Frequently asked questions about metal 3D printing

Metal question marks

It’s a fact that there are more challenges to getting started with metal 3D printing compared to plastic. To help you along the way, we have put together an FAQ to straighten out some of your question marks.

  1. How does metal 3D printing work?
  2. Are there different metal 3D printing technologies?
  3. What are the most common metal 3D printed applications?
  4. What metal materials and alloys can you 3D print?
  5. How much does a metal 3D printed part cost?
  6. How much does a metal 3D printer cost?
  7. Are metal 3D printed parts as strong as traditionally manufactured metal parts?
  8. How do you design for metal 3D printing?
  9. What are the advantages of metal 3D printing?
  10. What level of detail can you achieve with metal 3D printing?
  11. What are the main challenges of metal 3D printing?

How does metal 3D printing work?

Just as with plastic 3D printing, metal 3D printing is based on adding metal material, such as powder or filament, layer by layer. If you are using metal powder, each material powder layer, roughly 0.05 millimeter, is fused by a laser, or glued together with inkjet, to form a part. After printing a metal part, it needs to be postprocessed. This usually includes removing support structure, washing and heat treating the part. Sometimes sanding needs to be done, depending on what surface finish you want the part to have.

Are there different metal 3D printing technologies?

Yes, several, and they are all used depending on what properties you need for your printed parts. The most popular metal 3D printing technologies are Selective Laser Melting (SLM), Electron Beam Melting (EBM), Direct Energy Deposition (DED), Binder Jetting and Bound Powder Extrusion.

Selective Laser Melting

The majority of Powder Bed Fusion machines are Selective Laser Melting (SLM) machines. SLM machines use high powered lasers to fuse metal layers into parts. After a print, an operator removes the part (or parts) from the powder bed, cuts the part away from the build plate, and postprocesses the part. It’s one of the current standards for metal printing – most companies in Metal AM today sell SLM machines. As one of the most mature variety of metal 3D printing, SLM is often considered the standard that other technologies are evaluated against. SLM printed parts are great for precise, geometrically complex parts that would not be otherwise machinable. 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. Most materials available to be 3D printed today can be used on an SLM machine.

While these machines are groundbreaking, a wide variety of facility and postprocessing 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. After printing, most parts require significant postprocessing and heat treatment. In addition, the metal powder that these machines use is both extremely dangerous and expensive to handle: most fully baked SLM machines cost upwards of one million dollars to implement and a dedicated technician to run.

Electron Beam Melting (EBM)

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 one million dollars to set up and require a dedicated technician to run.

Direct Energy Deposition

Direct energy deposition uses metal feedstock and a laser to fabricate parts. Unlike powder bed fusion, the stock (which can be powder or wire) 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.

Binder Jetting

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. The field has exploded from a single manufacturer to a variety of companies in the last few years. Due to its speed and scalability, it may be the technology that propels metal additive manufacturing capabilities into production volumes.

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.

Bound Powder Extrusion

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 FFF 3D printing, yielding a “green” part that contains metal powder evenly distributed in waxy polymer. After printing, BPE has two postprocessing 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. As a filament based printing process, the part constraints of BPE parts closely mirror those of conventional FFF plastic printing. It works well for almost all part geometries, and can print with open cell infill. 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.

From design to finished part, the Bound Powder Extrusion process includes printing the green part, washing and sintering.

What are the most common metal 3D printed applications?

3D printing can be used across a product’s lifecycle, from prototyping to spare parts. There’s virtually no manufacturing vertical unaffected by 3D printing – aerospace, automotive, electronics, healthcare, robotics etc. The same goes for metal 3D printing. Here are five typical metal 3D printing applications.

Functional metal prototypes

Because metal 3D printing requires no tooling and very little machine setup, it offers a way to produce metal prototypes with minimal effort. This allows customers to have accurate metal parts in hand in a matter of days, helping evaluate designs more quickly while avoiding expensive tooling rework. Engineers can explore more designs in a shorter period of time, compressing their product development cycle.

End-of-arm tooling

Metal 3D printers can produce conformal end-of-arm tooling much easier and cheaper than traditional methods. 3D printing software automatically generates toolpaths, allowing engineers to skip the CAM process. Additionally, the part complexity of conformal grippers introduces no additional cost, so they can be optimally designed to grip parts securely and precisely.

