How do metal 3D printers work? What are their main advantages and limitations? How is metal 3D printing being used in the industry today?
How do metal 3D printers work?
Similar to all other 3D printing processes, metal 3D printers build parts by adding material one layer at a time based on a digital 3D design - hence the alternative term for additive manufacturing.
In this way, parts can be manufactured using geometries not possible with "traditional" subtractive (CNC machining) or forming (metal casting) techniques, and without the need for specialized tools (such as molds).
From here, the specific steps each metal 3D printer follows to make a part varies by technology:
Powder bed fusion
Metal parts are formed layer by layer by selectively bonding metal powder particles together using a high power laser (in DMLS/SLM) or electron beam (in EBM).
Metal powder particles are bonded together layer by layer with a binder to form a "green" part, which needs to be thermally post-treated (sintered) to remove the binder and form an all-metal part.
Metal material extrusion
A filament or rod composed of a polymer and loaded with a large amount of metal powder is extruded through a nozzle (as in FDM) to form a "green" part, which is post-processed (degreased and sintered) to form an all-metal part.
direct energy deposition
Metal powder or wire is melted by a high energy source and selectively deposited layer by layer.
Ultrasonic Additive Manufacturing
The metal foils are bonded layer by layer using ultrasonic welding and then CNC machined into the designed shape.
Over the years, other metal 3D printing systems have been developed based on established plastic 3D printing technologies such as material jetting or SLA.
3D printing is also used to make tools for "traditional" metal fabrication, such as sand casting or investment casting.
Today, the most used metal 3D printing process is direct metal laser sintering (DMLS)/selective laser melting (SLM), followed by binder jetting and metal extrusion.
In the remainder of this section, we will focus on general aspects of metal 3D printing that apply to all processes. We'll also explore how they compare to "traditional" manufacturing processes. In this way, you will gain a broader understanding of how to make the most of this unique manufacturing technique. But first, a brief history lesson...
A Brief History of Metal 3D Printing
In the late 1980s, Dr. Carl Deckard of the University of Texas developed the first laser sintered plastic 3D printer. This invention paves the way for metal 3D printing.
In 1995, the Fraunhofer Institute in Germany applied for the first patent for laser melting of metals. Companies like EOS and many universities are leading the way in this process.
In 1991, Dr. Ely Sachs of MIT introduced a 3D printing process that is now better known as BinderJetting. In 1995, the metal binder jetting technology was licensed to ExOne.
Metal 3D printing saw slow but steady growth in the 00s. That changed after 2012, when the original patents began to expire and companies like GE, HP, and DM made significant investments.
Today, Wohler's report estimates the metal 3D printing market is worth $720 million and is growing rapidly. In 2017 alone, sales of metal 3D printers increased by 80%.
The advantages and limitations of metal 3D printing
It is important to understand that metal 3D printing is a powerful tool with many unique advantages. However, its current limitations do not always make it the best choice for metal part fabrication.
Here, we summarize the most important advantages and disadvantages of metal 3D printing. Use them to understand where metal 3D printing is today and where it's headed in the near future.
The benefits of metal 3D printing
Geometric complexity at no extra cost
Optimized lightweight structure
Add part function
Combine assemblies into one part
A simpler manufacturing supply chain
Excellent material properties
Limitations of Metal 3D Printing
Costs higher than traditional manufacturing
Limited economies of scale
A unique set of design rules
Postprocessing is almost always required
Applications of Metal 3D Printing
Here, we have collected examples of key industrial applications of metal 3D printing. They illustrate some of the main advantages and limitations of the technology. Use them to better understand why engineers choose metal 3D printing for their specific application.
research and development
Creating lightweight structures is critical to the aerospace industry. It currently costs about $10,000 to $20,000 to launch a kilogram of payload into space. Therefore, metal 3D printing of topology-optimized parts has great potential here.
For example, Optisys is a supplier of miniature antenna products. They used DMLS/SLM to reduce the number of discrete parts in their tracking antenna array from 100 to just 1. Through this simplification, Optisys managed to reduce lead times from 11 months to 2, while reducing weight by 95%.
Metal 3D Printing Materials
The number of metal materials available for metal 3D printing is growing rapidly. Today, engineers can choose from the following alloys:
Copper base alloy
Precious metals (gold, silver, platinum...)
Rare metals (palladium, tantalum...)
Stainless steel is a metal alloy with high ductility, wear and corrosion resistance, and is easy to weld, machine and polish.
Aluminum is a metal with good strength to weight ratio, high thermal and electrical conductivity, low density and natural weather resistance.
The cost of metal 3D printing
The cost of metal 3D printers varies by technology. The average selling price for a DMLS/SLM printer is $550,000 and can go as high as $2 million. The cost of a metal binder jetting system is approximately $400,000. A MetalExtrusion printer will cost you around $140,000, including the post-processing unit.
A typical DMLS/SLM part costs about $5,000-10,000 to manufacture (including finishing). For adhesive jetting and metal extrusion, the cost per part can be 5-10 times lower than DMLS/SLM parts. At the time of writing, though, it's too early to assess the full operating costs of these systems.
The speed of metal 3D printing
Independent of the process, metal 3D printed parts take at least 48 hours and an average of 5 days to manufacture and complete.
About 50% of the total production time is devoted to printing. Of course, this depends on the volume of the part and the need for a support structure. For reference, the current productivity of modern metal 3D printing systems varies between 10-40 cm³/h.
The remaining production time is related to post-processing and finishing requirements. Heat treatment contributes significantly to the total production time: a typical thermal cycle lasts 10 to 12 hours. Mechanical finishing can also be a time-consuming step, as they require input from experts (5-axis CNC machining) or manual (hand-polishing).
Metal 3D Printing and Traditional Manufacturing
When you are choosing between metal 3D printing and subtractive (CNC machining) or forming (metal casting) technologies, always start with a cost vs. performance analysis.
Generally speaking, manufacturing costs are primarily related to yield, while the performance of a part is largely determined by its geometry.
The key advantage of metal 3D printing is its ability to create parts with complex and optimized geometries. This means it is ideal for manufacturing high performance parts. On the other hand, it is not as large as CNC machining or high-volume metal casting.
Typical unit costs and volumes for additive, subtractive and forming technologies
As a rule of thumb: the high cost of metal 3D printing only makes economic sense if it is associated with a significant increase in performance or operational efficiency. Of course, each metal 3D printing process addresses different industrial needs.
DMLS/SLM is the best solution for parts with high geometric complexity (organic, topology-optimized structures) that require excellent material properties to improve efficiency in the most demanding applications.
Binder jetting is the best solution for low to medium volume production, does not justify a large economic investment in molding methods, and is the best solution for parts with geometries that cannot be efficiently manufactured by subtractive methods.
Metal extrusion is the best solution for metal prototypes and one-off parts whose geometries require a 5-axis CNC machine to manufacture.