CNC Router Economically Produces Point-Of-Purchase Display Prototypes

A computer numerical control (CNC) router provides a very economical method of producing prototypes of counter display units. The displays are injection molded with molds that cost from $50,000 to $100,000 so prototypes must be built first to verify each design. The physical prototype is used to validate critical aspects of the geometry and obtain customer approval on the design geometry. Machining centers are used to build many of the prototypes, especially those with 3D contours. On the other hand, the CNC router, which costs much less than a machining center, very efficiently produces prototypes that require only 2 ½ D machining. The router is also used to machine fixtures used to build wire display components.

Alliance Display and Packaging is a leading producer of point-of purchase displays, particularly PDQ units used to display cosmetics in department stores. These counter-top display units are typically 30 inches wide, 15 inches deep, and up to 4 inches high. The display units are injection molded from styrene or polycarbonate. The injection molding process requires the construction of a large and complex mold prior to producing even a single piece. "If we were to build a mold to create prototypes, and we discovered a mistake in the design or the customer wanted to make a change, there would be a good chance that we would have to throw away the mold," said Mitch Nelson, Mold Shop Manager for Alliance Display.

Need for a physical prototype
While the latest computer modeling tools provide a very realistic view of a proposed design, there are often very important aspects of the design that go beyond visual appearance. One reason is that rendering software alone is unable to perfectly represent the way that an object appears under certain lighting conditions, certain angles or any combination of those two. The computer comes close, but close isn't good enough when you are about to make a decision to invest money to bring a new product to market.

The simple fact is, that nothing beats the reality of a three-dimensional model sitting in front of you. With a 3-D model you can see, touch and feel the subtle changes in a curve or line, or the way a door handle transitions into the door panel. You can walk around and look from any angle at the way the light reflects off a given surface. This holds true for any product whose appearance is very critical, not just point of purchase displays. Even the Art Center College of Design in Pasadena advocates the use of physical models for critical aesthetic decisions.

Building a prototype also forces the designer to resolve issues that would be too easy to gloss over in a computer model. There are hundreds of issues that usually don't begin to get addressed until the first prototype is built. Just exactly how do pieces fit together? Does it work the way it is intended to? How does the user hold the product? Exactly how will it be used? How does it fit in with other products that it is to be used with? Does it have the right feel? How does it look in the environment in which it will actually be used? How do the products potential purchasers react to it? You aren't likely to get an answer to any of these questions or many others until the first prototype is built.

Machining center provides costly approach
Alliance Display uses machining centers to produce prototypes out of styrene or acrylic sheet. The machining center is required for making prototypes whose geometry is very complex. "About a decade ago the company purchased a CNC router designed for machining plastic and wood for about $20,000," Nelson said. "This machine cost much less than either a machining center or a stereolithography machine but performed just as well in machining plastic prototypes. But over time, the software became outdated. We stopped using the machine."

Upgrading a CNC router provides solution
Recently, Nelson wondered whether it would be possible to upgrade the machine, which had performed very well. He contacted its manufacturer, Techno-Isel, New Hyde Park, New York, and discovered that the machine could be retrofitted to the latest LC series model electronics for a minimal cost. The retrofitting process included changing the axis motors from stepper to servo motors, a new control system, vacuum table, and new software. This new retrofit not only brought the machine up to current technology, but the machine ran faster and smoother then ever before. A closed loop servo control system provides constant position feedback, higher power, and smooth continuous motion that eliminates the possibility of losing position in the middle of a part. A big plus was the new Windows based GCODE interface. The interface was extremely easy for the operators to learn to use.

Nelson had also considered purchasing a new machine such as Techno's LC Series which is constructed on a heavy steel ground stress relieved base, and includes a heavy duty aluminum T-slot table and ball screws on all three axes with closed loop servo controls. Because the frame is a single welded piece, there is no chance for it to get out of square or require alignment. The machine comes fully assembled and includes Techno's Windows-based CNC G-code interface with free lifetime software upgrades.

The machine is available in five sizes, with work envelopes of 30 by 24 inches, 50 by 48 inches, 50 by 96 inches, 59 by 120, and 78 by 120. Each of these models provides a repeatability of 0.001 inches, a resolution of 0.0002 inches and a maximum speed of 250 inches per minutes. A wide range of optional equipment is offered including a laser scanning module, variety of spindle options, vacuum pumps, and fourth axis rotary table to name a few. This entire series of machine are very reasonably priced, for example the 4-foot by 8-foot model sells for $16,995 new. "Based on the advice from Techno stating that my machines mechanics were in perfect condition, I made the decision to simply upgrade the controls, and put off the purchase for a new Techno router until I require a larger work area," Nelson said. "Thanks to Techno my upgrade was simple, quick, and most importantly cost effective."

The new prototyping process
Alliance Display uses Strata 3D rendering software to produce their initial design concepts. The renderings produced with this software are shown to customers for approval. When the customer approves the rendering, the company then moves into the engineering stage and produces a solid model of the design using SolidWorks computer aided design software. The solid model is then moved into the Mastercam CNC programming environment where Nelson generates the toolpaths needed to produce the part on the router.

The operator simply mounts a sheet of styrene or acrylic on the vacuum table, calls up the appropriate program, and hits the start button. He then walks away while the router produces the parts. It takes between one hour and 30 hours to produce the display on the router. The finished pieces are then decorated with paint and pressure sensitive labels. The longer times are for complicated displays that might consist of as many as 50 components. The physical model provides a truer picture of the appearance of the display and also gives engineers a chance to resolve details that are difficult to verify on the computer such as snap features and interlocking. When engineering and the customer have signed off on the prototype, then Alliance Display can confidently begin producing the injection mold, working with the same geometry that was used to produce the prototype.

"The low cost of the CNC router means that we can produce prototypes very efficiently at Alliance Display," Nelson concluded. The retrofit has breathed new life into a 10-year-old machine at a very low cost. The machine has proven to be very reliable and easy to use. In approximately one year of operation since it was retrofitted the machine has performed without any problems. People that have never seen the machine before are able to operate it at full efficiency within an hour or two. The result is that we can provide our customers with beautiful prototypes at a low cost."

SOURCE: Techno-Isel