|Space on the circuit board and in the computer is valuable. Diameters and pitches on dual inline memory modules like these, and other connector products, continue to shrink to make room. Toolmakers are relying on wire EDM to help with the needed precision.
It's a cliche to say it, but perhaps there's no better example: Tool Tek is a mom-and-pop shop. Since owner/operator Terrence Bliss opened his five-person tool shop in 1987, it has specialized in building tools and molds for connector applications. About three years ago, Bliss bought a Charmilles Robofill 2020 wire EDM. Bliss's wife Elaine saw the new machine, took an interest, and is now the official Wire Guru.
It's a good thing, because when it comes to making tools for connector applications, wire EDM is the machine of choice for cutting steel. "We call it slicing and dicing," says Bliss. Tool Tek slices and dices eight to 10 connector molds a year from its small Irving, TX shop and prides itself on meeting the ever-shrinking specifications of the connector industry.
The shrinking specs are courtesy of the computer and electronics market, where manufacturers are on the lookout for any and all methods to save "real estate" on circuit boards. As a result, diameters and pitches are getting smaller as OEMs pack more wiring into smaller spaces.
The standard pitch in some connector applications, says Bliss, is down to about .5 mm, or .020 inch. The industry standard, however, is still about .1 inch. "It's pretty tiny when you have to get a core in there," he says. That's where the wire EDM comes in. Bliss says that to meet such specs he usually starts with a solid block of S7 steel and runs it through the Charmilles once, then turns it 90¡ and passes it through again. He'll pass it through up to eight times to get the finish he needs.
"Most people roll their eyes when they hear that, because most toolmakers use three passes," Bliss says. "But you can go right from the wire cut to 2000 sandpaper." In fact, Bliss says his shop doesn't even have a CNC mill, just the EDM, a Charmilles ram, and five Harig grinders.
Says David Musselman, tooling engineer at Robinson Nugent, one of Tool Tek's largest customers, "Wire machining is becoming more and more a necessity in connector designs today." Cores in such applications, says Bliss, are typically about an inch long and .030 inch in diameter. He prefers S7 because "it's pretty flexible and isn't so stiff that it would snap under high pressure." Nonetheless, breaking cores is a problem, and one addressed by molder Robinson Nugent.
Musselman helps design many of the molds the injection molder uses to manufacture millions of dual inline memory modules (DIMMs) and other computer connector parts each year. Musselman and Robinson Nugent devised a connector tool that uses a modular pin design to help reduce the cost of pin replacement. The pins, from Matthews Gauge (Santa Ana, CA), have a round base with a square head and run about $10 to $20 each - compared to several hundred dollars to have a new solid pin block made. "Interchangeability is a must for these molds," says Bliss.
The initial cost of such a tool is higher, says Musselman, but the lower replacement cost makes the initial cost worth it, at least in tools expected to produce between 1 million and 4 million parts per year. Robinson Nugent has converted about a dozen tools to use the interchangeable pins, saving the company "tens of thousands of dollars," Musselman says.
When it comes to molding DIMMs, Robinson Nugent was even more creative. The challenge is that different memory cards have different numbers of pins. The most common pin count, says Musselman, is 168, but new memory cards on the market have as many as 244. Should a molder build a separate tool just to add 76 pins?
At Robinson Nugent the answer to this question came in the form of face mount modules, homegrown MUD-like units that allow molders to change the pin count without changing the tool. "These units can be unscrewed from the face of the main unit to change the part from one length to another," Musselman says. It takes a few hours, but it's still less expensive than building a separate tool. He adds that Robinson Nugent has been using face mount modules for about 12 years.