How to design parts with Molded-In inserts?

[Helepolis]

Hi,

I want to incorporate a Molded-In Insert to one of the products I'm working on, but this is my first go at it so I'm not sure how to design the area of the part where the insert will be embedded.

For the ultrasonic assembly inserts there are hole size recommendations from the manufacturer but for the molded-in i can't find anything specific, the only thing i managed to find is that the material outer diameter around the insert should be at least 1.5D (where D is the outer diameter of the insert) but not sure how accurate this info is.

And another thing is how to make the correct annotation for molded-in insert in a drawing.

Thanks.

 

[IMF Plastic Mold]

you should ask the manufacturer

Andy Du
Supply Plastic Molds&Molding
Zhejiang IMF Plastic Solutions Co.,Ltd

http://www.injectionmoldfactory.com/

 

[Helepolis]

Yeah this is the obvious thing to do, and i thought about it but i thought there are basic rules of thumb that i can use before refining the area using the manufacturers guidelines because from what i saw in the catalogs of the inserts there are different installation guidelines for each brand.

 

[MikeHalloran]

You don't need to specify features for a molded-in insert, other than the location, and a hub that's large enough to provide decent wall thickness.

BUT, before you do anything else, call your molder and have a chat.

Using molded in inserts requires the operator to reach into the mold cavity, itself a violation of reasonable safety practices in many places, and individually place the inserts on some sort of pin to hold the insert, and be careful not to brush against the other dozen inserts already placed, so that an insert doesn't accidentally drop and lodge in the wrong place, causing expensive damage to the mold.

The time required to do all this manual labor in an awkward and dangerous location also adds random seconds to the mold's open time, which will affect part quality, because molds don't reach thermal equilibrium until a few cold cycles (and scrap parts) have been made.

I.e., chances are that your molder won't like using molded in inserts at all, so don't waste the time considering them.



Mike Halloran
Pembroke Pines, FL, USA

 

[dgallup]

We do millions of insert molding operations every year, it's no big deal. However, it will increase cost and cycle time and yes mold maintenance if one of your inserts gets out of position when the mold closes. You use two handed start buttons so the mold can't close while your hand is inside.

One thing you need to do from a design stand point is either make sure the mold will close off tightly on the insert to prevent flash or make the parting line in a position where flash is not important. Worst case you hand trim flash, a very undesirable condition.

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[IRstuff]

Every laptop case I've taken apart has molded-in threaded inserts for screws.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

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[MacGyverS2000]

Were they molded in, or press-fit, IR?

Dan - Owner

http://www.Hi-TecDesigns.com

 

[IRstuff]

fair point; I'm not sure. I'd guess molded, just because what I remember of the cases that I've broken, the plastic was pretty clingy to the insert.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[cowski]

Depending on the complexity of the part, using sonic welding to place an insert may be possible. This method would give much of the strength of a molded-in insert without the molding headaches (sonic welding brings its own headaches with it).

http://www.stanleyengineeredfasteni...ts/ultrasonic-threaded-inserts-straight-holes

 

[ornerynorsk]

Most manufacturers publish an actual design guide that cover boss sizes, wall thicknesses, etc that are specifically aimed at the types of inserts that they supply. It takes 5 seconds on Google to type in "molded insert design guide" and get a number of good hits.

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.

 

[MikeHalloran]

Ultrasonic inserts can be installed nicely with a practiced hand and a big soldering iron with a modified tip.


Mike Halloran
Pembroke Pines, FL, USA

 

[Helepolis]

Thank you for the great tips!

But i still cant find any reference on how to specify on a drawing the insert, because from the CAD point of view this is an assembly but theoretically the area without the insert will be a solid body without any holes as the polymer flow will fill the space that the insert would have occupied completely.

@Mike the final product will be a Mil. Spec. so no shortcuts .

 

[MikeHalloran]

For ultrasonic, or otherwise thermally installed, inserts, you specify a cored hole in the molded part, in accordance with the insert manufacturer's recommendations.
... not _no_ hole.

For a molded-in insert, you specify the location of the thread in the insert, which will usually have a blind threaded hole within it, and you make sure the boss around the insert has wall thickness in accord with the manufacturer's recommendations, etc.

I haven't done a molded MIL-spec part; do they even allow non-replaceable inserts?





Mike Halloran
Pembroke Pines, FL, USA

 

[Helepolis]

Apparently yes when it suits their needs, i don't argue, i just love the challenge and learning from the jobs i get from them!

Btw when you said that i need to mark the location of the thread of the insert, you mean that i mark the center axis of the thread using center mark, dimensions and just annotate the thread using the standard ISO (for example) annotation?

 

[MikeHalloran]

Yeah, something like that. Location, thread specs including depth, stuff you can measure, maybe an extended tolerance zone limiting misalignment of the insert depending on the mating parts, etc..

You also should annotate the callout or otherwise make the insert's presence clear, and show the insert's envelope as hidden lines in the drawing.




Mike Halloran
Pembroke Pines, FL, USA

 

[dgallup]

I always model the plastic with insert as an assembly if it's molded in. The assembly model is what goes into the plastic molding drawing. If you are going to install the insert post molding then as Mike said you have to model the molded in hole specified to the insert manufactures requirements.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.