Alumina Wheel Research Articles

Temperature control in CBN grinding

The main advantage of CBN grinding wheels is the long wheel life owing to the hardness of the CBN abrasive. Recent research has confirmed another advantage of CBN, which is cooler grinding. The new research allows the temperature in grinding to be predicted based on experimentally validated CBN thermal properties. This work also provides for in-process prevention of thermal damage in grinding. A well-documented feature of CBN grinding is the reduced risk of thermal damage to the workpiece. This advantage can allow a marked increase in removal rate whilst maintaining surface quality of the component compared to grinding with conventional abrasives such as aluminium oxide. The reduced risk of thermal damage in CBN grinding is sometimes attributed to the lower grinding specific energies. While lower specific energies when achieved are an advantage, this explanation ignores a fundamental advantage of the CBN abrasive. The experimental investigation has shown that a major advantage of CBN grinding is that a substantially lower proportion of the total grinding energy enters the workpiece compared to grinding with alumina wheels. The results further indicate that the effective thermal conductivity of CBN grains is considerably lower than its reported theoretical value of 1300 W(mK)−1.

Slot and Vertical Face Grinding of Aerospace Components

Workpiece profile accuracy, wheel wear, and thermal damage were investigated for the grinding of slots and vertical faces on MAR-M-247, Inconel 713C, and M-2 tool steel using both alumina and cubic boron nitride (CBN) grinding wheels. It was found when grinding with alumina wheels that the wheel corner and first 2.5 mm of the grinding wheel sidewall account for all the grinding forces in the vertical, horizontal, and transverse directions, and therefore is responsible for all the significant grinding done on the sideface of the workpiece. Since previous work links wheel wear and workpiece thermal damage during grinding to grinding forces, this finding suggests that the area around the wheel corner is the critical region of importance in grinding these types of profiles in terms of wheel wear and the heat input to the workpiece. These, in turn, are linked to workpiece profile accuracy and metallurgical damage. Results also show that striation marks inherent in sidewall grinding can be minimized by controlling the maximum normal infeed rate of the wheel. A method for minimizing the heat input into the workpiece by minimizing grinding force during vertical face grinding is also reported.

Inverse Heat Transfer Analysis of Grinding, Part 1: Methods

Thermal analyses of the grinding process generally require assumptions concerning the distributions of the heat flux to the workpiece within the grinding zone and convective cooling outside the grinding zone. The present work is concerned with the use of inverse heat transfer methods to estimate the heat flux and convection heat transfer coefficient distributions on the workpiece surface during straight surface grinding from temperature measurements within the workpiece. In the present paper, three inverse heat transfer methods are developed: temperature matching, integral, and sequential methods. Each method is evaluated for accuracy and stability using simulated temperature data. The selection of the sampling frequency of the temperature measurements and location of the temperature sensor are found to be critical for both estimation accuracy and stability. In a second paper, these inverse heat transfer methods are applied to estimate the distributions of the heat flux and convection heat transfer coefficients on the workpiece surface for grinding of steels with aluminum oxide and CBN abrasive wheels.

Inverse Heat Transfer Analysis of Grinding, Part 2: Applications

Distributions of the heat flux to the workpiece and the convection heat transfer coefficient on the workpiece surface during straight surface grinding are estimated from measured temperatures in the workpiece subsurface using inverse heat transfer methods developed in Part 1. The results indicate that the heat flux to the workpiece is distributed approximately linearly (triangular heat source) along the grinding zone with about 70 to 75 percent of the total energy transported as heat to the workpiece for grinding of steels with a conventional aluminum oxide wheel and only about 20 percent with CBN superabrasive wheels. The wheel-workpiece contact length corresponding to the region of positive heat flux to the workpiece is found to be generally close to but slightly longer than the theoretical geometric contact length. The convection heat transfer coefficient for cooling by the applied grinding fluid is greatest just behind the trailing edge of the grinding zone where fluid is directly applied, and negligible ahead of the grinding zone.

