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.
Cutting, Cutting Edge Geometry, Edge Preparation, Edge hone, Form Factor, Tool
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.
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)
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.
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.
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 h