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1、Effect of misalignment on the cutting force signature in drillingA. Al-HamdanMechanical Engineering Department, Mutah University, Mutah, Karak, JordanReceived 27 June 2000; accepted 2 January 2002AbstractThis paper presents a study which investigates the effect of misalignment between the axes of ro
2、tation of drill and the workpiece on thesteady-state anddynamicofthe axialcuttingforce andtorque.Anovelmethodologyhasbeenproposedtomeasure the misalignment betweenthe axes of rotation of the drill and the workpiece. This uses a laser-based system to measure this misalignment, where a reference beam
3、hasbeen generated by a laser tube, which is held in the chuck of the machine using a special enclosure. The laser beam is captured by a photosensor camera having a video capture card. To study the effect of the misalignment, the starting bush was intentionally misaligned by movingthe pressure head o
4、ver the carriage using the lead screw of the cross slide.Keywords: Metal cutting; Drilling; Deep-hole machining; Image processing; Misalignment; Cutting forces1. IntroductionThe relative position and motion between the tool andworkpiece may affect both the steady-state and dynamiccutting forces dram
5、atically. Thus it becomes difficult todistinguish betweenthe cutting signaturedue tothe dynamicresponse of the cutting process and that due to the noiseoriginating from any inaccuracy in the position of theworkpiece relative to the cutting tool. Surprisingly, therehasbeenlittleattentionpaidtothiseff
6、ectinpreviousstudies.Some of the scatter in the cutting force measurementsreported in the literature may be partially explained bythe mentioned inaccuracy. This becomes particularly impor-tant if a new model of chip formation has to be verified byexperiments.In deep-hole drilling (BTA), the relative
7、 location of thetool and the workpiece is defined by the relative location ofthe axes of rotation of the tool, workpiece and starting bushas shown in Fig. 1.Sakuma et al. 13 investigated run-out in deep holesdrilled under different misalignment conditions. The authorskept changing between gun drills
8、 and BTA drills whenrunning experiments with different setups. Thus the workhas no clear reference to a particular type of tool or toolgeometry.Furthertothisnoinformationwasprovidedontherigidity of the boring they used in the experiments.Intool rotating systemsthe misalignment of the pilot bushorato
9、olshanksupportmakesthe pathofthetooldeviate andcauses the axes to deviate from a straight path 4. Being aself-guided machining process, the straightness error on thehole axis is further affected by the rigidity of the toolworkmachine system. The straightness of the hole axes producedby BTA drilling
10、is usually measured as the run-out measure-ments are influenced by the setting errors while drilling,namely offset and nonparallelism of axes of tool and work-piece. Therefore, a different approach is necessary to studythe error on the straightness of the axis, eliminating thesetting errors 5.Katsuk
11、i et al. 6 studied the influence of the shape of thecutting edge on axial hole deviation in deep drilling.So far, there has been no systematic study of the overalleffect of misalignment on tool wear and tool performance,except for the study on its effect on run-out 3. In general,authors attribute a
12、variety of undesirable effects to misalign-of the misalignment assurance setup. This followed by thepresentation and discussion of the experimental results. Thelast section outlines the conclusions of this study.2. Cutting forces measurement2.1. Experimental setup1. Machine. Fig. 1 shows the drillin
13、g machine installationused in the experiments. The installation consists of adrive unit, a pressure head, a boring bar and the drillhead. The stationary workpiece-rotating tool workingmethod was used in the experiments.2. Dynamometer. A 2-component piezo-electric loadwasher (Model 9065) was used to
14、measure the cuttingforces. The transducer incorporates two disks, each witha ring of quartz crystals precisely oriented in thecircumferential and axial directions. The load washerwas integrated into a dynamometer to be held in thechuck. Based on the standard mounting as specified bythe supplier (Kis
15、tler), the load washer was preloaded bytwo flanges to 120 kN. At this preload, the range for theaxial force measurements was ?20 to 20 kN and therange for torque was from ?200 to 200 N m.Fig. 1 shows the schematic arrangement of cutting forcemeasurement setup. The load washer was connected to acharg
