1.2 Mechanics of Metal Cutting
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Transcript of 1.2 Mechanics of Metal Cutting
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MECHANICS OF METAL CUTTING
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Mechanics – Scientific study of motion and force
The Mechanics of Metal Cutting is controlled by three main elements.
•Rake Angles
•Lead Angles
•Clearance Angles
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Rake Angles
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Basic Cutting Tool Geometry
Back Rake
SCEA
Side Rake
Side Cutting Edge Angle
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Rake Angles Control Edge Strength
•TRS measures the bending fracture strength of carbides
FORCE
POSITIVE
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SUPPORTED:More Compressive Loading
NEGATIVE
FORCE
Rake Angles Control Edge Strength
•Measure of deformationresistance
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Edge Prep Alters the Rake Angle
FORCE
T-LandHone
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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
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Cutting Forces
Ft = Tangential Force
Ff = Feed Force
Fr = Radial Force
Fr
Ff
Ft
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Rake Angles control Cutting Forces
NEGATIVE
POSITIVE
-5
Cutting Forces change approximately 1% per degree of Rake change (mild steel)
+6
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Axial Rake has a greater impact on
cutting forces.
Radial Rake(+) (-)
Rake Angles control Cutting Forces
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Top Topography is used to Enhance Axial Rake
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Chip Flow Characteristics
Rake angles control the direction of chip flow
(+)(-) (-)(-) (+)(+)
Positive / Positive Negative / Negative Negative / Positive (Shear-Clear)
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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)
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Rake Angles:Reamers
Radial rake angle
Primary Clearance
Secondary Clearance
Axial Rake Angle
Neutral Axial Rake
Positive Axial Rake
Negative Axial Rake
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Lead Angles
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Lead Angle controls the Direction of Cutting Forces
Lead Angle
45
Table FeedRadialload
Axialload
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Direction of Cutting Forces
Direction of Cutting Forces
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Direction of Cutting Forces
Increasing the Lead Angle places the forces more into the Radial Plane.
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Lead Angles control direction Cutting Forces
Forces directed into the spindle
Forces directed across the spindle
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Lead Angles control direction Cutting Forces
140°90° 118°
The greater the angle, the greater the rigidity.
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Clearance Angles
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Clearance Angles
POSITIVE
NEGATIVE
5° Degrees Clearance
90 Degree included Angle79 Degree included
Angle5 degree Neg. Rake
5 degree Positive. Rake
6° Degrees Clearance
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Back Clearance
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Clearance Angles
Lip Relief Angle
Point Angle
DrillDiameter
BodyClearance(Radial)
FlankMargins
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Flute Design controls chip clearance
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Flute Design Controls the Amount of Chip Clearance
Parabolic FluteWeb = 25%
Conventional FluteWeb = 12% - 25%
Rolled Heel
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Web Design controls Chip Clearance
Flute Run-out
Core
Web
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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
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INSERTS – CHIP GROOVE GEOMETRIES
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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
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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
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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
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Chip Groove Geometries
.012
5°18°
.012
0°
Cutting Edge
Nose Radius G
“I”” “J”
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Chip Groove Geometries
Angled Back Walls serve to deflect the chip away from the finished surface of the workpieces.
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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
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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.
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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.
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INSERTS – EDGE PREPARATION
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Edge Preparation
Edge Preparation is an enhancement of the cutting geometry:1. Enhances the True Rake Angles
2. Alters the Clearance Angle
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Edge Preparation“Stronger” Cutting Edge
Edge Preparation Configuration :
Sharp Hone Radius “T” Land
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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
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Edge PreparationCVD Coatings
Cross Section of an Insert showing the Hone and CVD Coatings.
KC730
Cross Section of PVD Coating
Radius Hone
Sharp Edge
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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
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Edge Preparation“Keen” Cutting Edge
Flash
“Flash” is formed during the “Pressing” of carbide and must be removed to gain a “Keen” cutting edge.
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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
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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.
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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
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Impact Resistance
0100200300400500600700800900
1000
0.025mm 0.05mm 0.08mm
Hone Size (Radius)
Avg
. Im
pact
s (1
0 In
serts
)