Unbalanced shot 1

[sizzer33]

Hi everyone,

Some advice needed on one of my tool.

Here's some info on the part as i don't think i'm allowed to put a picture of it:-

Part shape: Mouse top key. Its curve, arc of circle around 90 deg.
Thickness: 2mm all the way with 2 clips and 2 bosses.
Gating: Sub to pin. (submarine gate to quarter of ejector pin). GAte is on one end of the part on the long side.
Gate dimension: its big, i think at least 1.5mm diameter. Its not exactly round, more like a pie shape as its quarter of an ejector pin.
Mould cavity: 4
Mould type: Hot sprue to cold runner.

THE PROBLEM: We are having problem with 50% and 90% fill shot. 2 parts are running slower than the other.

We've checked the mould temperature between cavity and its about 4 deg Celcius difference.

Since gating is so big, i presume we don't have a problem with gate shutting off.

We're testing the tool on a brand new german machine in suppliers side and made a hold time study, its very good result. So shouldn't be a problem with the torpedo. Fully filled parts have a good part weight ratio between cavities,less than 3%.

The cavity side of the tool is polish to around A2. We had some venting problems in the middle of the part so we increase some vents on the lifters(use to make the clips). PArt surface is shiny as ever.

Please advice on any other cause for this uneven flow.

Many thanks.

 

[patprimmer]

Pud

I couldn't agree more.

How many times does one have to restate the obvious.

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]

Thanks you guys. Our team and customer have accepted the parts and prepare to waive the unbalance short shots.

Since now the parts is in production and making 25,000ps cs in a week and SPC looks good for the past week. Hope it'll be ok in the future.

 

[Pud]

Sizzer33,

Missed your post 16 July.

Pleased reason prevailed. Look forward to many years production of the tool.

After 40 yrs in engineering, one finds that QC requirements, if not specified by engineers, complete b*lls. Someone has read a book, copied the bumph and considered it gospel! ( A little knowledge is a dangerous thing)

Well done man! (*Or Girl! - gotta be PC just in case!)

H

 

[plasticsguy01]

From Sizzer 33 on 8 Jul 08
"Some of our process guys would like to try out "melt flipper" way. I think mainly problem now should be in runner and controlling the flow by putting some turbulence on the faster flowing cavities.. We have check the gating size for all cavities and it doens't vary too much."


Plastic will never experience "turbulence" or turbulent flow due to being a laminar, non-Newtonian fluid. Calculate the Reynolds number if you want to see the proof. Instead think of it as flowing in layers almost like a ream of paper. And therein lies where I think your problem might be.

I totally agree with your process guys who mentioned trying the "melt flipper". As you describe your problem I'm assuming you have verified runner sizes, cav to cav steel dimensions and I see you measured gate diameters. Assuming all of that is good to go and the machine is up to par, then to me, it sounds like you have a case of shear induced fill imbalance. And that is exactly what the "Melt Flipper" is designed to resolve and usually it can easily be retrofitted into an existing mold. I'd give the guys at Beaumont Technologies a call and let them see if they can make it work. Go to

http://www.beaumontinc.com

or

http://www.meltflipper.com

to read more and to get in contact with them. They have some great info and also tell you how to run through their "5 Step Process" to determine what's coming from steel imbalance and what's from flow imbalance.

Ensure your giving your customer as similar parts no matter what cavity. You also might find you save precious cycle times, reduce scrap rates, and reduce material consumption by not over packing cavities and using more material than you need to produce a quality part.

just my 2 cents for what it's worth...

 

[sizzer33]

Thansk plasticguy01 for the inside on melt flipper.

we'll definitely apply this when we can stop the production of this tool. IT'll definitely benefit us later when we've passed the peak purchase order period. Now we jsut keep the tool on machine and non-stop pumping out parts.