【正文】 ere the tool will eventually break. Taking a Plunge Although standard microdrills aren’t generally available below , microendmills that can be used to “plunge” a hole are. “When people want to drill smaller than that, they use our endmills and are pretty successful,” Burton said. However, the holes can’t be very deep because the tools don’t have long aspect, or depthtodiameter, ratios. Therefore, a dia. endmill might be able to only make a hole up to deep whereas a drill of the same size （論文）外文翻譯 4 can go deeper because it’s designed to place the load on its tip when drilling. This transfers the pressure into the shank, which absorbs it. Performance offers endmills as small as 5 microns () but isn’t keen on increasing that line’s sales. “When people try to buy them, I very seriously try to talk them out of it because we don’t like making them,” Burton said. Part of the problem with tools that small is the carbide grains not only need to be submicron in size but the size also needs to be consistent, in part because such a tool is prised of fewer grains. “The 5micron endmill probably has 10 grains holding the core together,” Burton noted. He added that he has seen carbide powder containing grains, which is about half the size of what’s mercially available, but it also contained grains measuring and microns. “It just doesn’t help to have small grains if they’re not uniform.” Microvaporization Electrical discharge machining using a sinker EDM is another microholemaking option. Unlike , which create small holes for threading wire through the workpiece when wire EDMing, EDMs for producing microholes are considerably more sophisticated, accurate and, of course, expensive. For producing deep microholes, a tube is applied as the electrode. For EDMing smaller but shallower holes, a solid electrode wire, or rod, is needed. “We try to use tubes as much as possible,” said Jeff Kiszonas, EDM product manager for Makino Inc., Auburn Hills, Mich. “But at some point, nobody can make a tube below a certain diameter.” He added that some suppliers offer tubes down to in diameter for making holes as small as . The tube’s flushing hole enables creating a hole with a high depthtodiameter ratio and helps to evacuate debris from the bottom of the hole during machining. One such sinker EDM for producing holes as small as (11μm) is Makino’s Edge2 sinker EDM with finehole option. In Japan, the machine tool builder recently produced eight such holes in 2 minutes and 40 seconds through thick tungsten carbide at the hole locations. The electrode was a silvertungsten rod smaller than the hole being produced, to account for spark activity in the gap. When producing holes of that size, the rod, while rotating, is dressed with a charged EDM wire. The finehole option includes a Waxis attachment, which holds a die that guides the electrode, as well as a middle guide that prevents the electrode from bending or wobbling as it spins. With the option, the machine is appropriate for drilling hole diameters less than . Another sinker EDM for microholemaking is the Mitsubishi VA10 with a finehole jig attachment to chuck and guide the fine wire applied to erode the material. “It’s a standard （論文）外文翻譯 5 EDM, but with that attachment fixed to the machine, we can do microhole drilling,” said Dennis Powderly, sinker EDM product manager for MC Machinery Systems Inc., Wood Dale, Ill. He added that the EDM is also able to create holes down to using a wire that rotates at up to 2,000 rpm. Turn to Tungsten EDMing is typically a slow process, and that holds true when it is used for microdrilling. “It’s very slow, and the finer the details, the slower it is,” said , president and owner of Optimation Inc. The Midvale, Utah, pany builds Profile 24 Piezo EDMs for micromachining and also performs microEDMing on a contractmachining basis. Optimation produces tungsten electrodes using a reversepolarity process and machines and ringlaps them to as small as 10μm in diameter with roundness. Applying a 10μmdia. electrode produces a hole about to 11μm in diameter, and blindholes are possible with the pany’s EDM. The workpiece thickness