What Is Metal Sintering?

Most metal 3D printers use selective laser melting technology, which involves a laser that melts powdered metal. In fact, this method accounts for more than 80% of the metal 3D printer market.

The dominance of SLM tech may not be apparent at first since there’s different terminology in the industry to refer to the same technology. Aside from SLM, there’s direct metal laser sintering (DMLS), direct metal laser melting (DMLM), laser metal fusion (LMF), laser cusing, and laser powder bed fusion (LPBF),More often today, perhaps because of the various terms and its growing popularity, the technology is commonly referred to simply as metal sintering.

This metal 3D printing, or additive manufacturing, method, is a highly precise technology commonly used for both prototyping and production of end-use, complex metal parts for aerospace, automotive, medical, and industrial applications. It makes everything from tools and spare parts to rocket engines and medical implants.

The reasons behind its rapid growth and adoption are many. First, with an in-house metal 3D printer, companies can produce their own metal parts, such as injection molds, replacement parts, and tools, far faster and cheaper than having them made and shipped from overseas, especially in low volumes. Even ordering parts from a metal sintering service is faster than traditional manufacturing.

Next, metal sintering can produce parts with complex internal channels, lattice-infilled walls, and shapes simply not possible (or prohibitively expensive) with any other manufacturing methods, which leads to better, lighter, and more efficient parts.

Another benefit of metal sintering over traditional manufacturing is sustainability. Especially when printing with high-cost materials, such as titanium or silver. Metal sintering 3D printers use just the material required to build the parts, and the rest can be reused for another part.

How Metal Sintering Works

Like all 3D printing technologies, metal sintering is a digital process that starts with an electronic file of the part. The files is made with computer-aided design (CAD) software or obtained from a digital part repository. Then the design file is put through special build preparation software that breaks it down into slices or layers to be 3D printed. This software, which is often unique to the type of 3D printing and even the brand of 3D printer, generates the path and other instructions for the 3D printer to follow.

Once the part file, which can include dozens of individual parts, is fed to the 3D printer, it prepares to build.

Metal sintering involves a bed of metal powder and high-powered lasers used to selectively fuse metal powder together layer-by-layer on a molecular level until the final part is complete.

First, the printer hopper is filled with the desired metal powder, then heaters bring the powder to a temperature near the sintering range of the material. The printer pushes powder into the print bed where a recoater blade (like a windshield wiper) or roller spreads it into a thin layer across the build plate. The laser, or lasers, trace the shape of the first layer onto the powder thus solidifying it. The build platform then moves down a tiny amount, and another layer of powder is spread and fused to the first, until the entire object is built. During printing, the build chamber is closed, sealed, and in many cases, filled with inert gas, such as nitrogen or argon blends, which helps prevent debris from the melting process from affecting the part.

The packed powder on the printing bed supports the model during the printing process, but printed supports are also used. The unused metal powder can be mixed with fresh powder and reused for the next print.

After printing, parts are left to cool and the surrounding loose metal powder is removed from the printer. After printing, parts are removed from the powder bed and cleaned. Metal sintered parts can be treated like metal parts produced by conventional metal working for further processing, which may include machining, heat treatment, or surface finishing.

Metal Sintering Advantages & How To Choose

ADVANTAGES

• Extensive range of available metals
• Ability to realize complex shapes or internal structures, possibly without supports
• Reduced total lead times, due to no need for tooling
• Price per part much lower for single pieces or low volumes
• Part consolidation, allowing operators to create previously multi-component parts as one print
• Reduced waste, due to additive manufacturing and powder reclamation
• Ability to reduce standing inventory due to fast on-demand production
• Potential for mass-customization of parts

When selecting a metal sintering 3D printer, consider

• Scalability. If you outgrow the entry-level machine, is there another level to upgrade to?
• Build Speed. How many cubic centimeters per hour can the machine produce?
• Laser Scan Speed. This is not the only indicator in part build speed, but it contributes.
• Laser Spot Size. Can you adjust the laser for more or less detailed parts?
• Layer Height & Resolution. How detailed can the final parts be?
• Gas & Power Consumption. Some machines consume more than others. How does this affect final costs?
• Material Consumption. Machines with good powder feeding and sieving technology can waste less powder.
• Open or Proprietary Materials. If you have to use the printer manufacturer’s materials, it could affect your manufacturing flexibility and costs.

