A wide range of different metals can be used in powder form to manufacture parts through 3D printing. Titanium, steel, stainless steel, aluminium, copper, cobalt chrome, titanium, tungsten and nickel-based alloys are all available in powdered form for 3D printing, as are precious metals like gold, platinum, palladium and silver.
These different metals offer various properties, making them suitable for a range of applications. For example, stainless steel provides excellent corrosion resistance, making it ideal for printing pipes, valves and steam turbine parts.
Theoretically, any metal can be used for 3D printing if it is available as a suitable powder. However, materials that burn rather than melt at high temperatures cannot be processed safely by sintering or melting, but can be used when extruded through a nozzle for 3D printing. Wood, cloth and paper cannot be 3D printed using these processes.
It is also possible to use sintering (forming inside a mould at high temperature and extremely high pressure) to create solid items from metal powders and, in the case of those metals with very high melting points, sintering is the only reliable method to manufacture items from these materials.
As hinted above, there are several technologies for 3D printing metals. Powder bed fusion techniques, which include Direct Metal Laser Sintering (DMLS), SLM (Selective Laser Melting) and EBM (Electron Beam Melting), are the more widely used techniques for metal additive manufacturing:
Direct Metal Laser Sintering (DMLS)
This commonly used method uses a laser to sinter metal powder layer-by-layer to form an object. The process does not actually melt the metal and is used for prototyping and manufacturing finished parts including medical devices and instruments.
Selective Laser Melting (SLM)
This process involves using a laser to melt the material where required within a layer of powder in an inert gas environment. This proceeds layer by layer for creating objects with similar parameters to those produced with casting. SLM is often used to manufacture parts from aluminium and titanium, including those for the medical, automotive and aerospace industries.
Electron Beam Melting (EBM)
This process is similar to SLM, except an electron beam is used to melt the material rather than a laser. EBM is perceived as being faster and more precise than SLM and is often used to manufacture items from cobalt and titanium. EBM is widely used by the aerospace industry for items including engine components.
There are other techniques that can or have been used for 3D printing metals, although these are not as widely used as DMLS, SLM or EBM:
Laser Metal Deposition (LMD)
LMD is used in the aerospace, automotive and medical industries, creating objects by depositing heated metal on a metallic substrate layer-by-layer. LMD allows different materials to be used to build an object and is faster than other methods
Selective Laser Sintering (SLS)
Similar to DMLS, this process also uses a laser to sinter powdered materials. It has been used to manufacture items from a wide range of materials, including metal. However, these days it is mostly used for sintering plastics, such as polyamide and nylon
Binder Jetting
This process uses a special liquid to bind the powder material and is less expensive than DMLS, SLM or EBM. The accuracy and strength afforded by this process are not perfect and post-processing is often required. Hot isostatic pressing can be used to improve the strength and solidity of the finished object, but this increases the costs. Binder jetting is typically used for the manufacture of large scale and complex prototypes
Metal Injection Moulding
This combination of injection moulding and 3D printing is widely used for making small components in industries including medical and defence. The process works by mixing metal powder with thermoplastic and wax binders. This mix is heated until the binder melts and covers the powder, which is then granulated into pellets. These pellets are heated and injected into a cavity to form the object before the binder material is removed, usually via solvent extraction. The part is then sintered, evaporating any remaining binder and compressing the object into a dense solid. The object can then be finished as required.
There are a number of benefits and drawbacks associated with 3D metal printing, as follows:
Advantages
- Easy to manufacture items with complex shapes faster than traditional manufacturing methods
- Cheaper than many conventional manufacturing methods for some parts
- Capable of producing precise and highly detailed objects
- Because details can be included at time of assembly, it can save time and money compared to more traditional methods of manufacture
- Complicated forms can be created to create lighter objects without sacrificing strength, making 3D metal printing ideal for automotive, aerospace and space applications
- Very little material wastage
- Multiple parts of a complicated assembly can be combined into a single component, reducing part count and assembly costs
Disadvantages
- Slow to produce parts designed for traditional manufacturing, making high volume production uncompetitive on cost alone
- Powdered metal materials are more expensive than non-powdered metals (e.g. billet or bar)
- Metal 3D printers can be expensive
- Surface finishing and post-processing of 3D printed parts may be required
- Offers lower precision and tolerance than specialised CNC machining
- Heat treatment may be needed to reduce inner stresses in a 3D printed item, or achieve maximum strength in the metal
- Design of 3D metal parts can be complex and require the services of professional CAD engineers
- The size of parts is limited by the build volume of the 3D printer
The advantages and disadvantages of the process provide an insight into the purpose of 3D printing in metal, showing that it is well suited to manufacturing relatively small, complex parts, including prototypes. It can also facilitate tooling for conventional manufacturing technologies, lowering costs and reducing lead times.
By combining the flexibility of 3D printing with the mechanical properties of metal, this technology has found uses across industry, from inserts with cooling channels through lightweight structures for the aerospace industry, to complex parts to be used in highly demanding environments. Typical uses include fully functional prototyping, creating production tools, tooling for moulds or inserts, housings, ductwork, heat exchangers and heatsinks.
Of course, different metals lend themselves to the printing of different objects, for example:
- Stainless Steel: Perfect for objects that will come into contact with corrosive liquids, water or steam, due to the superb corrosion resistance
- Bronze: Pump impellors and marine propellers, fixtures and more decorative items, such as vases
- Gold: Can be used to print jewellery
- Nickel: Can be used to print turbine engine parts or even coins
- Aluminum: Ideal for metal objects, especially where lightweighting is required, such as with airframe parts
- Titanium: Capable of producing very strong, accurate parts such as medical implants (e.g. hip joints) and other solid fixtures and objects
Different 3D printing techniques use different solutions for industry with different materials and complexity, meaning that the cost of 3D printing in metal can vary substantially. However, most of the cost comes from the 3D printing machines, which can be a large proportion of overall costs for a production run, alongside labour, materials, preparation and post-processing. The requirement for high-quality powdered materials also adds to the cost of 3D metal printing as they are more expensive than non-powdered metals in the same quantities.
As mentioned, printer prices can be high, with costs of several or even hundreds of thousands of pounds, although these prices are comparable to a high quality CNC machine tool of a similar size. As technology and the market size improves, it is expected that the price of 3D printing machines will decrease.
As well as the cost of materials and the printer, there are design costs for the objects to be created. This can involve the need to buy specialist software or hire the services of CAD engineers with specialist knowledge of 3D printing. There are, of course, other labour costs for the operation and maintenance of the machines.
Finally, there are costs associated with post processing of printed parts. This can include cleaning, heat treatment, the removal of support structures and applying coatings to the surface.
3D printing with metal, or additive manufacturing, allows for parts to be made with almost the same strength as regular metal objects.
While it can be expensive and is not well-suited to replacing conventional manufacturing for high volume production of standard items, it is ideal for making smaller, complex items. 3D printing with metals also assists with lightweighting for parts used in industries including aerospace and automotive.
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