Micro Molding with Stack Plastics

November 16th, 2015 | Business, Manufacturing | Tags:

When it comes to manufacturing, something small has got to be easier to make than something big, right? Building a canoe is way simpler than building a cruise ship, so does that same comparison hold up across all types of manufacturing? Is smaller always easier? Absolutely not.

Micro molding (or micromolding or micro-molding) is the process of producing very, very small plastic parts via injection molding. Although it’s one of the most difficult manufacturing processes there is, Stack Plastics excels at micro molding.

Small Scale, Big Success

Micromolding is far more than simply making a smaller version of a standard injection molded part. Micro molded parts aren’t just small, they’re often microscopically so—hence, “micro” molding. When you’re producing parts that are dwarfed by a watch battery, there are certain factors that have to be considered in order to ensure quality and dimensional accuracy.

The first challenge that one faces in micro-molding reinforces the notion of just how small micro-molded parts can be. The varieties of plastic typically used for injection molding have rather large molecules (relatively speaking). When working large molecules into extremely small shapes, the molecules tend to behave differently than they do in normal-size molding applications. Fortunately, the Stack Plastics team has extensive knowledge of the unique polymer materials we work with—not to mention many years of experience—and we’ve long since mastered the art of molecular manipulation.

The second considerable challenge in micromolding is the equipment used. Miniature-scale plastic injected parts require miniature-scale plastic injection molds and tooling. Some mold pins and similar devices measure only a few thousandths of an inch in diameter—at that size, everything is fragile, even stainless steel (a common mold and tooling material). We work with expert mold- and tool-makers to create durable, custom molding apparatuses that will produce the parts you need with perfect precision and repeatability, even for high volume orders.

The Micromolding Experts

Though it’s not always easy, we have the skills, the experience, and the technology to turn any design into a tangible product. If you need high precision, micro-molded plastic injection parts for medical devices, electronics, or any other special application, look no further. Stack Plastics are the micro-experts. Contact us today!

Santoprene Discontinued

December 12th, 2012 | Uncategorized |




Certain grades of Santoprene have been discontinued.


Please see our link to see the notification from ExxonMobil:


Organization, Controlling your work space

November 29th, 2012 | Business |


How do you stay organized when you hardly have time to eat your lunch?

I’m sure we can find a hundred ideas. Today, I’m going to talk about what we at Stack Plastics have done.

I think it’s nearly impossible to be organized if you don’t start with an organized work space. Staying organized is enough of a challenge, going from a mess to a state of order is a whole other ball game. Some years ago it became clear to me that my own work space was out of control, papers stacked up in piles, files in places that made no logical sense, and most importantly no where to put anything… I made the choice to get help, my mantra at work (as CEO) is “have the right people in the right positions, give them the tools they need to do their job and then… let them do their job!) I hired Grace Bermudes of “Check it off your list” http://checkitoffyourlistnow.com/ Grace is a professional organizer and very good at her job. Grace came in and spent a couple hours with me getting an understanding of the problem, the work flow, generally how I operate and then came up with several paths to a solution.

I spent a total of about 4 hours on the project, Grace did everything else, including sorting files, purchasing, assembling and installing shelves and filing organizers, etc..


After experiencing the benefits of a well organized work area and seeing the improved productivity for myself, I attacked several areas of the organization that could benefit from this same process.

I have found that even the most “organizationally challenged” member of our team could improve their productivity when given a chance to start fresh in a clean, organized and logical work space.



August 8th, 2012 | Processing Challenges |

Continuing our discussion on good molding practices I wanted to talk about “Packing”.

 Packing is an industry term that refers to the process of applying pressure to the mold cavity after it has been filled.  In our previous discussion we talked about the filling process, today’s discussion concerns the next step in the molding cycle, packing.

 There are several items of consideration:

  • How much pressure is needed?
  • How long should this pressure be applied?
  • What size should the gates be? And what happens if they are too small or too large?

 The amount of pressure needed can be determined through a process that involves several steps.  First it’s important to start low; under-packing a part is much less likely to cause problems during this experiment than over-packing.  An under-packed part is likely to have sinks, voids and shorts.  Increase pressure in small increments until the part appears, visually, to be full, free of sinks and voids.  Use a generous amount of time in the step.   You should take dimensional readings at this point to assure the part is shrinking properly, too little pressure can cause excess shrink, too much can cause excess stress, sticking and warp.  If the part is now in spec we have a good idea that the amount of pressure is correct, if the part is exhibiting sinks, voids or other evidence of under-packing our gates are too small.  Remember a gate needs to be 40-60% of the wall section.  If the gate needs adjustment this needs to be done before continuing.

 The next step is to determine how long to hold this pressure.  We determine the packing time by conducting a “gate freeze study”.  Reduce the packing time to one second and run a part, increase the time by one second every few cycles and segregate the various parts.  Using a scale that has appropriate resolution for the size of part you are molding, weigh each set of parts and note the weight.  As time increases the mass of the part should also increase, the mass should continue to increase with each addition of packing time until the “gate freezes”.  The term gate is appropriate as it is the doorway into the cavity, when the plastic solidifies material can no longer flow in either direction, hence the door (gate) is closed.  This time is the minimum amount of time needed to assure your part will be Consistently and appropriately packed out.  It is also the maximum amount of time needed because, with the gate now closed, applying pressure is no longer having any effect on the part.  I stressed constantly because this is one of the most important reasons why Stack Plastics, Inc. does this kind of experiment; we want to make sure the parts we manufacture are consistently correct.  These studies take a lot of time and many shops don’t bother with them but we at Stack Plastics, Inc. understand the science of molding.  Remember, Injection molding is a science, not an art.

