Additive manufacturing

POST PROCESS:

1. MACHINE TOOLING: With A.M is possible to build a complicated shape but during the design is

need to be consider:

 Complex shape is difficult to post machining.

 Complex shape is difficult to clamping and fix the model in the machine, therefore the part need to

have some small bits that allow to fix the part in the machine.

2. SAND BLASTING: Is used to remove the powder particles that still attached on the surface “satellite

particles”. This process leads:

 Reduce the roughness

 Reduce fatigue failure (Fatigue is the bottleneck of A.M models)

3. SHOT PEENING: Is used to increase the fatigue life of the model because it generates a compressive

stress on the surface. Is more expensive than the sandblasting.

4. HOT ISOSTATIC PRESSING (H.I.P): Is used in the fields in which the failure is not acceptable. (ex:

medical, aerospace,..) Is used to removed the porosity and reduce the risk of failure.

BINDER JETTING

AM process in which a liquid glue is selectively deposited to join powder materials. The produced model is a

composite material in which the matrix is the glue and the fibers are the powder materials.

Powder material: Chalk, metal (steel) , Ceramic

Is the only metal that have less problem during the heat treatment by oxidation.

The machine uses a printer head that contain a several ejection nozzles to deposit polymeric binder

droplets (80 micrometer). Once a layer is printed, the powder is lowered and a new layer of powder is

spread on to it by recoater. (similar to inkjet printer of paper)

The process doesn’t require high energy (like a laser), is cheap and fast. The model has a poor mechanical

properties and so the only function is a visual representation ( helped by the possibility to have a different

color in the same model). The model can also be used for molds and cores in metal casting process.

The supports aren’t needed.

Accuracy in XY direction depends by a Dpi resolution.

For ceramic and metal powder, after the parts production, a full densification can be reached by Heat

Treatment. The binder is evaporates (DEBINDING) and the powder is sintered. During this process can occur

deformation and dimensional variation and so is suitable for bulky parts.

It is possible to improve surface quality and reach a full densification by infiltration material as COPPER OR

BRONZE (close a surface porosity).

Pro: Cons:

‐ Doesn’t require high energy ‐ Low dimension stability

‐ Deosn’t ivolve toxic material ‐ Suitable for visual model and

‐ Cheap and fast molds/cores for metal casting

‐ Model with different color

MATERIAL EXTRUSION (or FDM)

AM process in which the parts are created by extruding small filament of thermoplastic polymer that melt

in the nozzle and hardens immediately at the exit. The filament is selectively deposited by nozzle (moving in

XY direction) in order to create a layer. When a layer is completed, the extruder or building platform moves

along z direction by a layer thickness and new layer is deposited onto the previous one.

Usually there is a cross hatch between the direction in which the stripes are deposited

at each subsequent layer in order to reduce the anisotropy in XY plane. The mechanical

properties in Z direction are lower than other direction due to the superimposition

between subsequent layer. There is a low contact surface between different stipes that

reduce the cross section. The amount of voids depend by a nozzle size.

Dnozzle :

‐ % of Voids

‐ Building time 

‐ Layer thickness (it is a little smaller than nozzle diameter) D=0.4 Hmax=0.32

‐ Staircase effect

‐ Dimensional precision in XY directions

The market is divided in two class, machine for industrial purposes that produce a functional models and

machine for costumer usage that produce a visual model. nd

In the most advance machine there are 2 nozzles, the first deposits the build material and the 2 deposits

the support material. The support material can be removed by dissolution this leads:

‐ There aren’t mechanical stresses during support detach.

‐ The cavity support needs only a little hole to evacuate it.

Shell

Each slice is composed by: Infill (it possible to choose the Pattern and the percentage)

The support is needed for a surface overhanging of less than 45°.

There is an exception: BRIDGING allow to print a part without support. If a bridge is over

than 5 mm, support is needed.

>5mm <5mm

NEED SUPPORT DON’T NEED SUPPORT

The support pattern can be Lines, Grid, Tree‐like and the support can be removed by manually, chemical

dissolution, sacrificial tooling.

Materials:

‐ PLA (adopted for visual model)

‐ ABS (used for functional model) Carbon fiber composite:

‐ PC‐polycarbonate (the model is translucid) ‐ Long fiber thermoset ( low viscosity, is able

‐ PETG to wet easier the fiber )

‐ HT (high temp) ‐ Short fiberthermoplastic ( high viscosity )

‐ NYLON

‐ TPU 95A (adopted for flexible model)

‐ SPECIALS (composite material)

MATERIAL JETTING

MATERIAL JETTING

DROP ON DEMAND (wax) (polymer thermoset)

MATERIAL JETTING: AM process in which the printhead dispensing a photopolymer from a big number of

jets. As the droplets are deposited to the build platform, they are cured by a UV light.

Support are printed simultaneously during the build from a dissoluble material that is easily to remove

during the post processing. The support is always needed due to the low viscosity of thermoset polymer.

