Thermal modeling and optimization of interrupted grinding

Finishing parts such as blade tips of assembled engine rotors is an interrupted grinding process. Thermal issues such as burn often become more prominent for interrupted grinding because of the low thermal capacity during the entry and the exit of each interruption. This paper presents models to calculate the transient and steady state temperatures for interrupted grinding. The developed models are then used to investigate the influence of grinding process parameters and cooling on the transient temperature rise. The model results can be used to develop new grinding cycles with variable work speed to increase material removal rate while maintaining temperature below burn limit.     

Predictive modeling of surface roughness in grinding

The surface roughness is a variable often used to describe the quality of ground surfaces as well as to evaluate the competitiveness of the overall grinding system. This paper presents the prediction of the arithmetic mean surface roughness based on a probabilistic undeformed chip thickness model. The model expresses the ground finish as a function of the wheel microstructure, the process kinematic conditions, and the material properties. The analysis includes a geometrical analysis of the grooves left on the surface by ideal conic grains. The material properties and the wheel microstructure are considered in the surface roughness prediction through the chip thickness model. A simple expression that relates the surface roughness with the chip thickness was found, which was verified using experimental data from cylindrical grinding.     

Simulation for optimizing grain pattern on Engineered Grinding Tools

Engineered Grinding Tools (EGT) are characterized by a predetermined and controlled arrangement of the abrasive grains. The distribution of the abrasive grains can be used to enhance the grinding process by improving space for coolant supply and for chip removal. This is especially interesting for grinding operations with high specific material removal rates. A numerical method was developed to optimize the grain pattern on EGT. This method consists of a stochastic tool model, a kinematic process model, a material removal model and a grain wear model. The tool model comprehends the relevant geometric properties of the abrasive layer. The material removal model is based on the assumption of a kinematic-geometrical cutting condition. The wear model is based on a grain load limit and the grains’ load is assumed to be proportional to its cutting area. Once the cutting area of one grain exceeds the limit value, wear takes place. The model validation is presented comparing the wear behavior of EGT and workpiece roughness achieved with numerical and experimental methods.     

High-performance dry grinding using a grinding wheel with a defined grain pattern

This paper presents the potential of a superabrasive electroplated grinding wheel with a defined grain pattern for dry surface grinding operations. The grinding wheel's grain pattern is developed by kinematic simulation with special focus on the undeformed chip thickness. Current experimental investigations of dry grinding operations of hardened heat-treated steel are carried out with a material removal rate of Q^′w=70 mm³/mm s. The measured grinding forces, workpiece temperatures, as well as workpiece surface quality and workpiece integrity are compared to wet grinding and a standard superabrasive electroplated grinding wheel as a reference process.     

Fine grinding of silicon wafers: effects of chuck shape on grinding marks

Silicon wafers are used for production of most microchips. Various processes are needed to transfer a silicon ingot into wafers. With continuing shrinkage of feature sizes of microchips, more stringent requirement is imposed on wafer flatness. Fine grinding of silicon wafers is a patented technology to produce super flat wafers at a low cost. Six papers on fine grinding were previously published in this journal. The first paper discussed its uniqueness and special requirements. The second one presented the results of a designed experimental investigation. The third and fourth papers presented the mathematical models for the chuck shape and the grinding marks, respectively. The fifth paper developed a mathematical model for the wafer shape and the sixth paper studied machine configurations for spindle angle adjustments. This paper is a follow up of the above-mentioned work. A mathematical model to predict the depth of grinding marks for any chuck shape will be first developed. With the developed model, effects of the chuck shape (as well as the wheel radius) on the depth of grinding marks will be studied. Finally, results of pilot experiments to verify the model will be discussed.     

Fine grinding of silicon wafers: a mathematical model for grinding marks

The majority of today’s integrated circuits are constructed on silicon wafers. Fine-grinding process has great potential to improve wafer quality at a low cost. Three papers on fine grinding were previously published in this journal. The first paper discussed its uniqueness and special requirements. The second one presented the results of a designed experimental investigation. The third paper developed a mathematical model for the chuck shape, addressing one of the technical barriers that have hindered the widespread application of this technology: difficulty and uncertainty in chuck preparation. As a follow up, this paper addresses another technical barrier: lack of understanding on grinding marks. A mathematical model to predict the locus of the grinding lines and the distance between two adjacent grinding lines is first developed. With the developed model, the relationships between grinding marks and various process parameters (wheel rotational speed, chuck rotational speed, and wheel diameter) are then discussed. Finally, results of pilot experiments to verify the model are discussed.     

Evaluation of superabrasive grinding points for the machining of hardened steel

Small diameter grinding points offer greater flexibility for machining free-form contours compared to traditional grinding wheels, despite fewer effective cutting edges. The paper evaluates the influence of grit size (B32, B46, B76), feed rate (125, 250 mm/min) and depth of cut (20, 40 μm) when machining D2 tool steel using electroplated CBN grinding points. Highest G-ratios (～2441) were obtained using B32 tools with corresponding workpiece surface roughness (Ra) of ～0.8 μm after ～6000 mm³ material removed, due to the greater number of effective cutting edges. Attritious wear was the primary wear mechanism although material loading was observed with B76 tools.     

