Periodica Polytechnica Mechanical Engineering

Multi-Dimensional Bisection Method in HIL Environment: Stability and Chatter Prediction in Turning

2023-04-04T07:56:38+00:00

In turning operations, the harmful small-amplitude but high-frequency chatter vibrations are identified in hardware-in-the-loop (HIL) experimental environment by means of the application of a multi-dimensional bisection method. The dummy workpiece clamped to the real main spindle is excited by contactless electromagnetic actuators and the response of the workpiece is detected by laser-based sensors. According to the present and the stored previous positions of the rotating workpiece, the desired cutting force characteristic along with the surface regeneration effect can be emulated by means of a high-performance real target computer. While the conventional experimental results in the HIL environment identify the stability limits of the cutting operation accurately only in a high-resolution grid of the technological parameters, the embedded bisection method reduces significantly both the size of the required grid and the time duration of the measurement by path following the boundaries of the linear loss of stability. Based on this technique, the experimental stability boundary of the emulated turning process is presented in a wide range of spindle speeds.

Experimental Investigation on Churning Power Loss of Splash Lubricated Worm Gear

2023-07-16T10:37:36+00:00

Churning power losses are a complex phenomenon that produces critical power losses when considering the splash lubrication of gear units. This article describes the method to investigate the churning power loss in a worm gearbox. A particular test rig was designed and fabricated to experiment on single start worm gear incompletely submerged in an oil bath. The direct torque measurement technique was used to determine the churning power losses. Experiments have been conducted to determine the impact of a variety of operating conditions on churning power losses, including worm speeds, gear immersion depth, lubricant temperatures, and lubricant type (mineral and synthetic). It was found that the churning losses were significantly affected by the worm shaft orientation, speed of gear, and the depth of immersion (static head). The lubricant's temperature is more essential than the type of lubricant in terms of churning power loss.

Investigation of Weld Forces and Strength of Friction Stir Welded Polypropylene

2023-06-09T06:36:53+00:00

Friction stir welding (FSW) is an advanced joining technology specifically developed for welding materials that are difficult to weld (e.g. polymers). Over the last two decades, more and more research has been published on the applicability and development of the technique on polymeric materials. The aim of the present study is to investigate the applicability of the method for welding polymeric materials and to analyse the effect of the parameters of FSW. In the tests, 4 mm thick polypropylene sheets were welded by varying two welding parameters (tool speed (n) and feed rate (v_f)) in four levels. Thus, a complete experimental design with 16 measurement points was created. During the welding process, the force components on the tool/workpiece were measured, from which the resultant welding force was calculated and the strength of the joints was characterized by tensile testing. The ratio of the tensile strength of the joints and the tensile strength of the material were used to characterise the process in terms of joint efficiency. During welding, the axial force component (F_z) was the dominant force value. The resultant forces (F_e) decreased with increasing n, while they increased with increasing v_f. The tensile strength of the joint, and hence the bonding efficiency, improved with increasing n, while it deteriorated with increasing v_f. The ratio derived from the ratio of n to v_f was also analysed, with an increase in the ratio showing a decreasing trend in the resulting weld strength and an improving trend in the bonding efficiency.

The Comparison of Effects of Liquid Carbon Dioxide and Conventional Flood Cooling on the Machining Conditions During Milling of Nickel-based Superalloys

2023-06-09T06:53:40+00:00

In this scientific study, the authors have dealt with the slot milling of nickel-based superalloys. These alloys are among the most difficult materials to machine and are widely used in aerospace and energy industries. Due to the properties of the material, slot milling is a particular problem because tool wear happens quickly, and tool breakages are common. When these superalloys are machined, very high temperatures occur in the cutting zone, which cannot leave due to the extremely poor thermal conductivity of the material and will therefore transfer to the edges of the cutting tool, causing it to anneal, break off and fail. So, the researchers initiated a new field of research: cryogenically-assisted machining. In this paper, the authors used two cooling methods, the conventional flood cooling and cryogenic cooling with liquid carbon-dioxide (LCO₂). The effects of these cooling methods were tested focusing on the cutting forces, tool wear, chip morphology and surface roughness of the bottom of the slots. The aim was to determine the best cooling methods for these materials. Based on the results, it can be concluded that, LCO₂ has a negative effect on cutting forces, tool life and surface roughness. It only has a positive effect on chip formation. It can be see that, the lubricating effect has a greater impact on tool life, tool load and surface roughness of the milled slots than cooling.

New Top Land Computing Method for Spiral Bevel Gears

2023-03-27T14:18:27+00:00

In this study, we present two methods for determining the top land of bevel gears. One of them that can be found in the professional literature is based on the Tredgold's virtual cylindrical gear model and, corresponding to this, deals with a limited accuracy. The alternative method developed by us is based on a mathematical modelling of the manufacturing process and involves in the computing of the top land dimensions theoretically perfect surface models.

