Moldbase Design Made Easy
-by Jim Buchanan

Designing a moldbase may not be as glamorous as coming up with a hood scoop for the next-generation Ferrari, but it's a critical first step in manufacturing injection-molded plastic products, which include everything from cell phones and toy cars to entire dashboards for real cars.

Today, plastics manufacturers are subject to ever-increasing demand for greater variety and faster time to market. Manufacturers have to scramble to produce the next new product, and that means the companies making their molds and moldbases must scramble as well.

An extra challenge. For many of today's moldbase designers, there's an extra challenge. Over the years, the delivery of moldbase-design information has evolved from drawings produced by draftsmen to drawings produced by 2D CAD systems. For some manufacturing shops, the evolution ended there, as moldbase creation just a few years ago was largely two dimensional in nature and consisted of stacking metal plates on top of one another to build up the moldbase.

But today, thanks to the ever-more-sophisticated curves and surfaces in plastic products, the essential task of designing the core cavities of the moldbase is now better served by 3D modeling. Some CAD designers might argue that the entire moldbase-design process is better served by 3D, in fact, but many manufacturers still prefer to work by 2D drawings. So today's moldbase designers frequently find themselves starting with a 3D model, then exporting their data into a 2D representation, and going from there.

This is where Pro/ENGINEER Expert Moldbase Extension (EMX) can make a big difference. Recently upgraded with some time-saving user-interface features, Pro/ENGINEER EMX builds a fully associative 2D representation that resides onscreen, next to the 3D model of the under-design moldbase. A moldbase wizard helps you along the design path and collects details that stays with the design - regardless of whether the finished deliverable is a 3D model or 2D drawing - helping produce the bill of materials, hole charts, and other relevant documentation.

Plates, patterns, and placements. Moldbase design starts with loading the assembly model from Pro/ENGINEER, selecting and dimensioning the plates that will build up the moldbase, then setting up component definitions and other basic parameters. The Pro/ENGINEER EMX wizard will guide you in selecting the plates, whether they come from a pre-existing design or from one of the many commercial plate libraries. The new user interface simplifies the process of renaming and re-dimensioning the plates.

Once you have used the assembly model information to design the core cavity and begun stacking plates in your 3D model, you can then place basic components - screws, bushings, bolts, locking rings, ejector pins - as well as the slider and lifter subassemblies. Here is where Pro/ENGINEER EMX delivers significant advantages over conventional moldbase-design methods.

Reducing tedium. There are several challenges in placing components and subassemblies. For basic components, tedium is the enemy. In the course of your design, you may have to place hundreds of screws, for example, and with each screw you - or the manufacturing engineer down the line - will have to impart the cutout locations and depths of the screw holes, as well as any counterbores or waterline information that might be related to that cutout. The same goes for every other basic component. The risk of not paying enough attention to detail can be great - a screw could rupture a waterline, for instance, once the moldbase is prototyped, causing a re-design and loss of time.

Pro/ENGINEER EMX reduces tedium by automatically adding all relevant detail automatically, based on your initial parts definitions. The wizard "senses" when you're placing components in a particular pattern, and asks if you want to place all screws or other components the same way.

The importance of interference checking. Moldbase design has the potential for component interference. An errant component placement might puncture a waterline, as mentioned above, for instance, or it might jam while the moldbase is opening. In either case, the consequence can be a loss in time, a complete redesign or re-build of the prototype, and cost overrun.

As you build your moldbase with Pro/ENGINEER EMX, you can move between the 2D representation - if you want to work in 2D - and the 3D model, with each updating the other as you go. At any point, the 3D model will let you check for any and all interference problems. Interference can come from something as simple as a misplaced screw or ejector pin, to something as complicated as a slider, lifter, or latch lock that fails to do its job of opening or closing the moldbase.

Pro/ENGINEER EMX checks these and others, and even calls Pro/ENGINEER mechanism animation into play to animate the processes of opening and closing the moldbase.

Keep it simple. "Pro/ENGINEER EMX manages to combine a high degree of control flexibility with simplicity of operation, thanks in part to the new user interface of EMX 5.0," says Francois Lamy, director of product management at PTC.

For instance, Pro/ENGINEER EMX can deliver its output in any number of forms - 3D or 2D information goes to the manufacturer, along with documentation, bills of materials, and hole charts that you can customize.

"You can change the design," says Lamy. "You can add your company logo if you're sending it to your customer for manufacturing; you can change part names or part numbers; you can decide to use Microsoft Excel as the format for your hole charts. And each of these steps, plus all the other steps in building the moldbase, typically takes no more than three to six mouse clicks."