Abstract
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.
Highlights
Automated tape lay-up of unidirectional (UD) prepreg combined with forming offers a cost-competitive manufacturing method for composite aircraft components.[1]
This paper presents an experimental study on how tailored temperature variations can be used to avoid radius thinning and bending-induced wrinkling during the high-pressure forming of a multi-stacked thermoset prepreg into a C-spar
Multi-stack forming of aerospace-grade prepreg components is often considered to be a bottleneck in production
Summary
Automated tape lay-up of unidirectional (UD) prepreg combined with forming offers a cost-competitive manufacturing method for composite aircraft components.[1]. Hallander et al.[3] showed that fast forming of multi-stacked UD prepreg could be performed using a high-pressure method (in this case fluid cell press forming). When using high forming pressures in the span of 100–400 bars, inplane material movement occurred due to the pressure gradient developed (squeeze flow), which influenced the forming result. Yanagimoto and Ikeuchi[4] presented a technique for hydraulic press forming where multi-stacked prepreg was sandwiched between two mild steel sheets. Hallander et al.[3] showed that this technique was used when forming a double curved spar in the fluid cell press at 400 bars pressure. The study showed that the squeeze flow effects were effectively reduced on the spar web and flanges when using the steel sheet sandwich technique.
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