Enhanced mass transport during the high temperature processing of ceramics by microwave heating, generally known as the 'microwave effect', has been observed by many researchers and some hypotheses have been proposed to explain it. However it is still a controversial issue, centring on temperature measurement accuracy. The primary goal for the present work was to achieve definitive evidence of the microwave effect via the microwave hybrid processing of ceramics using accurate temperature measurement.


Three temperature measurement techniques, viz. thermocouple, pyrometer and optical fibre thermometer, have been investigated to determine their accuracy during the hybrid microwave heating of ceramic materials. The experimental results, obtained from melting point measurement on vanadium pentoxide and the heating of three other materials with different loss factors and thermal conductivities, showed that the optical fibre thermometer was the best choice. An accuracy of ±2oC was obtained,
provided the probe had been calibrated and was protected from stray radiation from conventional heating elements.


Direct evidence for the microwave effect was sought from experiments involving the sintering and annealing of ceramics at different microwave power levels but using an identical temperature I time profile in each case. Sample temperature was monitored using optical fibre thermometry and sample size, composition and precursor powder size were all varied. Specifically, four main ceramics with different loss factors were investigated, viz. zinc oxide (very lossy), yttria stabilised zirconia (intermediate loss) and alumina and silica (low loss).


The results from the experiments showed that an increase in final density was observed for the samples that saw the highest microwave power level compared to


I
 
those sintered using pure conventional heating, nearly 25% in the largest case for zinc oxide with the highest loss factor among the four investigated materials. This was equivalent to an effective temperature increase of approximately 1OOoC. For the low
loss alumina samples, the increase was extremely small, with the yttria stabilised zirconia intermediate between the two. In addition, during annealing of fully dense ZnO ceramic pellets, enhanced grain growth was observed during hybrid heating compared to pure conventional heating. Temperature gradients within the samples, a major potential cause of the effect, were assessed using two different approaches and found to be

Evidence for the microwave effect during hybrid sintering and annealing of ceramics

Recently, electro-discharge machining (EDM) has become one of the preferred machining techniques for Ni-based super alloys. Although extensive research has been reported on EDM characteristics of Inconel 718, not much information is available on Inconel 825. Owing to the excellent resistance to corrosion, Inconel 825 finds particular application in highly corrosive environment. Therefore, the current investigation aims at studying the influence of different EDM process variable peak current (I p ), duty factor (T au), and pulse-on duration (T on) on various performance characteristics such as material removal rate (MRR), surface roughness (SR), radial overcut (ROC), and surface crack density (SCD). Experiments were designed and carried out using L9 orthogonal array. The most influencing factor for responses MRR, SR, and ROC was found to be I p with percentage contribution of 51.22%, 81.08%, and 54.78%, respectively, while it was T on for SCD with 39.54% contribution. Since EDM involves multiple performanc...

Experimental Investigation and Analysis of EDM Characteristics of Inconel 825

The current state-of-the-art metal additive manufacturing (AM) process still cannot meet the high industry requirements in terms of surface roughness. In addition, there are limited ISO/ASTM standa...

A review on the state-of-the-art of surface finishing processes and related ISO/ASTM standards for metal additive manufactured components

https://cyberleninka.org/article/n/1426657.pdf

A Review on Abrasive Flow Machining (AFM)

This article presents an experimental work and investigation on electrical discharge machining (EDM) of Inconel 718 and 625 superalloys. These superalloys are used for making parts like turbine blades, marine components, and nuclear reactor components. The precise components made up of superalloys which have cylindrical, square, and hexagonal machined features are required regular estimations of cylindricity, circularity, perpendicularity, and parallelism. In this work, EDM of the above said superalloys was carried out and form tolerances were analyzed. The significance of input parameters namely peak current, pulse-on time (T on), and pulse-off time (T off) on the form tolerances were investigated. In addition to these, the influence of individual parameters were also analyzed by analysis of variance (ANOVA) technique.

Analysis of Form Tolerances in Electrical Discharge Machining Process for Inconel 718 and 625

Inconel 718 is a nickel-based alloy designed for high yield, tensile, and creep-rupture properties. This alloy has been widely used in jet engines and high-speed airframe parts in aeronautic application. In this study, electric discharge machining (EDM) process was used for machining commercially available Inconel 718. A copper electrode with 99.9% purity having tubular cross section was employed to machine holes of 20 mm height and 12 mm diameter on Inconel 718 workpieces. Experiments were planned using response surface methodology (RSM). Effects of five major process parameters—pulse current, duty factor, sensitivity control, gap control, and flushing pressure on the process responses—material removal rate (MRR) and surface roughness (SR) have been discussed. Mathematical models for MRR and SR have been developed using analysis of variance. Influences of process parameters on tool wear and tool geometry have been presented with the help of scanning electron microscope (SEM) micrographs. Analysis shows significant interaction effect of pulse current and duty factor on MRR yielding a wide range from 14.4 to 22.6 mm3/min, while pulse current remains the most contributing factor with approximate changes in the MRR and SR of 48 and 37%, respectively, corresponding to the extreme values considered. Interactions of duty factor and flushing pressure yield a minimum surface roughness of 6.2 μm. The thickness of the sputtered layer and the crack length were found to be functions of pulse current. The hollow tool gets worn out on both the outer and the inner edges owing to spark erosion as well as abrasion due to flow of debris.

