high tensile residual stresses were found, probably existing in the ϵ-(carbo)nitride phase for the investigated plasma-nitrided tool-steel samples.

Wide-Angle X-Ray, Densitometric and Microscopical Studies on Injection Molded Polypropylene Disks

Abstract Circular disks (280 mm diameter, 2 mm thickness) were injection molded from two grades of isotactic polypropylene under systematic variation of processing parameters (melt temperature, mold temperature, flow rate, packing pressure, and packing time) according to a two-level fractional factorial design. The disks showed ring-shaped zones (“halos”) of enhanced turbidity. The wide-angle X-ray scattering of the disks was measured as a function of the distance from the gate at 13 positions along the radius, using a diffractometer and reflection geometry. These measurements yielded radial profiles of the orientation of α-PP and of the distribution of β-PP crystallites. Both kinds of profiles revealed clear correlations with the polymer grade and with the melt and/or mold temperature. Radial profiles of optical turbidity of the disks were obtained by means of a microdensitometer. Pronounced maxima of turbidity were found to coincide with the maxima observed in the radial distribution of β-PP. An analysis of variance (ANOVA) of the experiments showed that the mass temperature has the greatest influence on the radial distances of the maxima of turbidity. Increasing mass temperature led to decreasing radial distances of the turbidity maxima, whereas the mold temperature as well as the flow rate only had a small influence on the radial positions of the turbidity maxima. The investigation of cross-sections, which were taken from some disks at selected distances from gate, by means of optical microscopy using polarized light revealed significant changes in the morphology with increasing distance from gate, e.g., changes in the size and distribution of β-PP spherulites.

Comparative Wide-angle X-ray and Microscopical Studies on the Layered Structure in Injection Molded Polypropylene Disks

Abstract Circular disks (280 mm diameter, 2 mm thickness) were injection molded from isotactic polypropylene under systematic variation of processing parameters (melt temperature, mold temperature, screw velocity, packing pressure, and packing time). Sections were taken from the disks perpendicular to their surface, at 40 mm distance from gate, in different orientations, and were investigated by means of optical microscopy using polarized light and by spatially resolved wide-angle X-ray scattering. The results from X-ray scans of the cross-sections are presented in terms of several parameters characterizing the state of orientation of α-PP crystallites and the relative amount of β-PP crystallites. The profiles of the various X-ray parameters versus the distance from surface deliver a detailed picture of the layered structure of the cross-sections which is supported and supplemented by micrographs taken with polarized light. The comparison of the results obtained for disks molded under different conditions unveils clear correlations between processing parameters and morphological characteristics of the disks.