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