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Single Point Cutting tool
Under the action of force, pressure is exerted on the workpiece metal
causing its compression near the tip of the tool.
The metal undergoes shear type deformation and a piece or layer of metal gets repeated in the form of a chip.
Tool is continued to move relative to workpiece, there is continuous shearing of the metal ahead of the tool. The shear occurs along a plane called the shear plane.
Actual separation of the metal starts as a yielding or fracture depending upon the cutting conditions.
Deformed metal (chip) flows over the tool (rake) face.Friction between the tool rake face and the underside of the
chip is considerable , then the chip gets further deformed (i.e. secondary deformation)
Geometry of single point turning tools Single point: e.g., turning tools, shaping, planning and slotting
tools and boring tools Double (two) point: e.g., drills Multipoint (more than two): e.g., milling cutters, broaching tools,
hobs, gear shaping cutters etc. Concept of rake and clearance angles of cutting tools.The word tool geometry is basically referred to some specific angles or slope of the salient faces and edges of the tools at their cutting point.
Rake and clearance angles of cutting tools.
+
+ + +
- =0
VC
VCVC
VC
VC
R R R
Rake angle (): Angle of inclination of rake surface from reference plane clearance angle (): Angle of inclination of clearance or flank surface from the finished surface
(a) positive rake (b) zero rake (c) negative rake
Three possible types of rake angles
Rake angle is provided for ease of chip flow and overall machining
Positive rake –reduce cutting force and thus cutting power requirement. Negative rake – to increase edge-strength and life of the tool Zero rake – to simplify design and manufacture of the form tools.
Clearance angle -to avoid rubbing of the tool (flank) with the machined surface which causes loss of energy and damages of both the tool and the job surface.
Systems of description of tool geometry Tool-in-Hand System Machine Reference System – ASA system Tool Reference Systems
Orthogonal Rake System – ORS Normal Rake System – NRS Work Reference System – WRS
Tool-in-Hand System
Basic features of single point tool (turning) in Tool-in-hand system
1.salient features of the cutting tool point are identified or visualized2. No quantitative analysis
Machine Reference System(ASA system)(American standards Association)
Planes and axes of reference in ASA system
R - X - Y and Xm – Ym - Zm
R = Reference plane; plane perpendicular to the velocity vector X = Machine longitudinal plane; plane perpendicular to R and taken in the direction of assumed longitudinal feedY = Machine Transverse plane; plane perpendicular to both R and X
Tool angles in ASA system
Rake angles: x = side (axial rake: angle of inclination of the rake surface from the
reference plane (R) and measured on Machine Ref. Plane, X.
y = back rake: angle of inclination of the rake surface from the reference
plane and measured on Machine Transverse plane, Y. Clearance angles:x = side clearance: angle of inclination of the principal flank from the
machined surface (or ) and measured on X plane.
y = back clearance: same as x but measured on Y plane. Cutting angles: [Fig. 3.5]s = approach angle: angle between the principal cutting edge (its
projection on R) and Y and measured on R
e = end cutting edge angle: angle between the end cutting edge (its projection on R) from X and measured on R
Nose radius, r (in inch) r = nose radius : curvature of the tool tip. It provides strengthening
of the tool nose and better surface finish.
Tool Reference Systems Orthogonal Rake System – ORS
R - C - O and Xo - Yo – Zo
R
C
YoXo
Xo
Yo
Zo
Planes and axes of reference in ORS
R = Refernce plane perpendicular to the cutting velocity
vector, C = cutting plane; plane perpendicular to R and taken along the
principal cutting edge
O = Orthogonal plane; plane perpendicular to both R and C
and the axes;Xo = along the line of intersection of R and O
Yo = along the line of intersection of R and C
Zo = along the velocity vector, i.e., normal to both Xo and
Yo axes.
Tool angles in ORS system
Rake angles o = orthogonal rake: angle of inclination of the rake surface from
Reference plane, R and measured on the orthogonal plane, o
= inclination angle; angle between C from the direction of assumed longitudinal feed [X] and measured on C
Clearance angleso = orthogonal clearance of the principal flank: angle of inclination of
the principal flank from C and measured on o
o’ = auxiliary orthogonal clearance: angle of inclination of the auxiliary flank from auxiliary cutting plane, C’ and measured on auxiliary orthogonal plane, o’ as indicated in Fig. 3.8.
