moulding warping

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moulding warping

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FLD	FLD posted 9 Years Ago HOT Topic Details
Group: Forum Members Posts: 468, Visits: 2.7K	I went round to a friends house who's also a hobby moulder. He's been having trouble with his mouldings warping. They are CSM polyester and have moulded fine. Over time (up to a year) they are warping really badly. One example is a panel that has a 90 degree return / lip which has curled up beyond the 90 degree! I've never had this and all I could come up with was demoulding too early. Are there any other reasons he could be seeing this?
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Hanaldo	Hanaldo posted 9 Years Ago HOT Post Details
Group: Forum Members Posts: 2.5K, Visits: 28K	It's just shrinkage. Polyester shrinks horrendously, and does so for a long time. Unbalanced laminates make it much worse, and csm distorts easily because it is short strands. The natural modulus of a part will also play a role, flat sheets distort easier than a part with curvature.
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FLD	FLD posted 9 Years Ago HOT Post Details
Group: Forum Members Posts: 468, Visits: 2.7K	Blimey. Is there any way to reduce it? I'm just shocked that shrinkage could cause so much distortion. The part I mentioned is a hard top roof so has a slight compound curve and a lip front and rear. It's this lip that used to stick down but now sticks up. The lip has curled against the curvature of the roof (admittedly only on one corner).
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Hanaldo	Hanaldo posted 9 Years Ago HOT Post Details
Group: Forum Members Posts: 2.5K, Visits: 28K	Have you got photos? It does sound a little bit odd, but I've seen some serious distortion so it wouldn't surprise me.
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FLD	FLD posted 9 Years Ago HOT Post Details
Group: Forum Members Posts: 468, Visits: 2.7K	He won't let me take pics, he's too embarrassed! I wonder if it's different catalyst levels in gelcoat to laminate or gelcoat not cured enough when he layed up onto it.
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Hanaldo	Hanaldo posted 9 Years Ago HOT Post Details
Group: Forum Members Posts: 2.5K, Visits: 28K	Nah it won't be anything to do with the gelcoat. It is possibly undercatalysing of the reinforcement laminate prior to demoulding, as this would then take a very long time to cure and explain how long it has taken to distort. Potentially underpromoted resin as well, so even at correct catalyst levels it wouldn't cure properly. I've had a batch of resin that was so underpromoted it took 25% (yep, twenty five) catalyst to get it to go off.
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Warren (Staff)	Warren (Staff) posted 9 Years Ago HOT Post Details
Group: Administrators Posts: 2.5K, Visits: 8.5K	As has been said there are a number of factors that can effect the panel warping. Shrinkage of resins is certainly an issue. A few tips to try and ensure the panel is the flattest it can be: Slow full cure of the part for as long as practical. Early de-moulding is likely to cause more warpage. A very slow and gradual post cure will help stabilise the panel. Balanced layup, both in terms of materials within the layup and even so much as a thick gel-coat on one side is enough to bow some panels. Quasi-isotropic layup of the layers to help prevent internal stresses within the sheet. eg a mix of 0 and 90 degree fabrics as well as some +- 45 degree fabrics such a rotated layer or a bi-axial cloth. The thicker the laminate, the less it is likely to warp as the thicker structure tends to hold itself together better - especially the case with cored panels. However one note of caution, with cored panels, any discrepancy in a balanced layup is likely to be amplified. Warren Penalver Easy Composites / Carbon Mods - Technical Support Assistant
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FLD	FLD posted 9 Years Ago HOT Post Details
Group: Forum Members Posts: 468, Visits: 2.7K	Thanks guys, I'll pass these tips on. I'm not sure what level he catalyses to so that might be the cause.
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Zebra	Zebra posted 9 Years Ago HOT Post Details
Group: Forum Members Posts: 14, Visits: 32	I typically get warping or bowing on flat surfaces for one of two reasons: The first is if I am using a flexible mold like one made from silicone and it doesn't have a hard shell to make it hold it's shape. The same applies if the hard shell is not properly adhered to the mold so it doesn't support it sufficiently. The weight of the resin is enough to make it sink in areas where the mold is thinnest. If you are using an unsupported flexible mold then try putting the original pattern back in and coat the outside with something hard like epoxy putty or gypsum. This same thing could also happen with a semi-rigid mold like one made from fiberglass that is too thin (espiecially under a vacuum). The second reason is if the part is not sufficiently reinforced along the areas that are warping or bowing. You can use a layer of Kevlar or a stiffer carbon fiber on the rear side of the problem areas. I find that a 4x4 twill carbon fiber is usually enough for medium sized products (like 20" long). I would try and use a fast setting epoxy for this section and maybe use a little extra hardener. It will be more rigid and brittle but it won't matter in just that one section. For parts with particularly challenging angles where getting an exact shape is essential, I prefer to cure the part with a heavy rigid bladder on the rear side with weighs on top to hold it in shape and flat against the mold surface. This sometimes works better than a vacuum with problems like this. A vacuum can often be the cause of warping or bowing on it's own. If the vacuum is too strong the mold then....
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