Tool life and quality of surface finish of the workpiece influence production rate and production cost. Cemented carbide tools have found wide application in the production arena of Bangladesh. In the absence of any testing facility in the country for the selection of cost-effective tools, poor quality carbide tools are frequently imported. A testing method and a selection criteria were developed for testing carbide tools of different shapes and sizes and for selecting the most cost-effective tool. For each tool cutting tests were performed to generate tool life data under different cutting conditions. Mild steel served as the work material. The relationship between tool life and cutting speed was developed using a curve-fitting software on a PC. From these relationships the values of the constants of the Taylor’s equation were determined. The cost equation was then derived for each tool for a given

amount of work in a cutting speed range. Finally, the most cost-effective tool was selected on the basis of the relative location of the cost curves of the tools tested

Ahmed, Mahiuddin

Amin, A. K. M. Nurul

Karim, A.N. Mustafizul

Sarker, Md. Ruhul Amin

English

The International Islamic University Malaysia Repository

Journal of Materials Processing Technology 77 (1998) 59–63Selection of cemented carbide turning tools using EMF andoptimization criteriaA.K.M. Nurul Amin *, Md. Ruhul Amin Sarker, Mahiuddin Ahmed,A.N. Mustafizul KarimDepartment of Industrial and Production Engineering, Bangladesh Uni6ersity of Engineering and Technology, Dhaka-1000, BangladeshAbstractTool life and quality of surface finish of the workpiece influence production rate and production cost. Cemented carbide toolshave found wide application in the production arena of Bangladesh. In the absence of any testing facility in the country for theselection of cost-effective tools, poor quality carbide tools are frequently imported. A testing method and a selection criteria weredeveloped for testing carbide tools of different shapes and sizes and for selecting the most cost-effective tool. For each tool cuttingtests were performed to generate tool life data under different cutting conditions. Mild steel served as the work material. Therelationship between tool life and cutting speed was developed using a curve-fitting software on a PC. From these relationshipsthe values of the constants of the Taylor’s equation were determined. The cost equation was then derived for each tool for a givenamount of work in a cutting speed range. Finally, the most cost-effective tool was selected on the basis of the relative locationof the cost curves of the tools tested. © 1998 Elsevier Science S.A. All rights reserved.Keywords: Cemented carbide tools; Intensity of tool wear; Optimum cutting speed1. IntroductionBangladesh is a developing country and as with manyother developing countries, it is dependent on importedtechnology for its heavy industries such as fertilizerfactories, steel mills, jute mills, oil refineries, etc. How-ever, the country has to perform a substantial amountof metal cutting and processing operations for thesupply of these industries with spares, and for manufac-turing machinery for use in various sectors, such asagriculture, transport, textile and others.Cutting tools play a vital role in metal-cutting opera-tions. For cutting cast iron, stainless steel, heat-resistantalloys etc., especially at high speeds, the cutting toolhas to be heat- and wear-resistant. Until very recently,high speed steel (HSS) tools dominated the small scaleproduction sector of Bangladesh. However, due to theclear competitive advantage of cemented carbide toolsover HSS tools and also as a result of growing aware-ness amongst the local entrepreneurs, cemented carbidetools have replaced HSS tools, especially for turning,boring, milling, shaping, planning and similar otheroperations.In the local market, a variety of single-poing ce-mented carbide turning tools of various shapes andsizes are available. In most of the cases the compositionand cutting properties of these inserts are unknown. Asa result it is difficult to choose the correct tool for aparticular operation. The inserts are known in the localmarket by the brand–manufacturers’ name. Inserts ofChina, India, Poland, Sweden, etc. are very popular inthe local market. The local users select the insertsdepending on their past experiences. In the absence ofany testing facility in the country for checking thequality of cemented carbide tools poor quality toolswere imported on various occasions by different organi-zations of the country. Keeping this in mind, a testingset-up for checking the quality of carbide inserts hasbeen developed as part of the present work. Since theavailable carbide tools have variation not only in theirproperties but also in their purchase costs and dimen-sions, so cost effectiveness should be the criteria fortool selection rather than the properties of the toolalone.