(there isn’t self‐support angle. Also, for drop on demand). The use of solvent for thermoset material is

easier than a thermoplastic (M.E) material because the thermoset isn’t affected by solvent.

Types of construction:

‐ Glossy models: All surfaces that aren’t in contact with support, they have a glossy appearance

(shiny)

‐ Mat models: All the surfaces will be opaque because the model is fully covered by support material.

Better precision in tolerances because the perimetral support avoid that the droplet increase its

width due the low viscosity. CONS:

PROS: ‐ Longer build time than M.E and B.J

‐ High accuracy but shorter than MULTIJET FUSION.

‐ 16‐30 micrometer layer thickness (due to the little layer thickness)

(The staircase is negligible)

Functional models

Application: Injection molding molds

The main difficult is the choose of the material because the supplier don’t give the formulation but only the

main properties. Some materials are designed to look like a thermoplastic materials, called SIMULATED

THERMOPLASTIC MATERIALS (ABS,..). It’s possible to mix a flexible and stiff material to get a middle

flexibility or put them separately in the same model.

DROP ON DEMAND: AM process in which is produced a wax model that the only function is to be used for

lost wax pattern for metal casting. As in the material jetting there are two different materials for the model

and for the support (soluble). The wax is melted before to pass through the hole. The machine structure is

the equal to M.J. The only difference is that when one layer is built, it is precisely milled to ensure planarity

and achieve the best accuracy in the Z direction (layer thickness=6 micrometers), compared to other AM

technique. ( building time increase)

This Solution allows to reduce initial cost and lead time for the casting process.

Applications: There is an only one machine on the

‐ Jewelry market (solidscape)

‐ Medic (dental)

‐ Precision industry VAT PHOTOPOLYMERIZATION

AM process in wich liquid photopolymer in a tank is selectively cured by light source. Once a layer is

completed the building platform moves along Z axis and a new layer is spreaded upon the previous due the

low viscosity. DIGITAL LIGHT PROJECTOR (DLP):

LASER (SLA): ‐ Shorter time

‐ Longer time ‐ Less precision in XY direction (it depends

‐ More precision in XY direction from screen DPI)

‐ Continuos stripes ‐ Discrete stripes (due to the pixel)

‐ The XY precision is independent by the ‐ The XY precision depends by the machine

machine size. size.

‐ A post scan with UV light is needed when

the infill is scanned very quickly

compared to the perimeter, in order to

reduce the building time. But in this way,

there is a risk of deformation. COMMON FEATURES:

‐ The supports are needed for overhang.

‐ The Z direction can be reversed

‐ Same material for both (thermoset poly, composite ceramic because ceramic has the same

density of monomer and so it has a uniform distribution in the vat)

‐ The viscosity is lower than mat jetting an so it possible to have a smaller layer thickness (0,5

mm).

‐ Best transparency compared to other AM process.

Application: This process produces parts that are used as master pattern for SILICONE MOLDING.

MULTI JET FUSION

Is a new AM technique so there are 2 equipment on the market that are still under development.

The machine uses the printhead with a millions of ejection nozzle to deposits the FUSING AGENT and the

DETAIL AGENT moving on one direction (X or Y axes). FUSING AGENT function as a light‐absorbing ink that

increases the Infrared Radiation Absorptance of the ink‐marked area to sinter the powder particles and join

to each other. The DETAIL AGENT function as marker of surface edges and can dyeing the model with black

color. Once the droplets are deposited an infrared light sweeps across the bed and sinter the ink‐marked

area. Once the layer is completed, the building platform is lowered by layer thickness and a new layer of

powder is dispensed upon the previous one. After the job is completed, the box is moved to the post

processing station (cooling/cleaning).

The supports aren’t required but become important for design stability issues. For example, a wall with

thickness below 0.6 mm will deform under its weight. (due the low stiffness E= 2 Gpa)

Pro:

‐ Very fast (10x faster than material extrusion)

‐ Great mechanical properties and isotropy

‐ High resolution (0.05mm)

‐ Loose powder is recyclable

Materials: (thermoplastic polymer)

‐ Polyamide 11 (PA11)

‐ Polyamide 12 (PA12)

‐ TPU+PA12 (new!!)

Surfaces finish:

‐ Non‐dyed (we obtain a grey surface) Resists daily handling

‐ Non‐dyed polished

‐ Dyeing with color touch finish (satin look, black)

‐ Dyeing with color resist finish (matte look, black)

Resists friction

Layer thickness= 80 micrometer

Max volume= 400*3 cm^3

Minimum clearance (assembly) =0.5mm

It is possible to create:

 Interlocking parts

 Assemblies

 Enclosed parts

 Hollow parts (needs holes)

DIRECT ENERGY DEPOSITATION

AM process in which focused source of heat is used to melt the materials as they are deposited.

COAXIAL POWDER STEAM

CONVERGING POWDER STEAM

The deposition head integrates laser optics, powder nozzles and inert gas tubing. It deposits melted

material on the surface that can be a new part or an existing part ont