Yves Hagedorn - Fraunhofer Institute for Laser Technology

Selective Laser Melting of Net-Shaped Oxide Ceramics

State of the Art in Selective Laser Melting of Alumina Zirconia Ceramics

June 2012

Yves Hagedorn

Outline

Introduction

Process Development

Properties of Manufactured Parts

Cost Drivers

Conclusion

3

SLM of Net-shaped Ceramics

Competences Rapid Manufacturing Department Process Development Qualifying Selective Laser Melting (SLM)

for enlarging the scope of applicable

materials

Improving component’s quality

Increasing productivity

Developing systems and components

Application Development Qualifying Selective Laser Melting (SLM)

for series Production

Tooling

Dental applications

Medical implants

Turbo machinery

Mechanical engineering

Introduction

4


Selective Laser Melting (SLM) for Ceramics

Introduction

Principle

3D-CAD Model

in slices

Powder material

Complex, net-

shaped part in

series material

6


SLM Readily Applied in Industry

Undercuts Internal structures

as cooling channels

Complexity Filigree structures

without joining

Individuality Tool-less production

of customized parts

Tooling Spacecrafts Medical

Some Industrial Applications for Metals

© GFE Inno-Shape

Introduction

7


SLM for Ceramics

Positive Material

Properties

Industrial

Application

+ Mechanical Strength

+ Wear Resistance

+ Thermal Resistance

+ Bio-Compatible

+ Esthetics

SLM

Manufact. Process

+ Tool - Free

+ Complex Geometries

+ Fast

+ High Material Yield

+ Cost Efficient

Medical Applications

Dental Restorations

Implants

High-Tech Applications

Aerospace

Automotive

Advancements in SLM Allow for Fabrication of 3D Ceramics

Introduction

8


® BEGO Medical 2002

Selective Laser Melting (SLM) for Ceramics

Improved esthetics compared to Cr/Co

Exploitation of high material strength

Main Objective Development of SLM process for ceramics

Current Application Framework for dental restorations from

alumina / zirconia compounds

Introduction

Outline

Introduction

Process Development


Cost Drivers

Conclusion

10


The System Al2O3 / ZrO2

Process Development

Eutectic System

Utilization of eutectic powder ratio

S. M. Lakiza and L. M. Lopato. J.Am.Ceram.Soc.80 (1997), 893- 902

Simultaneous crystallization of

alumina / zirconia crystals

Fine-grained microstructure

11


SLM for Ceramics

High densities

High strength

Approach Complete melting of ceramic material

Process Development

12


First results High density

Micro-cracks throughout material

SLM for Ceramics

High thermal gradients during

selective melting

Low strength of manufactured

objects (10 MPa)

Process Development

13


Powder distribution

Pyrometer

Powder reservoir

Focussing optics

Nd:YAG-laser

ScannerHomogenisationoptics

CO -laser beam

(preheating)2

Heat isolation

SLM part Building plattform

Substrate

Experimental Setup I/II

CO2 laser-preheating

Decrease of thermal gradients

during selective laser melting

Crack-free specimens

SLM for Ceramics

Process Development

14


Experimental Setup II/II

SLM for Ceramics

Process Development

15


Experimental Conduction

Thermal Image

High-Temperature preheating

Preheating temperature

~ 1800°C

Homogenous temperature

distribution

Process Development

16


Experimental Challenges

1 High Density

> 99 %

2 Crack free specimens

High-temperature pre-heating

3 High Mechanical Strength

> 500 MPa (DIN Norm for dental restorations)

4 High Surface Quality

Rz < 100 µm (own specification)

Process Development

Outline

Introduction

Process Development


Cost drivers

Conclusion

18


Density & Powder

Spherical Powder

Excellent flowing ability

1 mm

No crack formation

Full density


19


Microstructure

SEM Image

Al2O3 matrix (dark)

Dendritic structure of ZrO2

crystals (bright)

