Effect of gas pressure on the microstructure of parts foamed with the novel microcellular injection molding technology Ku‐Fizz™

Abstract

The increasing demand for lightweight and economical automotive components boosts investigation of advanced materials and new lightweighting technologies. This work employs the novel microcellular injection molding technology Ku‐Fizz™. The process introduces gas with granulates at moderate low pressures into the feed zone of the injection molding machine. Ku‐Fizz is controlled by gas pressure; thus, a simple plate geometry was molded and the effect of various gas contents on the microstructure was analyzed. The material used was a chemically coupled glass fiber‐reinforced polypropylene compound. Optical microscopy was employed to measure the foam microstructure. Microcomputed tomography was used to quantify the fiber volume fraction and the orientation tensors. Results of the fully characterized microstructure showed cell density increasing and cell size decreasing with gas pressure and melt flow direction. Fiber length increased with gas content. Cell growth displaced fibers from the center of the part towards the mold surface, changing the fiber concentration and global fiber orientation.

Mechanical Response of Fiber-Filled Automotive Body Panels Manufactured with the Ku-FizzTM Microcellular Injection Molding Process

“…As shown in Figure 9 and previous work [4,50], the processing of glass fiber-reinforced PP in the presence of gas reduces the occurrence of fiber breakage during processing. For foamed and compact panels, a weight average length, L W , of 1.89 mm and 1.67 mm were recorded, resulting in a 14% increase in FL.…”

“…The foam morphology and its representative values, CD and CS, were determined by the procedure outlined in [4]. The technique consists of grinding and polishing the embedded specimen, followed by a microscopy and an image processing step.…”

“…To estimate the modal properties of the door panels, a free-free vibration hammer tap test was performed. The panels were hung on an adjustable steel frame with elastic FO and fiber concentration (FC) were obtained with the X-ray microcomputed tomography (µCT) approach described in [4]. Discs of dimensions 10 mm 2 × 2.0/2.2 mm were scanned with an industrial µCT system (Metrotom 800, Carl Zeiss AG, Oberkochen, Germany).…”

“…The presence of gas changes the matrix rheology, effectively modifying the velocity profile and its effect on FO. Additionally, bubble growth displaces and re-aligns fibers [4,50,53]. The global FO for compact and foamed panels is shown in Table 3.…”

“…Both foaming and LFTs have demonstrated their potential in the automotive industry [3,[5][6][7][8][9][10][11][12][13][14][15]. Previous work has shown that the foam and fiber microstructure (MS) obtained with Ku-Fizz differs from the leading microcellular foaming technology, MuCell [4]. It was found that the introduction of gas and the presence of foam cells significantly modified the fiber MS.…”