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Using tailored temperature variations to obtain flawless forming of multi-stacked unidirectional prepreg
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. SAAB AB, Sweden.ORCID iD: 0000-0003-0613-2680
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. SAAB AB, Sweden.
SAAB AB, Sweden.
SAAB AB, Sweden.
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2020 (English)In: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 54, no 26, p. 3999-4009Article in journal (Refereed) Published
Abstract [en]

In this article, tailored temperature zones are used to obtain improved quality during rapid, high pressure forming of multi-stacked unidirectional prepreg. Particularly in aerospace applications, commonly used forming processes for multi-stacked unidirectional prepreg are often considered a bottleneck in production since the forming cycle requires both heating and cooling ramps and consequently takes long time—often about 1 h. It is possible to speed up the process by using elevated pressure and temperature. However, higher pressure and temperature also increase the influence of pressure gradient-driven, in-plane material movement (squeeze flow). This typically appears as radius thinning when forming a C-spar geometry on a male mold. Decrease of lay-up temperature will decrease radius thinning, but due to obstructed interply slippage, instead bending-induced wrinkles appear on the spar flange. In this article, tailored temperatures at the radius and in the flange area are introduced by using a hot lay-up and a cold mold. The results show that temperature differences of 6℃–10℃ between the radius area and the flange edge of the lay-up decreases radius thinning while still avoiding bending-induced wrinkles. Except from the radius temperature also the stacking sequence and the choice of prepreg system showed a significant influence on the radius thinning.

Place, publisher, year, edition, pages
SAGE Publications Ltd , 2020. Vol. 54, no 26, p. 3999-4009
Keywords [en]
Composites, forming, prepreg, Aerospace applications, Molds, Elevated pressure, Heating and cooling, High-pressure forming, Pressure and temperature, Stacking sequence, Temperature differences, Temperature variation, Temperature zone, Flanges
National Category
Vehicle Engineering Aerospace Engineering
Identifiers
URN: urn:nbn:se:kth:diva-287997DOI: 10.1177/0021998320924714ISI: 000533916800001Scopus ID: 2-s2.0-85085496405OAI: oai:DiVA.org:kth-287997DiVA, id: diva2:1513113
Note

QC 20220530

Available from: 2020-12-29 Created: 2020-12-29 Last updated: 2022-06-25Bibliographically approved
In thesis
1. Tooling and processing for efficient and high tolerance prepreg composite manufacturing
Open this publication in new window or tab >>Tooling and processing for efficient and high tolerance prepreg composite manufacturing
2022 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Composite use is normally motivated in aircraft design by improved weight-specific mechanical properties as compared to metals. However, fatigue and dielectric properties may also be critical for material selection. In the modern world the environmental footprint, with reduced emissions in focus, will be lighter with the successful use of composites. Flight safety is the most important requirement for the aerospace industry. In order to benefit from the important properties which ensure the necessary performance of the aircraft, part materials must be according to material specification. This is not unique to the composite materials. However, since the composite material is often created simultaneously with the composite part, the manufacturing processes used are even more critical for a composite part than for a metal part. Tooling is required for most of the process steps in composite part manufacturing. The large number of tools required to complete a composite part and the relatively small series involved in most composite applications render tooling cost a major contributor to final part cost. This is especially true in the aeronautical field considering the high-quality requirements as concerns shape accuracy and laminate quality, as well as low production rates with annual production ranging from a few dozen to the rare thousands of parts. Since tooling adds a substantial contribution to the part cost, it is imperative to be aware of the different options available for each process step and how these affect process stability and cost. Göte Strindberg, a former technical director at Saab, often said “Ninety-nine per cent right can be one hundred per cent wrong in a composite manufacturing process”. Finding the correct parameters for the last per cent is key to composite part success. This has been the overall goal of this project. The beginning of the project focused on both process and tooling related improvements for hot-forming of prepreg laminates enabling new opportunities and improved ergonomics. The research results in improvements in laminate quality, for example, reduced thickness variation, and a significant increase in process efficiency. One conclusion is that an 80% reduction of cycle time can be achieved with maintained, or even improved, laminate quality. A novel method for compensation of forming tools is also presented. Research then continued with cure tool related issues. Shape fidelity and durability for composite cure tools was studied with the combined outcome of an in-depth understanding of composite cure tool performance at the elevated temperature and moisture conditions present during the use of the tools.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2022. p. 161
Series
TRITA-SCI-FOU ; 2022:10
Keywords
Tooling, Composite Manufacturing, Mould, Cure tool, Hot-forming, Compensation, Moisture, Shape distortion
National Category
Composite Science and Engineering
Research subject
Aerospace Engineering
Identifiers
urn:nbn:se:kth:diva-312115 (URN)978-91-8040-246-0 (ISBN)
Public defence
2022-06-08, https://kth-se.zoom.us/j/61052452396, F3, Lindstedtsvägen 26, Stockholm, 09:00 (English)
Opponent
Supervisors
Funder
Swedish Foundation for Strategic Research, ID15-0042
Note

QC 220512

Available from: 2022-05-12 Created: 2022-05-11 Last updated: 2022-06-25Bibliographically approved

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Hallander, PerGrankäll, TommyÅkermo, Malin

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