Effects of the cutting feed, depth of cut, and workpiece ...

1 ORIGINAL ARTICLEE ffects of the cutting feed , depth of cut, and workpiece (bore) diameter on the tool wear rateViktor P. AstakhovReceived: 8 February 2006 /Accepted: 17 April 2006#Springer-Verlag London Limited 2006 AbstractMost published studies on metal cutting regardthe cutting speed as having the greatest influence on toolwear and, thus, tool life, while other parameters andcharacteristics of the cutting process have not attracted asmuch attention in this respect. This is because of theexistence of a number of contradicting results on theinfluence of the cutting feed , depth of cut, and workpiece (bore) diameter.

2 The present paper discusses the origin ofthe aforementioned contradicting results. It argues that,when the optimal cutting temperature is considered, theinfluence of the aforementioned parameters on tool wearbecomes clear and straightforward. The obtained resultsreveal the true influence of the cutting feed , diameter of theworkpiece, and diameter of the hole being bored on the toolwear rate. It was also found that the depth of cut does nothave a significant influence on the tool wear rate. Theobtained results provide methodological help in theexperimental assessment and proper reporting of the toolwear rates studied under different cutting of of the workpieceNomenclatureCv,ChConstants determined by the propertiesof the work material ( )

3 Cv-oConstant in diameterdcwDepth of cold workingdwDepth of cutfCutting feedhhDimensional wear ratehrRadial wearhr-iInitial radial wearhsSurface wear ratehs-optOptimal wear rateLwWorkpiece lengthlTotal length of the tool pathliInitial length of the tool pathSArea of the machined surfaceTTool lifeTUDS pecific dimensional tool lifeTUD-oOptimal specific dimensional tool lifet1 Uncut chip thicknessvCutting speedvoptOptimal cutting speedxv,xhPowers determined by the specificsof the machining operation ( )xv-oPower in optOptimal cutting temperature Chip compression ratio1 IntroductionIn deforming processes used in manufacturing, concernover tool wear is often overshadowed by considerations offorces or material flow.

4 Except for hot extrusion, die life ismeasured in hours and days, or in thousands of parts [1]. Inmetal cutting , however, tool wear is a dominant concernbecause process conditions are chosen to give maximumproductivity or economy, often resulting in tool lifeInt J Adv Manuf TechnolDOI P. Astakhov (*)Production Service Management Inc.,1777 Highland Drive, Suite E,Ann Arbor, MI 48108, USAe-mail: in minutes. Central to the problem are: high contacttemperatures at the tool chip and tool workpiece interfaces,which lead to softening of the tool material and promotesdiffusion and chemical (oxidation) wear; high contact pres-sures at these interfaces and sliding of freshly formed (juvenile)surfaces of the work material layers promote abrasive andadhesion wear [2]; cyclic nature of the chip formation process,which can cause cracking due to thermal nature of tool wear, unfortunately, is not yet clearenough, in spite of numerous investigations.

5 Althoughvarious theories have been introduced hitherto to explainthe wear mechanism, the complexity of the processes in thecutting zone hampers the formulation of a sound theory ofcutting tool wear. cutting tool wear is a result ofcomplicated physical, chemical, and thermomechanicalphenomena. Because different simple mechanisms ofwear (adhesion, abrasion, diffusion, oxidation, etc.) actsimultaneously with predominant influence of one or moreof them in different situations, identification of thedominant mechanism is far from simple, and mostinterpretations are subject to controversy [1].

6 Theseinterpretations are highly subjective and are based on theevaluation of the cutting conditions, possible temperatureand contact stress levels, relative velocities, and many otherprocess parameters and factors. As a result, experimental,or post-process methods, are still dominant in the knownstudies of tool wear [1 12] and only topological or, simply,geometrical parameters of tool wear are selected and, thus,reported on in tool wear and tool life discussed in [13,14], the cutting temperature isunderstood as the mean integral temperature at the tool chip and tool workpiece interfaces as measured by a tool-work thermocouple.

7 As conclusively proven by Makarow[15], the temperature is the most suitable parameter tocorrelate the tribological conditions at the discussedinterfaces with tool wear. Therefore, the correlation of thecutting temperature with parameters of the cutting systemshould be a great body of experimental data, Makarow[15] formulated the law which was presented as the firstmetal cutting law (Makarow s law) by Astakhov [13,14]:For given combination of the tool and workpiecematerials, there is the cutting temperature, referred toas the optimal cutting temperature opt, at which thecombination of minimum tool wear rate, minimumstabilized cutting force, and highest quality of themachined surface is achieved.

8 This temperature isinvariant to the way it has been achieved (whether theworkpiece was cooled, pre-heated, etc).It was discussed by Astakhov [13] that the puregeometrical characteristics of tool wear as the depth ofthe crater KT and relief face or flank wear VB areunsuitable for proper wear characterization. First, they donot account for the tool geometry (the flank angle, the rakeangle, the cutting edge angle, etc.), so they are not suitablefor comparing the wear parameters of cutting tools havingdifferent geometries. Second, they do not account for thecutting regime (the cutting speed and feed (s)) and, thus,they do not reflect the real amount of the work materialremoved by the tool during the tool operating time, whichis defined as the time needed to achieve the chosen toollife criterion (KT or VB).

9 To evaluate tool wear objectively, the surface wear rateas the radial wear per 1,000 sm2of the machined area (S)was introduced [13,15] as follows:hs dhrdS hr hr i 100l li f m 103sm2 1 wherehr-iandliare the initial radial wear and the initiallength of the tool path, respectively, andlis the total lengthof the tool follows from , the surface wear rate is inverselyproportional to the overall machined area, and it does notdepend on the selected wear the notion of the optimal cutting temperature, thepresent work aims to reveal and clarify for practical use theinfluence of the cutting feed , depth of cut, and workpiece (bore)

10 Diameter on the tool wear Influence of the cutting feedThe cutting regime is understood as a particular combina-tion of the cutting speed, cutting feed ( feed rate), and depthof cut. It is well known that the listed parameters of thecutting regime affect the tool life [16]. Influence of the cutting feed in a wide range of cuttingparametersThe uncut chip thickness or the cutting feed has a directinfluence on the quality, productivity, and efficiency ofmachining. It is believed that the tool life decreases (and,thus, tool wear increases) with increasing cutting feed [5,16 18].