Hybrid Burnishing of Cylindrical Workpieces with a Modified Hole Surface
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id Burnishing of Cylindrical Workpieces with a Modified Hole Surface A. V. Shchedrina, V. F. Aleshina, A. A. Bekaeva, *, and N. Yu. Chikhachevab aBauman
bAcademy
Moscow State Technical University, Moscow, Russia of Quality Problems, Comprehensive Secondary School No. 1, Pokrov, Russia *e-mail: [email protected] Received June 29, 2019; revised July 15, 2019; accepted July 31, 2019
Abstract—A refined model is derived for the burnishing forces on hollow cylindrical workpieces when using a tool with regular microgeometry and metal-cladding lubricant. These conditions permit wear-free operation with Garkunov–Kragel’skii friction. Keywords: burnishing force, regular relief DOI: 10.3103/S1068798X20100251
Burnishing is a highly effective technique for hole shaping and finishing [1–3]. Improvement in this method is possible by means of self-organizing tribotechnologies, including regularization of the surface microgeometry (surface modification) for the tool and the hole in the workpiece; and the use of innovative metal-cladding lubricants ensuring wear-free operation with Garkunov–Kragel’skii friction [4–10]. That decreases the machining force by 20–40% and doubles the surface quality and productivity. The continuous formation of a protective copper film on the tool surface obviates the need to produce tools from expensive high-speed steel and hard alloys [11–14]. To assess the gain in efficiency on regularizing the surface microgeometry of the holes, we conduct experiments on the burnishing of LS 59-1 brass bushes (hardness 115 НВ; external diameter 39 mm; height 40 mm), by analogy with [14]. As a preliminary, holes with irregular microrelief (surface roughness Ra = 0.24–0.92 μm) are reamed. In Fig. 1a, we show a typical longitudinal profile of the irregular microrelief for the hole surface after reaming. The tool used is a Р6М5 steel mandrel (diameter 20.2 mm), with 5° vertex angles of the working and inverse cones and width 7 mm of the calibration strip. The working surface is strengthened by means of regular microrelief (single-turn helical channels of radius 1.5 mm, pitch 0.5 mm, and initial depth 8 μm in the calibration strip) [6]. The rated absolute deformation in terms of the diameter of the hole surface is ira = 0.1– 0.3 mm. The burnishing rate is 0.05 m/min. Two lubricants are employed: I-40 mineral oil; and a mixture of I-40 oil with 10 vol % Valena multifunctional metal-cladding additive, which ensures wear-free
operation with Garkunov–Kragel’skii friction [7–9]. At the hole surface in the workpieces, regular microrelief is applied in the form of single-turn helical channels of radius 1.5 mm, pitch 1 mm, and depth dch = 10 (Fig. 1b) and 20 μm (Fig. 1c). In Fig. 2, we plot the unit burnishing force qb against the absolute actual strain iac, for different surface microgeometry and different lubricant. Analysis shows that, together with the metal-cladding lubricant, the regular microrelief of the hole surface ensures minimum unit force qb within the narrow range ira = 0.16–0.19 mm. This is explained by the greater
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