Thin wall injection mould

[sizzer33]

Hi all,

I have a part which i'm supposed to get a quote from tooling supplier and also making unit price. I just need some pointers on the important areas that i have to focus on regarding tool design and moulding the part so i can estimate the level of difficulty in making this tool and producing the parts.

I'd love to attached the drawing but i'm not sure if its allowed. Anyways, the design of the part is simple:

- Imagine a rectangular container without the top cover.
- Height 5.4mm, length: 59.5mm, Width: 20mm
- Part thickness : 0.17mm-0.2mm (i've double checked the drawings and it is 0.17mm. Please inform if its impossible to mould such thin parts)
- part weight: 0.34g
- Material: PC w/CBT(i'm not sure what CBT is at the moment)
- On the bottom plane of the part, its filled with about 50 small holes (0.64mm) in diameter.

My main worry is:
- is PC material suitable for such thin wall moulding?
- What type of gate and which position on the parts should it enter?.. smaller side of the part (20mm) or the larger side of the part (59.5mm)
- Important notes in thin wall moulding as in , should there be special inserts for venting, also important venting area in order to fill the parts efficiently.

I hope the question is clear. any comments would be appreciated.
thanks

Sizzerpac
Program engineer

 

[patprimmer]

That is very thin, but just might be possible. I would have a mould flow analysis done. Flow path to thickness ratios tend to get better with very thin parts.

Bayer used to produce flow length to thickness graphs in their data. They may still be available and would help you a lot.

The part sounds simple and the mould should be straightforward if you have not left out details like holes in the side

An easy way to vent is to make small flats on the side of pins, but vents MUST vent to atmosphere and must increase in size a lot after they cross the land area.

Make a long flash style gate along the entire long edge with a thick runner down that side. Two cavities (one on each side of the runner would make less waste.

You will need a very easy flow grade and a very hot mould.

Another possibility is to thermoform from sheet.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[sizzer33]

Hi patprimmer,

Thanks for your input.

Regarding the flash gate, what degating method do you recommend to have a clean cut? I'm actually working in china and most of the degating are done with workers with hot pliers.

For ejection, where would you recommend to place the ejector pins?.

 

[patprimmer]

You might need to use poppets and blow it off with air.

You may need a tool to cut it off by stamping.

You might even incorporate that into the mould to operate during the mould opening process.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Pud]

Imho, it's an extremely difficult thing to mould. You will need a robust tool, a moulding press designed for packaging (i.e. high speed injection using accumulators, which you will be lucky to find one small enough for this shot weight).

The array of small holes would probably preclude the option of air ejection.

As Pat suggested, vacuum form and a press tool to trim the part and punch the 50 0.64mm holes in (if that can be done - I am not a press tool guy!) Assuming you can live with the varying wall thickness, that is.

If I was asked to quote for this, I would graciously decline...


Cheers

Harry

 

[sizzer33]

Thanks,

i will definitely take these ideas into consideration on our coming discussions.

cheers for the help.

 

[esqrkim]

sizzer33:

I agree with the flash gate mentioned above. Another option, however, would be to use a hot runner system with one or two nozzles dropping down to the bottom-side of the part (59.5mmx20mm side assumed). I would prefer two evenly distributed nozzles because of the thickness of the part. The only limitation would be the locations of those 50 small holes.

With a hot-runner system as described above, I would make sure the mold has perimeter venting. The depth of the vent land is dependent on the resin used. Separate pin vents are not necessary for your part. There are PC based resins with high flow capabilities. So, make sure you spec the appropriate resin for the process.

Provide as much positive angle to the side walls as possible to facilitate ejection. I do not think air ejection would be effective due to the 50 holes on the bottom-side of the part. Proper mold finish is also important for ejection. Pushing on the wall directly would be ideal for ejection. I think you can get away with it even though the wall is only 0.17mm thick.

Finally, processing is important. You need someone who will work with the mold, and not just blame the mold.


Eugene Kim

http://www.eeksolutions.com