A new method for analysing the efficiency of cutting inserts

Transcription

1 IOP Conferene Series: Materials Siene and Engineering PAPER OPEN ACCESS A new method for analysing the effiieny of utting inserts To ite this artile: Sándor Sipos 018 IOP Conf. Ser.: Mater. Si. Eng View the artile online for updates and enhanements. This ontent was downloaded from IP address on 13/01/019 at 08:31

2 A new method for analysing the effiieny of utting inserts Sándor Sipos Óbuda University, Institute of Material and Manufaturing Siene, Budapest, Népszínház u. 8., Hungary Abstrat The operational produtivity and the eonomi effiieny of turning, drilling and milling inserts an be expressed by utting performane. This omplex definition is omposed of several main and supplementary features, therefore it is not possible to haraterise it by only one indiator. In the present artile a new method will be introdued, being able to measure and ompare the produtive effiieny of turning inserts: the four most important features will be summarised in one indiator. The proedure has a low time requirement, it is built on instrumental investigations, so it does not require great finanial and material expenses, it makes possible to use the tools in an optimal way, aording to the four aspets, investigated by us, and to qualify the inserts in many ways. The so alled omplex effiieny indiator serves to measure the effetiveness of innovation, too. The proedure, developed by us, has already been used suessfully in ase of tools, produed by leading ompanies and having different funtions, design and materials. 1. Introdution Nowadays, in the area of utting operations there are appearing new versions of mounted tools. The utting elements, the inserts, optimised to the given task, are fixed in the tool holders, drill and milling utter bodies by the manufaturing ompanies. Although the amount of operationally appliable shape variations is quite limited, the number of the hipbreakers and edge designs, usable under different irumstanes, is onsiderably great. The operational produtivity and eonomial effiieny of turning, drilling and milling inserts an be mostly desribed by the utting performane. This term is a omplex feature of the tool (its edge geometry and/or material), serving to judge and qualify its behaviour during utting operation (wear, tool life, fore effets, the shape of the developed hips et.) and the ahieved surfae quality (waviness, roughness) of the mahined workpiee. The judgement is always built on pratial experienes, it provides a haraterisation, desribable with words, i. e. it has a quantitative harater. For example, an insert is onsidered to be appropriate if it breaks the hip well and its wear proess is low. The qualifiation is mainly built on instrumental measurements, it haraterises the produtive effiieny of the tested tool with the results of measurements, depending from the adjusted data ombinations, i. e. in a qualitative way [1][]. The following artile is going to introdue a method for measuring and omparing the utting performane of utting inserts. The proedure is built on short-time examinations; therefore it does not require great material, instrumental and finanial expenses. The developed method has been suessfully applied in ase of tools, having different tasks, onstrutions, utting materials and produed by world-famous tool manufaturing ompanies [3][4].. Mahinability and utting perfomane Among the speialists, being familiar with the tehnology, the pair of terms mahinability and utting performane is well-known. The first mentioned haraterises the workpiee material based on three different sets of parameters. The first set of parameters provides information on the hemial omposition of the workpiee: it refers to the perentage ratio of main and auxiliary alloy omponents, furthermore to the rate of the non-metalli alloys (for example, S, Ca, Se, Te et.), having a positive influene on the mahinability. The hemial omposition determines the possible mirostruture of Content from this work may be used under the terms of the Creative Commons Attribution 3.0 liene. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal itation and DOI. Published under liene by Ltd 1

