In the precision-oriented world of HP Multi Jet Fusion (MJF) 3D printing, designing effective threads and integrating threaded inserts are crucial for functional and durable assemblies. This article delves into best practices for creating threads and using threaded inserts in MJF designs, ensuring strong and reliable connections.
Designing MJF Threads:
MJF technology enables the printing of both external and internal threads, eliminating the need for mechanical thread-forming operations. For optimal results, it’s recommended to design threads larger than 6 mm (M6 or ¼ inch per the Imperial system). Smaller threads may require the use of self-tapping screws, threaded inserts, or machining after printing.
Using Self-Tapping Screws:
Self-tapping screws, which create their threads as they are driven into the part, are ideal for small threads up to 6 mm. They may require a pre-formed hole, with dimensions usually provided by the screw supplier.
When precision is paramount, especially for small threads, machining the part after printing is an effective method. The same tools used for machining technical plastics are recommended for MJF parts.
To machine internal threads, start from a pre-formed hole and then use the required tap. Drill size recommendations for metric plastic threads can be applied for designing the pre-hole.
For external threads, begin with a solid printed cylinder and machine the thread using the required die. The cylinder’s diameter should be slightly smaller than the die’s major diameter.
Standard Printed Threads:
For threads larger than 6 mm, following international standards like DIN 13-1, ISO 965-2, or ANSI/ASME B1.1 is advised. Use less restrictive tolerance values for internal threads and more restrictive ones for external threads.
Design all external and internal threads with a gap of 0.2 mm to 0.4 mm between them. Ensure to remove sharp edges and apply a minimum radius of 0.1 mm for HP MJF parts.
Threads should be cleaned using a sandblasting machine with glass bead particles to ensure fine detail. Avoid painting threads, as it can alter dimensional accuracy. Dyeing is preferred for coloring threaded parts.
Designing for Threaded Inserts in MJF Nylon:
Threaded inserts provide a strong, reusable thread in plastic parts and are ideal for assemblies requiring frequent disassembly.
Threaded Insert Recommendations:
- Hole Diameter: Ensure the hole diameter is appropriate for the insert type, considering the dimensional variations in MJF parts.
- Bosses: Use bosses for mounting purposes or as a receptacle for threaded inserts. The boss diameter is typically twice the size of the external diameter of inserts less than 6 mm.
- Mating Parts: Design the mating part hole larger than the assembly bolt but smaller than the diameter of the insert.
Understanding the intricacies of designing threads and integrating threaded inserts in MJF technology is key to creating strong, durable, and functional 3D-printed parts. By following these guidelines, designers can ensure their MJF prints meet the highest standards of precision and reliability.