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Injection molding tooling options

D

Don Y

Jan 1, 1970
0
Hi,

We're exploring different packaging configurations for
a product. The casing will either be a casting (aluminum,
etc.) or injection molded plastic.

For the plastic option, we are concerned as to how much
up front effort we should put into the tooling knowing
that wear is inevitable, etc.

Volumes are such that hard tooling is the only practical
option (~100K pieces/year). But, the question as to whether
to budget for tool rework/maintenance vs. simply replacing
the tooling on some <mumble> schedule.

The latter option allows us to plan for packaging changes
that might be beneficial (for engineering or cosmetic
reasons).

Any folks have a feel for when it makes more sense to just
toss the tooling and start fresh? (i.e., after 100K pieces,
the tooling doesn't "owe us anything" :> )

Thx,
--don
 
S

Spehro Pefhany

Jan 1, 1970
0
Hi,

We're exploring different packaging configurations for
a product. The casing will either be a casting (aluminum,
etc.) or injection molded plastic.

For the plastic option, we are concerned as to how much
up front effort we should put into the tooling knowing
that wear is inevitable, etc.

Volumes are such that hard tooling is the only practical
option (~100K pieces/year). But, the question as to whether
to budget for tool rework/maintenance vs. simply replacing
the tooling on some <mumble> schedule.

The latter option allows us to plan for packaging changes
that might be beneficial (for engineering or cosmetic
reasons).

Any folks have a feel for when it makes more sense to just
toss the tooling and start fresh? (i.e., after 100K pieces,
the tooling doesn't "owe us anything" :> )

Thx,
--don

Hi, don:-

There are different grades of plastic tooling. The good stuff will do
1m pieces with minimal maintenance. Skimp on components, raw
materials, hardening, etc. and you save some money up front in
materials and machining costs, but you might see deterioration after
<100k shots. There will also be a difference in productivity- a mold
functions as a heat exchanger from molten polymer to water, and the
efficiency with which it does that determines the cycle time, and thus
the machine-time component of the part cost. Then there's the hot
runner vs. cold runner trade-off. Cold runner molds can be quite a bit
cheaper, but parts cost more. OTOH, color changes are usually easier
if you don't have plastic stored in the runner system that has to be
purged.

These guys show the comparison of SPI mold classifications (I'm not
recommending them, it's just a convenient reference):

http://www.ftdinc.com/moldspecs.htm

Aside from the difference in cost, you might find some suppliers'
class 102 is really a class 103.. especially if the supplier is
offshore and particularly if you negotiate the price down. If you're
buying complete molds, they can be rebuilt. If you're only buying MUD
inserts it may not be cost-effective.

The optimal choice for your situation may depend on business factors
such as confidence that there will be no design changes over the life
of the tooling.


Best regards,
Spehro Pefhany
 
D

Don Y

Jan 1, 1970
0
Hi Spehro,

There are different grades of plastic tooling. The good stuff will do
1m pieces with minimal maintenance. Skimp on components, raw

Yikes! Some research for an earlier project suggested ~10K squirts
for cheap tooling, ~100K for better tooling. <frown> I dislike
getting dragged into packaging issues. Get somebody who's expert
in this sort of thing!! :-/
materials, hardening, etc. and you save some money up front in
materials and machining costs, but you might see deterioration after
<100k shots. There will also be a difference in productivity- a mold
functions as a heat exchanger from molten polymer to water, and the
efficiency with which it does that determines the cycle time, and thus
the machine-time component of the part cost. Then there's the hot
runner vs. cold runner trade-off. Cold runner molds can be quite a bit
cheaper, but parts cost more. OTOH, color changes are usually easier
if you don't have plastic stored in the runner system that has to be
purged.

I don't *think* color is an issue. Pick one and that's it. Material
choice will be more of a problem. The trouble is balancing look/feel
against durability, etc.
These guys show the comparison of SPI mold classifications (I'm not
recommending them, it's just a convenient reference):

http://www.ftdinc.com/moldspecs.htm

Aside from the difference in cost, you might find some suppliers'
class 102 is really a class 103.. especially if the supplier is
offshore and particularly if you negotiate the price down. If you're

No, this will be done domestically. "High value added" design so it
can afford the domestic fabrication costs (even the *boards*).
buying complete molds, they can be rebuilt. If you're only buying MUD
inserts it may not be cost-effective.

The optimal choice for your situation may depend on business factors
such as confidence that there will be no design changes over the life
of the tooling.

That was my point. If you are already planning for "other models",
perhaps just *plan* for the tooling to be discarded and rebuilt
for each new generation/model. Instead of budgeting to maintain
molds and/or worrying about quality slip as the mold ages.
 
S

Spehro Pefhany

Jan 1, 1970
0
Hi Spehro, ...

Yikes! Some research for an earlier project suggested ~10K squirts
for cheap tooling, ~100K for better tooling. <frown> I dislike
getting dragged into packaging issues. Get somebody who's expert
in this sort of thing!! :-/

1. On interpretation of the SPI numbers.. note that
10,000 is < 100,000. There are certainly ways to
get closer to 10k than 100k - just choosing soft materials
and nasty plastic is one easy way. Modern machines can cut
really nice materials fairly efficiently (EDM doesn't
really care). I recently was shown a complex CNC-milled cavity
that was almost ready to use without polishing.. milled
directly from hardened steel, very tight (micron)
tolerances. The "milling machine" wasn't a Harbor Freight
special though, it produced dust rather than chips and cost
about half a million dollars. In some places you can buy a
house for that. EDM can produce hardened parts (even from
exotic materials) that fit together so snugly that you can
barely see a gap.

2. I tend to agree with your conclusion, but it's nice to know
what questions to ask, particularly if you are the only one
with a systems perspective and/or if you have skin in the
deal.

