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December 1, 2001

4 Min Read
Molder, suppliers, customer join forces for bobbin and coil redesign


Replacing a thermoset-overmolded bobbin and coil, this new design uses integrated wire guides for coil winding, a snapfit cover, and interchangeable terminal locations.

Successful manufacturers don't simply pay lip service to the concept of collaboration, but adopt it wholeheartedly, forming intellectual partnerships with a variety of suppliers through all phases of part production. Tasks are divided, and companies with specialized capabilities apply their talents to tackle designated problems. Throughout the process, communication and freely flowing information keep involved parties abreast of the latest developments, pushing toward the ultimate goal: a successful part. 

Such was the case when the Cutler-Hammer Div. of Eaton (Milwaukee, WI) decided to take on the manufacture of a bobbin and coil for an electrical contactor. The company knew its relative inexperience in molding demanded knowledgeable partners. 

Uncharted Territory 
"This was something we hadn't done," Ed Boothroyd, Cutler-Hammer senior development engineer, explains. "All of it was essentially new. We wanted to bring this manufacturing in-house rather than buying [the bobbin and covers] from the outside." To do this, Cutler-Hammer looked to Plasti-Coil Inc. (Lake Geneva, WI), an electrical molder with formidable experience in bobbin molding. 

"We worked very closely with Plasti-Coil in developing a bobbin and cover design," Boothroyd says. 

A suitable design needed to satisfy several conditions. First, the contactor had to meet UL requirements as an electrical insulator and function under high operating temperatures. Automated secondary operations, which include terminal insertion and coil winding, placed additional stress on the part and required molded-in recesses for the terminals and integrated wire guides. In final assembly, the bobbin and cover snapfit together, and since the parts are meant to be field replaceable, consideration had to be given to the existing bobbin model's measurements to ensure a matching fit. 

Cutler-Hammer knew what it needed—all that was left was collaborating with the right companies to get it. 

Let's Do Lunch 
"Fortunately, [Plasti-Coil] is reasonably close to us geographically, so we had a number of meetings at Plasti-Coil, and [representatives] came up to talk to us in Milwaukee," Boothroyd says. "We probably had 20 meetings on this thing from the onset through the various stages of conception and modification before we finally got to a design we felt was going to be adequate." 

In addition to collaborating with Cutler-Hammer on part design, Plasti-Coil President Craig Ferguson says his company also worked with DuPont. 

"We had hundreds of hours of meetings and exchanged drawings and ideas and consulted with DuPont on various methods of how to make it work," Ferguson says. He explains that material choices were limited because of the UL requirements and cost restraints involved. 

After consulting DuPont, Plasti-Coil settled on the company's Rynite FR530. This 30 percent glass-reinforced PET had a maximum operating temperature of 130C and met Cutler-Hammer's requirement of four million contactor operations at 80C. 

A Happy Ending 
Plasti-Coil General Manager Bob Cordoba says the part's original design, which used a thermoset to encapsulate the coil, was an inefficient and costly process that Plasti-Coil abandoned without sacrificing standards. 

"[Cutler-Hammer] is saving a ton of money doing it the way it is now," Cordoba says. "In most cases when you make a switch of this magnitude, there are properties or there are electrical insulation requirements that are not met, but in this case, we managed to assist our customer in the design of the bobbin so that it wouldn't lose any of those properties." 

Using smaller-capacity (less than 88-ton) Boy molding machines, Plasti-Coil molded the bobbin and cover in two different two-cavity tools. Plasti-Coil worked closely with the two toolmakers that created the molds for the bobbin and the cover respectively. 

After enlarging one gate to compensate for uneven cavity fill, the parts now run on 18-second cycles. After molding, the bobbins are manually placed in a machine that automatically inserts terminals in any or all of four positions on the bobbin. Telinar (Crystal Lake, IL) teamed with Plasti-Coil and Cutler-Hammer to design the terminal recesses and provide the automation equipment for the insertion. 

From Plasti-Coil the bobbins are shipped to Cutler-Hammer assembly facilities in the Caribbean. The Dominican Republic plant winds the bobbins with coil using a three-spindle winding machine expressly designed for the job by Spanish wire-winding specialist Sipro. From there, final assembly is completed in Puerto Rico. 

In the end, seven different companies contributed to the design, tooling, molding, and assembly of the new bobbin and coil cover. According to Ferguson, that kind of teamwork pays dividends. 

Contact information
Plasti-Coil Inc.
Lake Geneva, WI
Craig Ferguson
(262) 249-5620

Cutler-Hammer Div. of Eaton Corp.
Milwaukee, WI
Ed Boothroyd
(414) 449-6000

Boy Machines Inc.
Exton, PA
George Dallas
(610) 363-9121

DuPont, Wilmington, DE
Nancy Eckrich
(800) 441-0575

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