1.2 Mechanics of Metal Cutting
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Transcript of 1.2 Mechanics of Metal Cutting
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Practical Applications of Tool Design
(Mechanics of Metal Cutting)
Gary D. BaldwinDirector,
Kennametal University
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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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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
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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 View(Top)
Radial Rake(+) (-)
Rake Angles control Cutting Forces
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Both axial and radial rake have comparable
effects on cutting forces.
Radial Rake(+) (-)
Rake Angles control Cutting Forces
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Negative Radial Rake
Positive Radial Rake
Designed for a specified clearance under the heel of the insert.
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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Rake Angles:Drills
Radial Rake Axial Rake Angle (Helix)
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“Chisel Point” Drill Point Cutting Action
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“S” Point Drill Point Cutting Action
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Negative Axial Rake
Spiral Point
Positive Axial Rake
Spiral Flute
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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
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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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Lead Angles control direction Cutting Forces
Lead Angle
Chamfer Angle
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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 Neg. Rake
5° Degrees Clearance
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Back Clearance
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Clearance Angles
Radial Rake(+) (-)Arc of the cut
Radial Rake is designed to provide a specified amount of clearance under the heel of the insert
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Clearance Angles
Lip Relief Angle
Point Angle
DrillDiameter
BodyClearance(Radial)
FlankMargins
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Drill Margins
Margins are a lack of clearance
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Flute Design controls chip clearance
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Flute Design Controls the Amount of Chip Clearance
Parabolic FluteWeb = 25% - 50%
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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Tap Margins
Concentric Grind (No Clearance)
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Tap Margins
CONCENTRICCONCENTRIC CONCON--ECCENTRICECCENTRIC ECCENTRICECCENTRICNo Clearance Partial Clearance Clearance
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