Introduction

Metal 3D printing, also known as Metal Additive Manufacturing (MAM) is a disruptive manufacturing technology that offers a whole new world of possibilities.It is a process that uses metal materials to build up parts and products, from a digital model, in layers. It can produce complex shapes that are difficult to achieve using conventional machining methods. Hence, it is true that in terms of offerings this technology not only offers new levels of design freedom but it is also about the sheer choice of metal materials that can be used with metal 3D printers. Metal Additive Manufacturing opens a world of new applications and opportunities —

1. One great example is in the transportation sector, where it can enable lightweight engineering and design techniques, which are becoming more important in efforts to reduce and redistribute a vehicle’s mass, in order to save energy during use, reduce manufacturing costs or improve the working performance.
2. In the medical and orthodontic sectors, it allows for the cost-effective production of customized products that are personalized and “tuned” to a patient’s individual needs — and this level of flexibility also points to the potential for use within the consumer goods market.

Metal Additive Manufacturing is being adopted by companies focused on innovation and creating new value. However, there are still some challenges that must be overcome — including education around applications, Design for Additive Manufacturing (DfAM), industry standards, regulations, certifications and metal materials quality — to accelerate its widespread adoption.

Different Metal 3D printing technologies

An important starting point is understanding the main Metal Additive Manufacturing technologies and processes, in order to define which is most suitable for a specific application. Further, the choice of the right technology and machine for your application completely depends on various factors, including specifications, budget, and product lifecycle.

Metal powder is the backbone of metal 3D printing. Though it is difficult and dangerous to handle in its raw state, its unique features make it the preferred metal stock type, hence, the vast majority of metal 3D printing technologies utilize metal powder.

There are a few different metal 3D printing technologies and these methods vary greatly, ranging from using high energy lasers to fuse loose powder to extruding bound metal powder filament. In this article, we will take a look at the most heavily used types of metal 3D printing:

1. Powder Bed Fusion: A common method that uses heat or light to fuse metal powder into layers, one on top of the other. Powder bed melting is currently the most common type of metal 3D printing. These machines distribute a fine layer of powder over a build plate and selectively melt a cross section of the part into the powder layer. There are distinct types of powder bed melting techniques based on the different ways of how they fuse the powder into metal parts:

   1. Selective Laser Melting: SLM is a type of rapid prototyping that uses a laser to selectively melt and fuse metallic powder material, layer by layer, to build a 3D part. It can produce geometrically complex parts,such as hollow, porous, or bonded structures, with great precision. They fit into a wide variety of applications: from dental/healthcare to aerospace. Build volumes range from very small (100mm cube) to large (800mm x 500mm x 400mm) and print speed is moderate. Precision of these machines is determined by laser beam width and layer height. While these machines are groundbreaking, a wide variety of facility and post processing requirements limit these machines to industrial users. SLM machines require trained professionals to operate them. Because of its intricate process, many parts need to be printed and tweaked a few times to yield results. Yet, the majority of Powder Bed Fusion machines are Selective Laser Melting (SLM) machines and it is the current standard for metal printing – most companies in Metal AM today sell SLM machines.

   2. Direct Metal Laser Sintering (DMLS): DMLS is another type of 3D printing technology that uses a laser to fuse together metal powder layer by layer. DMLS can create complex geometries, such as internal channels, lattices, and complex surface textures. It can be used for prototypes, low-volume parts, and end-use parts but unlike SLM, DMLS can be used with metals that have a high melting point, such as stainless steel and cobalt chrome. Also, DMLS offers a higher build rate than SLM, making it ideal for large-scale production runs. Perhaps the most significant limitation is the initial cost of the machines and materials.

   3. Electron Beam Melting: EBM machines use an electron beam instead of a laser to fabricate parts. GE Additive is the only company producing EBM machines. The electron beam yields a less precise part than SLM, but the process as a whole is faster for larger parts. These machines have almost all of the same constraints, costs, and issues as SLM machines, but are used more heavily in aerospace and medical applications than anywhere else. Similarly to SLM, EBM machines cost upwards of 1M to set up and require a dedicated technician to run.

