What is Direct metal laser sintering (DMLS)?

Direct metal laser sintering (DMLS) is a popular traditional 3D printing or additive manufacturing method, sometimes known as selective laser melting (SLM).

In this method, each layer of a part is made by focusing a laser on the powder bed at various points in space, which is controlled by a digitally made CAD (Computer-Aided Design) file.

After the machine prints a layer, it covers the part in more powder and repeats the process. This technique is superb for printing delicate, high-resolution components with complex shapes.

A DMLS machine utilizes a laser that actively melts the particulate material through a digital process that does not require the use of physical molds.

The parts made this way are very precise and have good surface finish, and their mechanical performance is almost identical to parts made through machining.

A DMLS printer is preferred when producing low volumes of industrial parts that are complicated to manufacture due to internal cavities, undercuts, difficult angles, and other intricate geometries.

DMLS is the most suitable option for low production volume components, and where the expenses for building a tooling are undesired. DMLS parts can be stored as digital files and printed later, which saves on inventory and promotes creative flexibility with designs.

How Does Direct Metal Laser Sintering (DMLS) Work?

Like every other 3D printing technology, the process of metal sintering begins with an electronic part file as its starting point. A part file is usually created using computer-aided design (CAD) software or downloaded from a database of parts. After that, a design file is

put in a special build preparation program that divides it into slices or layers for 3D printing. This software, which is often unique to the type of 3D printing and even the brand of 3D printer, determines the path and other parameters the 3D printer will use to print the model.

As soon as the part file, which may consist of a large number of individual parts, is uploaded into the printer, it gets ready to make the model.

Metal sintering uses a layer of metal powder and powerful lasers that scan and fuse the metal powder a layer at a time until the part is fully assembled.

Initially, a specific metal powder is loaded into the printer’s hopper, and heaters are activated to melt it to a temperature close to the material’s sintering range.

The printer inserts the powder into the print bed and a recoater blade (similar to a windshield wiper) or a roller moves across the build plate, spreading the powder into a thin layer evenly.

The first layer shape is drawn out of the solidified powder by one or multiple lasers tracing the outline, then the build platform moves downward slightly so that another layer of powder can be spread. Each newly spread layer is fused to the previous layer to build the entire object.

When the print is executed, it is done so within the closed chamber which is sealed and mostly filled with inert gas, argon or nitrogen mixes, that can help minimize the effects of melting detritus on the emerging piece.

The model is assisted by packed metal powder during the printing process, but support structures can also be added for complex prints. The excess powdered metal can be added together with new metal powder and utilized for the next print.

Letting a part cool while the surrounding unattached metal powder is swept away from the printer is the last step of the printing process. The used parts are lifted out of the powder bed, after which they are washed clean.

Parts made through metal sintering methods can further undergo machining, heat treatment, or scraping like any metal parts made using typical metal-working techniques.

Materials For Direct Metal Laser Sintering (DMLS) 3D Printing

1. Aluminums.

AlSi₁₀Mg, AlSi₇Mg0₆
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 has accomplished a great leap forward in metal additive manufacturing by expanding the list of viable materials with aluminum, titanium, steel, stainless steel, cobalt chrome, nickel alloys, and even precious metals on the roster.

Now, engineers can select both pure metals and metal alloys depending on the specifications required by the 3D printer.

Also, the hype around DMLS technology has prompted a lot of businesses to introduce new metal filaments.

#2. Direct Metal Printing.

Apart from a great range of metal alloys, DMLS also directly prints metal parts or prototypes. This innovation in direct metal printing allows engineers to preserve the properties of the metal alloy.

The feature is further exploited by many engineers to create innovative and sophisticated designs by mixing different metal powders.

#3. Production of Strong Functional Parts.

Enterprises, as I mentioned before, make use of DMLS technology to manufacture fully functional prototypes. DMLS is effective because of the versatility of the metal alloys that can be used to produce functional parts with high strength and durability.

Also, the creation of the metal parts does not involve the vaporization of the metal powder by the engineers. In this way, the mechanical behavior of the metal is preserved after the part has been manufactured.

#4. Mass Customization.

With DMLS technology, engineers can create new designs of functional parts without the need for tooling or fixtures.

Tooling and fixturing removal allows better mass customization and adjustment of the produced metal components. Relevant design revisions can easily be carried out and numerous copies of the components can be produced in bulk.

#5. Freedom of Design.

DMLS is one of the additive manufacturing technologies where the engineers are not required to use any support structure.