3 the given material. It inludes also undesired alloy materials, getting into the material as pollution (for example, S, O, Si). The seond set of parameters refers to the ondition of the workpiee, inluding the method of the prodution (preprodution), the (preliminary) heat treatment and struture of the material et. To this belongs the different mahinability of the ast or forged pre-prodution produts (ompared to the basi struture). The third set of parameters is formed by the material properties of the workpiee. These over the mehanial, the thermo-physial and the metallographyal properties of the given grade. The first group of features inludes the strength and density at low and high temperature, et., the thermo-physial ontains, for example, the speifi heat, thermal ondutivity and absorption properties, while the last one involves the material struture, the ratio and mirohardness of hard phases, marohardness, tendeny of the self-hardening, ritial temperature, et. [5]. From the material properties of the workpiee, the listed ones have the greatest influene on the tool: basi hardness of the workpiee material (having a lose orrelation with the strength) has a signifiant influene on the utting fore and the temperature, to be developed during the mahining, and it determines the mehanial and thermo-physial load of the diret environment of the tool edge. good dutility (appropriate elongation) has a orrelation with the toughness. Some alloy materials (Cr, Mo, Ni, W) inreases the toughness, while in ase of other ones (Cr, Ni) it may be aompanied by the adhesion tendeny (to stiking) and it may be a preondition to the development of built-up edge. hard phases of multiphase materials (for example, the presene of the primary silion rystals with a great hardness in the hypereuteti aluminum alloys et.) have an inreased abrasive influene, therefore, they an ause an intensive tool wear. presene of some alloy materials (Cr, Ni et.) in the workpiee auses self-hardening during the mahining. If the allowane is detahed with some uts, then there is an inrease in the hardness of the upper layers, already mahined. thermo-physial properties of the workpiee an be influened by alloy materials. These features determine the ratio of the (thermal) energy, developed during the mahining and getting into the workpiee and hip, and also the perentage, ausing tool damage. In the last deades, a range of novel materials has appeared (ADI Austempered Dutile Iron, CGI Compated Graphite Iron, duplex orrosion resistant steels, heat resistant (HRSA) nikel- and obaltbased alloys, used in gas turbine manufaturing, AMC aluminum-based omposits, AMFS aluminum-based, syntati omposite metal foams et.), where the eonomi mahining auses a real hallenge for tool manufaturing ompanies. It means that the very poor workpiee mahinability should be offset by the inreased utting perfomane of applied tools. The utting perfomane is a measure of the effiieny of tools, having different designs, geometries and materials (inluding substratum and oatings, too), its main feature is the tool life (and its wear urve and wear model, desribing this). Without that knowledge it is not possible to alulate, analyse or ompare the manufaturing (operational) osts, the produtivity (expressed, for example, in piee/hour). It requires quite great material and finanial expenses to determine its value for a given task, while its validity depends to a great extent on the speifi onditions of prodution (the omposition, the ondition and hardness of the workpiee, the ondition of the mahine et.). The supplementary features of utting performane inlude several fators: material flow veloity (with other words, the material removal rate), utting temperature, utting fore omponents and power requirement, the shape and size of the hips, the mirogeometry (wavieness, roughness) and the layer properties of the mahined surfae. Some of the listed properties an only be measured with ompliated instruments (for example, the temperature in ase of dry-mahining) or the measurement an ause damage in the produed workpiee (for example, the material struture, the hange in the mirohardness, the distribution of the residual stress et.).

4 3. Examination of the effiieny of utting inserts In the indiator, developed to qualify utting inserts, researh and pratial experienes of two deades have been summarised. The quintessene of the developed method is to determine the utting performane of a single insert with four seleted supplementary features. Important fators will be onsidered that first an be easily alulated and observed, and, seond, they an be quite easily measured. An advantage of this proedure is that the test of the tool ours with material-, instrumentand ost-friendly way, i. e. with short-time use. This requires only nine different setups and it means turning a length of just mm. The utting performane is a omplex definition and it is impossible to express it with a single indiator. If we asked a pratiing speialist what are the harateristis of fine working tools than his reply probably would be the following: produtive and easy hip detahment, furthermore, favourable, foreseeable surfae roughness, resulting from the low utting fore and favourably broken hips. Aordingly, the seleted supplementary features are: the material removal rate (MMR), the hip shape, the ative utting fore and the Rz parameter of surfae roughness. The speifi feature of this method is that all the four fators are desribed with a single indiator and in this figure the most important requirements, onerning the tool, are summarised. In ase of any setting, the formula of effiieny indiator, desribing the utting performane of a turning insert, is the following: ' V g 1000 a f v g mm H = = ( 1), Fa Rz Fa Rz min N μm where there are: MMR (V, mm 3 /min), the figure, referring to the hip shape (g), the ative utting fore (F a, N) and the ahieved surfae roughness (Rz, µm). The formula (1) suggests that the greater material flow rate and more favourable hip shape is, the better the effiieny is. On the other hand, the smaller power requirement of the hip detahment and break is, and the smaller roughness on the mahined surfae is, the more favourable the use of the insert is. The seletion of the four ritial features (beside their simple measurability and exat determination) an be explained by the following onsiderations. 1. Material removal rate refers to the produtivity of the utting proess. In ase of turning operation it is the produt of depth of ut, the feed and the utting speed, and after substitution it has the unit of measurement: m 3 /min. By reason of the sale of H indiator it is reommended to use the unit mm 3 /min in formula (1). During the tests, the depth of ut has a onstant value, while aording to the funtion of tested insert the feed rate and utting speed values were varied on three-three levels (i. e. altogether 9 settings). The utting perfomane features an be really shown when there is a several-fold inrease in the intensity of the hip detahment during the tests. During the tests the tool wear should not affet the results of the measurements, therefore all the three tehnologial data have to be adjusted to the workpiee material (utting speed), and to the hip breaking range of the insert (depth of ut and feed).. Favourable hip shape deisively affets the proess-sure operation of mahines with limited superivision (CNC-lathe entres, multitasking mahines et.), but it has an effet on the aestheti appearane of mahined produts, too. The rebound movement of hip to the mahined surfae may ause faulty produts, as the hip may ause damage on other learly visible surfaes or on the oated surfae. The hip samples, detahed during the tests, will be arranged in a hart form (in a so-alled hip hart ) and after that the value of g, reffering to the hip shape, an be determined. It is a mark (is a whole number) and its value may be between g= The most favourably broken hips were awarded the mark 5, while the dangerously tangled, flowing hips reeive the mark 1. We would like to note that this lassifiation matrix to our knowledge was applied first in Hungary by the authors [6][7][8]. 3

