What is metal 3D printing?
Metal 3D printing is an umbrella term for several families of Additive Manufacturing technologies. Simply stated, any technology that creates metal objects layer by layer with sintering, melting, and welding could be called metal 3D printing.
Metal 3D printing is sometimes introduced into existing supply chains to work alongside other manufacturing technologies.
In other instances, printers are used as a prime way of manufacturing metal components. Certain geometries of 3D printed objects in metal come out just as good as machined parts.
Metal printing is mainly used in prototyping, aerospace, mechanical engineering, specific tools, and more.
Metal 3D Printing is a disruptive manufacturing technology that offers a whole world of possibilities.
This is as true in terms of offering new levels of design freedom, as it is about the sheer choice of metal materials that can be used with metal 3D printers.
Take titanium as an example. Where conventional processes can be costly, metal 3D printing can be an attractive technology for the processing of this advanced material, and others like it, such as alloys which can only be manufactured under high cooling rates.
Metal 3D printing also allows for the cost-effective production of customized products in the medical and orthodontic sectors, 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.
How Does Metal 3D Printing Work?
The basic fabrication process is similar for both SLM and DMLS. Here’s how it works:
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. Unlike the polymer powder bed fusion process (such as SLS or MJF), the parts 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 manually removed 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.
Post-processing methods for metal 3D printing
Various post-processing techniques are used to improve the mechanical properties, accuracy, and appearance of the metal printed parts.
Compulsory post-processing steps include the removal of the loose powder and the support structures, while heat treatment (thermal annealing) is commonly used to relieve the residual stresses and improve the mechanical properties of the part.
CNC machining can be employed for dimensionally crucial features (such as holes or threads). Media blasting, metal plating, polishing, and micro-machining can improve the surface quality and fatigue strength of a metal printed part.
Types of Metal 3D Printing Processes
Metal powder is the backbone of metal 3D printing. Though it’s difficult and dangerous to handle in its raw state, its unique features make it the preferred metal stock type.
The vast majority of metal 3D printing technologies utilize metal powder. As a result, the major differences between types of metal printers relate to how they fuse the powder into metal parts.
These methods vary greatly, ranging from using high energy lasers to fuse loose powder to extruding bound metal powder filament.
1. Metal Powder Bed Fusion 3D Printing (SLS, SLM, DMP)
Powder 3D printer systems are referred to as Powder Bed Fusion (PBF) or Powder Bed Additive Manufacture (PBAM). This 3D printing technique uses either an electron beam, laser, or heat to melt and fuse metal.
Common metal 3D printer processes are SLS (Selective Laser Sintering), SLM (Selective Laser Melting), and DMP (Direct Metal Printing or commonly known as DMLS (Direct Metal Laser Sintering)).
PBF works by depositing powder onto the build table and spreading it across the platform using a roller or recoater blade.
A laser is scanned over the build area and pulsed to melt the powder. The table descends by the layer thickness, and the process repeats until all layers are printed.
Metal Powder Bed Fusion Pros and Cons
| Pros | Cons |
| Intrinsic support from the powder bed, no supports required | Some manufacturers offer a limited range of material compositions |
| Smooth surfaces direct from the printer | Requires high-quality, expensive lasers |
| 20 µm minimum layer thickness, commonly 35–50 µm | Some systems offer relatively slow build |
| Builds more-porous parts | High residual stresses result from unstable melt pools |
| Printed parts are not equally strong or resilient from all processes; always weaker and more fracture prone than EBM parts |
2. Directed Energy Deposition (DED)
DED (Directed Energy Deposition) is a metal 3D printing process that uses a focused energy source. This energy can either be a laser, a plasma arc, or an electron beam.
DED uses powder and wire to create 3D printed parts. The DED powder and DED wire processes are quite different from PBF but similar to each other.
With DED, deposition and fusion of metal occur at the same time. A nozzle deposits material into the energy source.
The feedstock is melted and deposited as the X-Y traverse of the printhead progresses. When the layer is complete, the build table drops by the layer thickness resolution and the process repeats.
When the build is complete, the part can be removed from the build table. Post-machining may be required for surface finish issues.
Directed Energy Deposition Pros and Cons
| Pros | Cons |
| Fast printing speed | Equipment costs are very high |
| Printed parts have high density and strength/resilience | Support structures cannot be built, so overhangs are not printable, limiting applications |
| Can be used for repair of high-quality functional parts | Relatively low build resolution |
| Large build tables available | Poor surface finish requires post-processing |
| Native material properties in parts | |
| Allows production of parts with minimal tooling | |
| Reduced material waste | |
| Can build parts with custom alloy (multi-material range capability) |
3. Metal Filament Extrusion (FFF, FDM)
The fusion filament processes of FDM (Fused Deposition Modeling) and FFF (Fused Filament Fabrication) in metal printing are in the early stages and have obstacles to overcome.
