A Gem of a Machine

CNC machine shrinks production of molds for display cases from three days to six and a half hours while improving accuracy.

Engineered Plastic Designs Inc. cuts highly accurate molds for earring display cases in just six and a half hours on a CNC machine, 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 machine 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 machine makes more accurate and repeatable cuts than are possible by hand, the consistency of the product also has improved.

Located in North York, Ontario, Engineered Plastic Designs specializes in the design and manufacture of plastic point-of-purchase displays. 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 and vitamins. In addition to base cabinets called showbeds, Engineered Plastics Design makes a variety of rotating counter-top display units that hold products such as earrings and watches.

Two Types of Plastic Parts

Engineered Plastic Designs 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 counter-top units, require vacuum-formed inserts to hold jewelry. Due to the 3-D nature of their shape, these pieces are not cut on the turning center, but are 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 is typically mounted on a 1.5-inch by 2.5-inch 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. This type of mold can be 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, NY), 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 machine they selected include a working area for the router five feet by eight feet, 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 machine included the CAD/CAM program, which is where the new mold design process begins. Originally designed for metalworking, this CAM program also is 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 feedrates 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 machine, the operator hits the "start" button and the mold is then carved automatically. This machine 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 machine 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 machine 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 machine translates into less time consumed in the molding area. Molds are produced with fewer errors - which has become a cost saving factor.

Engineered Plastic Designs has been very happy with the reliability of the Techno machine. With just routine maintenance, it functions effortlessly. Part of its reliability is due to the materials used in its construction. For example, the machine 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 machine is constructed on steel stress relieved bases with hardened steel linear ways, and ballscrews with servo motors 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 machine 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 those in the acrylic display industry become more innovative in creating displays - requiring today's technology to meet those challenges.

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