3-D solid modeling puts thermoforming tools in the fast lane.

Molds for custom thermoformed packaging can be made at least 50% faster, with higher quality and lower manufacturing costs, says Computer Designs Inc., a moldmaker in Whitehall, Pa. The company's secret is using 3-D solid-modeling CAD software, which is also having a big impact on injection moldmakers (see PT, Aug. '99, p. 48). Computer Designs, which may be the first thermoforming tool builder to adopt this technology, says its lead times now average three to four weeks instead of eight to 10 weeks for molds made with traditional 2-D wire-frame packages. "In special cases, we can have a mold ready to ship in one week," says engineering manager Paul Treible.

Shorter development time reduces overall engineering costs and helps customers get products to market quicker, he notes. In fact, 3-D software allows Computer Designs to build tooling from a preliminary design of the part to be packaged, such as a hand tool or medical device. Thus, the mold for the packaging can be ready even before there is tooling for the actual part. Designing and engineering molds faster has enabled Computer Designs to greatly expand its workload. "We are doing at least 100% more work now due to the use of solid modeling," says company president Scott McKeever.

Fast and flexible

Computer Designs selected a CAD solid-modeling package from Unigraphics Solutions Inc., Maryland Heights, Mo. It runs under both Unix and Windows NT. Unigraphics was chosen because it has design capabilities that other 3-D packages lack, says McKeever. "Evaluations of competitive products showed that they were unable to replicate the complicated radii and blends that are common in thermoforming molds. As a result, the molds produced with competitive CAD programs required considerable amounts of expensive hand finishing," says McKeever. The cost of the solid-modeling software ranges from $6000 to $20,000.

Here's how 3-D solid modeling has changed Computer Designs' procedures. With 2-D wire frame, mold-design work starts when a prototype of the package is received. Engineers develop drawings of the mold from the prototype and then cut a wax prototype of the mold. The wax prototype is used to produce a machined aluminum mold. Other thermoformers often turn the original product prototype and drawings over to woodworkers who produce a pattern. The pattern goes to an aluminum foundry for casting the production mold.

The wire-frame rendering of the mold makes it hard to see what the mold looks like since points along the mold are not connected. A revision means having to individually regenerate every boundary and point. Solid modeling can quickly and easily deal with the engineering changes that are inevitable at this early stage of the process. With 3-D solid modeling, so-called associativity of features in the model means that changes are automatically propagated throughout the design by the software's built-in intelligence. Unlike a 2-D wire frame, the solid model can be sectioned into individual pieces for tasks such as configuring paths for cooling lines or vacuum channels.

With Unigraphics, Computer Designs can design the entire mold in the CAD system, dispensing with the wax pattern. The company can start work using an e-mailed CAD file of the product even before a physical prototype of the product arrives.

Once a digital solid model is developed and approved, CAM software modules let the engineer generate CNC toolpaths, select mold surfaces, machine conditions, and type of cutting tool. The machined mold may vary no more than 0.001 in. from the digital model.