Methodology for Data Processing: Calculation of Cutting Force, Moment and Peak-to-Valley during Drilling Processes

Transcription

1 Methodology for Data Processing: Calculation of Cutting Force, Moment and Peak-to-Valley during Drilling Processes M. Tash 1, 2, F. H. Samuel 1, F. Mucciardi 3, H. W. Doty, 4 S. Valtierra 5 1 Université du Québec a Chicoutimi, Chicoutimi, Québec, Canada 2 Cairo University, Giza, Egypt 3 McGill University, Montreal, Québec, Canada 4 General Motors Powertrain Group, Metal Casting Technology,Inc.,Milford,NH, USA 5 Corporativo Nemak, S.A. de C.V., Research and Development, P.O. Box 1, Bosques del Valle Garza Garcia, N.L , Mexico

2 ABSTRACT Heat treated Al-Si-Mg and Al-Si-Cu-Mg cast alloys, belonging to the Al-Si alloy system and represented respectively by 356 (M1) and 319 (M2, M3, M4 and M5) alloys containing mainly α-fe-intermetallic and related to hardness levels of (1±1 HB), were selected for the machinability study, due to the high demand of these alloys in the automobile industry In this paper, one was provided with an introduction to the force and moment calculations that were used to evaluate the drilling processes as are outlined in a previous work. 1 A new technique was developed whereby a low pass filter was incorporated in the signal processing algorithm which was used in calculating the mean cutting force and moment during the drilling processes. All signals were independently monitored, digitized and recorded into Lab View. Universal Kistler DynoWare software was used for force measurements and data processing of cutting force and moments. Matlab programs were developed for data processing and for calculating the mean value of cutting force and moment and their standard deviations in drilling tests. The raw cutting force data were analysed using the application of a low pass filter and following the detection of points within each cycle in the signal in the drilling tests. 16 sample points per cycle were acquired for calculating the mean value of cutting feed force (Fz) and 12 sample points per cycle for the other five components of force and moment (Fx, Fy, Mx, My, and Mz) in each signal (115 cycle or hole/signal) however, 1

3 only 2 sample points per cycle were used for standard deviation or peak-to-valley calculations. 1 INTRODUCTION In this paper is presented an introduction to the force and moment calculations which are used as a way of evaluating different kinds of machining processes such as drilling. A new technique was developed whereby a low pass filter was incorporated in the signal processing algorithm which was used in calculating the mean cutting force and moment during the drilling processes. Evaluating machinability based on the cutting forces requires adequate piezoelectric sensor technology. The piezoelectric force measuring system differs considerably from other methods of measurement. The forces acting on the quartz crystal element are converted to a proportional electric charge. The charge amplifier converts this charge into standardized voltage and current signals, which can then be evaluated by signal processing. A Kistler 6-component piezoelectric quartz crystal dynamometer (type 9255B) was used for 6-component force and moment (Fx, Fy, Fz, Mx, My and Mz) measurement during drilling tests. A Kistler multi-channel charge amplifier type (517B18) with 8 independent measuring channels was used in combined force and moment measurement using piezoelectric multi-component dynamometers. The eight output signals were fed directly to the eight charge amplifiers by the eight-core connecting cable type 1677A5/1679A5. All signals were independently monitored, digitized and recorded into Lab View where DynoWare software was used for force measurements and data processing of cutting forces and moments. The Matlab output results for all components of force and moment and their standard deviations in drilling tests were put into an Excel 2

4 data sheet and followed by calculations to arrive at the total mean cutting force and moment, and their standard deviations as well as the peak-to-valley range. 2. EXPERIMENTAL PROCEDURES Drilling experiments were performed on a Makino A88E machine at fixed machining conditions to study the machining performance of the Sr-modified and α-fe intermetallic-containing 356 and 319 alloys. Chemical emulsion concentrate VHP E21 (5% cutting fluid +95% liquid) was applied to avoid the effects of the heat generated during machining. Machinability test sample after 23 holes were drilled (first and second group of holes), drill and tap geometry are shown in Figure 1. Carbide G drills of 6.5 mm diam. and with minimum 3 mm length, straight flute and coolant fed were used to drill two rows of through-holes in each rib of the waffle plate with 4 mm between rows. Optimum drilling conditions are listed in Table 2. Drilling was carried out at high speed machining for all metallurgical conditions (M1-M5) and all the data was recorded on to Lab View software. Each alloy/heat treatment condition was tested with the same drill. When the drill was broken during the drilling, two options were followed: 1) drilling was stopped then the test was changed for another condition or series, 2) in the case the drill was broken due to the presence of a defect or a large inclusion, the test was resumed with a new drill on the same block. 3

