General turning getting started
A
General turning
Turning theory de nition of terms
Cutting speed
The workpiece rotates at a certain number of revolutions (n) per minute. This gives a speci c cutting speed, vc (or surface speed), measured in (m/min) at the cutting edge.
B
Parting and grooving
Cutting depth
The cutting depth (ap) is the difference between the un-cut and cut surfaces. The cutting depth is measured in mm and at a right angle (90) to the feed direction.
vc =
Dn m/min 1000
Feed
The axial (or in face turning the radial) tool movement is called feed, fn, and is measured in mm/r. When feeding radially towards the centre of the workpiece, the rpm will increase, until it reaches the rpm limit of the machine spindle. When this limitation is passed, the cutting speed, vc, will decrease until it reaches 0 m/min at the component centre.
Chip thickness
The chip thickness, hex, is equal to fn when using a tool holder with an entering angle r = 90. When using a smaller entering angle, hex is reduced. hex = fn sin r hex = maximum chip thickness
Inclination and rake angles
= the rake angle is a measure of the edge in relation to
the cut.
= the inclination angle is a measure of the angle at which
the insert is mounted in the holder.
A 11
Information/ Index
Materials
Tool holding/ Machines
Boring
Drilling
Milling
Threading
A
General turning
General turning getting started
Tool life
The following graphs show the effect that each of the three machining parameters - speed, feed, and depth of cut - has on tool life. The depth of cut has the smallest effect, followed by the feed rate. Cutting speed has by far the greatest effect on the tool life of the insert. For best tool life: maximize ap to reduce number of cuts; maximize fn for shorter cutting time; reduce vc for best tool life.
B
Parting and grooving
Effects of depth of cut
Too small Loss of chip control Vibrations Excessive heat Uneconomical. Too deep High power consumption Insert breakage Increased cutting forces.
Tool life Little effect on tool life.
Threading
D
Effects of feed rate
Too light Stringers Rapid ank wear Built-up edge Uneconomical. Too heavy Loss of chip control Poor surface nish Crater wear/plastic deformation High power consumption Chip welding Chip hammering. Tool life
Cutting depth ap
Less effect on tool life than vc.
Milling
Feed fn
Drilling
Effects of cutting speed
Too low Built-up edge Dulling of edge Uneconomical Poor surface. Too high Rapid ank wear Poor nish Rapid crater wear Plastic deformation.
Tool life Large effect on tool life. Adjust vc for best cost ef ciency.
Boring
G
How to predict tool life
Tool holding/ Machines
Cutting speed vc
The spiral cutting length, SCL, is a method for predicting the tool life. For more information, see page A 37.
Safety precautions
Chips are very hot and have sharp edges; they should not be touched with bare hands. Chips can cause burns to the skin or damage to the eyes.
Materials
Be sure that the insert and the component are tightly and secured in the holder to prevent them from coming loose during use. Too much overhang can result in vibration and tool breakage.
I
Information/ Index
A 12
General turning getting started
A
General turning
Negative versus positive inserts
A negative insert has an angle of 90, while a positive insert has an angle of less than 90. The illustrations below show, how the insert is tilted in the tool holder. Some characteristics of the two insert types are listed below:
B
Parting and grooving
Negative inserts
Double and single sided High edge strength Zero clearance First choice for external turning Heavy cutting conditions.
clearance angle
Positive inserts
Single sided Low cutting forces Side clearance First choice for internal turning and for external turning of slender components.
clearance angle
Milling
Effect of entering angle
The entering angle, r, is the angle between the cutting edge and the feed direction. It is an important angle in selecting the correct turning tool for an operation, and in uences: Chip formation Direction of cutting forces Cutting edge length in cut.
Large entering angle
Small entering angle
Boring
Chip breaking against the tool
Chip breaking against the workpiece
Forces are directed toward the chuck. There is less tendency for vibration. Ability to turn shoulders. Higher cutting forces, especially at the entrance and exit of the cut. Tendency for notch wear in HRSA and case-hardened workpieces.
Reduced load on the cutting edge. Produces a thinner chip = higher feed rate. Reduces notch wear. Can not turn a 90 shoulder. Forces are directed both axially and radially, which may result in vibration.
A 13
Information/ Index
Materials
Tool holding/ Machines
Drilling
Threading
A
General turning
General turning getting started
Insert shape
The insert shape should be selected relative to the entering angle accessibility required of the tool. The largest possible nose angle should be selected to provide insert strength and reliability. However, this has to be balanced against the variation of cuts that need to be performed. A large nose angle is strong, but requires more machine power and has a higher tendency for vibration. A small nose angle is weaker and has a small cutting edge engagement, both of which can make it more sensitive to the effects of heat.
B
Parting and grooving
+ +
Scale 1 indicates the cutting edge strength. The inserts to the left have larger nose angles and are correspondingly stronger. The inserts to the right have better versatility and accessibility. Scale 2 indicates that vibration tendencies increase to the left, while power requirements decrease to the right.
