Metal Additive Manufacturing Flashcards
1
Q
What are the conventional metal processing techniques?
A
- Forming
- Cutting
- Casting
- Joining
2
Q
What are the features of metals?
A
- Closely packed atomic structure, lose their outer shell electrons
- Solid (exception Hg)
- Higher density than most non-metals
- Typically hard
- Generally malleable, ductile & fusible
- Shiny, good conductors of electricity and heat
3
Q
Mention different examples of casting
A
- investment casting
- die casting
- spin casting
- sand casting
4
Q
Mention different examples of subtractive/cutting processes (material removal)
A
- Milling
- Turning
- Grinding
5
Q
Mention different examples of forming processes (no material removal)
A
- Extrusion
- Drawing
- Bending
- Forging
- Powder Metallurgy
- Rolling
6
Q
Mention different examples of joining processes
A
- Welding
- Brazing
- Soldering
- Riveting
7
Q
What’s good about Metal AM?
A
- Geometric Freedom
- Customisation
- Quicker to market
- Cost savings
- Improved Design/Perfomance
8
Q
What’s the state of the market for metal AM?
A
Revenue from metals grew 38.3% to an estimated $24.9 million in 2013, up from $18 million the year before
9
Q
List the most important Metal AM techniques
A
- Powder Bed Fusion
- Powder/Wire Feed
- Binder Jetting
- Sheet Lamination
- Other
10
Q
Which of all processes is the most widely and extensively used when making metal parts?
A
Powder Bed Fusion (PBF)
11
Q
What are the features of PBF?
A
- Uses thermal energy, typically laser or electron beam
- Can produce high density fully functional parts in one step
- Excellent mechanical properties
- Good material variety and part properties
12
Q
Describe what happens during the PBF Process - draw a diagram!
A
Thin layers of metallic powder deposited onto substrate/base plate and melted with thermal energy from laser or electron beam
Unused powder recycled
13
Q
What happens to the unused powder of the PBF Process?
A
Unused powder is recycled
14
Q
What are the standard PBF Post-processing processes?
A
- REMOVAL OF EXCESS POWDER
by tapping, using compressed air or ultrasonic waves - THERMAL PROCESSING
to relieve stress of or improve mechanical properties. Furnace cycles or HIPPING to reduce pores and heal micro-cracks - SUPPORT REMOVAL;
Wire EDM or band saw to cut parts off platform. Often hand finishing (with pliers) to pull off remaining supports - SURFACE FINISH OPERATIONS;
machining, shot-peening, tumbling and hand benching, electro-polishing, abrasive flow machining (for internal cavities). Micro-machining, chemical reaction at surface of material driven by fluid flow
15
Q
Why is thermal processing important in the post processing of metal AM-ed parts?
A
It can relieve stress or improve mechanical properties. Furnace cycles or HIPPING to reduce pores and heal micro-cracks
16
Q
How do we remove the excess powder of PBF Parts?
A
tapping, compressed air, ultrasonic
17
Q
How do we remove supports of PBF Parts?
A
Wire EDM or band saw to cut parts off platform. Often hand finishing (with pliers) to pull off remaining supports
18
Q
What are some surface finishing operations for Metal AM-ed parts?
A
- machining
- shot-peening
- tumbling and hand benching
- electro-polishing
- abrasive flow machining (for internal cavities)
- Micro-machining/chemical reaction at surface of material driven by fluid flow
19
Q
Why is process control very important in metal AM?
A
Control of material, process parameters and environment conditions have major influence on final properties of part, e.g. microstructure, density, surface roughness etc
20
Q
What are the important process parameters in metal AM?
A
A. THERMAL ENERGY
Power, Spot Size etc.
B. SCANNING
Speed, Hatch distance, Exposure time/dwell
C. POWDER BED
Powder Morphology Powder particle size distribution Layer thickness Substrate type Pre-heat etc.
D. ENVIRONMENT
Inert gas/vacuum Pressure etc.
21
Q
What are the properties of components produced by metal AM?
A
- High Density
- Fine Microstructure
- Custom Microstructures
- Good fatigue strength and mechanical properties
22
Q
Why do metal AM components achieve high density?
A
Complete melting in single step, parts produced to full density
- Can match of exceed properties of cast and approaches that of wrought
- Less than full density compromises fracture toughness and fatigue properties. Could lead to premature failure, act as crack initiation sites when subjected to cyclic stress
- Compliance to specifications for toughness and fatigue properties critical in aerospace industry and orthopaedic and dental implants
23
Q
In which industry is compliance to specifications for toughness and fatigue properties critical?
