Powder Metallurgy Technology-ppt

1

© WZL / IPT

Primary Shaping – Powder Metallurgy

Manufacturing Technology II

Lecture 2

Laboratory for Machine Tools and Production Engineering

Chair of Manufacturing Technology

Prof. Dr.-Ing. Dr.-Ing. E.h. F. Klocke

© WZL / IPT Seite 1

Structure of the lecture „Primary Shaping- Powder Metallurgy“

Introduction: Variety of Applications of Powder Metallurgy

Powder Production and Powder Properties

Powder Compaction

Constructions of Compaction Tools

Sintering – Basics and Examples of Sintering Furnances

Sizing

Compendium of PM Manufacturing Technologies

Comparison of the PM Manufacturing Technologies

Summary

2




– Process Steps– Applications

Powder Production and Powder PropertiesPowder CompactionConstructions of Compaction ToolsSintering – Basics and Examples of Sintering FurnancesSizingCompendium of PM Manufacturing TechnologiesComparison of the PM Manufacturing TechnologiesSummary


Process Steps of Powder Pressing

Lubricant Graphite

Bronce PowderAlloyed Powder

Iron Powder

Powder Mixing Pressing Sintering Sizing

3


Application for Gear Boxes

source: Sinterstahl GmbH, Füssen


Applications in Automotive Engines

source: Sinterstahl GmbH, Füssen

4




Powder Production and Powder Properties– Powder Production Technologies– Powder Properties– Alloying Methods

Powder Compaction



Sizing



Summary


Reduction Mix of Coke Breeze and LimestoneIron OreDryingCrushingScreeningMagnetic SeparationCharging in Ceramic TubesReduction in Tunnel Kilns (1200°C)DischargingCoarse CrushingStorage in SilosCrushingMagnetic SeparationGrinding and ScreeningAnnealing in Belt Furnace, approx. 800-900°CEqualisingAutomatic PackingIron OreReduction Mix

123456789101112131415

16171819

Powder Production: Chemical Reduction, Sponge Iron Powder

source: Höganäs

5


Powder Production: Water-Atomizing-Process

PrincipleAtomizing the Melting by Means of Water Jet

Metal Scrap, Iron Ore, Roll Scale

Factors of Influence

ProductPure Iron or Alloy

source: Höganäs, EHW Thale

1

2

34

5

Foundry LadleMelting StreamHigh Pressure WaterNozzleAtomized Iron Powder

12345

Grain Size

Flowrate of the Melting

MeltingTemperature

Water Pressure

Principle of Water-Atomizing


1. Metallurgical Properties• Chemical Composition ⇒ Chemical Analysis• Texture of Powder Particles ⇒ Polished Cross Sections• Micro Hardness ⇒ Hardness Measurement

2. Geometrical Properties• Particle Size Distribution ⇒ Sieve Analysis• External Practical Shape ⇒ Scanning Electron Microscopy• Internal Particle Structure (Porosity)⇒ Metallographic Cut through the Powder Particle

3. Mechanical Properties• Flow Rate ⇒ Hall-Flowmeter (Standardized Cone)• Bulk Density ⇒ Filling a Bowl with a Standardized Cone• Compressibility ⇒ Pressing Standardized Stopper, results presented as a curve• Green Strength ⇒ Fatigue Strength of a Pressed Square Test Bar• Spring-Back ⇒ Elastic Extension of a Pressed Stopper, d=25 mm

Characterization of Iron and Steel Powder

6


Scanning Electron Microscope-Picture

Sponge Iron PowderNC 100.24

Cross Section

Atomized PowderASC 100.29

source: Höganäs

Particle Form and – Structure of Unalloyed Iron Powder


Alloying Methods of Iron PowdersCompletely Alloyed Powder

Mixed AlloyedPowder

Partially AlloyedPowder

7


Alloying Methods of Iron Powderswater-atomized powders, at which the molten material consists of the required alloying elements

powder-mixes consisting of at least 2 pure alloying components

long sintering times and high sintering temperatures necessary for homogenizing

Completely Alloyed Powder

MixedAlloyedPowder

PartiallyAlloyedPowder

diffusion alloyed: annealing of mixed powders

adhesion alloyed: usage of alloying elements which can`tbe bound on iron by a diffusion process





