Development of a tool wear-monitoring system for hard turning

This paper describes an in-depth study on the development of a system for monitoring tool wear in hard turning. Hard turning is used in the manufacturing industry as an economic alternative to grinding, but the reliability of hard turning processes is often unpredictable. One of the main factors affecting the reliability of hard turning is tool wear. Conventional wear-monitoring systems for turning operations cannot be used for monitoring tools used in hard turning because a conglomeration of phenomena, such as chip formation, tool wear and surface finish during hard turning, exhibits unique behavior not found in regular turning operations. In this study, various aspects associated with hard turning were investigated with the aim of designing an accurate tool wear-monitoring system for hard turning. The findings of the investigation showed that the best method to monitor tool wear during hard turning would be by means of force-based monitoring with an Artificial Intelligence (AI) model. The novel formulation of the proposed AI model enables it to provide an accurate solution for monitoring crater and flank wear during hard turning. The suggested wear-monitoring system is simple and flexible enough for online implementation, which will allow more reliable hard turning in industry.     

A mixed-integer linear programming model for part mix, tool allocation, and process plan selection in CNC machining centres

A mixed-integer linear programming model is developed for the simultaneous determination of part mix, tool allocation and process plan selection in CNC machining centres. Illustration of the use of the model in a hypothetical example and its application to a real problem arising in deep seabed operations demonstrate the utility of the model as one more step towards the integration of computer-aided process planning (CAPP) tasks in CNC machining enviroments.     

Measurement of milling tool vibrations during cutting using laser vibrometry

Spindle and tool vibration measurements are of great importance in both the development and monitoring of high-speed milling. Measurements of cutting forces and vibrations on the stationary spindle head is the most used technique today. But since the milling results depend on the relative movement between the workpiece and the tool, it is desirable to measure on the rotating tool as close to the cutters as possible. In this paper the use of laser vibrometry (LDV) for milling tool vibration measurements during cutting is demonstrated. However, laser vibrometry measurements on rotating surfaces are not in general straight forward. Crosstalk between vibration velocity components and harmonic speckle noise generated from the repeating revolution of the surface topography are problems that must be considered. In order to overcome the mentioned issues, a cylindrical casing with a highly optically smooth surface was manufactured and mounted on the tool to be measured. The spindle vibrations, radial tool misalignment, and out-of-roundness of the measured surface were filtered out from the signal; hence, the vibrations of the cutting tool were resolved. Simultaneous measurements of cutting forces and spindle head vibrations were performed and comparisons between the signals were conducted. The results showed that vibration velocities or displacements of the tool can be obtained with high temporal resolution during cutting load and therefore the approach is proven to be feasible for analysing high-frequency milling tool vibrations.     

Five-axis tool orientation smoothing using quaternion interpolation algorithm

In five-axis machining, abrupt changes of tool axes may deteriorate the part surface, hence smoothing of tool orientations becomes an important issue. In the present tool path generation procedure, the tool orientation smoothing method (TOS method) is coupled with the cutting error improvement method (CEI method). TOS method is used to smooth tool orientations in order to reduce cutting errors and increase the machining efficiency. CEI method modifies existing cutter location data (CL data) so that final cutting errors are kept within the required tolerance. Experimental results show that the tool paths generated by the present procedure have better machining efficiency, better surface quality, and no interferences between the tool and part surfaces.     

基于多决策属性的刀具选择规则提取算法研究

传统的规则提取算法只是对单一的条件属性特征推理单一的决策属性值进行规则提取,为实现刀具智能选择,本文提出了一种通过加工特征和工件尺寸对刀具进行选择的规则提取算法,采用粗糙集进行刀具型号的规则提取,对刀具尺寸的选择采用区间值的基本理论,最后通过一个实例验证该算法的有效性.     

直齿圆锥齿轮精密锻造工艺及模具设计

针对直齿圆锥齿轮精锻成形中齿形充填不满及成形力过大导致模具损伤等问题,制定了中心分流法精锻直齿圆锥齿轮的工艺方案.以工艺方案和数值模拟结果为依据,设计了预锻分流区和分流终锻两套模具,并对精锻模具的模膛和结构设计要点进行了阐述.     

