Digitized Scans Deflate Blow Mold Production Time

Creative Blow Mold Tooling's plant in Lee's Summit, MO, makes blow molds for plastic cosmetic, juice, water, and detergent bottles. Typically, a detergent bottle customer supplies Creative with only a finished bottle to use as a model. If the customer wanted to add a new size to an existing bottle series -- the most common design change request -- Creative adjusted the proportions of an existing bottle to achieve the desired volume.

When Creative's machine tools were driven by hydraulic tracing equipment, a request like this would set off a time-consuming four-step process. First, the bottle would be measured manually, the measurements would be used to generate a CAD drawing, the model would be scaled in CAD to achieve the new volume, then a pattern was built from the new model for use on the tracer.

This process led Mike Stiles, Creative's Vice President of manufacturing engineering, to think that some of the company's biggest mold-making bottlenecks were the bottles themselves.

Now, three of those steps have been eliminated. Recently, Creative replaced the tracing process with digitizing -- using the Cyclone dedicated scanning and digitizing system, developed by Renishaw.

The Cyclone is a 'continuous path' scanning station with a 23 x 19 x 15 inch XYZ envelope. It digitizes the model by sweeping its analog scanning probe in a series of rapid, narrow, step-over passes at velocities of up to 118 inches per minute. Data capture rates are as high as 1000 points per second.

Captured data can be exported to most CAM systems, including the Renishaw Tracecut CAM system used by Creative. Users can alter the model in the PC, and generate efficient NC toolpaths.

Instead of building a new pattern, Creative simply enlarges or reduces the model using Tracecut's automatic scaling command, then has the software generate toolpaths to match. According to Stiles, the switch to Cyclone and Tracecut not only streamlined the overall process by reducing the need for pattern-making, it has also cut mold machining time -- by roughly 40 percent.

Stiles explained, "With the scanning system, toolpaths don't have to relate in any way to the pattern of digitizing. This is a big improvement over tracing, which produces toolpaths that only match the path of the trace."

The tracers often forced Creative to use smaller machining steps than necessary for most of a pattern's surface. This ensured that all the mold's fine details would be captured, but the 'cost' was inefficient and over-precise machining passes for all the surfaces that were smooth and easy to machine.

Says Stiles, "Now, we just window the fine details of the scanned model in Tracecut and assign toolpaths accordingly. Then, we use system's automatic roughing function to have the machining program smooth over precision features until it reaches a depth close to the finished surface of the cavity. By making it easy to tailor the machining process to the individual part, digitizing on the scanner lets us cut each mold to spec in the shortest time possible."

Stiles described exploring a variety of alternatives in his search for a company-wide digitizing system.

"My first impulse was toward laser digitizing, and I took a hard look at these systems," he says. "But, I was warned by several users that laser digitizers often fail to register shallow draft angles -- a common feature of our models.

"Also, our models sometimes feature undercut surfaces that a laser could never detect. Contact scanning systems detect these surfaces by using a large ball stylus in much the same way that a ball end mill would be used to machine the same surface."

For these reasons, Stiles chose continuous contact digitizing -- but even in this family some models were inappropriate.

Stiles says, "We needed to be able to digitize plastic bottles directly, but most of the direct-contact digitizers we considered had stylus pressure so high that it would deform the bottle, making the data model useless. Only the Cyclone gave us the 'light touch' necessary to let a bottle hold its shape."

More Uses, More Places

The process improvements Creative achieved are not limited to detergent bottle molds. Others include:

Over the past three years, Creative has grown at a rapid pace in an attempt to become a major supplier of molds to the extrusion blow molding industry. The company has become more of a local supplier to the national molding operations that operate in multiple locations across the country. By strategically locating plants throughout the United States, Creative has been able to bring its services closer to its customers. The company targeted geographic locations that it felt were ignored by other mold builders when it came to the day-to-day service that a molding plant can require for efficient operation.

Creative has five plants with a total of forty-six employees and 24,630 square feet of facility space. Each facility is capable of new mold manufacture, as well as the modification, maintenance, and repair of existing molds. Besides the Lee's Summit, Missouri plant, Creative's other plants are located in Brea, CA; Grand Prairie, TX; Lithia Springs, GA; and Lakeland, FL.

Technologically, the company has tried to stay on the cutting edge. All five plants have virtually identical CNC capabilities, except for some additional features available at the Missouri facility. These features would be machines with greater size capacities and full 4-axis milling capability, along with conventional EDM for those applications that require sharp, difficult-to-machine shapes.

Now a standard part of Creative's mold development process, the single scanning system in Missouri performs the digitizing for all five facilities. Machining programs are transmitted to remote CNCs via modem. Also, all engineering functions, from product design through CNC programming, are completed at the Missouri plant and then electronically transferred to the point of manufacture, ensuring consistency across the operation.

The company can build molds simultaneously at separate plant locations, and ensure that they will be identical in quality and performance. Also, having multiple plants enables Creative to produce components over fewer calendar days and then bring those pieces together at the plant closest to the customer's molding facility for final assembly and completion of the mold.

Mold Quality Gains Three Ways

In some cases, the scanning system has helped Creative achieve not only increased speed and precision, but also, superior metal quality. "The best example," says Stiles, "is a series of figurine-shaped container molds that have been a steady source of Creative's business for several years.

"Because the detail is so fine, there's no way to efficiently machine these molds using tracers," Stiles says. "Before the scanning system, our only choice was to cast these molds, then laboriously hand finish them to achieve the required surface finish."

Now, instead of casting the molds, Creative digitizes the patterns, producing precise toolpaths that allow the figurine details to be machined without hindering overall machining time.

"The scanning system has let us improve our figurine molds three ways," Stiles says. "First, they're more accurate. Second, the surface is better, so we've eliminated the time and expense of hand-finishing. And third, we no longer have to give our customer cast aluminum molds. Instead, we're now using heat-treated aluminum, and achieving far higher mold quality than we ever could before."

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