A
Aerospace industry and orthopaedic and dental implants
24
Q
Is metal AM density of components comparable to conventionally manufactured components?
A
Can match of exceed properties of cast and approaches that of wrought
25
What does less than full density in components cause?
Less than full density compromises fracture toughness and fatigue properties.
Could lead to premature failure, act as crack initiation sites when subjected to cyclic stress
26
Why do METAL AM components achieve fine microstructure?
1. Rapid melting and cooling of thin layers of material produces uniform microstructure
2. Chemical composition is more uniform than casting resulting in
better mechanical properties
27
Does the microstructure of metal AM components compare with conventional processes such as casting?
1. Some material segregation may occur, but on a smaller scale compared to casting processes.
2. Chemical composition is more uniform than casting resulting in
better mechanical properties
28
Can metal AM components be produced with custom microstructures?
Yes.
Through the variation of parameters and conditions.
29
What are the limitations of PBF?
1. Residual stresses
2. Surface finish not great
3. Some parts require supports/anchors due to thermal warpage which limit geometric freedom.
4. Rapid heating & cooling
5. Large thermal variations
6. Cannot easily nest parts on top of each other
30
How do we tackle the limitations of PBF?
By:
1. Changing designs to reduce need for supports
2. Changing orientation to reduce number of supports
31
Why is thermal processing so important for METAL AM products?
STRESS RELIEF
Stress can cause problems even after support have been removed. This can be relieved with thermal processing (e.g. furnace cycles)
32
How can we reduce surface roughness during build?
By:
1. Using smaller powder particles
2. Laser re-melt strategies
3. Orientating parts differently
33
How can we reduce surface roughness after a build?
By:
1. machining
2. shot-peening
3. tumbling and hand benching
4. electro-polishing
5. abrasive flow machining (for internal cavities)
5. Micro-machining/chemical reaction at surface of material driven by fluid flow
34
Are there systems on the market that combine both conventional and AM processes to create a finished product with no need for further machining?
Yes.
The Matsuura SLM is a hybrid Laser Sintering and Machining system; machining happens at the same time as the additively manufactured component is being built!
35
What are the characteristics of Metal powders?
1. Powders are manufactured in different ways and come in different shapes and sizes (morphology)
2. Spherical powders are best, flow/deposit well and increase powder packing density
3. Do not degrade as easily as polymers
4. Average particle sizes for SLM 40-50um, slightly larger for EBM (powder is sized within an upper and lower range)
36
What do we mean by powder morphology?
Shape and size of powder particles
37
Which powders are the best and why?
Spherical powders are best as they flow/deposit well and increase powder packing density
38
What are the average particle sizes for metal powders?
Average particle sizes for SLM 40-50um, slightly larger for EBM (powder is sized within an upper and lower range)
39
What are the characteristics of finer powder particles?
Finer powder particles:
1. Require less energy to melt
2. Reduce surface roughness
3. Increase powder packing
4. Can be dangerous (wish of inhalation)
5. Can cause powder explosion (especially with reactive metals e.g titanium, magnesium, aluminium)
40
What are the advantages of finer powder particles?
Finer powder particles:
1. Require less energy to melt
2. Reduce surface roughness
3. Increase powder packing
41
What are the disadvantages of finer powder particles?
Finer powder particles:
1. Can be dangerous (wish of inhalation)
2. Can cause powder explosion (especially with reactive metals e.g titanium, magnesium, aluminium)
3. More costly?
42
What are the characteristics of larger powder particles?
Larger powder particles:
1. Are safer to handle
2. Increase surface roughness
3. Require more energy to melt
4. Cheaper?
43
What are the advantages of larger powder particles?
1. Are safer to handle
| 2. Cheaper?
44
What are the disadvantages of larger powder particles?
1. Increase surface roughness
| 2. Require more energy to melt
45
How are these metal powders made?
Gas Atomisation used to create powder
46
What are the different kinds of powders available to the market and their costs?
1. Steel alloys (316L, 17-4 etc.) (~£80/kg)
2. Titanium, commercially pure and alloys (TiCp, Ti-6Al-4V etc.) (~£140/kg)
3. Nickel alloys (In625, 718 etc.) (~£120/kg)
4. Cobalt Chrome alloys (Co28Cr6Mo) (~£90/kg)
5. Copper (~£70/kg)
6. Gold (~£9000/kg)
47
What are the categories of systems using PBF technology?
