Mitsubishi Heavy Industries Technical Review Vol. 57 No. 3 (September 2020)
1Manufacturing Technology of LAMDA Three-Dimensional
Metal-based Additive Manufacturing System UsingPowder DED Method

KOH ISHII*1

HIROHISA KURAMOTO*1

HIROYUKI TAUCHI*1

YUSUKE YAMAMOTO*2

TOMOHIRO WAKANA*3 HITOSHI YOSHIMURA*3

Powder DED (Directed Energy Deposition) metal-based additive manufacturing ischaracterized by its fast manufacturing speed and ease of increasing the equipment size. On theother hand, it also has issues such as metal deterioration caused by oxidation occurring in theprocess of melting and solidification during manufacturing, as well as securing the shape anddimensions. Mitsubishi Heavy Industries Machine Tool Co., Ltd. uses its own LAMDA powder
DED three-dimensional metal-based additive manufacturing machine equipped with a local shield
to manufacture sample aircraft parts while suppressing the oxidation of titanium alloy, which is anactive metal. This machine is also able to suppress shape collapse during manufacturing by
optimally controlling the heat input using the monitoring function system.

|1. Introduction
By using metal-based additive manufacturing, it is possible to reduce the part weight andintegrate parts due to the realization of shapes that could not be manufactured by conventionalremoval processing, improve design, enhance the functionality using multi-layer manufacturing of
dissimilar metals and reduce parts inventory. For this reason, metal-based additive manufacturing isattracting attention as a next-generation technology that can contribute to improvement in productperformance and supply chain innovation. The LAMDA powder DED three-dimensional
metal-based additive manufacturing system (hereinafter referred to as LAMDA), which wedeveloped, is characterized by its fast manufacturing speed resulting from the additive
manufacturing principle and the ease of increasing the equipment size. On the other hand, it has
issues such as securing the mechanical properties, shape and dimensions of the manufactured
metal, as well as stability over lengthy manufacturing processes. This paper describes an overviewof LAMDA, our approach to the issues it faces and presents manufacturing case examples.

|2. Additive manufacturing principle and features of DED method
Powder DED, which is also known as the directed energy deposition method, is a techniquethat uses a laser as a heat source to melt and solidify locally-fed metal powder together with asubstrate to manufacture a three-dimensional shape by overlay welding (Figure 1). Due to theadditive manufacturing principle, powder DED has the following features:(1) The manufacturing speed is about 10 times faster than that of the powder bed method.
(2) Metal powder is directly fed to the manufacturing position, so increasing the equipment size
is easy.
(3) Manufacturing on an existing part is possible, so adding shapes, repairing and coatingprocesses can be carried out.
(4) Multi-layer manufacturing of dissimilar metals is possible by switching the material during
manufacturing.
*1

Chief Staff Manager, Micro Machining System Group, Engineering Headquarters, Mitsubishi Heavy Industries Machine Tool*2

Micro Machining System Group, Engineering Headquarters, Mitsubishi Heavy Industries Machine Tool Co., Ltd.

*3

Process Technology Group, Engineering Headquarters, Mitsubishi Heavy Industries Machine Tool Co., Ltd.

Co., Ltd.

Mitsubishi Heavy Industries Technical Review Vol. 57 No. 3 (September 2020)
2Because of the features above , the technology is expected to be used to manufacturehigh-functionality parts and repair used parts in the fields of aerospace, energy and automotive, as
well as to innovate parts production processes. On the other hand, the use of active metals such astitanium—a type of high-performance material increasingly used in aircraft parts—has the problemof metal deterioration occurring due to oxidation during the process of melting and solidification inmanufacturing. In addition, manufacturing a large part with high accuracy and stability requires
control of the heat input according to the shape of the part, and a mechanism to stop the equipment
safely, when an abnormality in the manufacturing process is detected, is also necessary.

Figure 1

Powder DED metal-based additive manufacturing method|3. Overview of LAMDA
We market the series of LAMDA models according to the manufacturing size (Figure 2).
The LAMDA 200 is targeted for small-size manufacturing and is suitable for manufacturing smallparts, developing manufacturing methods, accumulating manufacturing expertise and evaluating
prototypes. The LAMDA 500 and LAMDA 2000 are capable of manufacturing larger parts, and themaximum manufacturing size of the LAMDA 2000 is 2000 mm x 1500 mm x 1600 mm.

