Design guide

Direct Metal Printing

3dsystems.com

Contents
03

Why Direct Metal Printing

04

The Direct Metal Printing (DMP) Process

05

Basic Principles of DMP

13Part Orientation Guidelines

19

Design Constraints

22

Design Guidelines

32

Post ProcessingWhy Direct Metal Printing
Direct Metal Printing (DMP) is an additive manufacturing technique that
produces parts in a broad variety of metal alloys.

BENEFITS OF DIRECT METAL PRINTING

Starting from metal powder the product will be manufactured layer by layer. Each layer
is then melted on to the previous one creating a strong and dense part (up to 99.9%)
comparable with conventional manufacturing techniques (milling, casting). In this process
almost no waste material is created and complex geometries can be built that could not be
manufactured otherwise.

Weight Reduction
e.g through lattice structure or topology
optimization

Customized products
e.g internal structures such as complex
cooling channels, that otherwise could not
be produced

Increased functionality of parts
e.g thermal, flow, structural functionality, orintegration of various functions into
one part

Fast production
no tools or extensive programming arerequired
Manufacturing “freeform” internal complexfeatures (e.g. conformal cooling channels) is
ideally suited for dmp

Combining multiple parts into one single product,eliminates the weakness of assembly processes
e.g. welding, thereby adding functionality

Direct Metal Printing Design Guide03

The Direct Metal Printing (DMP) Process
Scanner (2 mirrors)• No binders, no additives• High Power laser -> fully dense parts (up to > 99,9%)• High accuracy (down to 10µm layers)

Layer Deposition(roller/blade/scraper)• Process physics with extremely rapid cool downLaser• Unique super fine microstructure• Excellent mechanical properties• Print directly from CAD-model

Powder Feed
Cartridge

Microstructure of LaserForm Ti Gr5 (A) as built in
DMP process without additional stress relief or heat
treatments that further improve the structure

Build Envelope Piston

Powder Feed
Cartridge

Direct Metal Printing Design Guide04

Basic Principlesof DMP

Direct Metal Printing Design Guide05

Surfaces
Basic terminology
MIDDLE SURFACESUPFACING SURFACESDOWNFACING SURFACES

Staircase effect

The edge of downfacing surfaces
are built on unmolted metalNormaln+3n+3n+2n+2n+1

α = 90°n

α = angle between horizontal build platform
and tangent line of the object surface

n+3
Normaln+1

α = -90°nn+2n+1

α = -90°nUpfacing surfaces are characterized by thenormal of the object pointing away fromthe build platform

Downfacing surfaces are characterised by
the normal of the object pointing towards
the build platform.

Example of upfacing surfaces in different
angles ranging from: 0° (left) to 90° (right)
with steps of 15°

Example of downfacing surfaces in different
angles ranging from: 75° (left) to 0° (right)
with steps of 15°

Direct Metal Printing Design Guide06

Surfaces
Influences on quality
Stair size
Stair size
Down facing surface
ZZ

Slope angle

Z

Slope angle

Steep angles good!

Low angles poor

Bad surface impossible
Support structures required

Surface quality in DMP is dependent on the orientation of the surface
The stair stepping effect that is intrinsic
to all additive layer manufacturing
technologies can be reduced by building
more vertically or completely horizontallyoriented surfaces.
On upfacing surfaces this effect is clearlyvisible and important.

On down facing areas, the dross formation
effect is in most cases bigger than the stair
stepping effect. Dross is the undesired
amount of molten material and particles asa consequence of melting on loose powder.

• The lower the angle, the more dross formation
you have, resulting in worse surface quality• Low angles need support structure• Supported faces have worse quality
Dross formation:
In downfacing surfaces the melted layersags through the loose powder underneath,resulting in dross formation.

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Surfaces
Influences on quality
Surface quality depending on type of surface and angle

Ra (μm)UF (Upfacing surfaces)
MF (Middle surfaces)

20

DF (Downfacing surfaces)

15

Staircase effect

SURFACE QUALITY

Normaln+3n+210n+1

α = -90°n504590α (˚)

Direct Metal Printing Design Guide

08

Thermal Stresses
Basic principles
Why do we have thermal stress in the part?

