What is Direct metal laser sintering (DMLS)?
Direct metal laser sintering (DMLS) is a common 3D printing or additive manufacturing technique that is also referred to as selective laser melting (SLM).
In this process, each layer of a part is created by aiming a laser at the powder bed in specific points in space, guided by a digitally produced CAD (computer-aided design) file.
Once a layer is printed, the machine spreads more powder over the part and repeats the process. The process is ideal for printing precise, high-resolution parts with complex geometries.
DMLS machines use a laser to heat the particulate matter to its melting point in a digital process that eliminates the need for physical molds.
The resulting parts are accurate, have excellent surface quality and near-wrought mechanical properties.
DMLS printers are recommended when you want to print a limited number of industrial items that are otherwise difficult or impossible to fabricate because of hollow spaces, undercuts, challenging angles, and other complexities.
DMLS is ideal for low-volume parts and when you want to avoid the time and expense of creating a tooling. DMLS parts can be stored digitally and printed on demand, which reduces inventory costs and increases design flexibility.
How Does Direct Metal Laser Sintering (DMLS) Work?
Like all 3D printing technologies, metal sintering is a digital process that starts with an electronic file of the part.
The files is made with computer-aided design (CAD) software or obtained from a digital part repository.
Then the design file is put through special build preparation software that breaks it down into slices or layers to be 3D printed.
This software, which is often unique to the type of 3D printing and even the brand of 3D printer, generates the path and other instructions for the 3D printer to follow.
Once the part file, which can include dozens of individual parts, is fed to the 3D printer, it prepares to build.
Metal sintering involves a bed of metal powder and high-powered lasers used to selectively fuse metal powder together layer-by-layer on a molecular level until the final part is complete.
First, the printer hopper is filled with the desired metal powder, then heaters bring the powder to a temperature near the sintering range of the material.
The printer pushes powder into the print bed where a recoater blade (like a windshield wiper) or roller spreads it into a thin layer across the build plate.
The laser, or lasers, trace the shape of the first layer onto the powder thus solidifying it. The build platform then moves down a tiny amount, and another layer of powder is spread and fused to the first, until the entire object is built.
During printing, the build chamber is closed, sealed, and in many cases, filled with inert gas, such as nitrogen or argon blends, which helps prevent debris from the melting process from affecting the part.
The packed powder on the printing bed supports the model during the printing process, but printed supports are also used. The unused metal powder can be mixed with fresh powder and reused for the next print.
After printing, parts are left to cool and the surrounding loose metal powder is removed from the printer. After printing, parts are removed from the powder bed and cleaned.
Metal sintered parts can be treated like metal parts produced by conventional metal working for further processing, which may include machining, heat treatment, or surface finishing.
Materials For Direct Metal Laser Sintering (DMLS) 3D Printing
1. Aluminums.
- AlSi10Mg, AlSi7Mg0.6
- Aluminum F357
- Scalmalloy
2. Stainless Steels.
- 316L
- 15-5PH
- 17-4ph
- 1.2709
- H13
- Invar 36
- 1.4828
3. Nickels.
- HX
- Inconel 625, 718, 939
- Amperprint 0233 Haynes 282
4. Irons.
5. Titaniums.
- Ti6Al4V ELI (Grade 23)
- TA15
- Ti (Grade 2)
6. Cobalts.
7. Coppers.
- CuNi2SiCr
- CuCr1Zr
- GRCop-42
8. Hastelloy C22, X3.
Advantages Of Direct Metal Laser Sintering (DMLS)
#1. Wide Range of Metals.
DMLS facilitates metal additive manufacturing by supporting a wide range of metals – aluminum, titanium, steel, stainless steel, cobalt chrome, nickel alloys, and precious metals.
Hence, engineers have the option to choose from both pure metals and metal alloys according to the requirements of the 3D printer.
Also, many companies have been launching new metal filaments to leverage the growing adoption of DMLS technology.
#2. Direct Metal Printing.
In addition to supporting a wide range of metal alloys, DMLS prints the metal parts or prototypes directly. Direct metal printing helps engineers to keep the properties of the metal alloy intact.
Many engineers further leverage the feature to produce innovative and superior parts by combining multiple metal powders.
#3. Production of Strong Functional Parts.
As mentioned earlier, enterprises these days use DMLS technology to produce both fully-functional parts and prototypes.
The metal alloys make DMLS effective in producing functional parts that are both strong and durable. Also, engineers can create metal parts without melting the metal powder.
Hence, the mechanical properties of the metal remain intact after the part is produced.
