Matrix Plastic Products has been micromolding plastic parts since the mid-1990's, long before it was in vogue.  This pusher (shown) for a micro linear cutter cartridge is .031" x .040" x .040" and weighs just .0008 grams.  Most of our micro projects are for the medical industry, for minimally invasive surgical applications in particular, but we also provide micro components used in the electronics industry.  Weighing just fractions of a gram, some of these parts are smaller than a pellet of resin, with tolerances of five ten thousandths of an inch (0.0127 mm) or less.

I believe one of the main reasons we are not intimidated by projects like these is that we also have Matrix Tooling, Inc. under the same roof.  The close-tolerance and high precision of our molded products is rooted in our long history as a designer and builder of close-tolerance and high precision molds.  Our strength in specialty tooling has proven to be a key factor in our evolution into the successful micromolder we are today.

Matrix Tooling builds most of our micro molds with cold runners and low cavitations (8 or fewer) because that combination makes it easier to maintain tight specifications.  While mini hot runners are available, many of the resins we use in micromolding do not lend themselves to hot runner molding.

While almost any thermoplastic resin can be used in micromolding, Matrix Plastic Products commonly uses high-flow, high-temp grades such as LCP, PEEK and PEI.  These materials have predictable shrink, and the high mold temps involved help flow, especially in very thin-walled parts.  They also exhibit superior end use properties such as strength, stress crack resistance, thermal stability and dimensional stability.

Yes, much of our success in micromolding can be ascribed to our mold construction which must be tight and precise, well supported and robust. I asked Steve, one of our experienced moldmakers at Matrix Tooling (but who was new to micro moldmaking) what the key to his first successful micro mold was.  “Trusting our equipment,” he replied.  Matrix Tooling employs only state-of-the-art CNC moldmaking technology.

However, we also subscribe to scientific molding practices.  With a part that you can barely see, it is next to impossible to fill to 95% before transferring; but many other aspects of systematic/scientific molding are rigorously applied here at Matrix.  I will discuss “Scientific Micromolding” in a subsequent blog.

Matrix Plastic Products operates both hydraulic and electric presses in the smaller size ranges, and it is essential that the molding machine be sized according to the job at hand.  But for micromolding, we prefer the electric machines with their inherent precision and repeatability.

On jobs where the actual finished part is barely much more than an add-on to the sprue and runner, not only is the tooling critical, but the Quality Assurance can also be very demanding. Here again, Matrix meets the challenge with such equipment as OGP vision systems, Vision Engineering video microscopes, and a CGI cross-sectional scanner for First Article inspections. Microscopes are a common sight at Matrix: not only in QA, but in the molding, clean room and tooling areas as well!

We don’t “sweat the small stuff.”  Matrix Tooling, Inc. and Matrix Plastic Products has the equipment, know-how and experience to successfully handle any micromolded project.  We’re always happy to offer our insight into yours.

 

Brent Borgerson
Senior Process Engineer (Older Molder)
Matrix Plastic Products
Wood Dale, IL

 

Early in the history of injection molding, molders realized the problems inherent in producing high volume, fast cycling parts of commodity resins with cold runners, especially in high-cavitation molds.  Cold runners can stick or hang in the mold and interrupt or extend the cycle; and often the cold runner being the last part of the shot to set up, can dictate the overall cycle.

It soon became obvious that “runnerless” molding was the way to go.  Early hot runners were of the internally heated (torpedo) type or the externally heated manifold hot runner.  Both were prone to leakage and hard to (especially the torpedo type) change colors with.  Predating these systems were a type of runnerless mold called an Insulated Runner.

Insulated Runners had an oversized internal runner cut into both the top clamp plate and the “A” plate.  This runner was very thick and relied on the thickness of this runner-cull to keep the plastic in a molten state as long as the molding machine was cycling.  The walls of the runner were solid with only a molten center core providing melt delivery.  These led to cylindrical drops (also very thick) and generally to top-center-gated parts.

This system needed fast, uninterrupted cycles to keep the gates open and even momentary interruption caused one or more gates to freeze off.

Startup was also tricky with these molds.  Methods included hand injection of multiple shots into the mold before going to auto, making one big shot and going to auto, or boosting the back pressure way up and extrusion filling the runner cull.

Later the gate drops were heated with a probe which made startup easier and also made keeping the gates open easier, even allowing a brief disruption the the cycle.  With very fast cycles (3 to 6 second range) the heated probe insulated runner can have a fairly small thickness and in some cases, be reground and re-used in the product.

Though sometimes a bit tricky to startup and keep running, these systems could offer advantages over not only cold runners, but hot runners as well.  These include:

  • Quick cycles
  • Less regrind and scrap, though the thick cull wasn’t generally used back in molding
  • The tool was less expensive to build and maintain
  • Less chance for melt leakage.
  • Color changes were very fast compared to hot runners, as the whole colored cull was pulled after the molding machine’s barrel was cleaned. Often color changes can be preformed in 5 minutes with less than 5 pounds of scrap
  • Even if heated gate drops were employed, fewer and less sophisticated controllers were needed.

Yes, the insulated runner is an old technology, but if you have a multi-cavity, fast-cycling job using a commodity resin like PP or PE with frequent color changes, and want a more economical tool that is easier to maintain, then consider insulated runner tools.

Apprentice TrainingI’ve been involved in high school career education programs for much of the last 15 years. A good portion of that time was spent talking to educators and parents about careers in precision manufacturing being a viable alternative to the typical 4-year college program being pushed on our kids. Colleges have done a very good job of convincing us (and especially the parents) that the only way to a successful and rewarding career is to get a degree. I, for one, don’t agree. An apprenticeship can offer a young person another option; and the fact is that college is not necessarily the best choice for many high school students. Most teachers will agree with this logic. They know first hand which of their students are good candidates for advanced degrees and which are more likely to struggle. Most apprentice programs are struggling to attract talented young people, who by that time have had 12+ years of people telling them that they will need to get a degree in order to get a good job.

I know that the U.S. is not the only country with this problem. Much of Western Europe suffers from the same shortages. Many look down on those who work with their hands, but eventually, someone will need to learn and become the next batch of journeyman plumbers, electricians, toolmakers, etc. If not, homeowners better get ready to learn these skills or be ready to open up the checkbook.

I read an interesting article back in the mid 1990’s. In Germany (where an apprenticeship in a trade is still considered a viable career choice), the graduating number of architects outnumbered the number of apprentices from all skilled building trades combined. Think of how many architects it takes to build a home versus the number of workers needed from the various trades, and you’ll realize that something is seriously out of whack. Apparently the Germans, too, have spread the word that working behind a desk versus working with your hands is the way to go.

Hitting closer to home, we’ve struggled with finding quality candidates. Toolmakers today require skills far different than what was needed prior to the computer age, and the fact that few are training today makes for an unsustainable labor situation.

Written by:

Paul Ziegenhorn
President

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