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.     

A New Method for Chatter Detection in Grinding

A new method for automatic chatter detection in outer-diameter grinding is proposed which exploits significant changes in grinding dynamics caused by the onset of chatter. The method is based on monitoring of a non-linear statistic called the coarse-grained entropy rate. The entropy rate is calculated from the fluctuations of the normal grinding force. Values of the entropy rate close to zero are typical of chatter, whereas larger values are typical of chatter-free grinding. If the entropy rate is normalized, a threshold value can be set which enables automatic distinction between chatter-free grinding and chatter.     

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.     

轧机工作辊磨削振纹检测与控制

研究分析轧辊磨削振纹产生原因,通过对设备、砂轮、磨削工艺、操作等方面进行改进优化,研制了专用的辊颈振纹检测方法和分级控制规则,有效控制了磨削振纹的产生.     

塑性成形过程的振动应用技术

振动塑性加工是利用相关装置对金属塑性成形过程中的模具或坯料进行一定的激振,以降低坯料与模具之间的摩擦、提高坯料的成形极限.得到更好的成形效果.介绍了振动塑性加lT的研究现状,以及以超声波为主的振动在拉拔、冲压等塑性成形过程中的应用情况.     

Capability Profile of Hard Cutting and Grinding Processes

This keynote paper aims at matching the supply of research results with the industrial demands in hard cutting and grinding. The capability profiles of the processes are characterised and several manufacturing solutions are discussed. The comparison of hard cutting and grinding operations is carried out with regard to certain evaluation criteria based on the functionality of the machined workpiece itself, discussed at different levels, and the process economical efficiency. The basis for a roadmap of future development of hard machining technology is provided, e. g. the main technological developments associated with multi-processing hard machining concepts are given detailed consideration.     

振动研磨去喷孔毛刺实验

为了解决喷嘴的喷孔毛刺去除困难的问题,采用低频振动研磨去毛刺工艺进行去喷孔毛刺实验,由结果可以看出,该工艺方法能显著地去除喷孔的毛刺.且该低频振动研磨系统具有工艺易于实现、成本低且操作简便的特点.     

滚珠丝杠磨削加工中的振动测试与分析

振动是影响滚珠丝杠加工质量的重要因素。通过对振动信号的分析,可以提出相应减振措施来提高丝杠的加工质量。通过实验研究丝杠在磨削加工过程中8个关键位置处的x、y、z3个方向的振动特性。各位置的时域谱和频率谱的对比分析表明:产生振动的主要方向为工作台移动方向,主要来源是砂轮架、头架、砂轮架电机、头架电机的振动。提出相应的减振措施,为提高滚珠丝杠加工质量提供依据。     

TTCI数据概率评估840D车轮辐板孔裂纹扩展速率的研究

840D车轮辐板孔裂纹扩展速率da/dt具有很大分散性,其分散性主要来源于车轮载荷分散性,可用da/dt=Q·a(a≤35 mm时)来表达,裂纹扩展参数Q代表了da/dt的分散性.现场调查获得840D车轮辐板孔裂纹有效数据共3974组,是裂纹长度a及其形成时间t的孤立数据点.通过统计方法分析表明不同裂纹长度下的裂纹形成时间分布(TTCI)很好地符合双参数威布尔分布.建立了裂纹扩展的概率模型,通过不同裂纹长度及其对应的不同可靠度下的裂纹形成时间,拟合获得了不同可靠度下的裂纹扩展速率参数Q.数据分析表明Q服从正态分布,即,Q～N(0.918,0.3112).     

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。     

On the Influence of Drilling Depth Dependent Modal Damping on Chatter Vibration in BTA Deep Hole Drilling

BTA (Boring and Trepanning Association) deep hole drilling is applied for machining bore holes with a high length to diameter ratio. The slender tools involved make BTA processes highly susceptible to chatter vibration. Chatter-free states and states with chatter vibration corresponding to one of the first three torsional eigenfrequencies can be observed to alternate during processes with constant cutting parameters. A detailed FEA model of the significant BTA tool components involved was developed. This takes into account the drilling depth variant boundary conditions. Using this model, the state transitions can be attributed to drilling depth dependent modal damping of the involved torsional vibration modes.     

超声振动对珩磨加工过程中磨削液气泡空化作用的影响

为了对超声珩磨下的磨削液空化泡进行合理预测和控制,在分析磨削液空化机理的基础上,从气泡的控制方程出发,数值对比了超声珩磨与传统珩磨对磨削液气泡运动特性的影响,并研究了声压幅值和超声频率对磨削液气泡空化的作用,最后利用声强测量仪对磨削液气泡的空化强度进行了定量测量。结果表明:超声珩磨下气泡会发生膨胀及压缩的动力学过程,而传统珩磨下气泡会直接被压缩,且超声珩磨下气泡的溃灭速度比传统珩磨高两个数量级;当声压幅值较低时(pap0+ph),磨削液气泡不发生空化,随着声压幅值的增加(pa≥p0+ph),磨削液气泡的空化强度逐渐增强;超声珩磨装置共振时,磨削液气泡的空化强度最强,而超声珩磨装置非共振时,随着超声频率的增加,磨削液气泡的空化强度逐渐减弱。磨削液空化强度试验结果与理论分析基本相符。     

高速磨削脆性非金属材料时消振方法研究

脆性非金属材料(如玻璃)在高速高效率镜面磨削时,零件表面容易出现裂纹(或破碎的缺陷层),其根本原因在于加工工艺系统的振动.运用理论力学的方法对加工系统振动进行分析,在双级减振原理的基础上建立其数学模型并设计了消振试验装置.以工艺系统中的弹性介质(如冷却液)等作为减振元件,通过改变冷却液的流量和主轴转速的方法使砂轮工作在系统共振区外的区域,最大限度地减少了砂轮的振动,从而保证了高磨削效率下零件的表面质量.     

不同回火热处理状态下9Mn2V的磨削加工表面质量研究

通过实验分析不同回火热处理状态下冷作模具钢9Mn2V的磨削表面质量,主要包括金相组织、显微硬度、表面粗糙度、表面形貌以及表面残余应力。实验结果表明,回火后磨削表面质量明显改善。同时,材料经过淬火后,表面有很大的残余拉应力,当材料经过二次回火后,该残余拉应力显著减小。     

基于MATLAB的内圆磨削加工过程非线性振动仿真

建立了单自由度的内圆磨削非线性振动系统的动力学模型,考虑其中的非线性阻尼及非线性刚度,并用Matlab对其进行了参数计算和仿真分析,得到了加工过程中不同阻尼及不同转速下的分岔图、相图和Poincare图.从所得仿真结果分析阻尼及转速变化对切削稳定性的影响,经验证仿真结果与现场运行情况是相符合的.