KARDOS, Á.

LETTNER, F.

English

Periodica Polytechnica (Budapest University of Technology and Economics)

ON THE RELATION OF TOOL LIFE TO CUTTING FACTORS IN TURNING OF ALUMINIUM ALLOY By A. KARDOS Technical University, Budapest, Department of Technology of :Machine Production (Received December 7, 1962) Presented by Prof. F. LETTl'iER Investigation of tool life forms a certain part of machinability research. This report deals ,vith results and methods of tool life investigation referring to one kind of aluminium alloy (2.8% Cu; aB = 24 kg/mm2), and carried out within the machinability research program of the Technical University, Budapest, Department of Technology of Machine Production. During these tests, materials of abt. 1 ton weight had been used. 1. Determination of the relation of cntting speed to tool life In machinability research the machinability index of a certain mate-rial is usually determined by a cutting speed involving a given tool life, under established conditions. (For acceptance test purposes, a German statc factory of armaments was the first to prescribe machinability tests of the material, by considering the relation of cutting speed to tool life as an index of machinability [1].) The experimentally estimated value of cutting speed has been used by TAYLOR to characterize the machinability of materials (sequence of machin-ability indices on the basis of V 20 [2]), or according to American practice, on the basis of the mutual relation of cutting speed values (3, 4] and in addition, in standard specifications relating to machinability (in the Soviet Union [5], and in Hungary [6]). According to the above mentioned method of TAYLOR, one number suffices to determine the machinability of metals with respect to tool life. On the other hand, according GLEBOV'S suggestion [7], besides the cutting speed value V 60 (or V ZO' or generally vll ), the exponent "m" of tool life - as an index of variation - should be included. Subsequently, some other authors have- adopted the sa"me principle [8, 9, 10, etc.], and have elaborated methods in order to make it applicable for a more detailed estimation of larger quanti-ties of material. According to a recent tendency in scientific research, scientists. usually establish the entire relationship between cutting speed and tool life_ including the determination of relative machinability ~ \'\ t1S;o ~ \\[ /lfi ""'_ ...... '<- :...~ ::..~ 7'i~, -,.,., ...-:. J' ~M ~/tl\"~~ 6' _ \~}\-118 A. KARDOS In the first series of the here described experiments, 'we intended to deter-mine the relationship between cutting speed and tool life Cv versus T) just for a chip cross-section thateorresponds to well chosen experimental, as well as from workshop's viewpoints. During the preliminary tests [11], the tool's geometrical form was chosen as follows: y = 30°, a = a1 = 10°, ~ = 45°, 7: = 15°, T = 0.5 mm; in our further experiments, the same form has been maintained. All tools were sharpened at once in order to reduce the chances that might have unfavour-'1=2"029 mm2 v =3'19 m/mm ~ aJ' "'" ~ ~ 02 ~'" t; 01 ~ fO 20 30 ~O 50 60 culling lime t min 10 20 30 ~O 50 60 70 80 cullmg lime I mm Fig. 1 i!~~ i!~ q=2x029mw ~ 01 q=2x029mw ~ v =488,5m/min:l<' v =531 m/min '" 10 20 30 fO 20 30 culling lime I min. culling lime I min. Fig. 2 q=2x029mm2 v = 42Bm/ml17 '--~~-~~ 10 20 30 40 culjing lime I min able bearing on experimental results. For plotting the wear curves, the wear on the back of the tool, was measured by means of a Brinel-microscope. Time was measured by means of stoppers at an accuracy of 0,01 min. The results were obtained by taking 5 measurements into consider-ation. Wear curves are shown in Fig. 1 and 2; the initial testing data are given in Table l. When machining a given material by a given tool, in cutting a chip of a cross-section of q = 2 X 0.29 mm2, we obtained, on the basis of experimental results evaluated by a semi-graphical method (see Fig. 5), the following formula expressing the relationship between cutting speed and tool life: 1370 v=---. TO.33 In this formula the tool life exponent is greater than for steels and other heavy metals as known from other tables. This reveals the fact that OS THE RELATIO,y OF TOOL LIFE TO CUTTING FACTORS 119 Table 1 (First series of tests) Advance i Cutting Measuring ~Iarking Cut depth per speed Tool life item on the tip f, revolution v, T, mm e, mjroin mill mm/rev 1 6 2 0.29 335 75 2 10 2 0.29 379 53 3 5 2 0.29 428 31.5 4 14 2 0.29 488.5 20.6 5 15 2 0.29 531 17.3 - for the given alloy - the increase of cutting speed involves a slower diminua-tion of tool life than in the case of harder materials. 