Additive

Manufacturing
processes for
steel tools
manufacturing
and repairing
Adva ntages a nd limitations

Guilherme Assunção 10963405

Pedro Pessoa 10955670
Vera Carvalho 10994098
Advanced Manufacturing1 Processes B

This work aims to study the production of steel tools and the progress in that field,
focusing on Additive Manufacturing. It will be analysed how it is used in the industry,
and the advantages it brings, as well as its downfalls. To understand the potential of
this process, a comparison between a conventional process and an AM process was
also made.

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 Power Bed Fusion

• Direct metal laser sintering (DMLS)

• Eletron Beam Melting (EBM)
• Selective Heat Sintering (SHS)
• Selective laser melting (SLM)
• Slective laser sintering (SLS)

Power bed fusion

Power bed fusion, or PBF as we are going to call it from now on, is one of the most
important processes in the field of addictive manufacturing. Since we are going talk
about it along the project, we decided that it will be good to have some specific
knowledge about it.
We can print almost any kind of materials with PBF, but one of the most common
powder-based metal is steel. It's economic, and capable of doing parts with very
complicated geometries that are not possible in conventional processes. That’s why
this process is used in a lot of different areas from automotive and aerospace to
medical applications.
To print, the PBF uses one of these types of techniques:
• Direct metal laser sintering (DMLS)
• Electron beam melting (EBM)
• Selective heat sintering (SHS)
• Selective laser melting (SLM)
• Selective laser sintering (SLS)
The process is pretty simple. The machine starts by spreading a layer of material
powder in the platform, then the laser (or other type of fusing processes) fuses the

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powder making the first layer of the model. Then these two steps are repeated until
the complete model is created.
As we are going to see later in this project, this process also has some
disadvantages, for example, a decrease in a lot of the structural proprieties of the
models and its common use in low batches.

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 Selective Laser Melting
• La s er Power: 100 – 1000 W [3]
• La yer Thi ckness: 30 – 90 µm [4]
• Pa rti cle Size: 20 – 50 µm [4]

This process was developed in 1995 by German scientists[1] and consists on a high
powered laser joining/welding metal powder particles, by completely melting them.
The process is executed as a layer of powder is laid at the working plate, and a laser
melts specific particles, that will solidify into the pretended shape. The building
platform is then lowered a little bit allowing a new layer of powder to be laid on the
previous one, and the laser to act on that layer too. This process is repeated until the
desired part is obtained. In the end, the remaining powder is taken away and the
piece is ready. This allows the structure to be relatively dense (about 99.7 - 99.99 %
density[2]). To prevent the powder from oxidating, it is common practice to isolate it
from oxygen. To do so, a layer of an inert gas is added, creating an environment
reaction-free.

The evolution of this process, in a path towards increased feature resolution, relies on
the following characteristics: Laser beam diameter; Layer Thickness; Particle size. This
is always to improve the quality of the part, increasing its density , and improving
surface quality.

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 Selective Laser Melting - Limitations
• Powder Waste

One of the biggest advantages of AM processes is the lack of waste of material. In

this process in specific, that advantage is lost. As it requires the whole layer of
powder, but only part of it will be melted and turned into the actual part, the rest of
the powder is wasted. Most of the powder can and will be used again, but in practical
terms, it is needed way more material to fabricate a part than the material required
for the actual part. In some occasions the material might not even be recycled, if it is
contaminated or oxidized. The oxidation can be controlled by the use of an inert
shielding gas, that protects the powder from the oxygen, as seen before.

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 Selective Laser Melting - Applications
• Formi ng Tools for Hot Stamping

This process is widely used for materials like ceramics and metals. It has many
applications, being advantageous on the creation of complex structures, geometries
and thin walls. It is famous on the aerospace industry, as well as the medical
orthopedic industry. Considering the relatively good structural properties of a piece
produced by SLM, it can also be used to produce dies for hot stamping. Usually, when
opting for this technique, post heat treatment and surface finish processes are
required, but the mechanical properties obtained at the end might be as good, or
even better than the ones obtained through conventional methods. [2] This process
shows favorable avenues to explore in the future as it matures and solidifies its
position in the industry.

