Additive Manufacturing 09july2013

Transcript

09/07/2013 ADDITIVE MANUFACTURING PROCESSES FOR MATERIALS FORMING Part 1 : Basic principles and examples Claire Barrès, Jean-Yves Charmeau, Stéphane Dupin, Amir Msakni INSA-Lyon 1 Additive manufacturing technologies ❶ Basic principles ❷ 3D Printing ❸ @manufacturing 1 09/07/2013 Different types of material forming processes By ablation Sculpture By deformation Pottery By addition Building Rapid Manufacturing / Machining Stamping Additive processes ? Additive manufacturing technologies ❶ Basic principles ❷ 3D printing ❸ @manufacturing 2 09/07/2013 Creating a 3D physical model directly from digital data S.T.L. file 3D model from a computer (CAD file) Machine software fabrication 5 • STL file : – Description of the surfaces of the part by triangular facets 3 09/07/2013 SLICING The model is placed in the virtual space of the machine Slicing into thin layers (thickness depends on the process) 7 LAYER ADDITION Layer by layer building 8 4 09/07/2013 LAYER ADDITION AND SURFACE FINISHING Object after finishing Physical object out of the machine (final surface quality depends on the layer thickness ). 9 Additive manufacturing technologies ❶ Basic principles ❷ 3D printing ❸ @manufacturing 1 0 5 09/07/2013 3D Printing There are a number of 3D printing technologies. They differ in the way layers are deposited to create parts, in the materials that can be used, and they all work differently. Inkjet 3D-printing systems create the model one layer at a time by spreading a layer of powder (plaster, or resins) and printing a binder in the cross-section of the part using an inkjet-like process. This technology allows the printing of full color prototypes. The strength of bonded powder prints can be enhanced with wax or thermoset polymer impregnation. Some methods melt or soften material to produce the layers, e.g. selective laser melting (SLM), selective laser sintering (SLS), fused deposition modeling (FDM), while others cure liquid materials using different technologies, e.g. stereolithography (SLA). 1 1 PRINTER RESOLUTION • It describes layer thickness and X-Y resolution in dpi (dots per inch) or micrometers. • Typical layer thickness is around 100 micrometers (µm), although some machines such as the Objet Connex series and 3D Systems' ProJet series can print layers as thin as 16 µm. • X-Y resolution is comparable to that of laser printers. • The particles (3D dots) are around 50 to 100 µm in diameter. 1 2 6 09/07/2013 3D Printing Principle : using a printhead. Advantage : - Can be used in engineering and design depts, in drawing offices, at home Drawback : - Fragile parts Applications : - Prototyping, design office Materials : - Light sensitive resins, epoxy - Polymer melt - Polymer binder on polymer, metal, sand, ceramic powders. Some machine manufacturers : - Molten polymer thread: Stratasys - Light sensitive systems : Objet - Powder + binder system : Prometal. Dimensions : up to 4 x 2 x 1 metres (Voxeljet, binder jetting) Source Ex-one 1 3 FUSED DEPOSITION MODELING (FDM) 1 4 7 09/07/2013 Examples Fused Deposition Modelling (FDM) Stratasys 1 5 Fused deposition modeling (FDM) Advantages : – Functional and flexible models. – Soluble supports – Simple system, possibility of desktop use. – Non-toxic materials Machine manufacturer : Stratasys, USA • Materials : – ABS – Polycarbonate – PC-ABS – Elastomer Drawbacks : − Extrudable materials only − Layer thickness (0.2 mm mini) and wall thickness (0.3 mm mini) − Precision : +/- 0.15 mm 16 8 09/07/2013 BINDER JETTING ON A POWDER 1 7 STEREOLITHOGRAPHY (SLA) 1 8 9 09/07/2013 STEREOLITHOGRAPHY (SLA) Laser scanning point-bypoint solidification of