Tunable fine-grained

microstructure

Complete melting of ceramic material


20


0,00%

5,00%

10,00%

15,00%

20,00%

25,00%

30,00%

1600°C/2h 1650°C/2h 1650°C/4h 1700°C/2h 1700°C/4h

Elo

ng

ati

on

Temperature/time

Creep of Alumina / Zirconia Material

SLM

Sintered

High-temperature Creep


Sintered vs. SLM

Loading with 200 g

Eutectic material ratio

Max. elongation ~ 24%

This Analysis has been performed by Innalox bv, Netherlands

SLM material shows decreased creep compared to sintered material

21


XRD Analysis

Crystallographic distribution

Tetragonal ZrO2 crystals

Phase shift ZrO2:

tetragonal monoclinic

This Analysis has been performed by TNO Science and

Industry, Netherlands

Self healing abilities of ZrO2 persist despite complete melting


22


Mechanical Strength

Test Samples

Eutectic material ratio

Dimensions: ø 18 mm x 2.5 mm

Flexural strength > 500 MPa

Flexural strength of sintered

material > 1000 MPa

Specimen

Support

Load

r = 5 mm Mechanical strength sufficient for

dental restorations (DIN Norm)


23


Mechanical Strength

Material: Al2O3/ZrO2

Rz value: ~ 100 µm

Material: ZrO2

Rz value: ~ 10 µm

Conventionally

Max. load 1435 N 10 mm 10 mm SLM

Max. load 2299 N

Minimum load for application 1000 N

Sufficient strength for application despite weaker material and poor

surface quality


24


Surface Quality

Accuracy not sufficient for fitting

5 mm

Dimensional Accuracy

Milled part ~ 50 µm

SLM part ~ 150 µm


25


Surface Quality


Scanning Strategy

Large melt pool due to high

temp. preheating

Contour / hatch

Impact on surface quality

Contour parameters

Contour spacing

Improved surface quality due to small melt pool size at contour

Hatch

Contour

Contour

spacing

26


Surface Quality

Contour Parameters I/II

Rz ~ 112 µm

Sa ~ 54 µm

Laser output: 150 W

Scanning speed: 250 mm/s

2 mm


27


Surface Quality


Contour Parameters II/II

Rz ~ 60 µm

Sa ~ 14 µm

Laser output: 40 W

Scanning speed: 120 mm/s

Surface quality strongly depends on geometry

2 mm

28


Demonstration Object

10 mm

Employment of SLM for ceramic dental restorations

possible

Improved Surface Quality

Surface roughness Rz < 100 µm

Further improvements foreseen

(Rz < 50 µm)

New challenging applications needed


Outline

Introduction

Process Development


Cost Drivers

Conclusion

30


Cost drivers SLM Ceramics

0

10

20

30

40

50

-100 -50 0 50 100 150 200

Co

st o

f d

en

tal re

sto

rati

on

in

€

Relative change in %

Powder (200 €/kg)

Electricity (20 kWh)

Depreciation (5 years)

Manufacturing time (20 h/50 parts)

Personnel costs (25 Euro/h)

Total investment (450 000 Euro)

SLM part 22 €

Milled part ~ 30 €

SLM is competitive compared to milled dental restorations

Assumptions

Outline

Introduction

Process Development


Cost Drivers

Conclusion

32


Conclusion

1 First Bridges Produced

Sufficient strength, fitting subject to improvements

2 Great Environmental Gain

20 crowns 50 g material

3 Great Economical Gain

Forming & densification 1 process step

4 Possible new Applications

Increased thermal stability

33


Dipl.-Ing. Dipl.-Wirt.-Ing. Yves Hagedorn M.Sc. Tel.: +49-(0)241-8906-674 Fax: +49-(0)241-8906-121 [email protected] www.ilt.fraunhofer.de

Thank you for your attention! The research was partly funded by the

European 6th framework project „Custom

IMD“

Thanks to our project partners!

Yves Hagedorn - Fraunhofer Institute for Laser Technology

Technology

shaped ceramicsslm

process development

introduction slm of

process developmentslm

selective laser melting

introductionslm of net

shaped oxide ceramics

process application