8.1. Grinding New
Techniques for Grinding Sintered Carbides. E. Zmihorski. Machinery (London), v. 93, Nov. 19, 1958, p. 1186-1188. New method of rough grinding involves raising the temperature of the part to be ground to within 750 to 850°C, and maintaining it at this temperature during grinding. It has been found that at this temperature the sintered carbides are considerably less brittle, and, consequently, less prone to craze cracking. Basic Tests of Grinding Wheel Hardness. P. Roy Leaman. Tooling G Production, v. 24, no. 12, Mar. 1959, p. 63-64. Describes testing by use of tone or sound, density or penetration methods. The Influence of Different Factors on Metal Removal and Abrasive Consumption in Grinding Steel With Pendulum Grinding Machines. (in Swedish) Gunnar Wallquist, Bo Hamrin, and Hans Lund. Jernkontorets Annalau, v. 152, no. 9, 1958, p. 541-569. The influence of different factors on the metal removal and the consumption of abrasives during grinding of rolled steel billets with pendulum grinding machines were determined at several Swedish steel works. Nineteen grintling wheels of different types were tested, and of these five were investigated in detail at grinding pressures of 80, IOO, and 120 kg and at wheel periphery speeds of 35, 40, 45, and 50 mjsec. 8.2. Drilling Hard Metal-The New Rock Drilling Medium. L. S. Cole. Australasian Engineer, 1959, Jan. 7. P. 70 + 2 pages. In percussion drilling, the average drilling “life” of a forged steel or detachable head is about 42 inches. A hard metal tip can be used at greater drilling speeds and has an average life of about 35 feet before re-sharpening is necessary. Describes manufacture and use of hard-metal tips. Vibration Drilling Gets Further Study. Ralph Simon. Drilling, v. 20, Feb. 1959, p. 110. Drilling by vibration is accomplished by superimposing longitudinal vibrations onto the drill bit of an otherwise conventional rotary drilling system. A number of laboratory and field models of vibratory drilling machines have been designed, constructed, and used experimentally. The latest version encompasses a magnetostriction transducer that follows a
AND TOOL WEAR 101/s-in. rotary bit down the hole. It is tentatively concluded that vibratory drilling in rock of medium hardness may be just about economically competitive with conventional drilling.
8.3. Machining Equipment Requirements for Machining. H. J. Siekmann. Tool Engineer,
v. 42, no.
1959, p. 49-52. Ceramic tools can cut four times as fast as carbides. In order to utilize this potential productivity, machine tools of new design are required. Characteristics of such machines are outlined.
Electra-Erosion Machining of Cemented Carbides. (in Czech) V. Vicha. Stvojirenskri V’jroba, v. 7, no. I, 1959, p. *r-14. Basic data about the method and examples of the process of machining various parts. Hard Spots in the Machined Surface. Antoni Niedzwiedski. Tooling & Production, v. 24, no. 11, Mar. 1959, p. 57-59. Tries to explain how, while machining with feeds too fine, the cutting edges of milling cutters may slide over instead of cut the machined metal. These sliding cutting edges cold work the machined surface and thus form the hard spots. The very common phenomenon in finish milling steel with HSS milling cutters, known usually under the shop name of “hard of spots”, might not be due to any property the machined metal, but simply to certain inappropriate working conditions. 8.4. Tool Wem A Photo-Elastic Analysis of Machining Stresses on Rake Face. Eiji Usui and Hidehiko Takeyama. Journal of Mechanical Laboratory of Japan, v. 4, no. 1, 1958, p. 6-14. The stress distributions on the rake face were successfully determined photo-elastically by using a tool made of epoxy resin. The frictional stress on the rake face is uniform over a wide range of the tool-chip contact area regardless of the varying normal stress thereon, but it decreases steeply near the point of chipseparation. Friction on Relief Face of Cutting Tool. M. Okoshi and T. Sata. J. Sci. Research Inst. (Tokyo), v. 52, I)ec. 1958; 7 fig., 3 ref. Friction on the relief face of cutting tools is discussed in comparison with that on the rake face. Two components of the cutting force, shear angle and contact length on the