resin. Alternative light source : Digital Light Processing or DLP® projectors to project voxel data (volumetric pixels). Each voxel dataset is made up of tiny voxels with dimensions as small as 16µm x 16 µm x 15 µm in X, Y and Z direction 1 9 Stereolithography 3D Systems Envisiontec Examples of models for investment (« waste wax ») casting Objet 2 0 10 09/07/2013 STEREOLITHOGRAHY • Materials : – light-sensitive epoxy resins . – UV-curable flexible or high-T°resins… • Advantages : + Surface aspect, precision (esp. DLP systems) + Well-known, mature technology + Large volume machines + … • Drawbacks : – Only light-sensitive resins – Supports necessary – Quite fragile parts, UV-sensitive – Uncontrolled shrinkage 21 LASER SINTERING Selective Laser Melting : equivalent of SLS for metal powders 2 2 11 09/07/2013 Classification of additive processes Materials to be transformed Principles of transformation Technologies Acronyms Laser or UV flashing SLA STL DLP Stereo lithography Printhead Polyjet 3D printing Binding Printhead 3DP Sintering / fusion Laser, IR flashing, or electron beam SLS SLM DMLS EBM SMS Laser Sintering /Melting Projection DMD Deposition Deposition FDM Photo- Photo sensitive resin polymerization Powder : polymeric, metal, ceramic, sand Polymer filament Liquid state « welding » Pictures Main groups La fabrication Rapide peut être la 1ère étape pour la fabrication par réplication : moule sable, ou pièce modèle. 23 2 3 Additive manufacturing technologies ❶ Basic principles ❷ 3D Printing ❸ @manufacturing 2 4 12 09/07/2013 PRODUCT DEVELOPMENT : CONTEXT AND STAKES Industrial targets • Reduction of marketing times • Decrease of costs • Quality control (and standards) Trends : • Evolution towards small / medium size series, mass customization, increased complexity • Product lifetime • Delocalization of large series manufacturing, of mouldmaking industry … • Need for flexibility and reactivity of production Important economical stakes 25 COMPARISON OF COSTS ⊕ of AM development : Independant on part complexity Fast No specific tooling BUT : Limited choice of materials Materials cost Production time … Cost/part as a function of production volume 13 09/07/2013 SLS : on the way to Laser sintering industrial production principle: • Powder preheating below melting T° • Spreading of powder layer • Scanning with CO2 laser (infra-red), • Particles fusion and « sintering » • Build tank going down by a layer thichness • Next layer… Advantages : • Self-supporting powder • Great freedom of shapes, Main current materials available : • Possible assembling and functional Polyamide 11 or 12 : plain, filled : glass beads, systems aluminium, carbon, and/or flame retardant Polystyrene PEEK (specific machine, 1 in Germany) Drawbacks : • Few commercial materials available • Anisotropy of parts. • Limited part size Main machine manufacturers : EOS GmbH, 3D Systems. Dimensions : 700 X 380 X 600 2 7 Application field : • Prototyping, direct part manufacturing, rapid manufacturing. Frittage Laser Polymère EOS – Systèmes d’aide à l’assemblage EOS – chambre à air pour hélicoptère EOS – Maquettage EOS – prothèse EOS – centrifugeuse 2 8 14 09/07/2013 DEVELOPMENT OF ADDITIVE MANUFACTURING FDM machines at the production facility of RedEye On Demand, a business unit of Stratasys in Eden Prairie, Minnesota ADDITIVE MANUFACTURING PROCESSES FOR POLYMERIC MATERIALS FORMING Part 2 : Selective sintering processes for polymer powders - Analysis of SLS physical mechanisms - Introducing SMS 15 09/07/2013 IDENTIFICATION OF THE KEY MATERIALS PARAMETERS Prior to sintering, 2 conditions are very important for the process: Powder flowability Powder bed density Main influent