Milling
Threading
Factors affecting choice of insert shape
Basic-shape designation, nose angle R S 90 C 80 W 80 T 60 D 55 V 35
Drilling
Roughing (strength) Light roughing/semi- nishing (no. of edges) Finishing (no. of edges) Longitudinal turning (feed direction) Pro ling (accessibility) Facing (feed direction)
Boring
Operational versatility Limited machine power Vibration tendencies
G
Tool holding/ Machines
Hard materials Intermittent machining Large entering angle Small entering angle
Most suitable
Suitable
Information/ Index
Materials
The 80 nose angle (C-insert type), rhombic shaped insert is frequently used, as it is an effective compromise for all insert shapes and is suitable for many operations.
I
A 14
General turning getting started
A
General turning
Insert shape - number of cutting edges
The number of cutting edges on an insert varies depending on the choice of insert and nose angle. An insert with a negative basic shape normally has twice as many edges compared to a positive insert. In heavy roughing, a single-sided, negative basic-shape insert is recommended for best stability. For other roughing operations, a double-sided insert with twice as many cutting edges is recommended. The round insert has the highest number of cutting edges.
Basic shape Negative Double sided Single sided Positive
R
*)
S 8 4 4
C 4 2 2
W 6 3 3
T 6 3 3
D 4 2 2
V 4 2
B
Parting and grooving
C
*)
The no. of edges is dependent of the depth of cut in relation to the insert size.
Threading
Insert shape - depth of cut
The recommended maximum values in the table are intended to provide machining reliability for continuous cuts using a roughing geometry. Deeper cuts, up to the total cutting edge length, l, can be made for a shorter period.
la = 0.4 x iC
la = 2/3 x l
la =1/2 x l
la = 1/2 x l
la = 1/4 x l
la = 1/4 x l
Drilling
Insert size and depth of cut
The depth of cut in uences the metal removal rate, the number of necessary cuts, chip breaking, and the power required. Establish the effective cutting edge length la along with the shape of the insert, the entering angle, r, of the tool holder, and the depth of cut, ap. The minimum necessary effective cutting edge length can be determined from the table, which shows the relation between the depth of cut, ap, the entering angle, r. For extra reliability in more demanding operations, a larger and thicker insert should be considered. When machining against a shoulder, the depth of cut increases dramatically; in such cases, a stronger insert (thicker or larger) should be used to minimize the risk of insert breakage.
ap, mm 1 la, mm 90 1 1.05 1.2 1.4 2 4 2 2.1 2.3 2.9 4 8 3 3.1 3.5 4.3 6 12 4 4.1 4.7 5.7 8 16 5 5.2 5.8 7.1 10 20 6 6.2 7 8.5 12 24 7 7.3 8.2 10 14 27 8 8.3 9.3 12 16 31 9 9.3 11 13 18 35 10 11 12 15 20 39 15 16 2 3 4 5 6 7 8 9 10 15
105 120 135 150 165
75 60 45 30 15
22 30 58
A 15
Information/ Index
Materials
18
Tool holding/ Machines
Boring
Milling
la = 2/3 x l
la = 1/2 x l
A
General turning
General turning getting started
Insert size according to chip breaking areas
Finishing (F)
Operations at low depths of cut and low feeds.
Medium (M)
Medium to light roughing operations. Wide range of depths of cut and feed rate combinations.
Roughing (R)
Operations for maximum stock removal and/or severe conditions. High depths of cut and feed rate combinations.
B
Parting and grooving
Finishing:
fn = 0.1 - 0.3 mm/r ap = 0.5 - 2.0 mm
Medium:
fn = 0.2 - 0.5 mm/r ap = 1.5 - 5.0 mm
Roughing:
fn = 0.5 - 1.5 mm/r ap = 5 - 15 mm
General depth of cut recommendations for insert shapes, according to chip breaking for different geometries.
Insert shape
Selecting the insert size according to chip breaking areas.
Type of application Maximum depth of cut ap, mm
F M
Insert size
1 2 3 4 5 6 7 8 9
R
10 11 12 13 14 15
Threading
Round
Square
S
Rombic 80
06 08 10 12 15 16 19 20 25 32 09 12 15 19 25 31 38 06 09 12 16 19 25 06 08
Drilling
Milling
C
Trigon 80
Boring
W
Triangular
11 16 22 27 33 06 11 15
G
Tool holding/ Machines
T
Rhombic 55
H
Rhombic 35
Materials
11 16 22
I
Information/ Index
A 16
General turning getting started
A
General turning
Nose radius
The nose radius, r, on the insert is a key factor in turning operations. Selection of nose radius depends on the: Depth of cut, ap Feed, fn and in uences the: Surface nish Chip breaking Insert strength. Small nose radius Ideal for small cutting depths Reduces vibration Less insert strength. Large nose radius Heavy feed rates Large depths of cut Stronger edge Increased radial forces.
