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RESEARCH PAPERS

J. Eng. Ind. 1962;84(4):397-404. doi:10.1115/1.3667523.

The upper-bound solution for plane-strain problems is modified and applied to three-dimensional extrusion and piercing. Johnson’s graphical solution is used to solve axisymmetric, eccentric, and two-bar extrusion problems of a lead billet. Kudo’s unit-deforming region approach is employed to solve cylindrical piercing problems of six nonferrous metals. The analytical extrusion pressure is compared with Frisch and Thomsen’s experimental data. A reasonably close agreement is obtained in the first two cases. The calculated piercing pressure is compared with the experimental results of Fukui, et al. A remarkably good agreement is observed for all six cases. Therefore the upper-bound solution after slight modification can be extended to three-dimensional problems in extrusion and piercing. A general conclusion for extending the upper-bound approach to all forming operations cannot be drawn until further study is done along this line.

Commentary by Dr. Valentin Fuster
J. Eng. Ind. 1962;84(4):405-416. doi:10.1115/1.3667524.

Solution of the problem of dynamic stability for the machine tool-cutting process system depends primarily on the assessment of behavior of the cutting process under dynamic conditions. It has been found that under dynamic conditions, apart from force fluctuations due to variations in cutting conditions, additional force fluctuations take place as a result of cyclic variations of the shear angle in the cutting process. Difference in force response of a cutting process to the static dynamic variations of the cutting conditions has been explained by the presence of cyclic variations of shear angle under dynamic conditions. Peaks of the force wave, resulting from dynamic variation of the cutting conditions, are known to be displaced with respect to the originating wave. This displacement has been thought to be due to a time lag of the whole force response; however a sound physical basis for this point of view has not previously been found. The present investigation provides a physical basis for such observations, showing that the displacement of force peaks is caused by the skewing of the force wave by the presence of asymmetric force pulses due to cyclic variations of shear angle. The same event—the cyclic variation of the shear angle—has been recognized to be a sign of instability of the cutting process in itself, resulting in a cyclic chip formation process. Instability of the cutting process in itself has been found to depend mainly on the cutting conditions and not on the dynamic properties of the cutting system. Analytical expressions derived for the frequency and amplitude of cyclic chip formation have been found to be in a good agreement with the results of measurements of these quantities. Study of the effects of dynamic events in metal cutting upon tool life has revealed propagation of fatigue cracks on the wear land. The propagation of the cracks has been found to be in good correlation with the presence of force pulses due to the cyclic chip formation. The way in which the foregoing event affects the tool life has been reconstructed, allowing selection of those conditions which improve tool life.

Commentary by Dr. Valentin Fuster
J. Eng. Ind. 1962;84(4):418-421. doi:10.1115/1.3667527.

A method is given for systematically operating on the equations of motion of a linear dynamic system to produce the equations of a new system of many fewer degrees of freedom. This reduced system has a multiterminal response as close as desired to the original system in a limited frequency range. The result will always be better than that obtained with the normal mode approach and application to damped systems does not result in complex coefficients.

Commentary by Dr. Valentin Fuster
J. Eng. Ind. 1962;84(4):423-427. doi:10.1115/1.3667532.

Determination of the response time of a solenoid actuated mechanism is complicated by the fact that coil inductance varies with plunger position. In addition, the mechanical force developed by the solenoid is a function of the transient current in the circuit. The mechanism being actuated can introduce further nonlinearities in the displacement-time relationship of the plunger travel. This paper sets forth the dynamic relations governing this electromechanical system. A program utilizing the measured magnetization characteristics of the solenoid and a numerical integration technique has been mechanized on a digital computer. The effects of variation of certain design parameters on the response of the mechanisms are shown.

Commentary by Dr. Valentin Fuster
J. Eng. Ind. 1962;84(4):431-441. doi:10.1115/1.3667538.

Equipment and procedures for test grinding abrasive disks and for coating such disks in the laboratory are described. Criteria useful in evaluating performance are defined and discussed. Discard criteria for worn disks are analyzed and the suggestion made that the effective life of the disk ends when the cutting rate is some specified percentage of its initial cutting rate. This paper is the first of a series dealing with the mechanism of the cutting action of abrasive disks.

