3D printing suspended structure design: minimizing self-supporting angles and supporting materials

Basic concepts and challenges of suspended structures

Suspended structures refer to parts that are not supported by underlying materials during the 3D printing process. They are a typical feature that distinguishes additive manufacturing from subtractive manufacturing. The FDM process has limited suspension capabilities and usually requires additional support after the inclination angle exceeds 45 degrees. The SLA/DLP process has even weaker suspension capabilities and requires support for almost any horizontal projection area. The metal SLM process also requires a large number of support structures to conduct heat and control deformation. Improper design of suspended structures can lead to print failure, reduced surface quality, and difficulty in support removal. Understanding the concept of self-supporting angle is the basis for optimal design.

Self-support angle standards for different processes

The self-support angle refers to the minimum inclination angle at which a suspended structure can be successfully printed without additional support. The self-supporting angle of the FDM process is usually 45 degrees, that is, when the angle between the suspended surface and the horizontal surface is not less than 45 degrees, support-free printing can be performed. Some high-end FDM equipment can increase the self-support angle to 50-60 degrees by optimizing cooling and extrusion control. The self-supporting angle of the SLA/DLP process is larger, usually 60-70 degrees. The self-supporting angle of the SLS/SLM metal process varies depending on the thermal properties of the material, usually in the range of 30-45 degrees. The self-supporting angle standard needs to be determined according to the process used during design.

Design strategy for minimizing support materials

Reducing the use of support materials can reduce material consumption, shorten printing time, and simplify post-processing procedures. The first is to orient the part, so that the side with the largest suspended area faces the printing platform, or adjust the suspended surface to a steep angle. The second step is to add chamfers and change the suspended sharp edges into bevels to make the inclination reach the self-supporting standard. The third is to design hollows and change the solid suspended structure into a frame structure to reduce the horizontal area that needs to be supported. The fourth is segmented printing, which splits complex parts into multiple parts and prints them separately before assembly. Each part can be printed in the optimal direction. The fifth is to use the existing structure and use the walls and ribs of the parts themselves as supports during design.

Application skills of soluble supports

For suspended structures where support cannot be avoided, the use of soluble support materials is an effective method to reduce the difficulty of post-processing. The dual-nozzle FDM equipment can use the auxiliary nozzle to print PVA or HIPS supports while the main nozzle prints part materials. After printing, the part is immersed in water (PVA) or limonene solution (HIPS), and the support structure automatically dissolves. When designing a soluble support, attention should be paid to the contact area between the support and the part. If the contact area is too large, it will leave traces, and if the contact area is too small, the support will be unstable. The support density setting affects the removal speed, and it is recommended to set it to 10-20%.

Quality inspection and improvement of suspended structures

After printing is completed, special quality inspection of suspended structures is required. First check the surface sagging and measure the deviation between the actual position of the suspended surface and the designed position. The qualification standard is usually less than 2 times the layer thickness. Secondly, check the surface roughness. The top surface of the suspended surface is usually rougher than the side surface. It needs to be evaluated whether it meets the usage requirements. Third, check the edge sharpness. There may be rounded corners or burrs on the hanging edges, which require post-processing and trimming. For unqualified suspended structures, the reasons need to be analyzed and the design or printing parameters should be optimized. Common improvements include adjusting the print direction, adding supports, or reducing the print speed.