6TON mini-molding woes

[chadzeilenga]

Does anyone on this board have experience with 6TON presses? We are implementing them for some of our product lines and are running into some minor problems.
One of which is that we are constantly getting parting line flash 180° of the gate location. These are very small parts, about the size of a dime. I cannot understand why?

Thanks,
Chad

 

[patprimmer]

6 Tonne is a very small press.

How big is a dime (projected area).

What material are you moulding.

What is the thickness of the moulding.

How do you control mould temperature and at what temperature.

How rigid is the mould itself, and how well supported.

What is your injection pressure at the plastic. If not known, what is the hydraulic line pressure on the injection cylinder, the dia of the injection cylinder and dia of the screw.

Does the mould blank off. How have you tested the blank off quality.

Regards

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[chadzeilenga]

Hello Pat,
Yes, the 6TONS are very small presses, but with the small intricate parts (low cavitation 1-4) we do they have seemed to work pretty good. Also, dimensional stability is critical for our applications. Normal tolerances are ±0.05-0.10mm.
1. The projected area for one of our parts is 83mm^2 x 4CAVs = 332mm^2
2. We mold many different materials, but currently Lexan EM3110 (PC), Celcon M90 (POM) are the main ones for these molds.
3. A pic is attached. Thickness is 0.65-3mm
4. Mold temp: 125°F
5. The mold is well supported and clamped on all 4 sides. The mold fits into a moldbase.
6. Injection pressure: 11.50ips
7. What do you mean by blank off? I do know that we follow the RJG mold trials for our molds.

Thanks,
Chad

 

[patprimmer]

You have plenty of clamp force. You should only need 2 to 3 ton.

Your mould is to cold and should be around 170 F for optimum results with the materials listed.

I suspect you have to low a mould temp and therefore use to high a melt temperature or to much injection pressure.

What is an ips of pressure.

You need about 10,000 to 20,000 psi of pressure on the melt. Line pressure might be a lot lower as the injection cylinder will be a lot bigger than the screw.

Blank off is the fit of various mould parts. It needs to be good enough to form a plastic melt proof seal.

Moulds do bend under injection pressure.

If the mould blanks of OK (test by closing on carbon paper or by using machinist blue, and it still flashes, and the flash is tapered in thickness, the mould may well be bending. Many people refuse to believe that steel moulds bend, but unless very well supported by relatively big posts, moulds DO BEND.

Is it really getting the specified clamp. I once did a moulding trial, with an alleged 80 tonne clamp. Small parts flashed as the mould blew open under injection pressure, despite 80 tonne being at least 3 times what was required.

The problem was that a pressure relief valve in the hydraulic system was set at 10% of spec, ie 300 psi rather than 3000 psi line pressure.







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.