Environmentally Friendly Free Machining Steel.ppt

Machining Xcellence McMaster University

Environmentally Friendly

Free-Machining Steel

M E Finn and A K Srivastava, IAMSS V Subramanian and X Zhang, McMaster University


Environmentally Friendly Free-Machining Steel

Background

Machinability Cutting Tool Wear

Mechanism Target particles or inclusions Thermodynamic Models

Environmentally Friendly Free-Machining Steels


Background - Optimizing the Machining Cell

CUTTINGTOOL

MACHINETOOL

TYPEGRADEGEOMETRYCOATING

RIGIDITYPOWERREPEATABILITYCAPACITY

WORK MATERIAL

MACHINING PARAMETERS

SPEEDFEEDDEPTH OF CUT

CUTTINGFLUID

MACHININGACCESSORIES

TYPEFLOWTEMPERATURE

FIXTURINGHYDROBLASTTOOL SENSORSVISION MONITORS

TYPEGRADEMICROSTRUCTUREMECHANICAL PROPERTIES

Productivity/Quality

OptimizationCo

st


Background - Advanced Machining Technology• High speed machine tools

– up to 8,000 RPM turning steel rounds– up to 40,000 RPM rotating tools

• Hard and tough cutting tools– fine grained carbides, CBN, ceramics

• Wear resistant cutting tool coatings– multi-layered hard, tough and smooth

• Effective cutting fluids– effective cooling and lubricating


Background - Leaded Free-Machining

SteelHistorically, lead in combination with manganese sulfides is the best material for improving machinability of carbon and alloy steel at conventional cutting speeds.Pb + MnS steels – finish smoother– promote longer tool life


Background - Environmentally Friendly

Free-Machining SteelDevelopment of environmentally friendly and cost-effective free machining steel would allow -– Steelmakers to compete with other material makers– Automakers to continue making economical vehicles– Retention of highly-skilled machine operators– Significant reduction of Pb in the manufacturing

steam– Reduction of toxins released into the environment– Enhance the development of a cost-effective green

car


Background - Environmentally Friendly

Free-Machining Steel

Objective is to design a free-machining steel that is environmentally compatible with cost-effective machinability.


Machinability -Leaded and Environmentally

Friendly Free-Machining Steel

Bars from five heats of rephosphorized-resulfurized carbon steel with (Pb, ie SAE 12L14) and without lead (EF, ie SAE 1215):– hot rolled and cold drawn EF and Pb

EAF/INGOT– hot rolled EF EAF/CC– hot rolled EF and Pb BOF/CC


Machinability -Pb and EF Free-Machining SteelWear and cutting forces on cutting tool inserts while turning the bars dry.• WC cutting tool inserts– SNMG432A, VC5 uncoated– 0.010 ipr feed, 0.100 in. DOC– 500, 600 and 700 sfpm speeds• HSS cutting tool inserts– SPG442, M4 uncoated– 0.0105 ipr feed, 0.050 in.DOC– 225 to 425 sfpm speeds


Machinability -(WC) EAF/Ingot Steels

5

10

15

20

25

30

35

40

45

450 500 550 600 650 700 750

Cutting Speed (sfpm)

Too

l-Life

(m

in)

CD EF EAF/Ingot Steel CD Pb EAF/Ingot SteelHR EF EAF/Ingot Steel HR Pb EAF/Ingot Steel


Machinability - (WC) BOF/CC and EAF/CC Steels

10

15

20

25

30

35

40

45

50

55

60

450 500 550 600 650 700 750


Too

l-Life

(m

in)

HR EF BOF/CC Steel HR Pb BOF/CC Steel HR EAF/CC Steel


Machinability - (HSS) EAF/Ingot Steels

0

500

1000

1500

2000

2500

275 300 325 350 375 400 425 450


Too

l-Life

(se

c)

CD EF EAF/Ingot Steel CD Pb EAF/Ingot SteelHR Pb EAF/Ingot Steel HR EF EAF/Ingot Steel


Machinability -(HSS) EAF/Ingot Steels

150

175

200

225

250

275

300

275 300 325 350 375 400 425 450


Ave

rage

For

ce (

Ft-

lb)

CD EF EAF/Ingot Steel CD Pb EAF/Ingot Steel

HR Pb EAF/Ingot Steel HR EF EAF/Ingot Steel


Machinability -Leaded and Environmentally

Friendly Free-Machining Steel

• Lead is not offering any distinct advantage over non-leaded (EF) free-machining steel

• Leaded and non-leaded (EF) free-machining steel have similar machinability at high speeds

• Crater wear is more dominate at high speeds


Cutting Tool Wear Mechanism -Chip Schematic

ClearanceFace

Workpiece

Chip

Tool

Rake Face

Primary Shear Zone

Secondary Shear Zone


Cutting Tool Wear Mechanism -Consequence of Shear Localization in

Machining

Shear localization occurring in the primary and secondary shear zones cause temperature rise and consequent chemical diffusion wear at the cutting edge and on the rake face of the tool, respectively!


