Reason of lamination close-in (Negative springback)
I have a female mold which I’m using to laminate approx. 90 degree angles out of strips of veneer and sometimes bamboo fibre. My layup consists of three to five strips of 0.6mm veneer with bamboo fibre in between (if included). For glue I use epoxy. The bend in the cured laminate is allways thighter than the molds 90 degree angle. The close-in seems to vary according to the thickness of the laminate. The thicker the laminate the more close in. But not allways. For example five layers of veneer with no fibre in between the close-in is about five degrees, whereas just as thick laminate of three layers of veneer with 2 layers bamboo fabric in between them results in three degree close in. The gluing or pressing time, pressure or heat don’t affect the end result. My question is, what causes the close in?
Replies
Check the specs on the epoxy you are using to see what the shrinkage is on it. If I am following your discription it sounds like the more epoxy you have the greater the movement. All epoxy has a certain amount of shrinkage. Usually the faster it cures the more shrinkage it has but different fillers and other conditions do effect it.
Rich
Is there anything else that you have not told, like wetting the plys before pre-bending?
I have never had any issues with changes in the epoxy, but shrinkage in the individual plys would cause this problem.
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