Important influences on those stresses• High melting temperaturese.g. Titanium: 1650°C; Stainless steel: 1200°C

σT ~ A Thermal tension is proportionate to the melted surface area. To mitigate this:• Fast cooling rates (< 1ms – 100°C)• Stresses accumulate throughout layers, because
in each layer the top layers are heated and cooled
down again. Expansion and shrinking, blocked byalready solidified layers causes residual stresses• Deformation behavior is material specific• Reduce area to be melted per layer• Ensure longest direction of part along Z-axis• High number of small sections is better than one big section

σT ~ ΔT Thermal tension is proportionate to the temperature drop duringsolidification
Make sure you have good heat transfer to the baseplate and machine.
The better the heat is transferred, the less a part will warp.

Heat Distribution

Overheating

Thermal conductivity powder/supportDirect Metal Printing Design Guide09

Thermal Stresses
How to deal with them
How to handle thermal stresses• Residual stresses result in parts that want to warp
• Support structure is needed to avoid warping and keep part in position• Stresses remain in the part after building – if support is immediately removed,the part will still deform to the wanted position.
• Heat treatment is required after powder removal, prior to platform and support
removal, to release the stresses.

DESIGNED MODELWARP AND DROSS FORMATIONSUPPORT STRUCTURE

Direct Metal Printing Design Guide10

Shrink lines
Shrink lines appear when two separate entities are connected in one layer• The connection surface shrinks and pulls the two entities towards each other• Next layer is printed on original dimensions again• Line visible in the part
• Typical on bridges/internal channels

Up to 0,2m
A1 + A2

A3 > A1 + A2
Entities provide
low resistanceto deformation

OPTIONA3 = A4
layer 3 limits
deformationof layer 4

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11

Supports
Supports are necessary to minimize dross formation,warping and shrinking lines• Less dross formation on downfacing regions• Better heat transfer through solid supports• Prevent warping and keep part on fixed location• Minimize shrink lines

There are a multitude of possible support structures.
Here are some examples:

WallSupport

SolidSupport

Lattice
SupportSolid
WallConeSupport

ManualConeSkirtSupport

MultiExposure• Block supports are good against dross formation• Solid support is needed for heat transfer, to prevent warping
and reduce shrink lines

Direct Metal Printing Design Guide

12

Part Orientation
Guidelines

Direct Metal Printing Design Guide

13

Part Orientation
Overall build quality
Orienting the part based on overall quality is mainly based on
the downfacing surfaces.
Downfacing surfaces are the worst surfaces with a highroughness of the part. So by decreasing the amount ofdownfacing area we can say in general that we will increase
the quality of that part.
Downfacing surfaces are the surfaces below the self-supporting
angle (α).

The example below shows an example of this situation.
The left part has a leg that makes an angle with the buildplate of30°, so this leg has to be supported (because it is below the selfsupporting angle)*.
By rotating the same part 30° we see that the leg makes a 60°
angle with the buildplate. In this way we don’t need to put support
in this region increasing the overall quality of that part.

The self-supporting angle depends on material and the printing
process- Ti-alloys α=40-45°- Steel, CoCr, Aluminium-alloys α=50-55°*Metal Printers with a roller system, like ProX DMP 100, 200 and 300
can reach angles for Ti as low as 30°

Direct Metal Printing Design Guide14

Part Orientation
Avoiding downfacing surfaces
Avoid big overhang sections or large downfacing sections.

Avoid down facings
in design

Building orientation canhelp to avoid down facings

Parts will build much better if you have middle and upfacing
sections instead of downfacing areas.

Orientation in red is bad, because of large overhang.
Orientation in green is good because it is built immediately on the baseplate andhas no downfacing area.