16、e amplifier (Kistler model 5004) and in turn to a dual-channel FFT spectrum analyser (B&K Analyser Type 2032).The setup was calibrated statically and dynamically.The dynamic calibration of the dynamometerworkpiecemachinetool system was carried out to avoid measuring thevibration of the tool instead
17、of the force fluctuations anddetermine the frequency band, over which the dynamometercould be used for reliable measurements. Also, the fre-quency response was measured to determine the range offrequencies of the cutting forces, which could be measuredaccurately without distortion. The load washer w
18、ith alliedcharge preamplifiers and the FFTanalyser was calibrated byFig. 1. The schematic arrangement of the cutting forces experimental setup.84A. Al-Hamdan/Journal of Materials Processing Technology 124 (2002) 8391strikingthedynamometerwithKistlerhammer(Model912).To examine the validity of the mea
19、surement, the coherencefunction was calculated for the thrust force and the torque.2.2. Cutting toolBTAS system partioned boring heads of 1 in. diameter(Sandvik design) were used. A detailed diagram in Fig. 2shows the drill design and the geometry. The cutting edgeis divided into three sections. The
20、 geometry parameters ofthe drills were controlled according the American NationalStandard B94.50-1975. Each cutting edge was examined atmagnificationof20?forvisualdefectssuchaschiporcracks.2.3. Workpiece materialStainlesssteel(AISI303)wasusedasworkpiecematerial.The composition, the element limits an
21、d the deoxidisationpractice were chosen according to the requirements ofANSI/ASME B94.55M-1985 and were requested from thesteel dealer.3. Misalignment measurement setupThe schematic arrangement of the experimental setup onthe deep-hole machine is shown in Fig. 3. A photograph ofthe experimental setu
22、p is shown in Fig. 4. A laser-basedmeasurement system was developed to measure the mis-alignment between the axes of rotation of spindle nose andthat of the starting bush of the deep-hole machine. Areference laser beam was generated by a laser tube, whichwas held in the chuck of the machine using a
23、specialenclosure. The laser beam was captured by a photo sensorcamera havingavideocapture card.The outputimages weresent to image processing software to track the laser beamposition by processing these images. The output from theimage processing software provided the position of theFig. 2. BTAS tool
24、s of partioned cutting edges (Sandvik design).A. Al-Hamdan/Journal of Materials Processing Technology 124 (2002) 839185centroid of the laser beam on the photo sensor in a certainposition along the axis of rotation of the machine. Themisalignments were calculated by comparing the averagecentroid of t
25、he captured images when the photo sensorcamera and starting bush axes coincide and when thecamera and nose spindle axis coincide. To align themachine, this centroid had to be brought to coincide withthe zero reference point. The zero reference point wasestablished on the axis of the cylindrical came
26、ra housingwithin a reasonable tolerance (0.5 mm). A special accessorywas designed to hold the camera in different positions alongthe axis of rotation of the machine. To study the effect ofmisalignment, the starting bush was intentionally misa-ligned by moving the pressure head over the carriage usin
27、gthe lead screw of the cross slide. Fig. 5 shows a photographof the principal elements of the misalignment measurementsetup as follows:1. Laser (LTT4H adjustable alignment tool, EmergingTechnologies, Laseraim Tool Division, Little Rock, AR,Fig. 3. The schematic arrangement of misalignment experiment
28、al setup.Fig. 4. A photograph of the experimental setup for misalignmentmeasurement.Fig. 5. Photograph of the principal elements of misalignment setup.86A. Al-Hamdan/Journal of Materials Processing Technology 124 (2002) 8391USA). This laser projected a straight beam visible as adot of laser light on
29、 distant surfaces. This beam isused as a straight reference line over its entire length.The tool had an adjustable focus feature which cancontrol the laser dot size on a surface locatedperpendicular to the beam (referred to as the screen).This adjustment allowed the use of the smallest possibledot s
30、ize at a specific distance, thus facilitating moreaccurate measurements. Since the focus adjustment wasalso linear, a change in the focus would not affect the Xand Y alignment. In practical terms, this means that thesmallest possible dot size could be used close to the tooland then when the screen w
31、as more distance, the toolmay be re-focused again to the smallest possible dot,keeping the centroid of these two dots on the sameplane.2. A photo sensor digital camera Pulinx TM7 was used asthe screen. This camera contained a high resolutioninterline transfer 0.5 in. CCD (charge-coupled device).The
