To The Outer Limits of Design
Heads-up part and mold designs spark an aesthetic miracle
for Pitney Bowes' next generation of mailing machines
A few years ago, part and mold designers would have walked away from the challenge presented by Pitney Bowes' industrial design team-a concept part so complex that even today, many experts would deem it impossible to mold. Instead, a talented team made the miracle happen, staying true to the original concept and, in the process, expanding the window of possibility for injection molded part design.
This dream team consisted of four main players: Tony Sgroi, product design engineer, and Nizarali Virani, senior engineer and project coordinator, both of Pitney Bowes (Danbury, CT); David Akin, an independent mold designer from Akadco (West Dennis, MA); and Roger Poirier, vp of toolmaker Osley &Whitney (Westfield, MA).
Dubbed "the collar," the amazing part is one of 11 molded components that make up the housing for the Spark mailing machine, Pitney Bowes' newest product line addition. According to industrial designer David Beckstrom, the company wanted the Spark's design to be just as groundbreaking as the technology that it will bring to the mailing market.
"With Spark, we are striving to create a forward-looking image that connotes the same message about the unseen technologies inside," he says. "We also wanted to keep the footprint small, yet not allow the product to become visually bulky.
Figure 1. A preliminary mold design for the collar generated by Pitney Bowes' Tony Sgroi includes surfaces for core, cavity, three slides, and a cavity slide designed for wire EDM. Ultimately, five slides were required to mold this part.
Our in-house industrial designers-Joseph Sugrue and Patrick Thrailkill-decided to break the form into two parts that are functionally distinct. As a result, the user interface (or meter) stands upright and at an angle to make its presentation more user-friendly."
Modeling the Future
Designing the Spark in this way meant that the meter would be inserted into the machine at an angle close to 90. The collar was developed as the main nest for the meter, so that it too would bisect the horizontal machine. As a result, all of the other housing parts mate with the collar.
After industrial designers created the foam model and master curve file for the entire housing, they initiated a 3-D master model file in Pro/E that would be used throughout the project. Using an SLA 500 machine at Pitney's Shelton, CT facility, they created a one-piece SLA prototype of the entire housing from the Pro/E master file. Also, the decision to use plastic injection molding was made.
From this point, the project was handed to the Product Packaging Department, also in Shelton. After design engineer Tony Sgroi received the SLA part and the master model file, he began breaking down portions of the housing into separate components. "It was necessary to divide the housing into 11 parts, and the collar is a direct result of those part breaks, which are based on the surfaces that industrial design needed,"Sgroi explains.
When the main surfaces for all the parts were defined, it became clear to Sgroi that the collar would be the heart of the housing. "It provides all of the structural integrity because the other main housing parts bolt into it, which stiffens the entire assembly structure," he says. "It acts both as the main nest for the meter and as the mating surface for all other parts. Most of its surfaces are contoured, with a few flat areas appearing as ribs or internal features. Roughly, the dimensions are 9 by 7.5 inches, with a 4.75-inch depth."
Figure 2. Most part surfaces are formed by slides, as indicated in these views, rather than by core or cavity surfaces.
Luckily, Sgroi has a mold design background, and could approach the part design with a knowledge of tool construction. His first impulse was to simplify the tool design. However, that would have meant changing geometry from the original concept design, which was forbidden.
Sgroi realized that in its original state, the part appeared impossible to tool. Rising to the challenge, however, he began a preliminary mold design (Figure 1), generating surfaces for the core, cavity, a cavity slide designed for wire EDM, and three other slides. In operation, the cavity would pull up at a 90 angle, and the cavity slide would retract at an 8 angle relative to that normal direction. There was also a slide pulling through the core. Matters were quickly becoming complicated.
When toolmaker Roger Poirier saw the part and mold designs, he also had ideas aimed at simplification. First, he suggested molding the collar in two parts to reduce tooling cost and make the component easier to mold. But because of structural requirements, it couldn't be done. Secondly, he wanted to build the tool with the part laying on its side, rather than standing straight up in the mold. With this scheme, though, witness lines would have been at a spot where the customer would often be touching the housing. Aesthetic concerns nixed this idea.
Poirier contacted mold designer Dave Akin, and they began working on the concept mold design sent by Sgroi. Akin imported Pro/E files of the collar into his system (Cadkey with FastSurf), and created all of the molding steel as 3-D wireframes, along with a surface model for parting lines and mold surfaces.
"The major actions and parting surfaces were already defined," recalls Akin, "and my task was to design the steel around these components." But as the tool design progressed, more functionality and features were being added from Pitney Bowes' end. An added circuit board mounting, for example, required an additional slide.
Akin decided to use the existing slide that pulled through the core to activate this additional slide. "As the core slide pulls, the other one cantilevers out of the part," he explains. All of the slides are also interlocked in the B side of the mold to make them stronger. (For slide positioning, see Figure 2.)