Figure 2 LAMDA series

Mitsubishi Heavy Industries Technical Review Vol. 57 No. 3 (September 2020)
3This paragraph and the next describe the LAMDA main unit and peripherals. The machinemain unit has an XY-axis driven table and a Z-axis driven additive manufacturing head. When a2-axis rotary table is added, 5-axis additive manufacturing is possible. The additive manufacturing
head has a built-in optical system, which focuses laser beam on the substrate. It is possible toobserve the molten pool by installing a sensor such as a camera coaxially with the laser beam. The
head is equipped with a powder feeding nozzle on its tip, which feeds metal powder accurately tothe laser focusing position on the substrate. When a cutting spindle is also mounted, it is possible toperform preparatory processing before repair manufacturing or finish processing after
manufacturing.
The peripherals include a laser oscillator, a chiller and a powder feeder, as well as a dust
collector for powder recovery. Up to two pots can be installed for the powder feeder, and thematerial being fed can be switched during manufacturing.

|4. Features of LAMDAFor LAMDA, powder feeding nozzles for handling various manufacturing processes
according to the purpose are offered, as is a monitoring function for stable manufacturing overlengthy manufacturing processes.

4.1

Powder feeding nozzle and local shield

High-precision additive manufacturing means manufacturing a metal with the required
mechanical properties with high shape accuracy. For LAMDA, two types of nozzles—a 3-port
feeding type and an all-around feeding type—are available so that the nozzle can be selectedaccording to the shape of the part, required accuracy and manufacturing speed. Figure 3 shows thepowder convergence state of the two nozzles. The metal powder converges at the nozzle standoff
setting position during manufacturing, and the convergence diameter is approximately the focusing
spot diameter of the additive manufacturing head optical system. Accurately converging the metal
powder makes it possible to perform manufacturing with the target shape and dimensions. Inaddition, a local shield can be added to prevent active metals from oxidizing during manufacturing.
Figure 4 presents the local shield and the result of fluid analysis during shielding. By injecting aninert gas from the outer circumference of the nozzle, a shield is created locally at themelting/solidifying position, which prevents the inflow of air and avoids oxidation.

Figure 3

Powder feeding nozzle

Figure 4Local shield and result of fluid analysis

4.2

Monitoring function

The powder DED method performs manufacturing while melting the substrate with a laser
beam. However, since the melting degree of a metal changes depending on the material type andshape of the substrate and the degree of overheating and cooling during manufacturing, it isdesirable to change the laser power according to these conditions. If a metal-based additive
manufacturing machine has a function of optimally controlling the laser power according to theadditive manufacturing conditions, stable lengthy manufacturing processes are possible. To achieve

Mitsubishi Heavy Industries Technical Review Vol. 57 No. 3 (September 2020)
4

this, LAMDA has a monitoring feedback function. In addition, since sputter, fumes, etc., during
manufacturing may damage the equipment, we are developing an AI-based abnormality detection
function.
(1) System configuration
Figure 5 is a system configuration diagram of the monitoring feedback function. Acamera installed coaxially with the laser beam enables observation from directly above the meltpool during manufacturing. This is based on the idea that a change in the state of the substrateappears as a change in the melt pool. The melt pool image is analyzed by a dedicated PC in realtime during manufacturing, so it is possible to immediately detect changes during
manufacturing. Based on the detected amount of change, the manufacturing position and laser
output command can be feedback-controlled. By detecting abnormalities such as sputter at thesame time, the equipment can be safely stopped in order to prevent damage.

Figure 5

Monitoring function system configuration(2) Effect of feedback
Figure 6 shows the results of manufacturing with the feedback function turned ON andOFF. When the feedback function was turned OFF, as the additive manufacturing heightincreased, the balance between heat input from the laser beam and cooling collapsed and heat
input became excessive. This increased the melt pool size, and the shape collapsed as a result.
When the feedback function was turned ON, the laser output was controlled to stabilize themelt pool size during manufacturing. As a result, manufacturing could finish without causing
shape collapse.