2. Direct Energy Deposition: A method that uses a laser or electron beam to melt metal feedstock (which can be powder, called Powder DED or wire, called Wire DED) as it is deposited onto a build platform. Unlike powder bed fusion, instead of spreading powder on a bed and melting it with a laser, DED machines precisely blow powder out of a print head, using an on-head laser to fuse it to the part in construction. So, the stock and the laser both sit on a single print head that dispenses and fuses material simultaneously. The resultant parts are very similar to Powder Bed Fusion, with a few key differences and opportunities like DED machines can produce dense parts as they can work with high material deposition rates.

3. Binder Jetting: A process that uses a print head to deposit a liquid binding agent onto a thin layer of powder particles. The technology behind metal binder jetting reflects what a conventional (2D) printer uses to quickly jet ink onto paper. First, a binder jetting machine evenly distributes metal powder over its print bed, forming an unbound layer. Then, a jetting head much like one in a 2D printer distributes binding polymer in the shape of the part cross section, loosely adhering the powder. The process repeats until the machine yields a finished build of completed parts.

Parts printed on Binder Jetting machines require a post processing step called “sintering” to become fully metallic. In this process, the printed part is heated in an oven to just below its melting temperature. The binding material burns away and the metal powder unites into a full metal part. This process can be done in batches, meaning that it doesn’t significantly affect throughput.

Binder Jetting is a large-scale, high fidelity method of metal 3D printing that may replace SLM as the premier loose powder based method of 3D printing as Binder Jetting holds two main advantages over Selective Laser Melting. First, machines can print much faster by using multiple heads to jet in several places simultaneously. Second, the machine can make tens or even hundreds of the same part in one build. These parts can be sintered in a large furnace to achieve a manageable batch production infrastructure. As a result Binder Jetting is significantly faster on a per part basis than any other type of metal printing. Due to its speed and scalability, it may be the technology that propels metal additive manufacturing capabilities into production volumes but with this speed (and powder management requirements) comes massive costs – currently, the only machines in this space cost well over a million dollars.

4. Bound Powder Extrusion: A method that uses waxy polymers to bind metal powder together, so the powder isn’t lost. Bound Powder Extrusion (BPE) is an exciting newcomer to the metal additive manufacturing space. Unlike almost every other major 3D printing process, BPE machines do not use loose metal powder. Instead, the powder is bound together in waxy polymers in the same way that metal injection molding stock is created. The result is a material that’s much safer and easier to use than loose powder: bound powder extrusion material can be handled by hand and does not require the safety measures that loose powder machines do. BPE filament is extruded out of a nozzle in a manner very similar to standard FDM 3D printing, yielding a “green” part that contains metal powder evenly distributed in waxy polymer. After printing, BPE has two post processing steps: first, the polymer is mostly dissolved in a “wash” machine; second the washed part is sintered in an oven (similar to binder jetting). During the sintering process, the part shrinks to account for the space opened up by the dissolved binder, yielding a fully metallic part. Parts printed on BPE systems still often require post-processing – heat treatment for parts that need advanced properties (though this is required for every metal), and post machining/polishing for enhanced surface finishes – but there’s no powder management and reduced facility requirements. As a filament based printing process, the part constraints of BPE parts closely mirror those of conventional FDM plastic printing: it works well for almost all part geometries, and can print with open cell infill. BPE machines leverage a simpler process to be much more affordable than all other major types of metal 3D printing, with machines costing between $120,000 and $200,000.