Powder Compaction– Compendium– Filling– Pressing– Ejection



Sizing



Summary

8


The Compaction Cycle


The Compaction Cycle

Die

Fill Shoe

Upper Punch

Lower Punch

Powder Green Compact

Filling Compacting Ejecting

Green CompactGreen CompactCompact

9


Filling: Contour Filling

Without contour filling With Contour Filling

source: Osterwalder


Filling: Formation of Bridges when Filling Narrow Cross-Sections

Formation of bridges when filling narrow cross-sections

When high homogeneity requirementsof the components:

Pressed height of the component h < 15 mm: d > 2,5 mmPressed height of the component h > 15 mm: d > h/6

10


200

3 4 5 7,866 [g/cm³]

400

600

1000

MPa

Com

pact

ing

Pres

sure

Compressed Density

Compacting Pressure [MPa]: 0 80 200 400 800Density [g/cm³]: 2,5 4 5,5 6,5 7,2

Filling: Empirical Pressure-Density-Curve Defined at a Column of Powder


source: Höganäs

Pressing: Decreasing of the Axial Stress σa During Compaction

Frictional forces at the wall of thecompacting die restrain the compaction ofThe powder

With increasing distance from the face of the compacting punch, the axial stress σa,Which is available for the local densification of the powder, decreases.

Pa

σα

2 r

0

x

x + dx

K

K

F

f

Upper Punch

Die

F = πr2

f = 2πrdx

σa(x) = σa(0) e -2µ/r

σa(x + dx)σa(x)σa(0)

11


Pressing: Compacting Methods Used for the Production of Compacts

One-Sided Compacting Two-Sided Compacting

Compacting with Floating Die


0,0

0,2

0,4

0,6

0,8

1,0

0,0 0,2 0,4 0,6 0,8 1,0

relative Dichte ρ/ρ0 [-]

rela

tiver

Wer

ksto

ffken

nwer

t P/P

0 [-]

Pressing: Influence of the Density on the Material Properties

>12Notched Impact Strength

3.5 … 5.5Dynamic Strength

2.5 … 4.5Young’s Modulus

1.5 … 3.5Thermal Conductivity

Powder CoefficientMaterial Data

ρ Densityρo Full DensityP Material PropertiesPo Material Properties of the

Raw Materialm Powder Coefficient

( )m

=

++

0011

ρρ

νν ρ

m

PP

=

00

)(

ρρρ

Calculation of Material Properties Material Data of the P/M-Steel: Distaloy HP-1: Fe-1.5Mo-4.0Ni-2.0Cu

Poisson’s Ratio

Young’s Modulus

Dynamic Strength

Relative Density ρ/ρ0 [-]

Rel

ativ

e M

ater

ial D

ata

P/P

0 [-]

.

.

.

.

.

.. . . . . .

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Die BolsterBottom ram Bottom ram =ejector pin

DiePowderGreen CompactUpper Punch

Filling-Position Compaction-Position Pressure-Relief Ejection-Position

Ejection: Ejection Procedure


Source: Fachverband für Pulvermetallurgie

Upper Punch

Die

Bottom Ram

PowderCompact

Filling Compacting Lifting

Withdrawal: Withdrawal Procedure

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Ejection: Schematic Diagramm of the Ejection Force

source: Höganäs

Ejec

tion

Forc

e

Punch Travel

Die

Bottom Ram

Compact

εel, punch


Dl2

Dl1

Crack Formation at the Compact

Different elastic expansions oftwo lower punches

Ejection procedure at a sharp edge of the die

source: Höganäs

Avoiding crack formation by tapering the die exit androunding-off the upper rim

of the die!