1. Laser Beam Systems
| 2. Electron Beam Systems
48
What are the features of Laser Based Systems?
1. Materials are melted by ABSORBING laser energy
2. Typically fibre laser used
3. Lasers are versatile, accurate and have a high energy density
49
How are PBF laser based systems known as?
As:
1. Selective Laser Melting (SLM)
2. Direct Laser Metal Sintering (DMLS)
Both are the same thing
50
Describe the function of an SLM system
1. Powder layer of 20-40um is deposited on the plate
2. Laser operates at 50W-1KW powers
3. Build rate is ~30-50cm3/h
4. Chamber is purged with inert gas to prevent oxidation (Argon or Nitrogen)
5. Uses galvo mirror to direct laser energy and draw part geometry
51
How is oxidation of metal AM parts prevented during PBF SLM build?
The build chamber is purged with inert gas such as Nitrogen or Argon
52
How is the laser energy directed during an SLM PBF Process?
Use of galvo mirrors to direct laser energy and “draw” part geometric
53
Mention a typical SLM system
Typical System (EOS M280)
```
Key system characteristics
– Build volume: up to 250x250x300mm – Up to 400W Yb fibre laser
– Spot size: 100μm
– Layer thickness: 20μm to 80μm
– Build speed Up to 32.4 cm3/h
– up to 200C powder bed pre-heat
```
Part Surface finish
– As built: Ra~4-10μm
– After polishing: Ra~0.04-0.5μm
* Minimum wall thickness / feature size 0.04mm
* Accuracy – +/- 0.2mm
54
What are the features of Electron based systems?
1. Materials are melted by transfer of kinetic energy from incoming electrons
2. Process known as Electron Beam Melting (EBM) by Arcam
3. No moving mechanical part to deflect electron
beam, therefore extremely quick scanning.
4. High energy density beam that can be split into
multiple beams
5. 55-80cm3/h build speed
6. Can only process conductive materials
7. Operates in vacuum, pressure
55
Why is EBM PBF really quick in scanning?
No moving mechanical part to deflect electron
| beam, therefore extremely quick scanning.
56
What is the feature of the EBM beam?
High energy density beam that can be split into
| multiple beams
57
Which one between EBM and SLM is fastest at building?
SLM Build rate: ~30-50cm3/h
EBM Build rate: 55-80cm3/h
58
What is the limitation of EBM in terms of materials?
Can only process conductive materials
59
Why does the EBM build take place in a vacuum?
Operates in vacuum, pressure
60
What is a typical EBM system available to the market?
Arcam M280
```
• Key system characteristics
– Build volume: up to 250x250x350mm
– 3.5kW electron gun
– Spot size: 200-1000μm
– Layer thickness: 50μm to 200μm
– Scan speed 8000m/s
– Build speed Up to 55-80 cm3/h
– 1-100 spots
– ~700C pre-heat (can reduce residual stress build-up)
```
• Part Surface finish
– As built: Ra~25/35μm
* Minimum wall thickness / feature size 0.1mm
* Accuracy – +/- 0.05mm
61
Create a table of comparison for SLM and EBM systems for atmosphere, scanning, energy absorption, powder preheating, scan speeds, energy costs, surface finish, feature resolution, residual stress buildup, materials
Slide 40
62
What does SLM stand for?
Selective Laser Melting
63
What does EBM stand for?
Electron Beam Melting
64
Mention some machine vendors of PBF Systems and relative cost
Renishaw SLM (UK) £185-250K
EOS DMLS (Germany) £120-260K
Concept laser Lasercusing (Germany)£100-930K SLM Solutions (Germany) £125-430K
Realizer SLM(Germany) £80-310K
Phenix Systems SLM (France) £100-300K
Matsuura Luminex SLM (Japan) £500K
LaserCore SLM Beijing Long Yuan (China) £60-130K Arcam EBM(Sweden) £310-380K
65
What is purchase price of commercial PBF systems proportionate to?
