Vacuum-Assisted Hot-Forming Using Tailored Laminate Temperature

Tommy Grankäll,Per Hallander,Malin Åkermo

doi:10.1007/s10443-020-09858-8

Tommy Grankäll, Per Hallander + Show 1 more

Open Access

https://doi.org/10.1007/s10443-020-09858-8

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Abstract

A non-isothermal vacuum assisted hot-forming process using tailored laminate temperature is introduced. By using process simulation and manufacturing experiments, improved laminate quality is achieved compared to the standard hot-forming process. Furthermore, it is also shown that the manufacturing time in the clean room can be reduced to one tenth of the standard process time. In this study 8.4 mm thick quasi-isotropic laminates from unidirectional prepreg were laid up flat with an automatic tape laying machine and hot-formed to a U-shaped laminate. The laminates were then cured in a concave mould with standard bag on the inside. A complete tailored temperature hot-forming cycle of 7.5 min produced a very good final laminate quality with a total thickness variation as low as 4.0% and without wrinkles or indications of porosity. With a 4 min hot-forming cycle the thickness variation was also acceptable at 8%.

Highlights

Hot-forming is an automation technique which can be used to decrease manufacturing cost for thermoset prepreg parts
Previous work by Hallander et al [1, 2] indicates that this method is valid for many cases but that it is considered to be a bottleneck in production with industrial standard hot-forming process times in the range of 40–60 min
As the entire laminate comes into contact with the forming tool the bottom surface of the laminate cools down instantly

Summary

Introduction

Hot-forming is an automation technique which can be used to decrease manufacturing cost for thermoset prepreg parts. With this technique, several prepreg plies are laid up flat and formed simultaneously by heating the plies and forming them over a convex tool using a flexible membrane and vacuum. Several prepreg plies are laid up flat and formed simultaneously by heating the plies and forming them over a convex tool using a flexible membrane and vacuum This process, called multi-layer forming, can produce e.g. a U-shaped part. A hot-forming process with total cycle time of around 12 min has been reported for a thin (2 mm) laminate [3]

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