#4. Mass Customization.
While using DMLS technology, engineers can produce parts without using tools or fixtures. The absence of tooling and fixturing makes it easier for them to customize and fine-tune the metal parts during mass production.
They can simply make relevant changes to the design and produce many variants of the part on a mass scale.
#5. Freedom of Design.
DMLS is one of the additive manufacturing technologies that do not require engineers to use any support structure.
The absence of the support structure makes the technology effective in producing parts with complex geometries and dimensional accuracy. Enterprises these days leverage DMLS technology to produce parts based on stringent design rules.
#6. Smoothness.
Unlike FDM 3D printing technology, DMLS produces parts using filament. Instead, it prints various items using metal powder.
The metal powder is more effective than filament in ensuring the smoothness of parts printed using DMLS technology.
Engineers also have the option to make the printed parts smoother by opting for finer metal powders.
#7. Material Reusability.
Like SLS 3D printing technology, DMLS enables engineers to reuse the unsintered metal powder after the printing process.
The material reusability makes the technology effective in producing parts and prototypes without increasing material wastage and escalating overall material costs.
Disadvantages Of Direct Metal Laser Sintering (DMLS)
#1. High Printing Costs.
The overall cost of a 3D project varies according to both technology and filament. DMLS is one of the relatively expensive additive manufacturing technologies.
Enterprises have to incur both upfront and recurring expenses to combine the machine and materials.
That is why; DMLS is often described as an industrial additive manufacturing technology. It is widely mainly by enterprises to produce metal parts and prototypes.
#2. Porous Parts.
DMLS produces more porous parts than other metal additive manufacturing technologies. The engineers also have the option to control the porosity during the DMLS printing process.
But they lack the option to eliminate the porosity during the post-processing stage.
#3. Small Build Volume.
While planning 3D printing projects, engineers always choose and recommend the appropriate technology based on the build volume.
DMLS is one of the metal additive technologies that have relatively small build volumes. The smaller the build volume makes the technology suitable for small parts.
Enterprises often look for DMLS alternatives while producing large parts.
#4. Slow Printing Speed.
DMLS is not one of the fastest additive manufacturing technologies. Engineers can produce parts or prototypes in weeks using a DMLS machine. The slow printing speeds often escalate the cost of professional DMLS printing services.
#5. Post-Processing.
The post-processing activities in DMLS printing vary according to project needs. Some projects make post-processing mandatory to boost the quality and usability of the printed item.
Hence, enterprises have to incur additional expenses to carry on post-processing activities like heat treatment, surface finishing, machining, de-powdering, and part unloading. The post-processing expenses always escalate overall DMLS printing costs.
#6. Expertise.
DMLS is one of the complex additive manufacturing processes. In addition to creating the printing environment, enterprises need to deploy trained and experienced engineers.
That is why; many enterprises partner with 3D printing companies to create metal parts and prototypes by overcoming constraints related to skill and resources.
DMLS is a widely used metal additive manufacturing technology. Enterprises rely on DMLS to crate prototypes and functional parts using different metal alloys.
But you can make the most out of the metal 3D printing technology only by keeping in mind major DMLS advantages and disadvantages.
Also, you must boost the metal additive manufacturing process by adjusting the layer height and choosing finer metal alloys.
Applications Of Direct Metal Laser Sintering (DMLS)
Widely used by the automotive and aerospace industries for high performance parts. Other applications include medical prosthetics, tooling, functional prototypes and many more.
The areas that benefit greatly from the use of 3D metal sintering are the medical, dental, and aerospace industries.
Their parts frequently require the use of high-performance or exotic materials. Metal sintering can build parts that simply cannot be manufactured with conventional metalworking technologies.
1. Medicine.
Custom prosthetics can be modeled and printed in materials like titanium alloys to replace portions of bones lost to accident or disease.
They have high strength, are resistant to attack by the body, and the porosity helps bone grow into the prosthetic structure. Most importantly, each prosthesis can easily be made unique to the individual patient.
2. Dentistry.
Prosthetics, bridges, crowns, and partial dentures are easily modeled specifically for the patient then printed in high-strength materials like cobalt chrome.
Custom fit, strength, and long-term durability are quickly available through the metal sintering printing process.
3. Aerospace.
Metal sintering is a key part of reducing part count, creating complex geometries, and weight reduction while maintaining or increasing part strength and durability.
DMLS parts are used in commercial aircraft and rockets, from simple brackets to complex turbine parts and probes. Even complete rocket exhausts can be produced.