LEC2/LEC3

pre-processig:

• Product-Design

• Tansfer to Slicer-Software (Conversion to Neutral File Format NFF)

• Build Job Definition (Slicer-Software)

  
  

In-processing

Post-Processing

Product-Design:

• CAD-Design (out of a mental Model, decoupled from limitations of traditional machining)

• 3D Data Capture (out of a phyical Model)

• Topology Optimazation

• Generative Design

• Reduction of :

  • weight

  • Reduction of material consumption

  • required build time

• without reducing mechanical properties

• Starts with block of material/ pre-designed part + boundary conditions

• Load simulation to identify distribution of force

• Automatic reduction of material to ensure homogenous flow of force and sufficient stiffness without exceeding maximum stesses

Reduces:

• time

• required skill

to design a part

detaches design from established geometries

• allows for a transfer of physical geometries in digital forms

• helps to replace/ multiply objects without digital source

• 3D surface scan of physical model to digitalize geometry:

  • Computed Tomography: Structured light scanner

  • 3D Laser scanning: Photogrammetry

• Deduction (Ableiten) of volumetric body from surface model

• Repair/ Modification of volumetric model to correct scan/ errors

• Machining Allowances:

  • Adding extra material thickness to functional areas during the CAD phase.

    • Provides enough stock for subtractive post-processing

• Volume reduction:

  • Minimizing the actual printed material volume to achieve cost and time savings.

  • Comparison:

    • subtractive manufacturing - aims to reduce cutting volume

    • AM: reducing build volume to shorten print time & save powder/filament.

• Process specific model preparation:

  • Adapting the digital 3D model to match the physical capabilities and limits of the specific printer hardware being used

  • Example:

    • aligning the CAD wall thickness with the actual nozzle or laser beam diameter

• post-processing phase of binder jetting: shrinkage occurs

• shrinkage depends on multiple influences (like gravity and particle size)

  • part scaling to compensate for shrinkage is difficult and must be anisometric.

1. Watertight Model:

   • all surfaces must be smoothly blended and trimmed with zero gaps/ holes.

2. Clear Volume Orientation:

   • Surface normals must be correctly oriented to identify the volume

   • at triangulation: no construction aids (layers, axes, hidden elements) should be used

3. Solid Volume Conversion:

   • Surface models must be converted into solid volumes before triangulation to give the geometry a physical wall thickness and mass.

• Neutral File Formats:

  • used to convert diverse CAD file formats into a single, standardized data format

  • ensures that the geometry can be read and processed by different slicing algorithms across various 3D printing systems.

  
  

• STL

• AMF

• 3MF

  
  

Approximation of the geometry by different sized plane triangles

occuring errors:

• holes/ gasps in mesh

• flipped normal

• intersecting/ overlapping triangles

number of triangles:

• parameter for surface quality

• curvature: neccesarry triangle number needs to increase

• processing time increases

STL:

• Standart in AM since 1987

• plain text file

• surfaces defined by list of coordinate points of corners of triangles + outward facing surface-normals

  
  

  Pros:

• simple to read, write + process

  
  

  Cons:

• no scale or color information

• no validation of duplicates (overlapping triangles, vertices)

• standardized file format specifically designed for AM by ASTM / ISO

• surfaces defined by vertices and their inside volumes

• plain text file / compressed file (zip)

Pros:

• Includes scale, color, texture, material information

• Allows curvature of triangles

• Includes constellation of multiple parts to each other

Cons:

• Not yet supported by CAD software or AM system manufactures

• 3D printing file format defined by industry consortium

• Zipped XML package

Pros:

• Includes information about the AM process (could include process parameters in the future)

• Significantly smaller than other 3D formats

• Includes color information and unit scale

Cons:

• many but not all CAD programms support a .3MF export yet

• Sllicing

• Placement & Orientation

• Support Gerneration

• Processparameter

• Path Generation

Bounding Box:

• orthogonally oriented minimum perimeter cuboid that can span the maximum extents of the points on the surface of a 3D part.

Machine bounding box:

• Surfaces parallel to machine coordinate system

Working envelope::

• The volume containing every tool accessible point.

