Abstract major effect on determining cutting forces,

AbstractTool geometry is an important criterion that influences theperformance of a tool. As the tool geometry has major effect on determiningcutting forces, chip formation, tool life and temperature. Recent advancementin metal cutting has derived that the cutting edge geometry that is tool microgeometry also has a major influence on above said parameters. Here the effectsof cutting edge micro geometry especially the effects of honed cutting edge onperformance of tool have been discussed based on the recent works and theeffect of K factor on cutting tool parameters is focused.Keywords: MetalCutting, Cutting Edge Geometry, Edge Preparation, Edge hone, Form Factor, Toollife.

 INTRODUCTIONAs proper selection of toolgeometry influences performance of tool, the cutting edge geometry also has amajor influence on the performance of tool. The cutting parameters varyconsiderably as the cutting edge varies like sharper tool, chamfered edge,chamfered + honed edge and honed edge. The ploughing phenomenon also becomesdominant while machining with honed cutting edge. The honed cutting edge can bevaried from symmetric hone to asymmetric hone and based on this variation theprocess parameters vary significantly.

The merely increasing the cutting edgeradius will not serve the purpose. The suitable value of edge hone radius andit’s inclination towards the rake flank face depending on type of operation andwork piece material helps to increase the performance of tool. The above saidfactors are discussed briefly here.Cutting Edge Micro geometry:            The sharp cutting edge is often prone to chipping andbreakage resulting in lesser tool life. Thus the cutting edge micro geometryi.e. either honed or chamfered cutting edge enhances tool life by withstandingmore thermo mechanical and impact loads. The proper preparation of cutting edgedependent on the application provides a considerable increase in tool life.

Thus cutting edge can be prepared either giving a chamfer, edge hone or T-land.This preparation is termed as micro geometry as it has its own major influenceon tool performance other than tool macro geometries (Rake angle, clearanceangle, nose radius etc). The chamfered edges are found to develop more forcesthan the honed edges and more suitable to take impact loads. This study isfocused on the literatures mainly on effect of various honed edge designs andits influence on performance of tool. LITERATURE REVIEW Here the forces developedwhen machining with honed edges are discussed. When considering rounded cuttingedges, the force diagram has to be modified since the ploughing effect hassignificance value and the forces corresponding to ploughing action have to beincluded in the force diagram. This effect is not significant when sharperedges are used.

  Material in front oftool is compressed against work piece due to larger effective negative rakeangle developed and this exerts a force on tool called ploughing force. Thisaction is dominant when h/r ratio is less than 1. Thus rounded cutting edgesproduce more ploughing action and increase the passive forces. The initialoffset of forces in process force vs undeformed chip thickness diagramrepresents this component. This portion appears nonlinear in the due to theeffect of ploughing.   2 The paper considers sizeeffect phenomena in micro milling of tool steel. Higher specific cutting forceis revealed at the lower end of the ratio of un deformed chip thickness tocutting edge radius.

Non-linear increase of specific cutting force is observedwhen the feed per tooth is less than the cutting edge radius. This means thatwhen cutting edge radius is higher than the undeformed chip thickness, therewill be more ploughing and elastic deformation. 3 Here the chamfered andhoned cutting edges are compared and their effect on process forces areanalysed. The similarities between chamfered and honed edges are, in both toolsthe cutting and thrust forces increase with increasing uncut chip thickness.The chamfered tool produces larger forces but smaller chip thickness than doesthe honed tool. The relationship between the cutting forces and the uncut chipthickness is non-linear for the chamfered tool, but almost linear for the honedtool. (Particularly for the thrust force)4Cutting edge radius was varied between 10-50?m to find the effect of edgeradius while machining titanium.

The cutting force is less sensitive to achange in cutting edge radius than the feed force. Feed force increases withincrease in edge radius and is more affected. Ploughing force (mainly componentin feed direction) was found to increase with increase in edge radius. 5 Thecutting edge radius was varied between 25 to 120µm and its effect was analysedduring finish turning of AISI 52100 steel.

Here the results showed that themachined surface roughness increases as square of feed rate. For a given feedrate, the ploughing effect generally increases with increase in the edge honeradius. Ploughing pushes material sideways which increases roughness.

Here alsoit is proved that the effect of edge radius on feed force is more andtangential force is less sensitive to variation in edge radius.Theimportant factor in rounded or honed cutting edge is the Form factor (K) whichdetermines whether the cutting edge profile has inclination towards rake faceor flank face and it is the ratio of two parameters named S? and S? (K=S?/S?).The cutting edge with K=1 is called symmetric cutting edge and other than K=1is called asymmetric cutting edge.

The cutting parameters like forces, temperature, strain and chip formation are influenced by varyingthe above said K factor depending on work piece and the research has been goingon this field to determine the optimum values. The effect of ploughing forcehas a greater importance while selecting different K factors.   Waterfall edges have morecontact length l? on flank face and more friction surface is available and hence moreis the thermal load on wedge. The S? has little influence on thermal load. Thus bigger values of S? may givegood mechanical stability. K<1 induces higher feed forces and ploughingeffect.

