毕业设计外文翻译原文

1、Int J Adv Manuf Technol (2014) 72:277288ORIGINAL ARTICLEDOI 10.1007/s00170-014-5664-3Workpiece roundness profile in the frequency domain: an application in cylindrical plunge grindingAndre D. L. Batako & Siew Y. GohReceived: 21 August 2013 / Accepted: 21 January 2014 / Published online: 14 February

2、2014# Springer-Verlag London 2014Abstract In grinding, most control strategies are based on the spindle power measurement, but recently, acoustic emission has been widely used for wheel wear and gap elimination. This paper explores a potential use of acoustic emission (AE) to detect workpiece lobes.

3、 This was achieved by sectioning and analysing the AE signal in the frequency domain. For the first time, the profile of the ground workpiece was predicted mathematically using key frequencies extracted from the AE signals. The results were validated against actual workpiece profile measurements. Th

4、e relative shift of the wave formed on the surface of the part was expressed using the wheel- workpiece frequency ratio. A comparative study showed that the workpiece roundness profile could be monitored in the frequency domain using the AE signal during grinding.Keywords Plunge grinding . Roundness

5、 . Waviness . Frequency . Acoustic emission1 IntroductionGrinding is mostly used as the last stage of a manufacturing process for fine finishing. However, recently, high efficiency deep grinding (HEDG) was introduced as a process that achieves high material removal rates exceeding 1,100 mm3/ mm/s 15

6、. Grinding is mainly used to achieve high dimen- sional and geometrical accuracy. However, in cylindrical plunge grinding, vibration is a key problem in keeping tight tolerances and form accuracy (roundness) of ground parts.Machine tools are designed and installed to have minimum vibration (with ant

7、i-vibration pad when required). Neverthe- less, in grinding, the interaction between the wheel and the workpiece generates persistent vibration. This leads to varia- tion of the forces acting in the contact zone, which in turn causes a variation in the depth of cut on the ground workpiece. Consequen

8、tly, this creates waviness on the circumference of the workpiece. The engendered uneven profile on the work- piece surface leads to a modulation of the grinding conditions of the following successive rotations; this is called workpiece regenerative effect. The building up of this effect can take pla

9、ce in grinding cycles with longer duration. Similar effects occur on the grinding wheel surface; however, the process of the build up is slow 69.It is generally difficult to get a grinding wheel perfectly balanced manually, which is acceptable for general purpose grinding. For precision grinding, au

10、tomatic dynamic wheel balancing devices are used. Though current grinding ma- chines have automatic balancing systems to reduce the out- of-balance of grinding wheels, in actual grinding, forced vi- bration is still caused by the dynamically unbalanced grinding wheels 10. This is because any eccentr

11、icity in the rotating grinding wheel generates a vibratory motion.The stiffness of the wheel spindle and the tailstock also affects the wheel-workpiece-tailstock subsystem, which oscil- lates due to the interaction of the wheel with the workpiece. In practice, the generated force vibration is hard t

12、o eliminate completely. This type of vibration has greater influence on the formation of the workpiece profile. During the grinding process, the out-of-balance of the wheel behaves as a sinusoi- dal waveform that is imprinted on the workpiece surface. This, as in a previous case, leads to the variat

13、ion of depth of cut andA. D. L. Batako (*): S. Y. GohAMTReL, The General Engineering Research Institute, Liverpool John Moores University (LJMU), Byrom Street, Liverpool L3 3AF, UKe-mail: a.d.batakoljmu.ac.ukcreates low-frequency lobes around the workpiece, and this is the key target of the study pr

14、esented here.Other factors such as grinding parameters have to be taken into consideration in the study of grinding vibration becausethese aspects affect the stability of the process. This is because the resulting workpiece profile is the combined effect of different type of vibration in grinding 7,

15、 11. The studies carried out by Inasaki, Tonou and Yonetsu showed that the grinding parameters have a strong influence on the amplitude and growth rate of the workpiece and wheel regenerative vibration 12.The actual measurement of the workpiece profile is an integral part of the manufacturing proces

16、s due to the uncertain- ty in wheel wear and the complexity of the grinding process. Contactless measurement and contact stylus systems were developed to record the variations of the workpiece size and roundness. However, these techniques can be used as post- process checking as it is limited to a p

17、articular set-up and must be used without the disturbance of the cutting fluid in a clean air-conditioned environment with stable temperature 1316. In the industry, random samples from batches are usually inspected after the grinding process. Any rejection of parts or sometimes batches increases the

18、 manufacturing time and cost. Therefore, it becomes important to develop online monitoring systems to cut down inspection time and to minimise rejected parts in grinding. Some of the existing monitoring systems in grinding are based on the wheel spindle power. However, sen- sors such as acoustic emi

19、ssion and accelerometers are also used to gather information of the grinding process for different appli- cation. Dornfeld has given a comprehensive view of the appli- cation of acoustic emission (AE) sensors in manufacturing 17. Most reported applications of AE in grinding are for gap elim-ination,

