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Problems Solved: Micro Molding for Medical


Dynomax resolves issues with cracking, weld lines and short shots, resulting in top-notch micro molds for the medical industry 

By Tom Filippo
General Manager
Molding & Tooling Division

By Megan Krizman


Challenges (both large and small) arise in the manufacturing industry every day. The nature of the industry is problem-solving, and Dynomax Inc., founded in 1986 by CEO Richard Zic and headquartered in the Chicago land area, has battled and conquered its fair share of challenges. The company serves the medical, aerospace/defense, transportation, and energy industries. These markets are constantly developing in technological advancements, which means Dynomax has had to adapt by investing in new equipment and technology. Gasket Molded with Silicone Rubber Material

Of late, the most pressing change has been the shift towards increased micro-molding in all of these industries, but most particularly for the medical industry. There were several complications that arose when Dynomax increased its medical precision-molding production, specifically cracking, weld lines, and short shots. These are all caused by a combination of similar issues resulting from difficulties in filling the last place the mold fills with plastic. It is the most difficult area to fill for several reasons: First, air and molding gas are often trapped in this area, creating air pockets or shot shorts in the final molded part. Second, when the plastic enters the mold tool, it is at its highest temperature. However, as it fills in throughout the tool, the temperature cools at a very high rate, making the last place to fill (and the area where the plastic comes together) the most difficult. Lastly, the raw material itself can present a challenge.

It is very difficult to fill a high percentage of glass-filled material through thin-wall areas. When filling a mold with 30-40% glass-filled LCP in the areas that are only .003", it is possible for the glass particles within the material to be larger than the width of the wall. To solve these issues, Dynomax had to make certain adjustments. Simple fixes could be done to solve a few of the problems: better ventilation to keep air pockets from forming in the mold; using a custom formulated grade of material with smaller glass fibers to account for the thin walls; making adjustments to mold tools. Unfortunately, these solutions were not enough to fix every issue.

Dynomax began using mold flow analysis software with every new injection mold tool they designed and manufactured. Using this software, they were able to run a mold flow simulation prior to building the mold tool in order to determine the proper size and location of all the vents as well as the ideal location and size for the runner and gate.

Another step Dynomax took to improve their precision micro-molding process was to invest in new technological equipment. They purchased a new Arburg Micro Injection molding unit, and placed the device on an existing Arburg Allrounder 270 A injection molding press. The new unit is an all-electric press that is used for high-precision and accuracy. It operates with an 8mm injection screw, and is designed specifically for micro-molding parts such as the thin-wall components produced at Dynomax. The unit has a precision dosage control that allows injections of the exact volume of material needed to fill the mold tool, and has a continuous material feed to reduce temperature fluctuations throughout the mold. The micro injection molding unit was created with the mentality of first-in-first-out. This means there is less degradation of the material as the temperature changes within the mold, so the finished part will not have any of the common issues such as cracking, short-shots, or weld lines.

Besides the new investments, Dynomax was already using other technologies to mold parts with tight tolerances. One such piece of equipment is an AgieCharmilles EDM machine. These machines are capable of holding tight tolerances up to .0001", and the tooling is designed and built around a shrinkage factor for the molded piece part.

Micro-Molded Product Molded Out of Custom Blend LCP MaterialAnother device being used at Dynomax is a customized vision system that was designed and built around the products the company molds. Certain products are too small for the mold protection on the machine to detect, so the custom vision system is used to supplement the machine’s shortcoming. The vision system ensures whether or not material is missing from the initial shot, or if there is any material remaining in the mold cavity after the mold is removed prior to closing for the next shot. By using this method, Dynomax is able to maintain a high quality standard for their production by decreasing the number of rejected parts being made.

Over the last few years, Dynomax has been investing in automation, including 6-axis Fanuc robots to extract product from the machines. Injection molding of thin wall silicone products does not allow the use of knock out pins or any other standard method of extraction because of the possibility of damaging the finished part. Using robots to remove these parts from the mold guarantees consistent and reliable withdrawal of the parts, maintaining a high level of quality.

As a result of the strides Dynomax has taken to increase its capabilities in thin-wall micro-molding, they were able to eliminate the cracking, short shots, and weld lines which were formerly a big issue, and are now able to produce 100% good parts. Because of the non-existent scrap rate, Dynomax has incurred huge time and money savings from the increased rate of production, and the minimized loss of raw material and damage to mold tools. ME


This article was first published in the May 2012 edition of Manufacturing Engineering magazine.  Click here for PDF

Published Date : 5/1/2012

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