5 3. RESULTS AND DISCUSSIONS 3.1. DRILLING DATA PROCESSING: Methodology Drilling was carried out at high speed machining, all data was recorded in Lab View software with sampling rate of 1 Hz. Matlab programs were developed for processing the drilling data for all metallurgical conditions (M1 to M5). As an example of data processing, the data after drilling of the 356 (M1 aged at 18 C/2h.) alloy machinability test sample number 8 are presented in this paper to show the methodology for the first group of holes (115 holes). The complete programs can be found in the Appendix 2. The data were first separated according to each component of force and moment followed by an application of signal processing procedure for calculating the mean value of force and moment, standard deviations and their corresponding peak-tovalley range. There are two types of drift; normal drift and contamination drift. The normal drift was.3 pc/sec (pc= pico coulomb = coulomb) and for each cycle period (34 seconds) the total drift was 1.2 pc. The sensitivity for Fx, Fy and Fz channels was 7.87, 7.87 and 3.87 pico coulombs/mechanical unit (pc/n), respectively. So for each cycle which consisted of 115 holes in drilling, the normal drift in Fx, Fy, and Fz were 1.3 N, 1.3 N and 2.64 N respectively. 3 From the signal results, it was observed that the contamination drift was more significant. This drift came from oxidation and the coolant and also from the finger impressions during handling. In addition, the long period of 4

6 acquisition can also amplify such kinds of drift. Contamination error was treated in Matlab programs. Matlab graphs representing the steps of data processing for the drilling force and moment are displayed in Figure 2 to Figure 5. All components of force and moment are displayed in Figure 2(a). Drilling feed force (Fz component) was separated and its data was analysed and processed. The Fz component signal was filtered nine times by using a low pass filter (Filter (b, 1, Fz), b= [1 1]; b= b/sum) and a smooth signal was produced, see Figure 3(a). Slow changes were removed after taking the first difference for the filtered signal, Figure 3(b). Again, the second difference was taken for the filtered signal to detect one point within each cycle of the signal, Figure 4(a). Two points were determined within each cycle relative to the detected point (i.e. the second difference positive peak position in the blue dotted signal, Figure 4(a)). The first one (square point) represents the mean cutting feed force (Fz up ) without error treatment and the second (triangle point) represents the error (Fz down ), see legend in Figure 4(b). 16 sample points per cycle were acquired for calculating the mean value of the cutting feed force (8 data points left and 8 data points right from the squared point) and 12 sample points per cycle for the other five components of force and moment (Fx up, Fy up, Mx up, My up, and Mz up ) in each signal (6 data points left and 6 data points right from the same point) however, only 2 sample points per cycle were used for standard deviation or peak-to-valley calculations (1 data points left and 1 data points right from the circled point). 5

7 Total Drilling Force, Moment and Peak-to-Valley calculations and Results Output of results for all components of drilling force and moment with (Fx, Fy, Fz, Mx, My, and Mz) and without (Fx up, Fy up, Fz up, Mx up, My up, and Mz up ) error treatment for the first group of holes are displayed in Figure 5. The error was taken into consideration and was incorporated into the Matlab drilling program as the following set of equations; 1) Fx= Fx up -Fx down, 2) Fy= Fy up -Fy down, 3) Fz= Fz up -Fz down, 4) Mx= Mx up - Mx down, 5) My= My up -My down, and 6) Mz= Mz up -Mz down. After obtaining each component of the mean cutting force and moment as shown in Figure 5, the total mean cutting force and moment, their standard deviations as well as the peak-to-valley range in drilling was calculated. Drilling results for all metallurgical conditions (M1 to M5 ~6 machinability test samples each 23 holes) are displayed in Figure 6. These results were computed from the following set of equations. Standard deviation calculations for the total cutting force and total cutting moment were carried out by the following method. 4 σ f f = ( F / x * x) + ( F / y * y) + ( F / z * z) ) x t µ = ( µ + µ + µ ) y 1/ 2 z t t 1/ 2 Eq.2 And the total cutting force and total cutting moment are calculated by the following equations; F t M = ( F t 2 x = ( M + F 2 x 2 y + M + F 2 y 2 1/ 2 z ) + M 2 1/ 2 z ) Eq.3 6