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 Direct Metal Deposition

In the interest of metal tool manufacturing and repairing, the recent advancements in
tool steel manufacturing have gone a long way in facilitating and turning the process
more versatile. When designing a brand-new steel tool or mold, it can become quite
expensive only using conventional machining due to the complexity of the geometry,
the precision required and the materials used. It would be very advantageous to
employ a method in the realm of additive manufacturing, as a way to minimize waste
and increasing complexity without sacrificing cost, all in an effort to create something
more profitable.
Applying the concept of additive manufacturing to metals has yielded numerous
different production methods. One of those is of particular interest not only for tool
production but specially for tool repairing: Direct Metal Deposition (DMD).

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 Direct Metal Deposition

Schematic representation of laser metal deposition (LMD)

As an additive process, DMD consists of deposing metal powder on a liquid metal

pool of the material already present, created by an energy source. The volume of the
pool now increased, the energy source moves on, creating a new pool next to it and
letting the latter solidify. This creates a new layer of metal, thus, layer by layer,
forming a new part. As a reference, this could be seen as 3D printing for metals. If the
source of energy used is a laser, the process is then called Laser Metal Deposition
(LMD).
Looking with more detail at LMD we can define its components as follows,
• The laser beam, the source of energy used to melt the powder or wire used as
the additive material,
• The substrate, the surface serving as the base for the new part,
• The additive material, a metal, either in the form of a powder, in this case being
deposed via a coaxial nozzle, or of a wire, deposed laterally.
The process thus varies with a few parameters, the power of thew laser, the flow
rate of the gas, the feeding rate of the additive material and velocity of the
deposition. All of these parameters will influence the hardness, thickness and
precision of every layer.
[6]

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 Direct Metal Deposition

Mold Ma nufacturing Mold Repairing

The versatility of this manufacturing technique is evident, and now it is being

pondered as a way of more easily manufacturing tools (eg for molds used in forging)
and repairing said tools. In order to verify its usefulness in such domains, the
characteristics of the 3D printed tool need to be on par with the requisites in order to
handle the conditions demanded by the manufacturing process it will be used for. For
the repairing of existent tools, the discrepancy between the new and the old cannot
induce bad characteristics on the end product.
The cost aspect is worth looking at. LMD is a very expensive production method, as it
has a very high cost of entry, and as such, needs very careful consideration before
being integrated. The purpose of such methods is to be versatile not to be cost
efficient. This is why it is audacious to use such tools for repairing, since it wouldn't
be necessary to integrate it into a production line nor buy huge volumes of machines.
It can also be wise to use it as a prototyping method, since its versatility allows
experimentation.
Overall, LMD is a very promising technology that presents a whole new perspective
when it comes to the manufacturing and repairing of steel tools. As this
manufacturing process matures, it will become more prominent and less expensive,
making it a very good alternative to conventional manufacturing.

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 Direct Metal Deposition

Ideal Parameters for the repairing of steel tools with LMD

Comparison of the hardness of

Ductile Fracture of the Repaired Specimen each zone of the tool
(away form the repaired zone)

The repairing of conventional tools is, in general, a very good solution, replacing
traditional methods. Using the right parameters, the repaired part can be as good or
better than the rest of the tool. It is important to notice that after the deposition of
the material, the bonds between the old part and the new are very strong. When
submitted to tensile strength tests, the failure often occurred way from the repaired
part. Non the less, the hardness is not homogeneous right after the repairing, this is
due to the heat process the new bead goes through, the new material has a much
higher hardness then the original material. Thus, a heat treatment must be carried
out in order to ensure that the tool produces the desired outcomes.
[7]

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 Comparison of properties between additively and
conventionally fabricated tool steel
Examine and compare the structural characteristics
Analyze the tensile strength and fatigue tests
Study the fractures observed in the samples
Draw conclusions about the reliability of the two processes and their advantages and
disadvantages

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Finally, we considered that it would be crucial to examine and compare the structural
characteristics of a tool that was made both conventionally and additively using
power bed fusion. Plus, it is pertinent to look into any deficiencies in the AM
material's mechanical load capability using measurements of its oxygen content.
One of the biggest disadvantages of AM is the surface finish . Porosity and roughness
in the powder material are frequent problems that cause defects in the final models
and affect the structural properties, especially the fatigue strength. Frequently, the
roughness of the AM processes is due to an incomplete or unstable fusion of
powdered material. These defects can be resolved by post processing treatments,
like hot isostatic pressing (HIP) or extensive chemical etching.
In the article selected to do this investigation, the material used was a 1.2344 hot
working tool steel with 0.4% carbon.
The initial mechanical properties for this material fabricated via PBF are very well
documented:

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 The material chosen for the study was a 1.2344 hot working tool steel with 0.4% carbon.
Some initial mechanical properties for this material fabricated via PBF are very well documented.

