Kon-15.4126 Production Technology, Special Topics Vat Photopolymerization Pekka Lehtinen pekka.a.lehtinen@aalto.fi
Content Vat photopolymerization Photopolymerization Stereolithography Part fabrication Resolution Different stereolithography techniques Applications Summary 2
Vat photopolymerization 1 3
Vat photopolymerization 2 4
Photopolymerization Polymerization Monomers Photopolymerization Light initiation Polymerization Crosslinking Crosslinking Resin Curing: liquid resin solid by exposure to radiation 5
Resin Monomer (> 90 wt%) Acrylates, methacrylate, epoxies Photoinitiator (~ wt%) Produces radicals, light stimulus Neutral absorber (~ wt ) Absorb light and reduce penetration depth Other additives (~ wt%) 6
Stereolithography 1 The first AM technique SL, SLA Invented by Charles Hull 3D Systems founded 1986 World s first 3D printing company Curing liquid resin with laser Resolution ~100 µm 7
Stereolithography 2 Pekka Lehtinen 8
Part fabrication: preparation 1 File verification (repair) Part orientation Scaling, shrinkage compensation Support generation Multiple copies Multiple parts, parts nesting Large part segmenting Build simulation Built time estimator www.3dsystems.com 9
Part fabrication: preparation 2 CAD model.stl format Slicing Layer thickness Machine parameters Laser power Speed Material Automatic building process 10
Part fabrication: post processing Support removal Post cure (UV chamber) Part finishing Surface smoothing Painting http://1prototype.com/freeform_parts.html 11
Stereolithography 3 Video http://youtu.be/nm55ct5kwii 12
Commercial stereolithography machines Envisiontec: Perfactory 4 DPP Resolution: 25 µm 3D Systems: ProJet 6000 HD Resolution: 25 µm http://envisiontec.com/3d-printers/perfactory-mini-family/ p4-digital-dental-printer/ http://www.3dsystems.com/3d-printers/professional/projet-6000-hd 13
Desktop stereolithography machines Price range 1000-5000 Example: Formlabs: Form 2 Spot size 140 µm Layer thickness 25 µm 3299 DWSLAB: Xfab Feature size 250 µm Layer thickness 10 µm 5000 http://formlabs.com/products/3d-printers/form-2 http://dwslab.com/xfab-store/?v=cd32106bcb6d 14
Resolution and limitations Shrinkage Curl distortion Over curing Resolution Horizontal Optics Vertical Elevator Resin Working curve Bugeda et al., Rapid Prototyping Journal, Vol. 1, Issue 2, pp.13-23 15
Laser resin interaction Gaussian laser beam Beer-Lambert law of absorption 2w 0 z 0 b w 2w0 0 z 0 z 0 = Rayleigh length w 0 = beam waist Working curve equation: CC dd = DD pp ln EE EE cc CC dd Cure depth DD pp Penetration depth EE Exposure (energy of the beam) EE cc Critical Exposure In a semilog plot of CC dd vs. EE the slope of the curve is DD pp 16
Working curve 350 CC dd = DD pp ln EE EE cc Cure depth (µm) 300 250 200 150 100 E c = 5,6 mj/cm 2 C d = 32,0 ln(e) - 55,2 50 0 1 10 100 1 000 10 000 100 000 Exposure energy (mj/cm 2 ) Pekka Lehtinen 17
Resin properties CC dd = DD pp ln EE EE cc DD pp and EE cc are crucial resin parameters System must be adjusted accordingly Can be modified by changing the photoinitiator and neutral absorber content (especially the absorber content) Minimum layer thickness is defined by DD pp CC dd > DD pp 18
Different stereolithography techniques Projection stereolithography Microstereolithography 2-photon stereolithography Advanced materials Ceramics, metals, etc. 19
Projection stereolithography LCD or DMD mask Integral curing + Speed Broad spectrum + filter + Flexibility Pekka Lehtinen 20
Bottom-up projection stereolithography + Accurate layer thickness control + No sweeper + Part height - Sticking Coatings Peeling Pekka Lehtinen 21
Projection stereolithography videos Video, University of Southern California Fast PSL http://youtu.be/0tzwcwnvyew Video, Carbon3D CLIP (Continuous Liquid Interface Production) http://youtu.be/uph1zhuqy0c 22
Projection microstereolithography at Aalto University 1 1. Video projector 2. Collimation lens 3. Mirror 4. Filter 5. Microscope objective 6. Resin vat 7. Platform 8. Elevator Pekka Lehtinen 23
Projection microstereolithography at Aalto University 2 Resolution 1-10 µm Small part size Research at Aalto Pekka Lehtinen 24
2-photon stereolithography 1 2 photons Within resin No supports 2 µm Micro-Bull 10 µm long 7 µm high 120 nm details Kawata, Sun, Tanaka, Takada, Nature, Vol 412, 2001 25
2-photon stereolithography 2 Smaller details than operation wavelength Even sub-50 nm resolution Video, 2-photon lithography, Vienna University of Technology http://youtu.be/5y0j191h0ky Emons et al., Optical materials express, Vol 2, No. 7, 2012 26
Besides plastic materials Inserting powders in resins Ceramics Metals Graphene Investment casting SL is used for mold fabrication Materials that are not directly suitable for SL Jewelry Korhonen, Lehtinen et al., PSSA, 2015 DOI: 10.1002/pssa.201532761 http://www.met-l-flo.com/gallery.htm 27
Stereolithography applications Functional parts Fit and assembly Patterns for prototype tooling Patterns for metal castings Visual aids Presentation models Education/research Tooling components Anything! 28
Dentistry applications Invisible teeth aligners www.invisalign.com www.invisalign.com 29
Invisalign Imprint at the dentist office Conversion to digital form Stereolithography www.invisalign.com www.invisalign.com 30
Medical and other applications Hearing Aids Lab-on-a-chip xxx 10 µm 10 µm http://disruptiveinnovation.se/?tag=stereolithography Xu et al., Lab chip, Vol. 13, pp. 1677-1690, 2013 31
Summary Resin + Light + Elevator Vat photopolymerization processes Stereolithography (SL) Laser beam, scanning Resolution ~ 100 µm, handheld parts Projection SL Integral curing MicroSL Resolution 1-10 µm, small parts 2-photon SL Resolution < 1 µm, tiny parts Factors affecting resolution Resin (working curve), optics (spot size), elevator (layer thickness) Not only plastic products: resin powder infusion, casting 32
Thank you Pekka Lehtinen pekka.a.lehtinen@aalto.fi 33