SLM Overview

Compared to the SLA, FDM or SLS processes, which were all patented towards the end of the 1980s, selective laser melting emerged somewhat later. The first notable successes were announced in 1995 by the Fraunhofer Institute for Laser Technology in Aachen. In cooperation with the company F&S Stereolithografietechnik GmbH, the SLM 3D printing process was developed. The company split in the early 2000s into Realizer GmbH, which today belongs to DMG Mori AG, and SLM Solutions AG, which is still one of the leading suppliers for SLM metal 3D printing. The basic fabrication process is for SLM is:

• First, SLM metal 3D printers use a CAD file as a blueprint for the desired part. The data set is cut into a number of layers by a slicer. Each layer forms a cross-section through the component. A layer thickness in SLM 3D printing usually varies between 20 and 60 micrometers.
• The build chamber is first filled with inert gas (for example argon) to minimize the oxidation of the metal powder and then it is heated to the optimal build temperature.
• A thin layer of metal powder is spread over the build platform and a high-power laser scans the cross-section of the component, melting (or fusing) the metal particles together and creating the next layer. The entire area of the model is scanned, so the part is built fully solid.
• When the scanning process is complete, the build platform moves downwards by one layer thickness and the recoater spreads another thin layer of metal powder. The process is repeated until the whole part is complete.

When the build process is finished, the parts are fully encapsulated in the metal powder and are attached to the build platform through support structures. Support in metal 3D printing is built using the same material as the part and is always required to mitigate the warping and distortion that may occur due to the high processing temperatures.

When the bin cools to room temperature, the excess powder is removed, manually or automatically, and the parts are typically heat treated while still attached to the build platform to relieve any residual stresses. Then the components are detached from the build plate via cutting, machining or wire EDM and are ready for use or further post-processing.

SLM Printer Components

SLM machines consist of a laser, scanner system, powder bed, recoater mechanism and several main sub-systems and components that work together to enable the additive manufacturing process. Some key things to know about SLM equipment:

• Works with various metals including stainless steels, titanium, aluminum, nickel alloys, and more
• Uses a high power laser to selectively melt metal powder particles in a powder bed
• Builds parts layer-by-layer by spreading thin layers of powder and scanning the laser to melt the cross-section
• Produces fully dense metal parts with mechanical properties comparable to traditional manufacturing
• Enables complex geometries not possible with conventional subtractive methods
• Well-suited for small batch production, customized parts, and rapid prototyping

Some main components of a selective laser melting (SLM) machine are:

Few other components are various sensors and the integrated control software converts CAD data into instructions for the equipment to follow layer-by-layer.

SLM Printer Design

SLM machines involve precision design and engineering across optical, mechanical, electronic, and software systems. Some key design factors include:

• Laser optics – Well-configured galvo/mirror system for accurate laser steering and spot sizing.
• Powder handling – Minimizing jamming and ensure smooth powder flow.
• Gas flow – Managing laminar flow across powder bed.
• Build plate – Withstanding repeated high temperatures.
• Controls – Precisely monitoring and adjusting parameters in real-time.
• Filters – Capturing micron-scale metallic particles and powder.
• Contamination prevention – Keeping sensitive optics clean.
• Calibration – Maintaining alignment and calibration during operation.
• Automation-readiness – Allowing integration of material handling systems.

Careful SLM equipment design is needed to achieve repeatable, high-quality builds in a production environment. Leading manufacturers continue to refine the hardware and software for better process control.

SLM Printer Types

SLM machines can be compared by various technical specifications and performance parameters. Here are some key specifications to consider for SLM systems: like the inert gas consumable usage, filtering system effectiveness, software capabilities, and more:

• Build volume: The maximum size of part that can be printed, which can range from a few centimeters for desktop machines to over a meter for larger systems
• Laser type: Fiber lasers are faster, while CO2 lasers are less expensive
• Automation – Industrial systems have higher levels of automation and control.
• Inert gas use – Larger machines often use inert argon gas, while smaller machines use air
• Price – Desktop and benchtop models are lower cost with reduced capacity.In general, industrial systems offer larger build volumes, higher laser power, faster scanning speeds, and better process control compared to desktop models.

