Investigating the effects of multiple powder re-use cycles in

AM

Lucy GraingerProduct Marketing Engineer, Renishaw

Why even investigate powder re-use in AM?

• Feedstock should be reliable for process repeatability and predictability

• Powder properties and machine parameters are closely related

• Reduce potential waste

Why even investigate powder re-use in AM?

Why is titanium so special?

Why titanium?

Ti-6Al-4V alloy

High strength to weight ratio

High corrosion resistance

45 % lighter than steel $$$$$

Why use additive manufacturing?

Subt

ract

ive

Addi

tive

Billet CNC machining Component + waste – high buy-to-fly

Powder Powder bed fusion Near net shape + little waste – low buy-to-fly

What steps contribute to a re-use cycle?

Re-use cycle

Metal powder bed fusionRoutine build + test samples

Remove build plate

Sieving Remaining

un-melted powderRe-use

Return sieved powder to silo

repeat

AM250 system

AM250

Max build volume 250 mm x 250 mm x 300 mmBuild rate* 5 cm³ to 20 cm³ per hour

Layer thickness 20 to 100 µm

Laser beam diameter 70 µm at powder surface

Laser options 200 W

Power supply 230 V 1PH 16 A

Power consumption 1.6 kWh

Gas consumption < 30 l/hr* Build rate is dependent on material, density & geometry, not all materials build at the highest build rate.

Minimising possible contamination

Renishaw AM machines are unique in the way the inert atmosphere in the build chamber is created.

1. A vacuum is created, 35-50mbar:

• This removes air and any humidity from the entire system

2. The chamber is filled with ~600 litre of high purity argon.

3. The atmosphere is maintained at below 1000ppm (0.1%) oxygen and can be set to run below 100ppm (0.01%) for titanium (Ti6Al4v) and other alloys.

Key Benefit: Gas consumption is typically <30 L/hr and laser melting commences approx. 10 minutes after the process cycle starts.

All Renishaw systems are suitable for building reactive materials.

Both chemistry and physical properties of the powder are essential to the quality of the

end product!

Powder chemistry – Titanium alloy grades

Element%

Ti6Al4V Grade 5 Ti4Al4V (ELI)

Oxygen 0.20 0.13

Nitrogen 0.05 0.05*

Carbon 0.08 0.08

Hydrogen 0.0125 0.0125

Aluminium 5.5-6.75 5.5-6.50

Vanadium 3.5-4.5 3.5-4.5

Interstitial

Alloying

*Some grades quote 0.03% max

Physical characteristics of powder

Flow

PSD – Particle size distributionShape/morphology

Density/Packing

Flowability is important for consistent layers, it is directly influenced by PSD, packing and particle shape.

x

Test samples for analysis

Tensile test bars:3 x as built3 x as machined

Density block

Powder capsule60 g of powder approximately

Results - Chemistry

Chemistry - Oxygen

0

500

1000

1500

2000

0 5 10 15 20 25 30 35 40

Oxy

gen

/ ppm

No. of builds

1300 ppm Ti6Al4V ELI max.

2000 ppm Ti6Al4V grade 5 max.

• Initial study over 20 builds• Second study over 38 builds

Chemistry - Nitrogen

0

100

200

300

400

500

0 5 10 15 20 25 30 35 40

Nitr

ogen

/ pp

m

No. of builds

N ppm max

N ppm alternative max

• Initial study over 20 builds• Second study over 38 builds

Experimental results - Physical

Powder morphology

Virgin powder Build number 3Virgin powder

Powder morphology

Virgin powder Build no. 18 Build no. 38

Powder morphology

Build number 38

Particle size distribution and flow

Vol

ume

dens

ity /

%

Size Classes / µm

Little change in particle size distribution over 38 builds

Particle size distribution and flow

0.00

10.00

20.00

30.00

40.00

50.00

60.00

0 5 10 15 20 25 30 35 40

Part

icle

siz

e / µ

m

No. of builds

D90

D50

D10

Particle size distribution and flow

0.00

10.00

20.00

30.00

40.00

50.00

60.00

0 5 10 15 20 25 30 35 40

Part

icle

siz

e / µ

m

No. of builds

D90

D50

D10

Agglomerate

Small particle sintered to larger particle

Particle size distribution and flow

0

5

10

15

20

25

30

35

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 5 10 15 20 25 30 35 40

Flow

/sg-

1

D50

/µm

Builds

Flow

D50

Tensile properties

600

700

800

900

1000

1100

1200

0 5 10 15 20 25 30 35 40

UTS

/ MP

a

Build

Machined

As built

• Density – previous study showed consistently dense components

• Fractography of tensile test bars

• Repeat but over normal running conditions with new powder additions

Further work

• Re-use doesn’t seem to affect the AM process

• General but not significant changes to the powder both chemically and physically

• This is an extreme look at how powder is affected by being used in an AM process, regular topping up of the silo with virgin powder will most likely dampen the effect of the chemical and physical changed to the powder

• There doesn’t seem to be any requirement to dispose of powder - this obviously depends on the requirements of the component.

Conclusions

Email: lucy.grainger@renishaw.com