20、 touch dressing and thermal burn detection 1821.In cylindrical grinding processes, the generated chatter vibration causes the loss of form and dimensional accuracy of ground workpieces. The effect of vibration induces the formation of lobes on the workpiece surface, which are usu- ally detected usin

21、g roundness measurement equipment. High- precision parts with tight tolerance are increasingly in demand and short cycle times put pressure on manufacturing process- es. This leads to the need for developing in-process roundness monitoring systems for cylindrical grinding processes.The potential of

22、using acoustic emission to detect the formation of lobes on a workpiece during a cylindrical plunge grinding process is investigated in this work. The aim is to extract the workpiece roundness profile from the acoustic emission signal in the frequency domain. The extracted fre- quencies are compared

23、 with actual measurement in frequency domain, i.e. harmonic components. The key frequencies of the harmonic content are used to predict the expected profile on the ground part.2 The study of acoustic emission plunge grindingAE is an elastic wave that is generated when the workpiece is under the load

24、ing action of the cutting grits due to theinterfacial and internal frictional and structural modification. The wave generated is transmitted from the contact zone through the components of the machine structure 22, 23. In grinding processes, the main source of the AE signal is the mechanical stress

25、applied by the wheel on the workpiece in the grinding zone 24. The chipping action of the abrasive grits on the workpiece surface generates a multitude of acous- tic waves, which are transmitted to the sensor through the centres and the tailstock of machine. The machining condition is reflected in t

26、he signal through the magnitude of the acoustic emission, which varies with the intensity of the cutting, e.g. rough, medium or fine grinding. The key information of the machining process and its condition is buried in the AE signal. To extract any information of interest from the AE signals, it is

27、important to identify the frequency bandwidth and study the signal in details.Susic and Grabec showed that intensive changes of AE signal relate to the grinding condition, thus the ground surface roughness could be estimated based on the measured signal with a profile correlation function 25. A stro

28、ng chatter vibration in grinding is also reflected in the recorded RMS AE signal. As vibration could generate the waviness on the workpiece, hence, the AE signal was also used to study the roundness profile 26. A comprehensive study of the chatter vibration, wheel surface and workpiece quality in cy

29、lindrical plunge grinding based on the AE signal was carried out recently 27.In roundness measurement systems, the roundness of the part is also given as harmonic components. Generally, the frequency span given by the measurement machine is of low frequency500 Hz and below. This is because the round

30、ness profile deals with the waviness but not with the surface roughness that is always of higher frequency. Fricker 8 and Li and Shin 28 also indicated parts profile of frequency below 300 Hz. Part roundness profile is expressed in undula- tion per revolution. Therefore, lower frequency components a

31、re mainly targeted by the measurement equipment, but higher frequency components tends to ride on top of lower carriers. In most cases, the provided frequency profile is in the range of 300 Hz 8, 28. Therefore, this work studies the AE signal along the grinding process using the fast Fourier transfo

32、rm (FFT) with a particular focus on frequencies below 300 Hz. This allowed for a direct comparison between the results from this investigation and the actual roundness measurements.Figure 1 illustrates the equipment used in this study, where(a) is the configuration of the grinding machine with the l

33、ocation of the sensors and (b) is the roundness measurement machine. To improve signal transmission, the coating of the tailstock was removed from the location of the sensors as shown in this figure.During this study, observations of the shape of the recorded AE and the signal of spindle power indic

34、ated that there are three main phases in a typical cylindrical plunge grindingInt J Adv Manuf Technol (2014) 72:277288279Fig. 1 Experimental equipment: a grinding machine and sensors config- uration, b Talyrond 210 roundness measurement systemcycle, i.e. before grinding, actual grinding and dwell. I

35、n this work, the words “dwell” and “dwelling” are used to describe the “spark out” phase where the infeed stops and the grinding wheel enters a dwelling stage. For short notation, “dwell” is used in most figures.First phase (before grinding): at the beginning of the process, the grinding wheel appro

36、aches the workpiece in a fast infeed without any physical contact between the wheel and the workpiece.Second phase (actual grinding): when the grinding wheel gets very close to the workpiece, the rapid feed changes to the programmed infeed value then the grinding wheel gradually gets into contact wi

37、th the workpiece. The phase starts with the first contact of the wheel with the part and runs until the targeted diameter is reached.Third phase (dwell or spark out): when the target diam- eter is reached, the infeed stops and the wheel stays in contact with the part. The duration of the dwelling pr

38、o- cess varies depending on the grinding conditions and is intended to remove the leftover material on the part due to mechanical and thermal deflection and to reduce the outof roundness. The grinding wheel retracts from the work- piece at the end of the programmed spark out (dwell).In this study, t

