This additive prototyping method is based on the use of a high power fiber laser. The main consumable material is a powder metal alloy.

The developers of this technology are employees of the Institute of Laser Technology Wilhelm Meiners, Konrad Wissenbach and employees of F&S Stereolithographietechnik GmbH Dieter Schwarz and Matthias Fokele. An interesting fact is that Schwartz still works at the former F&S, which eventually turned into SLM Solutions GmbH, and Fokele created the main competitor of this company - ReaLizer GmbH.

But let's return to technology. SLM allows you to print objects with an accuracy within 20-100 microns; a layout in STL format is used as a drawing of the future product. A thin layer of powder is applied to the working surface, which is located in a chamber filled with an inert gas (mainly argon). The complete absence of contact of the metal with oxygen prevents its oxidation, which makes it possible to work even with titanium alloys that are difficult to process. Each new layer is fused with the previous one under the influence of a laser beam directed in the coordinate plane.

The consumable materials used are stainless and tool steel, gold, silver, aluminum, titanium and alloys based on cobalt and chromium. This technology is considered the best for the manufacture of thin-walled objects with complex geometries, which are successfully used in the mechanical engineering, aerospace industries, the automotive industry, and medicine.

The most similar technologies are direct metal laser sintering (DMLS) and electron beam melting (EBM).

SLM printing technology - the price of the best quality equipment

SLM is a modern technology for 3D printing of complex structures or parts by laser melting of metal powders. The method for obtaining 3D objects allows us to produce particularly accurate results, both individual elements and finished large-sized products. Our company invites clients to place an order for services for creating products that use SLM printing technology. The price on the website will pleasantly surprise you. You will also find a huge selection of 3D printers using SLM printing technology in an affordable price range. We work with official dealers, so we can reduce the cost of goods and services to a minimum without sacrificing quality.

Advantages of using SLM printing technology

With the help of SLM, manufacturers of products with complex geometric shapes have the opportunity to solve any technological problem. The technology is ideal for the manufacture of parts and structures with complex configurations, multiple cavities and channels on the inside.

SLM also allows you to significantly save on consumables, since construction is carried out by layer-by-layer adding the required amount of filament. Remaining materials are screened and prepared for reuse.

Since complex products are manufactured using technology, there is no need to purchase additional expensive equipment.

SLM technology has found wide application in various fields:

• at industrial enterprises;
• aerospace industry;
• mechanical engineering;
• instrument-making industry;
• in educational institutions;
• for research and experimental work.

How is a 3D object built with SLM technology?

The workflow is initially started by dividing the digital model into layers to produce a 2D image. Next, the resulting file is analyzed by the software, and after processing the information, the construction cycle starts:

• A layer of metal powder is applied to the platform.
• Then the surface is scanned with a laser beam.
• The platform is lowered down by an amount in accordance with the thickness of the construction layer.

After completing the work process, the platform is removed and the product is separated from the platform mechanically.

SLM or Selective laser melting is an innovative technology for the production of complex products by laser melting of metal powder using mathematical CAD models (3D metal printing). With the help of SLM, they create both precision metal parts for work as part of components and assemblies, and non-separable structures that change geometry during operation.

The technology is an additive manufacturing method and uses high-power lasers to create three-dimensional physical objects. This process successfully replaces traditional production methods, since the physical and mechanical properties of products built using SLM technology often exceed the properties of products manufactured using traditional technologies.

SLM installations help solve complex production problems of industrial enterprises operating in the aerospace, energy, mechanical engineering and instrumentation industries. The installations are also used in universities, design bureaus, and are used in research and experimental work.

The official term to describe the technology is “laser sintering,” although it is somewhat misleading, since the materials (powders) are not sintered, but melted until a homogeneous (thick, pasty) mass is formed.

Advantages

1. Solving complex technological problems

• Production of products with complex geometries, with internal cavities and conformal cooling channels

Shortening the R&D cycle

• The ability to build complex products without manufacturing expensive equipment

Reducing product weight

• Construction of products with internal cavities

Material savings during production

• Construction occurs by layer-by-layer adding the required amount of material to the “body” of the product. 97-99% of the powder not used in the construction after sifting is suitable for reuse. 3-9% of the material used to construct supports is disposed of along with substandard unfused powder that has not undergone sieving.
• Reducing costs for the production of complex products, because there is no need to manufacture expensive equipment.

Areas of use

• Manufacturing of functional parts for work as part of various components and assemblies
• Manufacturing of complex structures, including non-separable structures that change geometry during operation, as well as those containing many elements
• Production of forming elements of molds for casting thermoplastics and lightweight materials
• Production of technical prototypes to test product designs
• Creation of forming inserts for die casting
• Production of customized dental prostheses and implants
• Making stamps.

How it works

The printing process begins by dividing a digital 3D model of a product into layers ranging from 20 to 100 microns thick to create a 2D image of each layer of the product. The industry standard format is the STL file. This file enters special machine software, where the information is analyzed and compared with the technical capabilities of the machine.

Based on the data obtained, a production construction cycle is launched, consisting of many cycles of constructing individual layers of the product.

