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MatrixLogo horizontal white

Injection Molding and Moldmaking
with Surgical Precision

Injection Molding and Moldmaking
with Surgical Precision

Call us: (630) 595-6144

Call us: (630) 595-6144

Since we've added web conferencing several years ago, it becomes more and more evident how this tool significantly improves the design / build process as costs are scrutinized and deliveries compressed. One recent program stands out, a stapling device with numerous metal and plastic parts that were activated by a series of gears and pulleys. Our initial design review with the customer using our web conferencing program allowed us to review the entire assembly get an overview of the device with a diverse group of Matrix personnel. Representatives from our design, manufacturing and quality areas all reviewed the device from their own point of view. And with the convenience of a voip phone call, our marketing manager attended the meeting remotely. During the review, suggestions were made to the customer that allowed them to eliminate several parts by redesign of the current assembly. Parts were combined, reducing the part count in the assembly. Slightly more complicated tooling, but far less costly in the long run. The customer immediately embraced those suggestions, as their COGS target for the device was going to be difficult to achieve. The savings our suggestions allowed gave them an immediate benefit. And, during the review, a fundamental design flaw was flushed out when this group of a dozen technical people got into a spirited discussion on the mechanics of the device, which was corrected within days. And as our mold design work was firming up, we held a concurrent review of both tool and product design, which saved significant time. Mold design (ours) and device design (theirs) were being toggled back and forth, with mods to both being made as the meeting continued. A very fast and productive use of time, for sure.

- Paul Ziegenhorn

This subject has been discussed for twenty-five years or more; which direction to choose depends on the complexity of the application and type of manufacturing one does.

The basic process of creating drawings to represent objects has been around since the days of the caveman.  In the world of manufacturing, this process began with basic 2D drawings known as “blueprints” that showed three basic views of an object: Plan, Front and Side.  If additional views were needed (inside, outside, isometric, etc.), each of these views had to be created separately.  The designer had to first be able to visualize the whole entity in order to project each of the necessary views onto a blueprint.  Others could then read the blueprint to view and understand the whole entity.

Machine operators studied blueprints and extracted the information they needed to ultimately produce a physical object that matched the views shown.  They entered coordinates and determined cutter types & sizes, drill bits, taps, etc., and then began machining.

The time required to create a 2D drawing was relative to the complexity of the part or the assembly of parts.  A very simple part could be four lines that create a square, and if you need some through holes in the corners you could add four circles.  Notes and dimensions were added as required.  Creating an assembly required multiple sketches or drawings.  This could either be done by sketching on paper or using a drafting board.  When multiple copies were needed for distribution, paper sketches were copied by hand using see-through paper whereas drafting board drawings could be duplicated more quickly by a blueprint machine.

Then came electronic 2D design with CAD software.  This enhancement allowed a company with computer monitors throughout its facility to give everyone involved access to the drawings, making hard copy paper drawings unnecessary!  Any revisions to the original CAD drawing were automatically viewed by everyone opening it on their computer.  Electronic design software presented a distinct advantage because there everyone had access to the one and only “master” CAD model.  When changes were made to this master model, everyone instantly had access to the update.  This saved the time and expense of having to manually revise multiple copies of paper drawings.

From a manufacturing standpoint, 2D electronic data can be used to generate manufacturing programs that drive a machine tool to follow a given outline.  Since it is limited to XY vectors, 2D data is sufficient for Wire EDM (Electrical Discharge Machining) and the majority of all through machining applications, holes, slots, window pockets, spline shapes.

The introduction of 3D electronic data made it possible to represent a solid object in 3 dimensions.  It includes XY and Z vectors (or IJK vectors).  The benefits of creating a 3D model are numerous.

Once the 3D model is created, it can be viewed by multiple people as if they were holding the physical object in their hands.  It is a solid body with volume, mass, internal and external features, and it can be rotated to any viewpoint allowing you to extract the information you need.  At Matrix Tooling, Inc. our designers use NX software (formerly Unigraphics).

The time required to create a 3D solid model is dependent upon its complexity, and 3D solid assemblies of multiple parts can also be created; an automobile assembly, for instance, might be used for display, sale, mechanical function, or aesthetic purposes.

The availability of 3D data has virtually eliminated the need for any 2D drawings in manufacturing, although some customers will still ask for them.  It takes considerably less time to create views on a drawing using 3D data; it’s just a matter of placing canned or custom views on a drawing that are linked to the 3D solid model or assembly.  The views are always to size and if a revision is made to the model, the drawing views are updated automatically.

