Design for Additive Manufacturing (DfAM) DfAM - A generic term used to describe rules and parameters for a part design to be produced with an AM process DfAM - is the practice of designing products to reduce or minimize manufacturing and assembly difficulties and costs, DfAM aims To take advantages of the unique AM technologies capabilities to design and optimize a product/component, To utilize the characteristics of AM methods to improve the product/component functions according to the capability of the selected AM process. In doing so, the designers should tailor their designs to maximize the advantages of AM methods, such as complex geometries and lightweight Design Aspect and Design Consideration in AM Design aspect Any particular feature which can be quantified at the design phase. Includes; Geometric features of the part’s shape (overhangs, bores, channels, etc.) Part’s programming parameters (layer thickness, orientation, etc.). Design consideration The result on the manufactured part Specific properties of the process and quantified with certain key performance indicators. These includes; surface roughness, accuracy, build time, etc. Design Aspect and Design Consideration in AM With conventional manufacturing processes, these aspects are mostly a concern for the production engineer rather than for the designer; But, the significance of these aspects is high for the outcome in AM technologies.

1. BAHIR DAR UNIVERSITY
BAHIR DAR INSTITUTE OF TECHNOLOGY (BiT)
FACULTY OF MECHANICAL AND INDUSTRIAL
ENGINEERING
Rapid Prototyping & Reverse Engineering
[MEng6123]
Design for Additive Manufacturing (DfAM)

2. Design for Additive Manufacturing (DfAM)
• DfAM - A generic term used to describe rules and parameters for a part design to
be produced with an AM process
• DfAM - is the practice of designing products to reduce or minimize manufacturing
and assembly difficulties and costs,
• DfAM aims
• To take advantages of the unique AM technologies capabilities to design and
optimize a product/component,
• To utilize the characteristics of AM methods to improve the product/component
functions according to the capability of the selected AM process.
• In doing so, the designers should tailor their designs to maximize the advantages of
AM methods, such as complex geometries and lightweight

3. EN-MME/ Th. Sahner 3
Additive Manufacturing
Short introduction to the technology
“SEE THE DIFFERENCE IN THE CONCEPTION OF THE PART”
Conventionally designed and produced cast steel
nacelle hinge bracket for an Airbus A320 (top)
and optimised titanium version of the nacelle
hinge bracket made by additive manufacturing
technology.
• Commercial airplanes can have up to several hundred seat belt buckles.
• A standard buckle weight is around 155g in St. and 120g in Al.
• With AM the weight was reduced to 68 g in Ti.
• Saving over the lifetime of an A380:
• Fuel: 3.300.000 l
• CO2 emission: 0,74Mt
Design for Additive Manufacturing (DfAM)
This can be easily achieved with AM

4. Design Aspect and Design Consideration in AM
Design aspect
• Any particular feature which can be quantified at the design phase.
• Includes;
• Geometric features of the part’s shape (overhangs, bores, channels, etc.)
• Part’s programming parameters (layer thickness, orientation, etc.).
Design consideration
• The result on the manufactured part
• Specific properties of the process and quantified with certain key
performance indicators.
• These includes; surface roughness, accuracy, build time, etc.

5. Design Aspect and Design Consideration in AM
• With conventional manufacturing
processes, these aspects are
mostly a concern for the
production engineer rather than
for the designer;
• But, the significance of these
aspects is high for the outcome
in AM technologies.

6. Design Aspects
• The design aspects of the AM process, are organized in two main
categories: part’s geometric features and process parameters.
• Geometric Features
• Overhangs
• Bores & channels
• Bridging
• Minimum wall thickness
• Minimum feature size
• supports
• Process Parameters
• Layer thickness
• Build orientation

7. Design Aspects
Geometric Features
• Similar to conventional manufacturing, there are restrictions regarding
the geometries that can be built.
• The layer-by-layer principle followed by AM machines has its limitations
since each layer must be built directly above the previous one.
• That is, not every geometry is possible as each geometrical feature must
obey to a certain geometrical continuity.
• Once this geometric continuity is overlooked in the design, the resulting
part will suffer in its integrity (e.g., deformation, porous mass, reduced
density).
THINK ADDITIVELY - well-deployed DfAM requires not only skill but a new
mindset. Again, it’s really flipping from subtractive manufacturing to additive
manufacturing.

