Multiscale post-processing of

metal additive manufactured

parts by electro-polishing

technology

L.A. Hof, Md. M. Rahman, R. Wüthrich Electrochemical Green Engineering Group

Department of Mechanical and Industrial Engineering

Concordia University

2

Our Mission

Develop green advanced

manufacturing technologies

meeting the demand of the

fourth industrial revolution

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Our Expertise

Glass Machining

Post-Processing

Coating Industry 4.0

• Lab-on-Chip

• Multilayer chips

• Micro- to Macro-world

interfaces

• Multiscale

electro-polishing

• Down to Ra of 50nm

• Broad range of materials

including Titanium

• Complex parts

• Wide range of substrate

materials

• Tuning surface wettability

• Batch Size 1 production

• Internet of Things (IoT)

• Ultra low-cost tooling

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Glass Micromachining

Med Tech

Watch Industry

Consumer Electronics

Rapid Prototyping

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Electropolishing

SLM part

Counter electrode (CE)

3D printed CE holder

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Room Temperature Nanocoating

400 mm through glass via

Ni plated

Hydrophilic coating Hydrophobic coating

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Internet of Things

Application

Code

GeCo

Library

IoT Device PC, Tablet,

Smartphone, …

Local

Access

over LAN

Back Office

Remote Data

Acquisition

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Additive Manufacturing

Typical metals Aluminium alloys

Cobalt Chrome alloys

Maraging Steel

Nickel alloys

Nickel Chromium alloy

Stainless steel

Titanium alloys

Applications Aerospace

Medical

Automotive

Lifestyle

Tooling

Rapid Prototyping

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Additive Manufacturing: Limitations

Staircase effect & semi-melted beads Surface quality (1 – 100 µm Ra)

Geometrical accuracy

Surface defects decrease performance

100 µm

Solutions to overcome limitations:

• Process control (e.g. re-melting, finer powder)

• Post-processing: Electropolishing

Mechanical polishing

Abrasive flow polishing

Selective surface smoothing

control of micro- and nano-roughness

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Electropolishing Principle

• Workpiece immersed in electrolyte

(e.g. sulphuric acid)

• Anodic dissolution of workpiece

Surface profile before

electropolishing

Surface profile after

electropolishing

Mass transport mechanism:

• Peaks diffuse at higher rates than recesses

anodic leveling

• Random removal of atoms from surface

surface brightening

M s ↔ M+n + ne−

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Electropolishing Limitations

• Acts only on microprofiles (=> requires low initial surface roughness)

• Aqueous acidic solution limits removal of metal species

forming TiO2 layer stopping removal process

• Acidic electrolytes are very hazardous

Method to overcome limitations

• Pulse Technology control Nernst diffusion layer

• Water-free electrolytes

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Nernst Diffusion Layer Evolution

Nernst diffusion layer control by pulsed current

• Short pulses reducing large asperities (> 100 µm)

Diffusion layer contours

both small and larger sized

asperities

Diffusion layer contours

only effectively larger sized

asperities

Diffusion layer no longer

contours any of the

asperities

t = 0 ms t = 0.06 ms t = 1 ms

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Pulse Technology Effect of Pulse Width

Pulse Width [µs]

Ro

ugh

ne

ss S

a [µ

m]

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Pulse Technology Effect of Duty Cycle variation

Ro

ugh

ne

ss S

a [µ

m]

Duty Cycle [%]

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Pulse Technology Effect of Polishing Time

Ro

ugh

ne

ss S

a [

µm

]

Polishing time [min]

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-80.0

-60.0

-40.0

-20.0

0.0

20.0

40.0

60.0

80.0

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

[µm]

[mm]

Roughness Profile SLM part Ti-alloy

Before EP

After EP

Post-process Metal AM Parts

0

5

10

15

20

25

30

Ra initial [µm] Rz initial [µm] Ra after EP [µm] Rz after EP [µm]

Ti6Al4V

AlSi10Mg

EOS SS PH1

1.4 1.7

4.4

11.1

8.97

30.0

0.07 0.67 0.55 0.5

3.08

5.1

Ra 2.0 µm

Rz 7.2 µm

Ra 20.5 µm

Rz 72.6 µm

Ra | Rz before + after EP for various alloys

SLM part

Counterelectrode (CE)

3D printed CE holder

Reference

electrode (RE) Workpiece

(WP)

Counter

electrode (CE)

Potentiostat

Function

generator

Electrochemical

cell (electrolyte)

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Case Study Roughness Control

1. Titanium rod

2. ‘Spider-web’ SLM fabricated Ti-6Al-4V parts

Goal: 1. reduce semi-melted beads (50 µm - 100 µm)

2. understand global reduction in strut thickness

3. optimize parameters for control of roughness and process time

A

.

B

.

10 mm Ra=1.2mm

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Ti-rods Effect of Polishing Time

0

0.05

0.1

0.15

0.2

5 10 15 20 25 30 35

Ra

[m

m]

Polishing Time [min]

Ra=1.2mm

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Ti-Spider Web Effect of EP on Bead Removal

Unpolished

Polished (35 min)

500mm

500mm

200mm

400mm

100mm

100mm

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Polishing of Inner Surfaces

Unpolished Polished

unpolished

polished

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Conclusions

• Pulse technology is an effective tool to eliminate surface

asperities on AM parts

• Surface roughness is reduced typically by a factor 10-20

• Possible to tune the final roughness

• Possible to polish complex shapes

• Possible to polish inner surfaces

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Current industrial partners

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What we offer

R&D projects

Laboratory analysis

Continuing education

Collaborative platforms

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THANK YOU

Electrochemical Green Engineering Group

http://ege.encs.concordia.ca