* Corresponding author.0924-0136:98:$19.00 © 1998 Elsevier Science S.A. All rights reserved.PII S0924-0136(97)00394-4A.K.M. Nurul Amin et al. : Journal of Materials Processing Technology 77 (1998) 59–63602. Literature survey and aims and objectivesIt is reported that the wear of a cemented carbidetool is mainly due to diffusion [1] especially above alimit of a cutting speed limit beyond which there existsno built-up edge. The process of diffusion is intensifiedby rise of cutting temperature, which bears a directrelationship with the cutting speed, thickness of cut,material hardness, etc. If other parameters are un-changed, the intensity of tool wear increases with thecutting speed. Markov [2] has successfully established arelationship between the intensity of tool wear andcutting temperature. However, it is very difficult tomeasure the temperature developed at the ship–toolinterface, since at high cutting speeds the chip is fullywelded to the tool surface [3].As indirect and easier method has been adopted byvarious research schools to measure the temperature.Milton [4] has established that there exists a directrelationship between the cutting temperature and theElectro-Motive-Force (EMF) developed between theworkpiece and the tool. In this case, the workpiece andthe tool act as thermo-couple. If the tool is isolated andconnected to the workpiece by an electric circuit asshown in Fig. 1, a small current would flow betweenthem due to a voltage difference created by the EMF.This voltage may be measured by a milli-voltameter.Since both the intensity of tool wear and the EMF arefunctions of cutting temperature, the EMF may be usedas a criterion for testing the performance of cementedcarbide tools. For the simplicity of testing a smallvariation in the coefficients of proportionality betweenthe developed EMF and the cutting temperature maybe neglected for various groups of cemented carbidetools. Under this assumption a simple criterion [5]based on the EMF was developed to select the tool withthe best cutting properties.Fig. 2. Effect of the cutting speed on the EMF.It was observed during earlier experiments that theshapes and sizes of the tools were different and that thepurchase cost of these tools was not dependent on thesizes of the tools alone. Due to this variation in size andprice neither the tool wear nor the purchase cost of atool would be adequate to determine the overall perfor-mance in the selection of a tool. Evaluation of theeconomic tool life could be an appropriate approach inconsidering the above factors and the cutting condi-tions [6]. In the present study, the economic tool lifewas determined using the data [7] of previous experi-ments and used for the selection of the proper tools. Aranking of various tools was performed using thismethod as well as the EMF and the intensity of toolwear criteria.3. Methodology and experimental setupIn this study, 12 categories of carbide inserts fromdifferent origins were tested. Of these inserts, threegroups were manufactured in the former USSR, one inPoland, one in China, one in India, and the other six bya Local Government Organization (coded as BOF).The material of inserts USSR-1 was BK-8 having acomposition of 92% WC and 8% Co; the material ofinserts USSR-2 was T5K10 having a composition of5%, TiC, 85% WC and 10% Co; and that of USSR-3was T15K6 having a composition of 15% TiC, 79% WCand 6% Co. The composition of the other three groupswas not available.The tool geometry for the experimentation was takenas follows: rake angle, g0°; side clearance angle,a10°; end clearance angle, a120°; side cutting edgeangle, f45°; end cutting edge angle, f125°.A lathe machine (model Celtic-14) having a four-foot(1215 mm) long bed and a swing over the bed of 75 mmwas used in the test. A solid bar having a maximumdiameter of 102 mm and a length of 630 mm wasFig. 