Direct Metal Printing Design Guide15

Part Orientation
Specific features

Holes axes perpendicular to building direction- Holes will be oval
- Diameter > 8mm - Support needed
Holes axes parallel to building direction- Holes will be circular- Diameter < 8mm - Self supporting- Self-supporting

The quality of printing features like holes, pockets, screw
threads, etc. depends on the orientation of the part.
The best quality is when printing in the Z-direction(perpendicular to the build platform).
When printing these features in the X/Y-direction (parallel to thebuild platform) the quality of these features gets worse due tothe downfacing effect.

1.
2.

1. Holes in the z-direction
2. Holes in the X/Y-direction

Dross formation in downfacing
surfaces.

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16

Part Orientation
Thermal stresses
When orientating the parts we want to keep the thermal stresses
as low as possible.
These thermal stresses are created by first heating locally thepowder and a rapid cooling after melting the powder. One way
to keep the stresses as low as possible is to keep the crosssections (so what is actually scanned every layer) as small aspossible.
In the picture on the right: The left orientation has the smallest
cross-section and the thermal stresses would be reduced to aminimum. The orientation on the right can be printed but a very
rigid support structure is necessary to keep the part in place.

Small cross-section

Large cross-section

Direct Metal Printing Design Guide17Part Orientation
Avoiding shrink lines
Diverging orientation preferred over converging

Everywhere you have two entities coming together,you create a shrink line, so at every red circle you will
get a visible line.

In this design you are diverging and so new entities
are made instead of connected, thereby eliminating
shrink lines.

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18

DesignConstraints

Direct Metal Printing Design Guide

19Design Constraints
What can be built without support?1
Steel, stainless steel, Inconel

Horizontal circular holes• Big surface

α > 60°• SupportlessØin < 8mm

• Medium surface

α > 50-55°• Support neededØin > 10mm

• Small surfaceα > 45°

Titanium, aluminum

Horizontal bridges• Big surface

α > 50°• Supportless

L < 1,2mm• Medium surface

α > 40-45°• Support needed

L > 1,5mm• Small surface

α > 35°ZØ

L

Horizontal downfacing flange• Supportless

L < 0,75mm• Support needed

L > 0,75mm

Lα

These values are experience based for ProX DMP 320 printers and are subject tochange based on printer model, specific geometries and improved build styles.

1

Direct Metal Printing Design Guide20

Design Constraints
Small features1• Strongly dependent on- Material- Orientation- Part geometry•M inimal achievable values- Minimal wall thickness- 0,18mm (not gas tight)- 0,20 - 0,25mm (gas tight)- Minimal pillar size
- 0,18mm- Minimal hole size
- 0,30mm

This test sample illustrates geometry dependence.
The 0.3 and 0.5mm pillar and the 0.3 mm rib broke off,
as here they were designed as stand-alone features in50mm hight.
The smallest pillar was to fragile on this lenght that it
breaks very easily on unloading the part.

The smallest wall build up to a certain height, because than it starts
to bend, because it is to fragile, this shows that we can perfectly build
those walls but only for a limited height.
For the smallest hole size: if we need to print very small holes
horizontally, it is advised to offset them, so you compensate the drossformation on the top of the hole.

These values are experience based for ProX DMP 320 printers and are subject tochange based on printer model, specific geometries and improved build styles.

1

Direct Metal Printing Design Guide

21

DesignGuidelines

Direct Metal Printing Design Guide

22Design guidelines
Avoid downfacing surfaces and create
self supporting geometries
If overhang > 60°
Self-supporting

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23

Design guidelines
Design freeform structures• Avoid building parts designed for casting or CNC.
They typically have:• Use freeform structures- Sharp corners- Avoid downfacing area resulting in better surface
quality and less support needed- No progressive build up- Achieve higher level of accuracy- In many cases achieve more weight reduction

ZDirect Metal Printing Design Guide

24

Design guidelinesDimensional accuracy• Gradual transitions between layers:- Use fillets (radii), arcs
- Use chamfers- Use organic designs}

