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In the world of manufacturing, additive manufacturing, also known as 3D printing, has revolutionized the way products are designed and produced. One of the leading technologies in this field is the HP Multi Jet Fusion (MJF) with its advanced capabilities and high-quality output. If you’re looking to design parts for additive manufacturing using HP MJF, this comprehensive guide will provide you with all the information you need to create optimal designs that leverage the full potential of this technology.

Introduction to Additive Manufacturing and HP MJF

What is Additive Manufacturing?

Additive manufacturing, also referred to as 3D printing, is a process that builds three-dimensional objects by adding layer upon layer of material. Unlike traditional manufacturing methods that involve subtracting material from a solid block, additive manufacturing allows for the creation of complex geometries that were previously impossible to achieve.

The Advantages of Additive Manufacturing

Additive manufacturing offers a range of advantages over traditional manufacturing methods:

1. Design Freedom: Additive manufacturing enables the creation of highly complex and intricate designs that were previously unachievable.
2. Cost-Effective: With additive manufacturing, there is no need for expensive tooling or molds, making it a cost-effective solution for low-volume production.
3. Faster Time to Market: The ability to rapidly prototype and iterate designs allows for faster product development cycles.
4. Customization: Additive manufacturing allows for the customization of products, tailoring them to specific customer needs.
5. Reduced Material Waste: Unlike traditional manufacturing methods, where excess material is often discarded, additive manufacturing minimizes material waste by only using the exact amount required for the part.

Introducing HP Multi Jet Fusion (MJF)

HP Multi Jet Fusion (MJF) is a leading additive manufacturing technology that utilizes a process known as voxel-level fusion. This technology allows for precise control over the material properties at a voxel level, resulting in high-quality, functional parts.

The Benefits of HP MJF

HP MJF offers several advantages that make it a preferred choice for additive manufacturing:

1. High Speed: HP MJF is capable of achieving high production speeds, making it ideal for both prototyping and production applications.
2. High Resolution: With a layer thickness as low as 80 microns, HP MJF can produce intricate details and smooth surface finishes.
3. Mechanical Strength: Parts produced with HP MJF exhibit excellent mechanical properties, including high strength and durability.
4. Wide Range of Materials: HP MJF supports a variety of materials, including nylon (PA 12), which offers a balance of strength, flexibility, and chemical resistance.

Design Considerations for HP MJF

When designing parts for HP MJF, there are several important considerations to keep in mind to ensure optimal results. These considerations include file preparation, tessellation, and addressing common issues with STL files.

File Preparation

Before sending a job to an HP MJF printer, it’s essential to ensure proper file preparation. This involves converting the model into a suitable format and optimizing it for additive manufacturing.

Tessellation

Tessellation is the process of converting the model’s geometry into triangles, which are used by the printer to create layers. Proper tessellation is crucial to avoid inaccuracies and slow processing. The standard formats supported by HP MJF include 3MF and STL.

To achieve the best surface-to-file size ratio when exporting to STL, it’s recommended to adjust parameters such as angle tolerance and deviation chord height. These parameters define the resolution and file size of the part.

STL Problems

STL files can often suffer from various issues that may affect the printing process. Some common problems include:

1. Too Many or Too Few Triangles: Excessive triangles can increase processing time without providing any additional accuracy, while too few triangles may result in inaccuracies.
2. Holes in Triangles: STL models may have surfaces that are not properly joined, resulting in missing surfaces and holes.
3. Flipped-Direction Triangles: In some cases, triangles may be flipped, causing inconsistencies in the part’s geometry.
4. Tiny Shells: Parts may contain small, disconnected shells that can cause issues during printing.

To address these issues, STL-repairing software such as Magics, Netfabb, or HP SmartStream 3D Build Manager can be used.

Minimum Specification for Parts

To ensure optimal print quality and functionality, it’s important to adhere to certain specifications when designing parts for HP MJF.

Minimum Printable Features

The minimum printable features in the X, Y, and Z planes include:

• Minimum Hole Diameter (at 1 mm thickness): 0.5 mm
• Minimum Shaft Diameter (at 10 mm height): 0.5 mm
• Minimum Printable Font Size for Embossed or Debossed Letters or Numbers: 6 pt
• Minimum Clearance (at 1 mm thickness): 0.5 mm
• Minimum Slit Between Walls: 0.5 mm

Engraving

HP MJF technology allows for high-resolution engraving, providing the ability to print letters and drawings with excellent definition. To achieve the best results, it’s recommended to have a minimum depth or height of 1 mm for any text, number, or drawing included in a part.

