1.2 Mechanics of Metal Cutting

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

15

NEGATIVE AXIAL RAKE NEGATIVE RADIAL RAKE

16

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

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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

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

)