Demo Mold Teaching and Marketing Tool

You are looking at a demonstration mold containing a sample part from Proto Labs, Inc., a quick-turn manufacturing services provider in Maple Plain, Minnesota.

To make mold dissection easy they color-coded that various parts of the mold. Green for the cavity or A-side, blue for the core or B-side, gray for the side-action, yellow for the part and white for the ejector system. All the components are made from natural ABS with additive colorant. The mold came with a brochure taking you through your dissection in six steps, giving a visual feel for how it all works—the runner, sprue, edge gate, where the resin enters the mold cavity, the drafted sliding shutoffs,side-action and undercuts. I think this demo mold is a great teaching tool (and show-and-tell item) for any elementary schools.

If Proto Labs goes this far to put something in the hands of a potential customer then I wondered what kind of information they provide online. I was not disappointed. The company provides a variety of design guidelines and tips, white papers, case studies, design aids, a blog, and FAQs.

For example, for injection molding, there are some common troublemakers during part design: clips and snap fits, living hinges, bosses and stand offs, text on parts and overmolding. This list just happens to correspond with some of the more engaging features you can incorporate into your part designs, which is one reason why it’s so important to master them. Another is that, depending on your application, these features often provide more functional and aesthetic parts while reducing production costs. Here are some tips and techniques to help you do just that.

Living hinges, those thin areas in a plastic part along which the part can fold, are efficient ways to keep two halves of a molded container together. If properly designed, they can open and close thousands of times without ever losing strength or flexibility. The biggest consideration here is material. Where polycarbonate might make a good clip, it definitely won’t survive the thousands or millions of cycles expected of a living hinge. Shoot for polypropylene instead.

Breakaway tabs are similar to a living hinge. If you’ve ever peeled away the plastic cap on a refilled propane bottle or ice cream container, you know how they work. Whether tab or hinge though, some design accommodations must be made. The section should be thin enough to flex but thick enough to survive repeated bending. Depending on the expected range of motion, you might need a radius or groove at the midpoint of the hinge to allow it to fold over on itself. And because you’re attempting to mold two mating halves simultaneously and the material flow will likely be thick-to-thin-to-thick, flash and fill problems might occur. Be sure to pay close attention to the design for manufacturability (DFM) analysis you receive with your quote.

For the other four design tips, click here.