On Electro Discharge Machining of Inconel 718 with Hollow Tool

The dissimilar metal joints of have been emerged as a structural material for various industrial applications which provides good combination of mechanical properties like strength, corrosion resistance with lower cost. Selections of joining process for such a material are difficult because of their physical and chemical properties. The stainless steel and mild steel dissimilar material joints are very common structural applications joining of stainless steel and mild steel is very critical because of carbon precipitation and loss of chromium leads to increase in porosity affects the quality of joint leads deteriorate strength. In the present study, stainless steel of grades 202, 304, 310 and 316 were welded with mild steel by Tungsten Inert Gas (TIG) and Metal Inert Gas (MIG) welding processes. The percentage dilutions of joints were calculated and tensile strength of dissimilar metal joints was investigated. The results were compared for different joints made by TIG and MIG welding processes and it was observed that TIG welded dissimilar metal joints have better physical properties than MIG welded joints.

/pdf/a-study-of-tensile-strength-of-mig-and-tig-welded-dissimilar-uft8bc2c87.pdf

A Study of Tensile Strength of MIG And TIG Welded Dissimilar Joints of Mild Steel and Stainless Steel

The use of Al-6063 SiCp metal matrix composites (MMCs) in electronic packaging applications, heat sinks for printed circuit boards and for microwave housings necessitates certain degree of machinin...

Experimental investigations into triplex hybrid process of GA-RDECDM during subtractive processing of MMC’s

Ultrasonic-assisted abrasive flow machining (UAAFM) process is being investigated as an effective variant of traditional abrasive flow machining process. This process aims to achieve better surface finish at higher finishing rate. In this process, a relatively high frequency (5–20 kHz) is provided to the workpiece externally using a piezo actuator. This additional effect is also termed as ultrasonic assistance. Owing to this, the abrasives present in the medium hit the workpiece asperities mostly at an angle and at a higher resultant velocity, thereby making them more effective. In the present work, experiments were conducted on EN8 steels (AISI 1040) to evaluate the process performance of UAAFM on the double acting horizontal type setup. Response surface methodology (RSM) technique was used for designing the experimental plan with four input parameters—applied frequency, extrusion pressure, abrasive mesh size, and processing time. The results obtained after machining by UAAFM were also compared with traditional AFM process. It was found that significant improvements in surface finish could be recorded in UAAFM. The maximum percentage improvement achieved in surface finish was 81.02 %, while maximum improvement in material removal was 0.05 %. The machined surfaces were also investigated using different characterization tools such as scanning electron microscope (SEM), X-ray diffractometer, and three-dimensional optical profilometer.

Experimental investigations into ultrasonic-assisted abrasive flow machining (UAAFM) process

Abrasive flow machining (AFM) is a non traditional finishing process used for finishing parts with predominantly irregular geometry. In AFM, material removal and surface finish takes place by flowing viscoelastic abrasive carrier across the surface to be machined. The media (carrier + abrasive) is the key element in the process because of its ability to precisely abrade the selected areas along its flow path. In this study, an attempt is made to develop a new carrier as an alternative to the existing commercially available media. The newly developed carrier is characterized through Fourier transform infrared spectroscopy (FTIR) and Thermogravimetric analysis (TGA). Performance evaluation of the carrier is carried out by considering extrusion pressure, abrasive concentration, viscosity of media, and media flow rate as a process parameters and surface finish improvement and material removal as process responses. The ester based newly developed media is capable of withstanding a temperature to work up to 71°C without changing its characteristics. It is found that the developed carrier is flexible enough to be used in AFM process and performance study reveals that the new polymer based medium yields a good improvement in surface finish as well as material removal. Material removal does not get influenced significantly by the varying media flow rate, but surface finish increases with media flow rate above 796 Pa-s. An operational pressure of 20 bar and abrasive concentration of 50:50 (abrasives: carrier) is observed to be better parameter levels for the conditions attempted in the present study.

S. Rajesha

Papers

On Electro Discharge Machining of Inconel 718 with Hollow Tool

A Study of Tensile Strength of MIG And TIG Welded Dissimilar Joints of Mild Steel and Stainless Steel

Experimental investigations into triplex hybrid process of GA-RDECDM during subtractive processing of MMC’s

Experimental investigations into ultrasonic-assisted abrasive flow machining (UAAFM) process

Performance study of a natural polymer based media for abrasive flow machining