Avoid stress concentrations•U se enough supports to fix the part into position,

heat treatment will release the stresses afterwards• Topological optimized designs- Often easy to build- Often lower α’s possible without supports- Less supports > less deformation > better product!
•A pply conventional post-machining to increase

accuracy
Topologically optimized sattelite bracket for Thales Alennia Space• 189.0 x 229.5 x 288.5 mm• Better stiffness-to-weight ratio and 25% weight savings vs traditional design• Printed with LaserForm® Ti Gr5 (A) on a ProX® DMP 320 Metal PrinterDirect Metal Printing Design Guide25

Design guidelines
Add radii• Massive parts accumulate a lot of stress•N eed to take care of design to avoid cracking at thebaseplate or on geometry changes.
Crack initiates where you have a high stress concentration,for example on corners• Use radius and offset in connection with the baseplate• Typical radius: 2.5 - 5mm

Add radii

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Design guidelines
Channel design• Large (internal) overhangs are not feasible to print- Change design of internal channels (closing at >45°)- Angle part at a self supporting angle (45°)- Extra support structure possibly needed at the outside of the part

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Design guidelines
Weight saving techniques• Scaffold/lattice structures- Save weight- Increase bone attachment for medical applications• Different types of scaffold/lattice structures
are possible• Mechanical parts require additional analysis

This part shows different scaffold structures that all enable increased bone attachement inmedical implants.

Combustion chamber, Crosssection of an ESA
combustion chamber with signigicant weight savingwith a 12% volumetric density mesh

Antenna bracket (190 x 230 x 290mm) for
geostationary telecommunications satellites
produced by Thales Alenia Space

Direct Metal Printing Design Guide28

Design guidelines
Powder removal• Check internal cavities, on part because powder canbecome trapped here
- Add powder removal relief holes at strategic locations in the part
- Add small tubes to enable blowing air into the part more easily• Powder typically has good flowability, making removal
possible with pressurized air and vibrations

The inside of this part is hollow, so it contains a lotof powder. Holes at the bottom below the wire EDM
offset to remove the powder

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29

Design guidelines
Hybrid build-ups
Bulky parts are not always feasable for AM or maybe
too massive.
The following two approaches offer an economic solution:
1.

Building complex structure on already created CNC part
• Careful alignment in the machine is important• Top section needs to be flat2.

Building complex structure on baseplate and mill
baseplate afterwards:• Used for mold applications

Mold with conformal cooling printed on a CNCed section of the mold
- Lower left: Low complexity, cnced section of the mold
- Lower right: Complex conformal cooling channels in 3D Printed section of the moldDirect Metal Printing Design Guide30

Design guidelines
Do’s and Don’ts
DoDon’t• Increase added value• Design in a subtractive/conventional way• Functional requirement priority• α < 45°

• Design in an additive way: topology optimized, freeform• Converging• α > 45°
• Diverging design• Arcs/filles/chamfers• Straight corners, flat overhang• Section increase• Manufacturability priority• Decrease area = decrease volume• Avoid big area changes between layers• D etermine build orientation as soon as possible during
design process

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31

Post Processing

Direct Metal Printing Design Guide

32

Post Processing
Typical process flow
DMP
Manufacturing
Building the part

Cleaning
UltrasonicPowder
RemovalGet the powder out to avoid
sticking after heat treatment,making powder removal moredifficult

Finishing• Sand Blasting• Milling• Polishing

CNC

Heat treatment• Stress release• Chamnge mechanical properties• HIP Treatment

Supportremoval
Break off the supports

Improve accuracy and roughness
on interfaces where DMP is
inadequate

Baseplateremoval• Manual• Wire EDM• Band Saw

Direct Metal Printing Design Guide33

Post Processing
Additional post-processing options• Apply coating on parts• Quality checks:- X-ray to check internal channels- Optical scan to check dimensional accuracy- 3D Systems Geomagics software can deform the partbased on scan results to compensate for inaccuracies

Direct Metal Printing Design Guide34

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