Mold maker blowing smoke at me?

Tried any of the BeCu alloys?

 

Might add a bit to the size of the tool in some cases ... or
reduce the number of cavities ....

 

Great discussion, guys. Appreciate the good feedback. Learn something
new all the time. No, I didn't want to second-guess the mold maker on
this issue . . . just wanted to know whether he really was being
reasonable or jerking me around (again). And wanted to learn something
in the bargain. COMP.CAD.SOLIDWORKS participants ROCK. Absolutely one
of the best newsgroups around.

 

In some cases. Not in this one though. The shut off in question is on
the *inside* of a ring.

 

Was a very useful discussion for me too, learned at lot about things I
didn't know I needed to know!

Thanks

John Layne

 

I finally got to see the "RING". So I take it you have to have that
little step? If you could blend that into one slope it seems like that
would solve the problem.

BTW, to get in take the URL, remove the reference to the jpeg and then
you can browse for that and everything else you have in that directory.

 

OH, IS THAT RIGHT? S___, that's not cool!! I'll have to fix that.
Yes, I know that the step isn't right. I'm fixing it, but it ain't
easy. Got one side fixed -- took a Surface Cut that itself took 25
surfacing steps to get to. And that's only one of the two sides I need
to fix (opposite side -- 180 degrees). Doubtless I'm doing it very
inefficiently, but I have my doubts it would be a whole lot faster at
best.

 

John & others, on the "lock up" issue.

In all my time, which is now over 30 years, I've not had a pair of
tapered cores that mate metal-to-metal lock up, though indeed I've not
had a lot of them. The shutoff faces I have had have also tended to be
relatively short, <.50".

Basically, if the toolmaker made the contact "too tight" we ground off
..0005"-.001" and ran the mold again and generally relieved the pressure
to the point where there was insufficient contact pressure to cause
wear.

If you are using plastics like Polycarbonate which are more viscous,
even a .001" clearance won't generally flash between 2 cores, unless
you are way beyond normal injection pressures (>15,000 psi).

I have even had clearances like that in some of my Styrenics and
Polypropylene parts without flashing, though indeed you have to specify
how much flash = a flashing problem.

The newer all electric injection molding machines with fully closed
loop process controls are capable of far tighter injection controls
leading to far higher control of molded part size than what was
considered possible 10 years ago. I was astounded how closely I could
control flashing on an older mold (read worn out), to the point where
it was decided in numerous cases to hold off on replacing the mold. I
happen to be using JSW machines, but I'm sure others run likewise from
what I've heard.

Bo

 

Well, anyway, the parts as fixed can be seen at:

http://www.h2omarkdesign.com/img/connector_ring_fixed.jpg

The two surfaces could not be blended, simply because they are from
opposite sides of the mold, and therefore they have opposite draft on
them.

 

Hi,

We have designed many, many such parts, and use 5 degrees as a 'rule of
thumb'. Depending on how many parts you need to get out of the tool,
and the contact area between the tool faces in this area, you can even
use as little as 3 degrees - but it's risky.

I've found that most suppliers will recommend the absolute max. for
just about anything: sheetmetal bend radii, part wall section, tool
steel shut-off, draft angle etc. Experience shows that nearly all of
these rules can be broken.

Regards,

Anthony

 

And some things I really don't need to know!

However, I always figure that to understand something about a process that
you currently aren't using, will usually pay back in the long run. I don't
know how many times I have read through something like this thread, knowing
I don't do molds, but gleaning some little bit of info that does help me
with something. Plus, I have, in the past, designed a couple parts that we
had injection molded, and knowing something of the process helps immensely.

WT

 

Bo,

I totally agree with you. This guy knows what he is talking about
listen to him. We run a lot of polycarbonate, I wish everyone knew you
could have such gaps with polycarbonate then we would get better
venting. The newer close loop machines definately do a good job and I
havent even had trouble with the hydraulic machines. They can be
processed incorrectly and made to act like non closed loop if you dont
knwo what you are doing.

 

Your mold maker / client isn't going to be very happy about the "feather
edge" created by wrapping the shutoff around the radius on the lug. If that
radius can't be removed from the part, I suggest designing the tool so it's
easily repairable. I.e. "insert" that area of the tool, and make spare
inserts, as the feather edge will definitely fail in production.

 

Yes, I did realize that the razor edge produced will wear quickly and
ultimately fail, but I do need the radius there. I didn't really know
what to do about it, however, your comment made me realize that there's
something else that I can do about the problem to still keep the radius
but prevent a razor's edge from being required. Thanks for that . . .
I'll try to fix it.

'Sporky'

 

Design reviews at many stages are a good idea indeed <G>.
With folks from all groups involved.

 

Spork,
I can't tell for sure from the picture what the draft is on the right
side of that cored out opening, but you have a shut-off on that side also.
The wall looks 1 or 2 degrees. If not, disregard this message.

Good luck
Mike Eckstein

 

Terminology! I'm not sure I understand you, but the draft on the right
hand surface from bottom is 1 degree and also on the left hand surface
it's 1 degree from the top. The shut off between those two cored out
openings (where the drafts meet and cross) is 10 degrees.

 

Thanks to Michael Eckstein for pointing out another problem with the
part. He was kind enough to actually call me to explain what he meant
in his post, and as a result I'm rethinking the part entirely -- or
hoping the mold maker can come up with a threaded insert that will
eliminate the problem feature in the part. COMP.CAD.SOLIDWORKS denizens
are (on a cross-section) some of the best Netizens around.

 

You've gotten lots of good advice while I've been caught up in my work and
unable to read the group. I would be much more worried about the feather
edge at the radius than the angle of the shutoff.

I've still got my plastic product design standards from Mattel. They are
over 30 years old and Mattel was pretty conservative about their tooling.
(They wanted to build the tools fast and cheap and have them last for a
reasonable number of shots.) They asked for an offset (from top to bottom of
the angled face) of at least 0.010/0.015", with a minimum angle of 5
degrees. That meant that you needed more than 5 degrees on steps that were
less than 0.114" tall. They also asked for 0.060" lands on the sides that
you didn't want to flash.

We often use 3 degree shutoffs when we don't have room for five. You also
don't need the 0.010/0.015" offset if you use more accurate locating
features between the two halves of the mold, the parting line locks. (As I
recall, taper locks are more accurate than bullet nose locks, but I'm a part
designer, not a tool designer, and probably have the terminology screwed
up.) Running different mold temperatures on the two sides can cause you to
need more offset than normal.

Anyway, five degrees should be more than adequate most of the time. I would
try really hard to get a flat at the radius that is at least 0.020" if the
part is fairly small.

Jerry Steiger
Tripod Data Systems
"take the garbage out, dear"

 

Thanks, Jerry. I now have .015" flat instead of the feather edge or
what I called a razor edge. That's all I can give it, and that's
pushing some other limits of design for what I need the part to do. At
any rate I'm a lot more aware of several criteria than I was before I
began this thread, and have profited handsomely by the time that you and
others have spent here. Many thanks to all once again.

Mark