Lecture 13 Flashcards
1
Q
Additive manufacturing - Definition
A
- also know as 3D printing
- process of creating a physical object from a digital model by adding successive layers of material
2
Q
Methods of Additive Manufacturing
A
- Fused Deposition Modelling (FDM)
- Stereolithography (SLA)
- Selective Laser Sintering/Melting (SLS/SLM)
- Contour Crafting
- D-shape
3
Q
Advantages of Additive Manufacturing in Lunar scenarios
A
- Building parts on-demand -> versatility
- Reduction of waste
- Easier planning of components, tools & building elements
- Spare parts
- One process for many applications
4
Q
Steps from CAD to object
A
- CAD software to create the object
- Convert the designed object into a file readable by 3D printers (e.g. sth)
- Slice the object into layers
- 3D printing process
- post processing of part
- object
5
Q
Defects of additive manufactured parts
A
- Porosity
- Incomplete melting
- Surface roughness
- Most common:
- Warping
- Residual Stresses
- Delamination
6
Q
Warping Defects
A
- corners & edges of a printed part can curl/lift from the build plate due to ∆T during printing
- very common
7
Q
Delamination/Layer separation Defects
A
- Layers of a printed part separate from one another
- part. when the part has a large overhang
- part. if the adhesion is poor
- very common
8
Q
Porosity Defects
A
- tiny air pockets within the part
- reduces mechanical strength
- happens for parts built of powder beds (SLS)
9
Q
Residual Stress Defects
A
- rapid heating/cooling of fused powder -> residual stresses
- leads to warping/cracking
- very common
10
Q
Incomplete melting Defects
A
- laser or electron beam doesn’t melt the powder completely
- part can have weak points, porosity or structural defects
11
Q
Surface roughness Defects
A
- rough surface of part
- additional post-processing steps necessary
12
Q
Binder based processes - Binders
A
- Concretes
- Polymers
- Geopolymers
- Phosphoric acid
- Bio-based polysaccharides derived from algae
13
Q
Concretes
A
- Composition:
- cement-based: 15% cement + 10% water + 75% regolith
- sulfur-based: 20-35% molten sulfur + 65-80% regolith
- Done with D-shape process -> regolith is sprayed with binder
- binder recipe: MgCl2 + H2O + MgO -> Magnesium based Sorel cement
14
Q
Concretes - Pro/Con
A
- Pro
- Not sensitive to regolith composition
- Low T process (15-120° for cement based, 120° for Sulfur based concretes)
- Con
- not enough Mg in regolith to produce the magnesium based Sorel cement binder
15
Q
Polymers
A
- most used:
- PLGA (74-90% regolith + 10-26% PLGA)
- PLA (70% regolith + 30% PLA)
- Steps
- Preparation of ceramic suspension: bed of grinded regolith & 30 wt% binder
- 3D printing by adding binder to flat regolith bed
- Debinding at 600°C (polymer network gets destroyed)
- Sintering at 1000°C (Ceramic particles get sintered into one part)
16
Q
Polymers - Pro/Con
A
- Pro
- Relatively low T process, <200°C (without debinding/sintering)
- Relatively easy to extrude & deposit
- Con
- grinding of regolith required (particle size needs to be smaller than layer thickness
- Durability of polymers with thermal variations & radiations in space
- Recovery of Polymers during debinding TBC
17
Q
Geopolymers
A
- mixture of aluminosilicate powder in an alkaline solution
- (Lunar) regolith is a suitable aluminosilicate powder
- Sodium hydroxide pellets in water can serve as alkaline solution -> to reduce amount of water superplasticizer like Urea (from astronauts) can be used
- 78% regolith + 19% water + 3% urea
18
Q
Geopolymers Pro/Con
A
- Pro
- Controllable setting & hardening
- Low T (setting at 80°C)
- Not sensitive to regolith composition
- Con
- Availability of sodium hydroxide or other alkaline species
- Availability of urea or other superplasticizers
19
Q
Other binders
A
- Phosphoric acid: 37% Phosphoric acid + 63% regolith
- bio-based polysaccharides derived from algae: 1% additives + 30% water + 69% regolith -> 72h resting -> Sintering
20
Q
Types of sintering
A
- Solid-state sintering
- Liquid-phase sintering
21
Q
Solid-state sintering
A
- densification of powder by adding enough heat so that particles in contact rearrange themselves
22
Q
Liquid-phase sintering
A
- particles with the lowest melting point act as lubricant & binder for the larger ones
23
Q
Sintering & melting processes
A
- Selective Laser Sintering (SLS)
- Large Laser Melting
- Solar Melting & Sintering
- Microwave sintering
24
Q
Selective Laser Sintering
A
- uses regolith & CO2 laser
- regolith needs to be levelled
- needs to have powder feed boxes on either side
- bundled laser sinters a line -> 2d shape of current cut
- under build part build piston moves downwards for new layers
25
Q
SLS - Pro/Con
A
- Pro
- Only uses regolith
- Con
- Particle size distribution to change to ensure flowability of the regolith in the SLS 3D printer
- Larger particles to remove or grind to prevent defects
- Applications TBD
26
Q
Large Laser melting + Pro/Con
A
- melts instead of sinters
- Pro
- thick & solid glass obtained from solely lunar regolith
- Not sensitive to regolith composition or Particle size distribution
- Con
- 10 - 12 kW CO2 laser
- Cooling of glassy material, annealing possibility TBC
- Cracks when 3D-printing
27
Q
Solar melting/sintering
A
- uses concentrated sunlight as a laser
- uses mirror to direct the sun in the right direction
28
Q
Solar melting/sintering - Pro/Con
A
- Pro
- Only uses regolith & sunlight
- Suitable for large structure that do not require a high resolution - Con
- Difficult layer deposition
- Currently limited mechanical properties
- resistance to rocket exhaust TBD
- hard to find the T sweet spot for testing
29
Q
Future Processes
A
- Advancing existing processes
- Recycling of binders
- Durability of polymer-based structure (T variation, radiation)
- Adjusting process parameters & increasing printing efficiency
- Testing processes in their relevant environment
- Finding where the processes fit in human & robotic exploration scenarios
- Developing new processes
- process needs to be adjusted for regolith not other way around
30
Q
Applications
A
- Radiation protection of habitats
- Roads & Landing pads
- Spare parts
- in LEO manufacturing
31
Q
parameters for choosing a process
A
- what
- is manufactured
- resources are necessary & How much of each - When do the resources arrive from Earth
- Do benefits justify using space resources
- can you use this process for other needs