32、camera was requested from the manufacturer to beof super mini size that allows accurate and convenientmounting within the setup.3. Laser mounting fixture.4. A special case was devised to mount the camera indifferent positions along the machine bed. This case wasprecisely manufactured to: (a) match t
33、he cone in thestarting bushing liner, (b) match the diameter of thecamera and (c) match the outer diameter of the spindlenose.5. Video capture card. This card was a single-slot,accelerated, 24 bit-per-pixel, true-colour, designed tocapture and display high quality video images. The cardprovided the
34、complete set of camera control functionsrequired for capturing high quality images. The cardis also supported with a fully comprehensive softwarethat allows full exploitation of the hardware architec-ture. Captured images could be saved as BMP or TIFFfiles.6. Image processing software (Matrox Inspec
35、tor, Version2.0). The images captured by the camera were processedto find the centroid of the images. The centroidrepresented the centre of rotation of the boring bar.A typical example of the captured images and theprocessed images along with the results of the processingis shown in Fig. 6.4. Calibr
36、ation of the misalignmentmeasurement systemTo ensure the repeatability and reproducibility of theproposed technique, special care was paid to the calibrationof the proposed system. The first step in the calibrationprocedure was to align the laser beam parallel with the caseof the laser. This provide
37、d parallelism at any distance andcould be used as a reference over the entire length of thebeam.Toalignthelaser,aV-blockwasusedtocheckthattheprojected dot image was concentric and centre of the dotshould remain in the same position. The second step was tocheck that the laser coincided with the axis
38、of the chuck byadjusting the beam using the X and Y micrometer heads untilthe projected dot image was concentric with the chuck. Thethirdstepwastocalibratethelasercameraimageprocessorsystem. To do this, a coordinate device was designed asshown in Fig. 5. The setup of the calibration is shown inFig.
39、3. The camera was mounted on the coordinate deviceand was displaced in the X- and Y-directions by the micro-meter heads. The image produced by the laser beam wascaptured and processed. The results of the image processingwere compared with the actual displacements (intentionallydisplacement) of the c
40、oordinate device. Fig. 7 shows thecalibration curves for the system. It can be seen that anexcellent agreement between the actual displacements of thecoordinate device and the measured values of the proposedsystem was achieved.5. Experimental procedureTo obtain different misalignments, the starting
41、bush wasintentionally misaligned by moving the pressure head overthe carriage using the lead screw of the cross slide and thenthe misalignments was calculated by comparing the aver-age centroid of the images which was captured when thephoto sensor camera and starting bush axes coincide andwhen the c
42、amera and nose spindle axes coincide. To alignthe machine, this centroid has to be brought to coincidewith the zero reference point. The zero reference point wasestablished on the axis of the cylindrical camera housingwithin a reasonable tolerance (0.5 mm). Under each mis-alignment (15, 205, 422 and
43、 856 mm) value the autospectraof axial cutting force and the torque was measured forFig. 6. An example of the captured image and the results of the imageprocessing.A. Al-Hamdan/Journal of Materials Processing Technology 124 (2002) 839187Fig. 7. Calibration of the proposed misalignment measuring syst
44、em in the horizontal and vertical directions.Table 1Effect of misalignment on the measured steady-state axial cutting forcesRotational spindlespeed (rpm)Cuttingspeed (m/min)Feed (mm/rev)Measured axial cutting force (N) for misalignment of15 mm205 mm422 mm856 mm626500.082020.52306.52702.73100.40.1230
45、56.43200.63456.83890.20.163907.54106.94389.34620.9939750.081950.62356.92760.93178.90.123002.53245.13506.93910.90.163811.44165.24487.44710.612531000.081900.42400.62810.33206.90.122983.43290.23610.73967.90.163778.44208.74520.84804.8Table 2Effect of misalignment on the measured steady-state cutting tor
46、queRotationalspindle speed (rpm)Cutting speed(m/min)Feed (mm/rev)Measured cutting torque (N m) for misalignment of15 mm205 mm422 mm856 mm626500.0819.4921.2324.4728.830.1230.4332.8434.2338.720.1638.6941.5743.4445.91939750.0820.0121.8224.5428.950.1230.4233.1335.1938.940.1637.4541.8344.2846.9212531000.