Ejection: Cracking Risk when Removing the Compact

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Ejection: Spring-Back as a Function of Compact Density

source: Höganäs

Compacting Density[g/cm³]6,0 6,5 7,0

0,00

0,10

0,20

0,30

Sprin

g-B

ack

[%]

Iron Powder with 0,8% Zn-Stearatas Lubricant Addition

ASC100.29

NC100.24

SC100.26

( )d

dc100Sλλ−λ

⋅=(%)

S: Spring-Back in %

λc: Transversal Dimension of the(ejected) Compact

λd: Corresponding Dimension of the Compacting Die (After Ejection of the Compact)

Parameters Influencing the Spring-BackCompacting Pressure, Compacting Density,Powder Properties,Lubricants and Alloying Additions,Shape & Elastic Properties of the Compacting Die





Powder Compaction



Sizing



Summary

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source: Gräbener

Component 1

2

3

4

56

Filling Compacting

Opening Lifting

Upper PunchFill ShoeUpper Part of the Die, moveableLower Part of the Die, fixedBottom RodCore Pin

123456

Priciple of a Compaction Tool with a Split Die


4 5 6 7

1 Filling

2 Underfill by Die Lift

3 Closure of Die

6 Die Withdrawal with Upper Punch Hold Down Load

7 Full Demoulding by Inner Punch and Core Rod Withdrawal

4 Powder Transfer with Inner Punches

5 Compaction

Powder Compaction

Compaction Tool : Powder Compaction of Helical Gear

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Compaction of a Part With a Cross Hole

Compaction of a Part with DifferentFilling Heights

source: Osterwalder

Compaction Tool: Cross Hole and Complex Part with Different Filling Heights



Introduction: Variety of Applications of PowderMetallurgy


Powder Compaction


Sintering – Basics and Examples of SinteringFurnances

Sizing



Summary

17


Source: Höganäs

400

800

1200°C

700°C

1120°C850°C

150°C

zone 1 zone 2 zone 3 zone 4

Room Temperature

Gas Inlet

Smoke and Gas Outlet

Zone 1:Burning-Off Lubricants Zone 2: Sintering Zone 3:Re-Carbonizing Zone 4:Cooling

Tem

pera

ture

Sintering: Different Atmospheres in a Sintering Conveyor Furnace


Sintering: Diffusion Types at Sintering

source: Kuczynski

Legend:v: Volume Diffusions: Surface Diffusionb: Grain Boundary Diffusione: Evaporation/Condensation: Forces from Surface Tension(viscous flow)

x1 x2l1 l2

a2a1

v

a2

vv

be

a1

x2 > x1, l2 < l1 < 2a1, a2 ≤ a1,

Parameters Influencing the Diffusion:

Temperature

Time

Composition of Alloy

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Sintering: Influence of Sinteing Time on the Material Properties

0 15 30 60 90 120 150Sintering Time [min]

Tens

ile S

tren

gth

σB

[kg/

cm2 ]

0

5

10

15

Den

sity

ρ[g

/cm

3 ]

6,26,3

Speciment:Standard TensionTest Bar

Elon

gatio

n δ

[%]

850°C

850°C

850°C

1150°C

1150°C

1150°C

0

4

8

2

6

10

δ

σB

ρ


Different concepts of sintering furnaces

source: Höganäs

conveyor furnace

roller hearth furnace

pusher type furnace

walking-beam furnace

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Powder Compaction



Sizing



Summary


Sizing

Quelle: Höganäs

Sizing involves reduction or increase in the dimensions of the component, and this action is performed by forcing the component into a die or over a core

• Hardness of the part to be sized should not exceed HV 180 after sintering

• Wherever possible, the various surfaces of the part should be sized progressivelyand not simultaneously

• The external forms should be sized before the holes in order to prevent cracking

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Powder Compaction



Sizing



Summary


PressurelessSintering

Infiltration

Powder Production

Compaction

Sintering

Infiltration

Machining

Powder Production

Pouring

Sintering

Sizing

Oil Impregnation

High-PorousComponents

e.g.:Filters,Flam Traps,Throttles

Pore Free Components

Quelle: GKN

Process Sequences in PM-Technology 1

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Powder Production

Compaction

Sintering

Machining

Sizing

Heat Treatment

Conventional Sintering

Process Sequences in PM-Technology 2

Compaction (150°C)

Machining

WarmcompactionPowder Production

Sintering

Heat Treatment

Sizing

Re-Sintering

Re-Compaction

Double Pressing

Sintering

Sizing

Powder Production

Compaction

Heat Treatment

Machining

Inductional Heating

Forging

Powder ForgingPowder Production

Compaction

Sintering

Heat Treatment

Machining


PM Technology: Powder Forging

Compaction

Weight Control

Sintering

Heat Treatment

Inductive Heating

Automatic Handling

Powder Forging

ForgingTForge> T Recristallisation

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PM Technology: Metal Injection Moulding MIM