The layer construction cycle consists of standard operations:

1. applying a layer of powder of a given thickness (20-100 microns) to a build plate mounted on a heated build platform;
2. scanning a cross-section of a product layer with a laser beam;
3. lowering the platform deep into the construction well by an amount corresponding to the thickness of the construction layer.

The process of building products takes place in the SLM chamber of the machine, filled with inert gas argon or nitrogen (depending on the type of powder from which the construction takes place), with its laminar flow. The main consumption of inert gas occurs at the beginning of work, when purging the construction chamber, when air is completely removed from it (the permissible oxygen content is less than 0.15%).

After construction, the product along with the slab is removed from the SLM chamber of the machine, after which the product is separated from the slab mechanically. Supports are removed from the constructed product, and finishing processing of the constructed product is performed.

The almost complete absence of oxygen avoids oxidation of the consumable material, which makes printing with materials such as titanium possible.

Materials

The most popular materials are powdered metals and alloys, including stainless steel, tool steel, cobalt-chrome alloys, titanium alloys, titanium, aluminum, gold, platinum, etc.

Products made with SLM Solutions 3D machines

Products made by Realizer 3D machines

Video: using SLM technology

SLM (Selective Laser Melting) - selective laser melting - an innovative technology for manufacturing complex in shape and structure products from metal powders using mathematical CAD models. This process consists of sequential layer-by-layer melting of powder material using powerful laser radiation. SLM opens up the broadest opportunities for modern production, as it allows you to create metal products of high precision and density, optimize the design and reduce the weight of manufactured parts.

Selective laser melting is one of the metal 3D printing technologies that can successfully complement classical manufacturing processes. It makes it possible to manufacture objects whose physical and mechanical properties are superior to products of standard technologies. Using SLM technology, it is possible to create unique, complex-profile products without the use of machining and expensive equipment, in particular, due to the ability to control the properties of products.

SLM machines are designed to solve complex problems in energy, oil and gas, engineering industries, metalworking, medicine, etc. They are also used in research centers, design bureaus and educational institutions when conducting research and experimental work.

The term “laser sintering,” which is often used to describe SLM, is not entirely accurate, since the metal powder fed to the 3D printer under the laser beam is not sintered, but is completely melted and converted into a homogeneous raw material.

Examples of application of selective laser melting technology

Where is SLM technology used?

Selective laser melting is used in industry for the manufacture of:

• components of various units and units;
• structures of complex shape and structure, including multi-element and non-removable;
• stamps;
• prototypes;
• jewelry;
• implants and prostheses in dentistry.

Data analysis and product design

First, the digital 3D model of the part is divided into layers so that each layer, which is 20-100 microns thick, is rendered in 2D. Specialized analyzes the data in the STL file (industry standard) and compares it with the specifications of the 3D printer. The next stage after processing the received information is construction, which consists of a large number of cycles for each layer of the created object.

Layer construction includes the following operations:

• metal powder is applied to the build plate, which is fixed to the build platform;
• the laser beam scans the cross-section of the product layer;
• the platform is lowered into the construction well to a depth that matches the thickness of the layer.

The construction is carried out in the chamber of an SLM machine, which is filled with an inert gas (argon or nitrogen). The main volume of gas is consumed at the initial stage, when all air is removed from the construction chamber by purging. Upon completion of the construction process, the part and the plate are removed from the powder 3D printer chamber, and then separated from the plate, the supports are removed, and the final processing of the product is performed.

Advantages of selective laser melting technology

SLM technology has serious prospects for increasing production efficiency in many industries because:

• provides high accuracy and repeatability;
• the mechanical characteristics of products printed with this type of 3D printer are comparable to;
• solves complex technological problems associated with the manufacture of geometrically complex products;
• shortens the cycle of research and development work, ensuring the construction of complex-profile parts without the use of equipment;
• allows you to reduce weight by constructing objects with internal cavities;
• saves material during production.

SLM Solutions: integrated system solutions for metal 3D printing

Products created on the SLM Solutions installation

SLM Solutions, headquartered in Lübeck, Germany, is a leading developer of metal additive manufacturing technologies. The company's main activity is the development, assembly and sale of equipment and integrated system solutions in the field of selective laser melting. iQB Technologies is the official distributor of SLM Solutions in Russia.

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Parts & Materials

3D printing for industry: a detailed overview of the latest equipment and technologies

At the exhibition formnext Traditionally, the elite from the world of additive technologies and 3D printing gather. World-class experts have noted the transition from the creation of prototypes to the production of parts and blanks from metals and functional materials.

Classic SLM, EBM and DMD technologies when working with metals have been complemented by relatively new CSF and FDM-like technologies. A detailed review of equipment, materials and advanced solutions presented in Frankfurt am Main, from expert Kirill Kazmirchuk.

Selective laser melting(SLM - Selective Laser Melting)

A hybrid system that uses the SLM process and 3-axis CNC machining in one piece of equipment.

This approach makes it possible to obtain metal parts with internal channels of low roughness.