Metals for Metal Sintering

The working material for this 3D printing process is finely powdered metal. Metal powders produced for metal sintering are not the same as metal powders for injection molding. Powders for 3D printing are processed in various ways and differ from each other in their exact chemical makeup, how round the particles are, their density, and more.

Typically the manufactured size of the metal particles is 20 to 40 micrometers. The particle size and shape limit the detail resolution of the final part. Smaller metal particle size and less variation allow better resolution. The characteristics of the raw powder used in a process significantly affect the material properties obtained in the finished component. For this reason, there’s a wide range of material options depending on the application.

There are dozens of metals, including these below, suitable for metal sintering, but not every metal sintering 3D printer can handle the same materials. Some require more powerful lasers or special handling.

Materials for 3D Metal Sintering

• Aluminums
  • AlSi10Mg, AlSi7Mg0.6
  • Aluminum F357
  • Scalmalloy
• Stainless Steels
  • 316L
  • 15-5PH
  • 17-4ph
  • 1.2709
  • H13
  • Invar 36
  • 1.4828
• Nickels
  • HX
  • Inconel 625, 718, 939
  • Amperprint 0233 Haynes 282
• Irons
• Titaniums
  • Ti6Al4V ELI (Grade 23)
  • TA15
  • Ti (Grade 2)
• Cobalts
• Coppers
  • CuNi2SiCr
  • CuCr1Zr
  • GRCop-42
• Hastelloy C22, X

Previously, it was a challenge to 3D print with copper because of the metal’s reflectivity and high heat conductivity. Advances in printers and materials have largely met those early challenges. Today, 3D printed copper propulsion systems send rockets into space, 3D printed copper heatsinks keep CPUs cool, and 3D printed copper coils boost electric motor performance.

Why 3D Print Copper?

Copper has always been a highly useful metal due to its ability to conduct heat and electricity, resist corrosion, and even kill bacteria and viruses. Demand for complex copper parts is growing as 3D printing opens up even more applications and possibilities for this metal.

3D printing (also known as additive manufacturing) enables the production of exceptionally complex shapes, fine detail, internal structures, and lattice infills not possible with any other type of metal manufacturing. These features reduce weight, increase efficiency, and reduce manufacturing and assembly time. 3D printing requires less raw material — and wastes less — than other manufacturing methods, plus multi-part assemblies can be 3D printed as a single unit, which also reduces the amount of raw material while boosting efficiency. For companies interested in 3D copper printing, reducing raw material costs is critical.

If you already manufacture custom copper parts, you may be able to dramatically lower production costs while optimizing part performance with 3D printing. There’s also the major benefit of producing prototype copper parts for testing without the time and expense of mold making and tooling required for other metal manufacturing methods.

Key Applications for 3D Printed Copper

• Heat sinks
• Heat exchangers
• Induction coils
• Electronics
• Bus bars, hair pin stators, single coils
• Antennas
• RF shielding
• Radio frequency quadrupoles / wave guides

Copper Powder Bed Fusion 3D Printers

Powder bed fusion is the most popular metal 3D printing method, Because copper is highly reflective, processing the powder with lasers presented a hurdle to manufacturers. However, this technology and the materials have evolved to meet the challenge.

3D printer maker, developed an industrial green laser that makes it possible to 3D print materials, such as copper, copper alloys, and precious metals, that are difficult to process with infrared wavelengths. Blue laser technologies are also showing promise for copper processing.

metal 3D printing powder bed technologies, laser powder bed fusion (LPBF) , work by spreading a thin layer of copper powder on top of a platform inside the printer. The powder is heated while lasers trace the first layer of the part. As the particles in the layer are fused, the platform lowers slightly into the build chamber with fresh powder deposited on top, and the process repeats. Some of the copper powder left over from the process can be recycled for use in the next print.

Copper Material for 3D Printing

Raw copper or copper alloy material will be a large part of your 3D printing cost,so it’s good to know what your options are. copper powder for additive manufacturing is specifically processed to form rounder particles than powder used in other metal manufacturing.Other factors, such as low interstitial content and the right flowability, are also important.

Because of the difficulty of tuning your printer to a specific metal powder, it’s more common for users to stick with “approved” powders from your manufacturer to avoid the upfront work.