8 The standard deviation for force and moment can be obtained; σ σ ff fm = = / / 2 ( Fx * σ x + Fy * σ y + Fz * σ z ) /( Fx + Fy + Fz ) / 2 ( Mx * σ + My * σ + Mz * σ ) 1/ /( M + M + M ) x y z x y z 4. CONCLUSIONS In this paper, an introduction for the force and moment calculations which are used to evaluate the different kinds of machining processes (i.e. drilling and tapping) which are outlined in a subsequent paper. 1. A new technique was developed whereby a low pass filter in signal processing was used in calculating the mean cutting force and moment during both the drilling and tapping processes. 2. All signals were independently monitored, digitized and recorded into Lab View. Universal Kistler DynoWare software was used for force measurements and data processing of cutting force and moments. 3. Matlab programs were developed for data processing and for calculating the mean value of cutting force and moment and their standard deviation in both drilling and tapping tests. Contamination drift was treated in these programs. 7

9 ACKNOWLEDGEMENT Financial support from the Natural Sciences and Engineering Research Council of Canada (NSERC), General Motors Powertrain Group and Corporativo Nemak is gratefully acknowledged. 8

10 List of Table Captions Table 1 Table 2 Chemical compositions for 356 and 319 alloys used in the machinability work: a) M1-356 alloy, b) M2-to-M5-319 alloys. Optimum drilling conditions 9

11 Table 1 Alloy Code Chemical compositions for 356 and 319 alloys used in the machinability work: a) M1-356 alloy, b) M2-to-M5-319 alloys. Element (wt %) Si Fe Mn Mg Cu Ti Sr Mn/Fe Al 356 alloy- M alloys- M M M M Table 2 Optimum drilling conditions Parameters Speed Drill Dia. Depth Feed Rate Lubricant/Coolant Drilling m/min or 11 rpm. Carbide G drills 6.5 mm mm 44 IPM (.116 mm/rev) Chemical emulsion concentrate VHP E21 (5% cutting fluid +95% liquid) 1

12 List of Figure Captions Figure 1 Machinability test Sample, Drill and tap geometry, a) Machinability test sample after drilling 23 holes and b) Carbide G (RT 15) drill (O.A.L= 13mm, F.L=28mm and drill dia= 6.5mm) Figure 2 Data processing for drilling force and moment of the first group of holes (115- holes) a) original six component of force and moment b) Fz component. Figure 3 Data processing for drilling feed force-fz component of the first group of holes (115-holes) for Fz component a) filtration (9-times) b) point detection within each cycle-first difference of the filtered Fz. Figure 4 Data processing for drilling feed force-fz component of the first group of holes (115-holes) and point detection within each cycle a) first and second difference of the filtered Fz and b) points within each cycle one represent mean Fz without error consideration and another represent the error value. Figure 5 Output results for drilling force and moment of the first group of holes (115- holes)-plots with and without error treatment a) Fz, b) Fx, c) Fy, d) Mz, e) Mx and f) My. Figure 6 Mean total drilling cutting force and moment for all metallurgical conditions of Sr-modified 356 and 319 alloys containing mainly α-fe- intermetallics corresponding to alloy codes M1 (356 alloy) and M3 and M5 (319 alloys) (a) mean total drilling force of 23 holes (one block) (b) mean total drilling moment of 23 holes (one block). 11

13 First group of holes (115-holes) Second group of holes (115-holes) Feed (a) (b) Figure 1 Machinability test Sample, Drill and tap geometry, a) Machinability test sample after drilling 23 holes and b) Carbide G (RT 15) drill (O.A.L= 13mm, F.L=28mm and drill dia= 6.5mm). 12

14 Drilling Force(N) and Moment (N.m) F x F y F z M x M y M z T im e (m s e c ) x 1 5 (a) 8 F z 6 4 Drilling Force (N) T im e (m s e c ) x 1 5 (b) Figure 2 Data processing for drilling force and moment of the first group of holes (115-holes) a) original six component of force and moment b) Fz component. 13