Working area: 600 x 600 x 500 mm

Trumpf TruPrint 5000

SLM machine from a company that produces a wide range of laser equipment. The special feature of TruPrint 5000 is its replaceable working modules. They allow you to launch a construction without lengthy preparation. “Unpacking” of the build takes place outside the machine in a special “unpacking-cleaning” station.

Round working area: Ø300 x 400 mm

Materials: Al, Ti, Ni, Co-Cr, Steel.

SLM-Solutions SLM 800

The largest machine from the company, a pioneer in the SLM technology segment. At the beginning of 2017, the purchase of SLM-Solutions by industry giant General Electric was announced. The deal did not take place due to differences of opinion on the value of the shares. As a result, GE acquired another company, Concept Laser.

Car SLM 800 was announced at formnext-2016 and presented to the public at the 2017 exhibition. During the exhibition, according to SLM-Solutions itself, twenty units of this equipment were sold.

Working area: 280 x 500 x 800 mm

Materials: Al, Ti, Ni, Co-Cr, Steel.

Since the beginning of the year, more than 15 cars have been sold SLM 500, mainly to China.

Electro Optical Systems M400-4

SLM machine with working area 400 x 400 x 400 mm

Materials: Al, Ti, Ni, Co-Cr, Steel.

Four lasers are used, each covering a quarter of the working area. This allows you to significantly reduce the time for building a large number of small parts, but when manufacturing one large part, the time is reduced by up to 10%. Potentially, thermal distortion is reduced due to a more uniform fusion process.

Additive IndustriesMetalFab1

MetalFab1 is a complex of equipment: SLM machine + cleaning station + heat treatment furnace. Technologically, transitions take place in an isolated space; accordingly, the operator’s contact with metal powders is reduced.

Working area 420 x 420 x 400 mm

Materials: Al, Ti, Ni, Co-Cr, Steel.

Concept Laser (company acquiredGeneral Electric at the beginning of 2017)

The car was presented Atlas with a working area of ​​1000 x 1000 x 1000 mm.

Shown is a prototype of this machine and a part built on a 1000 x 1000 mm platform.

Materials: Al, Ti, Ni, Co-Cr, Steel.

The release date has not been made public.

Currently the current model is X- line 2000 with two lasers and a working area of ​​800 x 400 x 500 mm.

Orlas Creator

ORlaser has been known to develop heads for hot laser powder deposition for several years. Now we have introduced our own SLM machine with a working area of ​​Ø 100 mm x 110 mm.

This is a small device with a cylindrical working area. Additionally, it can be equipped with a spindle for CNC machining.

A French company developing with the active participation of tire manufacturer Michelin. The main products are SLM layer-by-layer synthesis machines.

The peculiarity of these installations is that they specialize in using finer metal powder (about 20 microns), while the typical particle size in similar equipment is 40 - 60 microns. A smaller particle size, on the one hand, gives better surface quality and elaboration of small geometric details, on the other hand, it imposes a significant limitation on the use of powder. Finer powder is more difficult to handle and requires isolated rooms and protective equipment for operators.

Working area: 350 x 350 x 350 mm.

DMG MORI

The company is a manufacturer of CNC machines for turning, turning-milling and milling groups. For about five years, it has been promoting to the market a hybrid technology for manufacturing metal parts: DMD surfacing + CNC machining. Hybrid technology in the automotive industry is mainly suitable for repair tasks - restoration of crankshaft journals, camshaft cams.

In 2017, the LASERTEC 30 SLM SLM machine of its own design with a working area of ​​300 x 300 x 300 mm was shown.

The applicability of the technology for the manufacture of heat exchangers and small brackets with complex geometry is shown.

A Portuguese company that produces a wide range of equipment for metal processing (hydraulic sheet benders, guillotine metal cutting, laser cutting, etc.). The newcomer to additive technologies, however, presented what they claim is the largest SLM machine with a working area of ​​1000 x 1000 x 500 mm.

The machine uses only one laser, and the principle of a movable construction zone allows it to cover a large area. The construction takes place on a platform measuring 1000 x 1000 mm; a square chamber with a radiation source and a local supply of inert gas moves above it. The construction process is step-by-step, and the metal is fused in the required places. Potentially, this approach involves greater consumption of inert gas and limits the construction of large parts. At the moment, the process is debugged only for steels.

3 D Systems

An interesting addition to the company’s line is the ProX 320 SLM machine with a working area of ​​275 x 275 x 420 mm.

An SLM machine was also announced DMP8500 with a working area of ​​500 x 500 x 500mm. The advantage of 3D Systems machines is the ability to work with both standard powder of 40-60 microns and fine powder of about 20 microns.

E.B.M.-technologies

Arcam Q20 Plus(purchasedGeneral Electric at the beginning of 2017)

The only company is a manufacturer of EBM machines. The equipment is specialized for the use of titanium alloys. Using an electron beam instead of a laser can significantly improve the quality of metal fusion and increase speed.

Working area: Ø 350 x 380 mm.

Material: Ti6Al4V.

Cold gas-dynamic surfacing (cold spray)

The essence of the technology is to apply powder particles using a supersonic jet of transport inert gas. Due to the high speed, the particles adhere to the surface, providing a dense metal structure. Potentially, this approach allows the construction of workpieces in less time than laser cladding, due to the absence of heating and subsequent cooling.