• Shape and size depend on individual system

• neccessity and characteristic of support structure

• Geometric and dimensional accuracy

• Surface Quality

• Mechanical Properties (Anisotropy)

• Ensure static strength of overhangs or bridges during the build process

• Can improve heat dissipation to minimize thermal stresses/ distortion

  
  

  !! Critical for the overall costs, as it has a significant impact on post-processing

Support required:

• Powder Bed Fusion (PBF)

• Material Extrusion (MEX)

No support needed:

• Directed Energy Deposition (DED)

• Binder Jetting (BJT)

• Powder Bed Insulation: Loose powder has very poor thermal conductivity, failing to cool the part.

• Support Connectivity: Solid supports create a direct physical pathway that enables rapid heat dissipation down to the build plate.

• zero geometric support from surrounding material for bridges and overhangs

• Filled composite systems only achieve full structural strength after post-processing (e.g., thermal sintering)

  • filigree parts depend entirely on support structures to remain stable and avoid collapsing

• Chemically: Support is built from second solvable material

• mechanically: Support & Part out of same material

• Procedure:

  • The 3D geometry is sliced into flat, two-dimensional planes separated by a constant distance (= layer height).

• staircase effect :

  • visible, step-like surface roughness that appears on curved or slanted (slanted) sections of a 3D-printed part.

    
    

• process stability & quality

• build time

• Resolution (Stair-Stepping Effect)

• geometrical accuracy of features defined by build orientation:

  • functional surfaces should be placed parallel to the building platform

• based on minimal z-resolution defined by layer height

• smaller layer height

  • increased geometric accuracy

  • but, increased build time (more costs)

    • Adaptive Slicing (variable layer height)

Process parameter

• get influenced by:

  • Ambient (Umgebung) condition

  • Process

  • System

  • Material

  • Part

• are influencing:

  • Part quality

  • Machine Code

  • Mechanical Properties

  • Design limitations

  • Build time

• contours:

  • the boundaries defining the outer/inner perimeter

• infill area:

  • The solid interior of the part, located entirely inside its outer walls (contours)

• Different exposure strategies have influence of the heat input and distribution

• Beam Offset Compensation:

  • must be applied at the contours to compensate for the laser spot diameter

• The laser path is physically guided across the powder bed by a laser galvo scan head

• only Path of contour (no size restriction, fast build rate)

• wide variety of kinematic actuators, including industrial robots, rotary tables, and linear actuators

• Kinematic-Dependent Machine Code:

  • path generation workflow & resulting machine code depend completely on the specific actuator combination

    
    

• Inkjet Analogy:

  • print head operates like a standard 2D inkjet paper printer

  • the entire build job is handled like printing a multi-page PDF ("page" = single sliced layer)

• Negligible Support Structures:

  • need for printed support structures is negligible

    • process involves zero heat input (eliminating thermal stresses)

    • part is continuously cradled by the surrounding powder bed

• Shrinkage Compensation:

  • Parts must be scaled up during data preparation and path generation to compensate for the significant volumetric shrinkage that occurs during the post-print sintering process.

• contours:

  • the boundaries defining the outer/inner perimeter

• infill area:

  • The solid interior of the part, located entirely inside its outer walls (contours)

• Different path strategies for Infill/ contours

• Visibility of a technology over Time

• Technology trigger

• peak of inflated expectations

• Trough of disillusionment

• slope of enlightenment

• Plateau of Productivity

• Mechanical Crushing

• Atomization

• Eloctrylsis

• Chemical reaction

• Equipment & Setup:

  • Ball Mill / Planetary Ball Mill:

    Utilizes a rotating chamber to reduce particle size.

  • Grinding Balls:

    out of a material with higher hardness than the target feedstock

    
    

    Core Size-Reduction Mechanisms:

  • Impact:

    • Direct collision between grinding balls and powder particles.

  • Abrasion:

    • resulting from particle-to-particle friction.

  • Shearing:

    • High energy input forces layers of material to decrease particle size

  • Compression:

    • Mechanical pressing of particles until they break.

• Gas Jet Atomization

• Water Jet Atomization

• Plasma automised wire

• Ultrasonic powder Atomization

• melt flows through nozzle

• gas/ water Jet hits outflowing melt with high velocity

• Atomization of melt flow in to small droplets

• used Gas: Ar, He, N2, air

• size distribution: 1 – 500 µm

• melt flows through nozzle

• melt flow reaches Ladel (metal plate with ultrasonic vibrations)

• vibration automises the melt into small droplets

• metal wire is uncoiled and fed into the system

• High-temperature plasma torches melt the wire tip and blast it into tiny droplets

• Droplets fall through a water-cooled jacket, rapidly solidifying into spheres

  -> spherical powder

Water Jet:

• irregular particle shape only

• for inert materials (=chemical unreactive) only

Gas Jet:

• spherical powder particles

• inert gas/ atmosphere possible

• satellite formation

Ultrasonic:

• spherical powder particles

• Minimal satellite formation

Agglomeration:

clustering or fusing together of individual powder particles to form a larger, irregular mass.