5 Figure 1 Chip hart and marks of the detahed hips Insert: CNMG10408 MP3 WPP0S Mahining onditions: C50 unalloyed steel (HB0±5); a= mm; dry mahining The Figure 1 shows the hip hart of an insert (together with the evalution, mark ). In the heading of the table the general hipbreaking effiieny is shown, it is a number, exatly the perent ratio of the sums of the marks, awarded to the inserts, and the sum of the maximum available marks (in this ase it is 9x5 = 45). 3. The ative fore is the summarised value of two fore omponents, determined by instrument measurement. Although the fore measuring equipment is able to register 3 fore omponents, the method, introdued earlier, is built on the simultaneous registration of utting (F ) and feed (F f) fore omponents. The passive fore is important from the point of view of the workpiee auray, therefore it will not be onsidered in ase of our method. The ative fore (F a) is the vetor resultant of F and F f fores therefore F a = F F f ( ). The utting fore determines beside its effets, arried out on the tool the neessary power requirement. The feed fore depends in ase of tools, having the same lead angle values, and inserts, having the same orner radius value mainly on the tool edge design (edge rounding off, edge preparation et.) and on the design of the hipbreaker. This F a fore omponent is able to haraterise the hipbreaking ability: the greater the F f fore omponent is, the greater the plus fore is, being neessary to ut (break) the detahed hips into piees of suffiient size. Therefore the qualifiation of inserts happens based on the ative F a fore and important onlusions an be drawn from the ratio of F f and F. Two-fator fore models (a=onstant ; v = m/min) 0,79 0,03 F 3185 f v [N] deviation : ±0 N ; R >0,95 0,41 0,07 F 100 f v [N] f deviation: ±15 N ; R >0,95 Figure The utting fore omponents and their models Mahining onditions: Ko36 stainless steel (HB170±5); a= mm; dry mahining On Figure the fore omponents and the two-fator model of fore omponents of an insert, having PP hipbreaking geometry and modern oating, and produed by a well-known ompany, are summarised and shown. As it an be seen well the feed rate has a determining effet on the development of both fore omponents, while the utting speed does not affet signifiantly the fores, developing during the mahining. 4. The fourth feature is the surfae finish produing apability of the tool, it learly belongs to the qualitative requirements. This term means that the tools are able to produe surfaes, having nearly the same roughness parameters, under determined irumstanes, almost independently 4

6 from their measured (or deteted) wear ondition in a way, where it an be alulated/predited planned in advane []. The roughness of the turned surfaes an be haraterised with different measures. On Figure 3 the development of the roughness (and R e theoretial roughness) is shown in funtion of feed rate in ase of different settings. Although the use of the average roughness (Ra) is quite widespread in the pratie in Hungary, in this ase the unevenness height (Rz) was used to ompare the different inserts. This an be explained by the fat that in the supplier segment almost only Rz parameter is applied, and the Rz shows an aeptable agreement with Re theoretial roughness in ase of some feed rate ranges. In ase if we know the value of orner radius (r ε, mm), then the lastly mentioned an be alulated [] with the following formula (Bauer-formula, 1937): f Re 15 μm ( 3). rε As it an be seen well on Figure 3, the theoretial roughness follows the development of Rz value in the range of 0,5 f, mm 0,35 mm; at the same time, the popular average roughness shows a moderate hange in the same range. We note that in ase of the tested insert the general rule Rz=(5 6) Ra prevails, it means that the approah Rz 4 Ra, ommonly used in the tehnial pratie, is not orret. The denial of this myth an be found in [9][10]. Two-fator Rz model: (a=onstant; v = m/min) Rz 103 f 0,99 v -0,15 m Deviation: ±0,34 µm; R >0,99 Figure 3 The roughness parameters of the mahined surfae Insert: CNMG10408 MR WP15CT Mahining onditions: C50 unalloyed steel (HB0±5); a= mm; dry mahining With the following example it will be presented how to substitute the fators, mentioned earlier, into the (1) relationship. In the Table 1 the effiieny indiators of an inserts, having the marking EM/YBN and produed by a well-known ompany, are presented. Table 1. The effiieny indiators of insert EM/YBN Effiieny of the utting insert (H) v a f V' F F f F a Rz g H 100 1,5 0, , , ,5 0,15, ,33 4 3, ,5 0,5 37, ,67 4 8, ,5 0, ,61 3 8, ,5 0, ,67 4 4, ,5 0, ,98 4 8,8 00 1,5 0, ,68 30,7 00 1,5 0, , ,9 00 1,5 0, ,41 4 4,4 Mahining onditions: dry mahining Insert: CNMG10408 EM YBN53 Workpiee: C50 unalloyed steel (HB 0±5) 5

