A Closer Look at 3D Printing Materials: Metals
Metal 3D printing is one of the fastest-growing advanced manufacturing technologies at industrial level. In fact, according to a report published by Grand View Research, the global market for this process was valued at $6.36 billion in 2022. What’s more, the sector is set to record a compound annual growth rate (CAGR) of 24.2% between now and 2030. This increase is due, in part, to the wide variety of materials that are compatible with this technology. Whether for 3D printers using powder-bed fusion, DED, EBM or even metal extrusion systems, the possibilities for these materials are virtually limitless. In this comprehensive guide, we present the metals most commonly used in 3D printing and the characteristics of each.
Aluminum offers an excellent combination of lightness and strength. As well as being corrosion-resistant, it can also be welded. Compared with steels, it is less resistant and more sensitive to high temperatures. It is mainly used in fields where weight is essential, such as mechanical parts for race cars, aerospace, bicycles, etc. It is rarely present in its pure state, and is more often found in alloy form with metals that improve its physical and mechanical properties, such as silicon and magnesium. A typical example is AISi10Mg aluminum, offered by German manufacturer EOS in powder form. With this material, it is possible to manufacture solid, complex parts.
As mentioned, aluminum alloys are more commonly found than the pure form and are traditionally used in many industrial, aerospace and automotive applications. What’s more, they boast a high strength-to-weight ratio, as well as good resistance to metal loading and corrosion.
As one of the most common metals used in industry, thus it is not surprising that steel was the first metal used in additive manufacturing. Within this group, we can find two types: stainless steel and tool steel. Stainless steel is widely used in everyday life, mechanical engineering and medicine. It has good metallic properties and produces a polished, shiny surface. Several manufacturers in the 3D industry offer this material, including EOS, ProMetal and Desktop Metal. Some of its properties include: hardness, tensile strength, formability and impact resistance. It is also possible to print bronze or gold parts using stainless steel as the base material. This is achieved, for example, by coating the stainless steel powder layers with bronze injection glue in the print. On the other hand, EOS has developed Tool Steel MS1, which is used in the manufacture of tools and molds, thanks to its strength and resistance to fracture.
Copper is another metal suitable for additive manufacturing. Its properties include high electrical and thermal conductivity, ductility (plastic deformation without breaking) and malleability (compression deformation). Copper is available in both filament and powder form for 3D printing. Its characteristics make this metal ideal for thermal management and electrical engineering applications (inductors, electrodes, heat exchangers, etc.), as well as for tooling and toolmaking. Some of its most common alloys are : CuNi2SiCr, CuCrZr, CuCP, Cu.
Even in R&D, gallium is used as an alloy with 25% indium, to print objects from small metal bubbles or self-supporting metal wires to assemble electronic components. The special feature of this alloy is that, in addition to melting at a low temperature of around 30°C, the two metals also harden in air, while the interior remains liquid, allowing the print to be flexible. However, price remains the main obstacle when it comes to commercializing this material for use in 3D printing.
Titanium is the material of choice for the medical and aerospace industries, thanks to its excellent properties in terms of strength and weight, as well as its high corrosion resistance and bio-compatibility. The metal is available in powder or filament form. All grades of titanium are extremely corrosion-resistant, ductile and weldable, although grade one is relatively more castable than grades two, three and four. Grade four is the strongest. 3D printing facilitates the manufacture of titanium parts and avoids the impurities obtained with traditional techniques during the welding phase. However, a major drawback of this material is its high cost, which is around 50 times that of steel.
Like aluminum alloys, titanium alloys have improved mechanical properties and chemical behavior. The Ti6Al4V alloy is the most widely used, occupying 56% of the total titanium market, due to its good balance of mechanical strength, ductility, fatigue strength and fracture toughness. These metals are used in additive manufacturing to produce a wide range of industrial components, including sheet metal, fasteners, rings, discs and containers. Titanium alloys are also used to produce high-performance automotive engine parts such as gearboxes and connecting rods.
Compatible with EBM and DMLS techniques, cobalt alloys are of higher quality than those obtained using traditional production methods, such as lost-wax casting. Like titanium alloys, cobalt-chromium alloys, known as CoCrMo, are widely used in medicine for the manufacture of prostheses in both orthopedics and dentistry. This is due to its rigidity, smoothness, wear-resistant surface and absence of corrosion. In addition, the automotive and aerospace industries use highly heat-resistant cobalt-chromium-molybdenum alloys. EOS offers MP1 and SP2 cobalt-chromium alloys that are resistant to high temperatures (600°C). GE Additive’s Arcam company markets ASTM F75, which is also widely used for tool and mold production.
Nickel is an incredibly versatile material, available in powder or filament form, and capable of being alloyed with other metals. Nickel-chromium superalloys, such as Inconel 718 and Inconel 625, enable the manufacture of strong, corrosion-resistant metal parts. These alloys are mainly used in the aerospace, automotive and petrochemical industries, where they are subjected to high stresses and temperatures. The mechanical properties of nickel-based alloys in additive manufacturing, such as Inconel 625, are greatly enhanced by using significant amounts of nickel, chromium and molybdenum in the metal.
We saw earlier that it was possible to add glue to inject bronze and gold into a printed steel object. Another way of printing with these metals is by metal casting. This casting is a lost-wax mold, finished by hand. This method is widely used in jewelry and in the manufacture of small objects. One of the problems and limitations of this casting method is that it must take into account the fine shapes to be avoided, as well as ensuring a minimum thickness of 0.8mm to 1mm to ensure that the walls are respected. The finishing phase is the key to a good surface finish, particularly for silver parts. With gold, it is possible to obtain different shades of color (pink, white and yellow).
Finally, it’s important to note that it’s now possible to modify the atomic structure of the metal during 3D printing. By doing so, you’ll have faster, more uniform solidification, which can result in a stiffer, stronger metal. To find out more about metal 3D printing technologies, you can read our full guide HERE.
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*Cover Photo Credits: Sigma Additive Solutions