Production Machining

OCT 2017

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

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Using Grinding Versus EDM to Finish Form Tools By Barbara Schulz O n a visit to German-based cutting tool insert manufac- turer, Schwanog, earlier this year, we were given a comprehensive plant tour. It included the company's insert finishing departments that included a bank of Haas grinding machines and Agie wire EDM units. ese two finishing operations begged the question: when should grinding be used and when should EDM be used as a finishing process? To meet tight tolerances and surface finish requirements, tool manufacturers usually opt for grinding as a finishing operation because it's fast and efficient. However, wire EDM can be the better choice and sometimes the only choice. Form tool systems, consisting of a toolholder and an insert blank, are designed to machine contours that cannot be produced as quickly while using a single-point turning process. Form tools use a plunge cut method to cut contours in a workpiece blank in a single axis stroke versus traversing the blank, often multiple times, to create the programmed geometry. e insert blanks are made of coated or uncoated hard metals, ceramics, boron nitride or polycrystalline diamond (PCD). Schwanog tools are manufactured to create part- specific contours of its insert blanks by either grinding or wire cutting (EDM). e cutting-edge geometries and final dimensions of PCD cutting tool inserts are typically produced on CNC tool grinders. However, since diamond, the hardest known material, is contained in both the workpiece and the grinding wheel, the machining time and tool wear are enormous when grinding. But PCD tool usage has been gaining momentum because titanium-based alloys, along with various composite materials, continue to see increased usage in the aerospace, automotive, medical and energy industries. ese materials have created new finishing challenges for tool makers such as Schwanog. PCD tools have a significantly higher service life than hard metal tools when it comes to working on nonferrous metals or plastic with glass or carbon fiber, for instance. However, because of the qualities of the diamond and CBN crystals in these materials, cutting into segments is difficult and requires EDM, Schwanog's Production Manager Franz Hummel explains. ere are two types of erosion machines used in producing PCD tools depending on the application; rotary erosion and wire EDM. Schwanog uses a wire EDM unit to remove PCD when manufacturing or regrinding PCD tools. In these machines, a wire uses electric charges to erode :: German form tool manufacturer uses grinding or EDM to finish its inserts depending on the necessary customer specifications, including geometry and surface finish. TECH BRIEF :: 29

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