ncremental sheet forming (ISF) is one the manufacturing methods for sheet metal parts which has an increased rate of flexibility combined with relatively simple and cheap common technological equipment. This paper presents the results of researches on ISF performed on a CNC lathe, for thin sheet parts made of DC04Am mild steel. The main objective of the paper was to establish the maximum wall angle of the parts and its dependence on the main parameters of the process: thickness and diameter of the part, the tool radius, the feed rate, the spindle speed and the lubricating/cooling conditions. The tests were performed with original equipment designed by the authors and the results were commented and presented in diagrams and images of the parts. The main conclusion is that ISF on a CNC lathe can be successfully used for manufacturing conical shaped parts made of mild steel thin sheet, having a certain maximum angle of the parts wall, for small sized batches. The limit values of the parameters analyzed are a useful technological database for engineers.
Incremental forming is one of the manufacturing methods which uses relative simple technological equipment and can assure a high rate of the process flexibility. These requirements can assure the efficiency demanded by the industrial market, in the case of small production batches, which occur more and more often nowadays. To ensure the stability of the process, the required quality and dimensional accuracy of the parts have to be well controlled. This requires the evaluation of the parts dimensions by certain measurements. For hollow parts, the measurement of their thickness is always a challenge, mainly when the dimensions are smaller and their depth is greater. This paper presents a digital method for the parts dimensional evaluation and analysis, which can be very accurate and does not need mechanical contacts with the part during measurements. The parts were scanned with a 3D blue light scanner, on their both sides and then the data was processed into specialized software, to obtain the parts digital surface from the 3D scanned data. The digital data was compared with the theoretical approach, to establish some conclusions on the validity of the sinus law and to point out the critical zones, where the thinning is strong and may cause fractures. The digital scanning method presented can be used also for quality control and inspection, as the processing steps are considered user-friendly and easy to adapt to certain specific requirements.
This paper presents a theoretical study of the dynamic behaviour of a wind turbine consisting of a wind rotor, a speed increaser with fixed axes, and a counter-rotating electric generator, operating in variable wind conditions. In the first part, the dynamic analytical model of the wind turbine mechanical system is elaborated based on the dynamic equations associated with the component rigid bodies and the linear mechanical characteristics associated with the direct current (DC) generator and wind rotor. The paper proposes a method for identifying the coefficients of the wind rotor mechanical characteristics depending on the wind speed. The numerical simulations performed in Simulink-MATLAB by MathWorks on a case study of a 10 kW wind turbine highlight the variation with the time of the kinematic parameters (angular speeds and accelerations), torques and powers for wind system shafts, as well as the mechanical efficiency, both in transient and steady-state regimes, considering variable wind speed. The analytical and numerical results are helpful for researchers, designers, developers, and practitioners of wind turbines aiming to optimise their construction and functionality through virtual prototyping.
The precision cold shearing is a production process used for intermediary parts or even final parts manufacture, from round metal bars or other laminated profiles, obtaining a high dimensional and geometric precision, and higher surface quality in comparison with conventional metal shearing processes. There are well-known two methods of precision cold shearing, by conventional shearing or by material torsion. The precision cold shearing by material torsion is suitable for parts manufactured from metal bars which do not have a round transversal section, or various laminated profiles, where the conventional shearing process is difficult to be implemented and to obtain similar results. In the literature, there is presented a special machine tool for metal bar shearing by material torsion. The disadvantage of this machine tool is that the manufacturing costs for such a machine tool are at a very high level. The paper presents a simple device for metal bar precision cold shearing by material torsion which can be easily implemented using a conventional simple action mechanical or hydraulic press. The device uses the principle of spatial material compression, before the proper shear, using a simple lever system, and it is recommended for precision cold shearing of hard and medium-hard materials.
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