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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

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Cutting Forces change approximately 1% per degree of Rake change (mild steel)

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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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