Fe

CHO

Mixing

Pelleting

Extrude/Inject

Sintering

Debindering:Chemic / thermal

Metal Injection Moulding

Powder:Grain Size: < 12 µm, Round Grain Form (Gas Atomised)

Highlights:High Added ValueComplex Geometry Component Mass: m < 500 g Thickness: s < 30mm, Debindering Time: t ~ s2

High DensitiesHigh Shrinkage


Quelle: (1) GKN; (2) (3)

WatchcaseGearing parts Medicine

Application: Synchronising Density: > 7,4 g/cm3

Heat Treat.: Case HardeningTensile Strength: > 450 MPaMass: ca. 28 g (1)

ca. 6 g (2, 3)

Application: Watchcase G-Shock

Material: Titan AlloyDensity: 4,38 g/cm3

Waterproof up to 200m

12 3

Material: Nickel Free, Stainless Steel

Density: 7,6 g/cm3

Yield strength: 552 N/mm2

Tensile Strength: 657 N/mm2

PM Technology: MIM Applications

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PM Technology: Isostatic Pressing

Mould Filling

Fluid Filling

Applying Pressure

Sintering

Fluid Discharge

Handling

Isostatic Compaction

1 2 3

Up to 100% Density

No Density Gradients

Great Material Spectrum

Low Cycle Time


PM Technology: Isostatic Pressing

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FWalz

MBrems MWalzρges,0

PM Technology: Surface Densification by Transverse Rolling

Process ConditionsWorkpiece:

Initial Density: ρges,0Gradient of Overmeasure: a(s)

Tool: Tool Geometry

Process: Transverse Rolling Force: FWalz ; Infeed: fRolling: MWalz or Braking Torque: MBremsNumber of Cycles: nÜ

Process ResultsWorkpiece:

Densification Gradient Densification Depth: tD,98%Gear Tooth Quality

Tool:Load: FStress: σDeformation: ε


PM Technology: Typical Deviations of Surface Densified P/M GearsProfile Deviation

– Positive Pressure Angle– Negative Crowning– Asymmetric Profile on the

right and left Flank

Densification Defects– Incomplete Densification in

Highly Loaded Areas– Asymmetric Densification on

left and right Flank

left Flank right FlankWorkpiece

Profile

1.0

mm

Tooth Root

20 µm

Addendum

1000 µm

Source: Höganäs AB

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PM Technology: FE Model of Surface Densification by RollingObjects

– Rigid Tool– Rigid Shaft– Porous P/M Gear

Number of Elements: 3374Number of Nods: 3580Weighted Mesh

Interobject Conditions– Shaft - P/M-Gear: Sticking – Tool - P/M-Gear: Contact

Simulation Parameters– Step: ∆t = 0,0005s– Direct Method Iteration– Calculation Time: 6h/cycle

FW

nWerkzeug

MBrems

P/M gear Porous

EvaluatedPair of Teeth

ToolRigid

ShaftRigid


PM Technology: Comparison of the Density Gradient determined through Simulation and Experiments

Comparison of the Density Gradient determined through Simulation and Experiments

– High Densification in the Addendum

– Nonuniform Densification on the left and right Flank

– Incomplete Densification on the right Flank

– Nonuniform Densification of the right and left Tooth Root

1.000

0.976

0.952

0.880

0.904

0.928

1000 µm

Rel

ativ

e D

ensi

ty ρ

/ρ0

[-]

Metallographic Picture FE Analysis Results

Source: Höganäs AB

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Powder Compaction



Sizing



Summary


Comparison: Production Costs

Cos

ts

high

mid

dle

low

7,2 7,4 7,6 7,8

Local Densification

MIM

Density [g/cm³] ( Strength)

ConventionalCompaction

WarmCompaction

Double-ProcessSintering

Powder Forging

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Comparison: Geometrie Complexity