Metal filament extrusion works by heating a filament made from both thermoplastic material and metallic particles.
The filament is drawn through a nozzle and deposited on the build platform, layer-by-layer. The complete part is placed in a sintering furnace to burn out the plastic and sinter the metal.
Metal filament extrusion is most useful for making metallic-looking parts that can be as accurate and detailed as plastic FDM.
Metal Filament Extrusion Pros and Cons
| Pros | Cons |
| No special build environment – room temp, normal atmosphere | Difficult post-process to sinter parts |
| FFF stresses in printed parts | Shrinkage makes dimensions in the finished part hard to control |
| Wide range of materials on the same machine | Part accuracy is largely unrelated to X-Y-Z resolution of print |
| Lower-cost equipment | Parts are low density and relatively weak after sintering |
| Lower technical skills required in operation | |
| Great for prototypes |
4. Material Jetting and Binder Jetting
Binder jetting is similar to the various PBF techniques, except that the particles are bonded with an adhesive that is deposited to build layers via an inkjet.
Material jetting, on the other hand, is a distinct process that is similar in many regards to DED but is closest in nature to PolyJet.
In binder jetting, the first powder layer is laid down; then, a printhead passes over the layer applying adhesive to bind the slice.
The table drops by the z-build height, and the process repeats until the model is complete. Material jetting works with the layer inkjet printed in a powder-loaded UV-cured polymer matrix.
This forms the layer and is cured in place by a UV light source. The table drops by the layer thickness, and the process are repeated until the “green” model is completed.
Binder jetting and material jetting must account for the shrinkage on 3 axes when scaling the print. A precise result can be achieved, however, with good control of the sintering process.
While the processes are different, there are several similarities in the pros and cons of binder jetting and material jetting.
Material Jetting and Binder Jetting Pros and Cons
| Pros | Cons |
| No special build environment—room temp, normal atmosphere | Two-stage process—powder bed is laid down, then the adhesive is ink-jetted to bond the layer |
| No internal stresses in printed parts | Delicate post-process to sinter parts |
| Wide range of materials on the same machine with no alteration in setup | Dimensional control requires finesse to ensure correct shrinkage |
| Lower-cost equipment | Finished part accuracy is not purely a result of X-Y-Z resolution of print |
| Lower technical skills required in operation | Parts are brittle and vulnerable before sintering |
| 35 µm minimum layer thickness |
What Are The Common Materials For 3D Metal Printing?
Nearly all metal 3D printing processes rely on metal powder. Whether used as a raw material or bound in a filament, it is the essential ingredient that enables machines to additively fabricate parts.
This means the availability of metal 3D printing materials in additive manufacturing depends almost entirely on how easily the powderized form can be fused together.
Let’s review some of the metal 3D printing materials available:
1. Stainless Steel.
Stainless steel is characterized by high strength and excellent corrosion resistance. This material is used across a vast range of industries and applications from manufacturing to assistive technology.
Examples of 3D printed stainless steels include the extremely corrosion resistant 316L and the heat treatable 17-4 PH Stainless Steel.
2. Tool Steels.
As the name suggests, this class of steels is used for a variety of manufacturing tooling. Anything on a production line that cuts, stamps, molds, or forms is probably made out of tool steel.
Tool steels can withstand such harsh conditions because of their high hardness, and excellent high heat and abrasion resistance.
Because of these properties, tool steels are very difficult and expensive to machine, making them an ideal candidates to be 3D printed. Popular powders and filaments include A2, D2, and H13 Tool Steel.
3. Titanium.
This metal is strong, incredibly lightweight, and heat and chemical resistant. Normally, titanium is extremely challenging to machine (contributing to its high cost), making it a great metal 3D printing material.
The most common 3D printed titanium is Titanium 64 (Ti-6Al-4V) and is used in situations when a very high strength to weight ratio is beneficial, such as aircraft.
4. Inconel 625.
While 3D printers can be used to produce parts out of common metals such as steel, they can also fabricate parts out of superalloys that are uniquely suited for extreme environments.
Inconel 625 is a strong, stiff, and very corrosion- and heat-resistant nickel-based superalloy that is often used in places like turbines and rockets.
Other types of Inconel, namely Inconel 718, don’t have the same heat resistance that Inconel 625 has.