SPEE3D

The American company SPEE3D introduced in 2017 a hybrid machine that allows you to create metal blanks using cold gas-dynamic surfacing followed by CNC processing.

Due to technological limitations, the technology is applicable for creating workpieces for subsequent CNC processing. The quality of the surface shown in the photo is comparable to casting.

Aluminum and copper alloys can be applied.

The German company - manufacturer of CNC machines presented its own hybrid equipment CSF + CNC machining.

Parts are formed sequentially from several materials, and cold surfacing is used to create cooling channels and cavities inside the molds. A more fusible metal is applied to the required areas and acts as a removable support. Aluminum and copper alloys can be applied.

ImpactInnovations

Equipment for cold gas-dynamic surfacing with switching of materials during the manufacturing process. Allows the application of aluminum and copper alloys (including on the surface of non-metals). The technology can be useful in creating bimetallic products (sliding bearings), as well as in applying conductive “paths” to textolite or other polymer products.

Hot surfacing

The essence of the technology is to apply powder particles using a jet of transport and protective inert gas; the metal melts upon contact with a laser-heated surface.

The technology is suitable for the manufacture of parts to a very limited extent, mainly only for creating a body. More suitable for repairing shafts and other rotating bodies.

InssTek,BeAM- Korean and French companies, respectively. The equipment is built on a similar principle and has similar capabilities.

It is possible to “switch” materials during the manufacturing process.

InssTek has a large working area of ​​4000 x 1000 x 1000 mm.

Products require subsequent thermal and mechanical treatment.

DMGMORI

Pioneer in hybrid (surfacing + CNC) technology for metal products. First, the lasertec 65 3D combination machine was released, then the lasertec 4300 3D was added to the hybrid line.

Similar machines are manufactured today by the Yamazaki Mazak company.

CEFERTEC

The equipment was developed with the participation of the FIT AG service bureau and, to put it simply, is a CNC metal welding machine.

Built on the basis of a portal and a rotary table.

The technology allows you to quickly create metal blanks. The approach raises many questions about product quality and properties, as well as inevitable warping during a localized thermal process.

Metals and FDM technology

The principle of construction is the extrusion of a plastic material (filled with metal powder) through a die. After creating a polymer-metal model, it is sintered in an oven (thermal or microwave). At this stage, the polymer binder evaporates and the metal particles sinter. In this case, the shrinkage of the part is 18-20%, see photo below. According to anecdotal evidence, this technology potentially allows parts to be built up to 100 times faster.

DesktopMetal And Markforged- American companies, they use similar technology, the working area is 330 x 330 x 330 mm and 250 x 220 x 200 mm, respectively. It is worth noting the significant difference in the degree of readiness for delivery. If DesktopMetal is not ready to supply equipment even to the local market, then Markforged is ready to supply both the USA and Europe. A feature of all Markforged equipment is that the file is sent for construction when connected to the Internet and company servers, which raises the issue of maintaining trade secrets.

On the one hand, FDM technology looks promising because it allows you to produce metal parts without the need to work with difficult-to-handle metal powders. On the other hand, many questions remain, such as the maximum wall thickness (may be limited due to the need to remove the binder), the lack of similar equipment with a large working area, etc. The technology will certainly find its niche, but it cannot be considered as a “killer” or replacement for SLM technology.

X- Jet

An Israeli company, the main staff of which are employees of Objet, the pioneer of PolyJet technology.

An analogue of this technology is also used in X-jet equipment: a water-based liquid binder is applied to the platform, in which metal or ceramic particles are distributed. The filler does not stick together and does not precipitate due to van der Waals forces.

The parts also require heat (and possibly pressure) treatment after the layer-by-layer synthesis process. The manufacturer does not specify the details of the technical process, and the metal and ceramic samples shown at the exhibition do not exceed a few centimeters in size, but the detailing is at a high level.

Working area 500 x 280 x 200 mm.

High strength PEEK thermoplastics

Group materials PEEK(polyetheretherketone) are very interesting for direct production due to their strength and heat resistance. Heat resistance up to 250 °C, and tensile strength 100 MPa (for comparison, for aluminum, depending on the alloy, it varies from 100 to 350 MPa). It is difficult to process such material due to its high melting point - above 340 °C. Three FDM machines for working with PEEK were presented at once: INNOVATOR 2 PEEK, INTAMSYS PEEK And GEWO 3D PEEK.

The largest machine has a working area of ​​450 x 450 x 600 mm and an extruder temperature of up to 450 °C.

Sand printers for foundries

VoxelJet

ExOne and Voxeljet were originally one and created equipment for working with sand and polymer materials for foundry applications.

The companies split in 2003, Voxeljet continues to develop both areas, while ExOne (formerly Prometal RCT) focuses only on sand technology and partly on working with steel-bronze materials.

Voxeljet's range includes several systems that can process sand to create molds and cores. All of them are similar in mechanics and process to ExOne equipment.

As part of formnext-2017, the company presented a system for working with functional polymer materials. The technology is based on the already mastered PolyJet with a photosensitive binder; this not only makes it possible to achieve improved properties, but also allows the creation of products of higher resolution. The technology is similar to what Hewlett Packard showed at the 2016 exhibition.