Geo

met

ry C

ompl

exity


Double ProcessSintering

WarmCompaction

Local Densification

MIM

Powder Forginghi

ghm

iddl

elo

w

7,2 7,4 7,6 7,8



Comparison: Precision


Double-ProcessSintering

WarmCompaction

Selective Densification

MIM

Powder Forging

Prec

isio

n

high

mid

dle

low

7,2 7,4 7,6 7,8


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Powder Compaction



Sizing



Summary


Conclusion: Principle, Advantages and Limits of P/M TechnologyAdvantages of P/M Technology

– Low Costs at Series Production– High Quality at Series

Production– Net-Shape Technology– Extensive Alloying Possibilities– Weight Reduction Because of

Porosity– 100% Raw Material Utilisation– Low Energy Consumption– Freedom in Profile Design

Limits of P/M Technology– Density Dependent Properties– Undercuts, Cross Holes and

Thread not Producible by Pressing

– Maximum Weight of Component 1 kg

Proceeding of Single Process Sintering:

Camshaft GearTest Gear

Source: Miba AGSource: Höganäs AB

Powder Mixing Pressing Sintering Sizing

Sintered Components:

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Classification of sintered steels according to alloying elements

The classification of sintered steels primarily acts upon the copper-content and themass of the remaining alloying elements.

with SINT: sintered materialcharacter: density dependency 1st digit: material composition2nd digit: serial number

0: sintered steel with percentage weight of 0% - 1% Cu, with or without C1: sintered steel with percentage weight of 1% - 5% Cu, with or without C2: sintered steel with percentage weight of more than 5% Cu, with or without C 3: sintered steel with or without Cu, with or without C, but with a percentage

weight of up to 6% of other alloying elements4: sintered steel with or without Cu, with or without C, but with a percentage

weight of more than 6% of other alloying elements5: sintered alloys with a percentage weight of more than 60% Cu6: sintered metals which are not included in no. 57: sintered light metals, e.g. sintered aluminium

e.g.: SINT D 30

gear

Cu- Ni-alloySINT-D 30

oil pump casing

Cu-infiltratedSINT-F 22


Classification of sintered steel according to porosity

porosityP [%]

sintered density ratioRx [%]

materialclass

filter, flame traps, throttlesSINT - AF > 27 < 73

plain bearings, sliding pats, medium-strengthparts, e.g. shock absorber parts, oil pump gearsSINT - C 15 ± 2,5 85 ± 2,5

plain bearings, seals, guide rings.structural parts for low loadsSINT - B 20 ± 2,5 80 ± 2,5

plain bearingsSINT - A 25 ± 2,5 75 ± 2,5

preferred applications

SINT - D 10 ± 2,5 90 ± 2,5 high-strength parts for high static and moderatedynamic loads

SINT - E 6±1,5 94 ± 1,5 high-strength parts for high static and highdynamic loads

<4,5 > 95,5SINT - F warm-compacted parts for highest loads

SINT - G < 8 > 92 with plastic or metal impregnated parts, high cor-rosion resistance, impermeable for oil and water

SINT - S < 10 > 90 warm-compacted plain bearings and sliding elements with internal solid lubricant

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Tolerances of different shaping processes

conventional PM-technology

powder forging

conventional PM-technologywith sizing

investment casting

diecasting

forming under compressiveconditions, hot extrusion

warm working extrusion

cold extrusion

turning

ProcessISO-Quality IT

5 6 7 8 9 10 11 12 13 14 15 16

cylindrical grinding

All tolerances are roughvalues and depend on thesize of the componentsand on the material!

diam

eter

tole

ranc

es


Catalogue of questions to summarize the lecture „Powder metallurgy“

Explain the two significant methods for powder production, the methods for thecharacterization of metal powders and the three different alloying techniques!

Sketch the phases of compaction (use a cylindrical compact)!

Explain the terms density distribution, ejection force and spring-back!

Explain an industrial sintering process on the basis of a sintering conveyor furnace!

Explain the reasons for a sizing operation!Explain then a sizing operation, as example use e.g. the ball sizing of bushes !

Specify and explain the schematic flow of conventional PM-processes!

Which possibilities are provided by PM-technology for producing highly loaded parts?

Specify and explain the influencing parameters on the produciton costs of PM-parts!

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