15 8 F z m F z 6 4 Drilling Force (N) T im e (m s e c ) x 1 4 (a) 8 m F z d i ff m F z 6 4 Drilling Force (N) T im e (m s e c )/ N o o f filt e r in g (b) Figure 3 Data processing for drilling feed force-fz component of the first group of holes (115- holes) for Fz component a) filtration (9-times) b) point detection within each cycle-first difference of the filtered Fz. 14

16 8 6 m F z d i ff m F z d i ff ( d i ff m F z ) Drilling Force (N) T im e (m s e c )/ N o o f filte r in g (a) 8 6 F z m F z u p m F z d o w n 4 Drilling Force (N) T im e (m s e c ) x 1 4 (b) Figure 4 Data processing for drilling feed force-fz component of the first group of holes (115- holes) and point detection within each cycle a) first and second difference of the filtered Fz and b) points within each cycle one represent mean Fz without error consideration and another represent the error value. 15

17 8 6 F z m F z u p m F z d o w n m F z 4 Drilling Force (N) T im e (m s e c ) x 1 5 (a) 8 6 F x m F x m F x u p m F x d o w n 4 Drilling Force (N) Figure T im e (m s e c ) x 1 5 (b) Output results for drilling force and moment of the first group of holes (115-holes)- plots with and without error treatment a) Fz, b) Fx, c) Fy, d) Mz, e) Mx and f) My. 16

18 8 6 F y m F y m F y u p m F y d o w n 4 Drilling Force (N) T im e (m s e c ) x 1 5 (c) 1 8 M z m M z m M z u p m M z d o w n 6 Drilling Moment (N.m) Figure T im e (m s e c ) x 1 5 (d) Output results for drilling force and moment of the first group of holes (115-holes)- plots with and without error treatment a) Fz, b) Fx, c) Fy, d) Mz, e) Mx and f) My. 17

19 1 8 M x m M x m M xu p m M xd o w n 6 Drilling Moment (N.m) T im e (m s e c ) x 1 5 (e) 1 8 M y m M y m M y u p m M y d o w n 6 4 Drilling Moment (N.m) Figure T im e ( m s e c ) x 1 5 (f) Output results for drilling force and moment of the first group of holes (115-holes)- plots with and without error treatment a) Fz, b) Fx, c) Fy, d) Mz, e) Mx and f) My. 18

20 M2-.1%Mg 319-M3-.1%Mg 319-M5-.28%Mg 356-M1-.3%Mg (1) : Polynomial-R2 =.99 (2) : Polynomial-R2 =.94 (3) : Polynomial-R2 =.76 (4) : Polynomial-R2 =.43 Total Drilling Force (N) (1) (1), (2) and (3) =1 HB (4) = 9 HB (2) (3) (4) No of Holes (Block No.) (a) Total Drilling Moment (N.m) M2-.1%Mg 319-M3-.1%Mg 319-M5-.28%Mg 356-M1-.3%Mg (1) : Polynomial-R2 =.97 (2) : Polynomial-R2 =.6 (3) : Polynomial-R2 =.63 (4) : Polynomial-R2 =.46 (1), (2) and (3) =1 HB (4) = 9 HB (1) (2) (3) (4) No of Holes (Block No.) Figure 6 (b) Mean total drilling cutting force and moment for all metallurgical conditions of Srmodified 356 and 319 alloys containing mainly α-fe- intermetallics corresponding to alloy codes M1 (356 alloy) and M3 and M5 (319 alloys) (a) mean total drilling force of 23 holes (one block) (b) mean total drilling moment of 23 holes (one block). 19

