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R.D Entwistle, Curtin University of Technology (Australia)
Brian J. Stone, University of Western Australia (Australia)
Most of the steady state grinding force models for cylindrical grinding show a dependence on the rotational speeds of both the workpiece and the grinding wheel. If, due to the flexibility of the workpiece drive, a torsional oscillation was superimposed on the mean rotational speed of the workpiece, then according to the cutting force models the cutting forces would also vary about their mean. Any variation in the nagnitude and/or phase of the cutting forces must have an influence on the chatter performance of the machine. Mathematical models have predicted that such would be thecase when the natural frequencies of the machine tool structure and the workpiece drive (torsion) are close. An experimental programme was undertaken to test this idea. An artificially flexible workpiece drive was arranged and the chatter of the machine monitored. It was found that the torsional flexibility prevented 'workpiece chatter from arising and, under certain conditions, grinding wheel chatter was suppressed. The paper briefly outlines the hypothesis, describes the experimental arrangement and presents the results showing the beneficial effects. Some practical applications are provided.
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Victor Poblete, Universidad Austral de Chile
Jorge P Arenas, Universidad Austral de Chile
Rolando Rios, Universidad Austral de Chile
E. Millar, Universidad Austral de Chile
This article presents the outcomes of a theoretical and experimental research on vibration and idling noise developed in a set of thirteen circular saws commercially available. The logical difficulty associated to the testing of these two generating sources of noise separately led to the experimentation of these two sources simultaneusly. Due to the fact that it was not easy to find out enough commercially circular saws that allowed the covering and testing of a wide range of variables affecting the generation of noise, modifications in workshop in the geometry of some of them were carried out. It was determined that the natural frequencies increased according to the teeth highness for saws with equal diameter and identical thickness. Furthermore, the natural frequency came out directly proportional to the dimensions of the fixing collar. During the rotation it could be noticed that the natural frequency is divided in two resonance frequencies linearly increased with the angular frequency of rotation. It was observed that the sound pressure level generated by these circular saws varied proportional to the peripherical velocity of rotation.
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Pietro Croce, University of Pisa (Italy)
Pietro Orsini, University of Pisa (Italy)
Walter Salvatore, University of Pisa (Italy)
Vibration control assumes great importance in test bench design, especially when test frequencies vary in a very wide range. The aim of the paper is to illustrate the studies carried out for the design of the insulating foundations of two big test benches to be built in the FIAT Research Center (CRF) in Turin, The benches, that will be located in a suitably modified existing building, are intended to be employed for comfort and fatigue tests on cars of different type and dimensions, Each bench is equipped with four actuators, able to act independently, producing load time histories whose frequency spectra can vary in a very general way between Oand 200 Hz, The two benches, whose individual surface is about 20 m2, differ mainly on the degrees of freedom of each actuator: in the first bench the load direction is vertical, while in the second one the loads can act in any direction, To satisfy the wide set of design constraints a twin insulation system has been foreseen, using both pneumatic suspensions and elastomeric pads, In the paper, the theoretical analysis carried out are illustrated and the results are discussed, justifying the design choices.
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M. Abdul Mazid, University of Technology, Sydney (Australia)
Nong Zhang, University of Technology, Sydney (Australia)
M. Alauddin, BIT Dhaka
M.J.S. Hashmi, Dublin City University (Ireland)
Machine tool spindle vibrations are the major causes of hampering its nor-mal workability. The spindle block elements themselves are the carriers of vibrations called as structure born. This work comprises the research of these reasons and the assessment of vibration by a novel parameter propo-sed to call as scattered energy of vibration. Bearing is a complicated elastic body in the spindle head. Allowed profile irregularities of outer and inner races of spindle bearing, allowed tole-rances of rolling elements manufacturing, fit gapes in the nests of the separator, eccentricity and ovality of these elements, allowed errors in assembly are Identified as the major reasons of vibrations. An effort has been made to show how vibrations are created due to those deficiencies which are accepted in design and manufacturlng of spindles. The spindle vibration is generally evaluated by its frequencies and ampli-tudes. These parameters can define the vibration level of spindle but do not assess vibration affect of spindle block life duration or changes in crystallic structure of materials. The impact forces emanated from vibra-tion or in other words scattered energy of vibration which is dissipited around are determined in the work based on simple mechanics. The total scattered energy can be used in predicting the working surface destruct-ion, suffered from vibrations.
sv970142.pdf (Scanned) TOPZbigniew Dabrowski, Warsaw University of Technology (Poland)
Minimizing of noise atthe operator's cage of engineering machines with complex structure requires the location and the identification of sources. Solving of this task is connected with serious difficulties, resulting from the fact that various sources are characterized by varied degree of correlation and that sound propagation, by the surrounding environment and by the machines structure (generally being a non-linear system) results in phase shift and in additional loss of correlation. Moreover, in the course of work the movements of working attachments cause essential changes of both the paths of propagation and the external field. In such a situation simple methods of separation fail to achieve their purpose. The work undertakes an attempt to propose a measurement procedure which would allow to account for the influence that individual sources have on the total noise in the operators cab, and thus to indicate which source should be silenced (eliminated) first. The work is a direct continuation of the study on modelling of the acoustical structure of engineering machines that was presented at the WESTPRAC 94 Conference, and is based on the extensive empirical material regarding vibration and noise in hydraulic excavators working in the most severe operating conditions (strip pits, quarries, etc.)
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Dae-Hyeon Cho, Samsung Aerospace Industries Ltd. (Korea)
Kwang-Joon Kim, Korea Advanced Institute of Science and Technology (Korea)
Electric motors are the most fundamental source of motion generation mechanisms in both industrial and household products. Noise and vibration problems in such products can be remedied in general at each of the three stages ; source-transmission path-receiver. Some problems, however, caused inherently by the motors can not be successfully resolved by working on the transmission path or the receiver alone. In this regard, importance of the noise and vibration problems in the motor itself has been increasing so far. In this paper, a method is presented, which can calculate electromagnetic forces in quantitative as well as qualitative aspects, based on equivalent transformer circuit. Here the rotor slot skew, permeance fluctuations and rotor dynamics are also taken into consideration. Even though this method does not yield information so detailed as the FEM, the computational burden is very low. By using this method, distributions of the electromagnetic forces in both spatial and temporal frequency domain are investigated and effects of the rotor eccentricity and rotor-slot-opening are also investigated. The reason why the exciting force increases and consequently the noise level goes up in reality with loading is explained. Finally, results of the simulation are compared with the experiments.
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