Microsoft Word - B_17_Molnar_R.doc HUNGARIAN JOURNAL OF INDUSTRIAL CHEMISTRY VESZPRÉM Vol. 39(2) pp. 219-224 (2011) COMPARISON OF HARD MACHINING PROCEDURES ON MATERIAL REMOVAL RATE V. MOLNAR , J. KUNDRAK University of Miskolc, Department of Production Engineering, H-3515 Miskolc-Egyetemvaros, HUNGARY, E-mail: viktor.molnar@uni-miskolc.hu The economic efficiency of machining plays an important role in the comparison of alternative procedures in the field of precision manufacturing too. It is not easy to performthe comparison because of the dissimilarities of material removal processes and/or procedures. However, there are some indicators that facilitate the analysis. The paper focuses on the economic comparison of the different finish procedures: grinding, hard turning and combined procedures. We analysed the practical material removal rate and the consumption of the used up coolant and lubricant (CL) as the basis of the operation time of the machining. Compared with grinding, hard turning and combined procedures showed lower operation time and higher material removal rate besides lower environmental load. Keywords: 9 hard machining, operation time, material removal rate Introduction The increasing customer needs referring to the quality determine the change of functional properties of the products. To achieve it, the increase of tenacity of the components is important. It can be reached with the hardening of the surfaces too. The hardening is a procedure which is also applied to simplify the production chain in some groups of components. The abovementioned also facilitate the increase of hard surfaces on the components. Hardening is generally followed by finishing which results the final geometry of the component. For a long time, grinding was the most often used finish procedure but today hard turning and the combination of these procedures play an important role in this field. However, it is not easy to outline the application fields where grinding may be substituted by hard turning [1, 2]. The application of hard cutting and combined procedures requires different machine tools and new production organizing methods. These changes affect the costs of production and other fields of the enterprise. That is why decision makers have to solve an optimization task extending to the whole production chain to compare the possible machining versions. To compare the procedures, the machined components have to be produced by the same accuracy and quality requirements. Grinding and hard turning are basically different procedures referring to material removal. If the specified accuracy and quality requirements can be assured by two or more procedures, those can be considered as the alternatives of one another. Besides ignoring or supposing the constancy of the costs of investments, human resources and other management processes, the practical material removal indicators can be useful to compare the alternative procedures by economic aspect [3, 4, 5, 6]. A special aspect of the investigation is the extent of environmental load. The environment pollution of machining includes several components but we focus only on the consumption of coolant and lubricant. The applied procedures and environmental load characterising the procedures The most often analysed hard machining procedures are grinding, hard turning and the combined procedure. Grinding had a distinguished importance in finishing of hardened surfaces referring to machining of engineering industrial components because the machining of hardened surfaces with high accuracy and low roughness was possible to be provided in most cases by this procedure only. Besides its several advantages, one of its disadvantages is that it particularly loads the environment. Grinding, because of the large amount of CL, pollutes the environment in large measure, damages the workers’ health and even the process costs are higher. Grinding requires expensive auxiliary materials, and among the remaining materials the mud and the used up lubricant are considered dangerous waste. The second hard machining procedure which spreads more and more nowadays is the hard turning. The rapid increase of the