What is Direct Metal Laser Melting (DMLM)

Direct Metal Laser Melting (DMLM) is a Laser Powder Bed Fusion (LPBF) technology, which is one of the most advanced and reliable processes in metal additive manufacturing (AM). Sometimes it is referred as Direct Metal Laser Sintering (DMLS) or Selective Laser Melting (SLM).

Unlike polymer 3D printed parts that are commonly utilized as a prototype for proof-of-concept or as visual design verification, metal 3D printed part mostly applied in end-part applications. Most of time, metal 3D printing is an alternative process to CNC machining, investment casting or metal injection molding for complex and low volume metal parts.

Quad lasers scan across the cross-section area of the parts simultaneously. - Courtesy of SLM Solutions

How Does It Works

1. Metal AM Pre-build Workflow

Supports are generated in the Materialise software prior to the metal 3D printing process. - Courtesy of Materialise

• CAD Model Design

Part is designed and exported as STL file. The 3D CAD model is then imported to the designated 3D printing software (e.g. Materialise Magics, Netfabb etc).

• Software Preparation

Step 1: Part Fixing

In STL file, all 3D CAD model surface are built-up with triangles. Sometimes the surface errors will introduce in the software when uploaded in the software. Common errors such as overlapping triangles or intersecting triangles that pop out in the error message box should be fixed. If those errors are not fixed, the following processes might not be able to carry out.

Step 2: Optimize the Build Orientation

Optimizing the build orientation is a very vital process in the overall metal 3D printing process. It will affect how much the supports are needed to anchor the part from build plate in order to maintain the part integrity during printing. The lesser the supports needed, the lesser the time of printing. Also, supports are non-recyclable. Hence, it will add cost to the overall cost and time spending in the entire process.

Step 3: Support Generation

Supports are very important in DMLM process to ensure the success of the print. In general, any down-facing surface area that is less than 45 degree from the horizontal, supports should be generated in order to ensure the dimensional stability and integrity of the part.

Step 4: Slice into 2D

The CAD model is then digitally sliced into layers and uploaded to the metal AM system. Each layer represents the cross section area of part.

2. Printing Mechanism

Schematic Diagram of Direct Metal Laser Melting. - Courtesy of ResearchGate

Step 1: A layer, typically 0.025mm – 0.1mm thick of metal powder is spread over the build platform.

Step 2: Ytterbium –fiber laser fuses the first layer of the model.

Step 3: The platform will move down a layer and then a new layer of fresh powder will spread across the previous layer using a recoater blade.

Step 4: The laser will then scan another layer of powder.

Step 5: The process continues until the part is finished printing.

3. Metal AM Post-Processing Workflow

Once the build is complete, cleaning is required to remove loose metal powder from the parts and the build platform. Once the excess metal powder is removed from the build area, the part will need to be heat treated for stress relieving process. The loose powder that is removed and collected in the powder container can be recycled and reused.

After heat treatment, the parts and supports will be removed from the build plate either manually or via wire EDM. Further surface finishing such as grinding, sanding, CNC post machining, passivation, etc. will be carried out depending on the final use of application.

The final post-processing step is inspection to measure and ensure the dimensional accuracy and integrity of the metal 3D printed part. The inspection techniques can range from simple measurement such as calipers and gauges to more sophisticated methods such as CMM and 3D scanning.

Common Metal 3D Printing Materials for DMLM

Materials	Material Properties	Applications
Titanium (Ti6Al4V)	1. High specific strength to weight 2. High temperature and corrosion resistance 3. Biocompatible	1. Aerospace and defense 2. Biomedical implant 3. Jewelry and art
Stainless Steel (SS316L)	1. High hardness and strength 2. High corrosion resistance	1. Surgical tools 2. General engineering
Aluminum(AlSi10Mg)	1. High stiffness and strength to weight ratio 2. High thermal and electrical conductivity	1. Automotive and aerospace 2. Electronic Cooling 3. Consumer products
Maraging Steel (1.2709)	1. High strength and hardness 2. High fatigue strength	1. Tooling inserts 2. Mold and die
Cobalt Chrome(Co28Cr6Mo)	1. High corrosion resistance 2. High strength-to-weight ratio	1. Dental implant
Inconel 718	1. High strength and corrosion resistant 2. High performance tensile, fatigue, creep and rupture strength	1. Aerospace and automotive

Benefits of Metal 3D Printing

1. Elimination of Tooling

Unlike other traditional manufacturing such as metal casting, metal injection molding and CNC, metal 3D printing reduces or eliminate the need for tooling and fixtures, which results in reduction in production lead-time and costs.

2. Small Production Runs

Small batch production of metal 3D printed dental implant

Metal 3D printing is very suitable for small to medium production runs. If customers require only 1 or 2 parts for the verification of their metal parts, metal 3D printing is the right choice for their project. It requires no tooling and hence will speed up the product development cycle and save in cost too.

3. Topology Optimization and Weight Reduction

Topology optimization is a method by using physics and mathematics to remove material that is not contributing to the improvement of the mechanical properties of a part. The geometric freedom offered by 3D printing enables parts to be designed to the same functional specification as conventional parts but with less material.

There is a lot of simulation software in the market now to perform the topology optimization of the part. Engineers must understand exactly which areas must bear with the certain load in order to perform the topology optimization.

Topology Optimization enables weight reduction of the part design without scarifying its mechanical property. - Source: Eureka Magazine

4. Mass Customization

Nowadays consumers are increasingly tend to value the importance of being recognized as unique and hence results in high demand in acquiring product that is designed to fit individual needs.

When it comes to mass-customization, metal 3D printing will present a certain benefit in comparison to conventional manufacturing. Unlike conventional manufacturing, metal 3D printing does not require any molds or specific tools in order to fabricate the metal part. Hence, mass customized products can be 3D printed without having bearing on additional costs.

Metal 3D printed orthopedic implants for patients. - Courtesy of Croom Precision Medical

5. Complex Geometry

Metal 3D printing has its benefit of being able to fabricate complicated geometries or geometries that are impossible to machine or cast, provided that the part is designed to the metal 3D printing process.

Metal 3D printed faucets. Adding complexity for free provided that the part is designed for 3D printing process. - Courtesy of 3DPrint.com