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The use of advanced brittle composites in engineering systems has necessitated robotic rotary ultrasonic machining to attain high precision with minimal machining defects such as delamination, burrs, and cracks. Longitudinal–torsional coupled (LTC) vibrations are created by introducing helical slots to a horn’s profile to enhance the quality of ultrasonic machining. In this investigative research, modified ultrasonic horns were designed for a giant magnetostrictive transducer by generating helical slots in catenoidal and cubic polynomial profiles to attain a high amplitude ratio (TA/LA) and low stress concentrations. Novel ultrasonic horns with a giant magnetostrictive transducer were modelled to compute impedances and harmonic excitation responses. A structural dynamic analysis was conducted to investigate the effect of the location, width, depth and angle of helical slots on the Eigenfrequencies, torsional vibration amplitude, longitudinal vibration amplitude, stresses and amplitude ratio in novel LTC ultrasonic horns for different materials using the finite element method (FEM) based on the block Lanczos and full-solution methods. The newly designed horns achieved a higher amplitude ratio and lower stresses in comparison to the Bezier and industrial stepped LTC horns with the same length, end diameters and operating conditions. The novel cubic polynomial LTC ultrasonic horn was found superior to its catenoidal counterpart as a result of an 8.45% higher amplitude ratio. However, the catenoidal LTC ultrasonic horn exhibited 1.87% lower stress levels. The position of the helical slots was found to have the most significant influence on the vibration characteristics of LTC ultrasonic horns followed by the width, depth and angle. This high amplitude ratio will contribute to the improved vibration characteristics that will help realize good surface morphology when machining advanced materials.

Performance of workers can be improved by effective design of work. Several work design factors, physiological, psychological, technological, organizational and social, have been identified in research literature. These factors influence the work in different forms, especially in combination with personal characteristics of workers. Manufacturing technologies are also changing with adoption of industry 4.0 practices. The objective of the research was to test whether workers with different personal characteristics had different relationships with work design factors in the conventional setting. The findings for the current conventional setup are extrapolated on an industry 4.0 work design model with important insights and observations. Managerial implications were inferred from the results which indicated age, education and family size as important variables affecting supervision (Mean μ = 4.29) HSE (μ = 4.23), training (μ = 4.35), aptitude (μ = 4.29), pay and welfare (μ = 3.58), job rotation (μ = 3.91), feedback (μ = 4.47), pace of operations (μ = 4.19), in conventional manufacturing. Old, experienced, educated and married workers with children give certain initiatives to management, which should be utilized for better performance in industry 4.0 production work.

Aramid fiber–reinforced polymer composite (AFRPC) is popular in aerospace and defense industries owing to its superior thermal and mechanical properties. However, its intricate hexagonal cellular structure and the material’s heterogeneous, soft, and brittle characteristics lead to significant surface defects, such as burr formation, wall tearing, roughness, dimensional inaccuracies, and uncut fibers during traditional machining. Such poor machining quality issues notably affect the operational lifespan and functional performance of its sandwich structural components. To address these issues, the rotary ultrasonic assisted machining (RUSAM) process has been introduced. To thoroughly investigate the RUSAM of AFRPC using various cutting tools, a 3D finite element model was developed and validated. This paper mainly investigates the effect of various machining parameters such as vibration amplitude (VA), cutting width (CW), feed rate (FR), and spindle speed (SS) on the cutting force, surface morphology, burr formation, and burr height during RUSAM of AFRPC structure by plane and toothed disc cutters. The burr height was found to decrease with the increase of spindle speed (60.82% and 71.00%) and vibration amplitude (78.15% and 82.32%), whereas increase with cutting width ( 149.81 % and 321.16%) and feed rate (156.53% and 314.83%) during RUSAM by plane and toothed disc cutters, respectively. The pattern of variation of burr height with machining parameters was found similar to that of the cutting force. Significance analysis based on 4 levels, 4 factors orthogonal L 16 ( 4 4 ) experiments revealed the cutting width to be the most influential parameter on the burr height and cutting force followed by the spindle speed, feed rate, and vibration amplitude during RUSAM of the AFRPC core by the disc cutters. Up to 62.54 % reduction in burr height was realized by rotary ultrasonic assisted machining compared to the conventional machining. Under specified operating conditions, the disc cutter generates a higher but less number of burr as compared to the toothed disc cutter without any tearing defects. 3–10% and 5–20% burrs were observed during rotary ultrasonic assisted machining compared to 20–50% and 40–70% burrs during conventional machining of AFRPC structure by plane and toothed disc cutters, respectively. This experimental research will be extremely useful to comprehend the burr formation mechanism and optimize the machining parameters for enhanced surface morphology of AFRPC structures.

