Low cost material

We are machining trays to carry parts in our manufacturing process. They are approximately 12"x20". In the tray there are a pockets where
material is removed down to about 0.050"-0.100" to hold the parts. These pockets are arranged in columns and rows. The problem we have is finding a low cost material which will not bow. These trays get sent through an oven that reaches around 200F. The removal of so much material coupled with the heat causes the trays to bow after a number of cycles. We have tried polypropylene (1/2" both stress relived and not), and ABS plastic (1/4") (both products in 4'x8' sheets). Does anyone have a suggestion of a low cost material that could maintain its flatness? We have looked into Phenolic but cost is too high (we need to make about 100 each of 10 different designs). We considered metal but it is too big a thermal load for our ovens. We also thought of adding a metal skeleton to each tray, but again this raises cost significantly.
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snipped-for-privacy@signaturefactory.com wrote:

How about ceramic? It won't bow, and the temperature is no problem. You could machine a mold, then cast and fire the pieces at a local pottery. You'd have to ask a potter whether 0.050" is thick enough -- you might have to cast thicker, then grind down to the final size after firing (or grind as an intermediate step between two firings).
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How about a thin aluminum sheet like a cookie sheet? Punch indentations in it to form the pockets you need. A muffin tin?
Fiberglass/epoxy; you want a material with a softening temperature considerably higher than 200F to prevent permanent deformation.
Or a thick aluminum plate. The heat capacity of a particular volume of AL is only about twice that of the same volume of PMMA.
Dave
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Phenolic to expensive? Maybe you should try wood ;) Frank
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