A Korean company that has several industrial additive manufacturing machines in its lineup:

– sand PolyJet printer with a working area of ​​300 x 420 x 150 (inorganic binder, more environmentally friendly);

– sand SLS printer with a working area of ​​600 x 400 x 400;

– SLM machine with a working area of ​​350 x 300 mm;

– hybrid machine (surfacing + CNC processing) with a working area of ​​250 x 250 x 250 mm.

Metal powders

The largest manufacturers of metal powder compositions were widely represented at the exhibition: Haraeus,LPWSMTChina,Oerlikon,EPMA And Polema(Russia).

AtomizerATOone

Installation for the production of powder metal compositions for layer-by-layer synthesis machines from the Polish company 3D lab.

This is an “office” atomizer with a height of no more than 2 meters; the typical size of industrial atomizers is 5-10 m in height and about 4 m in diameter.

Wire is used as the processing material, and the equipment’s capacity allows it to produce up to 200 grams per day.

Polymer materials and equipment

Composites

Markforged

FDM equipment is presented that allows you to work with thermoplastics filled with carbon, Kevlar and glass fibers. They can be either continuous or chopped.

The cost of installation is about 100-1000 euros.

In the photo from top to bottom:

– part made of Onyx material (chopped fiber);

– sectional view of a part made of Onyx material (chopped fiber);

– reinforced with continuous Kevlar;

– reinforced with continuous glass fiber;

– reinforced with continuous carbon fiber.

Stratasys

The company introduced Nylon CF material, compatible with the Russian Fortus 450mc FDM machine. It is a polyamide filled with chopped carbon fibers.

It provides better mechanical properties compared to standard unfilled materials. The photo shows a comparison of the behavior of materials under loading (right ABS, in the center Nylon CF, left Nylon 12).

Desktop SLA and elastic materials

DigitalWax And atum 3D

The working area of ​​the larger machine is 300 x 300 x 300 mm, photopolymer materials are available, both functional and elastic.

UNIZ SLA

The Chinese company UNIZ is a newcomer to the market. Two desktop SLA machines are presented with working areas: 315 x 185 x 450 and 192 x 122 x 200. The manufacturer claims that this is the fastest SLA machine. Experts have yet to figure out what kind of materials the system uses and what determines the speed of construction of 2500 cubic meters. cm per hour (50% filling).

Both systems use illumination of the photopolymer using LEDs (LCD-Stereolithography).

Japanese company with a long history. Engaged in the production of a variety of high-precision equipment - from printers to microscopes. Presented its own Agilista 3D printer using PolyJet technology. The emphasis is on the ability to produce flexible and heat-resistant silicone products. Such equipment can be useful in the manufacture of small series of grommets, door seals, air duct pipes, etc.

Working area: 297 x 210 x 200 mm.

Materials: polymer compositions based on silicone, including heat-resistant up to 100 °C.

Electro Optical Systems

SLS machine P500 from EOS - one of the market leaders. Working area 500 x 330 x 400 mm, two 70W lasers for accelerated work, sintering temperature up to 300 °C and building speed up to 6.6 liters per hour (20% more than market analogues).

The system is equipped with a replaceable work area with controlled cooling, which increases the load percentage and dimensional stability of products. The SLS machine software allows you to connect to the enterprise's ERP system and monitor the job completion percentage in real time.

Material: polyamide, PEKK in development.

Polish SLS machine, capable of working with polyamide powder.

Working area: 350 x 350 x 600 mm.

Large SLA machines

RPS was founded in the UK by employees of DTM and 3D Systems and has been in business for over ten years.

It began its activities with the maintenance and restoration of layer-by-layer synthesis machines.

A large SLA machine was released in 2016 NEO 800 own development.

Working area: 800 x 800 x 600 mm.

Materials: photopolymer compositions from DSM Somos and any others.

Stereolithography machine from a European company, manufactured in China.

Working area: 700 x 700 x 450 mm.

Materials: photopolymer compositions from DSM Somos and any others, including those from Raplas.

Ceramics

To work with ceramics, as a rule, they use SLA technology, these are companies Ceramaker And Lithoz.

In the classic SLA process, a workpiece is created, the so-called green model. After construction, it undergoes a heat treatment procedure, where the polymer component is removed and ceramic particles are sintered.

Services

In Europe, production sites are successfully developing, providing services for the production of prototypes from polymers, composites and metals using additive technologies.

The leading companies in this market are: PolyShape, Hoffmann, CitimGMBH,FITA.G.. The latter recently opened a branch in Russia.

The arsenal of such companies includes a wide range of DMD, SLM, SLS, FDM, EBM equipment; the number of additive manufacturing employees is usually about 100-200 people. The companies are in demand on the market; below are the revenue indicators for 2016: Hofmann GMBH – $833.2 million, CITIM GMBH – $27.3 million, FIT AG – $24 million.

It should be noted that in October 2017 the plant ACTech was acquired by Materialize and will soon develop direct production of metal parts using additive technologies.