procedure can be observed particularly in disc-featured components and by the machining of different bore-holes. Hard turning loads the environment less. Hard turning shows a much more favourable picture than grinding from the point of view of environment 220 protection, too, as those unfavourable effects do not occur. The machining can be completed without using CL. The chips are the same as the workpiece material, thus they can be recycled. Hard turning provides an entirely environment friendly, clear and hygienic machining of the workpieces while they have the same quality as by grinding [7, 8]. The third procedure is the combined procedure. Roughing is done by hard turning and smoothing is by grinding. To compare that with the traditional procedures, the major difference is, that the machining is carried out on the same machine tool in one clamping in one operation. That is why the smoothing allowance can be smaller. It is important because the environmental load caused by the operation is in proportion with the machining time of the two procedures. Experiments On disc-feature components, internal cylindrical surfaces were with different geometry machined. The sizes of the components machined at the plant and the technological data applied there in grinding were considered as basis. Hard surfaces are often internal cylindrical surfaces, which, in producing parts, are often to be formed. The machining of bore-holes in most cases is a more difficult and more expensive procedure than the machining of external surfaces. Earlier grinding was the major procedure for machining hardened internal cylindrical surfaces too. Bore-hole grinding is an often used, wide-spread procedure. Boring can also be done under more difficult conditions compared to external turning. That is why the machining with adequate efficiency of bore-holes and the surfaces being in connection with them is a particularly important task e.g. in the machining of gear- wheels. The aim of the experiments was to establish an order among the procedures. Conditions of the experiments The experiments were performed on workpieces (Workpiece: WP) with the same diameter but different lengths and also on workpieces with the same length but different diameters (Table 1). The data of the workpiece were as follows. − material: 16MnCr5 − hardness: 61..63 HRC − accuracy: IT5..6 − ℓ/d relationship: 0.41..1.04 − allowance: 0.15 mm − sequence size: 200 0.1 mm of allowance was removed by roughing and 0.05 mm by smoothing. The major technological data (machine tool, tool, allowance, feed, cutting speeds etc.) and the drafts of procedures are detailed in Table 2. Table 1: Geometric data of the workpieces Sign: WP1 WP2 WP3 WP4 Diameter, d [mm] 37±1 48 66 Length, L [mm] 29.85 38.45 27.35 Table 2: Technological conditions of the machining experiments Technological conditions Procedure Tool and machine tool Roughing Smoothing vf,L=2.2 m/min ae=0.02 mm nw=90 1/min vf,L=2.0 m/min ae=0.001 mm nw=90 1/min Sign vc [m/s] Sign vc [m/s] WP1 25 WP1 25 WP2 25 WP2 25 WP3 29 WP3 29 Grinding vf,L .   .   . .   .   . .      . .   .  . .     . .. . . . . . . ... .. .. . . . ... vw b L ae vc Roughing and smoothing: 40x20x16-9A80-K7V22 Machine tool: SI-4/A WP4 29 WP4 29 vc=180 m/min ap=0.1 mm Insert standard wiper f [mm/rev.] 0.15 0.24 Combined procedure vc b L ap f vf,R .   .   . .   .   . .      . .   .  . .     . .. . . . .. . ... .. . .. . . ... vw vc . . . . . ... . . . . . . oscillation Roughing: CNGA 120408S-Lo CBN Smoothing: 40x40x16-9A80-K7V22 Machine tool: EMAG VSC 400 DS vf,R,LA=0.108 m/min vf,R,N=0.005 m/min nw=90 1/min vc=45 m/s vf,R,S1=0.0033 m/min vf,R,S2=0.0016 m/min nw=90 1/min vc=180 m/min ap=0.1 mm vc=180 m/min ap=0.05 mm Insert standard wiper Insert standard wiper Hard turning vc b L ap f Roughing: CNGA 120408S-Lo CBN Smoothing: CNGA 120408 7020 Machine tool: Pittler PVSL-2 f [mm/rev.] 0.15 0.24 f [mm/rev.] 0.08 0.12 221 The three different machining procedures (PR) were performed on different machine tools in five different versions. − PR1: grinding (roughing and smoothing) − PR2: combined procedure (roughing by standard insert, smoothing by corundum wheel) − PR3: