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The status and research progress of selectivelaser melting additive manufacturing

Yongqiang Yang, Fan Fu, Di Wang, Changhui Song

(School of Mechanical and Automotive Engineering, South China University

of Technology, Guangzhou 510641, China)

Abstract: With the development and research progress of additive

manufacturing technology, direct manufacturing of metal functional

parts has become the research hotspot, and the application field has

also expanded to aerospace, biomedicine, automobile and mold.

This paper introduces the principle, characteristics, application and

domestic research status of SLM technology，elaborates the research

achievements of SLM technology in South China University of Technology

and the application of the technology in various fields. Material, molding

size, precision, performance and the application of SLM technology in

depth have been discussed, and analyzed.

Key words: additive manufacturing; selective laser melting; powder

material; applications

DOI: 10.7512/ j.issn.1001-2303.2017.13.26

Prof. Yongqiang YangEmail: meyqyang@scut.edu.cn

0 IntroductionWith the rapid development of additive manufacturing（AM）

technology, the mode of production and lifestyle formed since the

industrial revolution are gradually changing. As a strategic emerging

industry, AM technology has attracted huge attention from the United

States, Germany and other developed countries and these countries

promote the technology actively. In 2012, the US President Barack

Obama issued a statement of State of the Union speech giving strong

support to 3D printing which also named AM, then it became a hot

spot among the world's technology industry. In recent years, owing

to personalization, customization combined with digital network, AM

industry continues to develop and expand [1]. Up to now, several direct

manufacturing methods have been developed, like fused deposition

modeling (FDM), electron beam fusion (EBM), selective laser melting

(SLM), selective laser sintering (SLS), and digital light processing

(DLP) [2]. Among them, SLM direct manufacturing technology which

is the most cutting-edge and most potential technology in the AM

system, leads the development direction of advanced manufacturing

technology. SLM is beneficial to achieve the new concept "near

net forming" for material processing and is particularly suitable for

manufacturing metal parts with complex structures to meet limited

order requirements or special customization requirements in biomedical

areas, defense, aerospace [3], such as satellite applications, in particular,

radio-frequency components [4]. With the continuous upgrading of the

manufacturing industry, the development of science and technology

and the demand for application promotion, the utilize of SLM to direct

manufacture functional parts [5] has become the main direction of its

development.

1 The introduction of SLM additive manufacturing technologySLM is a kind of additive manufacturing (3D printing), adapting the

principle of rapid prototyping. That is, designing the three-dimensional

parts of the solid model on computer through software first, and then

the data will be sliced and the contour data of each section of the

three-dimensional model will be obtained through dedicated software[6].

The data will be imported into the rapid prototyping equipment.

The equipment then control the laser beam to selectively melt metal

powder of each layer and gradually stack into three-dimensional metal

parts according to these contour data. The laser beam rapidly melts

the metal powder and obtains a continuous fused channel, which

can manufacture metal parts in almost any shape, with complete

metallurgical bonding, high precision and density. The process of SLM

is shown in Figure 1[7], in the molding process, the right side powder

cylinder up a set value, the powder roller moves to the left and the left

Yongqiang Yang, professor, director of the Department of Electrical and Mechanical Engineering, School of Mechanical and Automotive Engineering, South China University of Technology.

He has been done the research work in the field of laser additive manufacturing technology, laser processing and welding technology, publishing more than 240 academic papers.

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side molding cylinder plate coated with a layer of uniform powder.

Then the metal powder layer melted by SLM, the three-dimensional

metal parts formed layer by layer. The entire process is carried out in

a molding chamber with an inert gas protection to prevent the metal

from reacting with other gases at high temperatures.

Fig. 1 Schematic diagram of SLM molding

The existing powder coating device in the SLM equipment show

high applicability to Fe-based, Ni-based, Ti-based and other types

metal powder materials, but the applicability to Al-alloy powder is low,

resulting in its SLM molding process is difficult to proceed smoothly.

2 The research status of SLM technology in ChinaIn recent years, SLM technology and industry developed rapidly,

new materials and process continue to emerge. The application of

SLM has been extended to aerospace, automobile manufacturing, bio-

medical, jewelry and other industries. In the past few years, aircraft

manufacturing and medical applications are the fastest growing areas

of SLM, industrial output maintain a large increase every year, more and

more enterprises engaged in. The research on the theory and process

of SLM for metal parts is relatively early abroad and a number of mature

SLM equipment manufacturers have emerged including EOS, MCP,

Concept Laser, SLM Solutions and American 3D company.

