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Rapid Prototyping
SLA Process - Hardware
K. Balamurugan
Lecturer in Mechanical Engg.
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Recent Advances in RP&M
Hardware
Software
Process
Mate
rials
Increa
singper
forma
nce
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Introduction
Hardware
Layer preparation
Thin layer of liquid 0.10 to 0.25 mm
Mechanical and Electrical subsystems
Software Control algorithms Imaging Phase
Selective solidification
Mechanical, Optical, Electrical and Electronicelements
Control algorithms for layer sequence
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Layer Preparation
Foundation of the house
Quality of resin surface Quality of the
part Uniform resin surface
Recoating blades
Fluid pumps
Surface finding lasers
Robotics
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Layer Preparation
Simultaneous actions
Resin Surface Location
Flat and Level of Resin Surface Controlling Resin Volume
As quickly as possible
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Resin Surface Location
Resin surface is the drawing plane of theimaging system
Resin surface must be maintained at thefocal plane of the imaging system
Changing Spots
Depth of Focus
Imaging System
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Resin Surface Location
Changing Spots
Diameter of the focused laser beam or
Spot Distance between the focusing elements
and the resin surface
Width of the cured line of resin Size and Shape control is vital
Cure depth, width of line, attachment
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Resin Surface Location
Depth of Focus
Shape, size, depth
Scanning mirror
Input beam
Beam waist
Resin surface
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Resin Surface Location
Imaging system
Calibration is based on resin surface
location Spherical to Planarmapping
Small positioning errors
Model scaling
Large positioning errors
Distortions in shape and scale of the model
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Flat and Level of Resin Surface
Resin surface must be uniformly flat, leveland free extraneous features
Flatness Layer-to-layer adhesion
Dimensional stability
Not uniformly flat
Thicker sections insufficient exposure >
partial layer separation Thin sections excessive resin exposure
-> residual stress, distortion
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Flat and Level of Resin Surface
Recoating and leveling system
Providing flat layer of liquid resin at the
proper thickness Operations
Lowering the part in the vat
Wiping away excess material
Smoothing the remaining material toprovide the desired thickness
Resin viscosity, surface tension
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Controlling Resin Volume
Resin surface must be be controlleddistance above the previously drawn
cross section of the part Sufficient resin volume
Shrinkage allowance
Resin level should be maintained at thefocal plane of the imaging system
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Imaging Phase
Responsible for translating the abstractdata of the CAD world into specific
patterns of UV exposure on the surface ofthe photopolymer
Vector representation -> Image on resin
More accurately, precisely, andrepeatedly reflect the geometry of theCAD model
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Imaging Phase
Data transformation
Geocorrection
Drift correction Linewidth compensation
Exposure control
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Data transformation
CAD space to SLA space mapping
Origin of the coordinate system
Resolution (units) Scaling, translation or rotation
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Geocorrection
Compensation for image distortion thatoccurs when planar coordinate space of
the data is imaged onto the flat resinsurface using spherical coordinate systembased scanning mirrors
Geometric correction theoreticallycalculable
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Drift Correction
Compensation for Images drift or imagemisregistration
Tiny variations Surface finish
Reasons
Temperature vat space, mirror location
Scanning mirror position sensor drifts
Reference points located in the imagespace
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Linewidth compensation
Spot 0.25 mm
Lw W0, Cd
Linewidthcompensation ON
Linewidthcompensation OFF
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Exposure control
Accurate laser exposure
Underexposure delamination
Overexposure curl Cure depth, Penetration depth
Residual stress
Photomodulus
Increased strength, internal stress
Advances in Leveling & Resin
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Advances in Leveling & ResinInterchange
Level sensing advances
Accurate, Fairly fast, Non-contact and insensitiveto the density difference
Resin surface
HeNe LaserBi-cell Sensor
Upper Cell
Lower Cell
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Advances in Imaging system
Acousto-Optic system
Alter the trajectory of the coherent
radiation through a solid medium, byintroducing sound into that medium
Piezo-restrictive transducer
BraggdiffractionPlanes
(sound fields)
Input beam
Deflected beam
Zero order beam
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Advances in Imaging system
Digital Signal Processor
Commanded path
Actual path
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Summary
Hardware
Layer preparation Phase
Image Phase Recent advances in the above