combined procedure (roughing by wiper insert, smoothing by corundum wheel) − PR4: hard turning (roughing and smoothing by standard insert) − PR5: hard turning (roughing by wiper insert and smoothing by standard insert) The roughing grade of the combined procedure included a grinding process too. The internal traverse grinding (sign A) was performed by two cutting speeds. The workpiece revolution was constant by the grinding procedures.The number of sparking out strokes was ik=16 by all gear-wheels. In case of hard turning an L’ length has to be defined, which is the sum of the bore- hole length and the running on and running off lengths of the tool. Calculation method Operation time is in close relation with the changing costs of the production. It includes e.g. the preparation, replacement or piece times besides the machining time, Therefore it gives a clear picture about the connection between the economic and technical aspects. Some parameters are calculated by the technological data and others include empirical values resulted by the concrete production. In the industry these empirical values have a major importance. In case of large sequence size the values can be well estimated as a result of a process monitoring. In differing cases the analysis is difficult because there are no acceptable, exact calculation methods. The empirical values were taken from the process documentation of the company where the production was performed. The machining time is the sum of machining time of roughing and smoothing. The details of the calculation are showed by equations 2, 3 and 4. , ,m m R m ST T T= + , [min] (1) − Grinding: , , , , , , 2 2 SR m sp f L R e R f L S e S ZZL L T i v a v a ⎛ ⎞⋅ ⋅ = ⋅ + ⋅ +⎜ ⎟⎜ ⎟ ⎝ ⎠ , [min] (2) − Combined procedure: , , , , , , 0.27 A SR m sp f R L f R N f R S ZZ T t v v v = + + + + ' w R L n f + ⋅ , [min] (3) where: isp – the number of sparking out strokes tsp – the time of sparking out − Hard turning: ' ' m R w S w L L T f n f n = + ⋅ ⋅ , [min] (4) The replacement time is taken from the technological documentation. − Grinding: Trepl = 0.4 min − Hard turning: Trepl = 0.2 min Base time is the sum of machining and replacement times. Tb = Tm + Trepl, [min] (5) The supplement time is given. When 1.5 < Tm < 8, value of Tsupp is the following. − Grinding: Tsupp = 0.15Tm, [min] − Hard turning: Tsupp = 0.2Tm, [min] The piece time is the sum of base and preparation times. Tpiece = Tb + Tsupp, [min] (6) − Grinding: Tpiece = 1.15Tb, [min] − Hard turning: Tpiece = 1.2Tb, [min] The preparation time is given from the data of technological documentation. − Grinding: Tprep = 180 min − Hard turning: Tprep = 20 min The operation time is calculated by the following equation: prepop piece T T T n = + , [min] (7) The theoretical value of the material removal rate (MRR) is a widely used indicator, which gives information about the efficiency of machining. It is defined as the amount of the removed material per second (equation 8 in internal traverse grinding, 9 in grinding and equation 10 in turning). Qw = ae·f·vw, [mm 3/s] (8) Qw = L·vf,R·d·π, [mm 3/s] (9) Qw = ap·f·vc, [mm 3/s] (10) This indicator ignores the factors of the machining included in one procedure and not included in an other. To resolve this hiatus a practical value of the MRR was introduced (eq. 11). The essence of the conception is, that the theoretical MRR is corrected by a properly chosen datum of time which is suitable for the actual investigation. Therefore the gained value will fit to the machining times and costs. , ' 60wp op x d L Z Q T π⋅ ⋅ ⋅ = ⋅ , [mm3/s] (11) where: d – bore-hole diameter L’ – sum of bore-hole length and running on and off Z – allowance Tx – relevant time of investigation (in present investigation: Tx=Top) 222 To get information about the environmental load, the percentage of the used up of coolant and lubricant was determined depending on the operation time by a simple proportioning. Results of experiments and evaluation The machining experiments were separated by the machined bore-hole geometry. In the first step we chose two components with different bore-hole lengths (L) besides the same bore-hole diameters (d). In