Workpiece Burn Research Articles

Selections of working conditions for creep feed grinding. Part(III): avoidance of the workpiece burning by using improved BP neural network

In this study, the grinding force of the creep feed grinding are modeled and forecasted by using the improved back propagation neural (BPN) network. The results show that the grinding energy can be accurately predicted by the application of the grinding force model. Due to the previous paper, the workpiece burning occurs as the grinding energy is greater than the critical grinding. Thus, a judgment for the occurrence of the workpiece burning can be achieved. Comparing with the experimental results, the applied algorithm of the improved BPN network is proved to be effective in forecasting the working conditions of the workpiece burning. Thus, a selection scheme of working conditions in view of the avoidance of the workpiece burning is further developed. Considering the working efficiency, the working conditions are selected to maximum metal removed rate, MRRmax. The results show that a larger size of wheel is available to have a better working efficiency.

Automatic detection of thermal damage in grinding process by artificial neural network

This work aims to develop an intelligent system for detecting the workpiece burn in the surface grinding process by utilizing a multi-perceptron neural network trained to generalize the process and, in turn, obtnaing the burning threshold. In general, the burning occurrence in grinding process can be detected by the DPO and FKS parameters. However, these ones were not efficient at the grinding conditions used in this work. Acoustic emission and electric power of the grinding wheel drive motor are the input variable and the output variable is the burning occurrence to the neural network. In the experimental work was employed one type of steel (ABNT-1045 annealed) and one type of grinding wheel referred to as TARGA model ART 3TG80.3 NVHB.

A NEW TECHNOLOGY ON ENHANCING HEAT TRANSFER AT GRINDING ZONE THROUGH JET IMPINGEMENT DURING CREEP FEED GRINDING

This paper presents a jet-impingement technology to enhance heat transfer at the grinding zone. The jet-impingement technology uses a new apparatus developed to spray grinding fluid onto the workpiece surface at the grinding zone from the radial holes of an electroplated CBN wheel. Because the fluid is sprayed normally on the workpiece surface at the grinding zone, the heat transfer to the fluid is significantly improved as compared to the conventional fluid delivery methods. Experimental results, obtained under both imitated grinding tests and actual creep-feed grinding of titanium alloys, show that the jet-impingement technology lowers grinding temperature significantly. Much higher material removal rates are possible with jet-impingement without workpiece burn.

Burn threshold of high-carbon steel in high-efficiency deep grinding

The burn-threshold of high-carbon steel (51CrV4) in the high-efficiency deep-grinding (HEDG) process is investigated. It is found that the burn threshold in HEDG is determined by the wheel-workpiece contact length, material removal rate and wheel speed. A theoretical expression for the burn threshold has been derived, which is based on the thermal modelling for deep grinding and takes account of the grinding parameters, wheel conditions, thermal properties of the workpiece and abrasive grain, and the heat convected away by the coolant and chips. The predicted upper and lower boundaries for occurrence of workpiece burn show good agreements with the experimental observations. It is shown that burn threshold in HEDG is related to the film boiling of process coolant and the critical heat flux increases as the specific material removal rate increases. The experiments were carried out on an Edgetek five-axis computer numerical control (CNC) grinding machine, which is capable of HEDG in a relatively wide range of process parameters.

Fundamental studies on enhancing heat transfer in contact zone during high efficiency grinding

On the basis of research on the thermal effect in grinding contact zone during high effi-ciency grinding, an idea of enhancing heat transfer in contact zone using high pressure water jet impinging is advanced. Fundamental heat transfer experiments on enhancing heat transfer with high pressure water jet impinging were completed. The maximum speed of jet impinging reaches 110m/s. The experimental results of transient and steady-state experiment prove that the critical heat flux and the heat-transfer coefficient of water jet impinging are 70 and 30 times those of the pool boiling, respectively. Furthermore, a new grinding fluid supply system was employed to en-hance heat transfer in grinding zone by high-pressure water jet impingement during creep feed grinding. The experimental results show that high-pressure water jet impinging has remarkable cooling effect. The temperature of the workpiece surface can be steadily kept below 100℃, while the workpiece is badly burnt with conventional coolant supply. The study will exploit an important research orientation that has great potentialities in the high efficiency grinding. Further perfection of this study will not only enable us to increase the available material removal rate to a new level but also solve the workpiece burn problem of the difficult-to-machining materials in high efficiency grinding,