21 List of Symbols F x1+2 and F x3+4 Cutting forces coming from sensor 1, 2, 3 and 4 in x-direction F y1+4 and F y2+3 Cutting forces coming from sensor 1, 2, 3 and 4 in y-direction F z1,f z2,f z3 and F z4 Cutting forces coming from sensor 1, 2, 3 and 4 in z-direction nlevel, Number of filteration =9 Diff k 1 st difference for filterd Fz (k) Difff k 2 ed difference for filterd Fz (k) nmin Miniumum number of points in filtered signal per cycle =5 ind, indd, tt, tt1, n, m, z, Matlab variables in drilling N, M, Z, time1,time2, time3, timeup and timedown, min, max, mean, Matlab Functions std,buffer,ones, length,filter, find and zeros mfx, mfy and mfz Mean cutting force calculated within cutting period in each cycle during the drilling (with error treatment) mmx, mmy and mmz Mean cutting moment calculated within cutting period in each cycle during the drilling (with error treatment) mfxup, mfyup and mfzup Mean cutting force calculated within cutting period in each cycle during the drilling (without error treatment) mmxup, mmyup and mmzup Mean cutting moment calculated within cutting period in each cycle during the drilling (without error treatment) mfxdown, mfydown and mfzdown Mean cutting force calculated within non-cutting period in each cycle during the drilling (represent error) mmxdown, mmydown and mmzdown Mean cutting moment calculated within non-cutting period in each cycle during the drilling (represent error) sfx, sfy and sfz,smmx,smmy and smmz Standard deviation for force and moment calculated within cutting period in each cycle during the drilling σ f, and µ f Standard deviation and combined functions (force or moment) µ x, µ y and µ z Standard deviation components F t Total cutting force in drilling M t Total cutting moment in drilling δft/δx, δft/δy and δft/δz Partial derivation of total cutting force respect to x, y and z δmt/δx, δmt/δy and Partial derivation of total cutting moment respect to x, y and z δmt/δz σ ff Standard deviation for combined function (total force) σ fm Standard deviation for combined function (total moment) σx, σy and σz Standard deviation for force or moment components (x,y and z) 2

22 Appendix : 1) Drilling Matlab Program close all;clear all,clc [fi,ch]=uigetfile('c:\machinabilitycta\m2-drilling\*.*','ouvrir...'); if ch== return end; Threshold=1; nom=[ch fi]; k=load(nom); k1=k(3,:); figure(14);plot(k1);grid on title('original plot (Fz=k)') xlabel('time (msec)') ylabel('fz (N)') b=[1 1];b=b/sum(b); k2=k1; nlevel=9; for i=1:nlevel k1=filter(b,1,k1); k1=k1(1:2:end); end t1=1:length(k); t2=t1(1:2^nlevel:end); figure(15);plot(t1,k2,'b',t2-*2^nlevel,k1,'r');grid on title('method of detection step (1); filtering') xlabel('time (msec)') ylabel('fz and mfz (N)') diffk=diff(k1); figure(16),plot(1:length(k1),k1,1:length(k1)-1,diffk),grid on title('step (2), difference(diff mfz) and comparison') xlabel('time (msec)/ No of filtering') ylabel('mfz and diff mfz (N) ') diffk(diffk<threshold)=; diffk(diffk>)=35; difffk=diff(diffk); figure(17);plot(1:length(k1),k1,1:length(diffk),diffk,1:length(difffk),difffk),grid on title('step (3) diffecnce (diff(diff mfz), comparison and detection') xlabel('time (msec)/ No of filtering') ylabel('mfz, diff mfz, and diff (diff mfz) (N) ') ind=find(difffk==35); ind=ind(1:end-1); %number of elements of diff(ind)=number of elements of (ind) - 1 min(diff(ind)) max(diff(ind)) nmin=5; 21

23 indd=zeros(1,length(ind)*nmin); for i=1:nmin indd(i:nmin:end)=ind+i-1; end tt=k1(indd); tt1=buffer(tt,nmin); [mfzup jj1]=max(tt1); [mfzdown jj2]=min(tt1); timeup=(ind+jj1+3)*2^9; timedown=(ind+jj )*2^9; NN=12; MM=1; ZZ=2; n=((:nn)-nn/2)'; m=((:mm)-mm/2)'; z=((:zz)-zz/2)'; N=length(timeup); M=length(timedown); time1=ones(nn+1,1)*timeup+n*ones(1,n); time2=ones(mm+1,1)*timedown+m*ones(1,m); time3=ones(zz+1,1)*timeup+z*ones(1,n); mfxup=mean(buffer(k(1,time1),121)); smfx=std(buffer(k(1,time3),21)); mfyup=mean(buffer(k(2,time1),121)); smfy=std(buffer(k(2,time3),21)); smfz=std(buffer(k(3,time3),21)); mmxup=mean(buffer(k(4,time1),121)); smmx=std(buffer(k(4,time3),21)); mmyup=mean(buffer(k(5,time1),121)); smmy=std(buffer(k(5,time3),21)); mmzup=mean(buffer(k(6,time1),121)); smmz=std(buffer(k(6,time3),21)); mfxdown=mean(buffer(k(1,time2),11)); mfydown=mean(buffer(k(2,time2),11)); mmxdown=mean(buffer(k(4,time2),11)); mmydown=mean(buffer(k(5,time2),11)); mmzdown=mean(buffer(k(6,time2),11)); mfx=(mfxup-mfxdown); mfy=(mfyup-mfydown); mfz=(mfzup-mfzdown); mmx=(mmxup-mmxdown); mmy=(mmyup-mmydown); mmz=(mmzup-mmzdown); results=[timeup;mfx;smfx;mfy;smfy;mfz;smfz;mmx;smmx;mmy;smmy;mmz;smmz]; txt1=['%4.4f' char(9) '%4.4f' char(9) '%4.4f',... 22