case of the other two gear-wheels the lengths were the same. We performed a detailed calculation referring to the machining times, material removal rate and environmental load. By traverse grinding, the machining times (Tm,R and Tm,S) was depended on the bore-hole length (Table 2, PR1). The reason for that was the type of the procedure: the bore-hole is longer than the width of the grind wheel having an alternating motion in axial direction. Therefore, the operation times besides the same bore-hole lengths were equal. BIn internal traverse grinding the operation time increases with the bore-hole length. In a combined procedure, the machining time of roughing (hard turning) increases with the bore-hole length (Table 2 PR2 and PR3) by 21–22 percent as well as with the diameter of the bore-hole (Table 3, PR2 and PR3) by 40–43 percent in case of both standard and wiper insert. But the roughing time with wiper insert shows 35–40 percent reduction (Tables 2 and 3, PR2 and PR3). The applied workpiece speeds were different by each part, id. est. WP3 and WP4 were machined at higher speeds. This is the reason for the smoothing machining time reducing with the increase if the bore-hole diameter. Other times were approximately equal by each workpiece. In hard turning, the machining times of smoothing are smaller than in the other procedures, which corresponds with the expectations. By the increase of the length or the diameter, these times increase too. In the first case this value is 16–23 percent, depending on which insert is used (Table 2, PR4 and PR5) and in the second the value is 36–40 percent (Table 3, PR4 and PR5). Table 3: Contents of operation time and CL quantity (by constant bore-hole diameters) Sign of workpiece Procedure WP1 WP2 Operation time, Top [min] T ra ve rs e gr in di ng PR1 0.14 1.97 1.68 3.78 0.17 2.54 1.77 4.48 3.78 4.48 0 1 2 3 4 5 6 7 WP1 WP2 PR2 0.14 0.33 0.43 0.27 0.63 0.17 0.41 0.44 0.3 0.72 0.90 1.01 0 1 2 3 4 5 6 7 WP1 WP2 C om bi ne d pr oc ed ur e PR3 0.09 0.330.43 0.18 0.66 0.11 0.41 0.43 0.19 0.75 0.84 0.95 0 1 2 3 4 5 6 7 WP1 WP2 PR4 0.14 0.260.42 0.83 0.17 0.32 0.44 0.92 0.83 0.92 0 1 2 3 4 5 6 7 WP1 WP2 H ar d tu rn in g PR5 0.09 0.180.39 0.66 0.11 0.210.40 0.72 0.66 0.72 0 1 2 3 4 5 6 7 WP1 WP2 Machining time (Roughing), Tm,R Machining time (Smoothing) Tm,S Other times (Top-Tm) Consumption of Coolant and Lubricant Dry machining 223 Table 4: Contents of operation time and CL quantity (by constant bore-hole lengths) Sign of workpiece Procedure WP3 WP4 Operation time, Top [min] T ra ve rs e gr in di ng PR1 0.12 1.81 1.65 3.58 0.12 1.81 1.65 3.58 3.58 3.58 0 1 2 3 4 5 6 7 WP3 WP4 PR2 0.16 0.38 0.43 0.3 0.68 0.23 0.33 0.43 0.4 0.58 0.98 0.98 0 1 2 3 4 5 6 7 WP3 WP4 C om bi ne d pr oc ed ur e PR3 0.10 0.38 0.43 0.19 0.72 0.14 0.33 0.43 0.27 0.63 0.91 0.90 0 1 2 3 4 5 6 7 WP3 WP4 PR4 0.16 0.31 0.43 0.91 0.23 0.42 0.47 1.12 0.91 1.12 0 1 2 3 4 5 6 7 WP3 WP4 H ar d tu rn in g PR5 0.10 0.200.40 0.71 0.14 0.280.42 0.85 0.71 0.85 0 1 2 3 4 5 6 7 WP3 WP4 Machining time (Roughing), Tm,R Machining time (Smoothing) Tm,S Other times (Top-Tm) Consumption of Coolant and Lubricant Dry machining In the investigation of operation times, it is observable that they increase with the bore-hole length because more material has to be removed. The traverse grinding showed the largest values and the hard turning the smallest. It seems, that this result allows the expectation that hard turning can be the most efficient procedure considering economic aspects but this simple indicator is not enough to enunciate it with absolute certainty. Using wiper inserts results lower operation times in both cases (combined procedure and hard turning). With the increase of bore-hole diameter, operation times are similar regarding grinding and the combined procedure but the wiper insert results lower values here too. In hard turning these times increase. We compared the environmental load of the different procedures. The extent of it was calculated by the operation times. Because of the above mentioned reason, hard turning is the most environmental friendly procedure. The lower circle diagrams in the Table 2 and 3 show the results