Specific Grinding Energy Research Articles

Quantitative characterization of surface damage to WC-cobalt composites by electrochemical grinding

Electrochemical grinding (ECG) of WC-cobalt cemented carbides leads to poor surface quality which can be attributed to the faster electrochemical dissolution velocity into the cobalt phase than into the carbide phase. A method for measuring the degree and depth of damage in the WC-cobalt surface layer, weakened by preferential electrochemical removal of cobalt after ECG, is developed based upon an analysis of the mechanical grinding transient which occurs after switching off the electrical current for ECG. The degree of weakening is expressed as the ratio of the specific grinding energy of the material in the surface layer to the normal specific grinding energy. It is found that surface damage from ECG can reduce the specific grinding energy by as much as a factor of 10 at the finished surface, and that the depth of the damaged layer is shallower with a lower current density and a faster infeed velocity.

Grinding of Glass: The Mechanics of the Process

An investigation of the material removal process in grinding glass and the effects of the grinding process on the surface structure and fracture strength of the finished product is reported in two papers. This first paper is concerned with the mechanics of material removal for grinding a large number of glasses and some glass-ceramics over a wide range of operating conditions with both silicon carbide and diamond grinding wheels. Experimental results indicate that the specific grinding energy generally increases with the softening temperature of the glass, and is an order of magnitude smaller for grinding with diamond wheels than for grinding with silicon carbide wheels. From observations of individual grinding scratches and an analysis of the experimental results, it is concluded that virtually all of the grinding energy is expended by viscous deformation. Material removal occurs by flow into chips with silicon carbide abrasive and by brittle fracture preceded by viscous deformation with diamond abrasive. The specific grinding energy with diamond is much less than with silicon carbide, since a much smaller volume of material undergoes viscous deformation when grinding with diamond.

Minimum energy in abrasive processes

An investigation is described of the relationship between the grinding energy and the energy required for melting of the workpiece. For a wide range of metals, the minimum specific grinding energy is generally found to be slightly larger than the energy required to melt a unit volume of material. On the basis of a model of grinding energy partition, it is concluded that the specific shearing energy for chip formation during grinding approaches the specific melting energy, which is the maximum allowable value. It is proposed that such a large shearing energy is attained in grinding because of the severe constraint due to having large negative rake angles on the abrasive grains.

An Experimental Study of Thermal Aspects of Cylindrical Plunge Grinding

The workpiece temperature in cylindrical plunge grinding is considered as a superposition of a base temperature and an interference zone temperature. A solution for the transient base temperature distribution is derived. A two-part experiment for determining thermal effects is described. The heat transfer coefficient at the workpiece surface is measured in the first part, and specific grinding energy and workpiece temperature are measured in the second part. The energy entering the workpiece during grinding is determined from the base temperature solution and experimental data. Results obtained with several grinding fluids and application systems are presented. The energy entering the workpiece was found to be 75 to 85 percent of the total grinding energy during dry grinding and 25 to 35 percent during wet grinding.

Effects of Grain Size and Operating Parameters on the Mechanics of Grinding

An investigation is described of the effects of grain size and operating parameters on the mechanics of grinding. Results indicate that the specific cutting energy in grinding, which is the total specific grinding energy minus the specific energy due to sliding between the wear flats and the workpiece, is independent of grain size and decreases with increasing table speed and downfeed. It is postulated that the specific cutting energy consists of chip forming energy which is independent of table speed and downfeed, and plowing energy which decreases with increasing table speed and downfeed. Results for G-ratio, surface finish, and burning conditions are also presented. Of particular interest are the effects of grain size on burning conditions. With finer grain size, burning occurs at larger wear flat area and energy input per unit area ground, but the G-ratio and grinding wheel tool life are less. This is related to increased attritious wear with finer grains.

プランヂカット研削法の研究(第2報)

Using the appaiatus reported in the previous paper, the author measured the grinding forces with "through wheel coolant" supply. The pieces of annealed carbon steel (Hv 132) and hardened high speed steel (Hv 800) were ground with various coolants ; water, emulsion, kerosene and soybean oil, besides dry grinding reference. The results obtained are as follows:1) Specific grinding energy varies remarkably with the change of coolant which is fed through the wheel. In grinding annealed carbon steel pieces by a A46N wheel, the specific grinding energy with soybean oil is about half of that with water or dry grinding, as shown in Table 1.2) Analysing the tangential grinding forces in the way reported in the previous paper, the values of the coefficient of friction in grinding are determined as shown in Table 2. When soybean oil is used, they become as small as one third of those in dry grinding.3) Specific shearing forces are calculated numerically as pure shearing forces of chips. For hardened high speed steel, they are about 4000 kg/mm2 ; and for annealed carbon steel, they are about 2000 kg/mm2.4) Experimental formulae representing the grinding forces are introduced for various coolants and work materials. And also the ratios of the shearing terms to the total forces are calculated as shown in Fig. 8.

Surface Temperatures in Grinding

Abstract Heat-transfer theory involving a moving heat source is applied to the grinding process to obtain an equation for the mean surface temperature in grinding. This equation predicts surface temperatures as high as 3000 F for a representative fine grinding operation. The analysis shows that in finish-grinding the surface temperature is reduced by decreasing the chip depth of cut but in snagging operations the surface temperature may be reduced by increasing the chip depth of cut. Representative values of the mean temperature between the chip and the grinding wheel obtained by the toolwork thermocouple technique are presented and discussed. The role of the grinding atmosphere in the production of sparks and in determining the energy involved in grinding is illustrated by experimental data. When the oxygen concentration of the atmosphere is very low, the specific grinding energy is found to be unusually high. The existence of high surface temperatures in fine grinding operations is demonstrated by the presence of a transformed surface layer that is largely retained austenite.