environmentally friendly free machining steel.ppt
TRANSCRIPT
Machining Xcellence McMaster University
Environmentally Friendly
Free-Machining Steel
M E Finn and A K Srivastava, IAMSS V Subramanian and X Zhang, McMaster University
Machining Xcellence McMaster University
Environmentally Friendly Free-Machining Steel
Background
Machinability Cutting Tool Wear
Mechanism Target particles or inclusions Thermodynamic Models
Environmentally Friendly Free-Machining Steels
Machining Xcellence McMaster University
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
Machining Xcellence McMaster University
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
Machining Xcellence McMaster University
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
Machining Xcellence McMaster University
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
Machining Xcellence McMaster University
Background - Environmentally Friendly
Free-Machining Steel
Objective is to design a free-machining steel that is environmentally compatible with cost-effective machinability.
Machining Xcellence McMaster University
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
Machining Xcellence McMaster University
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
Machining Xcellence McMaster University
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
Machining Xcellence McMaster University
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
Cutting Speed (sfpm)
Too
l-Life
(m
in)
HR EF BOF/CC Steel HR Pb BOF/CC Steel HR EAF/CC Steel
Machining Xcellence McMaster University
Machinability - (HSS) EAF/Ingot Steels
0
500
1000
1500
2000
2500
275 300 325 350 375 400 425 450
Cutting Speed (sfpm)
Too
l-Life
(se
c)
CD EF EAF/Ingot Steel CD Pb EAF/Ingot SteelHR Pb EAF/Ingot Steel HR EF EAF/Ingot Steel
Machining Xcellence McMaster University
Machinability -(HSS) EAF/Ingot Steels
150
175
200
225
250
275
300
275 300 325 350 375 400 425 450
Cutting Speed (sfpm)
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
Machining Xcellence McMaster University
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
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Cutting Tool Wear Mechanism -Chip Schematic
ClearanceFace
Workpiece
Chip
Tool
Rake Face
Primary Shear Zone
Secondary Shear Zone
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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!
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Cutting Tool Wear Mechanism
Sharp Tool
Wearland
Chip Contact Length
Depth of Crater
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Cutting Tool Wear Mechanism
Crater Wear
Clearance Face
Rake Face
Nose Wear
Flank Wear Depth-of-cut Notch
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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
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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!
Machining Xcellence McMaster University
Target Particles or Inclusions
Glassy inclusions
Workpiece
Lubricatinglayer
Seizure
IntermittentcontactWorkpiece
Cutting tool
Cutting tool
Abrasive inclusions
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Target Particles or 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.
Machining Xcellence McMaster University
Target Particles or Inclusions
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
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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
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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
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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
Machining Xcellence McMaster University
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.
Machining Xcellence McMaster University
Environmentally FriendlyFree-Machining Steel -
Inclusion Engineered
Optimize Inclusion Engineered Free-Machining Steel with cutting tool coating and cutting fluid at high speeds.