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January 1, 2001

5 Min Read
Are you ready for online design?  Part 2: Filling a need via the Internet

When does it make sense to perform an online moldfilling simulation?  A medical custom molder found its answer when sinks that appeared on a molded part couldn't be fixed by processing changes.

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1. Designers log on to Moldflow’s Plasticszone.com . . .

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2. . . . and select the Simulation Zone. Simulation answers the following questions:

  • Will my design fill? 

  • Where are the weldlines and air traps?            

  • Which material is best?            

  • What is the best gate location?            

  • How should I size geometry for optimal manufacturability?

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3.  Users run the iMPA client on a local computer. They open a CAD solid model (in STL format) and iMPA performs a model suitability check that creates a model-specific digital fingerprint.

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4.  Users again connect to Plasticszone.com to activate the model. The system uploads the digital fingerprint and the user pays for an activation key, which is downloaded to the user’s computer. The current fee is $349.

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5.  Users can run as many iMPA analyses as required on this model. The one-time fee offers unlimited filling, gate location, and process window optimization analyses. Designers can also make unlimited changes to gates (location and number), material type, and process conditions. Only geometry changes require a new activation key.

It was the type of situation custom molders dread: An older mold, built before moldfilling simulation was available, began to produce parts with sink marks in a critical, but not visible, location on the inside diameter of a molded hole. The part itself was insert molded from polyetherimide (Ultem).

Resistance Technology Inc.’s (RTI) Medical Infusion Group (Vadnais Heights, MN) went to work to correct the problem in three ways. To get good parts out quickly, operators removed the core pin, molded parts, and subsequently machined the smooth hole in a secondary operation. Simultaneously, technicians ran processing trials to determine the cause of the sink marks. Later, gate size was enlarged in an attempt to get better filling, and parting line venting was added to eliminate trapped air.

Seeking Answers
Project engineer Melissa Gardner explains, “None of the fixes solved the problem. At volumes of 100,000 per year, machining the holes was not considered a long-term solution. I decided to run a moldfilling simulation using Plasticszone.com’s iMPA product. It was one of the first projects where I used this service.” Previously, Gardner had contracted with other vendors for moldfilling analysis. Rather than purchasing the MPA (Moldflow Plastics Adviser) software outright, Gardner went to the website and paid a one-time fee to perform unlimited simulations on a single CAD model.

Pay-as-you-go software offered by vendors known as application service providers (ASPs) is becoming more popular among designers. Without investing in the software, users can take advantage of its benefits for a nominal fee. Services such as model healing and translation are also offered online by ASPs.

When Gardner ran the iMPA simulation using material properties from the software’s database, the program came back with warnings that the part would have sinks where they had appeared on the actual part. “This gave us a great deal of confidence in the results because the software duplicated what we saw in reality,” she says.

Gating Changes
In addition, the software predicted quality to be poor, and identified gate location as the problem. “We were gating into a thin section,” recalls Gardner. While the nominal wall thickness of the part is .070 to .075 inch, the plastic had to flow through thin sections, or baffles, of .050 to .060 inch to get to an area of the part that required good packing.

“With this software,” she adds, “you can ask for an ideal gate location. We did, but the suggested location wasn’t a practical one. Through more iterations on different gate locations, we found one that would be practical and that also checked out via filling simulation.” Engineers then redesigned the tool and had it rebuilt.

“People were skeptical of building a new tool based solely on the simulation results, so we modified the one we had and it produced sink-free parts from the first shot.” RTI is now in the process of building a new tool based on the redesign.

According to Gardner, it makes more sense to run moldfilling simulations on a pay-per-use basis for now at RTI. “Because the analysis is fairly reasonable over the Internet, we are planning to perform it for most of our new tooling, perhaps 20 to 30 per year. My expectation is that as the engineering and management departments at RTI see how valuable this tool is, they will be more anxious to invest in the software itself.” She adds, “Special projects such as this part may also require filling simulation, but new tooling that is replacement tooling or a very simple part may not."



0101i49a.jpgCompany Stats

   Resistance Technology is not only a custom molder for the medical industry, but it is also a custom manufacturer of high-density, ultraminiature microelectronics (examples of which are shown to the right).  With expertise integrating plastics and electronics, the company provides both design services and manufacturing.  Part of the Medical Infusion Group is dedicated to this captive effort in addition to providing custom molding services.
  Specialties include tight-tolerance insert and reel-to-reel molding, preproduction prototype molding, and automated assembly / subassembly work.
  RTI has expanded into two engineering and manufacturing facilitites totaling 70,000 sq ft.  It operates two clearoom facilities, a Class 10,000 for microelectronic hybrid production, and a Class 100,000 for medical plastic fabrication.  Nearly one-third of RTI's 450 employees are engineers, technicians, toolmakers, and machinists.  In addition to its Minnesota locations, RTI recently opened facilities in Singapore and California.



Editor’s note: Due to proprietary concerns, images of the part described in this article are unavailable.

Contact information
Resistance Technology Inc.
Arden Hills, MN
Roger Falde
Phone: (651) 604-9740
Fax: (651) 490-0612
Web: www.rtiplastics.com

Moldflow Corp.
Wayland, MA
Phone: (508) 358-5848
Fax: (508) 358-5868
Web: www.moldflow.com;
  www.plasticszone.com

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