Tomography

VisiConsult And Werth- manufacturers of tomographs presented their small devices for tomography of metal and polymer parts. The industry is starting to think about product control. This is a sign that parts are increasingly being used as end products.

Software

In this review, I tried to present in a popular form basic information about the production of metal products using laser additive manufacturing - a relatively new and interesting technological method that arose in the late 80s and has now become a promising technology for small-scale or single-piece production in the field of medicine, aircraft - and rocket science.

The operating principle of a laser-assisted additive manufacturing installation can be briefly described as follows. A device for applying and leveling a layer of powder removes a layer of powder from the feeder and distributes it evenly over the surface of the substrate. After which the laser beam scans the surface of this layer of powder and forms the product by melting or sintering. At the end of scanning the powder layer, the platform with the product being manufactured is lowered to the thickness of the applied layer, and the platform with the powder is raised, and the process of applying the powder layer and scanning is repeated. After the process is completed, the platform with the product is raised and cleared of unused powder.

One of the main parts in additive manufacturing installations is the laser system, which uses CO 2 , Nd:YAG, ytterbium fiber or disk lasers. It has been established that the use of lasers with a wavelength of 1-1.1 microns for heating metals and carbides is preferable, since they absorb laser-generated radiation 25-65% better. At the same time, the use of a CO 2 laser with a wavelength of 10.64 microns is most suitable for materials such as polymers and oxide ceramics. Higher absorption capacity allows you to increase the depth of penetration and vary the process parameters within a wider range. Typically, lasers used in additive manufacturing operate in continuous mode. Compared to them, the use of lasers operating in pulsed mode and in Q-switched mode due to their high pulse energy and short pulse duration (nanoseconds) makes it possible to improve the bond strength between layers and reduce the thermally affected zone. In conclusion, it can be noted that the characteristics of the laser systems used lie within the following limits: laser power - 50-500 W, scanning speed up to 2 m/s, positioning speed up to 7 m/s, focused spot diameter - 35-400 microns.

In addition to the laser, electron beam heating can be used as a source of heating the powder. This option was proposed and implemented by Arcam in its installations in 1997. An installation with an electron beam gun is characterized by the absence of moving parts, since the electron beam is focused and directed using a magnetic field and deflectors, and the creation of a vacuum in the chamber has a positive effect on the quality of products.

One of the important conditions for additive manufacturing is the creation of a protective environment that prevents oxidation of the powder. To fulfill this condition, argon or nitrogen is used. However, the use of nitrogen as a shielding gas is limited, which is associated with the possibility of the formation of nitrides (for example, AlN, TiN in the manufacture of products from aluminum and titanium alloys), which lead to a decrease in the ductility of the material.

Laser additive manufacturing methods, according to the characteristics of the material compaction process, can be divided into selective laser sintering (Selective Laser Sintering (SLS)), indirect metal laser sintering (IMLS), direct metal laser sintering (DMLS) ) and selective laser melting (SLM). In the first option, compaction of the powder layer occurs due to solid-phase sintering. In the second, due to the impregnation of a porous frame previously formed by laser radiation with a binder. Direct laser sintering of metals is based on compaction using the liquid-phase sintering mechanism due to the melting of a low-melting component in a powder mixture. In the latter option, compaction occurs due to complete melting and spreading of the melt. It is worth noting that this classification is not universal, as one type of additive manufacturing process may exhibit compaction mechanisms that are characteristic of other processes. For example, DMLS and SLM may exhibit solid phase sintering, which occurs with SLS, while SLM may exhibit liquid phase sintering, which is more common with DMLS.

Selective Laser Sintering (SLS)

Solid-phase selective laser sintering is not widely used, since a relatively long exposure under laser radiation is required for a more complete occurrence of volumetric and surface diffusion, viscous flow and other processes that take place during powder sintering. This leads to long laser operation and low process productivity, which makes this process economically unfeasible. In addition, difficulties arise in maintaining the process temperature in the range between the melting point and the solid-phase sintering temperature. The advantage of solid-phase selective laser sintering is the ability to use a wider range of materials for the manufacture of products.

Indirect metal laser sintering (IMLS)

The process, called indirect metal laser sintering, was developed by DTMcorp of Austin in 1995, which has been owned by 3D Systems since 2001. The IMLS process uses a mixture of powder and polymer or powder coated with a polymer, where the polymer acts as a binder and provides the necessary strength for further heat treatment. At the heat treatment stage, the polymer is distilled off, the frame is sintered, and the porous frame is impregnated with a binder metal, resulting in a finished product.