1. Experimental set-up.A.K.M. Nurul Amin et al. : Journal of Materials Processing Technology 77 (1998) 59–63 61Table 1Available and calculated data on the various parameters for carbide toolsConstant C Constant nTool code No. of regrind NtTip size (mmmm) Initial cost (Taka) CT1325Poland 553.45 0.3866 43 80.00476.42 0.422815.525 56USSR1 120.0015.525USSR2 791.47 0.4865 56 165.0015.525USSR3 608.29 0.4753 56 130.00489.85 0.44341225 37China 80.001212India 571.98 0.4266 37 50.00596.05 0.4548BOF1 5114.66.5 100.00527.40 0.430414.66.5 51BOF2 100.007.88.1BOF3 679.52 0.4763 15 95.00484.32 0.3047 15BOF4 95.007.88.1523.65 0.3334 52 110.0014.821.9BOF514.821.9 631.59 0.3791BOF6 52 110.00Note: *1 US$42 Taka (approximately).turned at cutting speeds of 80, 100, 120, 150 and 180mm min1, with a feed of 0.20 mm rev1 and a depthof cut of 1.0 mm.According to the experimental set-up shown in Fig.1, the EMFs developed in the cases of different testedcutting tools were measured [5] for identical cuttingconditions. For this purpose the tool insert holder waskept completely insulated from the tool post of thelathe machine. The tool insert was connected with aprobe to one end of the milli-voltmeter and the otherend of the milli-voltmeter was connected to a bolt ofthe fixture body which, in turn, was connected to agraphite rod. This graphite rod was also connected to asteel disc which was placed in the hole of the lathemachine spindle. To obtain the values of the EMF, thework material was turned for a few seconds with eachof the tool inserts and the corresponding milli-voltmeterreadings were recorded. These experiments were per-formed taking three carbide tips from each type ofinsert. The average values of these three milli-voltmeterreadings (i.e., EMF) for different groups of carbide tipswere calculated and are plotted in Fig. 2.An instrument microscope was used for measuringthe tool wear. Readings were taken at a regular intervalof turning. Using the experimental data of flank wearand cutting time, the intensities of tool wear werecalculated. The tool life corresponding to a flank wearof 0.5 mm was calculated. The tool life data obtainedduring these experiments were used to evaluate thevalue of C and n, in the constants of Taylor’s equation.The number of possible regrinds, Nt, of each tool wascalculated on the basis of the initial and the finallengths of the tips and the length reground each time.The following collected data [8] were utilized in deter-mining the optimum cutting speed: tool changing time(t1) 3 min; time to grind a tool (t2)15 min; labourand overhead rate (Rc and Rs)110 Taka* h1.The computed values of constants of Taylor’s equa-tion for the different tools along with their number ofpossible regrinds and initial purchase cost data arepresented in Table 1.4. Formulation for cost analysisEconomic analysis [9] was performed to compare thetested groups of cemented carbide tools. The cost of atool between two regrinds (Ct) can have three compo-nents, as follows: (i) tool changing costs, C1 t1Rc;(ii) grinding–sharpening costs, C2 t2Rs; (iii) pro-portion of the original cost of the tool, C3CT–Nt, inwhich: CtC1C2C3, where: t1 time to change atool (min); t2 time to grind or sharpen a tool (min);Rc labor and overhead rate applied to the metalcutting operation (Taka–min); Rs labor and overheadrate in the tool grinding department (Taka–min); Ntnumber of times the tool can be ground (includinggrinding performed during manufacturing); CTorigi-nal cost of the cutting tool (Taka).For a tool life of T min, the cutting cost over the lifeof the tool is CcRcT. During this time, the amountof metal removed in cm3 is:Fig. 3. Effect of the cutting speed on the intensity of tool wear.A.K.M. Nurul Amin et al. : Journal of Materials Processing Technology 77 (1998) 59–6362Fig. 4. Unit cost vs. cutting speed for different carbide tools.QTVmTfdwhere: f feed equivalent to width of cut (mm rev1);ddepth of cut (mm); Vm linear velocity (m min1).If C–Tn is substituted for Vm (since VmTnC) [8] inthe above equation, then:QTCTnTfdCfdTn1CGTn1where CGCfd.The total unit cost in Taka cm3 is:CuCCCtQTTn1(RCTCt)CGIf Cu is differentiated with respect to T and set equal tozero to find the minimum, the expression for the eco-nomic tool life becomes:Te1n1 CtRcIt is observed from the above equation that, if theparameter n is fixed, the economic tool life increaseswith the increase of Ct and–or decrease of Rc. Thisindicates that both the labor and overhead rate as wellas the cost of the tool influence the economic tool life.The corresponding optimum cutting speed can befound from Taylor’s equation, VTnC i.e.:VCTne5. Results and discussionThe relationships between the EMF and the cuttingspeed are shown (up to a limited value of cutting speed)in Fig. 2. The intensities of tool wear versus cuttingspeed are shown in Fig. 3. It may be observed fromFigs. 