LEC2

Preprocessing:

• Data processing (CAD, CAM)

• preparing Support structures

• Arranging the part in the building space

• Generating the layer data (slicing)

• Hardware related system preparation

Inprocessing:

• Layer-On-Layer build process

• Process Monitoring

Postprocessing:

• Depowdering

• Removing support structures

• steps to produced whished part quality

• Product design

• Transfer to slicer software

• Build job definition

1. Starts with block of material or pre-designed part and boundary conditions

2. Load simulation to identify the distribution of force

3. Removes material automatically to create a light part with high stiffness, smooth force flow, and no stress peaks.

Reduction of weight, material consumption, build time without reducing mechanical properties

• Starts with available room and boundary conditions

• Iterative growth of material until stresses and stiffness reach an desirable value

reduced time to design a part

detaches design from established geometries

1. Scanning a real object to turn it into a 3D digital Surface Model

2. Convert the surface model into a solid 3D volumetric mode

3. Repair scan errors and modify the model

transfer physical geometries into digital form

helps to replace/ multiply/ repair objects

• Structured Light Scanner (Computed Tomography)

• Photogrammetry (3D Laser Scanning)

• Machining Allowances (Aufmaße):

  • Extra material added to functional surfaces for post-processing (milling/grinding)

• Volume Reduction:

  • keep the part as small & hollow as possible

    -> faster print, less material, lower cost

• Process specific model preparation:

  • Even with high design freedom, CAD models must be adapted to the specific AM process limits (minimum wall thickness = nozzle diameter)

• All faces must be seamlessly trimmed and joined with no open gaps

• all surface faces must point outward

• Turn it into a solid body before exporting to STL.

reason:

• every CAD software works with its own CAD file format

• every machine and slicer has its own algorithm

  defintion:

• Interface between CAD Software and Slicer

• System and Programm independent interface

• Standard Triangulation Language (STL):

  • current standard due to release in 1987

  • 3D surface with planar triangles, which are build out of corner cordinates and normal vectors

  • Stored as plain text (ASCII)/ binary file

• Additive Manufacturing File Format (AMF)

  • standardized file format spefically design for AM by ASTM/ ISO

  • Uses curved triangles (curved mesh) to define surfaces and solid volumes.

  • XML based (plain text or zipped)

• 3D Manufacturing File Format (3MF)

  • 3D Printing file format defined by industry consortium

  • not all CAD Software support it yet

  • Still in development

  • XML based: zipped

  
  

• simple to read, write and process

• Missing scale/units and color information

• Does not validate mesh errors

• Includes scale/units, colors, materials, and author/software details

• can store multiple separate 3D objects in a single file instead of needing individual STL files for every piece

• rarely supported by CAD or printer software.

• Stores AM job settings

• Small file size due to efficient ZIP compression

• Includes units, colors, author info & license terms

• Approximates 3D CAD geometry using flat (planar) triangles

• Higher surface curvature requires more triangles

Golden Rule: Use as many triangles as necessary, but as few as possible

Common Mesh Errors:

• Holes / gaps

• Flipped normals

• Intersecting / overlapping triangles

Smallest orthogonal box/cuboid that fully encloses a 3D part

Surfaces parallel to machine coordinate system

The total 3D space/volume that the toolhead (laser, nozzle, extruder) can physically reach.

• Necessity and characteristic of support structures

• geometric accuracy

• surface quality

• mechanical properties (anisotropy)

• Ensures static strength for overhangs and bridges during the printing process

• Improves heat dissipation to reduce thermal stresses and distortion

• Significantly impacts total costs due to added material usage and required post-processing

• Material Extrusion (MEX):

  • create stable free standing structure

• Powder Bed Fusion (PBF):

  • avoiding heat dissipation/ heat accumulation

• chemically : Support is built from second solvable material

• mechanically: Support is built from the same material

1. 3D Geometry sliced into planes with same layer height

2. Defines exact laser/nozzle movements, hatch patterns, and contours for every layer

Decomposition of the component into individual layers

• process stability & quality

• build time

• Resoltuion (Stair-stepping effect)

• based on minimal z-resolution resulting from layer height

Rules:

• Functional surfaces should be parallel to the building platform

• Adaptiv slicing with variable layer height

  • increasing building time vs increasing accuracy

  
  

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• many slicer with different characteristics:

  • ability to create machine control code: Simplify3D

  • STL-Editor for manipulation of STL parts: Netfabb

• chosen individual parameter-set for every build job

• Infill: The filled solid area inside the part's shell (contour).

• Contour: The outer edges defining the part's shape.

• Beam Offset (b): Shifting the laser path slightly inward (by half the beam's width) so the final part doesn't turn out too big.

• Hatch Distance (h < 2b): The gap between side-by-side infill lines. It must be smaller than the beam's width (2b) so the lines overlap and leave no holes inside.

• Material allowance:

  • part printed to big so it can be milled/machined down to the exact final shape

• Moves using robots, rotating tables, linear actuators

• print paths depend directly on which combination of robots or moving parts are used

• allows alternative path planning strategies

  + no size restriction

  +fast build rate

  
  

  
  

  
  

• Works like a normal 2D paper printer spraying liquid binder (glue) onto powder

• no laser heat + surrounding powder = no support structures

• part must be printed slightly larger to make up for shrinking during later heating/sintering steps

• nozzle traces the outer and inner edges to form smooth walls.

• different path strategies for contour and infill