The applications of Nomex honeycomb composite (NHC) structures in aerospace, automotive and defence sectors have been significantly increasing due to their high compressive strength, hexagonal thin-walled structure, ultra-light weight and excellent thermal resistance. Specific applications include composite sandwich structures in helicopter propellers, satellite cabins, aeroplane floors, engine cowls, wings and nacelles. Accuracy of the machined surface of NHC structures is required for adhesive bonding with face-sheets. Conventional machining processes generate machining defects in terms of tearing, damaged cell walls, burr formation, delamination and poor surface quality that result in reduction of strengths of the core structure and its bond with face sheet. Ultrasonic machining is a proven technique to overcome such machining defects and improve the surface quality of NHC structures. Novelty of this research includes the development of a three-dimensional (3D) finite element model to analyse cutting forces, chip formation and machining quality of NHC structures using disc cutter through both ultrasonic and conventional machining processes by providing feed to the workpiece instead of the cutting tool. The significant influence of machining parameters such as depth of cut, feed rate, ultrasonic amplitude and spindle speed on cutting forces was investigated numerically followed by experimental validation. Numerical model in support with experimental results show that cutting forces decrease by increasing ultrasonic amplitude and spindle speed (up to 54.74% and 62.71%, respectively), and increase with the increase of depth of cut and feed rate (up to 60% and 60.48%, respectively). It was also found that the ultrasonic machining reduces the magnitude of cutting forces as compared to conventional machining (up to 42.74%). Surface morphology analysis through scanning electron microscope also indicated improved machining quality achieved by ultrasonic machining at NHC structures’ hexagonal cells, triple points and walls. A burr formation of 5% was observed during ultrasonic machining of NHC structures for Fy≤3N, while it was found up to 10% if Fy>3N, compared to at least 30% burr during conventional machining. To sum up, the employed methodology can be effectively applied for determining the effect of various machining parameters on cutting forces as well as surface quality, chip formation, structural integrity and dimensional accuracy of machined NHC structures during ultrasonic machining process.

Purpose Utilization of advanced hard and brittle materials in engineering applications has led to the need of non-conventional machining techniques such as rotary ultrasonic machining (RUM) to achieve high dimensional accuracy and low machining defects (delamination, burr and cracks formation, etc.). RUM performance greatly depends on vibration amplitude at tool end which is achieved through appropriate ultrasonic horn design. Longitudinal–torsional coupled (LTC) vibrations, generated by incorporating helical slots in horn design, improve ultrasonic machining quality of hard and brittle materials. In present investigative work, modified ultrasonic horns were designed and analyzed for RUM by producing helical slots in quadratic and cubic Bezier horn profiles to achieve high amplitude ratio ( T A / L A ) within safe stress limits. Methods Modal and harmonic analyses were performed to investigate the influence of depth ( D s ), width ( W s ), angle ( θ s ) and location ( L sp ) of helical slots on the modal frequencies, vibration amplitudes, torsional to longitudinal amplitude ratio and stresses in ultrasonic LTC Bezier horns using FEM. Modified ultrasonic horns were tested for three different materials: steel, aluminum, and titanium after validation with available literature. Results Presently designed horns were found to attain high amplitude ratio and low stresses as compared to the commercial step LTC horn for same end diameters and length. Different stresses (shear, von Mises, radial, tangential and axial) were also computed and plotted along horn axial length for optimum designs and were found well below the endurance limit. Conclusions For the same end conditions and length, cubic Bezier LTC ultrasonic horn is preferable to its quadratic counterpart due to 19.91 % higher amplitude ratio. However, stresses are 24.78 % less in quadratic Bezier LTC ultrasonic horn. The amplitude ratio attained by both types of LTC Bezier horns was found to be significantly greater than that in the commercial LTC step horn, with additional advantage of low stresses. Achievement of high amplitude ratio will help in reduced cutting force and improved surface quality of advanced hard and brittle materials as compared to standard LTC horn design.