Mechanics of Conventional Spinning

In conventional spinning of cones, the cone-wall thickness variation was studied using blanks of 1100-0 commercially pure aluminum sheet of 0.050-in. thickness. The results revealed that the radial stress induced in the unspun flange is the major cause of nonuniform wall thickness of spun cones. The theoretical tangential force component was derived by use of the deformation energy method. Qualitative agreement was found between the theoretical and the experimental values of tangential force component in the underspinning conditions.

The Mechanics of the Coining Process

The mechanism of coining is analyzed and several approximate solutions are given. The solutions were based on the strip, slip-line, and upper-bound methods of analysis. Comparison of the solutions for the local stress distribution could only be made for the strip and slip-line methods of analysis and it was found that the particular solutions obtained agreed reasonably well with each other in predicting coining pressures as functions of degree of coining. A comparison of the strip and upper-bound method of solution revealed that the predicted average coining pressures for a single central square groove are nearly identical for blanks having thicknesses of h0 = 1/16 in. for all values of b/b0 (degree of coining) except when b/b0 approaches unity. At b/b0 = 1 (deg of coining = 100 per cent), the modified strip method of analysis, using a cylindrical state of stress in the square corner of the groove, gave the highest average coining pressures. The upper-bound solution seems to overestimate the forging pressures for h0 > 1/16 in. for all values of b/b0, except when b/b0 is unity. A comparison of experimental average pressures, for coining 1-in-diameter blanks of commercially pure lead and aluminum, with the theoretical solutions, revealed that the modified strip method appears to be the best method for predicting the pressures when the ratio of b/b0 approaches unity. However, the exact pressure at b/b0 = 1 is indeterminable by use of this method. The analyses presented in the paper and comparisons of the solutions with experimental data reveal that a lowering of the coefficient of friction has a profound influence on decreasing the required coining pressures. The analyses further show that for high friction the pressure required for getting exact definition rises rapidly as the ratio b/b0 approaches unity.

Flank Friction Studies With Carbide Tools Reveal Sublayer Plastic Flow

Orthogonal cutting tests with artificial flank-wear lands were performed on steel SAE 1112 as-received (cold-drawn), steel SAE 4135 as-received (cold-drawn), aluminum alloy 6061-T6 (extruded), and alpha-brass as cold-drawn. Forces, workpiece temperature, average tool temperatures, and other pertinent data were taken. Each test was of short duration (approximately 10 revolutions of the workpiece or less) and the tools were reconditioned between each test run. The results show that, for steel SAE 1112, steel SAE 4135, and aluminum alloy 6061-T6, sublayer flow appears to take place when the flank wear-land clearance angle is set to a negative angle of magnitude −1 deg and the land is approximately 0.010 to 0.020 in. long. The condition for sublayer flow is predictable based on the state of plastic deformation and the stress-strain properties, at temperature and at appropriate strain rates for these materials.

Metal-Cutting Analysis—I: Re-Evaluation and New Method of Presentation of Theories

The orthogonal metal-cutting process was reanalyzed and the several existing theories are discussed. Alternate methods of presentation of the theories were derived in terms of energy ratios and are shown graphically in the paper.

A Theory of Shear Spinning of Cones

The theoretical deformation mechanism of shear spinning of cones was re-evalued. It was found that the predicted tangential or power spinning forces for commercially pure aluminum and lead for several spinning conditions agreed well with the experimental data. In addition, the normal force and axial force components were also evaluated and fair agreement between theory and experiment was achieved.

A Critical Comparison of Metal-Cutting Theories With New Experimental Data

The following alloys were investigated in orthogonal metal-cutting tests at varying cutting speeds, rake angles, and feeds: Steel SAE 1112 annealed and as-received; steel SAE 1020 as-received; steel SAE 4135, annealed, as-received, and Rockwell hardnesses 27 and 35–37; aluminum alloy 2024-T4; aluminum alloy 6061 in the 0 and T6 conditions; alpha brass. The new data obtained in the present investigation under wide variation of test conditions (speed for SAE 1112 annealed and as-received was varied from 0.083–1010 fpm) confirmed earlier observations [1, 3] that the shearing stresses are independent of the test conditions investigated. These observations were supported by theoretical considerations. Correlation of metal-cutting data with compression data on the basis of the incremental or distortion-energy theory was good for the ductile metals. Less perfect correlation was observed with SAE steel 4135 and aluminum alloy 2024-T4. It was found further that none of the known theoretical angle relationships were in agreement with all of the experimental data.

The Role of Friction in Metal Cutting

Metal-cutting studies were made with free-cutting steel SAE 1112 and alloy steel SAE 4135 in the as-received condition with artificially controlled tool-chip contact areas and flank contact areas (artificial wear lands). The experimental results for steel SAE 1112 at a speed range of 0.083 to 1010 fpm, reveal that friction under metal-cutting conditions on the rake face can be explained satisfactorily by a junction model with possible superimposed general plastic flow above the junctions in accordance with the general rules of plastic deformation (von Mises instantaneous yield criterion). The experimental results also reveal that the friction mechanism at the controlled flank-wear contact area is essentially the same as that occurring at the tool face. The difference in behavior of the two steels was attributed to the role that manganese sulfide appears to play in free-cutting steels.

Some Observations on the Shearing Process in Metal Cutting

It was found that shearing forces on the shear plane were linear functions of the area on which they acted. This was observed for all materials investigated; for SAE 1112 steel, 2024-T4, and 6061-T6 aluminum alloys, and alpha-brass, and also is in agreement with data taken from the literature. Furthermore, all data examined showed that the straight line of shear force Fs versus area As intercepted the ordinate at a positive force value. This was interpreted to mean that the intercept part of the shearing force was used up in overcoming workpiece deformation or friction at the flank of the tool and was not available for chip deformation. Accepting this concept, it can then be shown that the average shearing stress on the shear plane for SAE 1112 is constant and is independent of normal stress, cutting speed, or strain rate, extent of deformation or finite strain, and extent of prior deformation. The shearing stresses for the other materials tested or examined were also constant for the limited range of variables available.

In contrast to the shearing stress, the normal stress on the shear plane was not constant and appears to be a yet unknown function of the mechanism of friction on the tool face.

The shearing stresses calculated from the metal-cutting data showed good correlation with flow stresses at the same finite strains which were obtained from static compression tests. The reason for the uniqueness of the finite strains at which correlation is achieved is not as yet clear.