7 Analysing the data, gained from the nine different settings (v = m/min ; f = 0,1...0,5 mm) and in ase of onstant (a=1,5 mm) depth of ut, the following onlusions an be drawn: in ase of ombination of the feed and utting speed values, the insert has a greatly varying effiieny (H 1-9 = 18 56). The simultaneous inrease of both utting speed and feed values has a learly favourable effet on the mahining produtivity and on the tool effiieny, too. In ase of this ombination of hipbreaker/material, the fivefold inrease of the material removal was followed only by a moderate inrease in the effiieny; using the insert under the most favourable onditions, the value of its effiieny nearly tripled, ompared with the lowest value (H 8 = 56,9). It is mainly due to the reason that the material removal, already mentioned, inreases, at the same time, the hip shape and the roughness, ahieved during the proess, have a very favourable values; as it an be seen well, the insert effiieny is extremely good in ase of feed value of f = 0,15 mm (almost independently from the settled utting speed value). Based on the method, introdued earlier, it is easy to selet the best effiieny of appliation and the settings, enabling the favourable results (see the oloured olumns). With these, the optimal onditions of appliation an be seleted for any insert. With this method it is possible (moreover, from the aspet of the operational pratie it is desirable) to qualify the inserts in a form of tests (arried out under the same onditions), in a versatile and objetive way (taking four fators into onsideration at the same time), to ompare them (or to disover the differenes between same insert types). 4. The omplex effiieny of utting inserts It is not usually to ompare inserts, having different funtions (finishing, semi-finishing and roughing), material grades, edge onstrutions (ISO or wiper) and hipbreaking geometries. The method, proposed in the present artile, makes it possible to realistially ompare them with introduing a new term, the so-alled omplex effiieny. The basis of the omplex omparison of tools, intended for different fields of use, is the behaviour of the tested inserts: this will be determined based on the analysed utting data (v, a, f, V') and based on the measured and alulated features (F a, Rz, g, H). The omplex effiieny (H K) of any insert builds on H 1 H 9 values, determined for individual settings: it expresses the effiieny of the given insert geometry and/or edge onstrution in perentage, taking the examined four features into onsideration. Its value represents the average utting perfomane of an insert, with referene to all settings, it means it is a omplex, perentage indiator. When evaluating the inserts, the main statistial features (average, deviation, variane ratio) will be used, at the same time, the perentages of some measured/alulated values will be onsidered. The omplex effiieny an be alulated with the following formula: ' V% g% H K = 100 % ( 4 ). Fa Rz % % The interpretation and the alulation method of this formula will be introdued with a speifi example. Table. The omplex effiieny of an insert, having a shortened edge Value v a f V' F F f F a Rz g H Average 18,3 1,5 0,17 3, ,0 3,7 18, Deviation 6,1 0 0,07 14, , 0,5 5,1 Var,% 0,3 0 39,7 45, ,6 13,6 8, In % , Complex effiieny Insert: TT9080/09 PC H K = 31,% Mahining onditions: dry mahining Insert: CNMG PC TT9080 Workpiee: Ko36 austenisti stainless steel (HB 170±5) 6