Advantages of 3D Printing Aluminum

Aluminum alloys feature good chemical resistance, are very lightweight, and feature one of the best strength-to-weight ratios of any metal. Combined with silicon and magnesium, it’s the choice of many in the aerospace and automotive industry for its ability to withstand harsh conditions.

One of the biggest advantages of 3D printing in aluminum, or any metal for that matter, is that you can create parts with internal channels and features that aren’t possible to manufacture any other way. You can print a multi-part assembly as one unit, drastically cutting down on manufacturing and assembly time, and developing a more efficient part overall.

3D printing also does not create much waste. By contrast, CNC machining is subtractive. When you’re working with expensive raw materials, anything you can do to minimize waste is a big plus. This is particularly interesting for the aerospace industry, which constantly strives to improve its “buy-to-fly” ratio, the weight of purchased raw material compared to final part weight.

Casting or machining aluminum often has higher production costs and uses more energy during fabrication. There’s also the additional cost of acquiring tooling or molding. Compare that to AM production, using aluminum which can craft highly-precise complex geometries and shapes that would be impossible with any other manufacturing method.

Design work is done with software and manufacturing can be completed without creating physical tools or molds. Additive manufacturers can produce low-volume and custom parts quickly and affordably and emerging technology continues to make both larger production runs and lower operational costs a reality.

How to 3D Print Aluminum

Selective Laser Melting(SLM) is the most common aluminum 3D printing technology, but not every printer with this technology can handle aluminum. Based on the properties of the aluminum-based alloy to be processed, the SLM printing parameters must be optimized and tuned to control porosity, microstructure, and final material properties.

Know Your Aluminum Materials

Many of the current aluminum alloys for 3D printing are simple casting alloys, such as AlSi10Mg. These aluminum alloys are not particularly strong, nor can they manage high temperatures. Still, their mechanical properties are suitable for a wide range of applications and the material is “weldable” and, therefore, can be used in 3D printing without cracking. The properties of these materials may be all some companies are looking for in metal 3D printing, but others, especially aerospace and advanced manufacturing, need more.

While there are several different types of aluminum alloys on the market, here are some of the more common ones being used in AM.

• AISi10Mg is the most common aluminum alloy and features solid strength, hardness, and dynamic properties. Its light weight also supports good thermal properties and has strong buildability for use in challenging geometries. Uses include housings, ductwork, engine parts, and production tools.
• AlSi7Mg0 combines aluminum, silicon, and a small amount of magnesium to create a highly durable and lightweight allow suitable for fine objects and complex geometries. It’s used in applications that require a strength/mass ratio as well as good thermal properties.
• Al 6061 & Al 7075. 3D manufacturers are starting to have success with printing using 6061 and 7075, which were previously thought not to be conducive to the AM process. Merging nanoparticles is showing progress.
• Alloys in the 6000 series have properties that make them one of the most popular traditional manufacturing of electrical or electronic parts. They are ductile with high thermal conductivity, electrical conductivity, and corrosion-resistant. 6061 is a precipitation-hardened aluminum allow, containing magnesium and silicon.
• 7000 series alloy powders have a high zinc content, are known for excellent mechanical properties for higher strength and are heat treatable. 7075 is most commonly used in highly-stressed structural parts, such as aircraft parts, and is stronger than many standard structural steels.

Precision Products & Electronics

3D printing can create very thin-walled, intricate, and complex titanium parts, which is why it’s used for watch cases, such as the Panerai and Holthinrichs timepieces pictured above and rumored to be an upcoming part of the Apple Watch Ultra.

In 2023, smartphone maker Honor introduced the new folding Magic V2 featuring a 3D printed titanium hinge shift cover that’s lighter than the previous aluminum version and 150% stronger. The company says this this small titanium piece, which can be 3D printed in the tens of thousands, is the key to the product’s durable and smooth folding and unfolding.

Medical & Dental Implants

In the medical industry, 3D printed titanium implants are successful across spine, hip, knee, and extremity applications due to the metal’s inherent biocompatibility and good mechanical properties combined with 3D printing’s ability to tailor porous structures — which enable bone integration — and mass customization for better patient outcomes.