Manufacturing using 3D data allows a machine operator or a CAM specialist to generate any type of machine path, limited only to the machine tool’s axis – be it 2D or multiple axis.

While 3D software packages are certainly more expensive than 2D systems, we have found that the benefits far outweigh the costs.  In our business of designing & building complex plastic injection molds, 3D design has not only helped us become a leader but will also play a critical role in maintaining our advantage.

Written By:

Hans Noack
Design Mgr.

By Brent Borgerson

October, 2012

In my previous micromolding blog, entitled “Micro Molds, One Key to Success as a Micromolder, I mentioned “Scientific Molding,” a methodology that is also sometimes referred to as “systematic molding” or “scientific processing.”  Many molders who still harken back to the early days, when injection molding was more art than science, think it is impossible to scientifically micromold.

The chief reason for this thinking is the overwhelming popularity of Decoupled MoldingSM, a method first popularized by RJG Inc. founder, Rod Groleau.  This technique, which has since evolved into three distinct types, has been a major influence in the application of scientific principles to the process of injection molding.

Decoupled MoldingSM (and other “scientific methods”) breaks the molding process down into specific fillpack and hold portions.  A key principle is how the injection of the melt is separated into fill (1st stage injection) and pack (2nd stage injection) portions of the stroke.  In later versions of the method, the injection portion of the cycle is divided even further.  But a major tenet of all these scientific methods is transferring the fill at about 95% of a volumetrically filled part. It is this premise which leads many molders to believe they can't apply these methods to the molding of micro parts, many of which can't be seen without the aid of a microscope.

Scientific Molding is much more than just separation of the injection phase though; it is all the steps taken when molding a part with best end properties, using a robust and repeatable process. These steps rely on the following prerequisites:

  • A properly designed and constructed mold.

Without a robust mold, a robust process is next to impossible.

  • A properly selected, sized and maintained molding press.

If the mold is great but the machine poor, you get a poor process.  Barrel size must not be too small or too big for the intended shot size, and the press must possess abundant injection pressure to avoid a possible pressure limited condition.

  • Carefully chosen and handled resin.

Handling includes properly drying (neither over- nor under-drying the resin) and researching the resin to be used.

  • Molding the resin at the correct parameters.

Do your research, and set the mold as well as the melt temps correctly.  It is usually best to begin mid-range, but much depends on the part geometry and wall thicknesses.  Also use suggested pressures and speeds.  This includes screw rotation speeds and back pressures.

Once the above prerequisites have been met, the initial sampling of the micro tool is done.  And if the mold functions properly and produces visually acceptable parts, the optimization and validation of the scientific molding process is performed.  This is usually comprised of of 6 steps:[i]

  1. 1. Viscosity study (or melt rheology study):

Usually cannot be done with micro parts.

  1. 2. Cavity balance:

This can be done on a multi-cavity micro mold.

  1. 3. Pressure drop study

This usually cannot be done completely on a micro mold, but watch your injection pressure so that you are not nearing the maximum.

  1. 4. Process window:

This study can and should be done for micro parts. Both the aesthetic and dimensional portions should be done.  The result is also known as the MAD or Molding Area Diagram, and it illustrates how robust the process is.

  1. 5. Gate Seal (freeze):

On a micro part, this can be a bit hard to do and requires a very accurate gram scale (which is a prerequisite in micromolding.)  Remember that you pay a lot for each place to the right of the decimal.  If you have a lost weight moisture analyzer, remember that it has a super sensitive scale.

  1. 6. Cooling Study:

Many times in molding, the sprue/runner set up determines the cycle time.  Nowhere is this more evident than in micromolding. Chances are the parts will have achieved optimum ejection temperature long before the sprue/runner will.  Of course, in the case of a hot sprue/runner, a molder can do the cooling study.


At Matrix Tooling, Inc. /Matrix Plastic Products, we don’t accept that scientific molding cannot be applied to micromolded thermoplastic parts.  In fact, we apply these proven techniques to develop robust processes every day, regardless of whether we are running large parts, small parts, or micro molded parts.

I’d like to thank my friend, Suhas Kulkkarni, Molding and DOE expert, author, teacher, consultant and Principal of FIMMTECH Inc.  Suhas offered me advice and let me post questions about this topic on his Injection Molding Online forum, where other molders also offered greatly appreciated input.



[i] Robust Process Development and Scientific Molding, by Suhas Kulkarni (published by Hanser) is a good reference for the details in performing the 6 step optimization process.

 

 

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