Layer Manufacturing Flashcards
What are the 5 methods of Layer Manufacturing?
Fused Deposition Modelling
Stereolithography
Selective Laser Sintering
Laminated Object Manufacture
3D Printing
Describe Laminated Object Manufacture and draw a diagram
Roll of glued paper used as starting point
To generate a layer the paper is positioned on a base plate and heated by a roller to activate the glue
A laser beam then cuts the outline of the layer through the paper
Process continues until all layers have been added
At the end of the build the waste material is removed (cross hatched during build)
Paper models look like wood at the end of the process
Describe Fused Deposition Modelling and draw a diagram
It’s a very fine extrusion process
Material is extruded through a moveable head in lines with a layer generated through a number of parallel adjacent lines
Extruded material is molten but rapidly solidifies
Subsequent layers extruded on top
Normally used to generate components in ABS plastic
For some shapes a support structure is needed
1) Support material is always used and either broken off or dissolved out at the end of the build
2) Or have no support, unless overhangs
Describe 3 Dimensional Printing and draw a diagram
Powder based manufacturing process using similar technology to ink jet printers
Capable of making parts in most materials, including metals and ceramics
Layer of powder into which a binder is selectively printed
Piston is then lowered and fresh powder spread over the surface
Model can either be used as it emerges from the machine or treated as a green part and post-processed
Describe Stereolithography and draw a diagram
Process starts with a bath of epoxy resin and based on curing of liquid material to generate a solid model
A laser beam scans the liquid surface curing the photo-active resin with UV rays producing a solid surface layer
Once a layer is complete the base plate moves down and fresh material can flow in
The scanning process is repeated to generate the next hard layer of material
The object needs to be anchored so it doesn’t float away - these are designed to be easily broken off once the build is complete
When the last layer of solid material has been added the base plate is raised to lift the object clear of the liquid resin, the object is cleaned and washed, and the support structures are broken away
Can only generate parts in resins and other photo-curable materials
Describe Selective Laser Sintering and draw a diagram
Similar in principle to SLA but utilises powder material rather than resin
For building with polymer materials the process starts with a powder bed heated very close to its melting temperature
A laser scans surface -
where it hits the powder the energy from the laser raises the temperature above the melting temperature
Once a layer is scanned the powder bed is lowered and a fresh layer of powder is spread across the surface used a roller
The polymer is cooled and the solid component is removed and any loose powder is brushed or shaken off
Pros: Unheated powder serves as support component so no other support is needed. A wide range of materials can be manufactured using this technique
What are the advantages of Layer Manufacturing?
Very quick way to generate one off complicated geometric models - no time penalty for geometric complexity once the CAD has been completed
Able to generate any geometry which can be represented within a 3-D solid model
What are the limitations of Layer Manufacturing?
Machines are expensive
Size typically limited to 500 mm cube - although parts can be joined
Most systems are accurate to only ± 0.1 mm at best
Accuracy and surface finish are affected by “stair-stepping” and file manipulation errors
How do File Manipulation Errors occur?
Standard format used in layer manufacturing is stl file
The 3-D solid model is converted to a stl file before being send to the layer manufacture machine
The stl formant describes the component by defining a number of triangles which cover the surface of the component - and this can lead to errors if insufficient triangles are used
What/Where are the main applications for Layer Manufacture?
- Design verification
- Medical models
- Investments for casting
- Sand casting
- Tooling
Also emerging applications where the layer manufactured component is the final product
How can Layer Manufacture Systems be used for Design Verification?
The ability of layer manufacture systems to very quickly go from 3D solid model to physical part means that prototypes can be quickly generated
This gives designers very quick feedback on the quality of their designs
Parts will not normally be in the final material but can be used for form and fit tests, to evaluate alternative design concepts, and as demonstrators.
What are the Medical Applications of Layer Manufacture?
Ability of layer manufacture processes to generate complicated geometries means that biological geometries can be manufactured
Data from a CT body scan or similar process is electronic hence can easily be converted into a solid model
Parts made are personal rather than generic
Normally used to provide information (e.g. to a surgeon) or to generate surgical aids (e.g. drill jigs for implants)
Outline how Investment Casting is relevant to Layer Manufacturing
Most layer manufacturing techniques can generate parts in a material which can be either melted or burnt
These can be used directly as investments for investment casting
If the material burns rather than melting ash will remain in the mould - this can be blown out using compressed air
Outline how Sand Casting is relevant to Layer Manufacturing
An extension of the selective laser sintering process can directly generate complicated sand cores
The powder used in the process is foundry sand coated with a thermosetting binder
which hardens when hit by the laser- producing a sand/binder composite which can be used directly as a core in sand casting
Models made by any layer manufacture system can be used to quickly generate patterns for sand casting, with appropriate shrinkage allowance and draft generated in CAD
Models can also be used directly as core boxes
Outline how Tooling is relevant to Layer Manufacturing
Tool for processes such as injection moulding and die casting usually have complex geometries and are expensive
Layer manufacture techniques can help reduce the leadtime and cost of generating tooling - known as rapid tooling
Two distinct areas to consider: prototype tooling & production tooling