8. Design Aspects
Geometric Features
Overhangs
• Overhanging geometry is any geometry whose orientation is not
parallel to the build vector.BuildVector

9. Design Aspects
Geometric Features
Overhangs
• The magnitude of this parallel shift sets the limit for the maximum
overhang length and the maximum slope angle.
• The horizontal distance an AM machine can build without supports is
limited and if exceeded, the whole build could fail.
• The limit of an overhang length is affected by numerous factors and
the nature of the AM technology. These includes; the AM process, the
material used, and even the actual machine used itself.
BuildVector

10. Design Aspects
Geometric Features
Overhangs
• When part specifications call for a greater overhang, the decision to be made is
whether to modify the part’s geometry or to add supporting structures.
 To replace horizontal overhangs with angled ones.
 In case that an angled overhang adaption is not feasible, due to the
specifications and the geometry of the part, a support structure needs to be
used.

11. Design Aspects
Geometric Features
Overhangs
• When part specifications call for a greater overhang, the decision to be made is
whether to modify the part’s geometry or to add supporting structures.
Topology optimized cantilever beam successfully built with support (left) and
redesigned to be self-supporting (right). Arrows indicate where build failures
occur if no support strategy is implemented.

12. Design Aspects
Geometric Features
Overhangs
Overhang’s decision-making schematic

13. Design Aspects
Geometric Features
Angled Overhangs
• Angled overhangs is also a geometrical
limiting factor to most AM technologies.
• Some AM technologies can produce angled
overhangs of certain gradient where others
cannot
• For extrusion AM technologies, extreme
angled overhangs cannot be created as
material cannot be deposited in midair
• For powder bed fusion AM technologies, the
powder surrounding the part acts as a
support and thus, steeper angled overhangs
can be realized.
BuildVector

14. Design Aspects
Geometric Features
Angled Overhangs
• But, there is a drawback regarding surface roughness as the surrounding
powder is sintered unevenly on the downward facing areas of the part.

15. Design Aspects
Geometric Features
Bridging
• Similar to overhangs, a bridge is a horizontal geometry between two or
more non-horizontal features.
• Any surface in the part geometry that is facing down between two or
more features.
• In designing AM components, the designer must take into consideration
the maximum length that the machine can bridge. If this length
exceeded, the part will not be successfully manufactured

16. Design Aspects
Geometric Features
Bores and channels
• Manufacturing parts with internal geometries is a major benefit and
desirable feature for AM technologies.
• AM enables profound geometrical flexibility allowing the creation of
parts with internal concave channels
• This makes AM preferable for;
• Achieving great heat convention capabilities or optimum fluid flow
• Structural reinforcement
• Lattice structures

17. Design Aspects
Geometric Features
Bores and channels
• To properly implement these advantageous
features in the AM part design, compliance with
the AM design aspect is mandatory.
• Bores and channels are subject of the
overhanging geometries, acting as partially
overhanging cavities
Design Strategies
• Use diamonds and teardrop shapes for holes
normal to build direction
• If it does not have to be round will drastically
improve quality
• Removes supports & eliminate hole sagging
• If it is not possible to use diamonds and
teardrop shapes --- Use support structure
Teardrop and
diamond holes do
not need supports
Interior supports
needed for large ho

18. Design Aspects
Geometric Features
Hole orientation, in FDM
• Support for holes is best avoided by changing the print orientation.
• Removal of support in horizontal axis holes can often be difficult, but by
rotating the build direction 90 degrees, the need for support is eliminated.
• For components with multiple holes in different directions, prioritize blind
holes, then holes with the smallest to largest diameter
Re-orientation of horizontal axis holes can eliminate the need for support

19. Design Aspects
Geometric Features
Lateral Holes
Design Strategies
• Use diamonds and teardrop shapes for holes normal to build direction
• If it does not have to be round will drastically improve quality
• Removes supports & eliminate hole sagging
• If it is not possible to use diamonds and teardrop shapes --- Use support
structure

20. Design Aspects
Geometric Features
Vertical axis holes, in FDM
• The amount of undersize will depend on the
printer, the slicing software, the size of the
hole, and the material.
• Often, the reduction in diameter of vertical
axis holes is accounted for in the slicing
program, but accuracy can vary and several
test prints may be needed to achieve the
desired accuracy.
• If a high level of accuracy is required,
drilling the hole after printing may be
required.
Key design consideration:
If the diameter of your vertical axis hole is critical, printing it undersized and then
drilling the hole to the correct diameter is recommended.