8 In the Table the turning results of a hard-to-mahine, austeniti orrosion-resistant steel will be summarised, in ase of a fixed depth of ut a = 1,5 mm, (limit values: v = m/min; f = 0,1 0,5 mm). The data, shown in Table, have been alulated with formula (4). From the results, the following onlusions an be drawn: if the range of the test settings is the same, the average of the material flow (V' %) will agree, too, in the evaluation it means 100 perent. However, it there is any hange in the test onditions (for example, the omparison of semi-finishing and roughing hipbreaking geometries) then this hange has to be mentioned, V %= 100 V new%/v base% [%]; the perentage ratio of the ative fore (F a%) an be alulated in the following way: the average ative fore (F aave), measured during the tests, will be ompared to the average utting fore (F ave), it means: F a%=100 F aave/f ave [%]. Aordingly, the F a% is always greather than 100%, and, the greater the ratio of the feed fore is, the greater this deviation is. We note that this proportion depends ruially on the tool holder onstrution (PCLNR or PSSNR) and on the orner radius of the insert (r ). The average ratio of F f/f is a subsidiary, but very useful information, in this ase it was 53,5%. In the present ase of orrosion-resistant steels this value is in the range of 48-6% (in ase of PCLNR tool holder, orner radius is 0,8 mm, without edge preparation, depending on the hipbreaker onstrution); the perentage value (Rz %) of the surfae finish produing apability ompares the measured and theoretial roughness values. The average of the measured unevenness height was ompared with the average theoretial roughness, its value was alulated with formula (3) for the average feed. With the perentage data, indiated in the table, it is expressed that the measured values are approx. times greater than the theoretial roughness values. It is ommon in ase of orrosionresistant steels (Rz measured/rz alulated %) as at low utting speed and feed values there is a development of built-up edge. Some types of orrosion-resistant steels, having a stiky (tensile) harater, result in an undetahable material layer (so-alled Spanzipfeltheorie ), and its appearane requires rather to apply the Brammertz roughness model [11]. The tested austeniti steel is extraordinary inlined to self-hardening. The initial wear phase of the oating is not able to prevent the developing material adhesion on the rake fae, lose to the tool nose, and it makes the roughness even worse; the perentage value of hip shape (g %) expresses the average hipbreaking effiieny of an insert (see Figure 1). The hipbreaking effiieny of inserts, tested till now, varied in the range of 40-90%. It has been onfirmed by other tests that the applied PC hipbreaking geometry has an outstanding performane in ase of turning orrosion-resistant steels [1][13]; the value of omplex effiieny (i.e. 31,%), alulated aording to formula (3), is - in our experiene - markedly aeptable in ase of hard-to-mahine materials [10][13]. With introdution of the term omplex effiieny and with the formula (4) it beame possible to ompare the effiieny of tool materials and /or hipbreakers, formed on inserts, having the same shape, but modified sizes, to analyse the tools, having different edge onstrutions (for example, ISO or wiper) and to qualify the innovation effetiveness of ertain insert developments. The experienes of the tests, arried out till now, have been summarised in Table 3. Table 3. Evaluation of the omplex effiieny Conditions: Insert/workpiee material ISO Complex effiieny, HK, % poor proper good very good unalloyed steel stainless steel wiper unalloyed steel stainless steel The omplex effiieny of inserts an be divided into four ategories aording to the material grade of workpiees and the edge onstrutions of inserts. The outstanding performane of the wiper edge 7

9 onstrution an be explained mainly by the lower ative fore and with the very low roughness values. 5. The weigthed effiieny of utting inserts The requirements for the inserts are obviously different in ase of different mahining onditions or tasks, like roughing, semi-finishing and finishing. International surveys have been published in this topi (for example, the CIRP-study, published in the eighties), however, to our knowledge there was not arried out suh an assessment about the situation in Hungary in the seond deade of the 1st entury. Due to this reason, a questionnaire has been sent out to tool sales ompanies and some manufaturing ompanies to ollet their opinions: what ratios are represented by the four supplementary features - seleted systematially and onsidered to be the most important - during the turning operation, aording to their experienes. Three ompanies, having a lose partnership with our Faulty, summarised and sent us their pratial experienes, while the representation of tool manufaturing ompanies was the following: 4 ompanies from Sandvik Group, from IMC Group, 1 from Kennametal Group. The ten replies, reeived from the ompanies, have been averaged. The weighted numbers of requirements for the inserts, alulated from the data of questionnaires, are shown in Table 4. Table 4. Weighting of the requirements for the inserts Supplementary The weighted numbers of mahining Weighting features onditions ratios Roughing Semi-finishing Finishing Removal rate 0,4 0,3 0,15 λ1 Chip shape 0,3 0,3 0,35 λ Fore effets 0, 0,5 0,1 λ3 Roughness 0,1 0,15 0,4 λ4 Sum total 1,0 1,0 1,0 On Figure 4 it is expressively shown what kind of priority priniples are neessary to selet and to apply the appropriate insert. The data, gained from the questionnaires, have onfirmed our expetations as regards the material removal rate, the developing fore effets and the produed surfae roughness. Only the hipbreaking requirement had the same weight in ase of all the three mahining ranges. It is understandable in ase if the mahines, used during the turning proess, are able to operate under onditions of prodution with poor monitoring (with other words, unmanned mahining ). Comparing the data from the Table (1) and Figure (4), it is learly seen that in ase of roughing there is one, in ase of finishing there are two, while in ase of semi-finishing there are three features, having the greatest weight and playing a determining role. It means that the omplex effiieny of inserts, involved in the test series, has to be modified with weight numbers, expressing the usability based on the tool distribution trends and the operational pratial experienes. Figure 4 The perentage weight ratios of supplementary features 8

