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Design Concepts Turning InsertsEdge Preparation

P. MadhusudanQuality Assurance

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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

Rake

Enhanced Rake

Radius Hone

“T” Land

Rake

Enhanced Rake

Hones and “T” Lands change the effective Rake angle

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Edge Preparation

Radius Hone

Tangent Point with Workpiece

Hone level alters effective Clearance Angles

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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“Stronger” Cutting Edge

Cutting Forces tend to run through the Cutting Edge at Right Angles to the Rake Surface

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Edge Preparation“Stronger” Cutting Edge

A honed Cutting Edge directs some of the forces back into the body of the insert

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Edge PreparationHone Types

T

F

T=F Radius Hone

T>F Waterfall, Oval, Elliptical, Parabolic

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Edge Preparation“Stronger” Cutting Edge

The Optimum Radius Hone = the smallest Radius that eliminates mechanical chipping / notching as the primary failure mode.

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Edge PreparationThe Radius Hone is Feed Dependent.

The Feed rate in IPT / IPR should be greater than the Radius Hone .

ex: Radius Hone = 0.08mm Feed Rate should be greater than =/>0.08mm .08mmR

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Edge Preparation

.025mm/rev

.08mm R

Feed Rates lighter than the Radius Hone will result in:

• burnishing of the workpiece,

•chipping of the cutting edge due to thermal expansion.

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Edge PreparationThe Ideal Edge Prep.

The ideal edge Preparation is the smallest Hone that eliminates mechanical failure; Chipping, Notching, and Fracture.

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Edge Preparation“T” Land

Width

Angle

Direction of cutting forces

A “T” Land is a chamfer, with a specific width and angle, ground on the cutting edge

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Edge Preparation“T” Land Width

The “T” Land changes the entire Rake Surface:

Width

Angle

Direction of cutting forces

• If the width of the “T” Land is greater than the feed rate the total rake surface is changed.

• Feed = .13mm/rev and the “T” Land = .38mm

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Edge Preparation“T” Land Width

The “T” Land forms a compound Rake Surface:

Width

Angle

Direction of cutting forces

• If the width of the “T” Land is less than the feed rate the a compound rake surface is formed.

• ex: Feed = .13mm/rev and the “T” Land = .078mm

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Edge Preparation“T” Land Angle

Width

Angle

Direction of cutting forces

The “T” Land angle directs the cutting forces into the body of the insert. The greater the angle the greater theedge strength

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Edge Preparation“T” Land Angle

Width

Angle

Direction of cutting forces

The “T” Land angle directs the cutting forces into the body of the insert.

The greater the angle the greater Cutting Forces

Cutting Forces change approximately 1% - 1°of Angle Change

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Edge Preparation“T” Land Angle

Width

Angle

Direction of cutting forces

An angle greater than necessary to eliminate chipping will:

• Reduce tool life

• Increase cutting forces

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Edge Preparation“T” Land and a Radius Hone

Sharp Edge

Placing a Radius Hone on a “T” Land adds additional strength

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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 PreparationIdeal “T” Land

Width

Angle

The smallest angle and the narrowest width that eliminates mechanical failure is the ideal “T” Land.

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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

)

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