The initial mechanical properties for this material fabricated via PBF are very well
documented:
However, the amount of investigations on fatigue behavior for 1.2344 are still very
limited.
[8]

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 Specimens
To conduct this study, various PBF-generated specimens were produced, each for a separate set
of conditions and tests

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To conduct this study, various PBF-generated specimens were produced, each for a
separate set of conditions and tests: nineteen fatigue specimens and six tensile
specimens, all of which underwent post surface machining by turning.
Moreover, without undergoing any additional post surface machining, six more
specimens with PBF-surfaces were evaluated in order to examine the impact of
surface roughness on fatigue performance.
No additional heat treatment was applied to any of the specimens.
Tab 2. Quantities of specimens
Fig. 1. Geometry PBF specimens.

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 Tensile tests

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The tensile strength was tested by push-pull, to control the load on the specimens
until the sample was completely separated.
In the tensile tests there was almost no distinction between the specimens. The
specimens broke down at the fracture point due to a brittle fracture type without
necking. The average fracture elongation value was 1.5%.

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 Fatigue tests

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The fatigue tests were performed using the stair case method which means that
when the fatigue sample fails, the following stress amplitude decreases by 20 MPa,
whereas if the sample runs out, the next specimen is tested at a 20 MPa higher stress
amplitude. The specimens were considered to be run outs when the test was
stopped after 107 load cycles without a specimen failure. If a specimen ran out, it
was tested once more at a higher stress amplitude to determine the specimen's
weak point.

The specimens with PBF surface, started the test with an amplitude of 200MPa. As
we can see in the diagram above, all the batch of these samples fractured before 107
cycles. For the set of outcomes we can estimate that the endure limit is less than 100
MPa, therefore we conclude that rough surfaces lead to a strong decrease of the
fatigue strength. The initial value for specimens with surface post-processing was
higher, at 420 MPa. As seen in the diagram, 12 of the 19 specimens fractured before
the limit, but the remaining 7 specimens made it to run out. This samples kept being
examined, in order to discover more information about the fractures.

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 Fractures
The two main types are:
• Pores or cavities
• Lamellar structure

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In first place, the one feature that all specimens shared was that the orientation of
their fracture surfaces was perpendicular to the direction of the loading.
Since all the specimens with PBF surfaces failed in the surface, in this section we will
focus more on the results of the turned samples.

After doing the fatigue tests, different types of fractures were observed, but there
were two main cases. The first was on the pores or cavities and the second was on
the lamellar structure.

Homogeneously distributed throughout the sample volume, pores and cavities serve
as a critical weak point and, in the case of specimens with a turned surface, as the
initial point of fracture creation. These critical defects are mostly found close to the
surface and are less common in the volume area.

The origin of the second fracture, was the lamellar structure inside the steel matrix.
Even though there are currently pores and cavities that frequently appear inside the
specimen volume or close to the surface the lamellar structure appears to be cause
of failure.

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a)surface crack
b) volume crack
c) surface near cavity
d) volume
e) surface near lamellar structure as fracture type

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 Oxygen content
The presence of oxygen can lead to:

•Gas Formation
•Oxidation
The powder and material processed via
PBF have substantially higher oxygen
and nitrogen contents

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Gas Formation: Oxygen can react with metal powders, leading to the formation of
gas pockets or porosity within the printed part. Porosity can compromise the
structural integrity and mechanical properties of the material.
Oxidation: Excessive exposure to oxygen during the manufacturing process can lead
to oxidation of the metal powders. This can affect the mechanical properties and
structural integrity of the final part, making it more brittle and prone to failure.
When compared to material that is conventionally fabricated, the powder and
material processed via PBF have substantially higher oxygen and nitrogen contents. A
cross section of a single PBF specimen was used for the measurement. The only areas
with significantly greater oxygen contents are the pores and the active cracks. This
makes sense because the specimens were stored outside, which led to the formation
of an oxide layer on the specimen's surface.
[8]

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 Values comparation and conclusions
• PBF specimens have values of hardness and tensile strength very similar to the conventional
processes with post heat treatment

• In fracture elongation the PBF only have 1,5% when the conventional material presents 9%.

