Production Machining

AUG 2018

Production Machining - Your access to the precision machining industrial buyer.

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Contributed by John Powell Magnetic Workholding for Production Parts e use of magnets for workholding has grown well beyond its traditional role for flat-plate materials. Control of magnetic flux is now precise enough to securely hold a much wider array of workpiece configurations. T he introduction of high-power, square-pole, electro- permanent magnetic milling chucks to the North American market occured at IMTS 1994. At that time, conventional wisdom was that magnets were for grinders—relatively low power magnets holding a flat plate against stops. e grinding wheel created down force and the stops prevented sliding—everything worked great. However, a demo at that show that stopped people in their tracks was a round bar on a magnet—the bar was rolled against a side rail, giving line contact in Y and Z axes. Otherwise, the bar didn't move. In came a face mill to take an aggressive cut ; chips went flying and the bar stayed put. e cut finished, the magnet switched off, the chips all blew clear, and the part was released. Magic! Twenty-four years later, the electro-permanent magnetic chuck has become more compact, more efficient and an established workholding method for milling and turning. For mild steel, the chucks typically achieve more than 200 psi clamping force over the magnetic poles. For a 20-inch by 40-inch chuck covered by a mild steel plate, the clamping force is more than 80,000 pounds. Smaller production parts, however, present more of a challenge since contact areas and holding forces are smaller. However, the modularity and flexibility of magnets offer possibilities to effectively locate and clamp produc- tion parts and can also offer flexibility to accommodate families of parts. Magnetic Advantages Five-axis machining drives the need to hold workpieces with as much access to the five sides that the machine can reach. To achieve this, a clamping method that holds from one face only is required. By definition, clamps and vises grip across the part, which eliminates access to the "bottom" face and :: Square-pole, electro-permanent magnets continue to find applications that take advantage of the production benefits of this continually developing technology. WORKHOLDING 36 PRODUCTION MACHINING :: AUGUST 2018

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