Heat In Large Quantity Of Inserts Causes Issues

[110Ton]

I got the other job done in record time thanks to the help from this forum.

N
o
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...lets see if we can get some results from this job.

Attached is a crude sketchup diagram of the part. Vital details have been obscured for security reasons per customer request. This gives you a rough idea of what I am up against.


TYNEP P8150 is the material. Mold is set up with four loops on the stationary side, and four on the moving side.

Per the customer's requirement the part must be "very shiny." To do this I cannot alter my mold temps too much otherwise I start losing parts to cosmetic issues.

The other issue is all those god-damn inserts (brass AND steel!) plus two removable core sections for making a critical feature.

At this point I cannot alter the tool... I built a widget for placing all the inserts against the mold face in one motion, leaving me to place the ones along the sidewalls and the removable cores. This has dropped the cycle down almost 30 seconds.

Where I am losing the most parts is sink near the inserts. Naturally this is totally unacceptable to the customer. It doesn't impact the function of the part it just looks ugly. This part goes inside another part and only the two ends are seen not the long flat faces with the inserts.

Well... I can't change the customer requirements either... so I'm left with process-fu. I can reduce the sink to acceptable levels via process-fu but that extends my cycle time. Extended cycle time leads to other defects.


Any insight on reducing sink in a part like this without redesigning the tool or killing the customer?

TYNEP Problem Child Part.png

[POLYnnovation]

Hi 110Ton,

Always tricky to get a total feel for the problem just from the limited information you can share, but I appreciate the sensitivity aspect. Are the wall sections as variable as they look from the image? What is the range of wall thicknesses? Do you pre-heat the inserts? Do they need to be moulded-in, or can post-moulding inserts be considered? Either moulded-in holes (mini-core pins could be in BeCu, or with heat pipes inside them, for effective heat removal) or - as a radical idea - drilled out from the component. There'd be no sinks at all then, of course, but you'll need a drilling jig and swarf removal, etc. Just a lateral thinking idea. Ultrasonic, heat, self-tapping, etc.? PBT being semi-crystalline, sinkage is going to be more of a challenge that with amorphous materials, but I guess material selection is locked-in.

You may be able to get away with a small amount of blowing agent, to counter the sinks, but the risk is that swirling may be visible on the surface. MuCell (Trexel Inc., see http://www.trexel.com/) process variant, together with hot mould (sorry, mold, for US readers!) can reportedly give high gloss, but with partly microcellular core. Also, consider one of the systems for rapid heating of the mould surface just prior to injection (e.g., as featured on this web page http://www.gasinjection-ww.com/).

I hope this gives some fresh leads.

Regards,

John McLoughlin
POLYnnovation

[rickbatey]

I trust you are running the mold hot enough? Is the gate open long enough to pack the sinks out? I would bet that you can't pack the sinks out due to flashing of the inserts...... Do you leave the inserts in or are they hand loaded cores?
Here are some points to help. 1-Heat your inserts before placing them into the mold. This will help with knit lines and possibly sinks. 2-You need to increase the melt and/or mold temps to help with your gloss issue (and sinks). There may be a sweet spot that doesn't cost you as much loss (cycle time) as scrap. 3-Ramping the hold psi up, down, or running it in a pyramid may also help with your struggles. 4-Contact someone at Clariant for a Chemical Foaming Agent. These remove sinks and can allow you to have a class-A surface. 5-Build new tooling, this time with your input. 6-Pass the job to another company that wants to buy the work, and turn your energy toward other projects. Some parts should NOT be molded as designed. Others cannot be tooled in that fashion simply due to tooling costs (read CHEAP). Perhaps I will have an epiphany and provide you with a majic bullet, but usually not this late in the afternoon?!

[Will Call]

If the wall thickness is as depicted in the sketch and you con not use a blowing agent, how is the part gated? If it's a direct sprue you my be able to try to gas inject it. The part will have hollow spots, be lighter but you should be able to eliminate the sinks and still maintain the appearance requirements.

[110Ton]

The wall thickness is all over the place. That's one of the "fun" aspects of the job. All of the round holes are brass molded in inserts.

New tooling is out of the question...