Thermal analysis of creep-feed grinding

One of the major problems encountered in industrial experience of creep-feed grinding is thermal damage to the workpiece and grinding wheel. Thus, the application of cutting fluids is especially crucial. In this paper an analytical model of the heat transfer between the wheel, the workpiece surface and the grinding fluids is derived and verified. The model enables the prediction of the maximum surface temperature when grinding fluids are applied, demonstrates the thermal energy partitions between the abrasive wheel, the cutting fluids and the workpiece, and also determines the threshold of the occurrence of film-boiling. Despite its simplicity, the model provides remarkable agreement with published data from experimental investigations and from finite-element analysis, for various creep-feed grinding conditions. The cooling effect of water-based grinding fluids is better than that of oil-based cutting fluids, but the resistance to workpiece burning using water-based cutting fluids is worse than that using oil-based cutting fluids. When cutting fluids are applied in the grinding process, the strong cooling effect of the cutting fluids is apparent. In addition, a CBN grinding wheel shows a better performance than an Al 2O 3 grinding wheel in the avoidance of workpiece burning. The cooling effect of grinding fluid, R c, can be improved by decreasing the effective contact ratio. In general, this effective contact ratio can be achieved by selecting a grinding wheel with a higher porosity of structure number. Further, a shorter dressing time-interval is a better choice for decreasing the wear flat area and thus for improving the cooling effect of the coolant on the workpiece.

Optimal planning of an adaptively controlled robotic disk grinding process

In this paper, an adaptive control optimization (ACO) robotic grinding system is described. An industrial robot equipped with a pneumatic grinder, a six degree-of-freedom force sensor, and two non-contact inductive proximity sensors inter-linked with a PC are the integrated part of this system. The system is designed to grind the workpiece with maximum possible metal removal rate (MRR) within the constraints on workpiece burn and surface finish which, in turn, depend on the degree of disk dullness. A model-based approach has been used for the optimization. To perform the cutting operation, normal grinding force and robot feed speed have been selected as control parameters. The normal grinding force is effectively tracked on-line using an Adaptive Generalized Predictive Controller (GPC) algorithm, which was experimentally tested. The optimal robot feed speed is tracked due to the robot system's capability to accept on-line end effector path modifications by means of the robot's “ALTER” command. This system is able to plan and efficiently execute a multi-pass grinding sequence for removing large amounts of unwanted material. Several illustrative results are presented that confirm the practical feasibility of the optimization concept and demonstrate the performance of the ACO robotic grinding system.

Establishment of Optimum Grinding Conditions Utilizing the Fuzzy Regression Model.

This paper describes an expert system for grinding operations in order to establish the optimum grinding conditions, which satisfy the maximum removal rates, considering the constraints of grinding power, workpiece burn, chatter vibration, and surface roughness. Specialized knowledge of the grinding operations is acquired from the actual operation database. Coefficients in the experimental equations are obtained through the fuzzy regression model based on fuzzy set theory, and are stored in the actual operation database. The developed system is capable of determining the optimum grinding conditions, taking into account some problems, and practical examples of implementation are described.

Workpiece burn and surface finish during controlled force robotic disk grinding

Workpiece burn and surface finish during robotic disk grinding are studied under controlled force conditions. Workpiece burn occurs due to gradual deterioration in the sharpness of active grains participating in the cutting process. This change in the sharpness of grains can be indirectly monitored by the change in the average coefficient of friction and average depth of cut. Both of these parameters gradually reduce with increasing disk wear due to attrition. In this paper, an analytical expression is derived which can be used to predict the occurrence of such burns during controlled force grinding. The experiments conducted under these conditions using a finely tuned PID controlled showed fair agreement with the predicted results. The experiments also showed that the surface finish gradually improves during successive passes. Hence, an attempt has been made to explain and predict this changing behaviour in the surface finish on the basis of gradual deterioration in the cutting efficiency of the disk. These relations can be used for practical optimization of the robotic grinding process.

