Stability analysis and time domain simulation of multiple diameter parts during infeed centerless grinding

Multiple diameter part applications cope a relevant percentage of infeed centerless grinding operations. Nevertheless, general stability analysis and process optimisation has been mainly investigated for mono-diameter parts. This paper presents a time domain simulation software developed for multiple diameter parts that allows the simulation of average and particular evolution of process forces, power, machine deflections, thermal behaviour, real part diameter and roughness. First, a work rotation stability analysis is carried out. Then, with the use of both the stability analysis and the infeed cycle simulation, optimized process parameters and cycles are defined in order to increase process productivity.     

Optimization of Continuous Dress Creep-Feed Form Grinding Process

This paper is concerned with optimization of continuous-dress creep-reed grinding processes to reduce cycle time and wheel consumption by adaptively adjusting workspeed and dress infeed based on grinding models and in-process power monitoring. Heat flux is kept below the fluid burnout limits to avoid thermal damage to the ground surface. Grinding forces are controlled below the allowable values to avoid coating cracks caused by excessive strain on the blade. By implementing this approach, 40% cycle time reduction was demonstrated while maintaining the heat flux and grinding forces below their allowable critical values.     

Continuous workpiece speed variation (CWSV): Model based practical application to avoid chatter in grinding

The continuous variation of rotation speeds provides a means of avoiding chatter instability in different machining processes. This paper presents a time domain dynamic model that simulates chatter vibration during infeed centerless grinding for any continuously variable work rotation speed strategy. As a result of taking machine dynamics and main non-linear effects of the process into account, part roundness error is predicted for the whole grinding cycle. Lastly, experimental results have validated the model and verified that adequate speed variation strategies are capable of avoiding chatter and improving workpiece roundness and roughness, both for infeed and throughfeed centerless grinding.     

外圆磨削加工的仿真、优化及控制

磨削技术已广泛应用于最后加工有光滑表面和高精度要求的零件,在过去的30年里,经过广泛的研究,对磨削加工的许多方面有了一个较为清楚的了解。本论文的目的在于说明怎样利用我们对磨削过程的理解来预报磨削特性和获得最佳加工条件。一个集成了描述磨削过程中不同方面的分析模块的软件包已被开发出来。这软件包括三个主要模块：仿真,校准和优化,仿真模块作为一个虚拟磨床来预测磨削过程和零件质量,校准模块通过实测参数如功率,表面粗糙度和椭圆度等对模型的系数进行修正,从而对实际磨削特性进行学习,优化模块是以最小化周期时间或以基于服从工件质量约束校正模型后的周期时间为目标来确定磨削和修整参数。本软件已被集成进了PC开放体系控制器（OAC）,作为智能磨削系统（IGS）的基础。     

Time-domain dynamic modelling of the external plunge grinding process

This paper presents a time-domain dynamic model of the external plunge grinding process. The model consists of a block-based simulation tool that substantially simplifies the inclusion of different effects, the variation of process or machine parameters, and the study of the parameters which influence the process. Since it is a time-domain model, non-linear effects can be considered. Particular attention is paid to the inclusion in the model of the interference phenomenon between two consecutive workpiece revolutions. The inclusion of this phenomenon is particularly important when trying to explain why process parameters which cause unstable conditions during stability analyses can, however, lead to acceptable workpiece results. The model permits the visualisation of this lobe destruction effect between consecutive workpiece revolutions.The actual infeed constitutes the model input, i.e. different infeed rates and spark-out time. The importance of the different model parameters is discussed within the paper, with special attention being given to the application of this model to the grinding with CBN wheels.     

Model-Based Monitoring and Control of Continuous Dress Creep-Feed Form Grinding

This paper is concerned with process monitoring and control of Continuous Dress Creep-Feed (CDCF) form grinding using model-based simulation and in-process power measurement and its application to grinding of turbine blade root serrations. For blade root serration grinding, it is essential that the grinding force be maintained below a critical limit to avoid cracking of the Thermal Environmental Barrier Coating (TEBC) at the blade airfoils, and that the heat flux at the grinding zone be kept below the fluid burnout limit to avoid thermal damage to the part. A blade root form grinding process is first simulated and optimized by utilizing the variable-feed approach developed previously, whereby both the dress infeed and part feed rate are adaptively varied to minimize cycle time while maintaining the force and heat flux below specified limits. Both the grinding forces and heat flux are obtained from the measured power. Maintaining the monitored power signature from production processes within the acceptable power limits established in this way ensures a “normal” grinding process. Deviations from the normal process signature profile indicate possible process issues.     