Part is gated from two points, one on the top left and one on the bottom right side looking at the tool from the operator station. I have toyed with the idea of opening the gates up a bit but I'm nervous they said do not modify the tool aside from the cold-slug trap I put in. My worry is the gates are near inserts and if I alter the gate I might get flash over the inserts. Other idea I've toyed with is a slightly [SPAMMER]/deeper runner channel. My hands are mostly bound by the "do not modify" stricture.

I'm shut down for the weekend... Monday morning I'll send out some feelers about blowing agents. That might be a possible solution.


As for post mold insertion... they don't want to hear about anything other than "molded parts with inserts la la la la our engineer says it should work as designed blah blah blah."

Well it *does* work but it doesn't work well.

As I said Monday... I'll play around with it some more

[rickbatey]

Perhaps they need to hire an Engineer with plastics training or experience! I see parts most every day, with serious design flaws for plastics! You would think they (the OEM's) would learn to get their suppliers involved earlier to solve these issues BEFORE cutting steel!? Rick.

[110Ton]

9/10 of these situations arise from sticker-shock at the cost of tooling... Once the tooling is made it's "locked in" in the mind of the customer and they don't want to hear about further costs. A buddy of mine in sheetmetal stamping reports the same thing.

One shop I was at lost several molds from a customer when we charged them for the normal tool-upkeep-and-cleaning. I understand that customer has a habit of doing that. We got the jobs off the truck they needed repairs and cleaning so we did our magic and suddenly the tools were being pulled right as we were hanging them.

Other situations arise where a customer wants the product NOW and is unwilling to wait another two weeks for a mold change that would result in a much lower cost. Same shop ^ above built a prototype tool to make a filter part, and once the customer got parts in hand suddenly they wanted thousands of them per shift right now or else. We had to struggle but we got it done, finally the customer relented and we built a proper production tool.

I blame Sales. Salesman is friend of the owner and has no technical experience so he talks out of his ass to customers and god help you if you try to enlighten him as to why something won't work. Well I am Sales now and I won't hesitate to tell you why it won't work or what needs to be changed. This is a "second income stream" so I can afford to tell you to flush it if I can't get it working.

ANYWAY

Back to the current situation.

Contacted several suppliers in regards to blowing agents, got samples on the way. Also, as of right now I have the tool out of the press I am going to mod the runner just a bit. Finally I have a hot-oil unit on the way from a friend's shop I am going to try running the job with very hot surfaces just for g i g g l e s ... had a job once that in defiance of all processing-fu ran beautiful parts with 275 degree temps on the mold.

Plan is to mod the tool, run a few samples of blown parts and of superhot parts and send them off to the customer for great justice.

I don't think I am going to "perfect" this one I think it needs more tool-work than I can do on my own for "free" but I'll keep ya'll posted.

[110Ton]

I see this forum has quite a spam issue.


As of this morning I have a hot-oil unit and I am running the mold VERY HOT, 290 degrees... followed by a drop in the water tank under the press. I also cranked up the "pack" pressure and hold time and shortened the cooling time. Also made a "slight" mod to the gates with a file and stone. Don't tell the customer!

More or less the cycle runs like this: Handload, close and inject, cool, open and eject into water tank, handload, close and inject, and so on... every ten cycles or so I pull a couple of parts from the water tank.

Aside from the dial-in parts I haven't had any fallout due to sink or surface issues.

File this one under WTF.

Again thanks for the ideas everyone.

[Louis]

So hotter and packing it out worked. Hopefully you can recover some $$$ from the time that it took to solve the issue. Now the question is, when they pull the tool to give it to someone else, do you pass on the run conditions.

[110Ton]

Way way hotter than I normally run material of this nature... and I also altered the tool. I don't think the increase in packing pressure would have done anything by itself without the tool mod.

You do bring in an interesting point... I had to figure all this out myself (and with a little help from my friends). What is industry/other-shop practice in this situation? Since I started this enterprise I haven't gotten any sort of information from the "other shops." Just information from the customer. Drawings, part samples and memos/emails of "don't do this don't do that, this is acceptable and this is not" that kind of thing.

[rickbatey]

Sometimes you can get the customer to request a process sheet from the supplier, but often that leads to suspicious suppliers! Usually I just want to know cycle time, drier settings, machine size/specs currenlty being used, and info for the resin. It's good to know what NOT to do (over pack, over stroke the ejector and so on) as well.
So many times I see process settings for molding around machine issues, or poor processing methods, that I don't get much out of the previous suppliers paper work?! Rick.