Energy Partition to the Workpiece for Grinding with Aluminum Oxide and CBN Abrasive Wheels

An experimental investigation is reported of the energy partition to the workpiece for grinding of steels with aluminum oxide and cubic boron nitride (CBN) abrasive wheels. The energy input to the workpiece was obtained by measuring the temperature distribution in the workpiece using an embedded thermocouple technique and matching the results with analytically computed values. It was found that 60-75 percent of the grinding energy is transported to the workpiece as heat with an aluminum oxide abrasive wheel, as compared to only about 20 percent with CBN wheels. An analysis of the results indicates that the much lower energy partition to the workpiece with CBN can be attributed to its very high thermal conductivity whereby a significant portion of the grinding heat is transported to the abrasive instead of to the workpiece. The much lower energy partition to the workpiece with CBN wheels results in much lower grinding temperatures and a greatly reduced tendency for thermal damage to the workpiece.

Experimental Investigation of Heat Transfer in Grinding

New findings are presented for temperatures, heat flux distribution and the implications for workpiece damage and partition ratio. Workpiece temperatures were measured using a 25 u.m single pole thermocouple assembly. It was found that the critical temperature for the onset of temper colours for ferrous materials lies within the range 450 to 500 deg.C. Measured temperature distributions in the contact zone compared best with theory assuming a square law heat flux. The effective contact length for vitrified CBN and alumina wheels was confirmed to be greater than the geometric value. Substantially lower partition ratios were found with CBN compared to alumina.

Wear characteristics of nitrogenated chromium cast irons

The effect of only nitrogen and of both nitrogen and titanium together on the abrasive wear resistance of quenched and tempered 12 wt.% Cr cast irons has been evaluated using a modified pin-on-disc machine in which the experimental samples slid under load (22–66 N) against a bonded alumina wheel. The results indicate that the nitrogen addition improves the wear resistance of chromium cast irons provided that the retained austenite content is low (less than 10%). High retained austenite contents lead to deterioration in the wear resistance irrespective of the chromium-to-carbon ratio.

In-Process Measurements of Progressive Variation of Grinding Characteristics in Constant-Load Heavy Grinding

Constant-load heavy grinding was performed on 304 stainless steel with three different alumina wheel types. The variation of grinding characteristics such as removal rate and tangential force with the progress of grinding has been studied using in-process measuring methods. It was obvious that removal rate, wheel rate and tangential force changed remarkably with grinding time, and there are close correlations each other. Wear flat area of abrasive grains were also measured. The variations of grinding characteristics have been explained well with the progressive wear and the generation of self-sharpening.

ステンレス鋼の重研削の進行に伴う研削特性および砥粒切れ刃状態の変動について

In this research, a snag grinding was performed on a 410 stainless steel with two different alumina wheel types under constant load, using a specially made grinding machine. The variation of grinding characteristics such as metal removal rate and grinding force with the progress of grinding has been studied. On the other hand, the protrusion height and wear flat area of abrasive grains on the working surface of wheel were measured to discuss the results obtained on grinding characteristics. A close correlation was found among the variation of abrasive protrusion height, metal removal rate and tangential grinding force. Also, it was known that the wear area of grains increases with increasing grinding time. The attritious wear was accompanied with reductions of metal removal rate and tangential grinding force. Self-sharpening recovered the abrasive protrusion height and diminished the percent wear flat; this enhanced to improve the metal removal rate and a cutting action by an individual abrasive grain.

Thermal Aspects of Grinding: The Effect of Heat Generation at the Shear Planes

The model of heat transfer in the grinding zone which had been previously developed by the author has been modified to account for the fact that some of the grinding energy is generated at the shear planes. Examples are given to evaluate how much error was incurred in making the earlier simplification that all the heat is generated at the wear flat areas. For grinding with aluminum oxide wheels, it is found that the error is typically not huge, but may be significant, depending on the grinding conditions. For grinding with CBN wheels, however, the error is very important.