切入式磨削烧伤仿真预测与控制方法研究

基于磨削热传递模型和磨削去除率模型,提出了一种基于监控功率信号的切入式磨削烧伤仿真预测与控制方法,对砂轮在粗磨、半精磨、精磨、光磨各阶段的磨削功率信号进行监测,再利用计算机对机床数控系统各加工工艺参数进行控制,使砂轮实际磨削功率信号始终低于磨削烧伤最大功率边界的5%～15%,来避免出现工件磨削烧伤现象;同时,用轴承套圈内圆磨削试验验证了该方法的有效性和实用性。      

Virtual high performance grinding with CBN wheels

The development of future products requires designing, manufacturing, and testing components in a virtual environment before hardware parts are actually made. This paper presents a generalized process simulation and multi-constraint optimization strategy for five-axis grinding with cubic boron nitride (CBN) wheels to increase material removal rates while avoiding process problems such as damage to the machined surfaces and premature wheel failure. The wheel-workpiece engagement conditions under five-axis grinding are extracted from a CAM system by geometrically processing the NC program, the wheel geometry and the part geometry. The interpreted geometric contact data are used in combination with empirical grinding models to predict physical process parameters such as forces, power, heat flux, and temperature. These parameters are then used as the decision variables in a multi-constraint optimization to optimize process parameters such as workspeed to reduce cycle time.     

A study on the machining characteristics in the external plunge grinding using the current signal of the spindle motor

This paper describes the machining characteristics of external plunge grinding. The study investigates the process using the current signals of a spindle motor through a hall sensor. Grinding experiments were conducted under various grinding conditions such as wheel speeds, workpiece speeds and infeed rates with a conventional vitrified bonded wheel. Analyzing the current signal of the spindle motor, a relationship between current signals and the metal removal rate in terms of the infeed rate is induced. It was also shown that a hall sensor has similar capabilities in evaluation of grinding behavior compared to the AE signals, which are useful for monitoring the grinding process.     

Advances in Modeling and Simulation of Grinding Processes

In the last decade the relevance of modeling and simulation of grinding processes has significantly risen which is caused by industrial needs and is indicated by the number of publications and research activities in this area. This keynote paper results from a collaborative work within the STC G and gives an overview of the current state of the art in modeling and simulation of grinding processes: Physical process models (analytical and numerical models) and empirical process models (regression analysis, artificial neural net models) as well as heuristic process models (rule based models) are taken into account, and outlined with respect to their achievements in this paper. The models are characterized by the process parameters such as grinding force, grinding temperature, etc. as well as work results including surface topography and surface integrity. Furthermore, the capabilities and the limitations of the presented model types and simulation approaches will be exemplified.     

Increased productivity in centerless grinding using inertial active dampers

Regenerative chatter during centerless grinding processes is one of the main factors limiting the productivity. This paper presents a novel chatter suppression technique for centerless grinding using an active damping system based on inertial actuators. Dynamic characterisation of the machine with and without active damping is used first to compute theoretical stability maps. The active nature of the system allows stabilising a wide working range of infeed operations. Finally, experimental results validate the predicted increase of stable grinding area and verify that the technology is very effective for avoiding chatter, ensuring workpiece quality and increasing process productivity.     

Development of a honing process for the combination machining of hardened axisymmetric parts

This paper presents a novel concept to enhance the conventional combination machining ‘turning and grinding’ by a long-stroke honing process for finishing bores of axisymetric parts. Honing is the best choice when the surface integrity of tribologically highly-stressed parts is of vital importance. The presented approach reduces the required overall machining time when compared with that of the conventional machining sequence on separate machine tools, and also enhances the production accuracy through a single clamping setup. The fundamental details like tool design, infeed strategies and possible process-chains of the developed approach for honing on a combination machining center are explained. Experimental results of two different process-chains are analyzed: Firstly, the ‘turning-grinding-honing’ (TGH-chain), where honing is conducted after the grinding process; and secondly, the ‘turning-honing’ (TH-chain), where honing is applied directly after the rough turning. The experiments showed promising results for the applied position-controlled infeed strategy of the developed long-stroke honing process regarding the production efficiency.     

Modelling and simulation of process: machine interaction in grinding

This article presents an overview of current simulation methods describing the interaction of grinding process and grinding machine structure, e.g., vibrations, deflections, or thermal deformations. Innovative process models which describe the effects of the grinding wheel–workpiece interaction inside the contact zone are shown in detail. Furthermore, simulation models representing the static and dynamic behaviour of a grinding machine and its components are discussed. Machine tool components with a high influence on the process results are modelled more detailed than those with low influence. The key issue of the paper is the coupling of process and machine tool models for predicting the interactions of process and machine. Several coupling methods are introduced and the improvements of the simulation results are documented. On the basis of the presented simulation approaches, grinding processes and machines can be designed more effectively resulting in higher workpiece quality and process stability.     

