Changing the hardness of parts printed in TPU 90A Powder Using the PreForm Print Settings Editor

TPU 90A Powder is a fantastic material for printing high-quality elastomeric parts with the Fuse 1+ 30W, but the high hardness of the base powder makes it an ineffective choice for certain applications. Having a different material for each hardness would be impractical for an efficient workflow on a single printer.

Using the PreForm Print Settings Editor, you can modify the hardness of TPU 90A Powder. For many print applications, modifying the settings will create high-quality prints with the exact hardness desired. Unlike changing materials, changing print settings does not require any additional cleaning or modification between prints—you can print parts with different hardnesses back to back, all within the same workflow. However, there are risks associated with using the Print Settings Editor which may cause certain parts to fail or features to not resolve as they would at a 90A hardness.

There are two main settings that can be used to control the hardness of parts printed with TPU 90A Powder:

A range of Fill Laser Power and Fill Hatch Spacing values will produce usable parts at different hardnesses:

• Fill Laser Power: 15,000–28,500 mW
• Fill Hatch Spacing: 0.12–0.45 mm

The result of modifying these settings can be seen here. The raw data used to create this graph is given below.

Shore hardnesses of as low as 38 Shore A were achieved during testing. In general, Fill Hatch Spacing plays a much larger role in determining hardness, with Fill Laser Power amplifying the effect. For example, for a hardness of 60 Shore A, a good starting point would be a Fill Hatch Spacing of 0.35 mm and a Fill Laser Power of 21,000 mW.

Follow the instructions in Using the PreForm Print Settings Editor (SLS) to modify the print settings.

Sample print setting downloads

Here are sample print settings for achieving 40A, 50A, 60A, and 80A Shore hardness using TPU 90A Powder. Use these as a starting point when developing your own print settings, along with the graph above and testing data below.

• 40A hardness
• 50A hardness
• 60A hardness
• 80A hardness

Effect of Fill Hatch Spacing on part quality

At a Fill Hatch Spacing of 0.45 mm, there are visible surface effects from the hatch spacing, but features still typically resolve. Thick parts may still print with wider spacings, but they may have significant defects, as shown below. Formlabs does not recommend printing thin parts with greater than 0.45 mm spacing.

As the Shore hardness of a part decreases, the bulk density also decreases, with the part becoming more of a foam at the microscopic level. This impacts mechanical properties other than hardness as well as the watertightness of the parts. If you are planning on using the part in an application that requires a certain amount of mechanical resistance and wear, make sure to test the part fully.

Because the material is only partially sintered, there is a sharp dropoff in many properties, particularly elongation at break (EAB), ultimate tensile strength (UTS), and stiffness. This is easy to see on long strips like the tensile bars in this image. The rearmost bar has a Shore hardness of 40A, the middle bar has a hardness of 60A, and the front bar has a hardness of 80A. The 40A sample flexes down to the work surface under its own weight.

To quantify this effect more precisely, see the graphs below. Reducing the hardness from 90A to 80A also reduces the UTS and maximum strain of the parts by over 50%. This makes it more likely for parts to tear during depowdering, damaging fine features.

• As hardness decreases, the risk of print issues increases.
• Since the hardness of 90A is the hardness of the bulk material, it is not possible to significantly increase the hardness beyond 90A.
• Bed temperature variations occur from printer to printer and within a given build. These can have an effect on the resulting hardness of the part. In general, expect a +/- 5 Shore A variation throughout a given build. The variation will be smaller the closer the hardness is to that of the bulk material (90A).

The table below lists raw data from Formlabs testing on the effect of Fill Laser Power and Fill Hatch Spacing on Shore hardness. Reference this data when developing your own print settings.