75 75 70 60 <::'.60 .;;: 50 E; E: ..... ..... 'to ~ ~ :.::; ~5 :.::; C C 30 ~ ~ 25 20 \ I I \ I i \i I I '\ !\ i \ : \ I j\ i 300 400 500 300 ~oo 500 600 culling speed ;/ m/mm culling speed v mjmin. Fig. 3 According to the above obtained formula, a tool life of 1 minute is bound to a cutting speed of 1370 m/min. This is a decisive argument for refusing - mainly for practical reasons - the suggestion made by certain German researchers, according to "which short tests based on a cutting speed (vt ) involving the tool life of 1 minute should be taken as basis of comparison. From the given formula, the cutting speed (V60) that involves a tool life of 60 minutes is vso = 350 m/min. 2. Relation hetween tool life and cutting factors The task is, to find experimentally (usually in the explicit form for the cutting speed v) the expression for the follo'ving functional relationship: T = cp(v, e,j) 120 .4. KARDOS The further purpose of these experiments was to dra';v- the possible consequences, and to set up tables and nomographs for practical use. During ca. forty years, efforts have been made to find formulas for these relationships vvith reference to steel machining. As we know, similar experiments for deter-q=2xa~75mm2 v=319,5 m/min ID 20, 30 ~D 50, culling lime t min q=3x0,475 mm2 v = 310, m/mIf7. 10 20, 3D 40, cutting iime t min ~DJ~ cS ~ 0,2 c:: , ~"" 0,1 q=2x0,4mm-~' v =389 m/min 10 20 3D 40, cullino lime t min q,=4x0,29mm2 v =352 m/min. ;0, 20 3D 40 50, cutting lime I min Fig. 4 Fig. 5 Fig. 6 Fig. 7 q=2x02mm v =421 m/min 20 30 :,0, 50 60, 70, 80 cul!ing lime I min. q=2x0,4mm2 v =320 m/min '0 20 3D 40, 50, 50, q=3x0,29mm2 v';35o'm/min !O 20, 30 :'0 50 50, cutting tIme t mm mining the expression of these correlations, with reference to light metals and alloys, have not yet been carried out anywhere. Considering aluminium alloys, the main trend of these tests does not differ from that of the examination of steel machining. Generally the assumed form of the relationship put to test is: C T=----j. eZ .f'; . vm OS THE RELATIO,,' OF TOOL LIFE TO CUTTISG FACTORS 121 or In a more usual form: V= Cv where C and Cv are constants coordinated to the actual work and tool pair-On the other hand, the experimentally determined four constants C,., y, x, rn, are assumed to be invariable within a certain range of the cutting values. The wear curves are shown in Fig. 4-7. The measuring results are summarized in Table 2. By making use of the compensation method of calculation, the following formula is obtained: 741 V=--------fO.195 • eO.;;2 • TO.30 and the explicit form for tool life: )leasuring it£'m 2 3 4 5 6 7 3 2,23.109 ---Table 2 (2nd series of tests) ;.\-larking on Cut depth the tip f, 13 2 5 2 15 2 6 2 10 3 14 3 14 3 10 3 Advance per revolution e, mm/rev 0.2 0.4 0.4 0.475 0.29 0.4 0.475 0.29 Cutting ,peed-", m,min 421 320 339 319.5 350 323 310 352 Tool life T, min 69 47 23.3 40 47 37.5 30 435 Generally, experimental results are usually to be calculated by graphical methods. For comparison's sake, before finding results by calculation, we applied the graphical method of evaluation, too. 1. In order to plot the curves representing the functions v versus T as shown in Fig. 8, the tests were carried out in cutting a chip with the cross-section area 122 .4. KARDOS q = 2 X 0.29 mm2, and q = 2 X 0.4 mm2, respectively. The curves are drawn of the basis of visual compensation. 2. For determining the relationship v versus e, we applied two series of tests (f = 2 mm, and j = 3 mm). Since the measurements had yi~lded various values of tool life, we had to redress the numerical results according to the already established relation of v versus T. Therefore, we chose as basis 500~i""., ~~. " -;;. , wo -~ /""!, ' "'" ~' III I ,~~-:? ' ~JOOr • ~0-{I. I,~' zoo' · ~ JOO '" ~ "" ~ zoo '------'---zoo JOO 400 500 600, O,Z O,Z9 0," 0'175 2 J " cutting speed v m/min. a} e mm/rev b) r mm Fig. 8 Fig. 9 the tool life T = 60 min; consequently these curves represent the functions vso versus e, as shown in Fig. 9a. 3. In order to find the relationship v versus j, three series of tests (e = = 0.29 mm/rev.; e = 0.4 mm/rev.; e = 0.475 mm/rev.) were carried out. In the same way, as mentioned in point 2. the results were redressed on the basis of a 60 min. tool life (Diagram sho,ving vso versus j in Fig. 9b). 