Schemi riassuntivi Additive Mnufacturing

Materials: wax-like building and soluble support

Machines: only by Solidscape. Resolution: 5000x5000dpi; Accuracy: ±25µm (X,Y,Z); Layer thickness: 6,35-76µm.

Lost-wax casting: 3D modelDOD printingbuilding a mold around the modelmelting the waxmolten metal.

Applications: small lead time (to start production) (2/3 instead of 7 weeks); customization is never a problem for AM.

Jewelry manufacturing, industrial components, medical applications (dental).

Binder Jetting: liquid bonding agent selectively deposited to join powder material (colored bindercolored part).

Liquid binderinkjet printhead moves in X,Ybuild platform moves in Zroller spread new powder

Printer head contains several ejection nozzles do deposit 80µm droplets that form spherical agglomerates with powder.

Materials: Powders: chalk, metal powders (stainless steel, Inconel, iron-chrome-aluminum, cobalt-chrome), ceramic

powders (alumina, silica, titanium dioxide,…). Binders: furan, phenolic, silicate, aqueous-based (for metals), polymer.

Machines specifications: low energy requirements, safety/ease materialsproduction of large partslarge building

volume up to 250x217x186mm with 2700x1000x1700mm machine.

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Typical layer thickness 0.2-0.5mm.

Post-processing: remove powderinfiltrate the part to increase bond strength.

For metal or ceramic powders: green partthermal treatment (remove binder)sinteringfully densification.

PROs and CONs: low energy required, not involve toxic materials, inexpensive and fast, best technique for colored

models. Low dimension stability in metals (sintering), preferred for models and molds instead of final parts.

Applications: models, sand casting molds and cores, rapid casting (breaking mold after production).

operating principle, materials, machines specifications, post-processing, PROs, applications

6 – Powder Bed Fusion

Classification: SLS (plastic), SLM/DMLS (metals), EBM (metals), MJF (plastic), Metal Jet

Basic principle: laserscanner systempowder meltinggas flowplatform loweredre-coater passpowder

recyclingdetatching part from platformheat treatmentsurface finishing

Laser VS Electron Beam: 50-1000W vs 3000W; shielding gas vs vacuum; large vs small building volume; high vs less

residual stresses; wide vs limited material choice.

Laser and powder interaction: laser diameter 50µm Gaussian intensity distributionmelt pool diameter 100µm

Transverse Electromagnetic Mode (TEM ): m and n, number of minima in the cross section of the beam in x and y

mn

directions; rectangular or circular TEM distributions.

Process parameters: laser power (P), scan speed (v), layer thickness (δ), hatch distance (h) density (E )[J/mm ]

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energy v

Requesting them from the machine manufacturer or obtain them through Design Of Experiment right amount of

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specific energy to melt the powder (P isn’t the real power that melt the powder because of reflectivity of the platform).

Different between the core (chessboard or stripe (better for accuracy and shrinkage)) and the contours (single passes).

Supports: overhang angle: stainless steel 30°, titanium 20-30°, alluminum 45°, cobalt chrome 30°, polymers 0°.

Types: blocks, lines and cones (most common) different dissipation of heat and shrinkage contrast.

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Requirements: do not break, dissipate heat, easy to remove, not waste powder.

Areas that need supports: overhangs, islands, junctions, overheated areas.

Orientation: bigger areas must be lower than smaller areas, surfaces that need good finish: upskin, avoid islands

Materials: polymers: polyamide 12, TPE-A, polystyrene, PEEK; metals: maraging steel, stainless steel, nickel alloys,

cobalt chrome, titanium, alluminum, bronze, precious metals alloys.

Applications: aerospace, automotive, medical, tool and die, molds, consumer, remanufacture and repair

Multi Jet Fusion: binder and heat source used to melt powder (polymers only) (no need of supports) (similar SLS, BJ, MJ,

but 10 times faster).

Configuration (HP market): printer (print head, recoater, powder, platform), post-process module.

Voxel principle: sort of pixel with volume, contains volumetric information for desired properties.

Workflow: fusing agent (melting)detailing agent (no melting)energypowder removecooling (1h for 1h building)

Features: total time of single layer fixed to 7-8 s (independent from area of material consolidated) total building time

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only depends on the Z height.

Benefits: high productivity, high and isotropic mechanical characteristics, high detail resolution, low roughness,

completely recyclable unused powder, possibility to have different characteristics in different areas, no supports.

Material: only PolyAmide12: good elasticity and resistance, wide temperature range, chemical and light resistant.

Finishing: no dye, no dyeing+polishing, dye with color touch finish, dye with color resist finish

Printing constraints: layer thickness 80µm±0.3%, maximum size 370x274x380mm, minimum thickness for walls 0.6mm.

Design constraints: elastic modulus 2GPasupports on long and thin walls, different minimum wall thickness;

minimum clearance 0.5mm (excess material dicharge).

Metal Jet (not yet commercially available)(HP similar MJF): replicates products obtained by Metal Injection Molding.

Same operating principle of MJF + post-treatments.

