Surface texture measurement for AM

Nicola Senin1, Andrew Townsend2, Liam Blunt2, Richard Leach1

1 University of Nottingham, 2 University of Huddersfield

Surface metrology

Measurement and characterisation of surface topography = form + texture

AM Processes (e.g. SLM of metals)

Products or artefacts

Measurement instruments

Topography = form + texture

Surface texture measurement for AM

Measurement solutions

Areal topography datasets

Areal topography measurement instruments

Measurement solutions

CT scanning

Why characterise texture?

AM Process

Study texture as means to deliver function

Destined to a function?

Destined to post-processing?

Study texture as source of post-processing challenges

Study texture to understand and optimise the AM process

Regardless of destination…

feedback

Why characterise texture?

AM Process

Study texture as means to deliver function

Destined to a function?

Destined to post-processing?

Study texture as source of post-processing challenges

Study texture to understand and optimise the AM process

Regardless of destination…

feedback

Texture characterisation for “understanding” the manufacturing process

Mfg. process SIGNATURE / FINGERPRINT

What are these formations?

How were they generated?

Selective laser melting of metal alloy

The challenge of understanding

From: John S. Taylor, Met&Prop 2015

E.g. for SLM of metals

Scales of observation (spatial bandwidths) 20x

50x

100x

e.g. SLM of metals

Directional observation

x

y z

Measurement sets a viewpoint

A paradigm shift in texture characterisation

Sa

=1

Az (x , y ) dx dy

Aòò

Sq

=1

Az 2 x , y( )dx dy

A

òò

Sku

=1

Sq

4

1

Az 4 x , y( )

Aò dx dyòé

ëê

ù

ûú

pores

canyon

scratch

From “field” properties (texture parameters)…

… to selective characterisation of relevant features

Surface features in AM

Defect in SLM surface (inclusion?)

Overlapping weld tracks in SLM surface

Spheroidal formation in SLM surface (spatter/balling?)

Dimensional metrology of surface features

Feature identification

Extraction

Dimensional metrology

Characterisation of artefacts

SLM track Jetted formations – A. Husler, M. Alexander, R. Wildman (Uni. Nottingham)

Jetted tracks – J. Vaitilingham, E. Saleh, C. Tuck (Uni. Nottingham)

Dimensional metrology of jetted artefacts

Jetted tracks

J. Vaithilingam, E. Saleh, C. Tuck

(Uni. Nottingham)

Dimensional metrology of jetted artefacts

Jetted tracks

J. Vaithilingam, E. Saleh, C. Tuck

(Uni. Nottingham)

Localised asperities in SLM surfaces

Evolution of the top layer

Jetted formations

A.Husler, M. Alexander, R. Wildman

(Uni. Nottingham)

Selective laser sintering of polymeric material

Measurement challenges

NanoScribe - regular grids for light entrapment devices A.Knotts + 3DPRG (Uni. Nottingham)

Measurement challenges

Conclusions

- Profile parameters still dominant

- Ra most widely used

- Areal texture parameters have distinct advantages for AM

- Topography should be characterised in context (function, mfg. process)

- Measurement should be planned in context (e.g. spatial bandwidths)

- Texture parameters can be complemented by segmentation and dimensional metrology of relevant topographic features