There is no need for the support structure, and thus, the technology is productive for producing parts that have complex geometry dimensions and accuracy. Parts manufactured under strict design standards inevitably require DMLS technology.

#6. Smoothness.

Direct Metal Laser Sintering (DMLS) evolved from fused deposition modeling (FDM) 3D printing technology. Unlike DMLS, however, FDM uses filaments to create parts.

Parts printed with DMLS technology tend to have a surface roughness that is more preferable with metal powder than filament. Choosing finer metal powders increases the surface smoothness of the printed parts.

#7. Material Reusability.

As with Selective Laser Sintering (SLS) 3D printing technology, DMLS allows engineers to recover the non-sintered metal powder after the printing operation.

Material reusability is beneficial in minimizing waste and reducing material costs while maintaining efficiency in producing components and prototypes.

Disadvantages Of Direct Metal Laser Sintering (DMLS)

#1. High Printing Costs.

Every 3D project comes with its own costs that differ based on technology and filament used throughout the process. DMLS is one of the more expensive technologies for additive manufacturing.

Businesses must pay an initial and ongoing cost when purchasing a machine with the required materials. For that reason, DMLS technology is considered industrial grade additive manufacturing and is mostly used in enterprises to manufacture metal parts and prototypes.

#2. Porous Parts.

Compared to other metal additive manufacturing technologies, DMLS produces parts with a higher degree of porosity.

The engineers can also adjust the porosity of the part while performing the DMLS printing operation. However, removing the porosity during post-processing is not an option.

#3. Small Build Volume.

For every particular project in 3D printing, their strategic planning includes picking and recommending the suitable technology based on the available build volume.

DMLS is characterized as one of the metal additive manufacturing technologies with relatively small build volumes, which are optimal for the production of small parts. Often, enterprises seek alternatives to DMLS for the manufacture of large parts.

#4. Slow Printing Speed.

Also DMLS is not among the fastest of the additive manufacturing processes. Parts or prototypes can be made in a matter of weeks, using a DMLS machine, but can take much longer at the slower speeds. The slow speeds of printing sometimes increase the cost of professional DMLS printing further.

#5. Post-Processing.

In DMLS printing, the post-processing activities differ from project to project. Some projects do post processing as a requirement in order to improve the quality and functional value of the printed object.

In this way, enterprises are obliged to spend more money to cover the post-processing steps, such as heat treatment, surface finishing, machining, de-powdering, unloading the parts, etc. As always, the post-processing order costs add to the overall cost of DMLS printing.

#6. Expertise.

DMLS is one of the more sophisticated methods of additive manufacturing. In addition to the provision of the system, there is a need to have trained and competent personnel readily available.

That is why many businesses contract with 3D printing firms to manufacture metal components and prototype models while bypassing the limitations of skills and resources.

One of the most common types of metal additive manufacturing is DMLS. Businesses depend on DMLS for the production of prototypes and functional components from various metal alloys.

Now, maximizing the benefits of DMLS for metal 3D printing technology requires keeping in mind the major disadvantages associated with DMLS.

Moreover, you need to refine the processes of metal additive manufacturing by increasing the layer height and selecting lower grade metal alloys.

Applications Of Direct Metal Laser Sintering (DMLS)

These are extensively applied in the automotive and aerospace industries when it comes to weight-saving structural parts. Other uses include medical prosthesis, tooling, functional prototypes and many others.

The other industries that have gained significantly from the adoption of 3D metal sintering are the medical, dental, and aviation.

Such components usually need to be made from either advanced or super alloys. Parts produced through metalworking sintering can be produced through no other non machining metalworking processes.

1. Medicine.

Prosthetic devices can be custom-built and 3D printed using titanium alloys to replace bones compartments lost due to trauma or disease.

Their strength is high, resistance to body attack is favorable, and the porosity is conducive to the bone growing into the prosthetic structure. Most importantly, all prostheses can be tailored to an individual patient.

2. Dentistry.

Bridges, crowns, and partial dentures are also prosthetics that can be designed for the patient and printed using strong cobalt chrome alloy.

Custom fit, strength, and long-lasting durability are easily attained with the use of metal sintering printing technology.

3. Aerospace.

Part count reduction, complex geometry production, weight reduction, and strength and durability of parts are indispensable with metal sintering.

Commercial aircraft and rocket DMLS parts are produced from simple brackets to complex components like turbine parts and probes. Even complete rocket exhausts can be produced instead.