parameters ► Particle size ► Size distribution ► Sphericity DIFFERENT POWDER MORPHOLOGIES Duraform PA Innov PA 50µm 50µm ► InnovPA : Exceltec PA 2200 ► Duraform PA : 3D Systems ► PA2200 : EOS All of them need SiO2 as flowability agent (< 1 wt%) 50µm 16 09/07/2013 IDENTIFICATION OF THE KEY MATERIALS PARAMETERS Sintering of semi-crystalline polymers ► Warpage due to shinkage throughout the crystallization is a key issue Re-crystallization must be controlled Powder bed T° maintained in the processing window w : Tm - Tc Tc = 151°C Tf = 181°C Part warpage (« curling ») avoided Polyamide 12 mostly used thanks to very wide w range 3 3 MOST INFLUENT PROCESS PARAMETERS ► Process conditions of first order influence are : The heat provided to the powder during the whole fabrication cycle The energy provided to the polymer material by the laser 3 4 17 09/07/2013 Process parameters Thermal cycle Right feed heater Part heater 135°C 173°C Cylinder heater Piston heater Left feed heater 135°C 150°C ■ Different temperatures of preheating 3 5 Process parameters Energy Density ED : a single parameter Power supply by surface unit The energy supply depends on the: ■ Scan spacing (S) via laser beam superimposition ■ Laser beam celerity (v) Number of exposures Time of exposure ■ Laser radius (r) ■ Laser power (P) 3 6 18 09/07/2013 CHARACTERIZATION OF MICROSTRUCTURE 1- POROSITY ► By application of Archimedes’ principle on samples infiltrated with CH2I2 Calculation of open and closed porosities Closed porosity Open porosity filled by CH2I2 Evolution of the global porosity (vs. ED) : ■ Porosity decreases when ED increases ■ Porosity reaches a minimum value about 2% 3 7 ENHANCED CHARACTERIZATION OF POROUS MICROSTRUCTURE ► By 3D X-Ray tomography Analogy with medical scanner Succession of 2D sections of the sample After image analysis, 3D reconstruction of porosity distribution Computation of closed porosity fraction, information on size and spatial distribution of pores 3 8 19 09/07/2013 Example for Innov PA powder Characterization of porosity by Xray tomography Tomographic sections Position of the part in the build tank Position of the part during analysis 3 9 INFLUENCE OF ENERGY DENSITY ED ON POROSITY Example for Innov PA powder ►LOW ED : bad welding between layers Open porosity reaches core of parts ►Observation of the 2 types of porosity : open and closed 4 0 20 09/07/2013 INTERPRETATION OF PART ANISOTROPY InnovPA parts, ED = 0.024J/mm² ► Porosity is concentrated at the interface between successive layers ► This is mostly noticeable at low ED, but still present at high ED Mechanical properties are anisotropic 4 1 DENSIFICATION PARAMETERS During sintering 2 stages occur : Coalescence and melt densification ■ Evolution of the particles during coalescence : Frenkel’s model a0 a x With η : viscosity Γ : surface tension ■ Melt densification is due to diffusion/dissolution of gases from pores Final microstructure is governed by: Granular characteristics which impact powder bed density Melt viscosity Crystallization temperature (and build tank T°during proce ss) 4 2 21 09/07/2013 CHARACTERIZATION OF MICROSTRUCTURE – 2) CRYSTAL WEIGHT FRACTION AND RECRYSTALLIZED PHASE DSC shows the presence of both recrystallized and nascent fractions Recrystallised fraction (fr) can be calculated by a deconvolution method: Source: D. Jauffres et al, Polymer 48, 6375-6383, 2007 Recrystallized phase ∆HR Nascent phase ∆HN With ∆HR: recrystallized phase enthalpy of fusion ∆HN: nascent phase enthalpy XCN: nascent crystal weight fraction (50%) XCR: recrystallized phase crystal weight fraction (30%) Objective: measure the evolution of fr and Xc with ED 4 3 INFLUENCE OF THE ENERGY