Investigations on Laser Dressing of Grinding Wheels—Part II: Grinding Performance of a Laser Dressed Aluminum Oxide Wheel

Based on the results of the preliminary study on the influence of high intensity Nd: YAG laser radiation on grinding wheel constituents, an experimental set-up for dressing a grinding wheel was made. Studies were carried out to evaluate the performance of a laser dressed Al2O3 wheel in surface grinding under dry cutting conditions. Results confirmed the viability of this approach and indicated the existence of an optimal dressing condition for good results.

Surface Integrity of Grinding of Bearing Steel GCr15 with CBN Wheels

This paper gives the investigation on surface integrity of grinding of hardened bearing steel GCr15 with resin bonded cubic boron-nitride (CBN) wheels. CBN wheels, when well dressed, offer significant advantages compared with aluminium oxide wheels, especially at high metal-removal rates. The compressive residual stresses are only produced when CBN wheels are used, the harmful tensile residual stresses are formed very easily with aluminium oxide wheels. However, CBN wheels after dressing with SiC stick cannot get a good result, serious thermal damage and big surface roughness are induced on the ground surface. Two new dressing techniques— elastic dressing and ultrasonic vibration dressing have been advanced, they are successful in well dressing CBN wheels and make the wheels have a strong cutting capacity to obtain higher ground surface integrity. Our experiments show that in dry grinding of bearing steel GCr15 with CBN wheels boronization takes place, it can increase wear-resistance of the ground surface about 30%.

Thermal Aspects of Grinding with CBN Wheels

When grinding with CBN wheels, thermal damage is unlikely at the removal rates normally used in production. This decreased thermal damage with CBN wheels as compared with aluminum oxide wheels is usually attributed to the lower specific energies with CBN. Another contributing factor is the very high thermal conductivity of CBN, which enhances conduction into the grains. This beneficial effect may be offset by the sharpness of the CBN grains, which lowers the area over which conduct ion occurs. This paper presents a model of the thermal aspects of grinding which predicts the critical removal rate at which workpiece burn occurs. The effects of specific grinding energy, grain thermal conductivity, and wear flat area are explored. The model suggests that conduction into the CBN grains has the potential to increase the critical removal rate by a factor of 20 or more.

Surface-Technological Analysis of Metal Adhesion on Tungsten Carbide Tool and Prevention of Brittle Fracture due to Metal Adhesion

The objective of this study is to clarify the mechanism of metal adhesion on the cutting tool and to propose a recharacterizing methodology of tool surface for preventing its brittle fracture or chipping due to metal adhesion. The WC-Co sintered carbides, of which surfaces have been processed by diamond wheel grinding, aluminium oxide wheel grinding, electrolytic grinding, sandblasting and coating of TiC and TiN, are subjected to cutting tests in order to assess the cutting performances, and to analyzing of adhesive activity to be correlated with them.

切削工具材の表面工学的解析と欠損防止に関する研究 Ｉ 切削工具の凝着欠損に及ぼす工具表面仕上法の影響

The objective of this study is to clarify the mechanism of metal adhesion on the cutting tool and to prevent its brittle fracture due to metal adhesion. The WC-Co cemented carbides, of which surfaces were processed by diamond wheel grinding, aluminum oxide wheel grinding, electrolytic grinding, sandblasting and coating of TiC and TiN, were subjected to cutting tests, in order to assess the tool life in view of brittle fracture due to metal adhesion, and to surface characterization to correlate it with the cutting performance. The important findings are that the surface treatments of carbide tool greatly affect metal adhesion and hence brittle fracture due to metal adhesion, and especially, carbide tools ground with an aluminum oxide wheel exhibit excellent adhesion resistance to yield longer tool life in the sense aforementioned and superior quality of machined surface.

Effects of Impregnation of Grinding Wheel on Grinding Hardened Tool Steel

The high hardness and chemical effects of tool steels M2 and T15 cause a rapid grinding wheel wear and micro structural changes in the ground surface. The performance of sulphur-, wax-, and varnish-impregnated grinding wheels in grinding hardened tool steels M2 and T15 is investigated and compared with the performance of conventional alumina wheels. Impregnation with sulphur had in all cases beneficial effects by decreasing the grinding forces, increasing the maximum metal removal rate, improving surface integrity, and increasing considerably the grinding ratio. It also gave cost saving compared to the plain grinding wheel. The improvement was a result of the sulphur being more efficiently supplied into the chip formation process as compared to using grinding coolant only.

