Tribological studies of coated pistons sliding against cylinder liners under laboratory test conditions

The presence of coatings and surface topography play an important role in the tribological performance of sliding components. Depending on the coating used, it is possible to reduce friction and/or reduce wear. However, although there may be low friction and wear‐resistant coatings suitable for use in pistons, some coatings may hinder the tribological performance by changing the lubrication regime or by preventing additives from their intended function through chemical mechanisms. In this work, piston skirt segments extracted from a commercial aluminium alloy piston were coated with a diamond‐like carbon (DLC) coating, a graphite–resin coating or a nickel–polytetrafluoroethylene (Ni–PTFE) coating and were tribologically tested using a reciprocating laboratory test rig against commercial grey cast iron liner segments. The tribological tests used commercial synthetic motor oil at a temperature of 120 °C with a 20 mm stroke length at a reciprocating frequency of 2 Hz. Results showed that the graphite–resin coating, although it may serve as a good break‐in coating, wears rapidly. The Ni–PTFE coating showed friction reduction, whereas the DLC coating wore off quickly due to its small thickness. Furthermore, the higher hardness of the DLC coating relative to the cast iron liner surface led to pronounced changes on the liner counterface by polishing. In contrast with the uncoated piston skirt segments, all of the coatings prevented the formation of a visible tribochemical film on the cast iron surface. Copyright © 2012 John Wiley & Sons, Ltd.     

基于VERICUT的数控加工运动学仿真

介绍了运用VERICUT软件实现数控加工运动学仿真的过程及方法.通过加工实例实现了从三维建模、刀具管理、数控程序导入到加工运动仿真,得到了一种较理想的仿真方法.基于软件的Optimath分析模块,可以对加工程序进一步优化,提高加工效率.AUTO-DIFF分析模块通过对比仿真模型和设计模型实现仿真加工过程的过切和欠切分析.     

N叶非圆锥齿轮的加工仿真研究

针对N叶非圆锥齿轮节曲线会产生不连续等问题,提出了一种新的非圆锥齿轮节曲线的设计方法,该方法有效简化了非圆锥齿轮的设计。推导了非圆锥齿轮的节锥与球面的交线方程,以该交线作为非圆锥齿轮的节曲线,以球面渐开线锥齿轮为非圆锥齿轮的产形刀具,建立了刀具的节面与非圆锥齿轮节面的数学模型,提出了非圆锥齿轮齿廓的加工仿真算法;该算法通过仿真锥齿轮刀具在非圆锥齿轮节面上的包络运动,实现了对非圆锥齿轮齿廓的加工。研究结果表明,通过对Pascal曲线锥齿轮节曲线的设计,验证了该设计方法具有广泛的适用范围;同时,该算法对于提高非圆锥齿轮齿廓的加工效率也具有实际意义,可以很好地用于齿廓产形中。     

An analysis of the extrusion of bimetallic tubes by numerical simulation

This paper presents a numerical analysis of a high temperature extrusion process applied to bimaterial tubes made of two pre-bonded metallic materials with different plastic properties. The analysis has been carried out for different geometries and material combinations by using a FE code. An elasto-plastic behaviour with strain rate dependence has been assumed. A parameter related to the void growth rate at the bimaterial interface has been considered for fracture prediction during the extrusion operation.The influence of the different extrusion variables, namely the yield stress ratio, the location and relative thickness of the layers and the die angle, has been assessed. As a conclusion of the analysis, the yield stress ratio between the two materials turns out to be the most critical parameter of the process. Besides, the thickness fluctuations of the harder layer in the final product have been analysed for several material combinations. Those fluctuations can lead to an unacceptable geometrical heterogeneity under certain conditions. The results of the FE calculations are in reasonable agreement with the scarce data available from similar industrial operations.In short, the paper shows that use of FE calculations can be a pre-screening tool for the selection of material couples and extrusion conditions for the production of sound bimetallic tubes, before being engaged in very costly full-scaled trials.     

基于Vericut的圆柱沟槽凸轮的加工仿真

根据圆柱沟槽凸轮传动机构的运动原理,应用Vericut软件对圆柱沟槽凸轮进行数控仿真加工.首先根据主动件和从动件的运动机制确认其运动参数,其次根据运动关系模拟实际情况建立机床、毛坯以及刀具模型,然后计算刀具在凸轮上的运动数据编写初加工和精加工程序,最后得出仿真加工结果,确认其正确性并输出加工程序.     

基于UG IS&V的数控机床加工仿真

IS&V是UG软件中一个功能强大用于数控机床集成仿真和验证的专用模块.介绍了该模块的结构组成及工作原理,并在IS&V环境下建立了一台三轴数控铣床的仿真模型.在该模型的基础上分别对零件加工过程中的刀具路径和铣床运动进行仿真,预见和评估其加工过程中可能出现的问题并加以解决,最终提高企业的生产效率并使其获得"首试成功"的加工制造.     

