CNC Machine Shrinks Labor Time for Foam Samples

Programming and setup takes about 20 minutes, while actual cutting takes only 10 minutes to four hours, depending upon part complexity. The machines operate unattended except for loading the foam stock and removing finished pieces. "It's a huge labor savings because the prototype makers are free to do other work while the machine is in operation," says Bill Brokob, manager of Tuscarora's western regional technical center. Another benefit of the CNC machine is improved accuracy, especially for the complex 3-D shapes that Tuscarora's customers are now requiring.

Product Protection and Beyond

Tuscarora's foam molding group uses a variety of materials such as expanded polystyrene (EPS), expanded polyethylene (EPE), expanded polypropylene (EPP), copolymers such as ARCEL® and R-MER® and hi-heat resins. These raw materials are injected as beads into molds and then heated with steam, which causes them to expand and solidify into the finished shape. The resulting molded foam shapes protect and cushion fragile products better than virtually any other interior packaging or material handling product available today. Molded foam plastics also are cost-effective - resulting in less packaging labor and smaller carton sizes.

In addition to packaging applications, Tuscarora's molded foam plastics are used for products and components with a long service life. For example, foam's unique properties make it an excellent insulation component in building construction, refrigeration and shipping containers. Recently, Tuscarora began to offer an innovative molded foam assembly chassis for electromechanical devices that uses molded EPP foam to replace sheet metal and traditional fasteners.

Working With Complex Parts

As customers create products with more graceful curves, Tuscarora designers must match those shapes in the packaging components that they create. The use of solid modeling has helped them to do this. Many customers now provide CAD models of their products and the engineers then import the models into their CAD system and design the foam packaging components around the customer's geometry.

Most customers request one or more prototypes for testing prior to having the foam parts manufactured. Previously, prototypes were produced by hand - working from drawings, a prototype maker drew lines indicating the general shape of the part on a block of foam, and then used a Bridgeport milling machine to carve out the part. Some fine-tuning was usually required, so he chipped away at the foam with hand tools until it fit the customer's product. This was a slow process, requiring anywhere from one to eight hours, depending upon the complexity of the part. It also was somewhat inaccurate. "We could hold a tolerance of 1/16 inch at best working by hand," says Brokob.

Another limitation of making prototypes by hand became evident as the shape of customers' products became more aesthetic. "It was impossible to follow those curves accurately when we were cutting prototypes by hand," Brokob adds. "If we had two end caps, for instance, one for the right side of a monitor and one for the left, the two sides wouldn't always match."

This problem was complicated by the fact that as the shapes were getting more complex, customers also were raising the bar on the accuracy of the prototypes. "Some of our more high-tech customers have started to demand highly accurate prototypes," Brokob says. "If they want five samples for testing and verification, they want them to be virtually indistinguishable from each other. Hand samples are all different."

Finding the Right Machine

This machine was designed for production routing and drilling on a wide variety of materials including wood, plastic, MDF, solid surfacing materials and nonferrous metals. Its $25,000 price was affordable and its 0.003 inches/foot absolute accuracy and 0.0005-inch resolution and repeatability met Tuscarora's accuracy requirements. The company selected a Techno system with a 48"x 40" table size and a Z-axis height extension of 19⁷/₈ inches.

Implementing the Process

Tuscarora set up its CAM program so that it's "almost just the push of a button," as Brokob says, to generate toolpaths. Once this is done, the CAM file is exported into the ICAM post processor that creates the actual code, which drives the Techno machine. Total programming time, from when the Pro/ENGINEER model is imported into the CAM program until the machine code is complete, ranges from 10 to 15 minutes.

Another five minutes are needed to cut the foam stock to the right size and attach it to the Techno machine. The operator then hits the start button and the sample is automatically carved. It only takes 10 minutes per side to cut simpler pieces, while more complex pieces may take up to four hours per side.

One key advantage of using the CNC machine is the freedom it gives prototype makers to do other work. The machine does not require any supervision, except to remove the finished piece and attach a new foam block to repeat the process. "It's a significant labor savings," says Brokob. "Instead of spending one to eight hours cutting foam by hand, we just attend to the machine as necessary, which takes minutes. We quite often turn on the machine when we leave for the day, and when we come back the next morning, one side of a part is done."

After prototypes have been machined, they are checked against the customer's product. The Techno CNC machine makes this easy. Since parts are cut directly from CAD data, the shape of a prototype matches the shape of the customer's product perfectly, something that was almost impossible to achieve in the past. "The improvement in accuracy is an important part of customer satisfaction," notes Brokob. "It also differentiates us from our competitors who are still working by hand."

Achieving Highly Accurate Prototypes

Tuscarora has been pleased with the reliability of its Techno machines, which is due in part to the materials used in their construction. For example, each machine uses anti-backlash ball screws, which have excellent power transmission due to the rolling ball contact between the nut and screws, and this type of contact ensures low friction, low wear and long life. In addition, the machine is constructed on steel stress-relieved bases with hardened steel linear ways and ballscrews with standard servomotors. The shaft-and-bearing system produces very smooth, play-free motion and is an extremely rigid system that produces high-quality cuts.

Using CNC machines to manufacture foam prototypes has paid off for Tuscarora in a number of ways including more efficient use of labor, more accurate samples, better satisfied customers and a competitive advantage. "It has become more and more important that we supply highly accurate prototypes," says Brokob. "With the Techno machines, we can fulfill this requirement in a cost-effective manner."