Generally purchase price is proportionate to build volume
66
```
Compile a comparison table of
PBF vs Machining for the following aspects:
1. Speed of build and overall speed
2. Size of initial material
3. Material waste
4. Geometric complexity
5. Surface finish
6. Accuracy/resolution
7. Residual stress
8. Cost
9. Supports
```
1. Speed: CNC faster at finishing parts although setup time might be longer
2. Size: CNC needs block of material as big as part
3. Material waste: CNC Lots of material wastage
4. Geometric complexity: CNC Cannot machine certain intricate geometries
5. Surface finish: CNC can produce a better surface finish
6. Accuracy/resolution: CNC has better accuracy and resolution
7. Residual stress: PBF generates more residual stress than CNC
8. Cost: PBF cost independent of geometric complexity
9. Supports: PBF may require supporting structures
67
Compile a comparison table of
PBF vs Casting for the following aspects:
1. Solidification times
2. Microstructure
3. Mechanical properties
4. Surface roughness
5. Geometric complexity
6. Build volumes
7. Setup costs
8. Customisation
1. SOLIDIFICATION TIME:
PBF requires less time to solidify
2. MICROSTRUCTURE:
PBF achieves finer microstructure/more uniform microstructure overall, with chemical elements less likely to segregate; opposite goes for casting
3. MECHANICAL PROPERTIES:
PBF has better tensile strengths but worse fatigue life than cast
4. SURFACE ROUGHNESS:
PBF has higher surface roughness
5. GEOMETRIC COMPLEXITY:
More costly/restricted in casting
6. BUILD VOLUMES:
PBF is for small complex geometries in small/medium volumes; Casting better for large components
7. SETUP COSTS:
Casting has high setup costs for each new mold and limited materials (require material with high fluidity
8. CUSTOMISATION:
PBF better for customisation (e.g dental or medical implants)
68
General similarities/differences to polymer based systems for PFB
1. Similar benefits for part creations (e.g geometric complexity, low material wastage etc.)
2. Similar techniques/methods used to build polymer parts
3. Similar accuracy to polymer systems
4. Higher melt temperature than polymers, may require higher energy density to join layers
5. Larger temperature gradient, generally need to be built onto a substrate plate and may require supports
6. Generally lower build speeds due to requirement for a higher energy density
7. Generally more expensive systems than polymers due to hardware requirement for processing and handling of metal
69
Describe what happens during the Powder/Wire Feed process
Powder or wire fed into path of thermal energy source (e.g laser or
electron beam)
Similar to laser cladding or plasma welding
70
What are the features of powder/wire feed?
1. Moveable platform or nozzle (2-4 nozzles)
2. Fully melts material
3. Can process the same materials as used in PBF
4. Processes in an inert environment
5. Deposits 0.1-0.5mm layer
6. Surface roughness 25um
7. Good for the production of simplistic tall geometries
8. Can be used for repair operations (e.g turbine blades)
71
Can the powder/wire feed process use the same materials as PBF?
Yes
72
In what environment do the Powder/Wire feed processes take place?
In an inert environment.
73
How thick are the layers that the powder/wire feed process deposits?
Deposits 0.1-0.5mm layer
74
For which applications is Powder/Wire feed good?
Good for the production of simplistic tall geometries
Can be used for repair operations (e.g turbine blades)
75
What are the advantages of the Powder/Wire feed?
Advantages
1. Multiple material deposition
2. Can produce directional solidified single crystal structures. Especially important for turbine blades
3. Good for repairing
76
What are the disadvantages of the Powder/Wire feed?
Disadvantages
1. Cannot produce complex structures
2. Less than 100% material efficiency
3. High surface roughness 25um
4. Poor resolution
5. Slow build times
6. High residual stress, susceptible to cracking
77
What are some Powder/Wire Feed commercial systems and what are their costs?
Optomec LENS (USA) £300-660K
BeAM (France) £150-520K
Trumf Trulaser (Germany) £300-500K
InssTek (South Korea) £370-560K
Sciaky EBDM (USA) £870-3100K
NASA EBF3 (building parts in space!)
78
Describe the binder jetting process
1. Prints a binder onto pre-deposited powder bed.
2. Parts de-binded at low temperature.
3. Sintered at high temperature.
4. Infiltrated with copper or bronze for strength.
79
What are the features of binder jetting?
1. Produces metal parts and sand casting molds
2. Similar surface roughness to PBF system
3. High volume manufacture
4. Deposits 0.25-0.5mm layers
5. Resolution 0.1mm features
6. Best suited to industries requiring molds
for casting
80
What is a typical application for binder jetting?
Produces metal parts and sand casting molds; Best suited to industries requiring molds
for casting
81
What is the surface thickness of binder jetting?
Similar surface roughness to PBF system
82
What are the advantages of binder jetting?
1. Does not require support structure
| 2. Very large build volumes
83
What are the disadvantages of binder jetting?
