tolerances for polyurethane foam 1

[loughnane]

I'm looking for rough tolerance estimates for a polyurethane foam part.

It's about 11" long by 4" wide by 1", and I'm looking for a tolerance on the 11" dimension.

0.050? 0.060? I'm not looking for an authoritative answer ( I know it varies), but more a collection of gut feels. I am developing a concept and just need a ballpark.

Chris Loughnane - Product Design

http://www.pdnotebook.com

http://www.twitter.com/_chrisloughnane

 

[MintJulep]

If you are the designer than the tolerance is your decision. You specify what you need for your design to work.

Did you perhaps want to ask about the expected variation associated with some specific process?

 

[loughnane]

yes, by 'tolerance' i meant the estimated tolerance that manufacturers recommend designers incorporate into the design to deal with the inherent variation in injection molding polyurethane foam.

Chris Loughnane - Product Design

http://www.pdnotebook.com

http://www.twitter.com/_chrisloughnane

 

[1gibson]

If I could rephrase for you:

"What is the tightest tolerance I should specify to avoid a price increase from the supplier?"

Check with suppliers application/sales people, or to put it into terms that ensure it gets translated from the "front end guys" to the "pricing guys":

Ask for quotes at 0.025, 0.050, 0.075, 0.100" tolerances, up to the max you can accept.

 

[dvd]

One thing that I would consider when deciding on tolerances is the coefficient of thermal expansion for polyurethane foam. It may be very large (expansion due to moisture absorption may be large also). You should consider the temperature that the part will be formed at and the temperature at which the part will be inspected/assembled. There may be some significant size change.

 

[loughnane]

@dvd

good insight, much thanks.

Chris Loughnane - Product Design

http://www.pdnotebook.com

http://www.twitter.com/_chrisloughnane

 

[MiketheEngineer]

Foam tolerance?? If is is too big - just squeeze it a bit - too small - just pull it a bit?? Remember - you are not making a jet engine!!

 

[ornerynorsk]

Tolerancing will vary somewhat with the formulation that is being poured or injected. Your vendor will give the best guidance on reasonable tolerances.

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.