Evaluating the performance of “seeded gel” grinding wheels

This investigation was undertaken to compare the performance of grinding wheels containing newly developed “seeded gel” aluminum oxide abrasive with wheels containing conventional monocrystalline aluminum oxide. Experiments were conducted on a computer-controlled instrumented internal grinder over a wide range of removal rates with two dressing conditions on hardened bearing-steel specimens. It was found that wheels containing “seeded gel” abrasive required less grinding power and gave higher grinding ratios than monocrystalline abrasive wheels of the same grade with no significant difference in surface roughness. The potential improvement in productivity using “seeded gel” abrasive wheels was estimated using an optimization program which predicts the maximum possible removal rate subject to constraints on workpiece burn and surface roughness. As compared with monocrystalline abrasive wheels of the same grade, estimated optimal removal rates for “seeded gel” wheels were 15–30% higher while also providing 40–80% higher grinding ratios. With harder grade monocrystalline wheels to obtain comparable grinding ratios, estimated optimal removal rates with “seeded gel” were 40–60% higher. For comparable optimal removal rates obtained by using softer monocrystalline wheels, estimated grinding ratios with “seeded gel” wheels were as much as four times higher.

Coupled heat transfer to workpiece, wheel, and fluid in grinding, and the occurrence of workpiece burn

A model of heat transfer in grinding was previously developed which predicts the temperature in the grinding zone. This model is used here to predict the occurrence of film boiling of the grinding fluid, and to determine whether or not workpiece burn would subsequently occur. Both film boiling and workpiece burn are assumed to occur at critical grinding zone temperatures. The effects of various parameters are explored, such as fluid and abrasive grain types, and conventional or creep feed grinding conditions.

Studies on Mechanisms and Improvement of Workpiece Burn During Grinding of Titanium Alloys

Summary In this paper, the mechanisms of workpiece bum during grinding of titanium alloys were studied by the use of SEM, EPMA and XPS. In this study, special attention was given to the burnt surface topography and the variation of the composition on burnt surface layer, and a new acid washing method used to detect workpiece bum of titanium alloys was put forward on the basis of understanding of the characteristics of composition change as burn occurred. Based on the theoretical analysis and experimental research work, the solid lubricant treated wheel was developed in order to improve the grindability of titanium alloys. Experiment results showed that the performence of treated wheel is superior to that of ordinary wheel obviously. The mechanism for treated wheel to improve grindability of titanium alloys was also investigated, so as to widen the applications of treated wheel.

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.

高切込み円筒トラバース研削に関する研究 ＩＩＩ 研削焼け発生形態とその一防止法

This paper deals with the generated process and a preventive measure of the burning in the cylindrical traverse grinding of the high depth of cut. The experiment was carried out to examine the surface layer, the hardness and the surface configuration at the burning position of the workpiece. And also, the change of wheel configuration and the loading in the grinding process were investigated. The main conclusions obtained are as follows: (1) The workpiece burn occurs darkly at the starting position of traverse grinding, but disappears as the grinding proceeds. The reason why burning occurs is considered that spark-out grinding can not be done due to the shrinkage of workpiece diameter which is expanded by the generated grinding heat. (2) The workpiece burn exerts a bad influence on the dimensional accuracy and the machining properties. However, careful attention should be paid to the thermal damage even when no visual burning is observed. (3) The loading closely relates to the occurrence of workpiece burn. (4) The wheel dressed to the stepped configuration with the same width as the traverse feed has a good grinding performance in high depth of cut grinding and prevents the workpiece burn.

