Additive manufacturing (AM) of co-fired low temperature ceramics offers a unique route for fabrication of novel 3D radio frequency (RF) and microwave communication components, embedded electronics and sensors. This paper describes the first-ever direct 3D printing of low temperature co-fired ceramics/floating electrode 3D structures. Slurry-based AM and selective laser burnout (SLB) were used to fabricate bulk dielectric, Bi 2 Mo 2 O 9 (BMO, sintering temperature = 620-650°C, ε r = 38) with silver (Ag) internal floating electrodes. A printable BMO slurry was developed and the SLB optimised to improve edge definition and burn out the binder without damaging the ceramic. The SLB increased the green strength needed for shape retention, produced crack-free parts and prevented Ag leaching into the ceramic during co-firing. The green parts were sintered after SLB in a conventional furnace at 645°C for 4 h and achieved 94.5% density, compressive strength of 4097 MPa, a relative permittivity (ε r) of 33.8 and a loss tangent (tan δ) of 0.0004 (8 GHz) for BMO. The feasibility of using SLB followed by a postprinting sintering step to create BMO/Ag 3D structures was thus demonstrated.

Additive manufacturing (AM) has become more important and common in recent years. Advantages of AM include the ability to rapidly design and fabricate samples much faster than traditional manufacturing processes and to create complex internal geometries. Materials are crucial components of microwave systems and proper and accurate measurement of their dielectric properties is important to aid a high level of accuracy in design. There are numerous measurement techniques and finding the most appropriate method is important and requires consideration of all different factors and limitations. One limitation of sample preparation is that the sample size needs to fit in the measurement method. By utilizing the advantage of additive manufacturing, the material can be characterized using different measurement methods. In this paper, the additive manufacturing process and dielectric measurement methods have been critically reviewed. The test specimens for measuring dielectric properties were fabricated using fused filament fabrication (FFF)-based additive manufacturing and were measured using four different commercial dielectric properties measurement instruments including split post dielectric resonator (SPDR), rectangular waveguide, TE01δ cavity resonator, and open resonator. The measured results from the four techniques have been compared and have shown reasonable agreement with measurements within a 10 percent range.

In modern manufacturing and assemblies, high-dimensional accuracy and fine surface finishing play an important role. One of the most promising methods of fabricating such high-precision parts is magnetorheological finishing process. In cylindrical components grinding, the external surface is ground and by obtaining a high-precision finished surface these components will perform better in mechanical systems. This process is not readily applicable to magnetizable materials, if a high-magnetic field is used. This is due to the attraction of workpiece by magnetic force and preventing it to rotate. In this study, the main mechanism is responsible for the decrease of Ra on external surface of cylindrical workpieces made of non-magnetizable materials, and a new method based on MRF process is examined. The examined specimens in this study are made of aluminum (Al), it is known as a kind of non-magnetizable, soft, and lightweight materials. The apparatus that used for this experiment includes two main motions. The first one is using a rectilinear alternating motion to improve processing conditions, and the second one is specimen's rotational motion. The experiments of this study show the applicability of this method for finishing cylindrical surfaces made of Al.

Purpose The use of microstereolithography (μSL) parts as micro-injection molding (μIM) tools greatly reduces the time and cost to product and offers unique solutions for complex design issues. However, they present challenges to designers because of their strength, thermal characteristics and shorter lifetimes as compared to other mold materials. The purpose of this study is to use SL to build rapid injection mold tools directly combining micro features for short-run production. Design/methodology/approach In total, three tool inserts were produced. Two different μSL mold inserts were produced and evaluated in terms of different build approaches of micro features. One of the inserts includes micro features built horizontally, while the other one collaborates features built vertically, both having same geometrical dimensions. To evaluate the replication capability of prototype tools, two different thicknesses were set for micro features, that is, 30 and 120 μm. The mold inserts were assembled on a metallic mold frame and tested with polypropylene (PP). Findings It was observed that using inappropriate resin to fabricate the mold inserts can lead to inaccurate geometrical dimensions of the tool. Therefore, the material with high glass transition temperature (Tg) and low thermal conductivity is preferred. Also, the results of this research work showed that the processed material and technology play an important role both on part quality and tool life. After investigating the tool failure mechanisms during the injection, it was observed that tool failure occurred mainly because of excessive flexural stresses and ejection forces during the cavity filling and part ejection phases, respectively. Originality/value The paper describes the capability of μSL mold inserts for the production of small batches of micro-cantilevers which are used in MEMS relays.

No abstract

No abstract

Additive manufacturing of co‐fired low temperature ceramics offers a unique route for the fabrication of novel 3D radiofrequency (RF) and microwave components, embedded electronics and sensors. This study demonstrates the fabrication, materials analysis, and RF characterization of a multi‐material bismuth molybdate—silver (Bi2Mo2O9—Ag) artificial dielectric fabricated by laser assisted direct ink writing. The proposed fabrication technique enables 3D printing of dissimilar materials while minimizing inter‐material diffusion through the liquid phases. The permittivity of the artificial dielectrics increased up to 99% over the investigated frequency range (8–12 GHz) compared to the fabricated pure ceramic sample.

An experimental investigation is conducted to study the effect of middle length and inclination angle of an S-shaped channel on adiabatic two-phase flow patterns. To study this effect, three channel lengths of 0.25, 0.50, and 1.00 m, and four bends at the angles of 22.5˚, 45˚, A dimensionless analysis of obtained flow pattern maps is also carried out. It is shown that effect of geometry changes along S-shaped pipeline on two-phase flow pattern transitions is determined by either inclination angle or elevation difference between two horizontal lines. The explained flow mechanisms, obtained flow pattern maps and the transition lines can be used to predict the particular flow pattern that will be established for a given mass flux, inclined length and angle along pipelines.