Monitoring of tool fracture in end milling using induction motor current

This paper describes the use of induction motor current to monitor tool fracture in end milling operations. The principles of induction motors are studied in this paper to establish the relationship between the motor current and the motor torque. It is shown that the square of the stator current of induction motors is approximately proportional to the motor torque. Since the occurrence of tool fracture will cause variations in the motor torque, measurement of the stator current appears to be an indirect technique for monitoring tool fracture. A sensitivity analysis of the stator current to the occurrence of tool fracture is also reported. Finally, experimental results under varying cutting conditions have been presented to demonstrate the effectiveness of this approach for the detection of tool fracture in end milling operations.     

基于Web Service的刀具配送系统研究与实现

针对传统刀具管理系统存在的不足,提出了一种新的基于Web Service刀具配送系统,对系统的集成技术进行了研究,在此基础上完成了系统的设计,并成功实施。     

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.     

伺服刀架系统的反复反馈误差补偿控制

对于具有滞后特性的伺服刀架系统,采用自校正ＰＩＤ控制。在此基础上,为进一步提高伺服刀架系统的跟踪精度,提出了反复反馈误差补偿控制方法。理论分析和实验结果都表明,该控制方法以有效地提高伺服刀架的跟踪精度。     

基于知识的电子装配CAPP技术研究

在对电子装配工艺设计过程中用到的知识进行分析的基础上,建立了知识的对象模型,采用对象类与产生式规则相结合的方法表示电子装配工艺设计知识,从而搭建出一个完全开放且面向对象的电子装配CAPP知识管理系统.     

Subshoulder formation during friction stir welding of steel using tungsten alloy tool

Abstract

A study was carried out on the friction stir welding of low alloy steel plates, to understand the influence of the tool profile on the tool wear rate, using a tungsten alloy tool. Three tool profiles were used for the wear study, namely, tool A with a concave shoulder and tapered pin of 2·8 mm, tool B with a flat shoulder and tapered pin of 2·6 mm and tool C with a concave shoulder and tapered pin of 2·6 mm. The tool wear characteristic was analysed by three methods, namely, the profile projector, weight loss and the image processing technique, and it was found that tool C gave reduced tool wear, when compared to the other tool profiles. In tool C, an impression of a step-like formation was generated automatically in the pin during welding and named as a subshoulder, which proved to be the optimised design.     

机床主轴电机的选择研究

电主轴是机床的核心部件,本文就主轴电机的选择,从使用要求、控制要求和经济性要求等方面对各类电机进行了分析比较,结合相应调速系统的对比,选择出适合机床主轴用执行电机的类型和调速系统。     

A critical analysis of effectiveness of acoustic emission signals to detect tool and workpiece malfunctions in milling operations

The industrial demands for automated machining systems to increase process productivity and quality in milling of aerospace critical safety components requires advanced investigations of the monitoring techniques. This is focussed on the detection and prediction of the occurrence of process malfunctions at both of tool (e.g. wear/chipping of cutting edges) and workpiece surface integrity (e.g. material drags, laps, pluckings) levels. Acoustic emission (AE) has been employed predominantly for tool condition monitoring of continuous machining operations (e.g. turning, drilling), but relatively little attention has been paid to monitor interrupted processes such as milling and especially to detect the occurrence of possible surface anomalies.This paper reports for the first time on the possibility of using AE sensory measures for monitoring both tool and workpiece surface integrity to enable milling of “damage-free” surfaces. The research focussed on identifying advanced monitoring techniques to enable the calculation of comprehensive AE sensory measures that can be applied independently and/or in conjunction with other sensory signals (e.g. force) to respond to the following technical requirements: (i) to identify time domain patterns that are independent from the tool path; (ii) ability to “calibrate” AE sensory measures against the gradual increase of tool wear/force signals; (iii) capability to detect workpiece surface defects (anomalies) as result of high energy transfer to the machined surfaces when abusive milling is applied.Although some drawbacks exist due to the amount of data manipulation, the results show good evidence that the proposed AE sensory measures have a great potential to be used in flexible and easily implementable solutions for monitoring tool and/or workpiece surface anomalies in milling operations.     