The more flank wear is observed when using K<1 edge. 6 The newly definedparameter normalized ploughing area A?' (A?/l?) helps to visualize the effect of K factor on tool life moreeffectively. S? can be identified as the main factor on the normalized ploughingzone, whereas an increase of the cutting edge segment S? causes no significantinfluence, when S? remains constant.

The influence of K factor on tool wear isalso significant. The tool life map plotted has helped to visualize theseresults more clearly.  The wear behaviourin this area is changing from face wear (? ?1) to flank wear (? ?1) at a time of cut.7During machining of hardened AISI4140 steel, the observations proved the abovesaid results. Here higher forces are mainly obtained by employing higher valuesof S? due to a more dramatic increase in the contact length compared to higherS? values. Since the force related to this phenomenon isprojected on the plane perpendicular to cutting direction, the passive and feedforce components are more affected.

Specific cutting energy is not much affected by micro geometry. Thehigher ratio of thrust force to cutting force is obtained at higher values ofS?.8During orthogonal turning operations of AISI1045 with coated WC-Co inserts, themore detailed study on influence of S? and S? on different process forces areobserved. If un deformed chip thickness h

The experiments have shown that S? doesnot show a significant effect on the flank wear, while increasing S and S?leads clearly to higher flank wear. From the regression analysis it was foundthat the maximum tool life occurs at mean S=50µm. This may be around S?=30µmand S?=50µm.9 Thepaper focused on material flow, process forces and temperature behaviour due tovarious honed edge geometries. The influence of asymmetrically rounded cuttingedges of S? variable on the stagnant metal zone is significant. When S?increases, the height of material separation point also increases and theamount of material flowing underneath the flank face also increases.

Themaximum temperature shifts to rake face when S? is increased and flank facetemperature increases as S? is increased. It has been observed that thetransition surface area of contact influences the heat generation andtemperature. The previously discussed process behaviour was again observedduring this experiment also.10 Asdiscussed the variation in form factor significantly influences the tool wearand the thermo mechanical load. Here a proper development of a tool life maphas helped to view the tool wear behaviour due to varying values of S? and S?.Cutting tools with higher values of S? show an increased flank wear.

Theinitiation of crater wear is mainly influenced by S?. The temperature profileswere developed on tool rake and flank faces which had isotherm curves. Theorientation of these isotherms has proven that the S? doesn’t have muchsignificance effect on isotherm whereas S? has a major influence. The microgeometry influence on tool life is material dependent.   Depending on the wear criteria the values ofS? & S? need to be selected for a particular material.

11 Thework has again proved the effect of varying form factors on process forces asdiscussed. K=0.5 tool records higher process forces and especially feed force.This accounts for increase in contact length and increase in materialstagnation zone.

The more flank wear was also observed for the tool havingK=0.5.12 Theinfluence of different asymmetrical geometries on surface integrity isanalyzed. The different K factors were found to produce different levels ofgrain refinement and plastic strain. High maximum strain rates can be found forK>1 while K<1 exhibit much smaller maximum strain rates. Consideringseries1, For K<1, grain refinement takes place to much deeper depth and theinfluence of form factor on this is less apparent for K in between 0.6 and 5.

13 Theasymmetric geometry has a significant influence on the surface topography. Themain factor influencing the surface topography is material portion which is smaller than the minimum uncut chipthickness remains on the surface and generates the resulting surface roughness.The material side flow increases with increase in ER, but can be eliminated byusing K<1.

One more important factor is normal stress field due to elasticrecovery of material. For K<1, larger stress field with an increased contactlength and maximum normal stress occurs and surface roughness value is lesser.14This paper has helped to understand the overall development of cutting edgegeometry and has a brief collection of all research work related to cutting edgegeometry preparation, its influence on tool performance. The paper has detailsabout the introduction to cutting edge preparation, the various methods foredge preparation, the various cutting edge micro geometry measuring proceduresand the influence of edge preparation on machining performance.CONCLUSIONEdgeradius value has to be always less than the feed rate so as to maintain minimumh/r ratio thus to avoid ploughing action and to form chips. Increasing thecutting edge radius increases the process forces; especially the feed andthrust forces are mainly affected. Coefficient of friction also increases withincrease in edge radius.

Due to the increase in cutting edge segment on theflank face S?, temperature and process forces rise. Themainly affected force is feed and thrust forces due to increase in S?. Minimum uncut chip thickness hmin is mainly influenced byS? due to variation in height of material separationpoint.   Also, the flank wear increasesdue to increased frictional forces with higher values of S?. Maximum temperature point shifts to flank face by anincrease in S?.

At higher values of S?(K<1) lesser plastic strain rate is developed on the work piece and thegrain refinement extends to a larger depth. Larger stress field is developedfor K<1 and more material is under deformation thus the surface roughnessdecreases. Tool life is minimum at higher values of S?. S? does not have a major effect on process forces or thermalload. Increase in S? increases thestability of cutting edge. Higher S? value is used duringinterrupted cutting. The crater wear increases at higher values of S?. Maximum temperature point shifts to tool tip and furtherto rake face at higher values of S?.

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