• In terms of fatigue strength, the PBF with turned surface has a value of 283 MPa, which is
significantly lower than the traditional technique, which has a value of 600.

• In the case of specimens with PBF-surface the value is even more low.

• Based on the similarity of the values obtained from the conventional with heat treatment, we
can conclude that PBF may be a better option in many parameters.

• On the other hand, the fatigue strength values are entirely different, with the conventional
method generating nearly twice as much strength as the PBF process.

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Properties for PBF generated structures, such as hardness and tensile strength have
values very similar to the conventional processes with post heat treatment. But
relative to the fracture elongation, the PBF only have 1,5% when the conventional
material presents 9%.
In terms of fatigue strength, the PBF has a value of 283 MPa, which is significantly
lower than the traditional technique, which has a value of 600. And in the case of
specimens with PBF-surface the value is even more low When we look at the tensile
strength, we can assume that if the part produced by PBF were also subjected to a
post heat treatment, it would most likely have even better values than the
conventional processes. Based on the similarity of the values obtained from the
conventional with heat treatment, we can conclude that PBF may be a better option
in many parameters.
On the other hand, the fatigue strength values are entirely different, with the
conventional method generating nearly twice as much strength as the PBF process.
Since AM and conventional processes share many of the same values, I believe there
are several factors that could influence the final decision to choose between the two
processes. First, AM parts are much more affordable and have many advantages in
terms of part geometries and creation flexibility. However, fatigue is a very important
property in tools given the repetitive movements they undergo. If post-treatment can

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increase the value, then the PBF process might be taken into consideration.
However, this will depend on the specific tool and its intended purpose. [8]

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 Conclusion
• Allows machining of complex geometries
• Great for repairing tools
• Expensive technology
• Needs to be developed

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Considering the advantages and disadvantages studied before, using AM processes

on steel tools is an option to be explored, it has some advantages over conventional
machining, being the main one the versatility of machining complex geometries, and
being easily used to repair said tools. It still is an expensive technique, with some
other limitations, but with big possibilities to be improved. And that's where the
market is going.

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 References
• [1] Ratna, D 2022, Recent Advances and Applications of Thermoset Resins, 2nd edn, Elsevier

• [2] Macêdo, G, Pelcastre, L, Hardell, J 2023 'High temperature friction and wear of post-machined additively manufactured tool steel during
sliding against AlSi-coated boron steel', Wear, vol. 523, accessed 18 Decembre 2023,
<https://www.sciencedirect.com/ scie nce/ article/pii /S0043 1648 2300 1369 >

• [3] Leary, M 2018, Titanium in Medical and Dental Applications, Woodhead Publishing

• [4] Song, X, Zhai, W, Huang, R, Fu, J, Wang Fu, M, Li, F 2022, Encyclopedia of Materials: Metals and Alloys, Elsevier

• [5] Kumar, S 2014, Comprehensive Materials Processing, Elsevier

• [6] Oliari, Stella & D'Oliveira, Ana Sofia & Schulz, Martin. (2017). Additive Manufacturing of H11 with Wire-Based Laser Metal
Deposition. Soldagem & Inspeção. 22. 10.1590/0104-9224/si 2204. 06.

• [7] Rabiey, M., Schiesser, P., & Maerchy, P. (2020). Direct Metal Deposition (DMD) for tooling repair of DIN 1.2343 steel. Procedia CIRP, 95, 23–
28. https://doi.org/10.1016/j. procir. 2020. 01.1 51

• [8] R. Dörferta,⁎, J. Zhangb, B. Clausenb, H. Freißea, J. Schumacherb, F. Vollertsenc 2019, Additive Manufacturing, Elsevier

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