 Last year we inherited a mold from overseas.  Our customer’s reason for changing vendors was the parts had dimensional variation and excessive sink.  During the gate freeze study we determined that the gates were too small.  It was a simple thing to enlarge them to the appropriate size.  We reinstalled the mold and continued with the experiment.   We were now able to properly pack the part and have been seeing a 98.9% yield ever since.


PeBax Update

June 12th, 2012 | Business |

Arkamas promise to give 12 months’ notice if changing formula.

See the notice here



Medical Device Tax

June 1st, 2012 | Business |

June 1, 2012


Improvised Explosive Device Tax!


In the May 29th, 2012 addition of the Wall Street Journal (Review and Outlook) page A12 there is an important article describing the federal government’s attempt to drive Medical Device Manufacturing out of our country! This kind of stupidity needs to be STOPPED!

The “affordable care act’s” is coming in 2013, one part of this act will levy a 2.3% GROSS tax on medical devices, everything from Implants to delivery devices to scanners. Ya that’s right, let’s take one of our last stable manufacturing industries and tax it out of the country!

Support to stop this is starting to grow but everyone needs to get involved and write your representatives, vote out the incompetents that came up with this crap.

Arkema Pebax, Nylon 12, Grilamid, Vestamid

May 24th, 2012 | Business | Tags:


Nylon 12




If you need an update on the Arkema force majeure please go to:


Updates will be located at the bottom of the home page.



Rewood City Salt works Development

May 3rd, 2012 | Business |

Any one following the “salt works” project going on in Redwood City (Just up the road from us here at Stack) may be interested in the latest recommendation from the Committee.

Below is a copy of the latest release. Personally I like the marshes and hope they leave them alone, there is plenty of places to build with less impact.


For Immediate Release




Robert Bell

City Manager



City Council’s Ad Hoc Committee on Saltworks to Recommend Denial of Project Application


Redwood City, CA – The City Council’s ad-hoc committee assigned to research and report on options regarding the Saltworks development application will be recommending denial of the current application when the issue comes to the City Council on May 7th. This recommendation is being made on the grounds that despite having an application on file with the City for three years, the developer has yet to submit a complete project description and therefore the application remains incomplete and inactive.


If the City Council follows the recommended action and denies the project, the City would stop all current processing actions. The committee also recommends not proceeding with a public vote on the issue at this time. Since the developer has indicated that the scope of the project is to be revised, it would not be a prudent use of City resources to gather public opinion about a project for which a completed description and application does not exist.


The committee further advises that if and when the developer presents a new and complete project application to the City, the City will determine whether and how to proceed on that application, at that time. The committee’s full report will be available on the City’s website by 5 pm on Thursday, May 3, 2012.


Denying the current application would not prevent DMB from pursuing a new application in the future. In the meantime, the property would remain subject to current General Plan designations that have been in place since 1990.


The ad-hoc committee will be making its recommendations at the May 7th, 2012, City Council meeting, which begins at 7 pm in the Council Chambers at City Hall, 1017 Middlefield Road.


More information on the Saltworks proposal is available on the City’s Web site at www.redwoodcity.org/saltworks.






(sent by)
Malcolm Smith

Public Communications Manager

City of Redwood City, California


Office:      650.780.7305

Cell:         408.472.8536

Fax:         650.780.7225

Email:       malcolm.smith@redwoodcity.org

Web:        http://www.redwoodcity.org/

Twitter:     www.twitter.com/redwoodcity

Street:     1017 Middlefield Road

            Redwood City, CA 94063

Molds, what are they?

May 1st, 2012 | Processing Challenges | Tags:

I am going to have a series of short articles covering Injection molding. We will start with the very basics and move to the complex.

Today we will discuss Molds.


What’s an injection mold?

A hollow form or matrix into which thermoplastic resin is injected and which imparts to said material its final shape.


Injection molds, in simplest terms have a cavity, a core and a mold base which holds everything together.  Click here to see an example of a simple mold


Injection molds can have very simple to very complex geometries. They can also make a single part each cycle or many parts per cycle, some very high quantity production molds can have 128 cavities or even more.

A cycle consists of closing the mold and clamping it under pressure, Injecting plastic into the mold, allowing it to cool, opening the mold and removing the finished part.


Injection molds can also make several different parts each cycle; this type of mold is called a Family Mold.



April 26th, 2012 | Processing Challenges | Tags:


Over-molding is, in very basic terms, putting one plastic on top of another.  Most of the time this involves molding a soft elastomer onto a more rigid substrate, a two part toothbrush as example, rigid polypropylene substrate with a soft elastomer over-mold to give it a “soft” feel.

This is usually pretty straight forward as long as you have good dimensional control of the substrate. 

Recently we had an over-molding project that required molding a soft durometer over an even softer substrate. The substrate was pretty heavy walled as molded parts go, which makes this even more interesting.

First go-round we found the part was measuring too big, we checked the cavity, shrink, processing parameters, but everything was to spec. We had to scratch our heads for a few minutes until it occurred to us what was happening, the first mold (substrate) was actually compressing during the second molding, when the mold opened the part was allowed to decompress and it grew by nearly 10%. We were able to compensate for this using different molding parameters and get parts to spec, but it did have us for a while.

The main reason for mentioning this is to help keep us thinking, I have been molding for well over 25 years and have not seen this before, and it’s completely obvious in hind sight, but I didn’t think about it until it became a problem.

Moral: Don’t think you have seen it all, you haven’t! Look at each new project as if it was just invented.