21. Design Aspects
Geometric Features
Wall thickness
• There is a minimum wall thickness that is feasible to be manufactured
for each AM process.
• This is due to the building threshold determined by the fundamental
unit of the AM machine
• Diameter of laser beam,
• Flow focal point, or nozzle
• The fact that the machine needs to make multiple passes to build a
sufficient and solid feature.
• Another accountable parameter for thin walls is the height-to-
thickness ratio. Oblong wall structures tend to collapse.

22. Design Aspects
Geometric Features
Wall thickness
• Avoid thin walls/small isolated features
• See process/machine notes on possible minimum wall thickness

23. Design Aspects
Geometric Features
Splitting up your model
• What if you have a part that is too big to print?
• Simply just segment the parts by cutting the part into whatever
sections will fit in the printer and then bond them together.
• Dovetail joints can be used to have strongest cut and joint.
• There are benefits of segmenting parts that do fit entirely in the
printer.
• If a couple of portions of the part were segmented away and printed
separately significant time and material savings can be had

24. Design Aspects
Geometric Features
Splitting up your model
• Reduce its complexity, saving on cost and time.
• Overhangs that require a large amount of support may be removed
• The sections can be glued together once the print has been completed.

25. Design Aspects
Geometric Features
Add hardware/Inserts
• There are many different types of hardware that can be added.
• For example, if you have hot or abrasive issues with parts you can add
bushings to those particular areas that are having contact issues.
Example
Conformal cooling channels in an injection molding die. The cooling tubes were inserted
into the substrate mold (left), the tubes were ‘buried’ and the die was completed using a
laser-aided metal-based AM process (center), and the final tool was post-machined
(right). Adapted from

26. Design Aspects
Geometric Features
Add hardware/Inserts
Threads
• Better ways of thread manufacturing is to go with
• heated inserts
• Mid-print insert
• In this way we can have metal threads in our 3D printed part and it
will be great for long-term use.
• Only print large threads

27. Design Aspects
Geometric Features
Add hardware/Inserts
Threads

28. Design Aspects
Process Parameters
• Process parameters are selected at the slicing phase of the AM
process.
• They are highly interconnected with the AM technology and the
individual machine.
• The proper AM design considers the build orientation and the layer
thickness.

29. Design Aspects
Process Parameters
Layer Thickness
• Layer thickness is a factor that affects both the quality of the print
and the build time needed to complete the part.
• With smaller layer thickness,
• a more detailed part is produced,
• the staircase effect is minimized.
• potential voids and gaps are eliminated,
• the CAD file is being sliced with more precision and the geometry accuracy
is maintained.
• On the counterpart, with thicker layers, the printing time is reduced
• Regarding the staircase effect, another factor that is causing it is the
slope angle. As the angle increases, the stair size is proportionally
increasing
• A proposed solution to this matter is adaptive slicing.

30. Design Aspects
Process Parameters: Layer Thickness
Adaptive Slicing
• A proposed solution to this matter is adaptive slicing.
• The areas where detail is needed are sliced with thin layer height, whereas
areas that their quality is not affected are sliced with thicker layer height
to contribute to an effective build regarding time and energy consumption

31. Design Aspects
Process Parameters
Build Orientation
• The build orientation is one of the most crucial process parameters.
• The orientation of the part affects surface quality and build time
Surface Quality and Orientation

32. Design Aspects
Process Parameters
Build Orientation
• The orientation of the part relative
to the build vector of the
fundamental build unit determines
which geometrical features are
overhanging geometries.
• Subsequently, the build orientation
determines the volume of support
structures needed to successfully
manufacture the part.
• Moreover, it sets the axis on which
the mechanical properties show
anisotropic behavior.

33. Design Aspects
Process Parameters
Build Orientation
• Moreover, it sets the axis on which the mechanical properties show
anisotropic behavior.
How you place a part on the printing bed will lead to some
differences when it comes to your final part.

