Methods to peel off 3D object from vat floor in DLP 3D printer

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Contents

• Additive Manufacturing• Additive Manufacturing with DLP• DLP 3D printer• Digital Light Processing• Photopolymerization• Advantages• Disadvantages• Why does sticking take place?• Solutions to sticking problem• Active mechanism

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Contents(continued)

• Passive mechanism• Free Radical Photopolymerization• Continuous Liquid Interface Printing• Controlled Free Radical Polymerization Oxygen

Inhibition• Dead zone thickness• Cured thickness• Advantages • Disadvantages • Photopolymerizable resins

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Additive Manufacturing

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Additive Manufacturing with DLP

• DLP projector• Photopolymer• Linear actuator• Vat• Stepper motor• Bed • Chassis

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Digital light processing

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Photopolymerization

• Curing- by polymerization rather than vaporization• Photopolymer: Light sensitive resin that cures when light

hits it• UV light of 320-400nm

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• A black and white image or “slice” is a way to selectively cure the resin

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Advantages

• consistent build time independent of layer complexity or number of parts

• Reduced positioning errors• High resolution of 3D printed parts• Minimal or no supports required

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Disadvantages

• Continuous 3D object manufacturing • Sticking problem peeling mechanism• Limited range of photopolymers and their shelf life• Photopolymer resins that are used for DLP printing

are quite expensive($80 to $210 per liter) • Limited build volume• Support has to be of the same material as the build

material

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Why does sticking take place?

• Adhesiveness • Atmospheric air pressure

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Solutions to sticking problem

• Anti-stick solution1) A layer of PDMS on a solid vat floor-transparent at frequencies (240-1100nm)-can not sustain at high temperature-cloudiness of the PDMS-degradation if PDMS due to prolonged exposure

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2) Flexible film of FEP (Fluorinated ethylene propylene) on vat floor-requires silicon gasket to clamp the FEP film-can not be used with polycarbonate, polyethyleneEnvisionTEC Perfectory

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Active mechanism

• Gliding the printed object(shearing the part)

• Ex. B9Creator

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• Tilting mechanism-Various mechanisms can be used such as tilting mechanism ex. four bar mechanism, eccentric cams, spindles, etc.

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• Rotating vat • Ex. Little RP

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• Rotating build platform • projected images also have to be rotated in

synchronization with the bed rotation • Ex. Pimaker 3D printer, Blacksmith genesis

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Passive mechanism

• Using spring for tilting- use of high stiffness springs

• No need to use extra motor• Reduced precision

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Free radical polymerization

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Continuous Liquid Interface Printing

• Controlled free radical polymerization

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Continuous Liquid Interface Printing

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Oxygen transmissibility

• Dk- oxygen permeability function• t- thickness of the semipermeable membrane

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Dead zone thickness

• Φ0 - number of incident photons

• αPI - photoinitiator absorption coefficient• Dc0 - resin reactivity of a monomer-

photoinitiator combination

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Cured thickness

• α- resin absorption coefficient

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Advantages

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• Surface finish

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Technology Time takenSLA 11½ HoursSLS 3½ HoursPolyjet 3 HoursCLIP 6½ Minutes

• Producing a 51mm diameter complex object

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Disadvantages

• Need to maintain dead zone• Continuous provision of resin in Vat

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Photopolymerizable resin

• Photocurable hydrogel• Photocurable silicon resin• Biodegradable resins• Photocurable polyurethanes• High performance resin

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References• Stephen T. Newman, Zicheng Zhu, Vimal Dhokia, Alborz

Shokrani, Process planning for additive and subtractive manufacturing technologies, CIRP Annals - Manufacturing Technology 64 (2015) 467–470

• Erlita Mastan, Xiaohui Li Shiping Zhu, Modeling and Theoretical Development in Controlled Radical Polymerization, Progress in Polymer Science (2015)

• P. B. Morgan, C. Maldonado-Codina, Contact lenses: the search for superior oxygen permeability, Page No. 280-304

• Continuous liquid interphase printing,US WO 2014126837 A2.