3D printed titanium implants are gaining in both regulatory approval and demand. Because most medical implants are manufactured to cover large groups of people with the same condition, they aren’t an ideal fit for everyone. People suffering from rare conditions are often left out. Now, with 3D printing, it is possible to produce implants designed exclusively for individual patients.

Cycling

3D printed titanium is almost common in high performance bicycles today where every ounce of weight counts and high-strength is paramount. Used in cranks, break handles, stems, derailleur hangers, and even full frames, titanium is proving as strong as aluminum and as light as carbon fiber, without carbon fibers’ sustainability challenges.

After some prototyping, we found that 3D printed lattice-filled titanium cranks were as light as carbon but more robust in an area that is very exposed to impacts. 3D printed titanium enables it to custom fit bikes to riders’ preferences and the frames do not need any paint or coating.

Aerospace

In the aerospace industry, several titanium-based additively manufactured parts are currently in commercial and military use, with numerous other prototypes making their way toward FAA certification. 3D printed titanium is prized for its low “buy-to-fly” ratio — an aerospace term that refers to the correlation between the weight of the initial material and the printed part’s weight.

Titanium is one of the most commonly used metals in additive manufacturing, widely employed in aerospace, joint replacements and surgical tools, race cars and bicycle frames, electronics, and other high-performance products.

Titanium and titanium-based alloys are prized for high mechanical strength, a high strength-to-weight ratio, and better corrosion resistance than stainless steels. The material makes rockets and planes lighter, which saves fuel and increases payload capacity. It also makes for lighter weight electronics, such as smart phones and VR goggles. Likewise for medical implants. And, when you couple titanium’s inherent qualities with the unique features available when you 3D print with it, the advantages multiply.

3D printing enables more efficient manufacturing of this costly metal with lower consumption of raw material and lower waste. As an additive technology, metal 3D printing typically uses only the necessary amount of material for building a part, plus a relatively low amount for support structures.

3D printing also enables complex designs, such as internal channels, and hollow or lattice infilled parts to reduce weight, that are not possible with any other manufacturing method. Because there are no molds or tooling, titanium 3D printing enables cost-effective one-of-a-kind parts, such as patient-specific implants, prototypes, and research tools.

There are countless examples of 3D printed titanium advancing manufacturing, healthcare, space exploration, and much more.

Titaniums for Additive Manufacturing

Pure titanium is not typically used in engineering applications while it is common in the biomedical market for parts, such as knee and hip implants. Titanium-based alloys – controlled mixes of metal constituents that provide specific mechanical properties – are used in a wide range of industries that need to achieve very specific part properties. 

• Titanium 6Al-4V, grade 5 is the most commonly used in titanium alloy in additive manufacturing and it is ideal for prototypes and functional parts in the aerospace and automotive fields and for military applications. It is also an excellent material for the manufacture of parts with complex geometries and precisions, and production tooling.
• Titanium 6Al-4V, grade 23 is a biocompatible alloy commonly used for medical implants and prostheses.
• Titanium Beta 21S exhibits a higher strength than conventional titanium alloys such as Ti-6Al-4V and has superior oxidation resistance and creep resistance compared to conventional titanium alloys such as Ti-15V-3Cr. Grade 21 Titanium has one of the lowest hydrogen uptake efficiency levels of any titanium alloy. It is an ideal candidate for orthopedic implants and aerospace engine applications. Beta titanium is widely use in orthodontics.
• Cp-Ti (Pure Titanium), grade 1, 2 are extensively used in the medical field for a wide range of applications due to the biocompatibility of titanium with the human body.
• TA15 is a near-alpha titanium-alloy with additives of aluminum and zirconium. The high specific strength of components made of TA15 combined with their high load-bearing capacity and temperature resistance enable them to be used for heavy-duty components in aircraft and engine construction.

From cutlery and surgical tools to auto parts and turbine blades, stainless steel is all around us, and for a good reason. It’s highly resistant to corrosion and heat, and it’s a lightweight and affordable metal, making it ideal for 3D printing.

Today, 3D printed stainless steel is used for a multitude of industrial parts, as well as for design, architectural, and artistic applications. Why? Because it’s often faster, cheaper, and more efficient than traditional manufacturing methods.

Manufacturers have been stamping, cutting, molding, and welding stainless steel for well over 100 years. 3D printing the metal dates back only decades, but it already rivals traditional methods for speed and cost. Plus, 3D printing enables complex designs not possible with any other manufacturing method, which drives product innovation.

