Abstract major effect on determining cutting forces,

Abstract

Tool geometry is an important criterion that influences the
performance of a tool. As the tool geometry has major effect on determining
cutting forces, chip formation, tool life and temperature. Recent advancement
in metal cutting has derived that the cutting edge geometry that is tool micro
geometry also has a major influence on above said parameters. Here the effects
of cutting edge micro geometry especially the effects of honed cutting edge on
performance of tool have been discussed based on the recent works and the
effect of K factor on cutting tool parameters is focused.

Keywords: Metal
Cutting, Cutting Edge Geometry, Edge Preparation, Edge hone, Form Factor, Tool
life.

 

INTRODUCTION

As proper selection of tool
geometry influences performance of tool, the cutting edge geometry also has a
major influence on the performance of tool. The cutting parameters vary
considerably as the cutting edge varies like sharper tool, chamfered edge,
chamfered + honed edge and honed edge. The ploughing phenomenon also becomes
dominant while machining with honed cutting edge. The honed cutting edge can be
varied from symmetric hone to asymmetric hone and based on this variation the
process parameters vary significantly. The merely increasing the cutting edge
radius will not serve the purpose. The suitable value of edge hone radius and
it’s inclination towards the rake flank face depending on type of operation and
work piece material helps to increase the performance of tool. The above said
factors are discussed briefly here.

Cutting Edge Micro geometry:

            The sharp cutting edge is often prone to chipping and
breakage resulting in lesser tool life. Thus the cutting edge micro geometry
i.e. either honed or chamfered cutting edge enhances tool life by withstanding
more thermo mechanical and impact loads. The proper preparation of cutting edge
dependent 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 influence
on tool performance other than tool macro geometries (Rake angle, clearance
angle, nose radius etc). The chamfered edges are found to develop more forces
than the honed edges and more suitable to take impact loads. This study is
focused on the literatures mainly on effect of various honed edge designs and
its influence on performance of tool.

 

LITERATURE REVIEW

Here the forces developed
when machining with honed edges are discussed. When considering rounded cutting
edges, the force diagram has to be modified since the ploughing effect has
significance value and the forces corresponding to ploughing action have to be
included in the force diagram. This effect is not significant when sharper
edges are used.  Material in front of
tool is compressed against work piece due to larger effective negative rake
angle developed and this exerts a force on tool called ploughing force. This
action is dominant when h/r ratio is less than 1. Thus rounded cutting edges
produce more ploughing action and increase the passive forces. The initial
offset of forces in process force vs undeformed chip thickness diagram
represents this component. This portion appears nonlinear in the due to the
effect of ploughing.  

2 The paper considers size
effect phenomena in micro milling of tool steel. Higher specific cutting force
is revealed at the lower end of the ratio of un deformed chip thickness to
cutting edge radius. Non-linear increase of specific cutting force is observed
when the feed per tooth is less than the cutting edge radius. This means that
when cutting edge radius is higher than the undeformed chip thickness, there
will be more ploughing and elastic deformation.

3 Here the chamfered and
honed cutting edges are compared and their effect on process forces are
analysed. The similarities between chamfered and honed edges are, in both tools
the cutting and thrust forces increase with increasing uncut chip thickness.
The chamfered tool produces larger forces but smaller chip thickness than does
the honed tool. The relationship between the cutting forces and the uncut chip
thickness is non-linear for the chamfered tool, but almost linear for the honed
tool. (Particularly for the thrust force)

4
Cutting edge radius was varied between 10-50?m to find the effect of edge
radius while machining titanium. The cutting force is less sensitive to a
change in cutting edge radius than the feed force. Feed force increases with
increase in edge radius and is more affected. Ploughing force (mainly component
in feed direction) was found to increase with increase in edge radius.

5 The
cutting edge radius was varied between 25 to 120µm and its effect was analysed
during finish turning of AISI 52100 steel. Here the results showed that the
machined surface roughness increases as square of feed rate. For a given feed
rate, the ploughing effect generally increases with increase in the edge hone
radius. Ploughing pushes material sideways which increases roughness. Here also
it is proved that the effect of edge radius on feed force is more and
tangential force is less sensitive to variation in edge radius.

The
important factor in rounded or honed cutting edge is the Form factor (K) which
determines whether the cutting edge profile has inclination towards rake face
or 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=1
is called asymmetric cutting edge. The cutting parameters like forces, temperature, strain and chip formation are influenced by varying
the above said K factor depending on work piece and the research has been going
on this field to determine the optimum values. The effect of ploughing force
has a greater importance while selecting different K factors.  