B
Parting and grooving
Nose radius and maximum feed
Negative basic-shape inserts
Nose radius, r mm 0.4 Max. recommended feed, fn mm/r Finishing Medium Roughing 0.25 0.3 0.3 0.4 0.5 0.6 0.5 0.6 0.8 0.7 0.8 1.0 (1.0) 1.5 Wiper inserts should be used in high productivity applications or when high quality surfaces are required. For more information, see page A 94. 0.8 1.2 1.6 2.4
Positive basic-shape inserts
Nose radius, r mm 0.2 Max. recommended feed, fn mm/r Finishing Medium 0.10 0.15 0.2 0.3 0.3 0.4 0.4 0.5 0.4 0.8 1.2
Nose radius in relation to depth of cut
The nose radius also affects the chip formation. Generally, chip breaking improves with a smaller radius. As a general rule of thumb, the depth of cut should be greater than or equal to 2/3 of the nose radius, or 1/2 of the nose radius in the feed direction.
Tool holding/ Machines
The radial forces that push the insert away from the cutting surface become more axial as the depth of cut increases.
a p < r
ap = 2/3 r
ap >2/3 r
A 17
Information/ Index
Materials
Boring
Drilling
Milling
Threading
A
General turning
General turning getting started
Nose radius surface nish and feed
In turning operations, the generated surface nish will be directly in uenced by the combination of nose radius and feed rate.
B
Parting and grooving
Rmax
C
Conventional insert
Threading
Rmax r Rmax =
f n2 8 x r
A conventional insert has a single nose radius, which can vary between 0.1 2.4 mm, and the surface nish is directly related to the feed used.
1000
Rmax (wiper) r
Rmax (wiper) =
Rmax 2
Milling
Wiper insert
The nose radius on a wiper insert has a modi ed nose built up around 3 to 9 different radii. This will increase the insert's engagement length and positively affects the feed rate and the surface.
Drilling
F
Rules of thumb for wiper inserts: Two times the feed = same surface nish Same feed surface nish is twice as good.
Boring
G
Tool holding/ Machines
The modi ed nose radius of the wiper inserts is within the tolerance for C- and W-style inserts, while D- and T-style have a nose con guration that deviates from corresponding conventional inserts. For more information, see page A 94.
Insert style C and W Insert style D and T
Materials
Surface nish measurements
Different methods for measuring surface nish are described in chapter I.
I
Information/ Index
A 18
General turning getting started
A
General turning
Chip formation and choice of insert geometry
Breaking the chips
Chip control is one of the key factors in turning, and there are three principle chip breaking alternatives:
B
Parting and grooving
self breaking, for example cast iron
against the tool
against the workpiece
Factors that have an in uence on chip breaking are the: Insert geometry Nose radius, r Entering angle, r Cutting depth, ap Feed, fn Cutting speed, vc Material.
Insert geometries
Turning geometries can be divided into three basic styles that are optimized for nishing, medium and roughing operations. The diagram shows the working area for each geometry, based on acceptable chip breaking, in relation to feed and depth of cut.
Drilling
Roughing R High depth of cut and feed rate combinations. Operations requiring the highest edge security. Medium M Medium operations to light roughing. Wide range of depth of cut and feed rate combinations.
mm
Finishing F
mm/r
Operations at light depths of cut and low feed rates. Operations requiring low cutting forces.
-PF
-PM
-PR
Materials
A 19
Information/ Index
Tool holding/ Machines
Boring
Milling
Threading
A
General turning
General turning getting started
Example of chip breaking for a -PM geometry
Cutting depth ap (mm)
B
Parting and grooving
Threading
Milling
Feed fn (mm/r)
E
Chip breaking test of a CNMG 12 04 08-PM insert at different cutting depths and feeds. The chip breaking within the marked area is classi ed as good, and the results are transferred into a diagram.
Drilling
Insert geometries for different workpiece materials
Many insert geometries are optimized for a certain workpiece material type, i.e. PF, PM, PR for turning of steels, MF, MM, MR for stainless steels, and KF, KM, KR for turning of cast irons, etc. Other geometries, like WMX, WF, WM, WR, are suitable for both steel, stainless and cast iron.
Boring
For more information about insert geometries and workpiece materials, see pages, A 98 and A 22 -- A 45.
G
Wiper inserts
Tool holding/ Machines
Conventional inserts
Steel Stainless steel Cast iron Aluminium alloys
P M K N S H
WMX, WF, WM, WR WMX, WF, WM, WR WMX, WF, WM, WR
PF, PM, PR MF, MM, MR KF, KM, KR AL SM, SR HM, HR
Materials
Heat resistant alloys Hardened steel
I
Information/ Index
A 20