10 The individual measurement results and the hipbreaking behaviour of inserts an be gained with onsideration of Table (1) and with the orretion of formula (4). Conerning the suitability of inserts, the formula, to alulate the omplex effiieny, orreted by weight numbers and expressing the demands of the users, is the following: ' 1000( 1+ λ1 ) V ( 1+ λ ) g H SK = % ( 5 ). ( 1 λ3 ) Fa ( 1 λ4 ) Rz The interpretation of the published formula and the alulation method will be introdued with a help of an example. In Table 5 the results of semi-finishing turning operations are shown, arried out on C60 strutural steel grade, with wiper edge insert (limit values: v = m/min; f=0,15 0,34 mm). Based on the weighted, omplex effiieny indiators the following onlusions an be drawn: as a result of weighting, the average indiators have hanged only slightly, in ase of some of them there is an inrease (material flow, hipbreaking effiieny), while in ase of others, there is a derease (fore effets, roughness). It an be onsidered that in the ategory of semi-finishing, the weighting has not basially hanged the perentage ratios, reated by the omplex effiieny indiators. The reason for this is that three from the onsidered four supplementary features had almost the same weight; the effiieny of inserts, having a wiper edge onstrution, means a speial ategory, as it has already been introdued [14][15]. It is ontributed by the fat that all tested features are extremely favourable, in partiular, the surfae finish produing apability and hipbreaking effiieny are outstanding. We note that similar experienes have been gained in ase of tools with this (wiper) edge design, produed by other ompanies: the weighted omplex effiieny is nearly two times greater, ompared to the ISO edge tools; Table 5. The weighted omplex effiieny indiator of a tested insert Evaluation v f V s' F F f F as Rz s g s H s Average 170 0,4 78, ,8 5,1 150,9 Deviation 65,4 0,08 4, ,4 1,0 118,6 Var, % 38,5 35, 53, ,5 0,1 78,6 in % ,5 85,9 43, 101,1 Corretion fators Correted omplex effiieny λ 1 0,3 λ 0,3 λ 3-0,5 λ 4-0,15,651 Insert type: NF hip breaking geometry Mahining onditions: dry mahining Insert: CNMG NF (wiper) WPP0S Workpiee: C60 unalloyed strutural steel grade (HB 15±5) H SK=73% In this onnetion we note that based on our measurement results the passive fore omponent is extraordinary great in ase of wiper insert; due to this reason, the harateristi features of the edge desing have to be onsidered! For the purposes of produtivity, the longitudinal turning of omponents, having a small ratio of utting length/diameter, arried out on lathes with a great stiffness, ould be a favourable solution. In ase of mahining surfaes with tapering and other profile (for example, torus) shapes, the favourable derease in roughness does not our; on the other hand, the auray, ahieved during the mahining, develops unfavourable, due to the wiper edge geometry [14][15]. In order to inrease the reliability of all results, it is reommended to selet the inserts, to be tested, by thorough examinations (arried out with mirosope) and to test only inserts of appropriate (well pressed) ondition, intat oatings and orret edges. 9

11 6. Long-term effiieny of utting inserts The long-term effiieny of inserts is losely related to the deterioration of the tool (or with other words, the degradation of utting performane of the tool): by this term is understood the sum of unfavourable influenes, expressly resulting from the tool wear or maybe even indiretly they an play a role in it. As a result of the wear, there is a lear inrease in the utting temperature, in the fore, torque and power demand, in the vibration tendeny and noise impat, and there is a hange in the roughness and/or in the waviness, too [16]. It is obviously, a tool life, belonging to an appropriately determined wear riterion, an be onsidered as the main feature for the purposes of the workpiee mahinability and the utting performane of the tool. It would be a self-evident thought that the time, spent in mahining, had to be onsidered when alulating the effiieny, based on the formula () and ontaining four seleted features. To monitor the wear proess of a tool from the beginning till the end, would make the examinations very timeonsuming (and ost-intensive) as it would be neessary to ollet hip samples, to measure the values of fore omponents and the development of the Rz roughness parameter at the same times of individual wear measurements. Although the onstany of the utting data (a, f, v ) and material removal rate (V') an be ensured during the lifetime measurements, the other three features (hip shape, fore omponents and the Rz roughness values) hange to a great extent during the wear period of tool. The modifiation of the hip shape is illustratively shown on Figure 5. The hange, reated by rater wear, may ause even 3-lass differene in the value of g as the rater, developing gradually on the rake fae, impairs the initially favourable hipbreaking effiieny. In the first phase of the persistent wear proess, there are developing hips, having C and G shape and divided into small piees, later - depending from the plae, width and depth of the rater - there are ylindrial, spiral hips, having a length of mm, even later, there are unmanageable, dangerously oiled, flowing hips. When ahieving the wear riterion, there are again well manageable hips, having a C shape and/or hips, oiled up like a snake and spreading dangerously. The influene of the tool wear on the utting fore omponents is well-known. The hange in the F utting fore, resulting from the wear, means an inrease of 5-30 perent in the fore formula of Kienzle and Vitor []. This experiene has been onfirmed by our measurements, too (see Table 6). An even greater hange (i. e. inrease) is shown in ase of feed and passive fore omponents (F f and F p), thus it is understandable that the ondition monitoring systems are based, among others, on the hange of these two fore omponents (or their ratio). Time Phenomenon Cutting time, t, min 1 min 6 min 8 min 10 min 1min Flank wear Crater wear Chip shape Figure 5 The hange in hip shape due to the tool wear Insert: CNMG10408 PM K10+TiAlN-mono (PVD); Workpiee: C60 unalloyed steel (HB0±5); Mahining onditions: a=1,5 mm; f=0,5 mm; v =00 m/min; dry mahining 10

