Tutorial 1 Flashcards
What is additive manufacturing?
Additive manufacturing is the general term for those technologies that, based on a geometrical representation, create physical objects by successive addition of material.
Source: ISO/ASTM 52900
What are some common reasons for using 3D printing?
- Product Development • Personalised products • Reverse Engineering • Rapid tooling / mould manufacture • Home hobbyists • New capability / performance
Explain the five main necessary steps to go from a CAD model to a finished physical component via Additive Manufacturing?
Step 1: CAD – model the required CAD geometry using a 3D CAD program such as NX or SolidWorks.
Step 2: STL – convert the 3D CAD model to a .stl file by tessellating the surface of the CAD model with an airtight mesh.
Step 3: Setup Build – load the .stl file into the AM machines operating software and set the part orientation, number of parts, process parameters, and support
structures for the build.
Step 4: Manufacture the component – when the setup is correct the machine is initialised and the build process begins in an autonomous fashion.
Step 5: Post Process – when the manufacture of the component is complete it must be post-processed for the particular AM process. This may include but is not limited to excess powder removal, support structure removal, UV curing,
infiltrating parts.
List 6 current limitations of Additive Manufacturing
- Selection of materials
- Material properties
- Resolution & Surface finish
- Throughput
- Post processing
- Materials cost
Why can machining be preferred over Additive Manufacturing in some metal applications?
Machining is flexible, and can produce strong, accurate parts.
Cutting processes are very accurate and have broad capabilities in part geometry and materials. In addition, machining has low tooling requirements – reducing fixed costs and lead time.
How does machine capabilities affect the design of a part using Additive Manufacturing?
Within the same process different machine capabilities can impact: • Process speed • Support generation • Build volume • Resolution, dimensional accuracy and surface finish • Repeatability between parts • Types of materials processable • Part production cost
Discuss ways when designing a part to avoiding support structures.
- Change build orientation
- Fill the overhangs
- Use self supporting structure
- Segment the part
- Integrate supports
What are the limitations of the STL file format?
Large file size for higher accuracy/complexity
Limited function other than geometric representation
Do not represent colour
Do not represent texture
Do not represent material properties
Conversion errors are time consuming and costly
Briefly describe the ASTM standard for VAT Photopolymerization.
Liquid photopolymer in a vat is selectively cured (solidified) by light (photon) activated polymerisation
What is the advantage of using bottom-up imaging over top-down for the Stereolithography process?
A shallow vat can be used therefore less materials are required within the build system.
No re-coater system required. Therefore, cheaper and simpler system.
Name three VAT Photopolmerisation processes?
- Stereolithography
- Two-photon polymerization
- Continuous Liquid Interface Production (CLIP)
Explain the Stereolithography process
Top down exposure
• Laser based photopolymerisation uses a UV wavelength laser (typically around 350 nm).
• The laser scans the liquid surface and causes the liquid to polymerise. The platform then drops a layer which is recoated and then scanned.
Bottom-up exposure
• Projected image based Stereolithography – typically using a DLP
• Image projected from below and polymerises the given layer. The part is then moved one layer up and process is repeated
Very briefly describe the ASTM process category for Material Extrusion
A material is selectively dispensed through a nozzle or orifice.
Provide a process example for the material extrusion category. The example should include a description and diagram to explain the process.
A suitable example would be Fused Filament Fabrication (FFF). This technology extrudes a heated polymer filament through an extrusion head onto a heated build plate in a layer by layer fashion. The extruder head heats the material and drive wheels within the head force the molten material through a small diameter nozzle (typically 100 – 400 μm). The extruder is attached to a moving head which traces the pattern for the required layer in the x and y axis. Once the layer is complete the extruder assembling ascends one layer thickness and the next layer is manufactured (typical layer thickness is 20 – 200 μm). When the part is complete the build chamber cools and the part + support structure can be removed. Some systems use separate materials for the support structure.
List three advantages Material Extrusion has over Vat photopolymerization.
- The process is ‘office friendly’ due to:
- Stable materials in non-hazardous form
- Lack of dangerous bi-products of processing
- Simple operation mechanism that doesn’t require specialist training or knowledge
- A reliable technology with low maintenance costs
- Build materials are low cost and easily obtainable
- The available materials exhibit very good mechanical properties and are like traditional engineering polymers
- The machine can be, relatively, cheap with open access
- Some of the more expensive systems have soluble support structures
