Optimum Clearance in the Microblanking of Thin Foil of Austenitic Stainless Steel JIS SUS304 Studied from Shear Cut Surface and Punch Load

An extrusion-type fine blanking with a negative clearance was proposed by the authors instead of standard fine blanking for creating a full-sheared surface in the micro blanking process. In this study, micro blanking experiments and finite element analyses with narrow, zero and negative clearances are carried out for the optimizing the clearance at which a shear cut surface can be finished with a full-sheared surface with the minimized punch load. Fracture criterion, hydrostatic stress and maximum punch stress for the conditions with various clearances are investigated. As a result, it was clarified that the clearance at which the cut surface does not fracture and minimization of the punch load is achieved is gained by the use of clearance −4 μm.

Elucidation of Shearing Mechanism of Finish-type FB and Extrusion-type FB for Thin Foil of JIS SUS304 by Numerical and EBSD Analyses

A numerical analysis using FE (finite element) analysis was performed to clarify the shearing mechanism in the process of extrusion-type fine blanking (FB) for a thin foil of JIS SUS304 in this study. Extrusion-type FB, in which a negative clearance between the punch and the die has been developed and investigated experimentally to improve the quality of the sheared surface in the blanking of thin foils. The resultant sheared surface for extrusion-type FB indicated an almost completely sheared surface, and the fracture portion on the sheared surface was much smaller than that in conventional FB, the so-called finish-type FB. The material flow and fracture criteria in extrusion-type FB were analyzed in comparison with those in finish-type FB. The differences in material flow and so-called critical fracture value were verified for the two processes. The principal stress near the shearing surface has mostly compressive components in extrusion-type FB due to its negative clearance, and the critical fracture value was also less than that in finish-type FB, in which the principal stress near the shearing surface has mostly tensile components. Furthermore, SEM observation with EBSD (electron back-scatter diffraction) analysis of the shearing surface was performed to verify the phenomena. Reductions in deformation-induced crystal orientation rotation and martensite transformation in extrusion-type FB were confirmed in comparison with those in finish-type FB from the analysis results.

USE OF ADDITIONAL ASSESSMENT CRITERION FOR TRAFFIC SAFETY AGAINST RAILWAY WHEEL DERAILMENT FOR FORENSIC RAILWAY TRANSPORT EXAMINATION

A number of methods have been developed to determine the possibility of a wheelset derailment from track, which to some extent take into account specifics of their interaction. However, methods used in the calculation are different between themselves. The problem is complicated by the lack of sufficient experimental data which would allow to verify the adequacy of models used for calculations. Authors conducted research of an influence of an additional assessment criterion for traffic safety. According to this criterion the railway wheel derailment of a rolling stock was analyzed by actually raising the wheel flange to the railhead. It is noted that increase of the radius of wheels taken into account while calculating indicated criterion depends on transverse displacement of the wheelset, horizontal unevenness, numerical value of the wheel taper profile at the contact point with a rail, and the nominal gaps between the wheel flange and the inner edge of the railhead. On the basis of performed researches, it was concluded that use of an additional criterion, according to which the stability of the wheel from the derailment of a rolling stock is analyzed by actually raising the wheel flange on a railhead, allows to track the time when it is necessary to check the possibility of rolling the wheel on railhead. However, obtaining a negative clearance between the wheel flange and the railhead does not indicate that the wheel is rolling on the railhead. The indicated feature will allow to explore the development of a railway accident mechanism, to define more precisely its proximate technical cause and the sequence of intermediate technical reasons which have led to it.

Cutting Tool Parameters of Cylindrical Skiving Cutter With Sharpening Angle for Internal Gears

Gear skiving is a technique proposed a long time ago for cutting internal gears at high productivity. Until recently, many problems have prevented its widespread use. With current technological breakthroughs, however, skiving is drawing attention again. The present paper describes cutting tool parameters, which could be vital for the optimum design of skiving cutters. Cutting tool parameters include depth of cut, rake angle, and clearance angle at each point on a cutting edge. They continuously change with progress in the cutting process. The parameters are defined on the basis of an oblique cutting model, which is a three-dimensional extension of an orthogonal cutting model. The example calculations in this study revealed the following features: Although rake angles almost always remain negative, clearance angles remain positive. At the points where clearance angles are large, depths of cut are large, but rake angles are small (i.e., largely negative). The decrease in shaft angle between the cutter and working blank axes increases depths of cut and clearance angles, while reducing rake angles (i.e., yields largely negative rake angles). Meanwhile, the increase in cutter tool face offset; i.e., the axial position of a tool face measured from a reference point on the conjugate pinion, narrows the area where depths of cut and clearance angles are small, but rake angles become largely negative. These parameters could be useful for evaluating tool cutting efficiencies in internal gear skiving.

Influence of the Punch Penetration Depth in Half Punching on the Cut Edge after Shaving

Shaving is one of the precision shearing methods used to remove the rollover and fractured surface. The rollover and fractured surface formed in the punching stage are removed by shaving. It is expected that the rollover will be reduced when half punching with a negative clearance is carried out in the punching stage. In this study, the influence of the punch penetration depth in the punching stage on the cut edge after shaving was investigated. The results of this study clarified the followings: When the punch penetration depth in the punching stage with negative clearance is large, the sheared surface obtained by shaving after half punching with negative clearance is larger than that obtained by conventional punching. The sheared surface obtained by shaving after half punching with negative clearance increased with increasing the punch penetration depth in the punching stage with a negative clearance. The rollover produced by shaving after half punching with negative clearance is smaller than that produced by conventional shaving. In addition, the chip produced by shaving after half punching is connected to the sheet material under the punch. From the observed deformation of the chip produced in the shaving stage after half punching with negative clearance, the mechanism of shaving after half punching is considered to be cutting followed by shearing.