Analyzing plastics with FEA: Part 8

By: 
October 31, 1997


At times, the product development process can provide some unwelcome reality checks. Take a look at the following scenario, for instance, based on the real-life adventures of David Ruscak, principal design engineer for Polaroid's engineering model shop; it may offer a painfully familiar plot:

Step 1 - Polaroid creates a new camera design, consisting of roughly 30 molded parts.

Step 2 - Designers begin to source multiple molders.

Step 3 - Model makers download separate design databases.

Step 4 - Ruscak manually reviews part designs for moldability, performing additional reviews after each engineering change.

Step 5 - Parts suspected of being difficult to fill are sent to FEA analyst for mold filling review.

Step 6 - Results from analyst take several weeks.

Step 7 - Because of time constraints, some parts are not reviewed; in other cases, engineering revisions also bypass review.

Step 8 - Ruscak spends precious time at the production stage debugging parts that have unacceptable weld lines or won't fill.

Mold filling analysis may well be the key to shortening product development times; unfortunately, when designers need a quick yes-or-no answer on moldability, they don't often have the time needed to build a finite-element mesh.


After an initial analysis identified weld lines and air traps in a shutter design, Polaroid made modifications using Part Adviser. Within 30 minutes, the analysis showed Polaroid that the cmplex part would fill correctly and that a change in the tooling would be successful.

Recently, though, no-mesh versions of traditional mold filling analysis packages have appeared on the scene. Working seamlessly with 3-D solid models, the software attempts to quickly give users information such as confidence of fill, location of weld lines, and potential air traps. But does analysis without a user-created mesh really work?

Designers we polled say yes, unanimously, then tell us about a particular project or two that "sold" them on the idea. What follows are two of those success stories.

First, let's get back to Polaroid. Last November, Ruscak incorporated the beta version of a no-mesh analysis package, hoping to reduce the number of steps in the process. "At the time, we were developing the Digital Microscope Camera (DMC)," says Ruscak, "a competitively priced camera for medical and industrial imaging markets, and based on an electronic imaging camera design already in production." One change, a modified shutter design, required Ruscak and company to rework an existing tool. Manufacturing members of the product development team were uncertain about the new design's moldability.

To alleviate concerns, Ruscak put the new software, Part Adviser from Moldflow, to work. "I downloaded the existing gate location data and, using the software, demonstrated how the shutter would fill, as well as the weld line locations. Color hard-copy examples helped to convince everyone that the tool could be modified successfully." As a result, nine months after product conception, the DMC began shipping. Ruscak adds, "Part Adviser allows us to recognize problems we just can't see on a drawing or a 3-D solid model. It's a fantastic communications tool, especially for naysayers."

On reflection, Ruscak and other managers realize that deploying analysis early in the design cycle had a ripple effect throughout the project. As a result, Polaroid has organized a "Barrier Removal Team" to identify factors that hinder getting products to market faster and more affordably. "With the advent of Windows NT replacing Unix workstations, more engineering environments can access an integrated toolkit of solutions," says Ruscak, "For us, that consists of Part Adviser, Pro/E, SolidWorks, and Office 97. With these tools, we can extract the data we need to communicate."

Communication seems to be the rallying cry among designers, especially those working in teams. Ray Douillard, sourcing engineer for Digital Equipment Corp. (Maynard, MA), has found that the ability to evaluate moldability at the concept stage helped shorten time to market.

"I collaborate with early involvement design teams to help determine feasibility," he says. At Digital, Douillard uses Part Adviser to evaluate concept designs. "The team needs to know if a design will be difficult to gate or create flow problems. Often, I find that we need to do something smarter, perhaps make two parts instead of one, to contain cost targets for the project." Other pertinent parameters - optimum resin selection and potential knit lines and air traps - are accounted for via no-mesh analysis. Douillard can then use that information to roughly determine tool cost.

A second major benefit, according to Douillard, occurred when Digital wanted to revamp an older product line by switching to a precolored compound. "We had contracted with compounding companies for precolored ABS. The tools had previously been designed for polystyrene, and all of the molds were in the Far East, making mold trials cost prohibitive." Instead, Douillard used Part Adviser to perform virtual mold trials. The product, a front bezel for Digital's line of Alpha servers, required no modifications to the tool based on analysis results. "More than 20,000 sets are molded per year," he says, "and we haven't missed on one yet." The current plan is to use Part Adviser on every design.

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