To give an idea of the tool design complexity, Akin points to 28 E-size sheets required for detailed drawings of the mold layout. These show tooling details that include a floating plate on top of the mold to which the core is mounted with sliding gibs. All of the sliding actions are driven by in-mold mechanics, not hydraulics. "Without CAD/CAM, we could not have produced this part," he says.
Poirier agrees that advances in technology play a big part in this molding miracle. "Building the tool brought us to a new level of trusting our CNC equipment," he says. "There
Figure 3. Although the collar weighs only 150g, the resulting tool is a 10,000-lb giant. Core (top) and cavity (middle) each contain several mechanically actuated slides. Slides one, two, and three, like most of the five slides contained in the tool, can only be seen when the mold is disassembled (bottom).
wasn't any one feature that was more difficult than the others-we've produced unusual slides before-but we had never put these in combination with a geometry this complex. We had to machine directly from CAD files, and there was no way to know if the pieces would fit when we put them all together. Yet they did."
After getting the wireframe and surface files from Akin, and the Pro/E master file from Sgroi, Osley & Whitney toolmakers and programmers went to work. "We couldn't always get files into our Mastercam system, so we bought a seat of Pro/E for this project," says Poirier. "When files come in, we need to define the surfaces for EDM electrodes or CNC machining better, and with this project, we spent an equal amount of time programming and machining."
Programmers interrogated the Pro/E file for dimensions, bringing every surface on the molded part and every piece of steel into the Mastercam file. To verify that electrode dimensions were correct, toolmakers used CMM system outputs and compared them against the CAD file. About 75 percent of all surfaces were EDM machined because of the deep and unusual shapes, and slides were machined from blocks of steel. All of the other surfaces were CNC machined. Finally, heavy venting was added.
While the molded part itself weighs only 150g, the resulting tool tips the scales at a whopping 10,000 lb. "We had to sample the tool on a 500-ton press at Bayer's facility in Springfield, MA because it was too heavy for the cranes at Pitney Bowes' plant," he recalls. Bayer also supplied the PC/ABS material (Bayblend FR110) used to mold the collar. Injection pressures ranged from 10,000 to 12,000 psi.
When the dust settled, Poirier had a chance to appreciate how talented his programmers and toolmakers proved to be. The first shots off the tool were good, with only normal debugging required for a small amount of flash. Close-up views of the mold showing the core, cavity, and several slides can be seen in Figure 3.
Other than the radical design, a factor that made this project so surprising is that the design geometry did not change one micron from the concept to the production stage. Both Sgroi and Virani agree that Pitney Bowes learned the trade-offs required for strict adherence to a high-end aesthetic design. At the Danbury facility, a captive and custom molding operation, Pitney Bowes is currently molding all of the housing parts except the collar (see sidebar, below).
Molding the impossible part
Figure 1. Jim Robertson, a senior process technician at Alliance, helps a forklift guide the 10,000-lb mold through the tiebars on the 500-ton Toshiba. With only 2 inches of total clearance, it's a tight squeeze.
Pitney Bowes does much of its own injection molding, and might have molded the collar itself, if it weren't for the size of the 10,000-lb mold. The molding facilities at Pitney Bowes don't have a crane that can handle the load. The job went instead to Alliance Precision Plastics in Rochester, NY, a regular molder for Pitney Bowes.
Mart Raidmae is the director of engineering and tooling at Alliance and was tasked with running the mold. But running the mold is not what makes this part so challenging. Raidmae says Alliance was invited to the project late in the schedule and did not get mold dimensions until it arrived at the plant.
"When the tool first got here, lo and behold, we couldn't hang it in our press. It was too big," says Raidmae. "It was slated to run in a 500-ton press, and with the mold put together there wasn't enough tiebar clearance to get it in there."
Alliance was forced to improvise by putting the tool into the 500-ton Toshiba one half at a time. "We put the ejector side in first," Raidmae reports. "We turn it sideways, drop it between the tiebars, and then swing it into position." The other half of the mold is not so easy. "We load the cover side of the tool horizontally between the tiebars," he explains. Using a forklift and crane, the mold slides in sideways, with less than 2 inches total clearance between the tiebars (Figure 1). "It becomes a really complicated setup," says Raidmae.
Once it's in, however, Raidmae reports that the mold runs cleanly and well, despite the complicated set of slides and lifters that fills the tool. The part fills easily and, aside from a few last-minute engineering changes performed by Alliance, the mold performs as well as the molder could hope.
Raidmae says his primary concern right now is residence time. The 62-oz barrel on the 500-ton machine is too large for the part, which weighs only 150g (5.3 oz), though the mold does have a 7-inch cold sprue. So a smaller barrel may be in store for the future. Still, the machine runs the PC/ABS part in 1-minute cycles without incident. Raidmae says he's only sorry Alliance, also a moldbuilder, wasn't given a chance to build the tool. "I would have loved the opportunity to give it a shot. It's really amazing," he says.
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