12 The roughness data of mahined surfae are also in relation to the wear ondition of the tool. On Figure 6 the hange of the roughness features (Ra, Rz) is shown in funtion of the utting time in ase of a hard-to-mahine, austeniti, orrosion-resistant steel. As it an be seen well on the diagram, in the phase of uniform wear (t =...6 min) the value of Rz suddenly doubles, after that - in funtion of the urrent ondition and ironing effet of the edge - there is a sharp fall in the value of unevenness height. Figure 6 The hange in roughness of mahined surfae in funtion of time [10][17] Insert: CNMG10408 MT TT5100; Workpiee: Ko36 stainless steel (HB170±5) Mahining onditions: a=1 mm; f=0,1 mm; v =160 m/min; dry mahining Towards to the end of the tool life (t > 4 min), there is again an inrease in both measured roughness features. The hange of the surfae finish produing apability, shown on the mentioned figure, is not allowed, for example, in ase of series prodution of omponents, having a small diameter and length measurement or in ase of prodution onditions, when the speified quality has to be ensured. The protetive effet of PVD-oatings of different materials, strutural ompositions, thiknesses and nano-hardnesses, has been examined by long-term (lasting) test series. In the Table 6 the results of wear test of a single-layer oating are summarised. Table 6. The effet of tool wear on the effiieny of insert Long-term effiieny of inserts Wear data Fore values, N Roughness Chip Effiieny Time, min VB, mm F Ff Fa Rz, μm g H 1 0, ,0 0, ,3 4 0, ,5 6 0, ,7 8 0, ,1 10 0, ,8 1 0, ,8 Mahining onditions: dry mahining a=1,5 mm; f=0,5 mm; v =00 m/min; V =75 m 3 /min Insert: CNMG PM K10 + single-layer of TiAlN (PVD) Workpiee: C60 steel (HB 5±5) As long as the wear riterion (VB meg = 0, mm) has not been ahieved, there was a 3-lass differene in the lassifiation of hip shape, the ative fore (F a, N) inreased by approx. 5 perent, the feed fore (F f) grew nearly by 70 perent, while Rz, the unevenness height, hanged rhapsodially (almost following the development, shown on Figure 6). In funtion of the utting time, the effiieny first dereased gradually, then - unexpeted - fell to a third. In the last phase of the wear proess, the 11

13 effiieny indiator (H) inreased to suh a great extent that it exeeded largely the value, measured at the starting phase. This an be explained by the fat that the Rz roughness of the mahined (turned) surfae redued (due to the ironing effet of the tool edge) to a small proportion, the lassifiation of hip shape has beame better by three marks. The wear measurement results and the effiieny indiators of multilayer oating, having the same material, are summarised in Figure 7. Figure 7 Wear and insert effiieny in funtion of the time, in ase of different oatings Insert: CNMG PM K10; Coating: TiAlN single-layer and TiAlN multilayer oating (PVD) Mahining onditions: C60 steel (HB5±5); a=1,5 mm; f=0,5 mm; v =00 m/min; dry mahining The wear urve of TiAlN single-layer oating an be desribed by the formula VB(t )= t EXP 4,7 0,46t s = ± 0,007 while the TiAlN multilayer-oating by the following: VB( t ) t s 0,01 ; ; R EXP 4,3 0,33 t R + 0,03t = 0,97 0,0 t 0,945 [ mm ] Comparing the equations (6) and (7), it an be seen that the greater number of layers - reduing the wear on the flank land - improves the insert effiieny and inreases the tool life by 0 perent. In funtion of the utting time, the effiieny has a dynami dereasing tendeny throughout the proess in ase of single-layer oating, and it has a favourable value only shortly before the failure. At the same time, in ase of multilayer oating, the effiieny first dereases slightly, then it starts to inrease and at the next wear measurement there is a drastial redution. In the final phase of the wear proess, aording to the formula (1) we have again a great value. This an be explained by the fat that the inreasing value of developing fore effets an be ompensated by the edge, ironing the surfae (leaving a very low roughness values behind) and by the very favourable (snake/spiral-like) hip shape. Our opinion has been onfirmed by the results of durable tests that it is not reommended to apply the effiieny, alulated by the formula (1) to desribe the long-term produtive effiieny of inserts, due to the following reasons: the wear period of the tool has an inonsistent effet on the most important four supplementary features. With other words, the value of H indiator has a sudden and drasti redution lose to the inflexion points of wear urves (t = min); the flank wear, used as riterion in ase of lifetime measurement, has a lear effet only on the developing fore effets from the supplementary features (in ase of tools, having a great lead angle value, it affets mainly the F f omponent), it has an indiret effet on the developing roughness, while it has no influene on the hipbreaking effivieny; [mm] ( 6 ) ( 7 ) 1

