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Laser powder bed fusion (L-PBF) is an additive manufacturing technology capable of creating complex metal parts. This guide is for both beginners looking for help when designing a component and more experienced makers looking for some 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.
Just a tiny reminder: every production process, whether it’s 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
And general design tips
This guide will help you to also rethink existing designs with the new possibilities of additive manufacturing .
Designing Support Structures for L-PBF
During the design process, supports 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 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
The effects of not designing supports at certain angles
Designing the right supports is essential. Here are some other key 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.
The solidification of a part can’t start in the middle of the powder bed. It needs a connection to the build plate, either directly or through support.
Every area of the part facing the build plate with an angle lower than 45° requires support.
Looking to reduce costs when 3D printing with metals? This guide will give you some actionable tips to make it happen.
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 impacts 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 essential. The placement and amount of support material impact part quality, production time, and post-processing cost.
Orientation can also affect the surface finish of the part, especially when the part has rounded features. Not considering the orientation can cause the staircase effect. In this phenomenon, present throughout different additive manufacturing technologies, each printed layer becomes 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 with their axis vertically 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 height of the ellipse 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.
Fillet all corners. When designing a part, it’s generally good practice to fillet – or round – all sharp edges. 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. There should be a minimum of two escape holes per hollow area to remove the powder easily.
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.
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.