The main factors that differentiate SLM machine types include:

Based on the various technical specifications and performance parameters as discussed above, there are several categories and types of SLM equipment available from various manufacturers. Here is a comparison:

So in summary, desktop and benchtop SLM equipment is well-suited for prototyping and R&D purposes while industrial and large-format systems are designed for volume production applications. Consider build size, price, quality needs and other requirements when selecting an SLM machine type. PREPed Metal Powders

Market Players

There are a range of companies that manufacture and provide SLM 3D printing solutions. Here are some of the major suppliers:

In addition, there are a growing number of suppliers from Asia that offer more affordable desktop SLM printers including:

• Farsoon
• Longer 3D
• Raycham
• Wiiboox
• Creality

When selecting an SLM vendor, first narrow down the shortlisted vendors based on build specifications, price range, and risk tolerance. Then schedule equipment demos and evaluate sample part quality firsthand from potential suppliers before final purchase decision. The key considerations to select a vendor should include build quality, reliability, service, customer support, powder handling features, software capabilities, pricing, and prior user experiences. Original equipment manufacturers tend to offer proven technology and performance. Selecting the right SLM equipment and supplier should is an important decision. Here are key considerations when choosing an SLM supplier:

• Build quality – Evaluate sample parts to ensure good density, properties, accuracy.
• Reliability – Seek field data on meantime between failures and longevity.
• Technical support – Assess response time and support infrastructure.
• Warranty – Review warranty terms on hardware, optics, etc.
• Training – Check availability of operation and maintenance training.
• Materials range – Consider available powder materials and quality.
• Software – Examine built-in software capabilities and ease of use.
• Regional presence – Determine availability of local application engineers.
• Service contracts – Compare post-sale maintenance contracts and SLAs.
• Pricing – Balance purchase cost, TCO and performance value.

SLM Equipment Pricing

The cost of slm equipment can range quite widely depending on the build volume, features, and manufacturer. Here is an overview of typical pricing ranges:

In general, industrial SLM systems from original equipment manufacturers cost between $300,000 to $1,000,000. Larger build envelopes, higher powered lasers, and greater automation increase the price. Affordable desktop models from Asian suppliers are available under $100,000. Many offer similar capabilities to higher priced equipment but may lack reliability, performance, or service.

Total costs also include ongoing operating costs for metal powders, filters, gas supplies, maintenance, repairs, and spare parts which can be substantial. Both equipment purchase costs and operating costs should be considered.

SLM Printer Installation

Proper installation of SLM equipment helps ensure safe and optimal operation. Here are key installation steps:

• Unpack machine components carefully and check for damage.
• Position on sturdy frame or table to minimize vibration.
• Level build platform precisely.
• Connect chiller, gas supplies, ventilation ducting.
• Install fume extraction unit/filter.
• Connect electrical power supply.
• Install and calibrate all optics and laser path.
• Test motion of recoater, powder system.
• Integrate monitoring sensors.
• Establish closed-loop powder handling system.
• Initialize and calibrate machine settings.
• Perform sample test builds and validate quality.

Adequate facility preparation is also required including space, power supply, stable temperature/humidity, ventilation, hazardous material handling capabilities, and more. Installation is typically completed by the equipment manufacturer representatives.

SLM Printer Operation

Operating an SLM machine requires careful supervision, system monitoring, standard protocols, and build validation. Here are key operating procedures:

• Import and prepare 3D CAD model into slicer software.
• Select process parameters and generate build files.
• Sieve and load metal powder into system.
• Select and mount build plate.
• Adjust layer thickness, laser power, speed, etc.
• Initiate inert gas flow and preheat powder bed.
• Initiate first layer powder spreading and laser scanning.
• Periodically monitor temperature, powder levels, gas flow.
• Allow layers to complete until full build height is reached.
• Remove build plate when finished and recover part.
• Remove excess powder using blasting techniques.
• Post-process part as needed – annealing, machining, etc.

Critical process parameters that are controlled include laser power, scanning pattern, scanning speed, hatch spacing, layer thickness, preheat temperature and others. Real-time monitoring and adjustment is often required. Safety equipment for respiratory and eye protection along with hazardous power training is mandatory. Parts also undergo validation testing to verify required material properties.

