November Tip - Minimize material to maximize options

The accuracy of the rapid injection molding process is limited by our standard machining tolerances of 0.003" plus an additional tolerance for the molding process based on the resin you've selected (see table).

Because these combined dimensional tolerances are highly dependent on the part design and resin selected, Protomold cannot guarantee that a specific tolerance will be met. Conventional injection molders address this through the use of iterative "steel safe" mold-making techniques. But with the automated, fast-turnaround rapid injection molding process, we use the geometry specified in your 3D CAD model, incorporate a published shrink factor for the resin you've chosen and output CNC toolpaths to make the mold components.

So if you have features on your part that require tighter tolerances than our standard process can accommodate, consider a planned mold modification aimed at improving the accuracy of those features?. essentially a "simulation" of the conventional "steel-safe" approach.

The way to do this is to design your plastic features in the "minimum material condition" - because it is much easier to remove aluminum than add it (removing aluminum on the mold adds plastic on the part). As an example, consider the situation where the diameter of a through-hole is critical to the functionality of a design. As illustrated in the figure, it is better to initially design the hole in the part (and therefore the aluminum core in the mold) too large and then adjust to fit after some sample parts can be checked.

Because this type of mold modification and a subsequent run of new sample parts can typically be done for under $1000, by planning an iteration you might have a very cost effective way to get the greatest possible accuracy out of your rapid injection molded parts.

As always, you can visit the Protomold Design Guide for helpful Rapid Injection Molding design information.

November Designer Survey : Which 3D CAD software do you currently use? We asked this question about a year ago and thought it might be interesting to see if things have changed much since then. Please let us know and in the December Design Tip we will compare the results. Please suggest any ideas you may have for future survey questions. Just e-mail them to us at marketing@protomold.com.

What 3D CAD software do you use? AutoCAD Inventor AutoCAD Mechanical Desktop Pro/E SDRC Solid Edge SolidWorks Unigraphics Other None - 2D Only

October Designer Survey Results:

We asked "Who will get your vote for President?" The responses of the approximately 500 people who took part in this highly popular yet somewhat controversial poll are illustrated in the pie chart.