47、0819.5222.1224.8329.340.1229.7833.4535.9839.560.1638.3242.9545.4347.6788A. Al-Hamdan/Journal of Materials Processing Technology 124 (2002) 8391different combination of feed (0.08, 0.12 and 0.16 mm/rev)and rotational speed (626, 939 and 1253 rev/min).6. Results and discussionTables 1 and 2 quantify t
48、he effect of misalignment on thesteady-state axial cutting force and cutting torque, respec-tively, for different cutting regimes and misalignment. Thedata in these tables are obtained from the frequency auto-spectra of the axial dynamic cutting force and dynamiccutting torque at frequency of 0 Hz.
49、As seen from thesetables, the misalignment affects the results dramaticallysince an increase in the steady-state axial cutting forceand cutting torque can be noted as the misalignmentincreases. In particular, the axial cutting force and cuttingtorque increase with increasing cutting feed much moresi
50、gnificantly than with the cutting speed. The experimentalFig. 8. Effect of the misalignment on the cutting axial force signature. Cutting conditions: cutting feed, 0.12 mm/rev; rotational speed, 1253 rev/min.A. Al-Hamdan/Journal of Materials Processing Technology 124 (2002) 839189results readily exp
51、lain the significant scatter in the reportedexperimental results on the steady-state cutting force mea-surements in deep-hole machining 3,811. Since in theliterature, the misalignment has never been reported, thismakes correlation of different reported results very difficult.Also,thepresentresultssu
52、ggestthatpreviousstudiespresentan incomplete picture of the BTA. Deep-hole machiningcombines two processes: drilling and burnishing and theforces generated in drilling are used to complete burnishing.As shown by Griffiths 9, burnishing defines the quality ofthe machined surface in terms of its rough
53、ness, roundness,residual stresses, etc. It is also known that this process isrelatively sensitive to the burnishing force applied. For agiven drill design, the ratio cutting force:burnishing forceis constant and therefore a change in the cutting forcedirectly affects the corresponding change in the
54、burnishingFig. 9. Effect of the misalignment on the cutting torque signature. Cutting conditions: cutting feed, 0.12 mm/rev; rotational speed, 1253 rev/min.90A. Al-Hamdan/Journal of Materials Processing Technology 124 (2002) 8391force. This simple consideration explains a significant scat-ter in the
55、 reportedresults on quality inthe machining surfacein deep-hole machining. This also explains the relativelypoor productivity of deep-hole machining since the sametools are used in the machines having different misalign-ments that causes the scatter.Figs. 8 and 9 show the frequency autospectra of th
56、eaxial dynamic cutting force and dynamic cutting torque,respectively, under the same cutting feed and cuttingspeed for different misalignments. The misalignmentshows up as a series of harmonics associated with therunning speed. Comparing the autospectra of the axialcutting force under different misa
57、lignments for the samecutting feed and spindle rotational speed show that themisalignment introduce a series of different amplitudeharmonics at frequencies associated with the multiple ofthe running speeds (2X, 4X, 6X, etc.; X is the frequencycorresponding of the running speed). For example at 1253r
58、ev/min, the misalignments show up at 42, 84, 168 Hz, etc.In the case of the cutting torque, the misalignments alsoshow up as a series of different amplitude harmonics but atfrequencies associated with an odd number of the runningspeeds (3X, 5X, 7X, 9X, etc.; X is the frequency corre-sponding of the