PROVIDED BY THE LASER ON PARTICLE MELTING AND CONSOLIDATION Evolution of fr with ED ► Strong increase of fr up to ≈ 2.5J/cm² then stabilizes ► Occurrence of nascent particles between successive layers ► From ED ≈ 2J/cm², no more nascent particles in the core of parts, but still present at the surface 4 4 22 09/07/2013 INFLUENCE OF THE PROCESSING WINDOW Comparison between InnovPA and DuraformPA Build tank T° = 150°C Crystallization T° measured by DSC at 10°C/min : Innov PA Tc = 151°C / Duraform PA Tc = 147°C Crystalline fraction measured by DSC: ► Xc when ED because more nascent polymer is melted Eρ 45 Comparison between InnovPA and DuraformPA Build tank T°= 150°C Crystallization T°measured by DSC at 10°C/min : Innov PA Tc = 151°C / Duraform PA Tc = 147°C Nascent powders ► Xc lower for Innov PA samples lower Tc for Duraform PA slower crystallization, larger crystalline ratio Injection molded parts 4 6 23 09/07/2013 CONCLUSION ON FORMATION OF POROUS AND CRYSTALLINE MICROSTRUCTURE ►Powder bed density (granulometry and morphology of powders) strong impact on porosity formation ►Time spent in molten state (also depends on T° of build tank) strong influence on porosity and on final crystalline microstructure Innov PA : Duraform PA/PA2200 : high ED low ED low ED Eρ < 2 J/cm² high ED Eρ > 2 J/cm² Porosity can be also influenced by viscosity (coalescence) 47 RELATIONS BETWEEN MECHANICAL PROPERTIES (TENSILE) AND MICROSTRUCTURE P2 P1 General trend : when ED ductility because Xc , But relations are more complex Elongation at break is one of the most critical features of sintered polymer parts 4 8 24 09/07/2013 CONCLUSION Material parameters ■ Melt viscosity Microstructure ■ Porosity ■ Powder size/morphology Pore size Mechanical properties ■ Tm ■ Fr ■ Eab ■ Stiffness ■ Tc Process parameters ■ Xc ■ Laser features (ED) ■ T° of build tank ? ■ T° of powder bed surface 49 SMS – Selective Mask Sintering by IR flashing powder spreading printing flashing repeat cycle Principles of sintering by IR flashing through a mask Patent owned by Sintermask GmbH, Parsberg, Principales différences avec SLS : Germany • Each section (slice) is sintered as a whole by IR flashing through a mask which is regenerated for each layer • Potentially faster than SLS • Size part less limited • Present technological issue : mask generation • Process still in development 5 0 25 09/07/2013 SMS-IR flashing : Lab-built prototype machine at INSA Manually operated, but automatization in project Can be equipped with thermocouples for T°monitoring during sintering 5 1 Temperature monitoring in lab-IR machine (here 3 thermocouples inserted) Comparison with numerical simulation 5 2 26 09/07/2013 Some features of polymer sintering processes A few orders of magnitude : Maximum build velocities : SLS : ~ 25 mm/h (small area) IR-SMS : 35 mm/h , 10 à 20 s / layer, 5s target Cooling time ~ fabrication time Nb of powder re-uses : ~ 7 times, mixed with « fresher » powder (e.g. 50% from feed tanks, 50% from build tank, or 75% used + 25% fresh) Layer thickness : ~ 100 µm Minimum wall thickness : ~ 300 – 500 µm Diameter of laser beam : 250 µm Material cost : 50 - 150 Euros/kg 53 SOME CONDITIONS FOR THE INDUSTRIAL DEVELOPMENT OF ADDITIVE MANUFACTURING - Reliability of the production : - Availability of adequate materials - Good control over the process - Good understanding of the physical phenomena, and of the relations between process parameters, material features and final part properties - Development of quality control - Development of standardization and qualification of AM systems and materials - Increase production speed - Improve powder re-usability … still much work to be done ! 5 4 27