# Fabrication and Drag Reduction Performance of Flexible Bio-Inspired Micro-Dimple Film

## TL;DR

This paper presents a flexible bio-inspired micro-dimple film that reduces drag, suitable for aerospace and underwater applications.

## Contribution

A novel fabrication method for bio-inspired micro-dimple films using TPU and optimized injection parameters is introduced.

## Key findings

- Polishing significantly improves mold core surface roughness and film replication accuracy.
- Optimized injection parameters achieved a shape accuracy of 13.502 μm and bottom roughness of 0.033 μm.
- The film demonstrated a drag reduction rate of up to 10.26% with less than 5% discrepancy between simulation and experiment.

## Abstract

The flexible micro-structured surface found in biological skins exhibits remarkable drag reduction properties, inspiring applications in the aerospace industry, underwater exploration, and pipeline transportation. To address the challenge of efficiently replicating such structures, this study presents a composite flexible polymer film with a bio-inspired micro-dimple array, fabricated via an integrated process of precision milling, polishing, and micro-injection molding using thermoplastic polyurethane (TPU). We systematically investigated the influence of key injection parameters on the shape accuracy and surface quality of the film. The experimental results show that polishing technology can significantly reduce mold core surface roughness, thereby enhancing film replication accuracy. Among the parameters, melt temperature and holding time exerted the most significant effects on shape precision PV and bottom roughness Ra, while injection speed showed the least influence. Under optimized conditions of a melt temperature of 180 °C, injection speed of 60 mm/s, holding pressure of 7 MPa, and holding time of 13 s, the film achieved a micro-structure shape accuracy of 13.502 μm and bottom roughness of 0.033 μm. Numerical simulation predicted a maximum drag reduction rate of 10.26%, attributable to vortex cushion effects within the dimples. This performance was experimentally validated in a flow velocity range of 0.6–2 m/s, with the discrepancy between simulated and measured drag reduction kept within 5%, demonstrating the efficacy of the proposed manufacturing route for flexible bio-inspired drag reduction film.