The material is traditionally wildly expensive to machine; conversely, Inconel can be purchased in powder form and 3D printed for a fraction of the cost, opening the door to affordable Inconel components.
5. Copper.
Because it conducts heat and electricity far better than traditional metals, copper has long been used in industrial fabrication.
As a 3D printing material, copper is used for heat sinks and heat exchangers, power distribution components such as bus bars, manufacturing equipment including spot welding shanks, antennae for RF communications, and more.
How to Select the Best Metal 3D Printing Process for You?
Selecting the best type of 3D printing is complex. Below are useful steps to go through when deciding which metal 3D printing processes to choose:
- Review part requirements. For example, give consideration to the layer resolution, the need for the reproduction of fine detail, as well as the required mechanical properties and cosmetic quality considerations.
- Choose a material family for the part.
- Once the material has been selected, review the available processes that use that material to consider the best one to produce the desired results.
- Check the availability of resources, including suppliers for the material, time, and costs.
Differences Between SLM And DMLS Metal 3D Printing
Selective Laser Melting (SLM) and Direct Metal Laser Sintering (DMLS) are two metal additive manufacturing processes that belong to the powder bed fusion 3D printing family.
The two technologies have a lot of similarities: both use a laser to scan and selectively fuse (or melt) the metal powder particles, bonding them together and building a part layer-by-layer. Also, the materials used in both processes are metals that come in a granular form.
The differences between SLM and DMLS come down to the fundamentals of the particle bonding process (and also patents):
SLM uses metal powders with a single melting temperature and fully melts the particles, while in DMLS the powder is composed of materials with variable melting points that fuse on a molecular level at elevated temperatures.
Essentially, SLM produces parts from a single metal, while DMLS produces parts from metal alloys.
Both SLM and DMLS are used in industrial applications to create end-use engineering products.
In this article, we use the term metal 3D printing to refer to both processes in general and we describe the basic mechanisms of the fabrication process that are necessary for engineers and designers to understand the benefits and limitations of the technology.
There are other additive manufacturing processes that can be used to produce dense metal parts, such as Electron Beam Melting (EBM) and Ultrasonic Additive Manufacturing (UAM).
Their availability and applications are limited though, so they won’t be presented here.
Benefits Of Metal 3D Printing
For a long time machining was (and still is) one of the primary manufacturing methods for metal parts.
And it is believed that CNC machining is capable of almost any kind of work. But the truth is that this “almost” sometimes isn’t enough.
In some instances, there is a demand for components with new complex shapes, for example, for brand new tools and products.
And here comes the main advantage of metal 3D printing it’s almost boundless when one considers manufacturing objects with a complicated shape.
Other advantages of 3D printing with metal include:
- 3D printers can manufacture complicated details much quicker than traditional methods of manufacturing.
- The cost for short runs is cheaper in comparison with conventional methods of manufacturing.
- Depending on the chosen technology it’s possible to create precise objects with very small details.
- It’s possible to 3D print details in assembly, and as a result, save even more time and money.
- More complicated forms mean that the part can be lighter in weight without sacrificing strength. That’s why 3D printed parts are in such demand in the aerospace industry.
- 3D printing with metal almost doesn’t waste material.
To sum it up, 3D printing is highly recommended for intricate parts where other types of manufacturing are inefficient or difficult to use.
Limitations Of 3D Printing
As great as it is, 3D printing is not without its faults, too. First of all, it’s not as fast and affordable for regular and simple parts in comparison with traditional methods of manufacturing.
Your traditional U and V shapes, especially in large quantities, are better to be done through forming. Other limits of 3D printing metal include:
- Powdered metal is much more expensive than “regular” raw metal.
- Speed of production is comparatively slow for regular objects.
- Metal 3D printers are expensive and require special skills and training.
- Sometimes surface finishing is rough, so post-processing is needed for end-use components.
- Tolerance and precision are usually lower in comparison with CNC machining.
- Occasionally additional heat treatment is required to reduce the inner stress of a 3D printed object.
- Unused metal powder degrades after each run, so it requires adding fresh material every time.
- Designing for metal 3D printing can be more complicated in comparison to other manufacturing methods. So, it’s better to work only with experienced specialists that know all the technological nuances.
- Metal 3D printers aren’t extremely large, so the dimensions of solid parts they can create are limited. The biggest build volumes on the market are around 1000 x 1000 x 700 mm, and most metal printers are much smaller.
As can be seen, the limits are self-evident that 3D printing isn’t an efficient source of regular metal parts. In other, less standard cases, additive manufacturing is the real deal.