Tokio Morimoto

Work hardening and tool surface damage in burnishing

Abstract Work hardening of the surface and subsurface of an annealed steel bar burnished using a simple newly designed tool system and also the reduction in dimensions of the workpiece accompanying burnishing are investigated in this paper. The influence of the burnishing force, number of passes of the burnishing tool across the surface and feed rate on work hardening are examined. Furthermore, the tool surface is inspected and the retainer surface is examined using an electron probe microanalyser to identify the particles that scratch the tool surface: some of which are embedded in the retainer surface. The hardness of the material at the surface and in the subsurface is materially increased by burnishing. In particular, the burnishing force has the greatest influence on work hardening the surface and subsurface. The work-hardened layer beneath the surface often attains a depth of more than 200 μm.

Friction and wear in silicon nitride-steel and cemented carbide-steel pairs in lubricated sliding

Friction and wear tests between a stationary block and a rotating ring under high contact pressure of about 200 MPa were carried out at room temperature under lubrication with a light mineral oil at a sliding distance of 500 m. The block was silicon nitride and cemented carbide, and the ring was bearing steel. The effect of phosphorus and sulphur contained in the mineral oil on the friction, the roughness of the worn surface and the wear of the steel ring is discussed in relation to both pairs. Sulphur was effective in reducing the coefficient of friction of the cemented carbide block-steel ring pair, while phosphorus was successful in decreasing the wear of the steel ring paired with the silicon nitride block. The surface analysis of the steel ring using X-ray photoelectron spectroscopy (XPS) shows that the peak intensities of sulphur or phosphorus beneath the surface depend upon the material of the counterpart, silicon nitride or cemented carbide blocks.

Burnishing process using a rotating ball-tool — effect of tool material on the burnishing process

Abstract The cylindrical, machined surface of a steel bar was burnished under a rolling contact using a lathe and using a ball as a tool, i.e. a ball-tool; the ball-tool was rotated by the drive of the workpiece mounted on the lathe. To investigate the effect of the tool material on the burnishing process, five types of ball-tools, i.e. cemented carbide, silicon nitride, silicon carbide, alumina ceramic, and bearing steel were used. The burnishing force pressing the ball-tool against the workpiece ranged from 5 to 170 N and the burnishing speed was 100 m min −1 . Although the burnishing (or running) distance was usually short, less than 100 m, the influence of the burnishing distance on the burnishing process was also examined by long-distance burnishing processes, continuously extending over a distance of up to 760 m. The cemented carbide ball-tool accomplished the best results among all types of ball-tools used; it produced the smoothest surface and its own surface was hardly damaged after use for long-distance burnishing. The silicon nitride ceramic ball-tool also produced a smooth surface. Neither, the silicon carbide nor the alumina ceramic ball-tool gave satisfactory results.

Examination of the burnishing process using a newly-designed tool

Abstract The cylindrical surface of a mild steel bar has been burnished by a simple newly-designed tool system using a lathe: the burnishing tool is a commercially available cemented carbide ball, elastically supported by a spring and rotated by the drive of the workpiece. The influence of the burnishing force, tool feed, burnishing speed, tool size, lubricants, number of passes of the tool and supporting methods for the tool on the roughness of the finished surface are examined. The burnishing process can be carried out at speeds of up to 400 m min − . The roughness of the machined surface, of about R max = 8 μ m, was found to have decreased to R max μ m when burnishing with one pass of the tool, whilst it reduced to R max μ m when burnishing with repeated passes of the tool.

Effect of tricresyl phosphate on wear of silicon nitride sliding against bearing steel

Abstract Wear tests of a silicon nitride ball pressed against a bearing steel rod were carried out at room temperature under lubrication with a light mineral oil using a lathe. The wear of the Si3N4 ball was measured at various fixed sliding distances up to a maximum distance of 3000 m. A mineral oil of low viscosity (base oil), and a mineral oil containing different amounts of phosphorus (added as tricresyl phosphate) and 0.2 wt.% S were supplied to the contact region between the Si3N4 ball and the steel rod. An addition of 0.5 wt.% P to the base oil reduced the wear volume of the Si3N4 ball by about 90% of that with the base oil. The reduction in the wear is ascribed to surface film formation. When using the base oil alone, the wear of the Si3N4 ball decreased more at high sliding velocities than at low sliding velocities.

Effect of Lubricant Fluid on Burnishing Process

A burnishing experiment is performed by forcing a cemented carbide ball or a steel ball through a slightly undersized machined hole, which is the so-called ballizing. The effect of lubricant fluid is studied with the measured ballizing force for steel workpieces. It is found that the viscosity of the fluid has the most marked influence on the process. The deformation of the workpiece material in the surface layer and the state of the tool and the material interface in the process arc also examined. The following observations are made; (1) the height of bulge in front of the tool reaches a few times as large as the finishing allowance and it also depends on the viscosity of the fluid. (2) the “micro shear-flow layer” exists at the burnished material surface, and (3) the effect of the viscosity on the working force and the bulge of the material etc. is closely related with the “micro shear-flow layer”.

Effect of lubricant fluid on the burnishing process using a rotating ball-tool

Abstract A cylindrical surface of a medium carbon steel bar is burnished using a lathe and using a ball as a tool, ie a ball-tool. The ball-tool is rotated by the drive of a workpiece mounted on the lathe. To investigate the effects of lubricant on the burnishing process, various mineral oils (low viscosity JIS-VG10, and ores containing separately sulphur and phosphorus as additives) are used for six kinds of ball-tool, ie cemented carbide, bearing steel, silicon nitride, silicon carbide, and alumina ceramic ball-tools. The surface of the ball-tool used is also examined for surface damage by a surface profilometer and analysed using electron probe microanalysis and X-ray photoelectron spectroscopy. Tricresyl phosphate used as a phosphorus additive has an excellent effect of reducing roughness of the burnished surface when the cemented carbide, silicon nitride ceramic and bearing steel ball-tools are used.

Effect of lubricant fluid on plastic metal flow in sliding contact

Abstract Plastic metal flow in surface layers, especially “abnormal metal flow”, in which the direction of metal flow in the inner surface layer is different from that in the layer nearer the surface, in sliding contacts between a pin of cemented carbide and a ring of steel under lubrication is discussed in this paper. Low viscosity mineral oil is used as a base oil. Sulphide and chloride extreme pressure additives are also mixed with the base oil. Such a lubricant has a great influence on the plastic metal flow of a ring. While base oil produces severe plastic metal flow, the sulphide additive causes the plastic metal flow to be very mild. In contrast, a lubricant containing a chloride additive causes abnormal metal flow, where cracks can be seen. Conditions for and causes of abnormal metal flow are investigated.