無負荷運転時における研削と石の温度分布と熱変形

This paper deals with the temperature distributions and the thermal deformations of the grinding wheels. The investigated wheels are a conventional vitrified bonded alumina wheel and a CBN wheel. The hub material of CBN wheel is an aluminum alloy. From the experimental results measured with the thermographs, it derived that the temperature of aluminum hub is directly affected by the heat flowed from the rotating wheelspindle. However, the influence of heat flow on the vitrified bonded wheel is restricted to the inner abrasive layer of wheel. This difference of temperature distribution between both wheels can be explained by the differences of the thermal conductivity and the air-cooling ability of the wheels. The distance between both peripheries of CBN wheel and wheel spindle remarkably increases with the increase of wheel running time. It can be considered that this large expansion is almost contributed by the thermal expansion of aluminum hub.

Important Results on External Cylindrical Plunge Grinding with Unusual Workpiece Peripheral Speeds and Speed Ratios q in the Range of -0.2 to -20 000

The speed ratio q is defined as quotient of cutting speed vc and workpiece peripheral speed vft at the principle point D. The speed ratio may be negative or positive (up-grinding or down-grinding). The grinding process is influenced by the speed ratio. The cutting traces of the single grains are nearly circular for high speed ratios and can be extremely cycloidic for low speed ratios. Speed ratios q between 50 and 100 are normally used for most external plunge grinding operations. Important characteristic quantities of the grinding process like workpiece roughness, cutting forces, grinding temperature and wheel wear are presented as functions of the speed ratio For the first time the speed ratio was varied between 0,2 and 20000. The wheel speed and the metal removal rate were constant. The investigations were made with aluminium oxide wheels and with a CBN-wheel in creep feed grinding.

The Surface Roughness Produced when Austenitic Stainless Steel is Ground by Alumina Wheels

It has been shown elsewhere that according to the magnitude of the removal rate, three distinct grinding mechanisms can be observed when austenitic stainless steel is ground by alumina wheels. Using a previously obtained expression relating the CLA roughness to grinding parameters, the observed variation in the surface finish with grinding time, with the effective wheel depth of cut, d, and with wheel parameters is explained qualitatively for each of the grinding mechanisms. When wheel loading occurs (i.e. at the high removal rates) it is found that the relation between the CLA roughness and the effective depth of cut is of the predicted form viz., a power function but the index is greater than 0.3, the value to be expected from the empirically observed relation between the Peak-to-Valley roughness, R t , and the CLA roughness, R a . In fact, with loaded wheels it is found that R a = d 0.78 which, remarkably, is exactly the relation obtained elsewhere when data obtained during high speed grinding was analysed.

Wheel wear when grinding workpieces exhibiting high adhesion

The forms of wheel wear occurring during each of the three grinding mechanisms which can occur when materials exhibiting high adhesion are ground by alumina wheels are examined and it is shown that at very low removal rates, when the grains wear attritiously, the wear occurs via a thermally controlled wear mechanism. At higher removal rates, when workpiece material adheres locally to the grains, the wear occurs via combined thermally and mechanically controlled mechanisms, while at the highest removal rates, when wheel loading occurs, wear is essentially mechanically controlled. It is shown that in this latter form of grinding, the primary source of wheel wear is grain loss from the wheel which occurs when the adherent material becomes detached from the wheel surface. The adherent material is shown to be made up of individual grinding chips which first adhere to the “rake” face of the grains and then to each other to form a compacted mass which, after going through its life cycle, becomes detached from the wheel. The dependence of the longevity of the adherent blocks on grinding conditions is deduced and from this the influence of the factors affecting wheel wear when loading occurs is explained.