RP - SLA - Hardware

8/6/2019 RP - SLA - Hardware

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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 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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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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Depth of Focus

Shape, size, depth

Scanning mirror

Input beam

Beam waist

Resin surface


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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

RP - SLA - Hardware

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