24 char(9) '%4.4f' char(9) '%4.4f' char(9),... '%4.4f' char(9) '%4.4f' char(9) '%4.4f' char(9),... '%4.4f' char(9) '%4.4f' char(9) '%4.4f' char(9),... '%4.4f' char(9) '%4.4f' char(13) char(1)]; fid=fopen([fi '.xls'],'w'); txt2=['timeup' char(9) 'mfx' char(9) 'smfx',... char(9) 'mfy' char(9) 'smfy' char(9),... 'mfz' char(9) 'smfz' char(9) 'mmx' char(9),... 'smmx' char(9) 'mmy' char(9) 'smmy' char(9),... 'mmz' char(9) 'smmz' char(13) char(1)]; fwrite(fid,txt2,'char'); fprintf(fid,txt1,results(:));fclose all; figure;plot(t1,k(1,:),'b',timeup,mfx,'.-m',timeup,mfxup,'.-r',timedown,mfxdown,'.-y'),grid on xlabel('time (msec)') ylabel('drilling Force (N)') figure;plot(t1,k(2,:),'b',timeup,mfy,'.-m',timeup,mfyup,'.-r',timedown,mfydown,'.-y'),grid on xlabel('time (msec)') ylabel('drilling Force (N)') figure;plot(t1,k(3,:),'b',timeup,mfz,'.-m',timeup,mfzup,'.-r',timedown,mfzdown,'.-y'),grid on xlabel('time (msec)') ylabel('drilling Force (N)') figure;plot(t1,k(3,:),'b',timeup,mfzup,'.-r',timedown,mfzdown,'.-y',timeup,mfz,'.-m'),grid on xlabel('time (msec)') ylabel('drilling Force (N)') figure;plot(t1,k(4,:),'b',timeup,mmx,'.-m',timeup,mmxup,'.-r',timedown,mmxdown,'.- y'),grid on xlabel('time (msec)') ylabel('drilling Moment (N.m)') figure;plot(t1,k(5,:),'b',timeup,mmy,'.-m',timeup,mmyup,'.-r',timedown,mmydown,'.- y'),grid on xlabel('time (msec)') ylabel('drilling Moment (N.m)') figure;plot(t1,k(6,:),'b',timeup,mmz,'.-m',timeup,mmzup,'.-r',timedown,mmzdown,'.- y'),grid on xlabel('time (msec)') ylabel('drilling Moment (N.m)') figure;plot(mfx); xlabel('no of holes') ylabel('drilling Force (N)') figure;plot(mfy) xlabel('no of holes') 23

25 ylabel('drilling Force (N)') figure;plot(mfz) xlabel('no of holes') ylabel('drilling Force (N)') figure;plot(mmx); xlabel('no of holes') ylabel('drilling Moment (N.m)') figure;plot(mmy); xlabel('no of holes') ylabel('drilling Moment (N.m)') figure;plot(mmz); xlabel('no of holes') ylabel('drilling Moment (N.m)') 24

26 5. REFERENCES 1 M. Tash, F.H. Samuel, F. Mucciardi and H.W. Doty, Effect of Metallurgical Parameters on the Machinability of Heat-Treated 356 and 319 Aluminum Alloys, Prepared for submission to the Materials Science and Engineering, J.R. Taylor, An Introduction to Error Analysis: The Study of Uncertainties in Physical Measurements, University Science Books, Mill Valley, California,