ornerynorsk
Industrial
- Feb 5, 2002
- 3,198
Hi All,
A question came up during a discussion of what we believe to be molded-in stresses occurring in a part with a rather large surface area-to-thickness ratio. Flat part, minimal rib structure, 0.100 inch avg wall, and approximately 210 square inches of surface. Upon ejection, the part is being allowed to cool in still air until near ambient has been reached. The part is still flat at this point. The part is now packaged, say 15 to the carton, individually poly-bagged, and stacked orderly so as not to induce weight related warping. Cartons loaded into a container, 6 weeks to our door, and a third of them are coming out warped, as much as 2 cm out-of-plane, basically a twist running from one corner to its opposite corner, diagonally across the part. The warpage is very consistent in the parts that exhibit the warpage, but does not occur in all parts. The vendor claims that the equipment molding the parts are holding process parameters tightly. We are not seeing any inconsistencies at the back of the gate area, no blush, gas marks, orange peel, or the like.
My question is: What length of time must pass before nearly complete crystallization or "set" is occurring in the parts, so as to reveal any molded-in stresses that may be occurring?
We have fixture annealed sample parts with very good results, but 2nd ops add extra cost and time. After annealing, the parts are flat and they stay flat.
Ideas? Thanks in advance.
It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.
A question came up during a discussion of what we believe to be molded-in stresses occurring in a part with a rather large surface area-to-thickness ratio. Flat part, minimal rib structure, 0.100 inch avg wall, and approximately 210 square inches of surface. Upon ejection, the part is being allowed to cool in still air until near ambient has been reached. The part is still flat at this point. The part is now packaged, say 15 to the carton, individually poly-bagged, and stacked orderly so as not to induce weight related warping. Cartons loaded into a container, 6 weeks to our door, and a third of them are coming out warped, as much as 2 cm out-of-plane, basically a twist running from one corner to its opposite corner, diagonally across the part. The warpage is very consistent in the parts that exhibit the warpage, but does not occur in all parts. The vendor claims that the equipment molding the parts are holding process parameters tightly. We are not seeing any inconsistencies at the back of the gate area, no blush, gas marks, orange peel, or the like.
My question is: What length of time must pass before nearly complete crystallization or "set" is occurring in the parts, so as to reveal any molded-in stresses that may be occurring?
We have fixture annealed sample parts with very good results, but 2nd ops add extra cost and time. After annealing, the parts are flat and they stay flat.
Ideas? Thanks in advance.
It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.