Domestic research on SLM start relatively late, at the beginning of

1990s, Xi'an Jiao Tong University, Huazhong University of Science and

Technology, Tsinghua University, Beijing Longyuan company has made

significant progress in molding equipment, typical software, materials

and other aspects of SLM research and industrialization under the

support of the State Ministry of science and technology. Subsequently,

many domestic universities and research institutions have carried

out relevant research, such as Northwestern Polytechnical University,

Beihang University, South China University of Technology(SCUT) and

other units.

In the research of SLM on light alloy such as titanium alloy and

Aluminum Alloy. The Gu Dongdong team of Nanjing University of

Aeronautics and Astronautics has systematically developed Ti-based

metal element with high precision, complex structure, net molding,

shape and property control [8]. Northwest University of Technology

Huang Weidong team made an in-depth study on AM process of high-

performance metal in the field of aviation and has successfully repaired

aero engine blades, some developed metal parts as shown in Figure 2 [9].

Fig. 2 Complex parts developed by Northwest University of Technology

The Beijing University of Aeronautics and Astronautics Wang

Huaming team long-term commit to the research on laser direct

manufacturing process, internal quality control and application of large-

scale titanium alloy structure, the manufacturing process for high-

performance metal components has been successfully used in the

development of a variety of domestic large aircraft [10].

Lu Bingheng team of the Xi'an Jiao Tong University made a deep

research on laser AM process of titanium alloy. Based on powder

focusing control, combined scanning mode, layer-by-layer power

control and other molding process basis, the complex titanium alloy

whole turbine blade sample was molded out [11]. Yang Yongqiang team

of SCUT focus on the research and development of SLM equipment

and has developed DiMetal-240, DiMetal-280, DiMetal-100 and other

types SLM equipment [12], as shown in Figure 3.

(a) DiMetal —100 (b) DiMetal —280

Fig. 3 Two SLM equipments developed by SCUT

3 The application status of SLM technology in ChinaIn recent years, as SLM technology continues to become mature and

commercial, its application area become more and more broad. SLM

has high molding precision and excellent comprehensive mechanical

properties, can directly mold precise metal parts to meet practical

engineering applications. So it has important applications in many fields,

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such as biomedicine, mold manufacturing, automobile, jewelry, aviation

and spaceflight.

3.1 The application of SLM in biomedicine

The application of AM technology in domestic medical industry

began in the late 1980s, initially mainly for the rapid manufacturing

of 3D medical models. In recent years, with the development of AM

technology and the growth of precise and personalized medical

needs. Additive manufactured biomaterials such as 316L stainless steel,

titanium-6 aluminum-4 vanadium (Ti6Al4V) and cobalt-chromium

(CoCr) are widely used in clinical practice [13]. The application of SLM

in medical industry has continued to grow and gradually use for direct

manufacturing Orthopedic implants, customized prostheses and

prostheses [14]. There are also some domestic enterprises that carry out

research and explorations in SLM for biomedicine, such as Changzhou

Watson medical equipment, Trauson medical equipment, Guangzhou

Medprin regenerative medical technologies Co., Ltd, Shenzhen KTJ and

other enterprises. Changzhou Watson Medical Devices has developed

a full range of orthopedic products for different regions (especially for

our Asian human body). Including the series of spine, trauma series

(stainless steel and titanium alloy plate series, bone screw series and

intramedullary nail series), a new series of locking plate, artificial joints

and prosthesis series of orthopedic products.

( a ) Customized orthopedic implant ( b ) Anterior cervical plate system

Fig. 4 Two SLM medical products developed by Watson

Dongguan EONTEC is committed to the development of

biodegradable magnesium alloy orthopedic implants products, and is

expected to achieve the clinical application of degradable magnesium

alloy in short term. Degradable magnesium alloy which is regarded as

the new generation of biomedical materials with many advantages

over traditional materials, in line with the development trend of

biomedical materials, can be used to develop new medical devices with

unique performance. its clinical application will be a milestone in the

development of biomedical materials.