Parameter Study of a Loss Reducing Passive Flow Control Method in a Square-to-square Sudden Expansion

2023-06-08T21:32:58+00:00

The energy consumption of mechanical ventilation in buildings needs to be reduced. An efficient way to achieve this goal is to reduce the hydraulic resistance of the ventilation duct system elements, for example, that of sudden expansions. Ventilation ducts and pipe fittings are frequently of rectangular cross-section. The present paper investigates a passive flow control method in order to reduce the loss coefficient of a square-to-square sudden expansion, where the loss-reducing appendages are short guide vanes, termed as miniflaps, placed at the step edge of the sudden expansion. The turbulent flow is examined numerically using the generalized k-ω model of the Ansys Fluent software for different area ratios of the sudden expansion, miniflap lengths, and miniflap angle setups. The Reynolds number is kept constant at 1.08·10⁵. Based on the results of the numerical simulations, the loss coefficient of the sudden expansion can be reduced by ~20–25% for an optimum miniflap angle between 9° and 12°. Increasing the length of the miniflaps leads to a greater reduction of the loss coefficient up to a miniflap length of 0.3 d_h₁, where dh₁ is the upstream hydraulic diameter of the duct.

The Advantages of Fuzzy Control for Heat Pumps Systems

2023-06-09T06:43:50+00:00

Application of fuzzy control has been observed in various engineering fields due to its ability to handle uncertainties and non-linearities. In this study, the advantages of using fuzzy control in heat pump systems are being investigated. Specifically, the performance of a heat pump system with a conventional proportional-integral-derivative (PID) controller is being compared to that of a heat pump system with a fuzzy logic controller. It has been demonstrated by the results that the fuzzy control-based heat pump system offers better performance in terms of energy efficiency, temperature control, and overall system stability. This study contributes to the understanding of the potential benefits of fuzzy control-based heat pump systems and provides a foundation for further research in this area.

Design and Analysis of EN19 Centre Crankshaft

2023-06-15T09:13:04+00:00

Crankshaft is the one of the most important components in internal combustion engines, it converts the translation motion of piston generated due to gas force into rotational moment of engine shaft though oscillatory motion of connecting rod. It mostly experiences the bending and torsional moment. The present research is focused on investigation of alternative material for crankshafts. Material EN19 is considered in this study and strength performance is verified under different operating conditions. Analytical design calculations, 3D modelling and analysis of EN19 crankshaft is carried out under maximum bending moment and maximum torque. 3D modeling and analysis was done in Creo parametric software and Ansys respectively. The compressive stresses, Von-Mises stresses, shear stresses and deformation in crankshaft are found to be within the permissible limits. Result shows cost effective material EN19 can be used as one of the alternative materials for crankshaft as it satisfies the all-strength requirements.

Robotic Drilling of Aluminum Alloy

2023-07-13T20:08:45+00:00

This paper presents an experimental approach to evaluate the ability of a six-axis industrial robot to drill aluminum alloy parts. A strategy based on statistical tests has been studied to quantify and predict the relative contribution of cutting parameters on cutting force and shape errors during drilling. This technique is based on the identification of relevant sources of error during high-speed robotic fitting. The machining quality was quantified in terms of dimensional and geometric tolerance, chip formation and evacuation, burr formation, edge build-up, tool wear and surface damage. Statistical analysis of the experimental results reveals a strong dependence between part accuracy and drilling force. An experimental model was developed to represent and predict the cutting force during drilling and an accurate error prediction capability was distinguished. It was found that at high cutting speed and feed rate, the cutting force was the main source of error affecting the accuracy of the machined parts. Verification experiments are performed, and the results reveal that dimensional defects are significantly reduced by a heat treatment effect (90 HRE) and the thrust force decreases with an increase in cutting speed. The recommended cutting speed for robotic drilling is 6000 rpm with a feed rate of 0.15 mm/min. This study provides important technical guidance for improving the robotic drilling of aluminum alloy in practice.

Investigation of the Effect of Heat Treatment Time in Case of Recrystallization of Al99.5

2023-06-19T11:27:30+00:00

In this study the effect of heat treatment time was investigated in case of recrystallization of Al99.5 material samples. Two different type were manufactured based on the previously applied cold forming. 12% and 24% cold forming was applied to the samples before the heat treatment procedure, which was always at 570 °C and cooled in water. Six different heat treatment time were investigated, namely 5, 10, 30, 60, 120 and 240 minutes. After the recrystallization procedure the microstructure and the mechanical properties were determined. It was found that in the case of the 12% cold formed samples after 30-minute-long heat treatment there were still signs of the original microstructure, however it does not affect the mechanical properties. The yield strength and the ultimate tensile strength were independent of the heat treatment time; they were only dependent on the grain size which was expected. A strong dependency can be discovered between the elongation at break and the heat treatment time. A tangent hyperbolic function was fitted on the measured data, which showed that the asymptote was ~29% for both type of samples. This is a 25% increase compared to the 5-minute-long heat treatment time samples, and this value was reached after ~120 minutes. Another result was that the elongation at break dependency on the grain size is decreasing with increasing heat treatment time.