Sep 01 2008


Published by at 2:18 pm under Uncategorized

Yes, COST IS (sometimes) IS KING but material is darn expensive.  For a buyer this is simple:  “Gimmie low cost parts” he croaks and places the job off shore.  Then as time wears on he finds his parts are brittle or not the proper dimension and ultimately his engineers say the parts are made of Poly-what-do-you-call-it AKA Mystery Polymer Blend.  Was it low cost?  Yup.  Is his supply chain full of them?  Yup.  Can he do anything?  Nope, he is sooooo busted.

Now let’s look at the other side of the coin:  Regardless what our brethren in Asia say, in most cases the cost of the tool, when amortized into the life long production of the product is more than overwhelmed by the material cost.  Doing a little algebra a slight increase in the mold cost that can save material has a huge impact on the overall project cost.

Since I’m still getting e-mails from supposedly ‘high tech’ mold builders in China asking me why I should even put in waterlines; So I won’t try to bring up the subject of hot runner combo molds, valve gates, coefficients of thermal expansion to get the proper alignment of the hot runner or the finer points of PID, PID2, ART, or PIDD temperature controllers.  They need a lot more experience before that conversation makes any sense.

Instead of doing the CHINA SYNDROME trick of  prostituting or switching materials and hoping you won’t get caught, why not minimize the material usage for each shot?  This takes a bit of salesmanship on the part of the mold builder.  Yes, hot runners are spendy.  But, they have the advantage of running faster and more consistently because the sprue and runner eliminate the thickest cross section of the shot and therefore the cycle time.  Less material per shot, less regrind to recycle, better balanced molds, faster cycles and less (expensive) material usage are all good things.

But the sales side of this is ugly. There are a lot of buyers who need the education of what a hot runner is, what it does, and what it saves (NOT what it costs).  OK, fairly easy: – crank up your ‘puter and with a little help from the folks who make hot runners go to your best customers and put on a ‘brown bag seminar’.  You show up in the cafeteria, they show up, you do the Dog and Pony Show.  The purpose of this PowerPoint Extravangza isn’t to sell hot runners on your molds.  It’s to make people aware that this technology is here, inexpensive at the end of the day, and very price competitive.  Show the technology and then show the numbers.  The universal language is money.

Here’s another trick – there’s no sin to a retrofit AND you have the choice of telling (or not telling) your customer.

(1) The three plate retrofit. The easiest retrofit is with a three plate mold because everything is already aligned.  The hot runner manifold simply replaces the third plate mechanism.

(2) The combo tool. Many 24-48 cavity molds (for no reason I can understand) have runner like a map of the Los Angeles Freeway System.  With a little creative thought while it’s expensive and difficult to build a 24-48 hot runner system without totally rebuilding the mold; it isn’t an overwhelming problem to have one drop of your system service 4-8 cavities.  While it doesn’t eliminate the runner, it does eliminate a vast portion of the runner system.

(3) The replaceable runner.  This is a little tricky and requires some snazzy scheduling.  Many people will tell you for low or medium volume tools there is no payback for using a hot runner unless it’s a stack tool.  This was the same type of argument I heard when the Master Unit Die concept was introduced.  Yes, the main frame of a MUD die is spendy; but the inserts are so inexpensive and a common sprue and ejector configuration can be easily dealt with.

Why not do the same thing with a four or eight drop hot runner?  The positions of the drops are fixed.  The hot runner portion of the mold is modular so that it can be bolted to many mold bases.  Now, with a little thought, you can have one ‘standard’ hot runner system service several molds.  I saw this trick wonderfully applied using a hot runner system cannibalized from a mold that was being ‘retired’.  The hot runner system was perfectly usable.  These tricks can be part of your presentation or you can be quiet about them.

I had a client who used #3 and didn’t tell his customer.  He bought a fully functional mold base, and substituted his old hot runner building the mold to accommodate the hot runner’s spacing.  Sure enough, as predicted, the buyer had “A dozen guys in the lobby that could mold for a lower price than you”.  The threat wasn’t particularly creative but Wolfrick was a very good poker player.  He told the buyer to give it to the ‘cheaper guys’ and he’d call back in six weeks to see if the prices were actually cheaper.  He took out his system, plugged the holes for the hot runner, cut in a conventional sprue and runner system and shipped off the mold.  It took six months for the buyer to return the mold.  Wolfrick quoted a higher price, blocked off the conventional runners, removed the plugs and put his system back in.  He never told the buyer how he did it.  He also never let the buyer or his engineers inspect the mold ‘for insurance reasons’.

(4) The replaceable sprue bushing or extended nozzle. Even something as simple as a hot sprue that has wires sticking out the back of the mold saves both time and money.  Many of the heated sprues are now ‘drop in’ replacements for conventional sprue bushings.  If you’re not into heated sprue bushings, take a long hard look at nozzle extensions. Not using them is throwing additional cash in the trash.

(5) The Salvaged Runner System:  Customers retire molds with hot runners all the time.  The product’s useful life has come to an end, you hold onto the tool for a few years, then offer to sell it for scrap metal prices or bill them $1,000/year to store it until it turns into a rust pile.  Pay the customer the going rate for scrap steel.  Remove the runner system and if you want, send it off to be cleaned internally.  If you have to get the heaters replaced they are relatively cheap.  When you have your next mold come up with the proper cavity count you can re-install the system and pocket the extra cash and never tell the customer.

Are hot runners worth it?  Sure, with very few exceptions.  All molders are here to manufacture and sell parts; not parts and runners.

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This article is virtual.  You can do a quick survey of your molds and see if there are any candidates where you can squeeze some extra profit out of your molding operation with a heated sprue, extension nozzle or a hot runner system.  Or you can read it, decide it too much work and money to do anything about it and delete it.  OR you can use it to scare the rats in the warehouse and go back to sleep.

Your choice.

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