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Replacing tracer machining with scanning and digitizing at 1,000 points per second improves mold quality, eliminates patternmaking to reduce pre-machining time, and permits tool path generation through CAM to cut machining time by 40 percent.
According to Mike Stiles, VP of manufacturing engineering for Creative Blow Mold Tooling, Inc., some of the company's biggest moldmaking bottlenecks used to come from bottles themselves.
Based in Lee's Summit, Missouri, Creative makes blow molds for cosmetic, juice and water bottles as well as for handleware detergent bottles, which are subject to periodic design changes. In lieu of a pattern, however, the detergent bottle customer typically supplies Creative with only a finished bottle to use as a model. If the customer wants to add a new size to an existing bottle series, the most common design change request, then it has Creative adjust 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: measure the bottle manually, use the measurements to generate a CAD drawing, scale the model in CAD to achieve the new volume, then build a pattern from the new model for use on the tracer.
Now, three of those steps have been eliminated. Recently, Creative did away with tracing in favor of digitizing, using the Cyclone dedicated scanning and digitizing system, developed by Renishaw (Schaumburg, Illinois). A "continuous path" scanning station with a 23" x 19" x 15" XYZ envelope, Cyclone digitizes the model by sweeping its analog scanning probe in a series of rapid, narrow-stepover passes, achieving velocities of up to 118 ipm, for data capture rates as high as 1,000 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 and generate efficient NC tool paths.
Creative now digitizes the detergent bottle itself. Instead of building a new pattern, it simply enlarges or reduces the model using Tracecut's automatic scaling command, then has the software generate tool paths to match. According to Mr. Stiles, the switch to Cyclone and Tracecut has not only streamlined the overall process by reducing the need for patternmaking, it has also cut mold machining time, by roughly 40 percent.
Mr. Stiles explains, "With the Cyclone, tool paths don't have to relate in any way to the pattern of digitizing. This is a big improvement over tracing, which produce only tool paths that match the path of the trace."
The tracers often forced Creative to use smaller machining steps to ensure that all of the mold's fine details would be captured, but the `cost' was inefficient and over-precise machining passes for all of the surfaces that were smooth and easy to machine.
Says Mr. Stiles: "Now, we just window the fine details of the scanned model in Tracecut and assign tool paths accordingly, then use Tracecut'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 Cyclone lets us cut each mold to spec in the shortest time possible."
Mr. Stiles reports 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. "However, I was warned by several users that laser digitizers often fail to register shallow draft angles-- common feature of our models."
"In addition, our models sometimes feature undercut surfaces that a laser could never detect. However, contact scanning systems can 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, Mr. Stiles chose continuous contact digitizing, but even in this family some models were inappropriate.
Mr. 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."
According to Mr. Stiles, there have been other process improvements. Where Creative used to make patterns for both mirror-image cavities, it now makes only one pattern and uses Tracecut's mirroring function to generate tool paths for the other half. This not only reduces pattern-making cost, says Mr. Stiles, it also reduces bench work by ensuring that the two cavities will match to spec right off the machine.
Another part of Creative's business is repair of existing blow molds, most of which have seen long service, and no longer come with written engineering data. To machine repair inserts to match the original mold specs, Creative used to have to make a casting of the mold, then make a female model of the casting to use on the tracer. Now, says Mr. Stiles, Creative simply digitizes the mold prior to repairs, and lets the CAM system "remember" the original dimensions of the part.
In some cases, the Cyclone has allowed Creative to achieve not only increased speed and precision, but also superior metal quality. The best example, says Mr. 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," he says. "Before Cyclone, 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 on the Cyclone, producing precise tool paths which allow the figurine details to be machined to spec without hindering overall machining time, because the fine details appear only in the NC program's finish machining layer.
"Cyclone has let us improve our figurine molds three ways," Mr. Stiles says. "First, they're more accurate. Second, the surface is better, so we've eliminated the time and expense of hand-finishing. But 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.
Now, using the Cyclone scanning station from Renishaw, Creative digitizes the bottles directly, and converts the data into efficient NC tool paths using Renishaw's Tracecut CAM software.