Geometric,kinematical and thermal analyses of non-round cylindrical grinding

This paper is concerned with the analyses of grinding geometry and kinematics in the grinding zone and develops a thermal model, along with a chip-thickness-dependent value of specific grinding energy into the workpiece. The grinding geometry and kinematics are modeled for arbitrary non-round workpiece forms. Unlike other models, which are based on a fixed, constant geometry, the model presented here is based on first principles using a fundamental, transient, non-constant geometry and thus constitutes a much-needed advancement in grinding technology. A novel experimental approach is also taken, which uses the specific grinding energy into the workpiece, rather than the total specific grinding energy coupled with an estimate of the energy partition, an estimate which previously has proven difficult to achieve accurately. The model is verified with experimental work and predicted temperatures are in reasonable agreement with temperatures associated with the onset of thermal damage, determined via metallographic examination and Barkhausen noise. Finally, some of the challenges of using Barkhausen noise to evaluate thermal damage are investigated, namely the differing response characteristics of stressed and overtempered material vs. rehardened material, and how these can be overcome in practice.     

Blanking tool wear modeling using the finite element method

One of the main objectives of the numerical process design in metal forming is to develop adequate tool design and establish process parameter in order to increase tool life and to improve part quality and complexity while reducing manufacturing cost. The prediction of tool wear in sheet metal blanking/punching processes is investigated in this paper using the finite element method. A wear prediction model has been implemented in a finite element code in which the tool wear is a function of the normal pressure and some material parameters. A damage model is used in order to describe crack initiation and propagation into the sheet. The distribution of the tool wear on the tool profile is obtained and compared to industrial observations. Furthermore, a numerical investigation has been carried out to study the effect of tool wear on the burr formation.     

Application of Taguchi and response surface methodologies for geometric error in surface grinding process

The geometric error in the surface grinding process is mainly affected by the thermal effect and the stiffness of the grinding system. For minimizing the geometric error, the selection of grinding parameters is very important. This paper presented an application of Taguchi and response surface methodologies for the geometric error. The effect of grinding parameters on the geometric error was evaluated and optimum grinding conditions for minimizing the geometric error were determined. A second-order response model for the geometric error was developed and the utilization of the response surface model was evaluated with constraints of the surface roughness and the material removal rate. Confirmation experiments were conducted at an optimal condition and selected two conditions for observing accuracy of the developed response surface model.     

Investigation on cooling efficiency of grinding fluids in deep grinding

The cooling efficiency of grinding fluids in deep grinding, at different material removal rates and grinding speeds, has been investigated. Two ‘inverse’ methods have been proposed to determine the level of convective heat transfer coefficients of grinding fluids, by matching the theoretical and experimental grinding fluid burn-out thresholds or matching the theoretical and measured grinding temperatures. Instead of using a constant chip melting temperature to estimate the energy partition to the grinding chips, the chip temperature and chip energy were calculated using the newly developed approach considering the variation of chip size, deformation and heat transfer at the abrasive/work interface. The variation of grinding heat taken away by the process fluids and grinding chips under different process parameters has been calculated, which shows the importance of cooling effects by the grinding fluids and the transition of thermal characteristics of deep grinding from cooling dominant to ‘dry’ grinding regime, where a large percentage of grinding heat is taken away by the grinding chips.     

Experimental study on grinding force and grinding temperature of Aermet 100 steel in surface grinding

This paper investigates grinding force and grinding temperature of ultra-high strength steel Aermet 100 in conventional surface grinding using a single alumina wheel, a white alumina wheel and a cubic boron nitride wheel. First, mathematical models of grinding force and grinding temperature for three wheels were established. Then, the role of chip formation force and friction force in grinding force was investigated and thermal distribution in contact zone between workpiece and wheel was analyzed based on the mathematical model. The experimental result indicated that the minimum grinding force and the maximum grinding force ratio under the same grinding parameters can be achieved when using a CBN wheel and a single alumina wheel, respectively. When the phenomenon of large grinding force and high grinding temperature appeared, the workpiece material would adhere locally to the single alumina wheel. Grinding temperature was in a high state under the effect of two main aspects: poor thermal properties of grinding wheel and low coolant efficiency. The predicted value of grinding force and grinding temperature were compared with those experimentally obtained and the results show a reasonable agreement.     

Simulation of surface grinding process, part 2: interaction of the abrasive grain with the workpiece

This paper is the second part of the two-part series, which describes the kinematic simulation of the grinding process. The complex wheel–workpiece interaction is taken into consideration in the generation of the workpiece surface. An algorithm is proposed to identify the active abrasive grains and their attack angles from the wheel topography. Based on the critical values of the attack angle, the abrasive grain is determined either to cut, plough or rub the workpiece. A numerical example is used to validate the approach.     