59、running speed). For example at runningspeed of 1253 rev/min, the misalignment shows up at 63,105 and 147 Hz, etc.From these figures it was easy to distinguish between theharmonics caused by the misalignment and that caused bythe imperfections of the machine by comparing frequencyautospectra of the a
60、xial dynamic cutting force and dynamiccutting torque when the machine is near perfect (misalign-ment: 15 mm) and when the machine is under misalignmentof 205, 422 and 856 mm.Comparing the autospectra of the axial cutting force andcutting torque under different misalignment for the samecutting feed a
61、nd spindle rotational speed show that theamplitudes of the different harmonics increase as the mis-alignment increases.Also, it can be noted that in the case of the axial cuttingforces, the dominant amplitude is associated with the secondharmonic (2X) of the operating speed where the amplitudesof th
62、e spikes which are observed at the forth, sixth, etc.,harmonics are seen to be progressively lowered. In the caseof torque, the dominant amplitude is associated with thethird harmonic of the operating speed. This spike which wasobservedatthethirdharmonicwasalsoseenatfifth,seventh,etc., though the am
63、plitude was seen to be progressivelyreduced.7. ConclusionsThe important conclusions which follow from theobtained results are:1. The deep-hole machining system has very distinctdynamic signatures under different misalignments. Asseen from the results, if the deep-hole machining systemis aligned, it
64、is much more dynamically stable. Inpractical terms this means that there is a reducedpossibility of lobbing which is considered as an inherentfeature of deep-hole machining 3,10,11 to occur.Unfortunately, in the known literature on these commondefects, the misalignment has never been considered.2. T
65、he misalignment changes the autospectra in suchmanner that it becomes difficult to distinguish betweenthe spectra that reflects the cutting process contributionand the spectra that come from other sources.References1 K. Sakuma, K. Taguchi, A. Katsuki, Behavior of tool and its effects onprofile of ma
66、chined hole, Bull. Jpn. Soc. Prec. Eng. 14 (1980) 143148.2 K. Sakuma, K. Taguchi, A. Katsuki, The burnishing action of guidepads and their influence on hole accuracies, Bull. JSME 23 (1980)1623.3 K. Sakuma, K. Taguchi, A. Katsuki, Self-guiding action of deep holedrilling tools, Ann. CIRP 30 (1) (198
67、1) 811815.4 A.S. Choudhury, H.R. Guptha, R. Srinivasan, Experimental result onprecision hole making using BTA system, in: Proceedings of the 10thAIMTDR Conference, Durgapur, India, December 1982, CentralMechanical Engineering Research Institute, p. 136.5 M.S. Shunmugam, On assessment of geometric er
68、rors, Int. J. Prod.Res. 24 (2) (1986) 413425.6 A. Katsuki, K. Sakuma, H. Onikura, Axial hole deviation in deepdrillingthe influence of the shape of the cutting edge, Bull. Jpn.Soc. Prec. Eng. 14 (1987) 5056.7 ASTME (Ed.), Gundrilling, Trepanning and Deep Hole Machining,Dearborn, MI, 1967.8 B.J. Grif
69、fths, The machining action during deep-hole boring and theresultant hole force and force system, in: Proceedings of the SecondInternational Conference on Production Research, Copenhagen,Denmark, 1973.9 B.J. Griffiths, An investigation into the role of the burnishing pads inthe deep hole machining pr
70、ocess, Ph.D. Thesis, Department ofProduction Technology, Brunel University, 1982.10 K. Sakuma, K. Taguchi, A. Katsuki, Study on deep-hole drillingwith solid boring tool the burnishing action of guide pads andtheir influence on hole accuracies, Bull. JSME 23 (185) (1980) 121.11 K. Sakuma, K. Taguchi, A. Katsuki, Study on deep-hole boring by aBTA system solid boring tool-behavior of tool and its effects on theprofile of the machined hole, Bull. JSME 14 (3) (1980) 143.A. Al-Hamdan/Journal of Materials Processing Technology 124 (2002) 839191