Custom tools

While most tools are mass produced, many situations call for specialized instruments that are manufactured in low volumes. Metal additive manufacturing allows engineers to bypass steep overhead and create custom tools at a low cost per part.

Complex bracketry

Metal 3D printing offers an alternative way to create intricate brackets that are difficult or impossible to machine. Thin, complex lattices pose no challenge the the 3D printing process, allowing for the inexpensive production of brackets with specialized geometries.

Low-volume end-use parts

Metal additive manufacturing can remedy high part costs for low-volume production. 3D printers make parts without tooling, getting rid of the need to spread overhead across thousands of parts.

What metal materials and alloys can you 3D print?

The most common metals for 3D printing are stainless steels, tool steels, titanium, aluminium and specialty alloys, such as Inconel, cobalt chromium, copper and more.

Stainless Steels

Stainless steels are strong, stiff steels that possess excellent corrosion resistance due to their significant Chromium content (at least 12%, often up to 18%). They come in two different varieties, austenitic and martensitic. Austenitic stainless steels are the most common type of stainless steel. They’re corrosion resistant and can be both machined and welded, though they cannot be heat treated. 303 and 304 are the most common types of austenitic stainless steels, and 316L is a variant that maximizes corrosion resistance.

Martensitic stainless steels are much harder than austenitic steels, but more brittle and less corrosion resistant. As a group, they lack the general versatility of austenitic steels — however, they can be heat treated and precipitation hardened. They’re best when you need a hard and stiff stainless steel. 17-4 PH is a particularly useful type of martensitic stainless steel that can be heat treated to fit a variety of material properties — it’s also the most common martensitic steel, though others (like 420) are also printed.

Tool Steels

Tool Steels are named for their central application — tooling of all varieties. They contain carbide, an extremely hard compound that’s critical to their ability to cut, grind, stamp, mold, or form. Generally, they’re very hard, abrasion resistant, and usable at high temperatures. Tool steels are categorized by the AISISAE grading systems, divided into types by function. The three types most commonly metal 3D printed are A series, D series, and H series tool steels.

Titanium

While Titanium is by no means a common material to fabricate conventionally, its unique properties and high base cost make it a great candidate for 3D printing. It’s strong, incredibly lightweight, heat and chemical resistant, and can be biocompatible. Though there are a few different types of Titanium that can be printed, one is by far the most common: Titanium 64 (Ti-6Al-4V). Ti64 is the most common type of Titanium in both 3D printing and conventional fabrication. It possesses an excellent strength to weight ratio and can be heat treated to further improve strength. The material also excels in adverse environments due to its corrosion and heat resistance. As a result, it’s used heavily in aircraft (missiles, rockets, airplanes) medicine (as orthopedic implants) and other places where high strength to weight ratio is beneficial.

Aluminium

Aluminium is notoriously difficult to print. As a result, it’s a relatively uncommon printing material despite being exceedingly common in conventional fabrication. The varieties that are printed are generally casting grade aluminium, not more common machinable types like 6061 or 7075. These casting grade aluminium alloys all contain significant (up to 12%) Silicon content, and are weaker and less stiff than 6061. It’s not immediately clear when Aluminium will become more readily available as a 3D printing material, but until then materials like steel and titanium achieve similar strength to weight ratios when printed with open cell infill.

Inconel

Inconel is the most common and best known proprietary nickel alloy. It’s an extremely strong, stiff, and corrosion resistant material used in places like turbines, engine seals, and rockets. There are two main formulations that are 3D printed: Inconel 718 is stronger and tougher, and Inconel 625 is more heat resistant. Both materials are incredibly expensive to machine conventionally, making 3D printing a cost-effective alternative to fabricating high fidelity parts.

Cobalt Chrome

Cobalt Chromium is a superalloy known for its biocompatibility, high strength to weight ratio, and corrosion resistance — it’s essentially a higher-grade, more expensive version of Titanium. Like Inconel, it’s used in turbines and other hostile environments. Unlike Inconel, it can be used in medical applications as orthopedic or dental implants.

How much does a metal 3D printed part cost?

To calculate price per part, or price per cubic centimetre, there are several variables. To name a few, these are print time, type of material, and post-processing. Many 3D printing service bureaus will bill based on an hourly rate, while others may bill according to cubic inches or a combination of both.

You should also know that metal powders are rather expensive. You can expect to pay between 350 and 550 euros per kilo.