34. Design considerations
• Any resulted affection on the finished product. That includes mechanical
properties of the part, key performance indicators of the AM process or
even more abstract goals like first time right design and manufacture.
• Presented below are the most important design considerations.
• Anisotropic mechanical properties
• Accuracy
• Surface roughness
• Build time
• Part’s cross-section area

35. Design considerations
Anisotropic mechanical properties
• Anisotropic - (of an object or substance) having a physical property
which has a different value when measured in different directions.
• AM technologies produce parts with anisotropic mechanical properties.
• The causes of anisotropic behavior in AM includes
• Lamellar nature,
• Cylindrical extrusion shape (FFF technologies),
• Short fibers within the raw material, and
• Scaffold and lattice structures within the volume of the part

36. Design considerations
Anisotropic mechanical properties
Causes of anisotropic behavior in AM
Lamellar nature Cylindrical extrusion
shape FDM Process
Short fiber alignment
during the extrusion
process of a composite
Lattice Structure

37. Design considerations
Anisotropic mechanical properties
Anisotropic nature of FDM printing

38. Design considerations
Anisotropic mechanical properties

39. Design considerations
Anisotropic mechanical properties
• Mitigating the anisotropy with heat treatment improves to some
extent the mechanical properties. However, it is not feasible for
components that cannot fit to a furnace, thus it needs to be pointed as
a design consideration for AM.
• Design considerations for improving anisotropic mechanical properties
of AM parts
Orient the designed part in such a way that the loads are received
in the direction which the AM technology has the greatest
mechanical strength.
Optimize the shape of part to have the required mechanical
strength by considering anisotropy

40. Design considerations
Accuracy (xy plane vs z axis)
• Another important design consideration is to distinguish between the
machine’s accuracy on the xy plane and z axis.
• The accuracy of the machine that will produce the desired part is
crucial for the designer at the designing phase.
• For pre-assembled builds or assemblies in general, the dimensional
accuracy with which the machine can manufacture has to be
considered for the build to be a success.

41. Design considerations
Surface roughness
• The roughness of the completed part is important, as it determines
the post-processing steps in order to achieve the desired surface
quality.
• The resulted surface roughness is not uniform throughout the entire
surface of the printed part.
• This is caused by the geometry’s slope angle and the unintentional
sintering under angled overhangs
• Another reason for surface non-uniformity is the gaps resulted from
insufficient filling of the path planning

42. Design considerations
Build time
• Refers to the total time required for an AM machine to manufacture
the part.
• The build time and build orientation of the part are highly related that
is due to the fact that material deposition speeds on xy plane and z
axis are not the same.
• The build unit (e.g., nozzle, laser) moves, thus builds the part, with
greater speed on the xy axis, then the speed that the layers are
adding up.
• Changing the build orientation will affect the time needed for the AM
machine to complete the part.
• Horizontally orientated parts will in general be printed faster than
vertically orientated ones.

43. Design considerations
Part’s cross-section area
• The part’s cross-section area (normal to build vector) is an important
design consideration.
• The cross-section area affects the manufacturing process in two ways
depending on the AM technology.
1. Machine’s build plate and part’s base consideration
• The first layers of the build are crucial for its completion.
• The part must be restrained at the build plate; thus, the adhesion
between the part’s base surface and the machine’s plate is to be
considered, apart from securing the part, through that common
surface heat dissipation is achieved.
• A thermal simulation for the heat concentration provides a picture for
the design engineer, regarding residual stresses

44. Design considerations
Part’s cross-section area
2. Part’s cross-section and developed stresses consideration
• For the AM technologies that develop residual stresses (e.g., FDM,
SLM), it is desirable to maintain a small cross-section area to minimize
residual stresses and thus deformation.

