Liberty Displays Inc.

CNC Router Shrinks Production of Molds for Display Cases
from Three Days to Six and a Half Hours While Improving
Accuracy

Liberty Displays Inc., cuts highly accurate molds for earring display cases in just six and a half hours on a CNC router, compared to the three days needed previously to cut them by hand. The mold shape is programmed in CAM software, which then generates the cutter toolpath. Once the programming is done, the CNC router automatically carves out the desired shape much faster than a person can cut it using hand tools, saving more than two days of work on this typical item. Also, because the CNC router makes more accurate and repeatable cuts than are possible by hand, the consistency of the product has also improved.

Located in North York, Ontario, Canada, Liberty Displays Inc. specializes in the design and manufacture of plastic point-of-purchase displays (POP). The company's displays can be found in stores such as Sears and Wal-Mart and are used to display a wide range of products–everything from jewelry, to cleaning products, to vitamins. In addition to base cabinets called showbeds, Liberty Displays Inc. makes a variety of rotating countertop display units that hold products such as earrings and watches. You can visit their Web site at www.libertydisplays.com.

Two types of plastic parts
Liberty Displays Inc. cuts the large, flat components of its plastic displays, such as the side, top, and bottom panels, on a Record 120 vertical turning center with a flat bed. Some display cases, such as rotating countertop units, require vacuum-formed inserts to hold jewelry. Due to the 3D nature of their shape, these pieces are not cut on the turning center but molded out of styrene or acrylic. An earring display case provides a good example of the type of piece that must be molded. A pair of earrings are typically mounted on a 1.5" x 2.5" plastic card. The card has a tab at the top, which is used as a pull tab. The case is laid out with six, nine, or 12 cavities and each cavity has a groove in the top that matches the tab on the earring card. The component of the display case that contains the grooves is the piece that must be molded.

Previously, the molds for these more complex pieces were carved by hand out of wood or aluminum using jigsaws and chisels. The mold was produced by assembling numerous smaller wood or aluminum pieces to form the complex shape. Then styrene or acrylic is heated to soften and then vacuum-formed to form the mold. The materials are not heated very high, which is why the molds can be made of wood. There were two problems with making the molds by hand, however. One was the time it required. Producing a typical mold for an earring display case took one person eight hours. Usually, three molds were needed for the entire case, so the company spent a minimum of a day and a half on this task. The second problem was that there was no consistency in the size of the grooves from mold to mold. As a result, some earring cards would fit snugly into the display case and some would be loose.

In an effort to solve this problem, company management decided to look into automating mold production using CAM software and a CNC router. They did not want the expense of another large CNC machining center; however, they wished to remain competitive with the latest technology. After receiving a catalog from Techno Isel, New Hyde Park, New York, they realized that a Techno CNC router was an excellent solution in meeting their objectives. Its affordable price was well below that of a large machining center, yet the machine could handle production routing and drilling on a wide variety of materials including wood, plastic, MDF, solid surfacing materials, and nonferrous metals. The technical specifications of the Techno router they selected include a working area for the router 5 feet by 8 feet, and Z-axis height of 12 inches, and a raised gantry for large part clearance. They wanted such a large working area so they could cut multiple molds at once.

New mold production process
The price of the Techno router included the CAD/CAM program, which is where the new mold design process begins. Originally designed for metalworking, this CAM program is also well-suited for plastics because of its ability to generate the most complex contours with little programming effort. When the company gets an order for a new case that requires molded parts, the shapes are first modeled in the CAM software. Then the programmer/designer gives the command and the software creates the toolpaths for cutting the mold. The only additional input required is information such as feed rates and cutting speeds. Total programming time, including modeling the mold and generating the toolpaths is approximately 30 minutes for the grooved pieces in an earring display.

After a piece of wood is fastened to the Techno router, the operator hits the "start" button and the mold is then carved automatically. This router cuts a mold required for an earring display case in two hours. Frequently, the three molds are programmed and cut together at the same time for a total production time of four and a half hours: 30 minutes for programming and four hours for cutting. Once the router is set up, it can operate unattended. So a process that formerly took three days now requires only 30 minutes of an employee's time. Another benefit of using the Techno router is that when the company needs to increase mold production, they can do so without adding more people. They can simply load the machine with multiple molds and let it cut unattended.

To manufacturers, the improved precision from the Techno router translates into less time consumed in molding area. Molds are produced with fewer errors that have become a cost-saving factor. Liberty Display Inc. has been very happy with the reliability of the Techno router. With just routine maintenance, it functions effortlessly. Part of its reliability is due to the materials used in its construction. For example, the router uses anti-backlash ball screws. These screws 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. The ball screws also make it possible to produce parts to the machine resolution of 0.0005 inch. In addition, the router is constructed on steel stress-relieved bases with hardened steel linear ways, and ball screws with servomotors standard, which offer the best precision performance, speed capacity, and machine longevity. This shaft and bearing system produces very smooth, play-free motion and is an extremely rigid system that produces high-quality cuts.

For Engineered Plastic Designs, the Techno CNC router has made it possible to automate a previously time-consuming task and free up employees for other work. It has also ensured a greater ease for consistency as they (those) in the acrylic display industry become more innovative in creating displays, which require today's technology to meet those challenges.