To give you an idea of part cost, we are using a fork gripper printed in stainless steel. The dimensions are 179 x 119 x 366 millimeters and the material cost alone for this part is about 100 euros. You then have to add labor cost for postprocessing, such as washing, sintering and sanding.

How much does a metal 3D printer cost?

The price for a metal 3D printer can range from 50,000 euro up to one million euros. But it’s fair to say that you should expect to pay at least 100,000 euros. And that’s for the 3D printer alone. To get a fully functional net part, you will also need a washing solution and a sintering furnace. The heat treatment is necessary to reduce stress, solidify the part and/or burn off plastic material which holds the metal powder during printing.

Learn more about the different 3D printer technologies and their cost by downloading our Buyer’s Guide ebook.

Are metal 3D printed parts as strong as traditionally manufactured metal parts?

It depends on what you compare with and which 3D printing technology you are using. But in general, 3D printed metal parts can be as strong as traditionally manufactured metal components. If you 3D print parts in a printer using Selective Laser Melting technology, then these have mechanical properties that are equivalent to casting. Also, the porosity of a 3D printed metal part can reach 99.5% density, depending on the technology used.

How do you design for metal 3D printing?

The design process for metal 3D printing is difficult to sum up in an article. But here are a few recommendations that will improve part quality, dimensional accuracy and surface finish.

Identify Critical Dimensions

3D printers have higher precision in planes parallel to the build plate, because the print head can better approximate the cross-section of a feature when drawing it out on the plane of the print bed than when building it up step-by-step in the layer-based printing process. Identify your part’s critical dimensions and try to orient them to be flat or parallel to the print bed. Anisotropy is not a big concern in metal 3D printing because the metal powders fuse across layer lines during the sintering process, so orienting your parts for strength is not as important, unlike with plastic & composites 3D printing.

Maximize Bed Contact

Maximizing the contact your part has with the bed improves part success for multiple reasons, including print time, sintering performance, and supports necessary. Printing with the larges face of your part flat on the bed generally reduces the amount of support you need, thus cutting material usage and print time. Additionally, top-heavy parts are more likely to topple during sintering, so putting the larger features at the base of your print will also improve sintering performance.

Reduce Supports

Fewer supports reduce printing and processing time on the printer. While supports are necessary to prevent overhang collapse during printing and sintering, reducing supports by adding features as simple as chamfers and fillets on edges can decrease the supports needed, overall cutting down on print time and material consumption. The supports are printed metal, just like the part, and enable uniform shrinkage between part and supports for a successful finished product. A release interface allows the supports and raft to separate from the part with a set of pliers or a mallet. While metal supports are easy to remove with hand tools, make sure that they are accessible and can be removed before you kick off the print. If not, consider modifying some of the overhangs to improve support removal.

Consider Batch Processing

The more parts you can pack into a sintering run or a wash, the lower cost you achieve per part. If you are producing parts in volume, it is important to consider how parts will be processed in batch. Consider how your parts will pack within the wash and furnace to save time and processing costs.

What are the advantages of metal 3D printing?

There are three clear benefits of 3D printing in metal: The cost per part is consistent regardless of volume, complex parts are not more difficult to 3D print than simple parts, and you can create parts that are impossible to make with any other fabrication method. Read more below for a more thorough answer.

Cost per part

Almost every fabrication method in existence gets cheaper on a cost/per/part basis with increased volume. Casting, machining, and forming (among others) are perfect examples of this. At low and medium volumes, they can be prohibitively expensive to implement. However, at large scale they are far and away the cheapest way to fabricate a part. This is due to the difference between overhead costs — the costs incurred to be able to make a part — and per-unit costs — the costs required to make one additional part. Casting and Injection molding are excellent examples of high overhead/low per unit costs — at low volumes, the distributed cost of the molds required drive the part cost up to unreasonable levels. However, since the added cost per-unit is extremely low, the overall part cost becomes very cheap at high volumes.

Metal 3D Printing subverts this by utilizing a largely automated process that incurs almost no overhead costs. There’s minimal extra upfront labor in printing the first part over the 100th, and the system uses the same amount of consumables (for the Markforged Metal X this is filament, washing fluid, and sintering furnace gas) on every part.

Metal 3D printing isn’t the most cost effective manufacturing method for all volumes — at high volumes, most other manufacturing processes are significantly more affordable. However, for a significant slice of low to medium volume production, metal 3D printing can be the most affordable way to make parts.