基于VERICUT仿真和优化的复杂曲面加工策略研究

结合具有复杂曲面特征的人面模具数控加工编程,进行了工艺分析与规划,采用了特定的加工操作实现加工工艺,执行后处理生成能驱动特定数控机床的NC代码,利用数控加工仿真系统VERI-CUT软件对NC代码进行模拟、验证、优化,从而提高了所编数控程序的可靠性、高效性,实现复杂曲面加工策略的优化,提供了模具高速加工的系统性方法。     

Machining simulation and system integration combining FE analysis and cutting mechanics modelling

This work presents a method for machining complex three-dimensional surfaces using only one axis of controlled motion for positioning a cutting tool on a specially designed numerically controlled (NC) machine. This single controlled axis lathe is configured like a lathe, but is used to produce complex sculptured surfaces out of wood. This is accomplished by mechanically linking two axes of motion to produce a fixed helical footprint of a tool path with constant step-over distance. As the linked axes are rotated, their location is measured by an encoder and passed directly to a personal computer (PC). Software running on the PC determines the depth of the computer-controlled axis. The depth information is used to control the depth axis. Several test pieces have been machined out of cedar for evaluating the method.     

Stress and fatigue analysis of engine pistons using thermo-mechanical model

Journal of Mechanical Science and Technology - This paper presents a thermo-mechanical finite element analysis model for the stress and fatigue analyses of engine pistons. The model consists of the...     

Surface treatments for pistons and their effect on engine performance

Surface treatment alters the frictional behaviour of pistons in I.C. engines and can be used to improve engine performance. Surface treatments applied to aluminium alloy pistons of a high speed diesel engine and their effect on the engine performance are described. Certain piston surface treatments improve engine performance and also reduce the run-in period.     

再制造加工及其机械加工方法

失效零件的再制造加工是保证再制造产品质量、降低再制造费用的核心内容。本文叙述了再制造加工的概念,分析了失效零件进行再制造加工的条件,并对再制造加工技术方法进行了分类;重点分析了失效零件机械加工法再制造的特点,并探讨了常用的修理尺寸法、钳工再制造恢复法、镶加零件法、局部更换法、换位法和塑性变形法等再制造修复方法。     

Driving mechanism of tapered pistons in bent-axis design axial piston pumps

In order to assure the quality of the bent axis design axial piston pumps driven by tapered pistons, it is necessary to know the characteristics of force applied to tapered pistons and the mechanism for driving the tapered pistons. Since they are able to perform both reciprocating and spinning motions in cylinder block, it is difficult to understand the driving mechanismand-tomeasure the forces applied to tapered pistons experimentally. In the presem study, the theoretical mechanism for driving the tapered pistons is studied by use of the geometric method. The driving area of tile tapered pistons is measured by measuring the strain of a cylinder forced against a tapered piston using an electric strain gauge and a slip ring. The forces applied to tapered pistons is also investigated with the change of discharge wessure and the rotational speed As a results of this investigation, it is concluded that the cylinder block is driven by one tapered piston in a limited area and flue driving area is changed due to space angle of the tapered pistons and the swivel angle of the cylinder block. It is also observed that the force applied to tapered pistons increases as the discharge pressure and the rotational speed increase.     

基于六轴数控铣齿机的点接触曲线圆柱齿轮加工仿真

点接触曲线圆柱齿轮是一种新型平行轴传动齿轮,用常规的机床和刀具难以完成其齿形的高效加工.利用六轴数控铣齿机和面铣式刀盘完成该齿轮的模拟加工.首先,根据该齿轮的成型原理,推导齿面的数学模型,求解齿面点云数据,基于点云数据在三维建模软件中构建齿轮实体模型;然后,在VERICUT中构建数控铣齿机和刀具,再编写齿轮加工的数控程...     

特种加工技术在精密微细加工中的应用

介绍了特种加工技术的概况及特点 ,并对精密微细加工中常用的特种加工方法的技术特点、应用领域及加工精度进行了评述。     

数控加工中工序划分与加工路线的确定

根据数控加工的工艺特点，应力求采用工序集中的方法，并选取最短的加工路线，这样有利于保证零件的加工精度，提高数控机床的生产效率。     

超精密加工精度分析

介绍超精密加工技术概要;从加工精度角度出发分析超精密加工技术国内外动态及今后发展的目标;探讨进一步提高主轴和导轨运动精度以及微进给和超精密测量精度等的可能性和关键技术问题;展望超精密加工技术在微细加工领域的发展前景。     

典型曲轴零件加工工艺分析及专用铣夹具设计

曲轴加工制造的质量直接决定柴油机的正常工作和寿命。针对曲轴零件的结构特点,详细分析了零件的技术要求、加工方法以及工艺路线,并在此基础上设计了其中一道工序的铣键槽夹具。该夹具结构简单,操作方便,定位精度高,大大提高了零件的加工效率。     

干切削在数控加工中的应用

分析了干切削在数控加工中对刀具、机床、工件的要求，阐述了刀具实现干切削的途径及刀具材料与工件材料适宜匹配的具体要求。     

椭圆弧齿线圆柱齿轮加工方法分析与加工仿真

在分析现有圆弧齿线圆柱齿轮基础上,阐述了一种渐开线椭圆弧齿线圆柱齿轮的主要几何参数:齿廓为渐开线齿廓,任意垂直轴线的截面上周向齿厚、周向齿槽宽、分度圆处的压力角相等,齿线在分度圆柱面上的展开线是对称椭圆弧.推导了齿轮齿面方程、端面齿廓方程和接触线方程.提出了倾斜式旋转刀盘齿轮加工方法,利用VERICUT建立齿轮专用加工...     

机械加工精度的影响因素及提高加工精度的途径

在机械加工过程中,加工误差不可避免,本文分析总结了影响机械加工精度的主要因素,并提出了提高机械加工精度的途径。