How to define Dimensional Tolerances for Plastic Injection Molded Parts

M

michu

Hello,

Does anyone has an idea how to define dimensional tolerances range for plastic injected parts?. I've been working in plastic injection for 2 months and i don't have good feeling in that field.
For example - what should be maximum tolerance range for plastic part with the length of 400 mm. (+/- 0,6 mm???)
Is the tolerance directly connected with the lenght of the injected part?

I read a lot that measuring the plastic injected parts is not recommended but that is our customer requirements

Thanks in advance for your help

michu
 

Coury Ferguson

Moderator here to help
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Re: Dimensional tolerances for plastic injected parts

Any plastic experts out there that might be able to help?
 
A

achorste

Re: Dimensional tolerances for plastic injected parts

EDIT - Misunderstood
 
Last edited by a moderator:
W

world quality

Michu,

The best I have seen is DIN 16901
DIN 16 901 Plastic Moldings, Tolerances & Acceptance Conditions for Linear Dimensions (English Language Version)

This covers tooling and part dimensions it is in metric.
 
W

world quality

STIJLOOR and Michu
Din 16901 covers how to tolerance your mold.
Your inspection tolerance for either common or tighter tool control tolerance.
More Plastic Engineers here in the US should use it more.
It also defines what and what not to put in your tooling/mold.
 
G

gholland

Your tolerance range depends on your design and your supplier. The question is not 'what should I put on the drawing?', instead you should be pushing back to your design engineer asking 'what do you need according to your tolerance stackup?' If you are designing a toy your tolerances are going to be much greater than if you're designing a heart valve for example. If your design does not need +/- 0.6mm tolerance then you will be paying more for each part unnecessarily. Tighter tolerance = more supplier cost = higher part cost. Putting tight tolerances on stuff that doesn't need it wastes a lot of money!

Your selection of suppliers will also dictate your tolerance ranges. A supplier with excellent process control and equipment will be able to hold up to +/-.1mm or less.

If you are just looking for a 'rough guess', we use standard block tolerances on our drawings unless the tolerance stackup dictates tighter tolerances... if the dimension has one decimal place (400.0mm) then we would use a standard tolerance of +/- 1.0mm. Two decimal places (400.00mm) would use +/- .10 mm.

Why would you not measure plastic parts? There are a lot of non-contact methods of accurately measuring parts if you are worried about deformation.

:2cents:
 

bobdoering

Stop X-bar/R Madness!!
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There are comments here about specifying molds - its own unique science. The OP's question appears to be specifying parts. Unlike machined part tolerances, things tend to make plastic parts more "organic" - shrinkage and deformation. Other considerations for part specification: draft to allow parts to eject from the mold, whether or not to include the depth of ejector marks, amount of flash permitted, finish, color, etc. It really does depend on the final use to what degree all of these characteristics are specified. GD&T zones may help, such as hard gages from MMC callouts (if it fits, its a good part).

Just a thought....:cool:
 
P

Phil Fields

This also depends on the type of material that is being molded. I have been out of injection molding for over 13 years, but we had some tolerances of ±.060" and some as molded dimensions of ±.0008"

Phil
 
P

plasticmedicalmold

The best I have seen is DIN 16901
DIN 16 901 Plastic Moldings
 
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