Fig. 5 Biodegradable Mg-Alloy implant developed by Eontec

3.2 The application of SLM in mold

From a global perspective, the production of molds mainly

concentrated in China, Japan, the United States and Germany. The

quantity of mold enterprise in China is up to 20 000. At present,

the application of SLM technology in the field of mold is mainly

concentrated in the production of high-end metal mold with cooling

channel [15], which has obvious effect on improving the manufacturing

capability of high-end mold [16]. Dongjiang mold, Dongguan

RATC, Shenzhen Sunshine, Shanghai Risemold Laser and other

Chinese companies have implied SLM technology maturely to mold

manufacturing. Dongjiang mold use SLM process to manufacture

conformal waterway inside the mold, which greatly enhance the mold

cooling efficiency. The injection cycle increased by 21.7%, injection cost

decreased 110000RMB and monthly economic benefits increased by

94 000RMB. Shanghai UREAL 3D technology developed a wave roller

washing machine mold through the design of balanced distribution of

waterway to provide superior cooling consistency, to ensure uniform

product contraction and improve product quality. The high-efficiency

conformal waterway inside cannot be limited by shape, completely

attached to the surface of mold, substantially increase the efficiency

of mold cooling to reduce the deformation caused by uneven mold

temperature, as shown in Figure 6.

Fig. 6 A wave roller washing machine mold with high-efficiency

conformal waterway developed by UREAL

3.3 The application of SLM in aerospace

SLM technology helps aerospace companies create extremely

complex parts without molding and forging, shorten production cycles,

reduce component weight and the number of parts required for the

equipment, resulting in cost savings and increased reliability [17]. Due

to the molding size constraints of SLM, the research work focuses

on the molding of small precise parts of aeroengine and spacecraft.

Northwestern Polytechnical University and Beihang University are

the most representative units in China to research AM technology in

aviation manufacturing field. Recently, SCUT has also begun to research

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the application of SLM process in aerospace.

In 2016, Northwestern Polytechnical University and China Aerospace

Science and Industry Corporation 31 Institute made a breakthrough in

SLM application in the field of turbine engine applications [18], realized

the SLM of rotor parts, which was the first time in China to achieve SLM

molding process on rotor parts.

3.4 The application of SLM in other fields

In addition to the application of SLM technology in the field of

biomedicine, mold manufacturing and aerospace, the application trend

is also deepening in jewelry, automotive, home appliances, cultural

creativity, innovative education and other fields [19]. Jewels manufactured

by SLM have high density and complex geometric shapes which

can bring designer freedom. In the future, the personalization and

customization of jewelry will be further developed, bring consumers

more choices, as well as in the field of cultural creativity and innovative

education.

4 The research progress of SLM technology in SCUT4.1 SLM equipment development

Since 2002, the AM research team of SCUT gradually make some

progress in SLM and then start SLM equipment research work. Under

the joint efforts of the team, the AM laboratory of SCUT developed

the first set of domestic SLM equipment DiMetal-240 in 2004[20], and

in 2007 developed DiMetal-280, in 2012 DiMetal-100 developed,

in which the DiMetal-100 equipment has entered commercial stage

and the tiny DiMetal-50 equipment is also in development stage. The

main application areas of these equipments include precise industrial

components, biomedical prostheses or auxiliary equipment. Figure

7 shows that the SLM series equipments are equipped in the AM

laboratory of SCUT which also developed independently by itself.

Fig.7 The SLM series equipments equipped in the AM laboratory of SCUT

4.2 Clinical application of personalized and customized surgical Guide

The AM team of SCUT entered the medical field to research medical

applications of SLM by virtue of the SLM series equipment developed

independently, and promote SLM technology a rapid development in

biomedicine. In 2013, Professor Yang led the team to overcome the

development work of personalized and customized surgical Guide[21]

which has high processing speed, high dimensional accuracy and

nice appearance after molding. The surgical guide is manufactured

through SLM equipment with stainless steel or titanium alloy. The

surgical guide made by SLM not only can meet the requirements of

personalized surgery which means manufacturing a matching surgical

guide according to the requirements of different patients, but also can

ensure the operation stable for the reason that the surgical guide made

by SLM owns better biomedical compatibility, high safety and sufficient

mechanical strength. The research work done by SCUT provide a new

processing method for personalized medical implant and auxiliary

equipment.

