Moldmaker Finds Expanded Role Beyond Just The "Making"

The moldmaker as a provider of end-product design support may seem like a violation of the natural order, but this company has established precisely that role for itself.

Case Study From: 2/1/1997 Modern Machine Shop

The moldmaker as a provider of end-product design support may seem like a violation of the natural order, but Duplicraft, Inc., has established precisely that role for itself. In its search for ways to add value in the mold making process, the Schaumburg, Illinois company hit on the idea of applying the digitizing technology it purchased for tool path generation to help its customers modify, analyze and refine their designs. "The expanded range of services strengthens our bond with customers," says Duplicraft's Darold Faurot. "Now, our involvement in customer processes begins long before there's a final mold to be machined."

Mr. Faurot says finite element analysis (FEA) explains much of the need on which his company capitalized. Duplicraft makes molds and secondary tooling for extrusion blow molding -- meaning its customers are almost exclusively makers of plastic bottles or similar containers. For these customers, bottle design used to be a hit or miss process that left the strength and functionality of end product indeterminate. Questions related to the behavior of the liquid when poured, the bottle's resistance to impact, and its ability to bear the weight of crates stacked on top of it during shipping, all had to wait until a finished mold produced a finished bottle that could be tested. FEA changed that, says Mr. Faurot. Now, Duplicraft's customers answer most of these questions using only a "virtual" container derived from the CAD model.

There's just one problem: The use of CAD in the container industry is relatively new, and far from universal. What about bottle designs that aren't created in the computerlike hand-made models, or semi-new designs resulting from direct alterations to molds created years ago?

In these cases, says Mr. Faurot, customers now turn to Duplicraft. The company uses high-speed, high-resolution digitizing to measure and map out physical models and cavities, and translate them into digital equivalents that can be evaluated through FEA -- often after modification in CAD. Sometimes, the company even digitizes actual bottles -- allowing it to make proposed changes to the design entirely in the computer, and submit a digital prototype of the new bottle to the customer for evaluation.

"The technology allows us to grow beyond just our metalworking specialty -- a change we see as key to the continued success of the business," he says. "We're not just mold machinists anymore; we are our customer's partner throughout the development and production of molded products."

Duplicraft uses the continuous-path Cyclone digitizer offered by Renishaw Inc., also in Schaumburg, Illinois. Said to be much faster than point-by-point touch trigger digitizers, the Cyclone scans the model by sweeping its analog probe in a series of rapid passes, sometimes in excess of 100 ipm. The probe reaches an XYZ work zone measuring 23 inches by 19 inches by 15 inches. Users select the data capture technique that best matches the characteristics of the model, choosing from among a series of 2D traces along the model profile, or a 3D digitizing pattern comprised of parallel, radial, or circular moves.

Users also select the format to which the data output is structured. Choices here include outputting an NC part program customized to the user-selected machine tool controller brand, or a CAD/CAM-compatible data file formatted to DXF, VDA, ASCII or IGES. Virtual models in one of the CAD/CAM formats can then be modified directly in the computer using CAM software, with tool paths generated to match the revised part. The Tracecut software that controls the Cyclone can do this job, but so can third-party software like the Camax system Duplicraft uses.

Mr. Faurot says that Duplicraft's design and engineering applications for the Cyclone came later. The company originally purchased the unit because it was an efficient means of tool path generation that was less expensive than laser digitizing.

"Before the Cyclone let us digitize efficiently, our tool paths came at the discretion of whomever measured the model. Even skilled technicians interpret fine radius gage measurements differently, but when those measurements went into the CAM system, the range of interpretation became the margin of error between the machined cavity and the model it was meant to reproduce."

He goes on to say that Duplicraft has now effectively eliminated this discrepancy. "With the Cyclone, what you see is what you get."

Digitizing on the Cyclone is now a standard part of the mold making process for any design that does not come from the customer as a CAD file. Though the unit can send data directly to an individual CNC, Duplicraft's Cyclone shares the company's DNC network with 16 CNC machines, generating surface data models that can be used to program any of them via workstations running Camax software.

Once the part is set up, says Mr. Faurot, the Cyclone runs unattended. Digitizing a typical part or model takes one to two hours, up to a maximum of six hours for the most complex bottle designs.

Says Mr. Faurot, "The unit lets you achieve as much speed as the design will allow, by choosing the `pick' between surface coordinate measurements to match the surface complexity." For example, a recent model for a hand-held spray bottle included a series of 0.015-inch radius ribs, which could only be accurately captured by digitizing at 0.004-inch pick. At the other extreme, Mr. Faurot cites a model for a motor oil bottle, whose smooth and unbroken surface permitted a pick of 0.100-inch. The Cyclone's Tracecut software also lets users define multiple meshes for a single model, with each mesh defined by a different combination of pitch and stepover. This lets users establish high data density only where it is needed, which is key when the model combines regions of complex detail with an otherwise smooth surface.

A "chordal tolerance" default parameter lets the Cyclone minimize computer processing time, by reducing the data file to the lowest number of points necessary to define the model. Chordal tolerance dictates how far off a chord a data point must lie to merit inclusion in the model. The Tracecut software stitches chords together on the fly while the digitizing progresses, and uses this parameter to determine which data points are redundant and therefore unnecessary. Setting the chordal tolerance low and pick high--for example, 0.002-inch and 0.050-inch, respectively--allows the Cyclone to capture the fine detail of a mode's complex areas, without wasting samples or data points on the areas that are smooth.

These are new software features, but Mr. Faurot says Duplicraft takes advantage of a special hardware feature of the Cyclone, too. Its stylus pressure is so low, he says, it lets the company digitize not just bottles models but actual bottles, too.

"It's a quick way to see what's possible with a mold that may have been out of service for three or four years," Mr. Faurot says. "Maybe the customer wants to change the handle angle, or open up the cavity to increase the bottle's volume. Based on the digitized model of the old cavity, we can show where inserts will be needed, and massage the new design in Camax until we get a cavity that's metal-safe."

"Machining, rebuilding, reverse engineering, product evaluation we are still finding new ways to turn digitizing on the Cyclone into a service for our customers," Mr. Faurot says.

Sometimes unique opportunities present themselves. Mr. Faurot recounts one example, involving a customer who had to go overseas to give a presentation related to line of bottles that didn't yet exist. The customer gave Duplicraft a rough sketch of his idea for one representative of the line, but needed something more formal for his speech and needed it quickly.

Creating the bottle in CAD would have taken too long, Mr. Faurot said. Instead, a Duplicraft patternmaker quickly created a male model from the sketch. After this was digitized on the Cyclone, engineers scaled and modified the resulting computer model to produce other members of the line.

"From one hand sketch, we were able to give the customer precise 2D article drawings detailing the entire line," said Mr. Faurot. Duplicraft got the order to begin machining those molds soon after the customer returned from overseas. MMS

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