Severe flash issue

[BruceBagheri]

Dear Members,
We are having issue with our supplier and cannot find solution for it. We are manufacturing composite materials. Our parts are made of carbon and glass impregnated and laminated with resin. Then this parts are sent to injection over molder who adds plastic material over our part experiencing excessive flashing. There are two parts, left and right, in each shot.
We are looking at various possibilities for this issue. One thing I am suspected is our parts thickness range and tolerances. We sent our part thickness range as 1 mm to 1.1 mm to the molder and they designed their mold based on this range, however, later on we discovered that our parts range is from 0.9 mm to 1.2 mm. I am sure that this wider range is causing issue, but I am not sure how severe this issue is. Your input and advise is greatly appreciated.

Kind regards,

Bruce

[rickbatey]

It could be their final dimensions in the tool and the decision of how they decided to deal with this tolerance range. It could even go back to insufficient support pillars in the moving half of the mold allowing mold plate deflection during injection pressure. Their pressure required to fill the tool may be much higher than they expected resulting in the flash. It could be due to too cold mold temp, too high melt temp, or too low MFI on the over mold resin. I'd say you're just getting started trying to root cause this issue.
BTW- What kind of reaction does the insert have to the melt temp of the resin? It may expand at a much higher rate than expected resulting in the mold trying to contain an additional force trying to open the mold.
Rick n

[3NGLENN1889]

What kind of overmold material is being used? G.P.

[BruceBagheri]

It could be their final dimensions in the tool and the decision of how they decided to deal with this tolerance range. It could even go back to insufficient support pillars in the moving half of the mold allowing mold plate deflection during injection pressure. Their pressure required to fill the tool may be much higher than they expected resulting in the flash. It could be due to too cold mold temp, too high melt temp, or too low MFI on the over mold resin. I'd say you're just getting started trying to root cause this issue.
BTW- What kind of reaction does the insert have to the melt temp of the resin? It may expand at a much higher rate than expected resulting in the mold trying to contain an additional force trying to open the mold.
Rick n

Hello Rick,
Thanks for the reply. This is what they emailed me.
My two cents for your reference:
1), This tolerance seems to be too wide to accept for any injection over molding factory (Because a 0.3mm tolerance band, equal to a possible Max. 0.3mm mold-closed clearance between cavity and core mold while over molding one pair of formed parts with Min. thickness on one side and Max. thickness on another side in one shot, which is much more than injection flow’s overflow margin (TPU/Pebax: 0.02mm), will result in serious injection fash).
2), Again, in the past, we have seen a notable nominal thickness difference between Charcoal TPU panels and Glittering Gold Pelax panels which might result from the different thickness of TPU and Pebax adhesive film (tie layer). Please see the email we ever sent to Tayin for their opening the injection mold reference.

[BruceBagheri]

What kind of overmold material is being used? G.P.

Hello,

Thanks for the reply. The materials are either TPU or PeBax.

[3NGLENN1889]

Just curious-is your molder properly drying the material?

[rickbatey]

Bruce, they could add some spring loaded inserts into the mold to allow for greater tolerance range of the insert. But I've been that guy trying to make such things run and the range of the thickness being under better control and with a smaller range would help everyone's bottom line. His tool must squeeze the insert enough to stop the resin from the areas required but give you room for the molten resin to flow and still vent out the air. Sounds much easier than it really is. Could you bond or fuse the resin and insert together in some other process with some tweaking to the parts?
Rick.