Exploring Advanced Manufacturing Technologies. Steve Krar
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Fig. 3-1-14 Polycrystalline tool blanks and inserts consist of a thin diamond or CBN layer bonded to a cemented carbide substrate. (GE Superabrasives)
Fig. 3-1-15 Polycrystalline tool blanks and inserts are available in a wide range of shapes and sizes. (GE Superabrasives)
▪Triangular, the most versatile tool shape, can be used to produce a wide range of shapes or forms on a workpiece
▪Square, a strong insert that provides good support for the cutting edge, but cannot produce sharp corners on the workpiece
▪Round, the strongest insert shape, provides more cutting edges than other shapes, but cannot produce corners on the workpiece
ADVANTAGES OF POLYCRYSTALLINE TOOLS
The advantages that PCBN tools offer industry more than offset their initial higher cost, Fig. 3-1-16.
▪Long Tool Life that consistently outperforms conventional tools from 10 to 700% and reduces tool wear, resulting in less machine downtime and dimensionally accurate workpieces.
Fig. 3-1-16 The main advantages of PCBN cutting tools. (Kelmar Associates)
▪High Material Removal Rates that allow higher cutting speeds to be used because tools can withstand the heat and excessive wear encountered.
▪Cuts Hard and Tough Materials including materials of Rc35 hardness and higher and, in some cases can replace grinding, which is a relatively slow material-removal process.
▪High Quality Products that are produced faster and at reduced costs, that reduces the need for frequent inspections.
▪Uniform Surface Finish, often in the single digit microinch range, because of reduced tool wear.
▪Lower Tool Cost per Piece because tools stay sharp longer and cut efficiently, producing longer production runs.
▪Reduced Machine Downtime that results in more machine time spent producing parts and less time spent changing and resetting cutting tools.
TYPES OF MATERIALS MACHINED WITH PCD (COMPAX®) TOOLS
Polycrystalline diamond (PCD) tools are used for turning and milling nonferrous or nonmetallic materials, especially where the workpiece is hard and abrasive. The largest group of nonferrous metals is generally soft, but can have hard particles in them, such as silicon suspended in aluminum or glass fibers in plastic. These hard abrasive particles destroy the cutting edge of conventional tools. PCD tools often have a wear life of 100 times more than cemented carbide tools in such an abrasive machining application.
The materials most successfully machined with PCD tools fall into three general categories: nonferrous metals, nonmetallic materials, and composites, Table 3-1-3.
TYPES OF MATERIALS MACHINED WITH PCBN (BORAZON®) TOOLS
Polycrystalline cubic boron nitride (PCBN) tools are used for turning and milling operations on abrasive, and difficult-to-cut (DTC) materials. PCBN tools can remove material at much higher rates than conventional cutting tools, with far longer tool life. Wherever PCBN cutting tools were used to replace a grinding operation, machining time was greatly reduced because of the higher metal-removal rate.
Table 3-1-3 The materials best suited for machining with PCD cutting tools. (GE Superabrasives)
The best applications for PCBN cutting tools are on materials where conventional cutting-tool edges of cemented carbides and ceramics are breaking down too quickly. Their long-lasting cutting edges are capable of transferring the accuracy of computer controlled machine tools and flexible manufacturing systems, thereby producing accurate parts, increasing productivity, and reducing expensive machine downtime. Table 3-1-4 lists some of the common metals that are machined efficiently with PCBN cutting tools.
Table 3-1-4 PCBN cutting tools are best for machining ferrous metals. (GE Superabrasives)
Compax® is a registered trademark of GE Superabrasives of Worthington, Ohio.
Borazonz® is a registered trademark of GE Superabrasives of Worthington, Ohio.
For more information on SUPERABRASIVE TECHNOLOGY see the Website: www.geplastics.com/superabrasives
(Dr. George C. Ku, Professor – Central Connecticut State University)
PART 1 CARBIDE TOOLING
Among all the manufacturing processes that can be applied to shaping and forming of raw materials into useful products, the machining process has always been one of the most important operations. The fundamental cutting processes in machining, those of bringing the work into contact with the cutting tool, are still very much in evidence and should remain mainstays of the industry.
One of the most important components in the machining process is the cutting tool; its performance will determine the efficiency of the operation. Consequently, much attention has been directed to the selection of the tool materials, the cutting tool angles and their coating materials. Recent demands for high productivity combined with closer tolerance to machine heat resistant materials have made carbide tooling an important aspect of manufacturing technology.
CEMENTED CARBIDES
Cemented carbides are produced by a powder metallurgy process. These cutting tools are largely composed of tiny powder particles of tungsten carbides (carburized tungsten), carbon powder, and cobalt (the binder), that are sintered together at temperatures between 2550 and 2730°F (1400-1500°C). The process for manufacturing cemented-carbide tools involves the steps shown in Fig. 3-2-1.
▪Blending: mixing the right amount of carbide powders and cobalt together for the type of cemented-carbide required.
▪Compacting: molding the green powder into size and shape in a press.
▪Presintering: heating the green compacts to approximately 1500°F (815°C) in a furnace to hold their size and shape.
▪Sintering: the final heating process, 2550 to 2730°F (1400 to 1500°C), to cement the carbide powders into a dense structure of extremely hard crystals.
The powder metallurgy process produces a wide variety of hard metals. Powdered metals such as titanium (Ti), columbium (Cb), tantalum (Ta), and niobium (Nb), are also used in manufacturing cemented carbide to provide cutting tools with various characteristics. Cutting tools made of cemented carbide can increase cutting speed about three to five times faster than those used for high-speed steel tools.
Table 3-2-1 shows the Valenite, Inc., system of uncoated carbide grades used for metal-removal operations on various applications, types of materials, cutting tool characteristics, and machining conditions. Although the coding system may vary from manufacturer to manufacturer, the characteristics and use of