Commentary by Dr. Valentin Fuster
J. Eng. Ind. 1962;84(4):442-450. doi:10.1115/1.3667539.

Performance data for 24-grit aluminum oxide disks on mild steel and on stainless steel are presented. The dressing mechanisms are shown to be different on mild steel and on stainless steel since the whole grit is the cutting tool on mild steel while micropoints are the cutting tools on stainless steel. It is shown that the total weight of metal removed during the life of the disk depends primarily on how long the dressing mechanism continues to function, and that erect grain orientation favors dressing on mild steel but is not a factor in dressing on stainless steel.

Commentary by Dr. Valentin Fuster
J. Eng. Ind. 1962;84(4):451-465. doi:10.1115/1.3667540.

It is shown that the worn surface of a grit has a camber which causes decreasing depth of cut, leading to glazing. Orthogonal cutting theory is modified accordingly and equations are developed for rate of cut and for total metal removed. It is shown that erect grain orientation favors high rate of cut on mild steel but is not a major factor in rate of cut on stainless steel. It is predicted that decreasing the number of active grits will improve disk performance up to the point where dressing becomes excessive.

Commentary by Dr. Valentin Fuster
J. Eng. Ind. 1962;84(4):466-476. doi:10.1115/1.3667541.

Variations in power during disk grinding have been explained and equations developed to represent the power in terms of the grinding variables. It has been shown that depth of cut is below the critical magnitude so that ultimate shear strength of the metal is involved for all but the initial 30 to 120 seconds of grinding. It has also been shown that the coefficient of friction is higher against stainless steel than against mild steel, and that the basic differences in performance and mechanism on these two metals originate in this property. Photomicrographs of microflats are shown. The mechanism of microdressing is explained in terms of thermal shock and mechanical impact in relation to the effect of applied load upon grinding efficiency.

Commentary by Dr. Valentin Fuster
J. Eng. Ind. 1962;84(4):483-489. doi:10.1115/1.3667547.

The effects of electrolytic grinding on surface conditions and residual stress characteristics has been experimentally investigated. Surface finish, uniformity of material removal, and corrosion resistance are found to be dependent on mechanical removal rate as determined by wheel downfeed as well as electrolyte flow rate. Downfeeds of approximately 0.002 in. in the process do not produce measurable residual stresses and therefore it was further established that electrolytic grinding with moderate downfeeds can be used in place of swab etching techniques for evaluation of residual stress distributions. The maximum residual surface stresses were found to be not more than 22,000 psi, well below the yield strength of the material and were induced during the most severe grinding conditions.

Commentary by Dr. Valentin Fuster
J. Eng. Ind. 1962;84(4):491-501. doi:10.1115/1.3667550.

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.

Commentary by Dr. Valentin Fuster
J. Eng. Ind. 1962;84(4):502-508. doi:10.1115/1.3667553.

Coining with a superimposed vibrational load of 800 lb and with a relatively low frequency of 130 cps was investigated. The materials were commercially pure lead and aluminum which were chosen to give an indication of the coinability during hot-working and cold-working, respectively. All blanks had a constant diameter d0 = 1 in. and three initial thicknesses h0 to give ratios h0 /d0 , of 0.250, 0.125, and 0.0625. The definition or degree of coining and surface finish was examined when coining these materials with three punches which were provided with different grooves of equal width. The shapes of the grooves had the following cross section: square, triangular, and semicircular. It was found that superimposed vibration upon static loading reduces the peak pressure required for the same degree of coining (measure of definition) significantly for dry lead, but to a lesser degree for dry aluminum. The improvements for h0 /d0 = 0.0625 were 30 to 35 per cent for lead and 5 to 7 per cent for aluminum. It was also found that unlubricated specimens give a better surface finish and that the tendency to form folds, as is observed at times with lubricated blanks, at the point of coring, apparently is eliminated.

Commentary by Dr. Valentin Fuster

DISCUSSIONS

Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster

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