Directed Energy Deposition

Question 1

What is directed energy deposition?

Answer 1

Focused thermal energy is used to fuse materials by melting as the material is being deposited
Uses a beam of energy to enable the creation of parts by melting a powder or wire feedstock

Question 2

What typical materials are used for DED?

Answer 2

Basic approach can work for polymers, ceramics and metals however predominantly used for metal powders

Question 2

What typical materials are used for DED?

Answer 2

Basic approach can work for polymers, ceramics and metals however predominantly used for metal powders

Question 3

What sources of thermal energy are used for DED? What process is this similar to?

Answer 3

Laser, electron beam or plasma arc are used to melt the feedstock material
Makes the process similar to powder bed fusion processes

Question 4

Why is DED typically referred to as a near net shape process?

Answer 4

Near net shape means that the initial production of the item is very close to the final (net) shape, within 5mm.

Question 5

What does LENS stand for and what process category is this?

Answer 5

Laser engineered net shaping

Directed energy deposition

Question 6

What is the difference between LENS and PBF?

Answer 6

Powder is delivered to a specific zone rather than already there in a bed as in powder bed fusion

Question 7

Describe the LENS process

Answer 7

Powder metal particles are delivered in a gas stream into the focus of a laser to form a molten pool
Deposits are typically made in a controlled argon atmosphere. This may be within a sealed box or just through the sheath gas stream containing argon
sheath gas compresses powder stream
The part is then driven on an x/y stage to generate a 3 dimensional part by layer wise additive processing

Question 8

What are the 2 feedstock options for directed energy deposition?

Answer 8

Powder fed and wire fed

Question 9

Powder vs wire feed comparison

Answer 9

Powder

• most versatile
• Most metals and ceramics available in powder form
• not all powder is captured in the melt pool ( less than 100% capture efficiency)

Wire feed

• 100% capture efficiency
• allows for more porosity
• harder to achieve complex 3D geometry

Question 10

What are the differences between using a single nozzle or 4 nozzle system?

Answer 10

Single

• cheaper to produce
• slower deposition rate

4 nozzle

• 90 degree separation
• faster deposition rate
• wider range of alloys

Question 11

What are the 4 different types of heat energy source in DED? Compare them

Answer 11

Laser beam

• cheaper and more flexible
• does not require vacuum
• Inert atmosphere required

Electron beam

• requires vacuum (challenging for large working area)
• space based applications

Plasma

• investigated by research groups
• used in combination with milling
• larger heat affected zone and process control issues have kept this from commercialisation

Electric arc
- can generate plasma arc

Question 12

What are some benefits of DED compared to PBF?

Answer 12

Multimaterial
Larger parts
No issues with support structures
micro structure

Question 13

What influences the microstructure of parts created DED and why is this an advantage?

Answer 13

Due to the small melt pool and high travel speeds, deposits cool very fast
This results in a fine grain micro structure that may be one order of magnitude smaller in size than comparable wrought products (wrought = heated up and cooled fast)
High hardness
Mechanical properties and the quality of the deposits are typically better than castings

Question 14

How can you control/change the material composition and grain structure of DED parts?

Answer 14

Changing powder composition, laser spot size, laser energy and other process parameters

Question 15

Advantages of directed energy deposition

Answer 15

Fine microstructure, high hardness
Control of microstructure
High density parts
Functionally graded metals 
good 'buy to fly' ratio

Question 16

Disadvantages of directed energy deposition

Answer 16

Slow deposition rates when compared to PBF
Requires inert or vacuum atmosphere
Poor resolution and surface roughness
Cannot product complex structures like PBF

Question 17

What is a buy to fly ratio?

Answer 17

The buy-to-fly ratio is simply the ratio of the mass of the starting billet of material to the mass of the final, finished part.

Question 18

Common materials used in DED?

Answer 18

Stainless steel 
Tool steels 
Nickel/nickel alloys
Cobalt and alloys
Titanium and alloys
Ceramics

Question 19

What materials are difficult to use in DED? What form is most common?

Answer 19

Reflective and conductive metals are difficult to process (e.g. aluminium + copper)

Powders are more common than wires as they can be easily fluidised into the gas stream

Question 20

What are the 4 categories of applications for DED?

Answer 20

Research (new alloys and applications)
Direct part production
Repair, overhaul and modernisation of metallic structures
Adding features to existing metallic or other structures to improve performance

Repair when the asset is worth a lot of money (shaft repair, aerospace parts, turbine blades, bearing housing)

Question 21

What are some future applications of DED?

Answer 21

3D printing on the moon (moon dust) to build structures
But expensive and difficult to carry raw build materials
Sun is thermal source
Electron beam
Already in vacuum