Cold runner mold vs. Hot Runner Which fares better on SPC

does anyone know where i can find this piece of equipment to purchase?

This was a somewhat loaded question, does anybody have a product made from both a cold runner and a hot runner mold ...... a direct comparison of SPC/SQC capability?

Granted it was stated as a hypothetical example to get input - but - surely somebody out there has both and done a study.

Bill,
Have you tried going to members tab and re-loging in. I seem to have to do that alot so it does not appear Anonymous. Just a thought.

Robert

Hey Bill,

No problem. Appears I have the same issue with the Anonymous thing also. Can't find the "login" button these days. Waiting to see how this one turns out once I click save.

Dave

Dave

Thanks for reposting my post.

Bill

This is actually one of the more interesting threads in a long time, in my opinion anyway. We help companies optimize both types of systems...sometimes using gadgets (but not always) because some things by themselves simply are not robust.

Of course both runner types have their places as Bill points out, and everyone will justify one or the other for a given project. And both also have an extensive list of pros and cons.

But I will try to focus on the question(s) "Which system hot or cold over its life will give the best Dimensional results if optimized properly when first qualified? Day in ....day out for the life of that mold?".

So presuming the upfront engineering was done properly so that both were fully optimized for shot size of a given part and press, that the machine is also optimized and robust, the melt delivery channels are optimized for pressure loss and we have the same material properties flowing to and within every cavity, etc,

...in regards to "when first qualified", I would think both would perform equally well. But if I needed to pick one for the initial start-up part of the question, I would think a cold runner would do better due to the simplicity of it.

In regards to "Day in, day out for the life of that mold" I would choose a cold runner mold. I say this simply because there is less chance of failures down the road (no thermocouples or heater bands that wear out or drift over time, no wires to pinch, less of a thermal process involved, etc...). Thus over the life of a mold it seems to make sense that a cold runner mold would provide more consistent dimensions.

The reason I mentioned material properties earlier is to address the question on my end of if you are looking at SPC data on a given cavity or comparing every cavity in a multi-cavity mold. I say this because even if you do have a robust process and mold but don't have the same material properties to and within every cavity then your SPC on a given part dimension may not be very good from cavity to cavity. This is because the parts may warp differently due to different shrink caused by different filler distribution, filling patterns, and temperature profiles. For each cavity to be the same, you need three main things:

1. identical steel conditions (design and build a robust mold)

2. identical process conditions shot to shot (robust machine)

3. identical material properties to and within every cavity (robust melt delivery system)

Dave

SPC/SQC are all about robust processes, NOT gadgets

Hot Runners are all about economics. Paul's company wouldn't know what to do if someone had a part with a lifetime run of 1,000 pcs. They specialize in millions of parts/run. In that light not making a runner only makes good sense.

HOT RUNNERS V. COLD RUNNERS.
Hot runners are really complex and intricate extended machine nozzles.
--PROS - you save a lot of material because you're usually only making parts and not parts AND runners
--CONS - by their presence they make the mold's stack height bigger. This usually forces the mold into a larger machine and here's where the problems come:

(1) It's difficult to maintain a controlled process when you're shooting less than 10% of the shot capacity. Problems created are: long residence times, small shots, high shot inventories, difficult to control temperature profiles. However with careful attentional to all the variables, runnerless molding is wonderful.

(2) Hot runner systems are expensive. With customers shouting "Kost Is Cing" it takes an interesting sales pitch to show an increased mold cost is easily offset by a lowered part price. However this again in volume dependent.

SPC/SQC
All the gadgets and toys you can hang on a mold won't help your reliability if the machine is not repeatable and well maintained. Well maintained tools and machines coupled with the knowledge of how to set up and keep a robust process is all you need for SPC/SQU.

My two cents

Somehow this %^#!!!@@### forum has made me Anonymous. So if you wish to honk on my for the comment below go ahead.

Bill Tobin

SPC/SQC are all about robust processes, NOT gadgets

Hot Runners are all about economics. Paul's company wouldn't know what to do if someone had a part with a lifetime run of 1,000 pcs. They specialize in millions of parts/run. In that light not making a runner only makes good sense.

HOT RUNNERS V. COLD RUNNERS.
Hot runners are really complex and intricate extended machine nozzles.
--PROS - you save a lot of material because you're usually only making parts and not parts AND runners
--CONS - by their presence they make the mold's stack height bigger. This usually forces the mold into a larger machine and here's where the problems come:

(1) It's difficult to maintain a controlled process when you're shooting less than 10% of the shot capacity. Problems created are: long residence times, small shots, high shot inventories, difficult to control temperature profiles. However with careful attentional to all the variables, runnerless molding is wonderful.

(2) Hot runner systems are expensive. With customers shouting "Kost Is Cing" it takes an interesting sales pitch to show an increased mold cost is easily offset by a lowered part price. However this again in volume dependent.

SPC/SQC
All the gadgets and toys you can hang on a mold won't help your reliability if the machine is not repeatable and well maintained. Well maintained tools and machines coupled with the knowledge of how to set up and keep a robust process is all you need for SPC/SQU.

My two cents

How about a hot runner with the drops feeding cold sub-runners?

Then what does the Molder really want,good SPC stats or plenty of good parts?
For really tight tolerances, in my opinion, nothing beats a cold sprue/runner with few or a single cavity.
Another issue is gate seal. Does one truly seal the gate with a true direct gate hot runner/sprue? I am not bringing valve gates into this picture!

Keep on Molding!

brent

Nearly all of the moulds we make are hotrunner multi cavity moulds for caps, closures, cutlery and thin wall containers and I can tell you that the dimensions are always within 5% from all cavities-including product weight.

Hot runner moulds will give balanced cavity filling.

My experience with cold runner moulds however, is that they will not give balanced cavity filling. A simple 8 cavity layout with even runner lengths to all gates making a simple product could not be balanced properly. The dimesnional difference was greater than 10%. All dimensions for the runners, gates, cavities and venting were triple checked but they were all the same.

Not long after that experience I read an article that a cold runner will not be balanced in its simplist form because of what is going on inside the material when it is flowing around the corners of the runner. I will leave the technical details out.

So from my point of view, hot runners are better.

Paul.