metal powder reuse in additive manufacturing

Metal powder reuse in additive

manufacturing

Alessandro Consalvo

AM Support Engineer, Renishaw spa

• World leading metrology company

founded in 1973.

• Skills in measurement, motion

control, spectroscopy and

precision machining.

• 2011 MTT acquisition making

Renishaw the only UK

manufacturer of metal additive

manufacturing systems.

Renishaw

70 offices

32 countries

> 3800 employees

Renishaw worldwide locations

AM250 system

AM250

Max Part Build area245 x 245 x 300 (x,y,z)

(z extendable to 360mm)

Build rate* 5cm³ to 20cm³ per hour

Layer thickness 20 to 100µm

Laser beam diameter 70µm at powder surface

Laser options 200W or 400W

Power supply 230V 1PH 16A

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.

3D model is sliced in layers with thickness from 20 to 100 µm.

Near net shape metal component with density and mechanical properties comparable to those obtained by casting.

The machine builds up the part layer by layer, using a high powered fibre laser to fuse fine metal powder particles together.

x

y

Powder bed laser melting

A layer of fine gas atomized metal powder is deposited and a high power fiber laser

melts the particles together to form solid dense metal following the 3D model.

The platform is lowered and a new layer is deposited and melted by the laser.

The process is repeated until the merger of the last layer of the model.

The unmelted powder is recovered and it can be used again after a sieving process.

Retractable

Platform Z

axis

Build

Metal

Powder

Build

Chamber

Laser

Window

Powder

distributio

n System

Inert

Gas

Laser

beam:

70 µm

How Laser Melting works

Powder reuse cycle

1. Fill hopper

2. Inert atmosphere

3. AM

4. Collect overflow

5. Sieve

6. Reuse sieved powder

Powder reuse cycle

1. Fill hopper

2. Inert atmosphere

3. AM

4. Collect overflow

5. Sieve

6. Reuse sieved powder

Powder reuse cycle

1. Fill hopper

2. Inert atmosphere

3. AM

4. Collect overflow

5. Sieve

6. Reuse sieved powder

AM250 inert atmosphere generation

Renishaw AM machines are unique in the way build atmosphere is

created. All Renishaw systems are suitable for building reactive

materials.

1. A vacuum is created, approx.1 atm below ambient:

• 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.

Gas consumption is typically <30 L/hr and laser melting is achieved

approx. 10 minutes after cycle start.

Powder reuse cycle

1. Fill hopper

2. Inert atmosphere

3. AM

4. Collect overflow

5. Sieve

6. Reuse sieved powder

Overflow powder down here

Powder reuse cycle

1. Fill hopper

2. Inert atmosphere

3. AM

4. Collect overflow

5. Sieve

6. Reuse sieved powder

Overflow capture

flasks

Powder reuse cycle

1. Fill hopper

2. Inert atmosphere

3. AM

4. Collect overflow

5. Sieve

6. Reuse sieved powder

Used overflow powder

Sieved used overflow

powder

Powder reuse cycle

1. Fill hopper

2. Inert atmosphere

3. AM

4. Collect overflow

5. Sieve

6. Reuse sieved powder

• An area of AM that needs fully understanding.

• Feedstock should be reliable for process

repeatability and predictability.

• Powder bed and machine parameters are closely

related.

Why investigate powder re-use for AM?

Why titanium?

Ti-6Al-4V alloy

High strength to

weight ratioHigh corrosion

resistance

45 % lighter than

steel$$$$$

Buy to fly ratio

20kg Titanium billet

1 kg Titanium powder

1 kg

Ti component

AM

Machining

19 kg Waste Ti

Powder characteristics - Chemistry

Element %

Ti Grade 5 Ti Grade 23 (ELI)

Oxygen 0.20 0.13

Nitrogen 0.05 0.03

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

Powder characteristics - Physical

Flowability

PSD – Particle size distribution

Shape

Density/Packing

Flowability is important for consistent

layers, it is directly influenced by

PSD, packing and particle shape.

• 20 routine builds using same Ti powder batch

in same AM250 system

• Powder capture capsule

• Tensile bar and density block

Experimental procedure

Powder analysis Build analysis

Oxygen and Nitrogen Tensile

PSD Density

Flowability Powder capture

capsuleTensile test

piece

Density block

Experimental results – interstitial elements

Maximum O level for grade 23

Maximum N level for grade 23

Steady increasing trend

trend.

Steady increasing trend

trend.

Experimental results – interstitial elements

Grade 23

Maximum

Grade 5

Maximum

Powder analysis

Experimental results – Particle size distribution, PSD

Build 16 • No general trend in

PSD with increased

numbers of builds.

• Builds 11 and 16

have more wide and

narrow distributions

respectively.

Build 11

Experimental results - Flowability

Flow initially increase

between 0-5 builds

followed by a general

decrease.

Experimental results – Melted powder: Tensile

Upper tensile strength

Yield strength

• After 20 builds the powder is not significantly

changed either in terms of interstitial

elements or physical properties.

• Results indicate significantly more reuse

potential.

• Careful powder handling contributes to

sustainability of powder.

• Continued investigations required, including

blending of powders to sustain repeatability.

Conclusions