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1
MECHANICS OF METAL CUTTING
2
Mechanics – Scientific study of motion and force
The Mechanics of Metal Cutting is controlled by three main elements.
•Rake Angles
•Lead Angles
•Clearance Angles
3
Rake Angles
4
Basic Cutting Tool Geometry
Back Rake
SCEA
Side Rake
Side Cutting Edge Angle
5
Rake Angles Control Edge Strength
•TRS measures the bending fracture strength of carbides
FORCE
POSITIVE
6
SUPPORTED:More Compressive Loading
NEGATIVE
FORCE
Rake Angles Control Edge Strength
•Measure of deformationresistance
7
Edge Prep Alters the Rake Angle
FORCE
T-LandHone
8
Radial Rake(+) (-)
Radial Rake has a greater impact on cutting edge strength
Rake Angles Control Edge Strength
Radial Rake absorbs the interrupted cut
Axial Rake
9
Cutting Forces
Ft = Tangential Force
Ff = Feed Force
Fr = Radial Force
Fr
Ff
Ft
10
Rake Angles control Cutting Forces
NEGATIVE
POSITIVE
-5
Cutting Forces change approximately 1% per degree of Rake change (mild steel)
+6
11
Axial Rake has a greater impact on
cutting forces.
Radial Rake(+) (-)
Rake Angles control Cutting Forces
12
Top Topography is used to Enhance Axial Rake
13
Chip Flow Characteristics
Rake angles control the direction of chip flow
(+)(-) (-)(-) (+)(+)
Positive / Positive Negative / Negative Negative / Positive (Shear-Clear)
14
POSITIVE AXIAL RAKE POSITIVE RADIAL RAKE
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NEGATIVE AXIAL RAKE NEGATIVE RADIAL RAKE
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POSITIVE AXIAL RAKE NEGATIVE RADIAL RAKE
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Rake Angles:Drills
Radial Rake Axial Rake Angle (Helix)
18
Rake Angles:Reamers
Radial rake angle
Primary Clearance
Secondary Clearance
Axial Rake Angle
Neutral Axial Rake
Positive Axial Rake
Negative Axial Rake
19
Lead Angles
20
Lead Angle controls the Direction of Cutting Forces
Lead Angle
45
Table FeedRadialload
Axialload
21
Direction of Cutting Forces
Direction of Cutting Forces
22
Direction of Cutting Forces
Increasing the Lead Angle places the forces more into the Radial Plane.
23
Lead Angles control direction Cutting Forces
Forces directed into the spindle
Forces directed across the spindle
24
Lead Angles control direction Cutting Forces
140°90° 118°
The greater the angle, the greater the rigidity.
25
Clearance Angles
26
Clearance Angles
POSITIVE
NEGATIVE
5° Degrees Clearance
90 Degree included Angle79 Degree included
Angle5 degree Neg. Rake
5 degree Positive. Rake
6° Degrees Clearance
27
Back Clearance
28
Clearance Angles
Lip Relief Angle
Point Angle
DrillDiameter
BodyClearance(Radial)
FlankMargins
29
Flute Design controls chip clearance
30
Flute Design Controls the Amount of Chip Clearance
Parabolic FluteWeb = 25%
Conventional FluteWeb = 12% - 25%
Rolled Heel
31
Web Design controls Chip Clearance
Flute Run-out
Core
Web
32
A A
B B
Web thickness
Section B-B
Chisel edge length
Drill Diameter
Web thickness
Section A-A
Chisel edge length Drill
Diameter
Web Design controls Chip Clearance
33
INSERTS – CHIP GROOVE GEOMETRIES
34
Chip Groove Geometries
The simple Chip Breaker has evolved into topographic surfaces that alter the entire rake surface of the cutting tool controlling:
• Chip control• Cutting Forces• Edge Strength• Heat Generation• Direction of Chip Flow
35
Chip Groove Geometries
A traditional chip groove has six critical elements. Each affects;
• Cutting Force, • Edge Strength, • Feed Range
Each elements can be manipulated to provide chip control, optimum cutting force and edge strength for particular applications
36
Chip Groove Geometries
A = Land Width
B = Land Angle
C = Groove Width
D = Groove Depth
E = Front Groove Angle
F = Island Height
“G” Groove(CNMG)
“C”A
E
DB
“P” Groove(CNMP)
C
F
D
A
E
B
Traditional Chip Groove Geometry
37
Chip Groove Geometries
.012
5°18°
.012
0°
Cutting Edge
Nose Radius G
“I”” “J”
38
Chip Groove Geometries
Angled Back Walls serve to deflect the chip away from the finished surface of the workpieces.
39
Chip Groove Geometries
Nose Radius Geometry Many chip groove designs have different geometry on the nose radius than on the cutting edge of the insert.
(0.305)
.012
5°18°
.012
0°
Cutting Edge
NoseRadius
Different Geometry
40
Chip Groove Geometries
Scalloped Edges Scalloped edges located on the front wall of the groove, the floor of the groove, and on the island serve to suspend the chip.
• Reduces surface contact between the chip and the rake surface of the insert • Reduces heat and cutting forces.
41
Chip Groove Geometries
Spheroids and Bumps (J) Serve to both impede chip flow providing chip control while reducing surface contact reducing heat and cutting forces.
42
INSERTS – EDGE PREPARATION
43
Edge Preparation
Edge Preparation is an enhancement of the cutting geometry:1. Enhances the True Rake Angles
2. Alters the Clearance Angle
44
Edge Preparation“Stronger” Cutting Edge
Edge Preparation Configuration :
Sharp Hone Radius “T” Land
45
Edge Preparation
Edge Preparation is added to a cutting edge for one of three basic reasons:
1. To facilitate the CVD Coating Process
2. To provide a “Keener” cutting edge
3. To strengthen the cutting edge
46
Edge PreparationCVD Coatings
Cross Section of an Insert showing the Hone and CVD Coatings.
KC730
Cross Section of PVD Coating
Radius Hone
Sharp Edge
47
Edge Preparation
Without a Radius Hone CVD Coatings tend to grow thicker at the Cutting Edge
CVD Coatings
• leads to chipping of the coating
• Insert movement due to an unstable platform
48
Edge Preparation“Keen” Cutting Edge
Flash
“Flash” is formed during the “Pressing” of carbide and must be removed to gain a “Keen” cutting edge.
49
Edge Preparation
GrindingFlash
Rotation
Feed
“Keen” Cutting Edge
Grinding Flash is created during rough and finish grinding. Removal is necessary for a “Keen” Cutting Edge
50
Edge Preparation“T” Land Angle
“T” Lands are ground on these two inserts. The left insert has a .15mm wide x 10 degrees; the insert on the right has a .15mm wide x 30 degrees.
51
Edge Wear Resistance
010203040506070
0.025mm 0.05mm 0.08mm
Test 1Test 2Test 3Test 4To
ol L
ife (m
in.)
Radius Hone Size
Hones actually pre-wear the insert
52
Impact Resistance
0100200300400500600700800900
1000
0.025mm 0.05mm 0.08mm
Hone Size (Radius)
Avg
. Im
pact
s (1
0 In
serts
)