Design Tips for Optimal Performance

To optimize the performance of parts produced with HP MJF, consider the following design tips:

Solid Part or Structural Fill

HP MJF enables the printing of topology-optimized designs and lattice structures. These designs help reduce the weight of the part and the quantity of material used, making them suitable for weight-sensitive applications. When designing lattice structures, ensure a minimum gap of 1 mm to facilitate the removal of excess material.

Cantilevers

When printing a cantilever, the minimum wall thickness depends on the aspect ratio, which is the length divided by the width. For cantilevers with a width less than 1 mm, the aspect ratio should be less than 1. No specific recommendations exist for widths greater than 1 mm.

Wall Thickness

The minimum recommended wall thickness for short walls oriented in the XY plane is 0.3 mm, while for short walls oriented in the Z plane, it is 0.4 mm. For parts with a high aspect ratio, consider increasing the wall thickness or adding ribs or fillets to reinforce the structure.

Assembly and Clearance

When designing parts that need to be assembled after printing, ensure a minimum gap of 0.4 mm (±0.2 mm tolerance for each part) between the interface areas to ensure proper assembly. For parts printed as assemblies, maintain a minimum clearance of 0.7 mm. Parts with thick walls above 50 mm should have a larger gap to ensure proper performance.

Hollow Closed Geometries

If a part is hollow, it’s crucial to include drain holes to remove excess material. The recommended minimum diameter for these holes is 2 mm, and including at least two holes is advised.

Glue Lines

For larger parts that exceed the maximum build size, they can be printed in multiple sections and joined together using glue or other methods. To facilitate the bonding process, include interlocking features or additional spacing between parts.

Ducts

To remove material from narrow ducts, consider designing and printing a strip or a chain through the duct. After printing, the chain can be pulled out to dislodge most of the material, with any remaining material removed during the cleaning process.

Orientation and Optimization

When designing parts for HP MJF, the orientation of the part within the build chamber plays a crucial role in achieving optimal results. Consider the following factors when determining the orientation of your design:

Aesthetics

To avoid visible stair-stepping on curved or sloped surfaces, it’s recommended to position those surfaces at angles greater than a certain threshold with the horizontal (XY plane). The minimum and maximum angle thresholds depend on the layer thickness, with values ranging from 0° to 20°.

Accuracy

The accuracy of parts produced with HP MJF is better in the XY plane than in the Z direction. To ensure the highest resolution for features that require precision, place them in the XY plane whenever possible. Additionally, orienting cylindrical bodies vertically can further enhance accuracy.

Surface Smoothness

To achieve the smoothest surface finish, position surfaces that require a high level of smoothness upside down in the build chamber. This orientation helps minimize layer lines and improve the overall aesthetic quality of the part.

Sharp Surfaces

When designing parts with sharp surfaces, it’s recommended to print them facing up to ensure optimal resolution and surface quality.

Mechanical Properties and Load-Bearing Features

To maximize the mechanical properties of a part, position load-bearing features, such as pins or clips, horizontally in the XY plane. This orientation ensures optimal strength and load-bearing capabilities.

Warping Minimization

To minimize warping and achieve the best print quality, position long flat surfaces flat in the horizontal plane. This is particularly important for long and thin parts. Placing critical parts in the center of the build chamber can also help achieve uniform cooling and minimize warping.

Design Considerations for Curved Surfaces

To optimize the smoothness of curved surfaces, position them upside down in the build chamber. This orientation helps minimize the visibility of layer lines and ensures a high-quality surface finish.

Repeatability and Printer Stability

To ensure maximum repeatability and printer stability, try to maintain consistent printing conditions, including the position of the part within the build chamber.

Distance Between Parts

When printing multiple parts simultaneously, maintain a minimum distance of 2 mm between them to ensure printer stability and prevent interference between parts.

Why Generate a Sinter Box?

When printing small or delicate parts, it’s beneficial to generate a sinter box to protect and organize the parts during the printing process. Some software can automatically generate a sinter box, which can also be customized by adding names or QR codes for easy tracking and identification.

Conclusion

Designing parts for additive manufacturing, specifically HP MJF, requires careful consideration of various factors to ensure optimal results. By following the guidelines and design considerations outlined in this comprehensive guide, you can harness the full potential of HP MJF technology and create high-quality, functional parts that meet your specific requirements. With its speed, resolution, and material capabilities, HP MJF opens up new possibilities for innovative and efficient manufacturing processes. Start designing for the future of manufacturing today!