1. Poor accuracy
2. Requires further sintering/infiltration cycles
3. Limited materials with limited mechanical properties due to the requirement of 40-60% copper/bronze infiltration (not fully dense)
84
Mention some system examples for binder jetting and relative costs
Fcubic AB (Digital Media) not commercialised yet
ExOne (USA) 180-600K GBP
85
Describe the Sheet Lamination process
Thin sheets of metallic foil bonded together using an ultrasonic sonotrode (plastic deformation and solid state bond)
The machine tool cuts out geometry
86
What is a sonotrode?
In ultrasonic machining, welding and mixing, a sonotrode is a tool that creates ultrasonic vibrations and applies this vibrational energy to a gas, liquid, solid or tissue.
A sonotrode usually consists of a stack of piezoelectric transducers attached to a tapering metal rod. The end of the rod is applied to the working material.
87
What are the characteristics of Sheet Lamination?
1. Foil 100-150um thick
2. Materials steel, nickel, aluminium, copper
3. Sonotrode vibrated at 20kHz
4. Baseplate preheated to 200C
5. Must have clean contact between foils
6. Intimate contact between materials
7. Retains microstructure maintained within bulk of foil
8. Microstructure generally anisotropic
88
What is the resulted microstructure of sheet lamination products?
Microstructure generally anisotropic; Retains microstructure maintained within bulk of foil
89
What is the necessary vibration of the sonotrode and the temperature of the base plate for sheet lamination?
Sonotrode vibrated at 20kHz; Baseplate preheated to 200C
90
What metals can we use for sheet lamination?
1. steel
2. nickel
3. aluminium
4. copper
91
What are the advantages of Sheet Lamination?
1. Excellent surface finish
2. Low heat input, embed electrical components,
fiber optics
3. Reduced thermal stresses due to low heat input
4. Bond dissimilar metals
92
What are the disadvantages of Sheet Lamination?
1. Material wasted
2. Wasted material has to be removed
3. Cannot build overhangs, no supports
4. Voids along interfaces (roughness, insufficient energy, damaged areas
5. Component are~85% as strong as bulk material, worse in z-axis
93
Mention an example of a sheet lamination system available on the market
Fabrisonic (USA)
Generally not many systems sold
94
Mention some other processes for Metal AM beyond the basic 4
1. Aerosol Jet (Optomec)
2. Metaljet (OCE)
3. Powder spray cold forming
4. Micro-stereo-lithography
5. 3D Systems sintersation SLS of metals (indirect processing)
95
To which industries is metal AM relevant?
1. Aerospace
2. Fashion
3. Medical
4. Jewellery
5. Tooling
6. Automotive
7. Furniture
8. Dental
9. Machinery
96
Mention examples of use of metal AM in the aerospace industry
GE Fuel Injector was manufactured using AM as one part in 2013 (conventional manufacturing requires 20 metal parts to be welded together)
GE titanium fan blades to be manufactured by in AM for full scale production by 2016. Saves 50% material compared to conventional manufacturing (forged and machined)
Titanium alloys– high tensile strength/toughness and low weight makes it desirable for aerospace
Nickel alloys – high mechanical strength and resistance to creep at high temperatures, good corrosive resistance makes alloy suitable for engine components
97
Which metals used in AM are particularly relevant to the aerospace industry and why?
Titanium alloys– high tensile strength/toughness and low weight makes it desirable for aerospace
Nickel alloys – high mechanical strength and resistance to creep at high temperatures, good corrosive resistance makes alloy suitable for engine components
98
Any examples of use of metal AM in automotive engineering?
Bloodhound Project, chassis bolt housing produced at the UoS
Land vehicle attempted 1000mph (early 2013)
99
Mention examples of Metal AM medical applications
Medical implants
Custom fit
Walter Reed National Military Center have implanted nearly 100 cranial implants
Ti64 and TiCp used in implants due to biocompatibility (non toxic and not rejected by body).
Lower modulus of elasticity to more closely match that of a human bone.
100
Mention examples of Metal AM dental applications
Dental
AM used in dental labs to produce dental copings, bridges, crowns and partial denture frameworks
Cobalt Chrome (and Titanium) alloys used.
Excellent strength and corrosion and wear resistance.
101
Why is metal AM relevant to the fashion and jewellery industry?
Capitalise on geometric freedom and to produce complex/intricate geometries
Used to produce jewellery in precious metals
102
How much can metal AM advance?
Robert McEwan, general manager of Manufacturing Technologies at GE Aviation, believe that in our lifetime 50% of a jet engine will be made using AM. Profound statement, right people could make it happen.