Fig. 8 The applications of surgical guide manufactured by SLM

4.3 The design and direct manufacturing of personalized knee

prosthesis and implant

The traditional standardized prosthesis implantation method

has changed to personalized SLM direct manufacturing aided by

computer design. In the study of the design and direct manufacturing

of individualized knee prosthesis and implant based on SLM

technology [22], the most suitable knee prosthesis model is going to

be designed according to individual characteristics of the patient.

Using SLM equipment, adapting stainless steel or cobalt chrome alloy

and other materials as raw material for manufacturing bought high

processing speed and dimensional accuracy [23], which also opened up

a new processing method for personalized medical implant with high

performance and achieve the application of SLM technology in clinical

surgery.

( a ) ( b )

( c ) ( d )

Fig. 9 Design process demonstration of knee prosthesis

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Fig. 10 SLM direct modeling of knee prosthesis

4.4 Study on SLM process and performance of personalized CoCr Alloy

dental crowns and fixed bridges

The AM team of SCUT specializes in the research and development

of medical materials AM process, such as cobalt-chromium alloy and

titanium alloy. The connected research project of this technology is

the manufacturing process and performance research of SLM for

personalized CoCr alloy CoCr Alloy dental crowns and fixed bridges.

In the field of oral medicine, CoCr alloy is treated as an important

medical dental material because of its good mechanical properties,

biocompatibility and corrosion resistance [24]. SLM process not only

meets the trend of stable, fast and low cost of modern digital dental

technology, but also can meet the individual needs of patients,

realizing digitalization, customization, networked treatment and rapid

manufacturing [25]. A SLM equipment can replace the 10 000-month

production line of denture by worker, of which the quality of stability

and consistency are far more than the traditional casting process and

other processes. Figure 11 and 12 shows the process of manufacturing

cobalt-chromium alloy dental crown and fixed bridges by DiMetal-100.

Fig.11 The printing process of DiMetal--100

Fig. 12 Personalized dental crowns and fixed bridges by SLM

5 Development Trend of SLM technology5.1 Study on new material

SLM technology and industry ushered in a high-speed development

period since 2012. New materials and processes continue to emerge,

the materials that have been developed are Fe-based alloy, Al-based

alloy, Ti-based alloy, Ni-based alloy, Co-based alloy, Cu-based alloy

Materials, gradient functional materials and other materials [26]. Currently

the most widely used metal powder in the market is cobalt-chromium

alloy, Ti6Al4V, austenitic stainless steel, tool steel and other powder. The

materials mentioned above own a density of nearly 100% by SLM, its

mechanical properties are better than castings and some performance

indicator even far beyond the forging level. Rhenium alloy, molybdenum

alloy, tungsten alloy, titanium, tantalum, vanadium, gradient functional

materials, intermetallic compounds and other aerospace materials

are also gradually developed SLM process or connected laser direct

manufacturing process.

5.2 Study on size, precision and performance of parts manufactured by SLM

In order to ensure the mechanical properties of parts in traditional

CNC machining, more time was spent on the parts for aging, heat

treatment and other related work in the production process. In

SLM process, it cannot guarantee the toughness and strength of

components because of a lack of heat treatment, which is one of the

toughest problems in SLM technology that needs to be overcame [27]. The

next key research point is how to improve SLM technology, combined

with metal heat treatment technology to improve the strength,

toughness, surface hardness and other mechanical properties of the

components manufactured by SLM. In addition, due to a "step effect" in

SLM process, the accuracy of molding parts needs to be improved, such

as product shape accuracy, dimensional accuracy, position accuracy,

surface roughness. SLM technology now is mainly used in rapid

development of new concept products and the manufacturing of small

parts in small quantities to shorten the processing cycle. The application

of SLM for the processing of bulk products is still very small.

5.3 Study on the application of SLM

There is no doubt that SLM has a bright future, but the constraints

of it in the current stage is also very obvious. With the deepening of

research on SLM technology in China, if we can effectively solve the

species scarcity of raw material, size of the molded parts, precision

problems and some defects caused by itself, such as "step effect", SLM

technology will have a wider application space.

6 Conclusion(1 ) This paper introduces the principle, material, application

and commercialization of SLM technology, describes in detail the

manufacturing process and technical details of SLM and points out

some existing problems in SLM process.

(2) In view of the research and application of SLM technology in

China, this paper discusses materials, processes and applications of

SLM in detail and clarifies the research focus and achievements of SLM

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Reference: