# Flexible joints performance assessment of additive manufacturing FDM 3D printed TPU

## TL;DR

This paper studies how different 3D printing parameters affect the mechanical behavior of flexible joints used in robotics.

## Contribution

The study introduces a method to assess the damping and spring coefficients of TPU 3D-printed joints using the Box-Benken design and statistical analysis.

## Key findings

- Density, layer thickness, and width most influence damping behavior.
- Raster angle has the greatest impact on the spring coefficient.
- 3D-printing parameters significantly affect the mechanical performance of flexible joints.

## Abstract

Given the increasing adoption of flexible 3D-printed joints in the field of robotics, it is essential to characterize the stiffness/spring coefficient and damping of printed specimens to understand the effects of various processing parameters and their interactions under different loading conditions. This study aims to research the effects of 3D-printed parameters and geometric dimensions, i.e, printing density, layer thickness, raster angle, length, width, and height. The Box-Benken design of experiments is conducted to obtain 44 different parametric combinations to characterize the damping and spring coefficients CF, KF, 𝐂τ, 𝐊τ under a dynamic load. The damping and spring coefficients are characterized using the minimum squared method. Depending on the force decomposition, the damping and spring coefficients are different in each direction. To analyse the experimental results, a MANOVA, ANOVA analysis, and a correlation heatmap are used to show that the density, layer thickness, and width have the most influence on the damping. In contrast, raster angle has the most influence on the spring coefficient. Finally, the results show that the geometric and 3D-printing parameters play a significant role in the mechanical behaviour of flexible joints. The technology can be used in the design of robots that require energy-saving and releasing mechanisms, and to avoid the use of ball bearings under a dynamic load.