The effects of system and geometric parameters on abrasive water jet nozzle wear

Nozzle wear dependence on abrasive water jet system parameters and nozzle geometry is experimentally investigated. Experimental procedures for evaluating long term and accelerated nozzle wear are discussed. Accelerated wear tests are conducted to study the effects of nozzle length, inlet angle, diameter, orifice diameter, abrasive flow rate, and water pressure on wear. An empirical model for nozzle weight loss rate is developed and is shown to correlate well with experimental measurements.     

Fine grinding of silicon wafers: a mathematical model for the chuck shape

Fine grinding of silicon wafers is a patented technology to manufacture super flat semiconductor wafers cost-effectively. Two papers on fine grinding were previously published in this journal, one discussed its uniqueness and special requirements, and the other presented the results of a designed experimental investigation. As a follow up, this paper presents a study aiming at overcoming one of the technical barriers that have hindered the widespread application of this technology, namely, the difficulty and uncertainty in chuck preparation. Although the chuck shape is critically important in fine grinding, there are no standard procedures for its preparation. Furthermore, the information on the relation between the set-up parameters and the resulting chuck shape is not readily available. In this paper, a mathematical model for the chuck shape is first developed. Then the model is used to predict the relations between the chuck shape and the set-up parameters. Finally, the results of the pilot experiments to verify the model are discussed.     

Industrial challenges in grinding

This keynote paper aims at analyzing relevant industrial demands for grinding research. The chosen focus is to understand what are the main research challenges in the extensive industrial use of the process. Since the automotive applications are the most important driving forces for grinding development, the paper starts with an analysis on the main trends in more efficient engines and the changes in their components that will affect the grinding performance. A view from 23 machine tool builders is also presented based on a survey made in interviews and during the EMO and IMTS machine tool shows. Case studies received by the STC G members were used to show how research centers and industries are collaborating. A view from the authors and the final conclusions show hot topics for future grinding research.     

Dynamic modeling of a novel workpiece table for active surface grinding control

In order to implement active control during surface grinding, a workpiece micro-positioning table utilizing a piezoelectric translator has been developed. The workpiece table has a working area of 100×100 mm and a nominal working range of 45 μm. The resolution of the workpiece table is less than 20 nm and the natural frequency is 579.2 Hz. The rigidity of the workpiece table under the open loop condition is approximately 17 N/μm. Under the closed loop condition, the rigidity is better than 400 N/μm. The design of the workpiece table is presented together with considerations to achieve the high dynamic characteristics, where the maximum acceleration is up to 33g (g is the acceleration of gravity). The dynamic models of the piezoelectric translator and the workpiece table have been established. Experimental testing has been carried out, verifying the performance of the workpiece table and the established dynamic models for the workpiece micro-positioning table.     

Application of region growing method to evaluate the surface condition of grinding wheels

Grinding is a time-varying process affected by factors such as wheel construction, dressing parameters, operating parameters, workpiece material and cooling. The influence of these factors on wheel wear can be evaluated by monitoring the wheel condition. Measurement of wear flat area provides information on the condition of the wheel, but unfortunately it can be a tedious, time consuming, and expensive process. In this paper, a new system to measure wear flat area is presented. This system is mounted on the grinding machine and automates the measurement process by using computer control to automatically position the wheel and capture digital images of the wheel between grinding cycles. Image processing software is then used to analyze the digital images and measure the wear flat area. The proposed measurement system was validated using a scanning electron microscope. Experiments were performed on a Brown & Sharpe Micromaster 824 surface grinder to examine the relationship between wear flat area, normal force and depth of cut. The results agree with the literature.     

Fine grinding of silicon wafers

Silicon wafers are used for the production of most microchips. Various processes are needed to transfer a silicon crystal ingot into wafers. As one of such processes, surface grinding of silicon wafers has attracted attention among various investigators and a limited number of articles can be found in the literature. However, no published articles are available regarding fine grinding of silicon wafers. In this paper, the uniqueness and the special requirements of the silicon wafer fine grinding process are introduced first. Then some experimental results on the fine grinding of silicon wafers are presented and discussed. Tests on different grinding wheels demonstrate the importance of choosing the correct wheel and an illustration of the proper selection of process parameters is included. Also discussed are the effects of the nozzle position and the flow rate of the grinding coolant.     

Model-based manufacturing and application of metal-bonded grinding wheels

The tool properties of grinding wheels can vary in a wide range due to the variety of processes. The properties, in turn, affect the grinding process and the grinding results. Understanding the interdependencies from the initial manufacturing to the final grinding results is the key to achieve the target-oriented generation of the grinding wheel properties for the grinding task at hand. This paper presents a novel approach to model the interdependencies between the manufacturing of bronze-bonded grinding wheels and the resulting grinding behaviour. The manufacturing steps are described with sub models in order to forecast properties and application behaviour.