39、he power and AE signals were recorded simultaneously; however, the acceleration of the tailstock was also recorded for further investigation. The recorded signals are illustrated in Fig. 2 with a delimitation of the three phases.In addition, the actual grinding phase was subdivided to introduce the

40、notion of “grinding-in”, “steady grinding” and “pre-dwell” as depicted in Fig. 3. The steady grinding ends with a pre-dwell period. There is a transition state between the grinding in and the steady grinding states; this is where the cutting process starts entering the steady state. This is illus- t

41、rated by an ellipse in Fig. 2. During the grinding-in, the depth of cut increases from zero to a constant value per revolution, then the steady-state grinding runs under a constant depth of cut. The pre-dwell section is not an obvious technological phase, rather it is a tool used in this study.To ai

42、d the signal processing techniques, especially the fast Fourier transform and Yule Walker methods, a referenced sampling was introduced using an RPM pickup (see work- piece rotation in Fig. 3). Recording the workpiece rotation simultaneously with the AE signal helped portioning the signal to reduce

43、processing time and to study time-varying process in the grinding.3 Simulation and modelling3.1 Workpiece responseIn this investigation, it was necessary to filter out from the recorded signals the frequencies of other parts of the grinding machine, especially the natural frequency of the workpiece.

44、Fig. 2 Recorded power and acoustic emission signals with process phases .2.2Consequently, the dynamics of the waviness formed with time t at the surface of the part can be expressed as follows: sint 3Therefore, the equation of the wave generated by the wheel at the surface of the workpiece was deriv

45、ed as follows:. sin t 2.43.3 Simulation of the workpiece profileFig. 3 Typical AE signal for one full grinding cycle with RPM outputTherefore, the workpiece response was studied using finite element analysis (FEA) and an experimental impact test to identify its natural frequency. The result of this

46、study is depicted in Fig. 4, where it is seen that the natural frequency of the workpiece is 1,252 Hz. The outputs of the impact test and the FEA are in good agreement and show that the natural frequency of the workpiece is over 1 kHz; consequently, it will not appear in the range of low frequencies

47、 of interest.3.2 Process modellingDesignating the wheel rotational frequency by fs and the workpiece rotational frequency by fw, the ratio of these two entities was expressed as follows: f s= f w1The notion of frequency ratio () helps understanding the generation of the workpiece profile as it relat

48、es key processDuring the roundness measurement process, the machine uses a single trace of the stylus on the workpiece circumference to generate the profile of the workpiece. Here, the stylus is in direct contact with the measured part.However, in this study, an attempt is made for the first time to

49、 predict the final workpiece profile using process signatures extracted from the recorded signals. The link between the prediction model and the grinding process is the sensor, which collects the signal from the entire process. Therefore, the model predicts an average workpiece profile in contrary t

50、o measuring machine which gives only a single trace on the part. The procedure of capturing and extracting process sig- nature is schematically illustrated in Fig. 5.The procedure works as follows: throughout the grinding process, the acoustic emission, vibration and RPM sensor record the signals. T

51、he signals are processed using various techniques (e.g. FFT) to obtain the system response in the frequency domain. The model extracts process-inherent key dominant frequencies, and uses these frequencies and their respective amplitudes to generate the expected profile of the workpiece.The following

52、 expression in Eq. (5) is used to predict the final profile of the ground part.parameters and defines the fundamental harmonic, which naffects the part profile. In this study, it was found that the wheel-workpiece frequency ratio has a direct effect on the Xi1icos2 tf i randt5workpiece roundness as

53、it constitutes the fundamental har- monic for this specific machining configuration.During the grinding process, there is a relative lag between the grinding wheel and the workpiece due to the difference in their rotational frequencies. This difference () is numerically equal to the decimal part of

54、the frequency ratio. This causes the currently forming wave to creep, with reference to the wave formed in the previous revolution of the part. By ex- pressing the wheel angular speed as , and the decimal part of the frequency ratio in Eq. 1 as , the relative shift of the wave on the workpiece surfa

55、ce was defined as follows:Where fi is the ith dominant frequency with an amplitude of i, and t is the time. rand(t) is the added random noise to incorporate the randomness of grits cutting actions.4 Experimental workIn this investigation, the response of the machine tool was studied at different sta

56、ges, namely idle, running by switching its components one by one and recording the signal from oneInt J Adv Manuf Technol (2014) 72:277288287Fig. 4 Workpiece response: aexperiment and b FEAsingle location, and finally in operation conditions while grinding. This allowed identifying and discriminatin

57、g fre- quency components belonging to the machine tools structure and those frequencies induced by noise and interference from nearby operating machineries.An analogue to digital (A/D) converter (NI 6110) was used to record the analogue signals from the power of the motor, the acceleration and the acoustic emission sensors through the tailstock. This A/D device had four channels with a sampling rate up to 5 MS/s per channel, providing a total sampling rate of 20 MS/s. This device allowed for a simultaneous four-channel sampling of analogue inputs