referring to the used CL. The practical values of material removal rate are summarized in Figs 1 and 2. They include the concrete values of the five investigated procedure versions. Generally it can be stated that the values of the MRR indicator corrected by the operation times are lower besides smaller bore-hole diameter or shorter length. One exception is the internal traverse grinding. With the same diameter, the value of practical MRR is independent of the bore-hole length. Besides different bore-hole lengths or diameters, the practical MRR values are in proportion with the change of these parameters in hard turning. Furthermore, it is observable that the values are significantly higher by using wiper insert. In combined procedure the effect of the insert type determines these values only to a small extent (7–10 percent). By increasing the bore-hole diameter, the values of combined procedure are sharply different. The reason for that is the higher workpiece speed. Besides the material removal rate the other widely used indicator is the surface rate. We defined the practical value of that too. But because of the different allowances 224 and thus the different d.o.c’s, this parameter gives not such exact information about the econimic efficiency as the practical MRR. 2,4 9,9 10,610,8 13,6 2,4 10,7 11,511,8 15,1 0 4 8 12 16 PR1 PR2 PR3PR4 PR5 L = 29.85 mm L = 38.45 mm Qwp,op [mm 3/s] d=37±1 mm Figure 1: Practical values of material removal rate based on the operation time by the same bore-hole diameter 2,9 10,6 11,311,4 14,5 4,0 14,4 15,812,7 16,7 0 6 12 18 PR1 PR2 PR3PR4 PR5 d = 48 mm d = 66 mm Qwp,op [mm 3/s] L=27.35 mm Figure 2: Practical values of material removal rate based on the operation time by the same bore-hole length Conclusion Focusing on industrial demands, the applicability of hard machining procedures and the determination of their fields of application have been invariably a key research topic. The required workpiece characteristics (e.g. form- and dimension accuracy and surface roughness), can be provided by the high level reliability of the production processes in these types of machining. Several decisive advantages and disadvantages of hard cutting and grinding procedures are known, but further research is needed to reduce for example the process time or the environmental load. To reduce the whole process-chain in the hard machining of more and more parts (components) is possible for example by using only one machine tool for the whole process. Further task: within one process as big part of the allowance should be removed by hard turning as possible. The experiments proved that the application of hard turning in the finish operation involves both economic and environmental benefits. The comparison of hard turning and grinding in machining bore-holes showed the significant advantage of hard turning referring to economic efficiency. The existing differences were revealed by all investigated parameters, like operating time and the practical values of material removal rate. The combined (hybrid) machining provides economic efficiency similar to hard turning. ACKNOWLEDGEMENT The work was presented by the support of the Hungarian Scientific Research Fund (Number of Agreement: OTKA K 78482), which the authors greatly appreciate. The described work was carried out as part of the TÁMOP-4.2.1.B-10/2/KONV-2010-0001 project. REFERENCES 1. F. KLOCKE, E. BRINKSMEIER, K. WEINERT: Capability Profile of Hard Cutting and Grinding Process. Annals of the CIRP 54(2), (2005), 22–45 2. H. K. TÖNSHOFF, C. ARENDT, R. BEN AMOR: Cutting of hardened steel, Annals of the CIRP, 49(2), (2000), 547–566 3. T. TÓTH, J KUNDRÁK, K. GYÁNI: The material removal rate and the surface rate as two new parameters of qualification for hard turning and grinding, TMCE, 2004 4. J. KUNDRÁK, B. KARPUSCHEWSKI, K. GYÁNI: Accuracy of hard turning, JMPT 202(1-3), (2008) 328–338 5. J. KUNDRÁK, T. TÓTH, K. GYÁNI: How to make a choice of machining methods on the basis of economy: comparison between hard turning and grinding The Eleventh International Conference on Machine Design and Production, Antalya, 2004, 31–45 6. J. KUNDRAK, I. DESZPOTH: Material Removal Rate and Surface Rate in Turning and Grinding Bore- Holes, microCAD 2007, Kharkov, 110–121, (ISBN978-966-8944-35-2) 7. J. KUNDRAK, A. G. MAMALIS, A. MARKOPOULOS: Finishing of hardened boreholes: Grinding or hard cutting? Materials and Manufacturing Processes 19(6), (2004), 979–993 8. J. KUNDRAK, K. GYANI, V. BANA: Roughness of ground and hard-turned surfaces on the basis of 3D parameters, International Journal of Advanced Manufacturing Technology, 38(1-2), (2008), 110 << /ASCII85EncodePages false /AllowTransparency false /AutoPositionEPSFiles true /AutoRotatePages /None /Binding /Left /CalGrayProfile (Dot Gain 20%) /CalRGBProfile (sRGB IEC61966-2.1) /CalCMYKProfile (U.S. Web Coated \050SWOP\051 v2) /sRGBProfile (sRGB IEC61966-2.1) /CannotEmbedFontPolicy /Error /CompatibilityLevel 1.4 /CompressObjects /Tags /CompressPages true /ConvertImagesToIndexed true /PassThroughJPEGImages true /CreateJobTicket false /DefaultRenderingIntent /Default /DetectBlends true /DetectCurves 0.0000 /ColorConversionStrategy /CMYK /DoThumbnails false /EmbedAllFonts true /EmbedOpenType false /ParseICCProfilesInComments true /EmbedJobOptions true /DSCReportingLevel 0 /EmitDSCWarnings false /EndPage -1 /ImageMemory 1048576 /LockDistillerParams false /MaxSubsetPct 100 /Optimize true /OPM 1 /ParseDSCComments true /ParseDSCCommentsForDocInfo true /PreserveCopyPage true /PreserveDICMYKValues true /PreserveEPSInfo true /PreserveFlatness true /PreserveHalftoneInfo false /PreserveOPIComments true /PreserveOverprintSettings true /StartPage 1 /SubsetFonts true /TransferFunctionInfo /Apply /UCRandBGInfo /Preserve /UsePrologue false /ColorSettingsFile () /AlwaysEmbed [ true ] /NeverEmbed [ true ] /AntiAliasColorImages false /CropColorImages true /ColorImageMinResolution 300 /ColorImageMinResolutionPolicy /OK /DownsampleColorImages true /ColorImageDownsampleType /Bicubic /ColorImageResolution 300 /ColorImageDepth -1 /ColorImageMinDownsampleDepth 1 /ColorImageDownsampleThreshold 1.50000 /EncodeColorImages true /ColorImageFilter /DCTEncode /AutoFilterColorImages true /ColorImageAutoFilterStrategy /JPEG /ColorACSImageDict << /QFactor 0.15 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /ColorImageDict << /QFactor 0.15 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /JPEG2000ColorACSImageDict << /TileWidth 256 /TileHeight 256 /Quality 30 >> /JPEG2000ColorImageDict << /TileWidth 256 /TileHeight 256 /Quality 30 >> /AntiAliasGrayImages false /CropGrayImages true /GrayImageMinResolution 300 /GrayImageMinResolutionPolicy /OK /DownsampleGrayImages true /GrayImageDownsampleType /Bicubic /GrayImageResolution 300 /GrayImageDepth -1 /GrayImageMinDownsampleDepth 2 /GrayImageDownsampleThreshold 1.50000 /EncodeGrayImages true /GrayImageFilter /DCTEncode /AutoFilterGrayImages true /GrayImageAutoFilterStrategy /JPEG /GrayACSImageDict << /QFactor 0.15 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /GrayImageDict << /QFactor 0.15 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /JPEG2000GrayACSImageDict << /TileWidth 256 /TileHeight 256 /Quality 30 >> /JPEG2000GrayImageDict << /TileWidth 256 /TileHeight 256 /Quality 30 >> /AntiAliasMonoImages false /CropMonoImages true /MonoImageMinResolution 1200 /MonoImageMinResolutionPolicy /OK /DownsampleMonoImages true /MonoImageDownsampleType /Bicubic /MonoImageResolution 1200 /MonoImageDepth -1 /MonoImageDownsampleThreshold 1.50000 /EncodeMonoImages true /MonoImageFilter /CCITTFaxEncode /MonoImageDict << /K -1 >> /AllowPSXObjects false /CheckCompliance [ /None ] /PDFX1aCheck false /PDFX3Check false /PDFXCompliantPDFOnly false /PDFXNoTrimBoxError true /PDFXTrimBoxToMediaBoxOffset [ 0.00000 0.00000 0.00000 0.00000 ] /PDFXSetBleedBoxToMediaBox true /PDFXBleedBoxToTrimBoxOffset [ 0.00000 0.00000 0.00000 0.00000 ] /PDFXOutputIntentProfile () /PDFXOutputConditionIdentifier () /PDFXOutputCondition () /PDFXRegistryName () /PDFXTrapped /False /CreateJDFFile false /Description << /ARA /BGR /CHS /CHT /CZE /DAN /DEU /ESP /ETI /FRA /GRE /HEB /HRV (Za stvaranje Adobe PDF dokumenata najpogodnijih za visokokvalitetni ispis prije tiskanja koristite ove postavke. 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