14 the wear on the front of the insert (mainly the rater wear formation) has a heti effet on the hip development; the atual ondition and real shape of the tool edge, depending from the wear status, may make the roughness measurement on the workpiee unsure. An instabile utting proes, the urrent shape of tool edge, having been opied and/or the ironing effet at the same time, may lead to flutuations, shown on Figure 7. Due to the reasons, mentioned above, it is not reommended to make any onnetion between the effiieny, as interpreted by us and alulated aording to formula (1), and the long-term produtive effiieny of inserts. It does not offer an appropriate solution to average the effiieny values, belonging to the dates of wear measurements or even to weight these values. 7. Result and disussion In the present artile a new qualifiation method has been introdued, it an be benefiially applied when determining the utting ability of inserts. The method is able to ompare inserts, having a different shapes, edge onstrutions, sizes, hipbreakers, material grades and oatings, in an objetive way; furthermore, it makes possible to make effiieny rank orders and to measure the of suess the innovations, too. It defines three important effiieny elements whih enable to selet the optimal data settings, using the formula (1) and, defining the omplex effiieny (see the formula (4)), there is only a single perentage ratio to desribe the tested insert. The appliability, modified with weighted numbers based on the manufaturing trends and operational pratial statistis, an be alulated with formula (5). With the weighted omplex effiieny it is possible to ompare inserts, having different funtions, in an objetive way. The advantage of the elaborated method is that it is based on four, simple features (to be exat: the material removal rate, hip shape, ative fore and surfae roughness): these an be easily alulated, evaluated and measured; furthermore, this proess is suffiiently ost-effetive as it needs a low time-, material and finanial expense. The disadvantage is that it is possible to make only short-time tests with this. It is well-known that the main feature of the utting performane of an insert is the long-term produtive effiieny, with other words, the wear behaviour and the edge durability of the tool. The onnetion between the wear proess development (see formulas (6) and (7)) and the effiieny is rather aidental. The example, introdued in the present artile, illustrates that the effiieny, alulated from four main parameters of the supplementary features, should not be onfused with the produtive effiieny of inserts. Three world-leading tool manufaturing ompany groups provided us with inserts to these tests; the usability and the adequay of method has already been onfirmed by test results, arried out on 85 different inserts. In the future we are going to test newly developed inserts with the method, desribed earlier: these inserts, to be launhed on the market, an almost revolutionise the turning operation. Aknowledgements The author wishes to thank to his olleagues, taking part in the measurements and in the preparation of the previous artiles. Speial thanks must go to Dr. Zoltán Pálmai, for his valuable professional omments. Referenes [1] Sipos S, Palásti-Kovás B 007 A forgásoláskutatás néhány eredménye a szerszámminősítés területén Nemz. Gép. & Bizteh. Szimp. (Budapest) p 8 [] Sipos S, Palásti-K B, Horváth R 015: Forgásoló tehnológiák és szerszámai (Budapest, p 410 [3] Biró Sz, Sipos S, Kisa Zs, Uras P 009 mirocad Int. Sie. Conf. (Miskol) M pp 7-33 [4] Biró Sz, Cselle T, Hájek V, Sipos S 010 mirocad Int. Sie. Conf. (Miskol), N pp 5-3 [5] Pálmai Z 1980 Fémek forgásolhatósága Budapest, MK p 30 [6] Sipos S 1990 Korszerű tehnológiák, vol 4 No 5 pp

15 [7] Sipos S, Repáruk I 1990 Gépgyártástehnológia vol XXX No 7 pp [8] Palásti-Kovás B, Dajs L, Sipos S 1990 Gépgyártástehnológia vol XXX No 8 pp [9] Palásti-Kovás B, Sipos S, Czifra Á 01 Pro. Intl. Conf. on Tools (Miskol) pp [10] Palásti-Kovás B, Sipos S, Biró Sz 014 Ata Polytehnia Hungaria vol 11 pp 5-4 [11] Brammertz P H 1961 Industrie Anzeiger vol 83 No pp 5-3 [1] Biró Sz, Nagy A, Sipos S 010 Int. Conf. on Manufaturing (Budapest) on CD ISBN [13] Biró Sz, Nagy A, Sipos S 011 mirocad Intl. Sie. Conf. (Miskol) L pp 17- [14] Sipos S, Biró Sz, Biró J 005 Int. Sie. Conf. on Met. Cut. DMC005 (Kosie) on CD ISBN [15] Sipos S, Biró Sz, Tomoga I 006 Gépgyártás vol XLVI No 4 pp 17-4 [16] Sipos S 1997: A forgásolás minőségbiztosítása (PHARE), TDQM-HU /B, Budapest, pp [17] Palásti-Kovás B, Sipos S, Biró Sz 014 Gyártóeszközök vol XX pp