4. The above stated expressions suffice to determine the general basic formula. To this end, the constants y and x can be calculated; and by extrapola-tion the cutting speed involving a 60 min. tool life in cutting a chip ,\ith a cross-section of 1 mm2 can be found. In Fig. 8 sho,ving the diagram v versus T, the straight line correspond-ing to m = 0.33 (for q = 2 X 0.29 mm2), and the point belonging to the values q = 1 mm2 and T = 60 min, are delineated. By dra,ving, through the aforementioned point, another straight line parallel to the former one representing m = 0.33, we find by the section point on the v axis the cutting speed value VI belonging to the tool life T = 1 min, OS THE RELATIOS OF TOOL LIFE TO CUTTLVG FACTORS 123 numerically equalling the constant C that represents the interdependence of 'work and tool. As a final result we obtain: 800 v=-------eO .56 fo.23 • TO.33 Although these constants deviate from those obtained by pure calculation, the magnitude of variations does not affect the practical applicability. Con-sequently, the graphical method can be recommended for the calculation of tool life tests. 3. Recapitulation of consequences 1. Relation of cutting speed to tool life: for a chip cross-section of q= = 2 X 0.29 mm2, and for the aluminium alloy put under test, the formula deduced by a semi-graphical method is as follows: v= 1370 TO.33 The exponent m = 0.33 is responsible for the relationship characterized by a slower tool life diminuation involved by an increased cutting speed, than would be the case in steel turning. 2. The relationship between tool life and cutting factors can be expressed as follows: 2.23.109 T=------fO.63. el.iO • V3.25 namely, within the experimental range of basic values that were evaluated by calculation; or in a more conventional form: 741 v=-------/0.195 . eO.E2 • TO.20 . 3. The series of tests should not only help us in finding scientific cor-relations, but also in satisfying practical claims, namely, by yielding useful information data for workshop practice. Based on these experimental results, (Fig. 10 and 11) and tables were set up for the experimental All the basic values given in this table refer to a 60 min tool life. In 124 Feed, mm!rev 0.2 0.25 0.3 0.35 0.4 0.45 0.5 COllversion factors: T ndn KT 30 1.23 .4. KARD08 Cutting speed. Vr,o m/min 439 390 354 327 305 286 273 45 1.08 Cut 2.5 376 341 314 293 276 262 depth, f mm 360 332 302 282 264 252 60 340 341 285 268 250 23i 75 0.93 Fig. 10 e mm/rev. Sample: f=2mm e=0,3mm!rcy T=60min v=35ft m/min. iff,~------~~~~-----.~ 600 500 ~OO 350 JOO 250 200 culling speed v m/min Fig. 11 h. ~ ;.:;:: 90 0.68 addition, correctional factors are given for the purpose of conversion. The correctional factor for a 90 min tool life ha:; been determined by means of extrapolation of the results, permissible from well considered viewpoints; also tool advance (per revolution) limits have been extrapolated, for an admis-sible, not important range. 0.'1 THE RELATION OF TOOL LIFE TO CUTTING FACTORS 125 Summary In this paper a series of experiments relating to tool life in machining a given aluminium alloy is reported; testing principles and experimental details are described, the problem of evaluation of results is dealt with. Finally a table and a nomograph is given for their use in workshop practice. References 1. SCRLESINGER, G.: Bearbeitbarkeit und 'Vechselwirkung zwischen Werkstoff und Werk-zeu!!:. Werkstatt-Technik. 1927. S. 605. 2. TAYLo~R, F. W.-WALLICRS; A.: Uber Dreharbeit und Werkzeugstahle. Berlin, Springer, 1908. 3. :MONARCH, F.: Economical speeds and feeds for production turning. Tool Engineer 1955. Febr. S. 119. 4. :Machining theory and practice. New York. American Society for metals, 1950. 5. GOST. 2625-44. MCTa,lJlbJ. 1\lcT0l111Ka onpe;J,eJleHll51 oopaTbIBae~IOCTlI ~!eTaJI.l0B pC3aHlle,\l. 6. :MNOSZ 2663-53. Acelok forgacsolhatosaganak vizsgaIata (Hungarian Standard Speci-fication: Testing method of the machinahility of steel). 7. GLEBOV, S. F.: TeOpl151 HaHBblrOl1Hel:WCrO pe3aHl151 ~!eTaJ1JlOB. Gosmashlitizdat, :Moscow, 1933. 8. OPITZ, H.-ZIl\DIERM.ANN. 'V.: Die Zerspanbarkeitseigenschaften der Automaten-Leicht-metall Legierungen. Metallkunde. 1937. Sept. 96 S. 9. ADAM, 1.: Yiccne110BaHll51 oopaoaTbIBaeMocTll ~!e;J,HbIX CITnaBOB. :Moscow, :Mashgiz 1951. 10. ZLATIN, N.-KAHLES. J. F.-BRIGGS. C. W.: Machinability of cast steels. Tool Engineer 1953. Febr. p. 59. 11. KARDOS, A.: Az optimalis eIszogek meghatarozasarol (On the determination of the optimal values of rake angles). Gep. 1959. 12. sz. 467. o. A. KARDOS; Budapest, XI. Sztoczek u. 2 sz. Hungary 

ON THE RELATION OF TOOL LIFE TO CUTTING FACTORS IN TURNING OF ALUMINIUM ALLOY

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ON THE RELATION OF TOOL LIFE TO CUTTING FACTORS IN TURNING OF ALUMINIUM ALLOY

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Periodica Polytechnica (Budapest University of Technology and Economics)