The effect of cryogenic cooling on grinding forces

Grinding forces are important parameters to judge the performance of any grinding process. Cryogenic cooling in grinding is a new concept to control the high grinding zone temperature without polluting the environment. The paper presents a hypothesis on the mechanics of grinding under cryogenic cooling. Experiments have been carried out to study the effect of cryogenic cooling on grinding forces and to check the validity of the hypothesis. The results indicate substantial reduction in the grinding forces under cryogenic cooling over range of infeed and dressing procedure for different commonly used steels.     

Realisation of grinding-hardening in workpieces of curved surfaces—Part 1: Plunge cylindrical grinding

This paper investigates the feasibility to achieve grinding-hardening in a plunge cylindrical grinding process. To understand the mechanisms, a temperature-dependent finite element heat transfer model incorporating a triangular moving heat source was developed to describe the temperature field, thus to predict the thickness of the grinding-hardened layer. The analysis carried out included the variation effect of depth of cut caused by the change in wheel-workpiece engagement. The model was applied on quenchable steel 1045 and the analysis was verified experimentally. It was shown that the heating cycle in plunge cylindrical grinding is the result of consecutive heating and cooling processes, varying from location to location in a workpiece. The ratio of the workpiece speed to the infeed rate plays an important role in the heat treatment cycle.     

基于Simulink仿真的凸轮轴高速磨削稳定性判定

以凸轮轴高速磨削工艺系统稳定性为研究对象,建立磨削系统的凸轮轴-砂轮-支撑系统动力学模型。通过理论分析与数值计算来辨识磨削力的动态影响因素——凸轮轮廓曲率半径和瞬时磨削深度。基于所建立的磨削动力学模型搭建Matlab/Simulink颤振仿真模型,并从稳定性叶瓣图中选取相应的磨削工艺参数组合进行数值仿真分析,将仿真振动位移时域图所得的稳定性结论与稳定性叶瓣图的磨削稳定区域进行比较,验证了建立的磨削动力学模型和数值仿真方法的有效性。      

径向磨削加工过程的智能控制策略研究

针对径向切入式磨削加工过程（尤其是薄壁工件），提出了一套新的磨削工艺程式；并在充分分析磨削机理的基础上，导出了与之相适应的以最终尺寸精度为目标的自适应预测最优控制算法，仿真与试验结果表明，该方法能较好地实现磨削尺寸精度的在线控制，可在更短的时间内获得理想的加工效果，对于薄擘件的磨削加工其效果尤其显著。     

Origin,modeling and suppression of grinding marks in ultra precision grinding of silicon wafers

A phenomenon commonly encountered in grinding of silicon wafers is the grinding marks, which are difficult to remove by subsequent polishing process, and have been a great obstacle to the manufacture of silicon wafers with higher flatness. In this paper, the grinding marks formation mechanism was clarified, a grinding marks formation model and an angular wavelength model were developed, and a grinding marks suppression method was proposed. A series of grinding experiments were carried out to verify the developed models and investigate the effect of the wafer rotational speed, the wheel rotational speed, the infeed rate, the axial run out of the cup wheel and the spark out time. The results show that: (1) grinding marks are waviness generated on silicon wafers caused by non-uniform material removal circumferentially due to the axial run out of the cup wheel; (2) grinding marks present multiple angular wavelengths characteristics; (3) the angular wavelength of grinding marks is a one-variable function of the rotational speed ratio of the wheel to the wafer; and (4) grinding marks could be suppressed significantly by properly selecting the rotational speed ratio.     

Chatter Stability of Metal Cutting and Grinding

This paper reviews fundamental modeling of chatter vibrations in metal cutting and grinding processes. The avoidance of chatter vibrations in industry is also presented. The fundamentals of orthogonal chatter stability law and lobes are reviewed for single point machining operations where the process is one dimensional and time invariant. The application of orthogonal stability to turning and boring operations is presented while discussing the process nonlinearities that make the solution difficult in frequency domain. Modeling of drilling vibrations is discussed. The dynamic modeling and chatter stability of milling is presented. Various stability models are compared against experimentally validated time domain simulation model results. The dynamic time domain model of transverse and plunge grinding operations is presented with experimental results. Off-line and real-time chatter suppression techniques are summarized along with their practical applications and limitations in industry. The paper presents a series of research topics, which have yet to be studied for effective use of chatter prediction and suppression techniques in industry.     

Optimization of peripheral non-round cylindrical grinding via an adaptable constant-temperature process

This paper introduces two new concepts in peripheral cylindrical grinding of non-round workpieces: (1) choosing process parameters based on a thermal model for achieving a constant temperature; and (2) optimizing the grinding process for shorter cycle times while applying the concept of constant temperature. The modeling of geometry, kinematics and thermal aspects accounts for large variations in specific material-removal rate, contact length and workpiece velocity as the workpiece rotates. Optimization is validated both in simulation and with grinding experiments, including measurements of Barkhausen noise. Significantly reduced cycle times are obtained along with a better ability to avoid thermal damage.