Metal Additive Manufacturing Flashcards
What are the conventional metal processing techniques?
- Forming
- Cutting
- Casting
- Joining
What are the features of metals?
- 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
Mention different examples of casting
- investment casting
- die casting
- spin casting
- sand casting
Mention different examples of subtractive/cutting processes (material removal)
- Milling
- Turning
- Grinding
Mention different examples of forming processes (no material removal)
- Extrusion
- Drawing
- Bending
- Forging
- Powder Metallurgy
- Rolling
Mention different examples of joining processes
- Welding
- Brazing
- Soldering
- Riveting
What’s good about Metal AM?
- Geometric Freedom
- Customisation
- Quicker to market
- Cost savings
- Improved Design/Perfomance
What’s the state of the market for metal AM?
Revenue from metals grew 38.3% to an estimated $24.9 million in 2013, up from $18 million the year before
List the most important Metal AM techniques
- Powder Bed Fusion
- Powder/Wire Feed
- Binder Jetting
- Sheet Lamination
- Other
Which of all processes is the most widely and extensively used when making metal parts?
Powder Bed Fusion (PBF)
What are the features of PBF?
- 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
Describe what happens during the PBF Process - draw a diagram!
Thin layers of metallic powder deposited onto substrate/base plate and melted with thermal energy from laser or electron beam
Unused powder recycled
What happens to the unused powder of the PBF Process?
Unused powder is recycled
What are the standard PBF Post-processing processes?
- 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
Why is thermal processing important in the post processing of metal AM-ed parts?
It can relieve stress or improve mechanical properties. Furnace cycles or HIPPING to reduce pores and heal micro-cracks
How do we remove the excess powder of PBF Parts?
tapping, compressed air, ultrasonic
How do we remove supports of PBF Parts?
Wire EDM or band saw to cut parts off platform. Often hand finishing (with pliers) to pull off remaining supports
What are some surface finishing operations for Metal AM-ed parts?
- 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
Why is process control very important in metal AM?
Control of material, process parameters and environment conditions have major influence on final properties of part, e.g. microstructure, density, surface roughness etc
What are the important process parameters in metal AM?
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.
What are the properties of components produced by metal AM?
- High Density
- Fine Microstructure
- Custom Microstructures
- Good fatigue strength and mechanical properties
Why do metal AM components achieve high density?
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
In which industry is compliance to specifications for toughness and fatigue properties critical?
Aerospace industry and orthopaedic and dental implants
Is metal AM density of components comparable to conventionally manufactured components?
Can match of exceed properties of cast and approaches that of wrought
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
Why do METAL AM components achieve fine microstructure?
- Rapid melting and cooling of thin layers of material produces uniform microstructure
- Chemical composition is more uniform than casting resulting in
better mechanical properties
Does the microstructure of metal AM components compare with conventional processes such as casting?
- Some material segregation may occur, but on a smaller scale compared to casting processes.
- Chemical composition is more uniform than casting resulting in
better mechanical properties
Can metal AM components be produced with custom microstructures?
Yes.
Through the variation of parameters and conditions.
What are the limitations of PBF?
- Residual stresses
- Surface finish not great
- Some parts require supports/anchors due to thermal warpage which limit geometric freedom.
- Rapid heating & cooling
- Large thermal variations
- Cannot easily nest parts on top of each other
How do we tackle the limitations of PBF?
By:
- Changing designs to reduce need for supports
- Changing orientation to reduce number of supports
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)
How can we reduce surface roughness during build?
By:
- Using smaller powder particles
- Laser re-melt strategies
- Orientating parts differently
How can we reduce surface roughness after a build?
By:
- 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
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!
What are the characteristics of Metal powders?
- Powders are manufactured in different ways and come in different shapes and sizes (morphology)
- Spherical powders are best, flow/deposit well and increase powder packing density
- Do not degrade as easily as polymers
- Average particle sizes for SLM 40-50um, slightly larger for EBM (powder is sized within an upper and lower range)
What do we mean by powder morphology?
Shape and size of powder particles
Which powders are the best and why?
Spherical powders are best as they flow/deposit well and increase powder packing density
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)
What are the characteristics of finer powder particles?
Finer powder particles:
- Require less energy to melt
- Reduce surface roughness
- Increase powder packing
- Can be dangerous (wish of inhalation)
- Can cause powder explosion (especially with reactive metals e.g titanium, magnesium, aluminium)
What are the advantages of finer powder particles?
Finer powder particles:
- Require less energy to melt
- Reduce surface roughness
- Increase powder packing