--sp



Best regards,
Spehro Pefhany
 
D

Don Y

Jan 1, 1970
0
Hi Spehro,

1. On interpretation of the SPI numbers.. note that
10,000 is< 100,000. There are certainly ways to
get closer to 10k than 100k - just choosing soft materials
and nasty plastic is one easy way. Modern machines can cut

The impression I got, at the time, was that there is a difference,
IN PRACTICE, between what can be *claimed* vs. can be *actualized*.
I.e., "derate liberally" -- or, end up "watching CAREFULLY!"
really nice materials fairly efficiently (EDM doesn't
really care). I recently was shown a complex CNC-milled cavity
that was almost ready to use without polishing.. milled
directly from hardened steel, very tight (micron)

Yes, a friend owns a machine shop. He's been systematically
replacing all the Bridgeports, etc. with wire EDM machines.
I think he has 4 of them, currently.

(But, he specializes in very exotic work... very high piece part
prices, etc.)
tolerances. The "milling machine" wasn't a Harbor Freight
special though, it produced dust rather than chips and cost
about half a million dollars. In some places you can buy a
house for that. EDM can produce hardened parts (even from
exotic materials) that fit together so snugly that you can
barely see a gap.

2. I tend to agree with your conclusion, but it's nice to know
what questions to ask, particularly if you are the only one
with a systems perspective and/or if you have skin in the
deal.

I think it boils down to "laziness" (bad choice of words but it
fits my vocabulary). Easier to pass off a task to someone
standing in front of you than it is to go looking for the
*right* person to do the job. (I've had clients ask me to
hire staff for them, train them, etc. "Um, what makes you
think I *want* to do those sorts of things???!").

And, I can either argue with them expounding on my ignorance
of the subject -- or, go through the motions of getting the
"low hanging fruit", dropping it in their laps, shrugging my
shoulders and saying, "You'll have to figure out how to
interpret this and factor it into *YOUR* business decisions..."

I just *really* dread the "doing things over" mindset: "That
might make economic sense to *you* but it's not how I want to
spend *my* time!" :-/
 
J

josephkk

Jan 1, 1970
0
Hi Spehro,



The impression I got, at the time, was that there is a difference,
IN PRACTICE, between what can be *claimed* vs. can be *actualized*.
I.e., "derate liberally" -- or, end up "watching CAREFULLY!"


Yes, a friend owns a machine shop. He's been systematically
replacing all the Bridgeports, etc. with wire EDM machines.
I think he has 4 of them, currently.

(But, he specializes in very exotic work... very high piece part
prices, etc.)


I think it boils down to "laziness" (bad choice of words but it
fits my vocabulary). Easier to pass off a task to someone
standing in front of you than it is to go looking for the
*right* person to do the job. (I've had clients ask me to
hire staff for them, train them, etc. "Um, what makes you
think I *want* to do those sorts of things???!").

And, I can either argue with them expounding on my ignorance
of the subject -- or, go through the motions of getting the
"low hanging fruit", dropping it in their laps, shrugging my
shoulders and saying, "You'll have to figure out how to
interpret this and factor it into *YOUR* business decisions..."

I just *really* dread the "doing things over" mindset: "That
might make economic sense to *you* but it's not how I want to
spend *my* time!" :-/

Just a wild guess here. I but that some better molding houses have
someone on staff that knows just what you need, and the outfit sells this
person's time by the hour or as part of a product run. Negotiated up
front. Maybe that is a useful way for you to approach this one.

?-)
 
D

Don Y

Jan 1, 1970
0
Hi Joseph,

Just a wild guess here. I but that some better molding houses have
someone on staff that knows just what you need, and the outfit sells this
person's time by the hour or as part of a product run. Negotiated up
front. Maybe that is a useful way for you to approach this one.

IME, once you drag a vendor into a deal, it's hard to push them
back *out*. Now, you've got someone *else* injecting their
wants, urgency, etc. into a process that is already ripe with
those issues. They want to "make the sale happen". I/client
want to "gather information". The sale might *never* happen
though the vendor doesn't look at that option as objectively as
I/client might.

I much prefer getting some education before approaching a vendor
with my requirements. Then, let him suggest alternatives and
*reasons* for those alternatives. But, I need to be able to
understand and evaluate those alternatives from my/client's
perspective: "No, that won't work because..." or "But, isn't
a consequence of that ..."

In the past, I've had IE's available to tell me what was possible
and the (approx) costs/consequences of each option. So, I could
approach vendor candidates with a shopping list and hear their
reactions to the alternatives that I am willing to explore
("Gee, why is this guy pushing the low end product so hard?
maybe he can't *make* the better product?")
 
J

josephkk

Jan 1, 1970
0
Hi Joseph,



IME, once you drag a vendor into a deal, it's hard to push them
back *out*. Now, you've got someone *else* injecting their
wants, urgency, etc. into a process that is already ripe with
those issues. They want to "make the sale happen". I/client
want to "gather information". The sale might *never* happen
though the vendor doesn't look at that option as objectively as
I/client might.

I much prefer getting some education before approaching a vendor
with my requirements. Then, let him suggest alternatives and
*reasons* for those alternatives. But, I need to be able to
understand and evaluate those alternatives from my/client's
perspective: "No, that won't work because..." or "But, isn't
a consequence of that ..."

In the past, I've had IE's available to tell me what was possible
and the (approx) costs/consequences of each option. So, I could
approach vendor candidates with a shopping list and hear their
reactions to the alternatives that I am willing to explore
("Gee, why is this guy pushing the low end product so hard?
maybe he can't *make* the better product?")

I have seen enough of what you speak of. Just an idea that has worked for
me a couple of times. It is your fish, fry it as you see fit.

?-)
 
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