Selective Laser Melting

The most widely used method for metal 3D printing is laser powder bed fusion (LPBF), also called selective laser melting (SLM) or simply metal sintering. LPBF 3D printers use high-powered lasers to selectively melt a metal powder. The melted parts fuse together layer-by-layer on a molecular basis until the homogenous model is complete. The packed powder on the printing bed provides support to the model during the printing process so supports are rarely required.

Depending on your application, when considering an LPBF 3D printer, you’ll look at the level of laser power, the laser beam diameter, the scan speed, the possible layer thickness (from 20 to 120 μm), the scan strategy, the part cooling strategy, and other features that set different brands, and different models within brands, apart. The surface finish of the final melted part is rough and, depending on your requirements, it may need post-processing to achieve a smooth and shiny result.

There are many kinds of stainless steel, and within each type, there are almost infinite variations. The most used types of stainless steel in 3D printing are:

• 316L Stainless Steel: The most popular choice for 3D printing for its corrosion resistance and mechanical properties. It is widely used in various industries, including aerospace, medical, and automotive.
• 17-4 PH Stainless Steel: This precipitation-hardening stainless steel offers excellent strength, hardness, and corrosion resistance, making it suitable for functional parts and industrial applications.
• 420 Stainless Steel: This stainless steel grade is often used for applications requiring high hardness and wear resistance, such as tooling and molds.
• 2205 Duplex Stainless Steel: Duplex stainless steels have a good combination of mechanical properties and corrosion resistance, making them suitable for certain challenging environments.

Complex geometry is another reason manufacturers turn to metal 3D printing for molds. For example, tire manufacturers Michelin and Bridgestone use metal 3D printing for tire molds because they can produce more complex tread patterns easier and faster than conventional methods.

Metal 3D printing is used to create molds for final product production and prototypes. The same digital mold file you would feed to the CNC or mill in conventional mold making can be used instead to create a 3D printing file, which is then uploaded to a 3D printer that creates the mold. That original file can also be improved upon to take advantage of the unique features of 3D printing.

The fine detail possible with metal 3D printing technology, such as laser powder bed fusion, enables manufacturers to skip several steps in the conventional mold-making process and eliminate the need for skilled machinists.

The driving factor behind the surging use of metal 3D printed molds is entirely different from the benefits of plastic 3D printed molds. In fact, metal 3d printed molds can, in certain circumstances, be more expensive and take as long to make as traditional metal molds, but they have one significant advantage: conformal channels.

This feature, that’s only available with 3D printed molds, is igniting a revolution of sorts in the mold-making industry.

Cooling channels are essential in metal injection-molding tools so that parts can be cooled faster and uniformly. The cooling stage represents 70% – 80% of the entire cycle time, so reducing that time over the lifetime of a mold results in significant savings for manufacturers. Proper cooling also affects the dimensional accuracy, surface quality, and mechanical properties of the final product.

Using conventional machining technologies, cooling channels are added to the mold by drilling in straight lines. The more complex a component’s geometry, the more difficult it is to maintain precise cooling along the contour of the mold. This can make the conventional production of sophisticated components extraordinarily laborious and costly.

Compared to traditional processes, additive manufacturing can create curved cooling channels within a mold shaped to conform to the part’s geometry and provide cooling where it is needed most to improve part quality and reduce cooling times as much as 70%.

Conformal cooling channels are added at the mold design step in CAD software, which can simulate and predict the ideal placement of channels. This design phase, however, adds time and cost to a new metal mold.

Although usually a faster process, metal 3D printing isn’t always. Depending on the complexity of the mold or tool, it can take several days or weeks to produce a final mold. The benefits of metal 3D printed tooling are typically realized in part production, not in the building of the tool itself.

In the ever-evolving landscape of shoe mold manufacturing, a groundbreaking trend is taking center stage.3D metal printing technology (LBPF) is emerging as the game-changer, outshining the traditional CNC machining methods. This innovative approach offers unmatched precision, unparalleled efficiency, and rapid production capabilities, elevating the industry to new heights. As shoe manufacturers worldwide embrace this transformative shift, they unlock a world of possibilities, enabling them to deliver superior products with reduced lead times and increased customization options.