Workflow: with constant energy: spread powder (bidirectional)print agent(water-based with polymer)evaporation

(liquid part of binder), decakingsintering (polymer decomposes)(high density)coolingfinishing

Features: parts can be freely arranged on several levels, no build platform required, resolution 1200x1200dpi in a layer

thick 50-100µm, isotropic properties, high reusability of powder, part density >93%.

MIM VS Metal Jet: raw metal in 93% vs 99% in powder, long vs short debinding process (wax), higher vs lower weight

fraction of polymer. Both have high shrinkage in sintering, 20%.

7 – Characterization

Common metal powders: stainless steel, aluminium alloys (AlSi10Mg), titanium alloy (Ti6Al4V), maraging steel, nickel

alloys, cobalt-chrome alloys.

Applications: alluminium functional prototypes in motorsport and aerospace, titanium prosthesis (strenght/weight

ratio, corrosion resistance, bioadhesion), maraging steel molds, tooling (machinable, hardenable, thermal conductivity),

nickel alloys functional prototypes in motorsport and aerospace (heat-resistant, high strenght, corrosion resistance,

buy-to-fly ratio), cobalt-chrome prosthesis and medical appl., aerospace, motorsport (high strenght, temperature,

corrosion resistance).

Powder characterization: size distribution and shape influence physical properties of partspowder characterization

always before parts production.

ASTM 3049-14: scope: characterization for BJ, DED, PBF. Significance and use: necessary for components with known

and predictable properties.

Powder specs: spherical shape (flowability), particle size 50-150µm (layer thickness), particle size distribution,

chemical composition, gas content.

Powder manufacturers have less cost powder and large material choice, but machine manufacturers sell powder which

are tested on their specific machines.

Powder production: ingots of alloymeltingatomisation (plasma, gas, water)post processvalidation.

Only plasma or gas atomisation is usable in PBF because of the form of particles (only spherical for flowability).

Characteristics: water atomisation: 0-500µm, irregular morpology. Gas atomisation: 0-500µm, wide range of alloys (even

reactive), high productivity, spherical shape. Plasma atomization: 0-200µm, extremely spherical, high costs, feedstock

wire or powder form (not ingot).

Powder grain size: it affects flow rate, apparent density, energy to melt, sourface roughness. With a certain size, more

energy is needed to achive high density; giving a certain energy, smallest patricles achive higher density.

Characterization instruments: sieves (setacci), X-Ray Diffraction (dimension of crystalline phases), (SEM) Scanning

Electron Microscopy (searching agglomerates), flowability test (ASTM B213 or B964 (diffeerent geometries): flow rate)

Ti6Al4V: FeedStock: determined size distribution, shape, density and flowability; shall be free from impurities, with

adequate chemical composition; powder blends (mixing) are allowed. All characteristics have to be documented with

selling. Used powder is allowed, recording the proportion of virgin powder; powder is classified by the number of times

recycled powder have been used (class A,B,C,D,E)(no limits to recycle); chemical composition shall be analyzed

regularly for competitivity of the parts produced. Powder shall be sieved removing agglomerates. S

Recycle: higher the number of recycles, higher the oxygen and nitrogen, higher the particel size, lower the flowability

(there isn’t almost a limit of recycles); Average Usage Time (AUT) can be calculated, representing the processing time.

Part characterization: static tensile testing, fatigue testing, hardness testing on speciments produced with the parts,

deriving Young’s modulus, yield strength, Ultimate Tensile Strenght, elongation at break.

8 – Electron Beam Powder Bed Fusion

Machine = elecron gun + processing chamber

Electron beam: cathode emits electrons (crystal or filament heated)accelerated by anodic potential (40% speed of

light)magnetic lenses focus and deflect the beamprocessing chamber almost at vacuum (He flow)

The process: heating start plateeach layer is preheated (high speed defocused)meltingpost-heating

phaseplate lowered…job cools down in He flowdecaking

Preheating: forming strong connections between powder particlesno smoke phenomenon; make uniform

temperaturelow thermal gradientslow residual stresses (preheating 15000mm/s; melting 1000mm/s)

Features: metallic powder, preheated bed, under vacuum, hot process.

Advantages: excellent material quality, low residual stresses, low waste material.

Disadvantages: low cooling rate, low dimensional accuracy, low surface finishing.

Process parameters: layer thickness 0.05-0.2mm, up to 0.4mm; scanning strategy; line offset; scan speed; beam

current; focus offset.

Scanning strategy: Preheating one: full scanning of the bedPreheating two: preheating an offset of the area to melt

(60-70% of melting point to reduce T gradients)Melting: contour and infillPostheating: layer cooled down or further

heated (bigger areahigher energyhigher temperaturecool down; aim: T constant during the building) (process

parameters like preheating phase)

Melting strategy: Contours: MultiBeam (one beam, multiple spots); Infill: continuous (snake).

Line offset: menage good efficency; need to be a compromise (only melt the necessary).

Scan speed: the lower, the thicker melt pool.

Beam current: control the beam power (constant voltage) and the spot diameter.

Focus offset: additional current provided by electromagnetic lenses, translating focal plane, adjusting beam diameter.

EBM vs L-PBF: Powde