Production Machining

AUG 2018

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

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compromises access to the two contact faces—the best possible access is three complete faces, plus part of two more. Magnets allow parts to be gripped from one face, leaving five of the faces completely free. Fragile parts also can often be held magnetically when use of clamps or vises cause distortion. Since the magnetic grip is formed across the interface between part and magnet, there is no tendency to crush a fragile part. Square-pole magnet designs provide an excellent platform for tooling. ese steel blocks can be organized to create clamping faces to match the needs of the part. Magnetism flows from north to south poles and can create grip in X and Y axes as well as Z, or any combina- tion thereof. It is entirely possible to clamp prismatic parts on two or three faces, and it is also possible to arrange a sequential firing sequence, for example, clamp sideways and then down to ensure that a rail is positively located and pulled straight. Electro-Permanent Magnet Circuit e basic high performance electro-permanent magnet circuit is the double magnet (DM) system. e DM circuit comprises of a steel case in which a series of steel pole pieces (typically square) are mounted. Under each pole is a coil surrounding a permanent magnet that can be reverse- magnetized by the coil. e material used (typically AlNiCo—aluminum, nickel and cobalt) has good magnetic performance, but is relatively easy to magnetize, reverse- magnetize and demagnetize. Surrounding the steel pole pieces are a second set of magnets that do not switch— typical material is a neodymium rare-earth element that has good magnetic performance and is virtually impossible to reverse-magnetize or demagnetize. To switch on the magnetic circuit, the AlNiCo magnets are energized in the same orientation as the non-switch- able rare-earth magnets. e rare earths with north polarity against the sides of the steel pole are combined :: Figure 1: Drop blocks: A common requirement for magnetic workholding is to raise the workpiece off of the magnet surface to allow edge- and through-milling, as well as through-drilling and tapping. This is easily achieved using fixed pole extensions attached to each magnet pole with a screw. An excellent solution is the use of "drop blocks." First, small buttons are screwed into the tapped holes in each pole. Each pole is slightly larger than the screw head and made of case-hardened steel with a slippery radius engagement. The drop blocks are made as two pole grid plates. These plates are a single block forming two magnetic poles with counterbores in the base to engage the buttons. To configure the magnet, the drop blocks are simply moved by hand to what- ever configuration is required. Since each block is a bi-pole north/south pair, magnetic balance is assured. Magnetic Workholding :: 37

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