Process
Metal Powder-Bed Fusion—also known as Selective Laser Melting or Direct Metal Laser Sintering—is an Additive Manufacturing process using a laser to melt consecutive layers on a metal powder-bed. The powder fuses into the finished dimensional part, incorporating complex internal and external geometries.
The complete CAD-to-part process includes the following steps.
1. Pre-processing
- Optimizing CAD build file for additive manufacturing
- Support generation
- Slicing
- Selection of scanning strategy
2. Print Preparation
- Loading build file
- Preparing build volume and adding metal powder
3. Print
- Precision controlled fusion of the metal powder into layers that form the desired shape and volume
4. Separation of Part from Build Plate
- Removal of part from build plate with wire EDM, bandsaw, or flush cutting tool
5. Post-processing
- Removal of supports
- Final surface finishing
- Heat treating for mechanical properties
Within the Print stage, the part is fused layer-by-layer using the following steps.
POWDER FEED
Feed cylinder increments up placing powder in front of the recoater.
ADDING POWDER LAYER
Recoater moves across the feed cylinder delivering powder to the build cylinder.
FUSION
Laser fuses the cross section of the part.
BUILD CYLINDER
Build cylinder increments down one thickness layer.
COMPLETING THE BUILD
The process is repeated until the volume of the part is fully built.
BUILD PLATE AND PART REMOVAL
The build cylinder raises up and the build plate is removed.
Benefits
Additive Manufacturing systems print near-net-shape 3D components from Computer Aided Design (CAD) data. Compared to traditional machining and assembly processes, additive manufacturing significantly simplifies manufacturing and can produce components with highly complex features and all-in-one assemblies.
- Prototypes can rapidly be printed, which minimize the time from engineering to full production. By eliminating the set-up and tooling costs, and the long lead times of traditional manufacturing processes, metal powder-bed fusion can produce finished prototypes typically in four to 48 hours and allow rapid design modifications.
- Complex designs and difficult-to-machine parts, such as components with long or partial thru-holes, internal cavities, contours and tapered geometries, conformal cooling channels, and metal mesh or lattice structures can be efficiently printed with metal powder-bed fusion.
- Multiple assemblies can be made into one part, eliminating the cost and time of machining, welding and assembling multiple components.
- On-Demand Manufacturing minimizes manufacturing expense and time for one-off applications such as machine shop tooling for injection molding or die casting. Enables rapid printing of student-generated designs in college classes and graduate work.
- Remote manufacturing allows on-site build of critical replacement components from digital CAD files.
- Reduced physical inventory by replacing physical inventory cost and space with digital 3D CAD files. Components can then be rapidly and easily printed on-demand from the CAD files.
Technical Capabilities
Metal Powder-Bed Fusion enables manufacturing of complex geometries with many features not readily obtainable by conventional subtractive manufacturing processes such as machining and casting.
Applications
Metal Powder-Bed Fusion—also known as Selective Laser Melting or Direct Metal Laser Sintering—is an Additive Manufacturing process using a laser to melt consecutive layers of a metal powder-bed. The powder fuses into the finished dimensional part incorporating complex internal and external geometries.
Prototyping
Engineering prototypes are typically the first manufacturing step in evaluating new product designs. Metal powder-bed fusion allows engineering and development departments to print their parts locally without the need of large centralized 3D printing facilities.
The as-printed metal prototypes meet the specified dimensional tolerances and metal properties without the need for subsequent de-binding and sintering. Quick iterative prototype changes can often be printed overnight, reducing the total design time.
Tooling
Rapid manufacture and turn-around of in-demand tooling is often a challenge in conventional machine shops due to shop loading and timing. Complex geometries – including internal features and channels – are even more challenging to manufacture with subtractive machining processes. Metal powder-bed fusion uses conventional CAD files to generate a build file for the metal 3D printer. The as-printed, high-density parts meet the specified dimensional tolerances and can be heat treated to the required hardness similar to machined or cast metal parts.
Low-volume Manufacturing
Low-volume manufacturing of single parts or small batches is often impractical and expensive to make with conventional machining, casting or stamping processes. Metal powder-bed fusion offers an inexpensive alternative that provides on-demand printing, integrating into Lean Manufacturing production.
Simply upload the build file to the 3D printer, load the powder and press START. The final as-printed part has over 99% density, the required dimensional tolerances, and specified mechanical properties, all at a lower per-part cost over traditional manufacturing processes.
Training
Additive Manufacturing has been identified by both government and education experts as a critical solution in smart manufacturing and an important component of Industry 4.0. Future technicians, engineers and scientists are often limited in hands-on training because of the high cost, centralization and unavailability of the metal additive manufacturing printers.
The Xact Metal XM200C system addresses these needs as a reliable, affordable and accessible metal powder-bed fusion 3D printer. With simple set-up, intuitive simple-to-use interface and rapid turn-around between prints, the XM200C increases the number of students receiving important hands-on printing training.
Design Guidelines
Design of components for Metal PBF manufacturing requires consideration of several key guidelines. 3D CAD programs such as AutoDesk Netfabb® and Materialise Magics have features to assist in your design including modules devoted to Additive Manufacturing.
Height:Width Ratio
Tall, narrow features should have a maximum height:width (aspect) ratio of 8:1. Features with greater aspect ratios risk damage by the recoater during powder application. Adding a gusset to the component design will strengthen the feature and minimize damage.
Overhanging Surfaces
- 0 to 30 degrees: Need supports
- 30 to 45 degrees: Supports not needed but part may have poor surface on down-facing surfaces
- Greater than 45 degrees: Supports not needed; good quality surface finish
Flat Ceilings
Flat ceilings larger than 1 mm (0.04 in.) will require a solid or mesh support. Fillets can also be added to prevent warpage out of the build plane.
Geometry Support Structures
Solid or mesh mechanical supports can be added to optimize anchoring, minimize wall distortion from thermal gradients, support overhanging geometry, and provide solid anchoring between the component and the build plate to eliminate component movement during printing. The supports are removed after separation of the component from the build plate. Extra care should be taken when removing supports from thin walled parts; the process of removing the supports could potentially warp the parts.
Horizontal Hole Size and Shape
Horizontal holes with diameters less than 5 mm (0.2 in.) can be printed reliably without internal support. Larger holes will require an internal mesh support or design change. Changing to a tear drop, oval, or square shape will eliminate the need for internal supports.
Minimum Wall Thickness
Typical minimum wall thicknesses range from 100 to 200 microns
(0.004 to 0.008 in.).
Powder Escape
Holes are required to allow powder to escape from enclosed printed structures. A minimum hole diameter of 3.0 mm (0.12 in.) is recommended. Multiple or larger holes will increase the speed of powder removal.
Other Recommendations
- Add fillets to decrease stresses at geometry changes
- Minimize unnecessary blocks of printed material
- Parts with large solid volumes (∼10 cm3/4 in3) could require a thicker build plate to minimize warpage
- If practical, print internal holes parallel to the build direction (Z-axis)
