Fabrication of High Quality, Large Wet Lay-Up/Vacuum Bag Laminates by Sliding a Magnetic Tool

Abstract

This study presents a novel method to fabricate high-quality, large composite parts which can be used in a wet lay-up/vacuum bag (WLVB) process. The new method utilizes a commercial lifting magnet, which is commonly used for transporting ferrous plates, to apply a magnetic consolidation pressure on the WLVB composite lay-up. The pressure is applied on a large area of the laminate by slowly sliding the magnet over the vacuum bag surface, which leads to an improved laminate quality. When further improvement is desirable, multiple passes of the magnet can be performed, where each pass successively compacts the lay-up. To explore the feasibility of implementing this technique, random mat and plain weave glass/epoxy laminates were fabricated, and their properties compared to conventional WLVB laminates. The effects of the number of moving passes of the lifting magnet on the laminate microstructure and properties are also investigated. As a result of multiple passes, the fiber volume fraction in random mat and plain weave laminates increases to 34% and 53%, representing 80% and 16% improvements, respectively. In addition, the void volume fraction reduces almost by 60% to a very low level of 0.7% and 1.1%, respectively. Consequently, the flexural properties considerably enhance by 20⁻81%, which demonstrates the potential of the proposed method to produce WLVB parts with substantially higher quality. It is also shown that there exists an optimal number of passes, depending on the fabric type where additional passes induce new voids as a result of excessive resin removal.

Keywords: consolidation; lifting magnet; mechanical properties; polymer-matrix composites; wet lay-up/vacuum bagging.

Figure 1

(a) General view of lifting magnet; (b) bottom surface of the lifting magnet; (c) the handle on the lifting magnet at ON position; (d) the handle on the lifting magnet at OFF position; (e) schematic of magnetic field at ON position; and (f) schematic of magnetic field at OFF position.

Figure 1

(a) General view of lifting magnet; (b) bottom surface of the lifting magnet; (c) the handle on the lifting magnet at ON position; (d) the handle on the lifting magnet at OFF position; (e) schematic of magnetic field at ON position; and (f) schematic of magnetic field at OFF position.

Figure 2

(a) Compaction pressure of the lifting magnet versus gap (i.e., lay-up thickness) and (b) a photograph of the experimental set-up used for measuring the magnetic pressure. The open and solid circles represent the thickness of uncompacted and compacted 4-ply random mat lay-up. The open and solid triangles correspond to the thickness of uncompacted and compacted 6-ply plain weave lay-up.

Figure 3

Wet layup/vacuum bag lay-up under vacuum. The magnet was applied to the greased (red) area. A single pass of magnet included compacting the lay-up from point 1 to 2 and point 3 to 4.

Figure 4

(a) Thickness, fiber volume fraction, and (b) void volume fraction of random mat laminates fabricated with wet lay-up/vacuum bag (WLVB) and with an increasing number of magnet passes (i.e., 0, 1, 6, 12, and 18 passes). Note: Error bars show the 95% confidence interval (n = 6 samples for fiber volume fraction and void volume fraction; n = 70 samples for laminate thickness). The percentages shown in (a) correspond to the percent thickness reduction between number of passes labeled in the figure.

Figure 5

(a) Thickness, fiber volume fraction, and (b) void volume fraction of plain weave laminates fabricated with WLVB and increasing number of magnet passes (i.e., 0, 1, 6, and 12 passes). Note: Error bars show the 95% confidence interval (n = 6 samples for fiber volume fraction and void volume fraction; n = 70 samples for laminate thickness). The percentages shown in (a) correspond to the percent thickness reduction between number of passes labeled in the figure.

Figure 6

Scanning electron microscopy (SEM) images of random mat laminates (at 20× magnification) made by WLVB process and sliding lifting magnet over the saturated lay-up with (a) 0 pass (arrows show the resin-rich inter-tow regions); (b) 1 pass; (c) 6 passes; (d) 12 passes; and (e) 18 passes.

Figure 7

Scanning electron microscopy (SEM) images of plain weave laminates (at 35× magnification) made by WLVB process and sliding lifting magnet on the saturated lay-up with (a) 0 pass; (b) 1 pass; (c) 6 passes; and (d) 12 passes.

Figure 8

Scanning electron microscopy (SEM) images of plain weave laminates (at 150× magnification) made by WLVB process and sliding lifting magnet on the saturated lay-up with (a) 0 pass; (b) 6 passes; and (c) 12 passes. Note: Arrows point to the small voids inside the fiber tows.

Figure 9

(a) Flexural strength and (b) modulus of random mat laminates fabricated with WLVB and increasing number of passes of a lifting magnet (i.e., 0, 1, 6, 12, and 18 passes). Void and fiber volume fraction values are also presented. Note: Error bars show the 95% confidence interval (n = 14 samples).

Figure 10

(a) Flexural strength and (b) modulus of plain weave laminates fabricated with WLVB and increasing number of passes of a lifting magnet (i.e., 0, 1, 6, and 12 passes). Void and fiber volume fraction values are also presented. Note: Error bars show the 95% confidence interval (n = 14 samples).