Sam Allison and his fellow EDM professionals at Makino’s Die/Mold Division enjoy a challenge. “The difficult applications provide opportunities to demonstrate the power of our EDM technology and to push the envelope in terms of EDM practice,” says Allison, an EDM Applications Engineer. He points to a recent headlamp housing application as an example.
“The customer needed to develop headlamp housing molds for the reflector headlamps that we’ll soon be seeing on new cars,” says Allison. The inner surface of the housing consists of numerous intersecting squares called reflectors. For the headlamps to perform as designed, the dimensions of these small squares must be exact and their edges must be precisely detailed.
“After EDMing, the molds were being polished,” notes Allison, “and as a result of polishing the reflector edges were losing their detail.” This loss of detail degraded headlamp performance, resulting in unacceptable scores in federally mandated headlamp tests. The customer realized that in order to avoid polishing, the mold needed a mirror finish. Despite its considerable resources, though, the customer was unable to obtain the desired finish with conventional EDM technology from their suppliers. It was at that point that they came to Makino.
“They had seen a mirror finish part that we had done and were impressed by it, so they came to us and asked us if we could produce a mirror finish on a mold of this complexity,” Allison says. “We did some testing, then told them we were confident we could produce the part they needed on our equipment.”
Working from the customer’s geometric model, Makino developed programs for rough machining the mold steel and for milling the dozens of graphite electrodes needed to burn the complex series of intersecting reflectors. In the process, Makino discovered errors in the customer’s geometric model, and assisted the customer in correcting their data.
The mold cavities were burned on a Makino EDNC-series EDM. “The EDNC was able to deliver the dimensional accuracy, the precisely-detailed reflector edges and the mirror finish the customer was looking for,” relates Allison. “The need for polishing was eliminated and the headlamp’s optical problems were solved.”
Why did the EDNC succeed where other machines had failed? “The main reason is the basic technology embodied in the EDNC that makes it an exceptionally accurate machine.” Among other things, Allison points to the EDNC’s 32-bit adaptive control that dynamically reacts to machining conditions and suppresses DC arcing. This precise control of electrode movement enables complex orbiting patterns that make it possible to safely EDM difficult shapes without the need for flushing holes. The EDNC’s ability to machine effectively at low power with either copper or graphite electrodes also contributes to the obtaining of very fine finishes.
“The capabilities of our SNC64 graphite mill also played a part,” he notes. The SNC64 is a fully enclosed milling machine designed specifically to perform high-speed, high-definition milling on graphite. “The accuracy and finish of the electrodes produced by the SNC64 was an important factor in the success of this application.
“The long and short of it,” concludes Allison, “is that the customer was under intense time pressure and could not get acceptable parts. We provided them with molds that could produce quality parts, and did it in the time allotted. In the process, we were able to demonstrate some of the advanced capabilities of our EDM, programming and integrated process technologies.”