What is it?
Direct Metal Laser Sintering (DMLS) also known as Selective Laser Sintering (SLS) is an additive manufacturing process for metal or metal 3D printing. It is used for both prototyping and mass production of metal parts.
It consists of a bed of powders that is selectively sintered by means of a laser, the process is repeated layer by layer until the desired part is generated.
Use cases
◦ Fast delivery: Parts made with DMLS are produced in 1 to 3 days. This makes DMLS an option to consider if you need parts within a week.
◦ High complexity: Difficult-to-machine parts, customized medical parts, hollow or artistic parts fall into this category, DMLS is ideal for complex parts.
◦ Continuous revisions: Product development and iterative designs are adapted to DMLS technology because they do not have setup costs as in the case of conventional manufacturing processes.
Advantages
◦ Ability to do highly complex designs
The main advantage of DMLS is the ability to manufacture parts that cannot be made with conventional processes or are too expensive.
◦ Production rate
Conventional manufacturing processes require a lot of time for setup prior to fabrication which involves fixturing and jigs, whereas in DMLS the part is printed on demand without the need for tooling, resulting in reduced time compared to CNC.
Things to consider
◦ Support structures
Because DMLS uses powders as inputs the support structures are not optional and need to be removed during post-processing. During post-processing the printed metal part is treated the same as a conventional metal part in its raw material stage and requires additional work to obtain the finished part.
◦ Surface finish
The surfaces of parts made with DMLS will not have the smoothness that CNC machined parts have, nor will it be easy to achieve the desired finish. If post-processing is required to achieve the finish the cost of the part will increase accordingly.
◦ Mass production
Mass production tends to remain a determining factor in industries for the adoption of technologies and this is the point where DMLS technology falters and cannot compete with a conventional production line. Hence, DMLS is recommended for small quantities of parts as it becomes very costly to make volumes comparable to conventional manufacturing processes.
◦ Availability of materials
In the case of metal 3D printing, the amount of materials available is smaller, which can be limiting when looking for certain mechanical properties for the part to be manufactured.
◦ Build volume
When it is required to manufacture a part of considerable volume it is better to use CNC machining. To make it clear, in DMLS the maximum recommended size is 250 x 250 x 325 mm, while in CNC machining volumes up to 2000 x 800 x 1000 mm are possible. The difference in volume shows the limitations of DMLS due to the size of the powder bed.
◦ Shrinkage and repeatability
With DMLS it is difficult to produce identical parts due to the natural shrinkage process, dimensional changes are caused by a combination of three sources: thermal shrinkage, sinter shrinkage and the expansion that occurs due to the fall of metal particles during sintering. Errors of 2% are present in the Z-axis (vertical shrinkage).
Buy equipment or printing services?
The most important factor in determining whether it is desirable to implement a printing technology within the company instead of hiring the services of a specialized company is the work environment you have. In the case of FDM or PolyJet systems, they are suitable for an office environment. Laser sintering processes (such as DMLS) involve raw material in the form of powders which implies a special handling, adding the working temperature of DMSL printers makes necessary a controlled working environment as well as extra space for storage and recycling of powders. These factors make it more appropriate to contract a printing service for parts manufactured by DMLS.
Which materials can I use?
Among the most common materials:
◦ Aluminum, with alloys such as AlSiMg
◦ Steels, such as MS1 tool steel, 17-4 stainless steel and 316L stainless steel
Inconel, such as Inconel 718