Consolidation and Tow Spreading of Digitally Manufactured Continuous Fiber Reinforced Composites from Thermoplastic Commingled Tow Using a Five-Axis Extrusion System

Mark E Bourgeois,Donald W Radford

doi:10.3390/jcs5030073

Abstract

During the development of digitally manufactured, commingled tow continuous fiber reinforced composites, consolidation force was controlled using a controlled spring force that yielded a repeatable tow width. However, the use of the extruder face to consolidate the material requires that the extruder remain perpendicular to the placement surface throughout the process. When considering more complex tool contours including sloped surfaces, more than three axes of motion are necessary to maintain the perpendicularity of the extruder tip to the surface. In this effort, a five-axis system is developed and used to demonstrate the ability to consolidate over complex contours. In addition, the nozzle face temperatures required for good consolidation and wetout result in poor tow path fidelity when complex paths are introduced. The implementation of an automated, computer-controlled localized cooling system enables both good wetout and consolidation while also enabling more accurate changes in tow path due to improvements in local tow tack. With the development of the five-axis system it is also shown that the tow width can be adjusted by rotating the existing placement nozzle to angles not equal to 90°. Thus, through a combination of controlled localized cooling and real-time control of the nozzle angle, a possible approach to control of tow width, independent of the tow placement angle and radius of curvature during tow steering, is described.

Highlights

A five-axis digital tow placement system is developed and used to demonstrate the ability to consolidate a high-volume fraction continuous fiber composite placed on tools with both horizontal and sloped surfaces and to utilize the multi-axis capability to adjust the placed tow width through a tow spreading operation
The impregnation of a continuous reinforcing fiber tow with thermoplastic matrix materials using techniques similar to fused deposition modeling (FDM) 3D printing can occur in three different locations: (i) wetting out the fiber before the printing processes, (ii) wetting out the fiber in the print head, and (iii) wetting out the fiber on the component [1]
The non-linear tow placement paths shown in Figure 11a demonstrate the challenges involved in simultaneously maintaining consolidation pressure and changing direction, even on the top horizontal surface

Summary

Introduction

A five-axis digital tow placement system is developed and used to demonstrate the ability to consolidate a high-volume fraction continuous fiber composite placed on tools with both horizontal and sloped surfaces and to utilize the multi-axis capability to adjust the placed tow width through a tow spreading operation. The current state of commercial composite manufacturing with fused deposition modeling (FDM)-based fiber placement may be considered to be the MARK TWO and MARK X from Markforged These machines are limited to adding in-plane continuous fiber reinforcement to individual layers of thermoplastic 3D printed parts. Wetting out the fiber before printing, by co-extrusion of continuous fiber and the thermoplastic matrix into a fiber reinforced thermoplastic printing filament, is a straight-forward extension of FDM printing, requiring only minor hardware changes to the 3D printer. This is the method that the MARK TWO and the MARK X use. Wetting out the fiber on the component is likely the most difficult approach to achieve good results due to the added complexity of creating two systems, one that places the dry fiber and the other that places the matrix simultaneously [2]

Methods

Results

Conclusion