The Laser Powder Bed Fusion (L-PBF) Design Guide

Laser powder bed fusion (L-PBF) is an additive manufacturing technology that creates complex metal parts. This guide is for beginners looking for help when designing a component and more experienced makers looking for tips to help improve the design process.

The Laser Powder Bed Fusion Process

L-PBF, also known as selective laser melting (SLM) or direct metal laser sintering (DMLS), is a laser-based process that melts metal powder particles onto a build plate. This process happens layer by layer, with each layer usually between 20 and 80 um thick. The powder is applied via a rake from storage onto the powder bed. The additive design process enables engineers to design intricate shapes and production parts while at the same time reducing weight and material consumption.

How LPBF Works

This is just a tiny reminder that every production process, whether additive, subtractive, or formative, has limitations and considerations. While some technologies may be new, designing for a specific manufacturing method is not a new concept. Design is always linked to the manufacturing process.

In this guide to L-PBF, you’ll learn about:

• Designing support structures
• Choosing the correct build orientation
• Effectively printing holes
• General design tips

Designing Support Structures

During the design process, support must be considered. With metal additive manufacturing technologies like L-PBF, support structures have vital functions:

• Supporting parts when there is an overhang
• Fixing and strengthening the part to the platform
• Diverting excess heat away from the part
• Preventing warping
• Preventing the melt pool from dropping into the loose metal powder
• Resisting the mechanical force of the powder-spreading mechanism of the part
• Preventing a complete build failure resulting from any of the above situations
• Designing supports in 3D printing

The effects of not designing supports at certain angles

Designing the proper supports is essential. Here are some other critical considerations with L-PBF.

The area melted at the laser point cools very quickly, creating stress that can curl the material upwards. Sometimes, this stress might be strong enough to detach the part from its support or split it completely. Supports can be an anchor on the build plate to avoid this.

A part’s solidification can’t start in the middle of the powder bed. It needs to be connected to the build plate directly or through support.

Every area of the part facing the build plate with an angle lower than 45° requires support.

L-PBF Print Orientation

Successfully designing a part for additive manufacturing won’t be possible unless you consider print orientation. The quality of every part (e.g., strength, material properties, surface quality, amount of support, etc.) depends on the print orientation.

Although support material is essential to guarantee the success of a design and the printing process, it should be limited to only what’s necessary. The placement and amount of support material impact part quality, production time, and post-processing cost.

Although support material is essential to guarantee the success of a design and the printing process, it should be limited to only what’s necessary. The placement and amount of support material impact part quality, production time, and post-processing cost.

Orientation can also affect the part’s surface finish, especially when the part has rounded features. Not considering the orientation can cause the staircase effect. This phenomenon, present throughout different additive manufacturing technologies, causes each printed layer to become visible. Instead of the expected smooth surface, the damaged surface resembles a staircase.

The staircase effect

Effectively Printing Holes

It’s best to print holes vertically with their axis if their roundness is critical to the part.

Holes printed horizontally will experience the staircase effect and end up slightly elliptical. Holes with a diameter of up to 8 mm can be built horizontally without additional supports. Larger holes will require supports, although this diameter varies on machine and material.

If you’d like to avoid the need for support structures in the holes, follow these guidelines:

• Elliptical holes for when the ellipse height is twice the width. It can be to approximately 25 mm high.
• Teardrop-shaped holes can be almost any diameter if the top angle isn’t less than the minimum support angle (45°).
• Diamond-shaped holes can be almost any size, but it’s best to fillet the corners to avoid stress concentrations.

Design Tips 

Fillet all corners. It’s generally good practice to fillet – or round – all sharp edges when designing a part. There are two reasons for this.

The first reason is safety. The object becomes easier to hold or use when external corners are rounded. Fewer sharp edges mean fewer dangers from handling sharp edges. The second reason is to ensure the strength of the object. Rounding internal corners reduces stress concentrations that might affect the overall strength of the object. A good rule of thumb is to make the fillet ¼ of the wall thickness of the feature (e.g., ribs or pins).

Print release holes for hollow structures. If your part has a hollow area, consider designing holes to release the powder from the inside. To remove the powder easily, there should be a minimum of two escape holes per hollow area.

Keep wall thickness constant. Designing a part that goes from thin structures to solid blocks generates additional stress, increasing the risk of warpage and bending.

Next Steps

Every good L-PBF design contains these three elements:

1. Using the lowest necessary amount of metal powders, reducing print time and costs

2. Considering print orientation

3. Designing proper supports

With those three elements, your L-PBF part can go from an idea to a complete, finished, and functional part.