🎯Getting Tolerances Right in Injection Molding: Why Standards Matter! (ISO 20457 & ISO 3302)

Figure 1: Overview of ISO 20457 for thermoplastics and ISO 3302 for rubber injection molded parts.

Hello and welcome to a new blog post. When it comes to plastic and rubber parts, achieving the right tolerances is key to ensuring quality, fit, and function. But did you know there are specific ISO standards that guide this process?

🔹 ISO 20457 for Plastics:

This standard provides clear guidelines for defining tolerances and acceptance conditions for dimensions of plastic parts produced by processes like injection molding, extrusion, or thermoforming.

Different tolerance groups (TG) are defined:

TG 6 for packaging parts

TG 5 for housing parts

TG 4 for precision parts (like gears)

Note: ISO 20457 applies only to unfilled thermoplastics.

🔹 ISO 3302 for Rubber:

For molded rubber parts, ISO 3302 is the go-to standard. It divides molded parts into four tolerance classes, from M1 (fine) to M4 (coarse). For most technical molded rubber parts, M3 (medium) is typically used.

In conclusion

Understanding and applying the right tolerance standards helps ensure your parts meet performance expectations and manufacturing requirements—saving time, reducing costs, and boosting customer satisfaction. 

As a rule of thumb, for precision injection molded parts such as gears, ISO 20457 TG 4can be applied. For housing parts TG 5 and packaging parts TG 3. For rubber molded parts,  ISO 3302 is key, and in particular M1 (fine) to M4 (coarse) (Figure 1).

Check out this post too, where tolerances are important to turn product requirements into plastic & plastic part specifications: read full post.

Thanks for reading & #findoutaboutplastics

Greetings, 

Herwig 

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Literature: 

[1] https://maxnext.io/de/blog/allgemeintoleranzen-im-spritzguss-nach-din-iso-20457-ehemals-din-16742-2/

[2] https://www.nh-technology.de/download/Design-Construction-Guide-Plastic-Parts.pdf

[3] https://www.zorge.com/gummi-lexikon/din-iso-3302-1/

[4] https://www.toleranzen-beratung.de/unternehmen/aktuelles/ansicht/iso-204572018-toleranzen-fuer-kunststoff-formteile-informationen-zur-neuen-norm/