For IMLS, powders of both metals and ceramics or mixtures thereof can be used. The preparation of a mixture of powder and polymer is carried out by mechanical mixing, while the polymer content is about 2-3% (by weight), and in the case of using a powder coated with a polymer, the layer thickness on the surface of the particle is about 5 microns. Epoxy resins, liquid glass, polyamides and other polymers are used as binders. The temperature of polymer distillation is determined by the temperature of its melting and decomposition and averages 400-650 o C. After polymer distillation, the porosity of the product before impregnation is about 40%. During impregnation, the furnace is heated 100-200 0 C above the melting point of the impregnating material, since with increasing temperature the contact angle of wetting decreases and the viscosity of the melt decreases, which has a beneficial effect on the impregnation process. Typically, impregnation of future products is carried out in a backfill of aluminum oxide, which plays the role of a supporting frame, since during the period from the distillation of the polymer to the formation of strong interparticle contacts there is a danger of destruction or deformation of the product. Protection against oxidation is organized by creating an inert or reducing environment in the furnace. For impregnation, you can use quite a variety of metals and alloys that satisfy the following conditions. The material for impregnation must be characterized by the complete absence or insignificant interfacial interaction, a small contact angle and have a melting point lower than that of the base. For example, if the components interact with each other, then undesirable processes may occur during the impregnation process, such as the formation of more refractory compounds or solid solutions, which can lead to the stop of the impregnation process or negatively affect the properties and dimensions of the product. Typically, bronze is used to impregnate a metal frame, and the shrinkage of the product is 2-5%.

One of the disadvantages of IMLS is the inability to regulate the content of the refractory phase (base material) over a wide range. Since its percentage in the finished product is determined by the bulk density of the powder, which, depending on the characteristics of the powder, can be three or more times less than the theoretical density of the powder material.

Materials and their properties used for IMLS

Direct metal laser sintering (DMLS)

The direct metal laser sintering process is similar to IMLS, but differs in that alloys or compounds with low melting points are used instead of polymer, and there is no technological step such as impregnation. The DMLS concept was created by the German company EOS GmbH, which in 1995 created a commercial installation for direct laser sintering of steel-nickel bronze powder systems. The production of various products by the DMLS method is based on the flow of the resulting melt-binder into the voids between the particles under the action of capillary forces. At the same time, to successfully complete the process, compounds with phosphorus are added to the powder mixture, which reduce the surface tension, viscosity and degree of oxidation of the melt, thereby improving wettability. The powder used as a binder is usually smaller in size than the base powder, as this increases the bulk density of the powder mixture and speeds up the melt formation process.

Materials and their properties used for DMLS by EOS GmbH

Selective Laser Melting (SLM)

Further improvements in additive manufacturing facilities include the ability to use a more powerful laser, a smaller focal spot diameter, and a thinner powder layer, which has made it possible to use SLM for the production of products from a variety of metals and alloys. Typically, products obtained by this method have a porosity of 0-3%.
As in the methods discussed above (IMLS, DMLS), wettability, surface tension and melt viscosity play a big role in the manufacturing process of products. One of the factors limiting the use of various metals and alloys for SLM is the “beading” effect or spheroidization, which manifests itself in the form of the formation of droplets lying separately from each other, rather than a continuous melt path. The reason for this is surface tension, under the influence of which the melt tends to reduce the free surface energy by forming a shape with a minimum surface area, i.e. ball. In this case, the Marangoni effect is observed in the melt strip, which manifests itself in the form of convective flows due to the surface tension gradient as a function of temperature, and if the convective flows are strong enough, the melt strip is divided into individual drops. Also, a drop of melt, under the influence of surface tension, draws in nearby powder particles, which leads to the formation of a pit around the drop and, ultimately, to an increase in porosity.

Spheroidization of M3/2 steel under non-optimal SLM conditions

The spheroidization effect is also facilitated by the presence of oxygen, which, dissolving in the metal, increases the viscosity of the melt, which leads to a deterioration in the spreading and wettability of the melt below the underlying layer. For the reasons listed above, it is not possible to obtain products from metals such as tin, copper, zinc, and lead.

It is worth noting that the formation of a high-quality melt strip is associated with the search for the optimal range of process parameters (laser radiation power and scanning speed), which is usually quite narrow.

Influence of gold SLM parameters on the quality of the formed layers

Another factor affecting the quality of products is the appearance of internal stresses, the presence and magnitude of which depends on the geometry of the product, heating and cooling rates, coefficient of thermal expansion, phase and structural changes in the metal. Significant internal stresses can lead to deformation of products and the formation of micro- and macrocracks.

The negative impact of the above mentioned factors can be partially reduced by using heating elements, which are usually located inside the installation around the substrate or feeder with powder. Heating the powder also removes adsorbed moisture from the surface of the particles and thereby reduces the degree of oxidation.

When selective laser melting of metals such as aluminum, copper, gold, an important issue is their high reflectivity, which necessitates the use of a powerful laser system. But increasing the power of the laser beam can negatively affect the dimensional accuracy of the product, since with excessive heating the powder will melt and sinter outside the laser spot due to heat exchange. High laser power can also lead to a change in the chemical composition as a result of metal evaporation, which is especially typical for alloys containing low-melting components and having high vapor pressure.

