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Lester Populaire
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Group: Forum Members
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+x+xYeh I'm gonna say it's a combination of both as Lester suggested. Really I feel the actual issue is the ramp rate was too fast and you don't have a fine enough control over the oven temperature (I've experienced warping when the actual temperature varies from the target temperature as little as 2 degrees C), which leads to stresses that cause the warping. Then you've got the resin build up in the corners which creates a big differential in temperature throughout the part, exasperating the stresses from the cure cycle. It makes sense that you haven't experienced warping in more complex tools, as the geometry can overcome the stresses that are trying to distort it. This is why the flatter your components are, the more important it is to balance the layup and have good control of the cure cycle. It can actually be quite difficult to make thin pre-preg sheets without getting distortion because of that lack of balance in the layup, while if there was even a slight bend in the panel then it becomes significantly more rigid. The resin build up is the least problem because the part actually warped the most on the high spots   ordered new oven cotroller and added more heater elements in the oven to get better controle. Third time good time I hope. I feel like you should mostly improve air circulation. more heater elements doesn't necessarily decrease the temperature gradient?
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K.C.C
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Group: Forum Members
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+x+x+xYeh I'm gonna say it's a combination of both as Lester suggested. Really I feel the actual issue is the ramp rate was too fast and you don't have a fine enough control over the oven temperature (I've experienced warping when the actual temperature varies from the target temperature as little as 2 degrees C), which leads to stresses that cause the warping. Then you've got the resin build up in the corners which creates a big differential in temperature throughout the part, exasperating the stresses from the cure cycle. It makes sense that you haven't experienced warping in more complex tools, as the geometry can overcome the stresses that are trying to distort it. This is why the flatter your components are, the more important it is to balance the layup and have good control of the cure cycle. It can actually be quite difficult to make thin pre-preg sheets without getting distortion because of that lack of balance in the layup, while if there was even a slight bend in the panel then it becomes significantly more rigid. The resin build up is the least problem because the part actually warped the most on the high spots ordered new oven cotroller and added more heater elements in the oven to get better controle. Third time good time I hope. I feel like you should mostly improve air circulation. more heater elements doesn't necessarily decrease the temperature gradient? Proble is that at higher temp with not enough heater elements it takes to long to get the temp rising but when it does it rises to much and then cools down again. So you got a temp that isn't stable . So I hope when got stronger heaters it wil be more correct. Its a big oven 
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Lester Populaire
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Group: Forum Members
Posts: 311,
Visits: 13K
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+x+x+x+xYeh I'm gonna say it's a combination of both as Lester suggested. Really I feel the actual issue is the ramp rate was too fast and you don't have a fine enough control over the oven temperature (I've experienced warping when the actual temperature varies from the target temperature as little as 2 degrees C), which leads to stresses that cause the warping. Then you've got the resin build up in the corners which creates a big differential in temperature throughout the part, exasperating the stresses from the cure cycle. It makes sense that you haven't experienced warping in more complex tools, as the geometry can overcome the stresses that are trying to distort it. This is why the flatter your components are, the more important it is to balance the layup and have good control of the cure cycle. It can actually be quite difficult to make thin pre-preg sheets without getting distortion because of that lack of balance in the layup, while if there was even a slight bend in the panel then it becomes significantly more rigid. The resin build up is the least problem because the part actually warped the most on the high spots ordered new oven cotroller and added more heater elements in the oven to get better controle. Third time good time I hope. I feel like you should mostly improve air circulation. more heater elements doesn't necessarily decrease the temperature gradient? Proble is that at higher temp with not enough heater elements it takes to long to get the temp rising but when it does it rises to much and then cools down again. So you got a temp that isn't stable . So I hope when got stronger heaters it wil be more correct. Its a big oven this sounds like a PID setting issue. you do not need a lot of heating power to get accurate control. and is this a convection oven or is there a blower anywhere? kinda hard to tell on this potato quality picture. I would probably build two air ducts that pick up air in the top and blow it back out in an opposing corner in the bottom and wire in a high temperature axial fan or something. will probably do 100 times more for accuracy.
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Hanaldo
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Group: Forum Members
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Nah I think some more heating elements will help too. I had the same issues with my 5x5x2m oven, it just couldn't heat fast enough to have a steady temperature, it had a lot of fluctuation. Had 3 shrouded fans and plenty of air flow, so it didn't have nasty hot spots, but it just wasn't very accurate. I put another 2 elements in and improved it a lot, gave full control of the heating to the PID rather than just being run flat out virtually all the time.
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K.C.C
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Group: Forum Members
Posts: 54,
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Oven got heater in the bottom with blowers control is now controlled with a new panasonic industrial heat controller . Temp is controlled over 0.1°C been busy on it for over a week to calibrate it and get it correct . Made a new part let it cure for 7days 22°C postcured it yesterday from 50°C ramp to 135° over 14H 16 min so ramp rate 0.1°/min hold it for 3H at 135°C and kept it in the oven over night with the same result . And this is not the result from heat controle or resin build up ! where the resinbuild up is the part didnt warped it only warps on the rond edges of the 2 parts pullung them together . So no Temp cotrol problem, No difference with full carbon or glassfibre layup 
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K.C.C
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Group: Forum Members
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It was stil possible to bolt the part together but when I started trimming the part gelcoat just started to crack from the stress in the part . 
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Hanaldo
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Group: Forum Members
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Ok so what I would be looking at now is balancing your layup better. What is your reinforcement schedule and how are you laying it up? You obviously have significantly more stresses from shrinkage in one direction than the other, which tells me your layup is unbalanced. You should rotate your reinforcement by 45° each layer so that you build up more of a quasi isotropic layup, and you also want to think about your neutral axis and flip the reinforcement upside down on that axis so that you properly balance the reinforcement with the way it is woven. So say if you were doing 6 layers of 200g twill, I would do the first layer at +45°, the second at -45°, and the third at 0/90°. The flip the material over and repeat that layup in reverse: 0/90°, -45°, +45°. Another obvious thing that I would recommend doing is adding a vertical return flange on the ends of your mould, as per my very crude phone sketch. That will add geometry and a lot of rigidity in the plane that you are having issues with. It will make your layup a little bit trickier, but not significantly so. That would make your layup schedule significantly more forgiving and if you don't get the balance quite right then it won't matter as much. 
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K.C.C
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Group: Forum Members
Posts: 54,
Visits: 117
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+xOk so what I would be looking at now is balancing your layup better. What is your reinforcement schedule and how are you laying it up? You obviously have significantly more stresses from shrinkage in one direction than the other, which tells me your layup is unbalanced. You should rotate your reinforcement by 45° each layer so that you build up more of a quasi isotropic layup, and you also want to think about your neutral axis and flip the reinforcement upside down on that axis so that you properly balance the reinforcement with the way it is woven. So say if you were doing 6 layers of 200g twill, I would do the first layer at +45°, the second at -45°, and the third at 0/90°. The flip the material over and repeat that layup in reverse: 0/90°, -45°, +45°. Another obvious thing that I would recommend doing is adding a vertical return flange on the ends of your mould, as per my very crude phone sketch. That will add geometry and a lot of rigidity in the plane that you are having issues with. It will make your layup a little bit trickier, but not significantly so. That would make your layup schedule significantly more forgiving and if you don't get the balance quite right then it won't matter as much. Thnx for your info , my layup is 3 normal 3 filped over but didnt do the 45° for getting as much as pussible strengt in the direction of the way it warps. Wil do the 45° layup like you say the flanges also I was also thinking about and wil try in the next try .
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