Satellite: Small particles attached to a bigger one

Mechanical Cruching (milling):

• production volume: high

• batch capacity (Chargenkapazität): continuous

• Paticle size: 5 µm – 10 mm

• Particle shape: irregular, sharp edge particles

• Purity: possibility of impurities (grinding ball)

Atomization:

• production volume: high

• batch capacity (Chargenkapazität): up to 3000kg

• Paticle size: 1- 500 µm

• Particle shape: spherical

• Purity: high

Electrolysis:

• production volume: small

• Paticle size: nano scale powders (size < 1µm)

• Particle shape: irregular, dendritic particles

• Purity: very high

Chemical reactions:

• production volume: small

• Paticle size: nano scale powders (size < 1µm)

• Particle shape/ Purity: irregular, clotted (verklumpte) particles

• delivered in high quantities

• particles are seperated (small particles down, big particles top)

  • Rotary Riffler

  • All-layer Collector

• morphology

• particle size distribution

• flowability

• density

• chemical composition

Measuring particle dimensions:

• different measurement methods:

  • diemensions relevant for sieving

  • Equivalent spherical diameter: volume -> circle ->diameter

  • sphere with equivalent sedimentation velocity (Sinkgeschwindigkeit)

• frequency over particle size: normal distribution

• cummulative frequency up to 100%

• D90 = 90% of the particles are smaller then this size

• D50 = median

• Apparent Density:

  • Powder flows freely through a standard funnel (Trichter) into a cup until it overflows.

  • Carefully scrape the excess powder flat off the top without vibrating the cup.

  • Measure the mass of the remaining powder inside the cup.

  • Density =powder mass / cup volume

• Tap Density:

  • Pour a measured mass of powder into a graduated cylinder (Messzylinder)

  • mechanically bounce (tapping machine) the cylinder a set number of times

  • Stop tapping once the powder volume stops shrinking

  • density = powder mass / tapped volume

• Apparent Density < Tap Density

determined by:

• particle size

• powder morphology

methods to measure:

• Flowmeters: measures time for powder to flow through a stadart funnel (Trichter)

  • Only qualitative values

  • Fails with fine powders because they agglomerate and clog the funnel.

• Powder Rheometer:

  • Best simulates actual AM conditions (like a recoater blade spreading powder).

  • Includes a pre-processing (conditioning) step to guarantee the same test conditions every time.

  • Requires only small amounts of powder to run the test.

• Dynamic Avalanching Behavior

  • Rotates powder in a glass disc and measures the optical angle/frequency of collapses (avalanches).

• Extrusion molding:

  • Raw molten metal is cast (gegossen) into a solid cylinder called an ingot.

• Forging:

  • Mechanical force hammers or presses the hot ingot into a rough rod shape (grobe Stabform)

• Rollign:

  • passes through successive rotating rollers to drastically reduce its thickness

• Coil (Spule):

  • thinned metal is wound up into a large coil for easier handling

• Wire Drawing:

  • coiled metal is pulled through progressively smaller dies (Matrizen( Zieheinheit) to reach its final, thin wire diameter

• Annealing:

  • intermediate heat treatment (annealing) during drawing to relieve internal stresses and prevent it from breaking.

• Final Heat Treatment:

  • lock in the required mechanical properties before being used in AM

• Wire Roll (Change Thickness)

• Wire Coil (Storage)

• Rod (Stange)

• solid wire

• cored wire (other materials inside)

drawability = Ziehbarkeit

• Porosity

• Lack of fusion

• Delamination

• Melt ball formation:

  • low laser energy/ high speed forces the molten metal track to snap into isolated spheres instead of a solid line due to surface tension

• Cracks caused by tension

  • choose better scanning strategy for better thermal management

• Lack of fusion porosity:

  • low energy density

• Keyhole Porosity

• Gas Porosity:

  • caused by hydrogen on surface of the powder

  • dissolved in melting