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Home » Heat Forming » Heat Forming Canopies on a Mold |
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PARENT CATEGORY Heat Forming |
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Heat Forming Canopies on a Mold OCID cn00000207 |
LINKED CATEGORIES Heat Forming |
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Heat Forming Canopies on a Mold by Oliver Max created 5/10/2001 submitted 11/11/2002 09:11:40 PM We visited Product A Manufacturing to learn more about manufacturing cockpit canopies through heat forming. Urethane foam is bad for hi temp molds (the hot plastic is at about 280 F). Most epoxies don't do so well at the high temperatures either (Hysol). Hence the delaminated edeges on the old mold, and the stripes in the bubble. They use lots of wooden molds. They suggested MDF, medium density fiberboard (the real smooth stuff), which can be found at Mintons Lumber (at Evelyn and Mtn. View by the railroad tracks). For gluing the pieces together, they suggested an aluminum filled two part epoxy (100:7 ratio or something), known as TC1650, made by BJB Enterprises, Inc. There is also a particular material that BJB makes which would be appropriate for a surface coat on the molds, we just need to call them and tell them what we're looking for. Their number is (714)734-8450 (fax 714.734.8929), and the business card I'm looking at has Jill Spilker, Sales & Marketing on it - so that may be someone to talk to. www.bjbenterprises.com They recommended making a new mold instead of salvaging the old one. The plastic most commonly used is PETG (same stuff as soda bottles). They can do acrylic though it is nowhere near as common, and can crack when it shrinks due to cooling. Lexan would not be possible on such a large part (it needs to be heated to 380, and cools in ~15 sec). Speaking of cooling, most parts cool .007" per inch of length of part. so a one foot part would be almost .1" smaller than the mold. Clear is the most common variety of PETG. It holds up as well as acrylic in UV (outdoors), is almost as tough as Lexan (better at repeated blows, but can't take as large of a single destructive impact). Standard thicknesses are 3/8, 1/4, 3/16, 1/8, .100, .080, .060, .040, etc. He wasn't sure what our old tinted bubble was made out of. Perhaps some acrylic/PETG combo. It was suggested that we don't start with anything thinner than 1/4" or maybe 3/16" for such a large part (it will thin down upon forming - basically the ratio of the projected area to the surface area). Their experience with fiberglass molds is not good. Parts usually come out lousy, although they did not give specifics. The part will be much easier to manufacture (and perhaps come out better) if the mold does not have vertical walls near the bottom. Any slant at all will make the situation better (kind of like removing fairings from a mold with vertical walls). We didn't even ask about blue foam and Bondo molds but I'm about 99% sure that would be asking for disaster. under full vacuum, blue foam will compress substantially (~5-10%) and all the Bondo will crack and flake off. Brian was the helpful man at Product A who provided all this information. If we've got more questions, he's the man to contact. 491 words | oomax
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