Complexity is free

Years of design for manufacturing training have left most engineers hard coded to design parts that are as simple to fabricate as possible. The justification behind this is as simple as it is economical: for the vast majority of fabrication processes, added complexity equals added cost. Complex parts require more work to program machines, more advanced machines to do the fabrication, and take more time to complete. Across most fabrication methods, this stays remarkably consistent; everything from mills to cast parts are affected. Metal 3D printing is not.

Nearly all metal fabrication processes rely on a subtractive process (even casting needs molds). Conventionally manufactured parts all begin as a block of metal, with the machine (usually a mill or something similar) removing material to create the final part. For complex parts, these operations can be both extremely difficult and time consuming to perform. The result is expensive parts that take a long time to fabricate and waste significant material.

Due to a largely automated additive process, metal 3D printing costs are driven by part size instead of complexity. Tool pathing is done by 3D printing slicing software, eliminating the labor and CAM costs native to conventional methods. With no programming and only small preparation responsibilities, part cost is only the material and maintenance of the machine. The additive process yields little wasted material and movement in the fabrication of a part. If a design is printable, complexity doesn’t cost extra.

Unique manufacturing technology

Every fabrication method has limits — 3D printing is no exception. However, due to its unique process, metal 3D printing is capable of fabricating parts that cannot be made with any other platform. The result is parts that can be truly optimized for their use case rather than limited by traditional manufacturing constraints. These parts range from ultra complex — like topology optimized parts from generative design software — to process optimized — like injection molds with conformal cooling channels or custom manifold design. Most of these “impossible parts” have one key feature in common: complex curves, shapes, or cavities where conventional processes simply can’t remove material.

The breadth of impossible parts that can be fabricated on metal 3D printers have not been fully explored yet, so applications are not fully known. As metal 3D printing is adopted by the manufacturing masses, we’ll likely see new design paradigms centered around the unique strengths of 3D printing as a process. Metal 3D printing is by no means the singular future of manufacturing — however, it presents an alternate method of manufacturing that opens up new opportunities that were previous cost or design prohibitive. Metal 3D printing will become an invaluable tool for engineers, designers, and fabricators everywhere.

If you want even more information on the benefits of metal 3D printing, please download our ebook.

What level of detail can you achieve with metal 3D printing?

In metal 3D printing, or any 3D printing for that matter, you need to separate resolution, or level of detail, and accuracy. Resolution has to do with how fine details you can print, measured in micrometre. Accuracy has to do with tolerance – how accurate can you 3D print compared to your digital 3D model?

Depending on the 3D printer, you can achieve several resolutions, depending on what the final application is. If you want to print jewelry, you want high resolution. If you want a quick and dirty prototype, you would go for lower resolution. The highest resolution you can print is roughly 35 micrometres. Minimum layer thickness (Z height) is about 35 micrometres and an X or Y resolution of about 50 micrometres. The minimum wall thickness about 150 micrometres.

What are the main challenges of metal 3D printing?

If we put aside issues like cost of acquisition, operational cost and staff, there are a few challenges you need to be aware of in metal 3D printing.

Postprocessing

Postprocessing is all steps after the print is finished. Often, these involves washing and heat treating the part, which can take several hours, if not a full workday. There’s also surface treatment, like sanding, depending on the surface quality you are after. All steps are highly manual and labour-intensive.

Heat treatment is something that needs to be done to many metal 3D printed parts to achieve final part density and eliminate residual stress.

Porosity

Porosity and density are closely linked. Porosity happens when cavities form in a 3D printed part during the print process. The microscopic holes can reduce the density of the part and can lead to cracks and fatigue. Porosity issues is hard to eliminate, but buying metal material powder from trusted suppliers means the likelihood of gas pockets in the material is kept to a minimum. But small cavities can also form due to the print process itself.
High density is something you want to achieve in metal 3D printing. For critical applications, you need a density of above 99 percent. As with porosity, density can be increased by using high quality metal powders where the particle size is uniform and spherical.

To sum up – maximum density is increasingly important when metal 3D printing is more and more being used for end-use parts that are subjected to cyclic loading, or fatigue.

Residual stress

Residual stress occurs in the 3D printing process due to temperature fluctuations. The part expands and contracts, which can lead to warping or cracking. One method for reducing residual stress, is to preheat the material.