of cast iron products. Many metal makers use a modifica- tion of the ISO 3685-1977(E) cutting tool life test in turning of wrought and cast bars. A modified cutting tool life test is being used by mem- bers of the Bar Machinability Subcommittee of the Steel Market Development Institute (a business unit of the American Iron and Steel Institute). Te steel makers have developed a database of machinability values for automotive bar steel for 36 carbon, alloy, resulfurized and microalloyed steel grades. Finn’s research took a similar approach. Face turning cast discs, however, required factorial designed tests to determine the optimum cutting tool type and geometry that wore the cutting tool uniformly without catastrophic failure. Additional studies were required to optimize the depth of cut (DOC). A compromise DOC was selected that would not rotate the disc in the chuck and wear the cutting tool edge enough to measure under a microscope. Cutting fluid type and machining parameters were also optimized to effectively and economically measure the machinability val- ues. Finn and his group determined the machinability values for five grades of gray and ductile cast iron, while AFS compiled values for other grades from metalcasters using the new testing procedure. In the methodology, the metal to be tested is cast into a sand mold in the shape of an 8-in. (20.3-cm) diameter circular disc that is 1.5-in. (5.1-cm) thick. The disc has a 2-in. (5.1-cm) diameter and 1.25-in. (3.2-cm) long hub for gripping in the chuck of a CNC center (Fig. 1). The interface of the cutting tool in contact with the workpiece disc is flooded with a 5 volume percent, water soluble oil cutting fluid to help maintain a constant tem- perature at the tip of the cutting tool between interrup- tions of the facing passes. An uncoated tungsten carbide insert is located in a cutting tool holder with a zero degree lead to minimize wear and catastrophic failure of the nose. The insert has a rhombic shape with an interior 0.5-in. (12.7 mm) diameter with a thickness of 0.1875 in. (4.76-mm), zero degree relief and a 0.03125-in. (0.8- mm) diameter nose radius. Te cutting tool catalog numbers used in developing the


machinability testing methodology are given in the user’s manual, although it may be necessary to select other sizes and grades for other ferrous and nonferrous castings. Te sizes and grades may be selected based on the following con- siderations: • Select simple geometries • Select simple chip breakers that minimize built-up-edge • Select nose radii that are less than the depth of cut • Select lead angles that minimize cutting with the nose of the cutting tool insert and wear the flank uniformly to the depth of notch. A minimum of three cutting speeds with a feed rate of 0.008 ipr (0.203mm/rev) and depth of cut of 0.075 in. (1.91 mm) are used in the testing. Cutting speeds listed in machining handbooks are used to select the following: • Low cutting speed that provides a tool life of 60 minutes • High cutting speed that provides a tool life of 10 or more minutes


60 | MODERN CASTING March 2013


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