Layered Manufacturing
How can we make physical form?
Additive Subtractive Deformation
Additive Process
Add materials bit by bit Less material wastage Usually need a mould Casting
Subtractive Process
Remove un-needed material from stockWaste materialUsually need only cutting toolsMilling, Sculpting
Deformation Process
Deform stock materialLess material wastageLimited form, need many different toolsBending, kneadingSometimes called Net-Shape
Manufacturing
Layered Manufacturing
Additive process in natureNo mould requiredNo special toolsOne machine, unlimited forms
Basic process
Basic process
Prepare CAD modelSlice model virtually into layersProduce the bottom most (or top most)
layer according to the layer profileOn top of (or beneath) the produced layer,
add subsequent layerLoop until completion
Freedom of LM
UndercutHollowJig and fixture not required
Advantage of LM
Reduce operator interventionEasy to learnTime and cost only related to size, not
complexity
Disadvantage of LM
Time and cost only related to size, not complexity
Limited choice of materialDouble approximation of the form, first
during polygonization and then by slicing
Common use of LM
Rapid PrototypingOne-of-a-kind manufacturingArt sculptingMedical modellingArchitectural modelling
Shape implications in LM
OverhangCliffsHolesSlicing errors
Exercise
Rapid prototyping process
Polygon model creationModel verificationPre-processing
Orienting and positioning Support generation (optional) Slicing
BuildingPost-processing
Rapid prototyping process
Data input
Almost all RP systems rely on STLA polygon model formatASCII and BinaryWith normal vectorsImplicit unitCan be generated from all major
applicationsOne file can contain multiple components
Data Input
An ASCII STL file
Model verification
LM can deal with only non-manifold polygon models Check for ‘leakage’ Check for naked edges Check for holes Check for reversed facets Check for model obscurities
Model obscurities
Crossed facets Overlapping
facets Degenerated
facets
Source of manifold errors
LM Errors caused by bad STL
Delaminate due to double facets
Reversed normals Ill-behaved CAD
translators
Verification applications
Major polygon modelling applications RapidForm, Surfacer, GeoMagics, etc.
Specific STL applciatons Magics SolidViews
Function of verification applications
Check and repair model errorsRotate and section model to facilitate error
correctionMerge and separate componentsMove, rotate, and scale modelsChecking dimensionsAdvanced editing
Advanced editing
Fill holes by adding facetsAdd draft angleShelling and hollowingSmoothing and re-sampling
Pre-processing
Done by equipment specific applicationsMove, rotate, and scale modelsSome contain basic STL repair functionsSome contain support generation and edit
functionsSlicing STL and generating equipment
control code
Supports
Position and size of model
Machine specific, usually lower left corner as the origin
Position and size can be verify in pre-processing application
Built-specific errors (beam width, thread width, growth, etc.) compensated by application
Shrinkage, form and fit, etc. compensated by operators
Building process
SLA Clear Epoxy Non-critical products
EOS Nylon / Steel ‘Usable’ products
FDM ABS Functional prototypes
3DP Plaster Concept prototypes
Thermojet Wax Concept prototypes
Post-processing
Draining and rinsingSupport removalPost-curing and heat-treatingSurface finishing