45. Supported Walls
• Walls that are connected to the
rest of the print on at least two
sides.
AM Method Minimum Wall
Thickness (mm)
Fused Deposition Modeling (FDM) 0.8
Stereolithography (SLA) 0.5
Selective Laser Sintering (SLS) 0.7
Material Jetting (MJ) 1
Binder Jetting (BJ) 2
Direct Metal Laser Sintering (DMLS) 0.4

46. Unsupported Walls
• Unsupported walls are
connected to the rest of the
print on less than two sides
AM Method Minimum Wall
Thickness (mm)
Fused Deposition Modeling (FDM) 0.8
Stereolithography (SLA) 1
Selective Laser Sintering (SLS) /
Material Jetting (MJ) 1
Binder Jetting (BJ) 3
Direct Metal Laser Sintering (DMLS) 0.5

47. Support & Overhangs
• The maximum angle a wall can
be printed at without requiring
support.
AM Method
Fused Deposition Modeling (FDM) 45°
Stereolithography (SLA) SAR
Selective Laser Sintering (SLS) SNR
Material Jetting (MJ) SAR
Binder Jetting (BJ) SNR
Direct Metal Laser Sintering (DMLS) SAR
SAR – Support Always Required
SNR –Support Not Required

48. Embossed & Engraved Details
• Features on the model that are raised
or recessed below the model surface
AM Method Width (mm) Height (mm)
Fused Deposition Modeling (FDM) 0.6 2
Stereolithography (SLA) 0.4 0.4
Selective Laser Sintering (SLS) 1 1
Material Jetting (MJ) 0.5 0.5
Binder Jetting (BJ) 0.5 0.5
Direct Metal Laser Sintering (DMLS) 0.1 0.1

49. Horizontal Bridges
• The span a technology can print
without the need for support
AM Method (mm)
Fused Deposition Modeling (FDM) 10
Stereolithography (SLA)
Selective Laser Sintering (SLS)
Material Jetting (MJ)
Binder Jetting (BJ)
Direct Metal Laser Sintering (DMLS) 2

50. Holes
• The minimum diameter a technology
can successfully print a hole.
AM Method Minimum hole
dia (mm)
Fused Deposition Modeling (FDM) 2
Stereolithography (SLA) 0.5
Selective Laser Sintering (SLS) 1.5
Material Jetting (MJ) 0.5
Binder Jetting (BJ) 1.5
Direct Metal Laser Sintering (DMLS) 1.5

51. Connecting/Moving Parts
• The recommended clearance between
two moving or connecting parts
AM Method (mm)
Fused Deposition Modeling (FDM) 0.5
Stereolithography (SLA) 0.5
Selective Laser Sintering (SLS) 0.3(MP) & 0.1 (C)
Material Jetting (MJ) 0.2
Binder Jetting (BJ)
Direct Metal Laser Sintering (DMLS)
(MP) – Moving Parts
(C) – Connections

52. Escape Holes
• The minimum diameter of
escape holes to allow for the
removal of build material
AM Method (mm)
Fused Deposition Modeling (FDM)
Stereolithography (SLA) 4
Selective Laser Sintering (SLS) 5
Material Jetting (MJ)
Binder Jetting (BJ) 5
Direct Metal Laser Sintering (DMLS) 5

53. Minimum Features
• The recommended minimum
size of a feature to ensure it
will not fail to print
AM Method (mm)
Fused Deposition Modeling (FDM) 2
Stereolithography (SLA) 0.2
Selective Laser Sintering (SLS) 0.8
Material Jetting (MJ) 0.5
Binder Jetting (BJ) 2
Direct Metal Laser Sintering (DMLS) 0.6

54. Pin Diameter
• The minimum diameter a pin can
be printed at.
AM Method (mm)
Fused Deposition Modeling (FDM) 3
Stereolithography (SLA) 0.5
Selective Laser Sintering (SLS) 0.8
Material Jetting (MJ) 0.5
Binder Jetting (BJ) 2
Direct Metal Laser Sintering (DMLS) 1

55. Tolerance
• The expected tolerance (dimensional
accuracy) of a specific technology
AM Method
Fused Deposition Modeling (FDM) ±0.5% (lower limit ±0.5mm)
Stereolithography (SLA) ±0.5% (lower limit ±0.15mm)
Selective Laser Sintering (SLS) ±0.3% (lower limit ±0.3mm)
Material Jetting (MJ) ±0.1mm
Binder Jetting (BJ) ±0.2mm (lower limit ±0.3mm)
Direct Metal Laser Sintering (DMLS) ±0.1mm