Mechanical properties of materials obtained by the SLM method (EOS GmbH)

If a product obtained by one of the methods discussed above has residual porosity, then, if necessary, additional technological operations are used to increase its density. For this purpose, powder metallurgy methods are used - sintering or hot isostatic pressing (HIP). Sintering allows you to eliminate residual porosity and increase the physical and mechanical properties of the material. It should be emphasized that the formed properties of the material during the sintering process are determined by the composition and nature of the material, the size and number of pores, the presence of defects and other numerous factors. HIP is a process in which a workpiece placed in a gasostat is compacted under the influence of high temperature and compression by an inert gas. The operating pressure and maximum temperature achieved by the gasostat depend on its design and volume. For example, a gasostat having a working chamber dimensions of 900x1800 mm is capable of developing a temperature of 1500 o C and a pressure of 200 MPa. The use of HIP to eliminate porosity without the use of a hermetic shell is possible if the porosity is no more than 8%, since at a higher value, gas will enter the product through the pores, thereby preventing compaction. It is possible to prevent the penetration of gas into the product by making a sealed steel shell that follows the shape of the surface of the product. However, products produced by additive manufacturing generally have complex shapes, which makes it impossible to produce such a shell. In this case, for compaction, you can use a vacuum-sealed container in which the product is placed in a granular medium (Al 2 O 3, BN hex, graphite), which transmits pressure to the walls of the product.

After additive manufacturing using the SLM method, materials are characterized by anisotropy of properties, increased strength and reduced ductility due to the presence of residual stresses. To remove residual stresses, obtain a more equilibrium structure, and increase the viscosity and plasticity of the material, annealing is carried out.

According to the data below, it can be noted that products obtained by selective laser melting are, in some cases, stronger than cast ones by 2-12%. This can be explained by the small size of grains and microstructural components that are formed as a result of rapid cooling of the melt. Rapid supercooling of the melt significantly increases the number of solid phase nuclei and reduces their critical size. At the same time, the rapidly growing crystals on the nuclei, coming into contact with each other, begin to impede their further growth, thereby forming a fine-grained structure. Crystallization nuclei are usually nonmetallic inclusions, gas bubbles, or particles released from the melt with their limited solubility in the liquid phase. And in the general case, according to the Hall-Petch relation, as the grain size decreases, the strength of the metal increases due to the developed network of grain boundaries, which is an effective barrier to the movement of dislocations. It should be noted that due to the different chemical composition of the alloys and their properties, the conditions for carrying out SLM, the above-mentioned phenomena that occur during cooling of the melt manifest themselves with different intensities.

Mechanical properties of materials produced by SLM and casting

Of course, this does not mean that products obtained by selective laser melting are better than products obtained by traditional methods. Due to the great flexibility of traditional methods for producing products, the properties of the product can be varied within wide limits. For example, using methods such as changing the temperature conditions of crystallization, alloying and introducing modifiers into the melt, thermal cycling, powder metallurgy, thermomechanical processing, etc., it is possible to achieve a significant increase in the strength properties of metals and alloys.

Of particular interest is the use of carbon steel for additive manufacturing, as a material that is cheap and has a high range of mechanical properties. It is known that with increasing carbon content in steel, its fluidity and wettability improve. Thanks to this, it is possible to obtain simple products containing 0.6-1% C with a density of 94-99%, while in the case of using pure iron the density is about 83%. In the process of selective laser melting of carbon steel, the melt path, when rapidly cooled, is quenched and tempered into a troostite or sorbitol structure. At the same time, due to thermal stresses and structural transformations, significant stresses can arise in the metal, which lead to the product being damaged or to the formation of cracks. The geometry of the product is also important, since sharp transitions along the cross-section, small radii of curvature and sharp edges cause the formation of cracks. If after “printing” the steel does not have a given level of mechanical properties and it must be subjected to additional heat treatment, then it will be necessary to take into account the previously noted limitations on the shape of the product in order to avoid the appearance of hardening defects. This to some extent reduces the prospects of using SLM for carbon steels.
When producing products using traditional methods, one of the ways to avoid cracks and leads when hardening products of complex shape is the use of alloy steels, in which the alloying elements present, in addition to increasing the mechanical and physico-chemical properties, delay the transformation of austenite during cooling, as a result of which the critical hardening rate decreases and the hardenability of alloy steel increases. Due to the low critical quenching rate, steel can be heated in oil or in air, which reduces the level of internal stresses. However, due to rapid heat removal, the impossibility of regulating the cooling rate and the presence of carbon in alloy steel, this technique does not avoid the occurrence of significant internal stresses during selective laser melting.

In connection with the above-mentioned features, martensitic steels (MS 1, GP 1, PH 1) are used for SLM, in which strengthening and increased hardness are achieved due to the release of dispersed intermetallic phases during heat treatment. These steels contain a small amount of carbon (hundredths of a percent), as a result of which the martensite lattice formed during rapid cooling is characterized by a low degree of distortion and, consequently, has low hardness. The low hardness and high plasticity of martensite ensures relaxation of internal stresses during hardening, and the high content of alloying elements allows steel to be calcined to a great depth at almost any cooling rate. Thanks to this, SLM can be used to manufacture and heat treat complex products without fear of cracking or warping. In addition to maraging steels, some austenitic stainless steels, such as 316L, can be used.

In conclusion, it can be noted that the efforts of scientists and engineers are now aimed at a more detailed study of the influence of process parameters on the structure, mechanism and features of compaction of various materials under the influence of laser radiation in order to improve the mechanical properties and increase the range of materials suitable for laser additive manufacturing.