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Materials Science in Additive Manufacturing 3D-printed LMPA-integrated soft robots

In our designed LMPA-integrated soft gripper, the was chosen due to its excellent flexibility, durability,
LMPA serves a similar function in both pneumatic and and compatibility with 3D printing processes. The TPU
cable-driven soft robots. The primary purpose of the filament had a diameter of 1.75 mm, suitable for precise
LMPA is to enhance stiffness and enable shape locking extrusion through the 3D printer nozzle.
through phase transition, which is beneficial in both For the LMPA-integrated gripper, an LMPA was used
actuation mechanisms. In this work, we utilized a cable- to fill the interior of the gripper. The LMPA, supplied by
driven soft gripper as a case study example. The cable Dongguan Houjie Dingtai Metal Materials LTD (China),
and the tip of the soft gripper are fixed together. The consisted of a composition of tin 12.5%, bismuth 50%,
cable passes through the interior of the gripper and exits lead 25%, and cadmium 12.5%, with a melting point of
through the center of the soft gripper. Upon actuation, 70°C. This specific alloy was selected due to its suitable
the cable induces bending in the gripper due to its uneven melting point, ease of handling, and excellent thermal and
structural design. The fundamental operational concept of mechanical properties.
the designed gripper involves the contraction of the arms
to grasp components when subjected to wire tightening, 2.3. Manufacturing process
as illustrated in Figure 1A. This mechanism ensures that
the gripper can securely hold objects of varying shapes and The manufacturing of the soft grippers was carried out
sizes, making it suitable for a wide range of applications. using a customized 3D printer from Polarbear 3D (China).
Detailed dimensions and structural features of the pure This printer was modified to include an additional nozzle
TPU soft gripper and the LMPA-integrated TPU soft specifically for injecting LMPA, as shown in Figure 3. This
gripper are depicted in Figure 2. dual-nozzle setup allowed for the simultaneous printing of
TPU and injection of LMPA, streamlining the fabrication
2.2. Materials process.
The primary material used for fabricating the soft grippers Key printing parameters for TPU were meticulously
was TPU, sourced from Polymaker LTD (China). TPU calibrated to ensure optimal print quality and structural

A

B

C

Figure 1. Working principle of soft robots integrated with low-melting-point alloys. (A) Soft gripper function illustration; (B) working process of the pure
TPU soft gripper; (C) working process of the LMPA-integrated TPU soft gripper
Abbreviations: LMPA: Low-melting-point alloy; TPU: Thermoplastic polyurethane

Volume 3 Issue 3 (2024) 3 doi: 10.36922/msam.4144