Workpiece Burn and Its Prediction in Creep Feed Grinding — Experimental Research of the Temperature Variance Process in Contact Zone

Summary On the basis of improving the experimental technique, the authors have obtained a set of experimental curves by developing uniquely designed experiments. The temperature distribution and its variance characteristics in contact zone during entire creep feed grinding process can be fully explored. According to the newly discovered experimental results, it was confirmed that the heating state of continuously renewed grinding surface during film boiling of coolant in creep feed grinding is quite different from that of boiler tubes. There exists a gradually developing process from low surface temperature in normal condition to burning temperature in contact zone during creep feed grinding. Therefore the prediction of workpiece burn can be realized. At the end of this paper, a scheme is proposed for in process prediction of workpiece burn during creep feed grinding used in production.

Study on improvement of machining accuracy in creep feed grinding with difficult-to-grind material. (1st Report, Estimation of profiled wheel wear).

The porous type wheel made for creep feed grinding with difficult-to-grind materials is excellent for the prevention of workpiece burning, but its wear is usually considerable. So we must exactly obtain the characteristics of wheel wear in the case of precision profile creep feed grinding operation. In this study, V profiled wheel wear is examined experimentally with SUS304 and SKD11(Hrc60) materials. From the results, characteristics of the edge wear and the linear relationship between wear and the inclined angle of the wheel surface are obtained. Further, a method is proposed by which any profiled wheel wear is able to be estimated using this relationship from a simple creep feed grinding test. And the usefulness of the method is examined experimentally.

The Prediction and Control of Workpiece Burn During Grinding Process — Application of Graphite-Penetrated Wheels

Many papers have shown that there does exist definite relationship between the workpiece burn and the grinding temperature. However, because of the lack of effective method for in-process monitoring the grinding temperature, the prediction and control of workpiece burn can only be done, in many investigations, by the use of indirect process parameters. Naturally, its application in practice was greatly limited. In this paper, by the use of natural thermocouple consisting of graphite-penetrated wheel and workpiece, the problem of in-process monitoring the grinding temperature was successfully solved. Furthermore, for certain work material, the threshold value of the grinding temperature causing workpiece burn was found by experiments and much more direct basis for the in-process prediction and control was provided. Because of the excellent effect of the solid lubrication of graphite, the graphite-penetrated wheel shows tremendous effect on the improvement of grindability of difficult-to-cut materials, the grinding temperature and force are greatly reduced. At the same time, the grinding ratio is greatly increased and the roughness of the ground surface is also improved. Due to the simplicity of the technique for treating the wheel, the method of prediction and control the workpiece burn by use of the grinding temperature monitored by graphite-penetrated wheel–workpiece thermocouple technique is cost effective.

クリープフィード研削における研削焼けの適応制御

クリープフィード研削における研削焼けの適応制御

A Comparison of Oil and Water as Grinding Fluids in the Creep Feed Grinding Process

This paper contains a comparison of water-based and neat oil grinding fluids when used in the creep feed grinding of a nickel-base alloy with an induced porosity wheel. Grinding with oil resulted in less wheel profile wear and improved surface finish but higher forces in the direction normal to the workpiece travel were obtained and workpiece burn occurred at lower stock removal rates. The implications of these findings for the creep feed grinding of nickel-base alloys are discussed.

Characteristics of Coated Grinding Wheels in Creep Feed Grinding : Effect of Coated Wheel with High Thermal Conductivity Metal (Nickel)

In this paper, the characteristics of a treatment of the grinding wheel (sulphur filled and nickel plated) has been examined in a creep feed grinding. It was found that the grinding forces always become smaller in a treated grinding wheel than in a normal grinding wheel and a critical depth of cut of which workpiece burning occurs, is large in the treated grinding wheel. Also, in comparison of the grinding wear and the grinding temperature, the Ni plated grinding wheel has smaller values than the normal grinding. Although the distribution of temperatures in the workpiece with normal grinding wheel concentrates in a small portion on contacting area, that of Ni plated grinding wheel does not show a steep temperature rise.