Pulled a cored panel under full vacuum and when I debagged it the foam had crushed and dimpled, worst along the edges and over a curved section. The bond looks patchy in those spots as well. Bit gutted, where did this go wrong?
A few things tend to cause that, and often it is a combination. Crushing usually means the core grade was too soft for the pressure you pulled, so full vacuum, roughly one atmosphere, simply overpowered a low-density foam, particularly where it was being forced down onto a curve. Dimpling frequently comes from too much bonding paste or resin that has nowhere to go, or from a scrimmed or perforated core where the vacuum sucks the skin down into every hole. Along edges it is often a lack of support, so the core deflects and cracks the bond line. Try a firmer core grade or drop the vacuum level once you have consolidated, use a controlled bond-paste thickness rather than a heavy bed, and support or chamfer the edges. If the bond is patchy, check your adhesive coverage, since the structural adhesives pages set out the general options. For a soft panel that has already crushed, it is best treated as compromised rather than reused.
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