Mechanism investigation of friction-related effects in single point incremental forming using a developed oblique roller-ball tool

Single point incremental forming (SPIF) is a highly versatile and flexible process for rapid manufacturing of complex sheet metal parts. In the SPIF process, a ball nose tool moves along a predefined tool path to form the sheet to desired shapes. Due to its unique ability in local deformation of sheet metal, the friction condition between the tool and sheet plays a significant role in material deformation. The effects of friction on surface finish, forming load, material deformation and formability are studied using a newly developed oblique roller ball (ORB) tool. Four grades of aluminum sheet including AA1100, AA2024, AA5052 and AA6111 are employed in the experiments. The material deformation under both the ORB tool and conventional rigid tool are studied by drilling a small hole in the sheet. The experimental results suggest that by reducing the friction resistance using the ORB tool, better surface quality, reduced forming load, smaller through-the-thickness-shear and higher formability can be achieved. To obtain a better understanding of the frictional effect, an analytical model is developed based on the analysis of the stress state in the SPIF deformation zone. Using the developed model, an explicit relationship between the stress state and forming parameters is established. The experimental observations are in good agreement with the developed model. The model can also be used to explain two contrary effects of friction and corresponding through-the-thickness-shear: increase of friction would potentially enhance the forming stability and suppress the necking; however, increase of friction would also increase the stress triaxiality and decrease the formability. The final role of the friction effect depends on the significance of each effect in SPIF process.     

Fabrication of off-axis aspheric surfaces using a slow tool servo

Off-axis aspheric surfaces have been widely applied in optical systems, but it is difficult to fabricate this kind of optical surface with high quality. Slow tool servo is one of the methods for turning off-axis aspheric surfaces on-axis, which have a large travel range without an additional device. This paper presents a theoretical and experimental investigation on the 3D surface generation in single point diamond tuning using slow tool servo. The form error of off-axis paraboloid caused by tool centering error is analyzed and verified by cutting experiment.     

End milling tool breakage detection using lifting scheme and Mahalanobis distance

In this paper, a novel method based on lifting scheme and Mahalanobis distance (MD) is proposed for detection of tool breakage via acoustic emission (AE) signals generated in end milling process. The method consists of three stages. First, by investigating the specialty of AE signals, a biorthogonal wavelet with impact property is constructed using lifting scheme, and wavelet transform is carried out to separate AE components from the original signals. Second, Hilbert transform is adopted to demodulate signal envelope on wavelet coefficients and salient features indicating the tool state (i.e., normal conditions, slight breakage, and serious breakage) are extracted. Finally, tool conditions are identified directly through the recognition of these features by means of MD. Practical application results on a CNC vertical milling machine tool show that the proposed method is accurate for feature extraction and efficient for condition monitoring of cutting tools in end milling process.     

Modelling machine tool dynamics using a distributed parameter tool–holder joint interface

Increasing productivity in machining process demands high material removal rate in stable cutting conditions and depends strongly on dynamic properties of machine tool structure. Combined analytical–experimental procedures based on receptance coupling substructure analysis (RCSA) are employed to determine the stability of machine operating conditions at different tool configurations. The RCSA employs holder–spindle experimental mobility measurements in conjunction with an analytical model for the tool to predict the dynamics of different sets of tool and holder–spindle combinations without the need for repeated mobility measurements. In this paper an alternative approach using the concept of tool on resilient support is adopted to predict the machine tool dynamics in various tool configurations. In the proposed model the tool, represented by an analytical model, is partly resting on a resilient support provided by the holder–spindle assembly. The support dynamic flexibility is measured by performing vibration tests on the holder–spindle assembly. Tool–holder joint interface characteristics are included in the model by considering a distributed elastic interface layer between the holder–spindle and the tool shank part. The distributed interface layer takes into account the change in normal contact pressure along the joint interface and comparing with the lumped joint model used in RCSA it allows more detailed representation of the joint interface flexibility and damping which have crucial roles in machine dynamics. Experiments are conducted to demonstrate the efficiency of proposed model in prediction of milling operation dynamics and it is shown that the model is capable of accurately predicting the dynamic absorber effect of spindle in a tool tuning practice.