Figure 6

Effect of monitoring feedback(3) Abnormality detection during manufacturing process
When an abnormality occurs, the melt pool image shows some changes from the normalstate. By capturing these changes, the abnormality can be detected. Typical types ofMitsubishi Heavy Industries Technical Review Vol. 57 No. 3 (September 2020)
5abnormalities are as follows.
1. Sputter
Sputter may be produced when the manufacturing conditions are unstable. Sputter
affects the manufactured metal quality.
2. Dirt on protective glass
Dirt may adhere to the protective glass in the manufacturing nozzle due to sputter
caused by poor manufacturing conditions or fumes generated from the melt pool. The dirt on
the protective glass lowers the laser transmittance and may cause defective manufacturing or
damage to the nozzle.
3. Foreign matter adhered to nozzle
If sputter, etc., produced during manufacturing adheres to the nozzle, the adhesion area
may generate heat and damage the nozzle.
Abnormality detection is not a matter of simply checking whether a threshold has been
exceeded, but rather requires complex criteria that are close to human perception. Therefore, we
incorporated AI in the monitoring system to detect abnormalities. The left side of Figure 7 gives
examples of abnormalities occurring during manufacturing, and the right side shows images of theabnormalities at the time of occurrence. It can be seen that there is a difference between the imagesof the normal and abnormal states. The prompt detection of anomalies during manufacturing not
only prevents manufacturing defects, but also protects the manufacturing head from damage. Thisreduces downtime as a result.

Figure 7

Abnormality detection during manufacturing|5. Manufacturing case examples
This section introduces manufacturing case examples of LAMDA.

5.1

Titanium alloy aircraft part

A titanium alloy (Ti6Al4V) simulated shape with a tilted cylinder and ribs, that is assumed tobe used as a general aircraft part, was manufactured under an atmospheric environment using a
local shield nozzle. Figure 8 shows the manufactured result. This part was manufactured using a
LAMDA 500 prototype machine with a cutting spindle. By adding a cutting process in the middleof the manufacturing process, a highly-accurate finish was obtained. By using near net shape
manufacturing of titanium alloy parts, it is expected that the product lead time will be shortened
and the processing cost will be reduced.

5.2

Low thermal expansion alloy bracket

Figure 9 shows a manufactured sample made of super invar, which is a low thermalexpansion alloy. Super invar has a very small coefficient of linear expansion, about 1/100 of that ofiron, and is often used for parts in environments with severe temperature changes and precisionparts. On the other hand, since it is a difficult-to-process material with low thermal conductivity,
the advantages of near net shape manufacturing are significant. In general, high-performancematerials often take a long time to procure. However, additive manufacturing of such a material canbe performed as long as the metal powder is in stock, so the lead time can be significantly
shortened.

Mitsubishi Heavy Industries Technical Review Vol. 57 No. 3 (September 2020)
65.3

Hollow gear

Figure 10 is a hollow gear manufactured as a sample for display by manufacturing stainlesssteel SUS304 on a SS304 substrate. The use of metal-based additive manufacturing makes it
possible to manufacture hollow parts that could not be made by conventional removal processing.

Figure 8 Titanium alloy
part

Figure 9 Low thermal
expansion alloy bracket

Figure 10 Hollow gear
sample|6. Conclusion
This report introduced the principle and features of powder DED metal-based additive
manufacturing, and the powder feeding nozzle, local shield and monitoring function of LAMDA
that realize the stable manufacturing of high precision parts. Moving forward, we will further
improve these technologies, actively promote trial manufacture and evaluation to expand
applications and work on the spread and practical application of metal-based additive
manufacturing technologies.
This research and development effort uses the achievements of the Ministry of Economy,
Trade and Industry commissioned project "Monozukuri Revolution Program using 3D shaping
technologies as a core (Technological Development for Next-Generation Industrial 3D Printers andUltra-High-Precision 3D Shaping Systems)," as well as from a project supported by the New
Energy and Industrial Technology Development Organization (NEDO).

References(1)(2)

Technology Research Association for Future Additive Manufacturing, Shaping inspiration! New
Manufacturing with Changing Designs，Proceedings of the 4th symposium p.54~60 (2018)，p.54～60
Haruhiko Niitani et al., Development of Metal-based Additive Manufacturing System with Directed
Energy Deposition Technology, Mitsubishi Heavy Industries Technical Review Vol. 55 No. 3 (2018)