Plastic Injection Molded Part Tolerances

[pdybeck]

I'm looking for a site that would have any information on tolerances that can be achieved with plastic injection molded parts. I understand that this could change from material to material. I have much more experience with metal casting part design. There is at least an agreed upon tolerance standard that pretty much all foundries follow and that is the one we use for metal sand castings. Is there such a set of standards for plastic injection molded tolerances? Is there a site where I can get this information? Thanks in advance.

Pete Yodis

 

[TVP]

There are consensus standards that have been developed for applying tolerances to molded plastic parts. DIN 16901 is one such standard. It is available in German and English language versions.

 

[APH]

Well..Here's what I did. I'm new to plastic injection molding also. my past experiences were machine parts.

Design your part and tolerance it they way you want it. Do whatever necessary to verify those tolerance by testing it, build a machine parts, or whatever. Once you do this, give it to several vendors. I'd suggest 10 of them ranging from big to small. Let them bid the quote, if they take it, they are responsible to make your part to your tolerancing. See how many of them take the bid. If they all take the bid then you kinda get a "feel" what is standard and what is not.

Let me know if you find a standar, I sure can use it too!

APH

 

[MintJulep]

To Profengmen and APH's points:

Many vendors will be responsive to RFQs that include a "please tell me if my design is making this part unnecessarilly complex to produce, or expensive, and do you have any suggestions for a better design."

Vendors that respond to such requests are probably the ones you want to form relationships with anyway.

Yes, there is some aspect of "please do my job for me" in this approach, but if the big picture is right, it can be advantageous to both parties.

 

[pdybeck]

Keeping designs portable in the iron and aluminum indusry also comes with a price. The patterns are never meant by the casting vendors to be the property of the customer and often times you are lucky if you can even get the pattern out the door and to another vendor. If the vendor goes out of business, this is sometimes not a problem if they are considerate enough in their own minds to let you take the pattern to another vendor that can adapt their system/process to the pattern. Even when this happens there is usually a set up cost, although I don't know on (average) percentage wise how this compares to plastic injection molds. It seems like with my limited experience, that designs never really get "thrown over the wall", as they come back for refinements, discussion with vendors as the produce parts, and consideration for design of future products and the chance to enhance those products over what was done in the past.

 

[hbarea]

You may want to take a look at the following publication from SPI: “Standards & Practices of Plastics Molders”, Guidelines for Molders and their Customers. You may also want to check other publications from SPI and SPE.