Cutting angles = principal cutting edge angle: angle between C and the direction of
assumed longitudinal feed or X and measured on R
1 = auxiliary cutting angle: angle between C’ and X and measured on R
Nose radius, r (mm) r = radius of curvature of tool tip
Auxiliary orthogonal clearance angle
ASA system has limited advantage and use like convenience of inspection. But ORS is advantageously used for analysis and research in machining and tool performance. But ORS does not reveal the true picture of the tool geometry when the cutting edges are inclined from the reference plane, i.e., 0. Besides, sharpening or resharpening, if necessary, of the tool by grinding in ORS requires some additional calculations for correction of angles.
These two limitations of ORS are overcome by using NRS for description and use of tool geometry.
The basic difference between ORS and NRS is the fact that in ORS, rake and clearance angles are visualized in the orthogonal plane, o, whereas in NRS those angles are visualized in another plane called Normal plane, N.
orthogonal plane, o is simply normal to R and C irrespective of the inclination of the cutting edges, i.e., , but N (and N’ for auxiliary cutting edge) is always normal to the cutting edge.
Normal Rake System – NRSRN - C - N and Xn – Yn – Zn Yn
Zn
n
n
oo
YoZo o (A-A)
n (B-B)
A A
B
B
R C
n
o
Zo Zn
Xo, Xn
(a) (b)
Yo
Yno
n
R
Rake angles n = normal rake: angle of inclination angle of the rake surface from R
and measured on normal plane, N
n = normal clearance: angle of inclination of the principal flank from C and measured on N
n’= auxiliary clearance angle: normal clearance of the auxiliary flank (measured on N’ – plane normal to the auxiliary cutting edge.
Designation of tool geometry in
ASA System – y, x, y, x, e, s, r (inch)
ORS System – , o, o, o’, 1, , r (mm)
NRS System – , n, n, n’, 1, , r (mm)
Purposes of conversion of tool angles form one system to another
To understand the actual tool geometry in any system of choice or convenience from the geometry of a tool expressed in any other systems
To derive the benefits of the various systems of tool designation as and when required
Communication of the same tool geometry between people following different tool designation systems.
Methods of conversion of tool angles from one system to anotherAnalytical (geometrical) method: simple but
tediousGraphical method – Master line principle:
simple, quick and popularTransformation matrix method: suitable for
complex tool geometryVector method: very easy and quick but needs
concept of vectors
Conversion of tool angles by Graphical method – Master Line principle OD = TcotX
OB = TcotY
OC = Tcoto
OA = TcotWhere, T = thickness of the tool shank
Use of Master line for conversion of rake angles
OA = cot
Conversion of tool rake angles from ASA to ORS
o and (in ORS) = f (x and y of ASA system)
½ OB.OD = ½ OB.OCsin + ½ OD.Occos Dividing both sides by ½ OB.OD.OC
OBD = OBC + OCD
½ OB.OD = ½ OB.CE + ½ OD.CF
cosφtanγsinφtanγtanγ yxo
cosφtanγsinφtanγtanγ yxo
sinφtanγcosφtanγtanλ yx
cosφOB
1sinφ
OD
1
OC
1
i.e., ½ OD.AG = ½ OB.OG + ½ OB.ODwhere, AG = OAsin and OG = OAcosdividing both sides by ½ OA.OB.OD
OAD = OAB + OBD
OA
1cosφ
OD
1sinφ
OB
1
sinφtanγcosφtanγtanλ yx
y
xo
tan
tan
sincos
cossin
tan
tan
Conversion of rake angles from ORS to ASA system x and y (in ASA) = f(o and of ORS)
cosφtansinφtanγtanγ ox
sinφtancosφtanγtanγ oy
ML of principal flankML of auxiliary flank
Fig. Master lines (ML) of flank surfaces
Conversion of clearance angles from ASA to ORS
Fig. Master line of principal flank
tann = tanocos
cotn'= coto'cos'
cosφy
cotαsinφx
cotαo
cotα
sinφy
cotαcosφx
cotαtanλ
y
xo
cot
cot
sincos
cossin
tan
cot
Conversion of tool angles from ORS to NRS
, o, o, o’, 1, , r (mm) – ORS
, n, n, n’, 1, , r (mm) – NRS
cotn = cotocos