Waterfall edges have more
contact length l? on flank face and more friction surface is available and hence more
is the thermal load on wedge. The S? has little influence on thermal load. Thus bigger values of S? may give
good mechanical stability. K<1 induces higher feed forces and ploughing effect. The more flank wear is observed when using K<1 edge.   6 The newly defined parameter normalized ploughing area A?' (A?/l?) helps to visualize the effect of K factor on tool life more effectively. S? can be identified as the main factor on the normalized ploughing zone, whereas an increase of the cutting edge segment S? causes no significant influence, when S? remains constant. The influence of K factor on tool wear is also significant. The tool life map plotted has helped to visualize these results more clearly.  The wear behaviour in this area is changing from face wear (? ?1) to flank wear (? ? 1) at a time of cut. 7 During machining of hardened AISI4140 steel, the observations proved the above said results. Here higher forces are mainly obtained by employing higher values of S? due to a more dramatic increase in the contact length compared to higher S? values. Since the force related to this phenomenon is projected on the plane perpendicular to cutting direction, the passive and feed force components are more affected. Specific cutting energy is not much affected by micro geometry. The higher ratio of thrust force to cutting force is obtained at higher values of S?. 8 During orthogonal turning operations of AISI1045 with coated WC-Co inserts, the more detailed study on influence of S? and S? on different process forces are observed. If un deformed chip thickness h1 while K<1 exhibit much smaller maximum strain rates. Considering series1, For K<1, grain refinement takes place to much deeper depth and the influence of form factor on this is less apparent for K in between 0.6 and 5. 13 The asymmetric geometry has a significant influence on the surface topography. The main factor influencing the surface topography is material portion which is smaller than the minimum uncut chip thickness remains on the surface and generates the resulting surface roughness. The material side flow increases with increase in ER, but can be eliminated by using K<1. One more important factor is normal stress field due to elastic recovery of material. For K<1, larger stress field with an increased contact length and maximum normal stress occurs and surface roughness value is lesser. 14 This paper has helped to understand the overall development of cutting edge geometry and has a brief collection of all research work related to cutting edge geometry preparation, its influence on tool performance. The paper has details about the introduction to cutting edge preparation, the various methods for edge preparation, the various cutting edge micro geometry measuring procedures and the influence of edge preparation on machining performance. CONCLUSION Edge radius value has to be always less than the feed rate so as to maintain minimum h/r ratio thus to avoid ploughing action and to form chips. Increasing the cutting edge radius increases the process forces; especially the feed and thrust forces are mainly affected. Coefficient of friction also increases with increase in edge radius. Due to the increase in cutting edge segment on the flank face S?, temperature and process forces rise. The mainly affected force is feed and thrust forces due to increase in S?. Minimum uncut chip thickness hmin is mainly influenced by S? due to variation in height of material separation point.   Also, the flank wear increases due to increased frictional forces with higher values of S?. Maximum temperature point shifts to flank face by an increase in S?. At higher values of S? (K<1) lesser plastic strain rate is developed on the work piece and the grain refinement extends to a larger depth. Larger stress field is developed for K<1 and more material is under deformation thus the surface roughness decreases. Tool life is minimum at higher values of S?. S? does not have a major effect on process forces or thermal load. Increase in S? increases the stability of cutting edge. Higher S? value is used during interrupted cutting. The crater wear increases at higher values of S?. Maximum temperature point shifts to tool tip and further to rake face at higher values of S?.   REFERENCES        I.            Albrecht P. New Developments in the Theory of the Metal-Cutting Process. In: ASME Transactions, Journal of Engineering for Industry, Series B, Vol. 82; 1960, p. 348-358     II.            Size effect and tool geometry in micromilling of tool steel A. Aramcharoen?, P.T. Mativenga ; Manufacturing and Laser Processing Group, School of Mechanical, Aerospace and Civil Engineering, The University of Manchester, UK  III.            Fang N, Wu Q (2005) The Effects of Chamfered and Honed Tool Edge Geometry in Machining of Three Aluminium Alloys. International Journal of Machine Tools and Manufacture 45:1178–1187.  IV.            Wyen C-F, Wegener K (2010) Influence of Cutting Edge Radius on Cutting Forces in Machining Titanium. CIRP Annals 59:93–96.     V.            Thiele J-D, Melkote S-N (1999) Effect of Cutting Edge Geometry and Work-piece Hardness on Surface Generation in the Finish Hard Turning of AISI 52100 Steel. Journal of Materials Processing Technology 94:216–226.  VI.            Denkena B, Koehler J, Rehe M (2012) Influence of the Honed Cutting Edge on Tool Wear and Surface Integrity in Slot Milling of 42CrMo4 Steel. 5th CIRP Conf. on High Performance Cutting. VII.            The influence of the cutting tool microgeometry on the machinability of hardened AISI 4140 steel Carlos E. H. Ventura1 & Heitor S. Chaves2 & Juan Carlos Campos Rubio3 & Alexandre M. Abrão3 & Berend Denkena4 & Bernd Breidenstein4 VIII.            Bassett E, Ko¨ hler J, Denkena B (2012) On the Honed Cutting Edge and its Side Effects During Orthogonal Turning.  IX.            Denkena B,Köhler J,Mengesha MS(2012) Influence of the cutting edge rounding on the chip formation process: part 1. Investigation of material flow, process forces and cutting temperature. Prod Eng Res Devel 6:329–338     X.            Operations of AISI1045 with Coated WC-Co Inserts. CIRP Journal of Manufacturing Science and Technology 5:108–126 Denkena B, Lucas A, Bassett E (2011) Effects of the cutting edge microgeometry on tool wear and its thermomechanical load. CIRP Annals – Manufacturing Technology 60:73–76  XI.            Influence of cutting edge geometry on tool wear performance in interrupted hard turning C.E.H. Venturaa,?, J. Köhlerb, B. Denkenab XII.            Influence of asymmetric cutting edge roundings on surface topography O. Maiss1 · T. Grove1 · B. Denkena1 Received: 10 March 2017 / Accepted: 15 May 2017 © German Academic Society for Production Engineering (WGP) 2017 XIII.            Influence of different asymmetrical cutting edge microgeometries on surface integrity Eric Segebadea,*, Frederik Zangera, Volker Schulzea