Direct Metal Laser Sintering & Selective Laser Melting
3D printing, or additive manufacturing to use an alternative term, is a type of technology which has been around for a surprising amount of time – the 1970’s infact. In the past 10-15 years, the technology has started to evolve more rapidly and has already developed sufficiently to grab the imagination of the public. To this day the technology is perceived as both cutting-edge and innovative.
Opening definitions for selective laser sintering process related terms
What is additive manufacturing?
Additive manufacturing describes a certain style, where materials are added to create the finished product, rather than removed such as in subtractive manufacturing (milling or turning for example). The process provides an incredibly cost-effective and efficient means of producing the finished item and provides a far greater range of possibilities because of the flexibility of the process. For additional information about the additive manufacturing process also read our article, how does additive manufacturing work?
A definition for sintering
Sintering is a process which increases the density of a material (e.g. metal or ceramic) through a melting process which creates bridges between the material’s particles. Following the sintering process, the material is transformed from being weak and porous into a high-density version.
A definition for melting
Melting is a process whereby a material changes from a solid state to a liquid state. Also sometimes called “fusion”, melting arises when heat or pressure is applied to the material, which causes the internal energy to increase. This causes the molecules of the materials to become less ordered and “melt”.
Selective laser sintering or melting
There are different ways to carry out additive manufacturing but one of the most popular is a method known as the selective laser sintering process or melting.
How does the selective laser sintering process work?
To create a product with a Laser sintering machine, the design first needs to be generated using CAD software which provides a 3D image ready for use. The file must first be converted into an .STL format (abbreviation for stereolithography) as this the type of file which can be read and interpreted by the selective Laser sintering machine.
The design is then sliced into superfine chunks horizontally before the sintering rolls into action. A chamber on the 3D printer is filled with powder; this is the material which will ultimately create the product. Typically, SLS works with plastics such as polymers and polyamides as other processes are more effective for the 3D printing of metal.
The SLS process is particularly ideal for rapid prototyping, which is one of its main current uses. SLS is almost exclusively an industrial application with very minimal home use due to the cost and danger of using this technology in the home.
What is Direct metal laser sintering (DMLS)?
The direct metal laser sintering process (often abbreviated to DMLS) is controlled by a computer which instructs the laser what shape to ‘print’, moving across the powder to trace a cross-section of the product. This Laser pulses to heat up the metal powder, either to just below melting point – this is known as metal Laser sintering, or just above melting point which is known as selective Laser melting.
This metal sintering or melting process fuses the powder together and creates a solid form. Once this first layer has been established, the printer platform drops, typically by no more than 0.1mm to expose a new layer of powder and the whole process of first tracing, then heating begins again.
These superfine layers are painstakingly created one at a time during the whole process until the shape is fully formed. Depending on the size and the complexity of its geometrics, the DMLS process can take many hours or possibly even days. Although this may sound like a long time, by comparison, it’s extremely quick and is one of the single biggest advantages of this technology.
The whole DMLS process is considered to be remarkably cost-effective because any powder which isn’t needed can simply be re-used so there’s no waste. Compare this to conventional machine manufacturing where up to 90% of the original materials can end up being thrown away, and it’s easy to see why direct metal Laser sintering is rapidly becoming so sought after. This is because traditional manufacturing is often an “extractive process”, whereas SLS is an “additive process”.
Watch the SPI Lasers video: Additive Manufacturing Revolutionising Industry:
Why use laser sintering metal melting instead?
The 3D printing process works very well, and the results are of a very high quality, and don’t require tooling or further processing. So why consider using a process of melting instead?
Whether you use a direct laser sintering or melting process, the same equipment is required. However, there may be some small differences in the laser sintering metal powder used. If you are opting to use the Laser to melt the powder rather than just perform 3D metal sintering, you will need a purer substance rather than an alloy. This is because there may be different melting points in an alloy, which could render the process difficult or make the results less stable. Because sintering doesn’t melt the laser sintering metal powder completely, an alloy of different powders may be used in the 3D printing process.
That’s not to say pure metals can’t be sintered rather than melted because they can; some which have a particularly high melting point such as tungsten would be better suited to this.
3D printing Laser sintering never actually consolidates the material; instead, the Laser simply allows the particles to merge. There is a subtle but distinct difference. Unlike the direct metal Laser sintering process, melting actually creates a pool where the materials can consolidate before reforming and hardening to create a new solid structure.
One of the reasons melting may be chosen over 3D printing sintering is that the final substance won’t be porous, thereby making it more suitable for a greater range of applications. If having a porous material doesn’t affect the required function for your part, direct Laser sintering will give you the results you want too.
Glossary of metal sintering related terms
There are various acronyms and names used for the process of using a direct metal laser sintering 3D printer, and these can be somewhat confusing. Infact, there’s some debate even among the experts as to what terms should be used and when!
The four phrases you are most likely to hear regarding metal sintering are:
- Selective Laser Sintering (SLS),
- Direct Metal Laser Sintering (DMLS),
- Selective Laser Melting (SLM) and
SLS and DMLS
SLS (selective laser sintering) and DMLS (direct metal laser sintering) are essentially the same process; both involve sintering rather than full melting. The only difference between the two is that SLS is normally used to describe the process when used for other materials. SLS is used in conjunction with materials such as plastics, nylons and ceramics whereas DMLS is used exclusively with metal and metal alloys.
SLM (selective laser melting) is fairly straightforward and used only when the powder is being melted rather than sintered. Although considered by many to be a subcategory of SLS, with SLM the metal part is fully melted into a new 3D solid part.
Finally, lasercusing is fundamentally a brand name for SLM and is a registered trademark of Concept Laser, Germany. The word “cusing” comes from the “C” in Concept Laser and the word “fusing”, to create the new term “lasercusing”. There are some fairly trivial differences to SLM, but the core concept is the same.
Related articles for further reading
Here are some further related articles from SPI Lasers to develop your knowledge further:
- Additive manufacturing – a definition
- Additive manufacturing processes
- Metal additive manufacturing
- Metal rapid prototyping
- What is selective laser sintering used for?
Contact SPI Lasers for all your laser sintering needs
Whatever your needs of the selective laser sintering process and additive manufacturing in general, SPI Lasers are here to help. Call us on 01489 779 696 or complete our enquiry form here to discuss your requirements. Also, why not click here to register for updates for all our latest SPI Lasers?
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