SLM Printer Maintenance

Routine preventative maintenance helps maximize uptime and performance. Maintenance tasks include:

• Cleaning – Keep optics, laser path and sensors clear of dirt and debris.
• Calibration – Realign and calibrate sensors, lasers, optics.
• Filter change – Replace air and powder filters regularly.
• Recoater – Lubricate/replace recoater blades, adjust gap.
• Laser – Monitor beam quality and adjust resonator alignment.
• Motion – Lubricate linear stages, replace worn components.
• Powder – Dispose excess powder regularly to avoid clumping/caking.
• Safety checks – Confirm status of gas detectors, alarms, sensors.
• Firmware – Install software and firmware updates from vendor.

Manufacturers provide maintenance manuals detailing schedules for daily, weekly, monthly recommended maintenance. Consumable parts like filters and recoater blades require routine change outs. Maintenance contracts can provide regular preventative service.

SLM Materials

Selective laser melting is used to process metals. The development of new materials is a continuously advancing field of research, and new suppliers or established companies are constantly entering the market with a greater variety of materials. The most established materials for SLM 3D printing include aluminum (AlSi10Mg), stainless steel (1.2709 & 1.4404) and titanium (Ti6Al4V).

SLM Applications

SLM technology is well-suited for various applications across different industries. Many industries like aerospace, automotive engineering, dental and medical technology, and mechanical engineering, benefit from selective laser melting as an additive manufacturing technology. The technology is used in particular for rapid prototyping, but small series can now also be economically produced using SLM metal 3D printing. The high precision, small feature size, and excellent mechanical properties of SLM make it ideal for consolidating assemblies into one part, weight reduction, complex cooling channels, freeform shapes, rapid turnaround, and fabricating lightweight, optimized and custom components across sectors. Here are some typical applications:

• Aerospace – Turbine blades, structural brackets, rocket nozzles
• Automotive – Lightweighting parts, custom tooling
• Medical – Orthopedic implants, prosthetics, surgical instruments
• Industrial – Heat exchangers, fluid handling parts
• Defense – Components for firearms, armor
• Jewelry – Customized precious metal jewelry

SLM Advantages and Limitations

Like the vast majority of 3D printing technologies, selective laser melting also brings with it a great deal of geometric freedom. This means that highly complex geometries and bionic lightweight construction projects can be implemented without tools. Assembly consolidation is another advantage of SLM and also other 3D printing technologies. This involves bringing together individual assemblies and printing them directly in one piece to reduce material and labor and assembly costs. But it’s not just the geometric freedom of the technology that makes exciting components possible. The component properties themselves can also be improved by the SLM process. For example, the components are characterized by a particularly high density and almost pore-free surfaces. But, like any technology, SLM has both advantages and limitations to consider:

Conclusion

SLM provides transformative capabilities for dense, high-performance metal part production. Understanding the different equipment types, working principles, specifications, applications, and advantages allows the technology to be leveraged effectively. With continual advances in machines, materials, software, and process control, SLM promises to become even more competitive against conventional manufacturing.

Reference

1. Shanghai Truer Technology Co., Ltd: https://am-material.com/news/complete-guide-to-slm-equipment/
2. Voxeljet: https://www.voxeljet.com/additive-manufacturing/3d-printing-processes/selective-laser-melting/#:~:text=The%20most%20established%20materials%20for,)%20and%20titanium%20(Ti6Al4V).
3. Markforged: https://markforged.com/resources/learn/design-for-additive-manufacturing-metals/metal-additive-manufacturing-introduction/types-of-3d-printing-metal
4. Protolabs Network: https://www.hubs.com/knowledge-base/introduction-metal-3d-printing/#how-does-metal-3d-printing-work
5. HP: https://www.hp.com/us-en/printers/3d-printers/products/metal-jet.html
6. IN3DTEC: https://www.in3dtec.com/metal-3d-printing-technologies-slm-vs-dmls/#:~:text=Unlike%20SLM%2C%20DMLS%20can%20be,of%20the%20machines%20and%20materials.