2 and 3 that above a cutting speed of 80 m min1the intensity of tool wear is approximately proportionalto the EMF developed by the different tests inserts.Thus, an insert which develops lower a EMF duringcutting in this cutting speed range is likely to show alower intensity of wear and consequently have a greatertool life.The cutting speed (m min1) versus the unit cost(Taka–cm3) curves for different carbide tools is shownin Fig. 4. The optimum cutting speed and its corre-sponding unit cost for all tools are given in Table 2.It is clear from Fig. 4 that the USSR-2 curve isalmost flat after the cutting speed of 160 m min1,which means that it is less sensitive in this speed range.With this tool, it is possible to lower the cutting speed(in case of machine limitation) without sacrificing muchcost. The curve of BOF6 is the most sensitive curve,A.K.M. Nurul Amin et al. : Journal of Materials Processing Technology 77 (1998) 59–63 63Table 2Optimum cutting speeds and costs for different toolsTool code Optimum unit cost (Taka per cu cm)103Optimum speed, V (m mm1) Rank38.45148.17 (2)Poland53.06USSR1 (6)119.5928.65181.08 (1) Best toolUSSR242.17 (3)USSR3 142.1252.48119.43 (5)China63.62India (11)144.2958.61143.49 (9)BOF145.27BOF2 (4)131.3353.35150.67 (7)BOF372.19BOF4 (12)147.9259.76155.22 (10)BOF5BOF6 53.76170.92 (8)which means that the change of cost for this tool withrespect to the speed is the highest amongst all of thetools. If USSR-2, Poland, USSR-3, and BOF2 tools arenot available in the market, then there is no singlegroup of tools which is better for the whole range ofcutting speed considered in this research. For example,the China tool is better for a cutting speed range of lessthan 140 m min1 and BOF4 tool is better for a cuttingspeed of greater than 170 m min1. The optimumcutting speed and its corresponding unit cost, as per thecurves discussed, for all the tools are given in Table 2.Ranking of the tested inserts according to the EMFcriteria in the cutting speed range of 25–60 m min1above a cutting speed of 80 m min1 is presented inTable 3. According to the tool wear criteria, the rank-ing of the inserts for cutting speeds of above 80 mmin1 is also given in Table 3. Ranking of the toolinserts according to the minimum cost criteria summa-rized in Table 3 indicates that there has been a re-ar-rangement of the ranking positions of the inserts ascompared to the ranks according to the EMF and thetool wear criteria. This is due to the influence of theprocurement cost and size and shape of the individualinsert.6. ConclusionsA method of testing the quality of carbide inserts hasbeen established using electromotive-force (EMF) asthe criterion. It has been observed that the EMFsdeveloped during turning with different carbide insertsare almost proportional to the intensities of wear ofthese inserts under identical cutting conditions.An alternative method is proposed to choose themost cost-effective tool from a number of differentcarbide tools using a minimum-cost criterion. Thismethod appears to be appropriate where a variety oftools is available with unknown chemical compositionand physical properties.References[1] T.N. Loladze, Metal Cutting Tool Wear, Moscow, 1958, p. 356.[2] A.D. Markov, Tool Wear and Tool Life, Moscow MachineBuilding, 1966, p. 262 (translated from Russian).[3] N.V. Talantov, N.P. Cheriomushnikov, A.I. Kurchenko, Influ-ence of Cutting Speed on Different Characteristics of MetalCutting Process and Tool Wear, Technology of Machine Build-ing and Automation of Production Process, Volgograd, 1978,pp. 29–49.[4] M.C. Shaw, Metal Cutting Principles, 3rd edn., India, 1957.[5] A.K.M.N. Amin, M.R. Islam, Investigation of a new method fortesting the cutting properties of different cemented carbide tools,J. Inst. Eng. Bangladesh 21 (1) (1993) 55–61.[6] G.C. Sen, A. Bhattacharyya, Principles of Metal Cutting, 2nded., Calcutta, 1969, p. 412–553.[7] M.R. Islam, A new method for testing quality of cementedcarbide tools and a comparative study of different cementedcarbide and high speed steel tools available in the local market,M. Eng. Project, Dept. of IPE, BUET, Dhaka, 1989.[8] Personal communication with Bangladesh Industrial and Techni-cal Assistance Centre (BITAC), Dhaka.[9] L.E. Doyle et al., Manufacturing Process and Materials forEngineers, 3rd edn., Prentice Hall Inc., Englewood Cliffs, NewJersey, 1985.Table 3Ranking of tool inserts according to different criteriaRanking of tool inserts (from best to worst)Criteria of judge-mentElectro Motive India, Poland, USSR2, USSR1, USSR3,Force (EMF) China (for 25 m min1BVB60 m min1).Poland, USSR2, India, USSR3, USSR1,China (for V\80 m min1).Intensity of tool Poland, USSR2, India, USSR3, USSR1,China (for V\80 m min1).wearMinimum cost USSR2, Poland, USSR3, BOF2, China,USSR1, BOF3, BOF6, BOF1, BOF5, India,criteriaBOF4 (for 80 m min1BVB220 m min1)..

Selection of cemented carbide turning tools using EMF and

optimization criteria

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Selection of cemented carbide turning tools using EMF and optimization criteria

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