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Injection molding tooling options

Discussion in 'Electronic Design' started by Don Y, Feb 22, 2012.

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  1. Don Y

    Don Y Guest

    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
     
  2. 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
     
  3. Don Y

    Don Y Guest

    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!! :-/
    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.
    No, this will be done domestically. "High value added" design so it
    can afford the domestic fabrication costs (even the *boards*).
    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.
     
  4. 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
     
  5. Don Y

    Don Y Guest

    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!" :-/
     
  6. josephkk

    josephkk Guest

    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.

    ?-)
     
  7. Don Y

    Don Y Guest

    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?")
     
  8. josephkk

    josephkk Guest

    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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