Cutting Tool Wear Mechanism

Sharp Tool

Wearland

Chip Contact Length

Depth of Crater


Cutting Tool Wear Mechanism

Crater Wear

Clearance Face

Rake Face

Nose Wear

Flank Wear Depth-of-cut Notch


Target Particles or Inclusions

SEM picture of WC cutting tool exhibiting flank and crater wear after machining Pb free-machining steel for 15 min. at a cutting speed of 500 sfpm


Target Particles or Inclusions Tool crater wear is caused by temperature rise due to seizure at the tool-chip interface. Seizure implies atomic contact at the tool-chip interface. Chemical dissolution of the tool material into the chip occurs by diffusion mechanism!

Since the tribology of seizure causes the temperature rise, crater wear can be suppressed by engineering glassy oxide inclusions in the steel. Particles or inclusions in the workpiece form in-situ during metal cutting a viscous layer of adequate thickness, which lubricates the tool-chip interface!



Glassy inclusions

Workpiece

Lubricatinglayer

Seizure

IntermittentcontactWorkpiece

Cutting tool

Cutting tool

Abrasive inclusions



• Deformable sulfide inclusions such as Type-II MnS are desirable to promote ductile fracture in chip formation.

• Hard abrasive alumina inclusions are undesirable as they promote tool flank wear. Modification of alumina inclusions into relatively soft calcium aluminate by calcium treatment is desirable to prevent physical wear.

• Deformable glassy oxide inclusions are desirable as they lubricate the tool-chip interface, preventing chemical crater wear of the tool. Glassy oxide inclusions are target for inclusion engineering.



The inclusion engineering steps in slag-metal treatment

1) Identify target indigenous inclusions, ie spessartitic glassy inclusions

2) Identify the inclusion composition in equilibrium with Mn and Si content of the base chemistry

3) Identify the window of soluble Al in equilibrium with target inclusions

4) Design synthetic slag to control the soluble Al within the window by slag-metal equilibrium

5) Protect against reoxidation before solidifying the melt after slag-metal treatment


SiO2

MnO

20

40

60

80

100

100

80

8060

60

40

40

20

200

0

mass, %

SAE 1215 (EF FM) iso-[ppm O] and iso-[ppm Al] [%C] =0.08 [%Si]=0.02 [%Mn]=1.0] [%S]=0.3 [%P]=0.08

Al 2O3

0

45

40

3530

1510 oC

ppm O

Spessartitic

glass2.0

0.5

1.0ppm Al

Thermodynamic Model

The target glassy indigenous inclusion composition region in Si-Mn deoxidizedAISI 1015 steel corresponding to the beginning of solidification in the caster at 1510 oC

100


A

SiO2

CaO Al2O3

0

20

40

60

80

100

100

100

80

8060

60

40

40

20

200

0

mass, %

30

50

30

60

40

A, B : ternary eutectics

Eutectic glass

ppm O

210.5

53

ppm Al

1550 oC

Thermodynamic Model

Iso-contents of soluble aluminum and soluble oxygen in the melt afterequilibration with CaO-SiO2-Al2O3 slag of eutectic B composition at 1550 oC

SAE 1215 (EF FM) iso-[ppm O] and iso-[ppm Al] [%C] =0.07 [%Si]=0.17 [%Mn]=1.0] [%S]=0.08

B


Environmentally Free- Machining Steel - Inclusion

Engineered

0

2

4

6

8

Dissolved W

(Chemical wear)

EF FMSteel

(with HfNcoated tool)

IE EF FMSteel

Pb FM Steel EF FM Steel

(Crater wear)

Total W

WC

(Mechanical wear)

Cutting speed: 525 sfpm

Comparison of tool wear in machining of leaded (Pb FC), non-leaded (EF FC) and inclusion engineered (IE EF) free machining steels with uncoated WC cutting tool and HfN coated cutting tool at a cutting speed of 525 sfpm.

W c

once

ntr

atio

n in

ch

ips,

pp

m


Environmentally Friendly Free-Machining Steel -

Inclusion Engineered1. Inclusion engineered steel is self- lubricating and is based on modifying the rheology of existing oxide inclusions in the steel to be glassy so that they form an in-situ viscous layer during metal cutting of required viscosity to lubricate the tool-chip interface. 2. Inclusion Engineered Environmentally Friendly Free-Machining Steel suppress crater wear during metal cutting more effectively than coating of the cutting tool, especially at high cutting speeds.


Environmentally FriendlyFree-Machining Steel -

Inclusion Engineered

Optimize Inclusion Engineered Free-Machining Steel with cutting tool coating and cutting fluid at high speeds.

Documents

Environmentally Friendly Free Machining Steel.ppt