Design for Additive Manufacturing Tips: Multi Jet Fusion

When designing parts for 3D printing services, leveraging Design for Additive Manufacturing (DFAM) best practices can help you save time and money. What’s less common knowledge is that the DFAM advice varies from one 3D printing technology to the next. 

If you’re considering Multi Jet Fusion for your part, it’s important to understand the benefits and limitations of the process so that you can design your part accordingly. MJF is a great 3D printing solution, and following DFAM best practices for this capability can help you get very accurate prototypes and high volumes of parts quickly and cost-effectively. 

Design Guidelines for Accurate Multi Jet Fusion Parts 

Design guidelines for MFJ parts are dictated by the specific printing process itself. All MJF production begins with a powder bed about 8.0 mm thick. A printing head uses infrared light that generates heat and combines two agents, a fusing agent and a detailing agent, to build the part. 

Due to the nature of the layering process and the heat built up during MJF, you’ll want to follow these design guidelines and specifications to maintain part accuracy:

Design Guidelines

• The standard thickness of a layer is approximately 80 microns (0.004”).  For successful prints, the minimum recommended feature size is 0.5 mm (0.020”).  Features with sizes below this value are likely not to print correctly or can be lost altogether.
• Be cautious about adding small or thin features to your design: MJF can create heat spots during sintering that warp or distort these features.
• Place small features with critical dimensions, like pins, holes, and raised texts, in the same plane when possible.
• Design parts with a smooth cross-section transition.
• When possible, include internal lattices or hollowed sections in lighter parts. Thicker parts should be hollowed out and contain at least two escape holes with a minimum diameter of 2 mm for powder removal.
• Avoid long, thin, flat parts with an aspect ratio—length vs. width—higher than 10:1. 
• Avoid parts with predominantly long and thin curved segments.
• Avoid ridges and ribs on large, flat areas.

In addition to these guidelines, honoring minimum feature specifications can help ensure that parts resolve as intended and without defects.

Minimum specifications

• Minimum hole diameter at a thickness of 1 mm: 0.5 mm
• Minimum shaft diameter at the height of 10 mm: 0.5 mm
• Minimum printable font size for embossed or debossed letters and numbers: 6 pt font
• Minimum clearance at a thickness of 1 mm: 0.5 mm
• Minimum slit between walls or embossed details: 0.5 mm
• Minimum width of printable features or details: 0.1 mm 
• Minimum depth and height for embossed or debossed features: 1 mm
• Minimum supported wall thickness: 0.7 mm
• Minimum unsupported wall thickness: 1.0 mm
• Maximum wall thickness: 20 mm 
• Minimum detail size: 0.25 mm
• Moving parts: 0.5 mm between surfaces
• Assembly clearance: 0.4 mm between mating surfaces

Dimensional Tolerancing for Multi Jet Fusion

Tolerance defines the customer’s range of acceptable deviation from specifications for the physical part. Many customers, especially those who are newer to 3D printing, may be used to standard ranges for CNC machining services, which can achieve tolerances as tight as a millionth of an inch with secondary operations. But additive manufacturing services as a whole require looser tolerances, and MJF is no exception. 

MJF can achieve good tolerancing compared to other 3D printing processes like FDM.  For well designed parts, tolerance of +/- 0.3 mm (+/-0.012”) plus 0.05 mm/mm (+/-0.002 in/in) for each additional 25.4 mm ( 1.000”) can typically be achieved.  Tolerancing may change depending on part geometry.    

If you’re interested in using MJF or another 3D printing service for your next part, let’s talk. We can consult on our design and recommend the best process for your project. Request a quote today!