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March 1, 2002

5 Min Read
Spending less time for better designs

Chances are that you've used a product made by Coinco, especially if you can't pass a vending machine without purchasing something. St. Louis-based Coinco (formally, Coin Acceptors Inc.) is a world leader in the design and manufacture of coin mechanisms, bill acceptors, and control systems for vending machines, the major equipment for the global food and beverage vending industry. 

Max Molenaar, a senior Coinco engineer, supervises the tool design and drafting departments, model shop, prototyping, and computer-aided engineering activities. The company uses several types of software, including Moldflow Plastics Insight (MPI) for flow and cooling analyses, Pro/Engineer Mechanica for stress analysis, and Unigraphics and Solid Edge for computer-aided design. 

Molenaar reports that among the challenges of designing the company's products are molded parts, such as gears, that require close tolerances. "Typically, coin changers are restricted in size and require small and accurate components," he says. "Designing and molding a plastic part to meet our expected criteria can be challenging." 

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A coin changer component, designed and photo-rendered in Unigraphics, contains molded-in flanges that create slots for coins (left). Part of the complexity of this part stems from numerous bosses, ribs, and molded-in attachment points on the rear side (right).


In addition, Coinco customers demand products that are reliable and tamper-proof. "A combination of good design, careful analysis, and testing helps us achieve reliability and tamper-proof devices for our customers," he says. 

Time Is Money 
To perform a flow or cooling analysis, Coinco engineers must first create a finite-element mesh from the part CAD file. In the past, this step has taken a great deal of time. In fact, Molenaar figured out that he and his colleagues were spending up to 8 hours per model to generate meshes and clean them up using midplane meshing tools. 

Switching to MPI with faster meshing tools, he's realized savings so far of 120 man-hours. Over time, he calculated that the company would save more than $26,000 per year as a result of implementing the new software. "The company's return on this investment will be realized in less than a year," says Molenaar. 

As a result of the faster meshing tools available in MPI/Fusion, he and his colleagues have been able to reduce modeling time by 80 percent. "When we participated in the beta test for MPI/Fusion," he says, "I selected a small, complex gear as a test model. Using C-Mold Express, our former analysis package, it took 4 hours to generate a mesh and another 3 hours of manual labor to correct the mesh. Moldflow's Mesh Generator generated the mesh in about 5 minutes, but the mesh didn't look any better than the Mesh Express version." 

Both products required additional labor to create something usable. How-ever, using MPI/Fusion, he generated the mesh in just 2 minutes and spent another 15 minutes cleaning it up. 

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Running a cooling analysis in MPI helps Coinco designers to determine if cooling circuits in the tool will be adequate.


Optimizing Designs 
Molenaar and his peers have been using MPI/Fusion software since September 2001. However, the tool design department had already been using flow analysis software at Coinco since the early 1990s, when the company introduced software from C-Mold for flow analysis. (Moldflow acquired C-Mold in 2000.) Molenaar migrated to MPI as a beta customer for Synergy, the new user interface that debuted with MPI 3.0. 

"We use MPI for analyzing each newly designed plastic part," adds Molenaar. "The software is an integral part of the overall design process because it allows us to achieve the accuracy, the reliability, and the consistency that our customers expect." The company established a policy several years ago of performing flow and cooling analyses on each new part during tool design. 

"Another benefit of analysis is that we can optimize the design accurately at the beginning of the design cycle, and eliminate subsequent design iterations. In addition, the analysis allows us to plan and position the cooling lines before machining them. This helps prevent costly and time-consuming retooling." 

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Melt front advancement plot of the changer component shows areas filled first (blue) and last (orange) during the 1.5-second fill time.


Eliminating Rework 
Upfront analysis also helps Molenaar make more informed decisions. "We could have a scenario where instead of cooling the mold with water, we could opt for using beryllium copper. Analysis helps us save time and money because it takes the trial and error out of the design cycle. It also allows us to establish a process for the production floor so operators can easily initiate the startup process for the mold. They have a processing window ready for them." 

Molenaar and his team are currently using MPI to design new plastic parts—some as large as 6 inches wide by 18 inches long, and as small as gear pieces with .25-inch diameters. 

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After being optimized, the coin changer component is analyzed for volumetric shrinkage using MPI. Blue and green colors correspond to a low percentage of volumetric shrink.


"Using Synergy for a current project is particularly helpful because we are almost 99 percent sure that the gate locations and cooling lines are accurate," Molenaar explains. "There are aesthetic issues with any product so we make sure that unsightly knit- and weldlines do not appear in critical areas. That's why it's also very important to perform analysis during the design cycle, to make sure that we don't have imperfections in cosmetically critical areas." 

Contact information
Coin Acceptors Inc.
St. Louis, MO
Max Molenaar
(314) 725 0600, ext. 384
www.coinco.com
[email protected] 

Moldflow Corp.
Wayland, MA
(508) 358-5848
www.moldflow.com

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