金刚石绳锯加工弧区锯切力分布的研究

本文针对金刚石绳锯的柔性加工以及长锯切弧区的加工特点,采用弧区内分段的实验方法,在弧区七个位置选取了50 mm的微段,对每个微段进行锯切力的测量,进而总结出锯切加工弧区内锯切力的分布情况.研究结果表明:当线速度和进给速度较小时,整个弧区的锯切力的波动较小,随着线速度和进给速度的增大,弧区锯切力在整个弧区的波动随之变大;...     

Identification of the specific cutting force for geometrically defined cutting edges and varying cutting conditions

Cutting force modeling is a major discipline in the research of cutting processes. The exact prediction of cutting forces is crucial for process characterization and optimization. Semi-empirical and mechanistic force models have been established, but the identification of the specific cutting force for a pair of tool and workpiece material is still challenging. Existing approaches are depending on geometrical idealizations and on an extensive calibration process, which make practical and industrial application difficult. For nonstandard tools and five axis kinematics there does not exist a reasonable solution for the identification problem.In this paper a co-operative force model for the identification of the specific cutting forces and prediction of integral forces is presented. The model is coupled bidirectionally with a multi-dexel based material removal model that provides geometrical contact zone information. The nonlinear specific forces are modeled as polynomials of uncut chip thickness. The presented force model is not subjected to principal restrictions on tool shape or kinematics, the specific force and phase shift are identified with help of least square minimization. The benefit of this technique is that no special calibration experiments are needed anymore, which qualifies the method to determine the specific forces simultaneously during the machining process. In this paper, experiments with different cutting conditions are analyzed and systematically rated. Finally, the method is validated by experiments using different cutting conditions.     

A three-dimensional analytical cutting force model for micro end milling operation

In the present day manufacturing arena one of the most important fields of interest lies in the manufacturing of miniaturized components. End milling with fine-grained carbide micro end mills could be an efficient and economical means for medium and small lot production of micro components. Analysis of the cutting force in micro end milling plays a vital role in characterizing the cutting process, in estimating the tool life and in optimizing the process. A new approach to analytical three-dimensional cutting force modeling has been introduced in this paper. The model determines the theoretical chip area at any specific angular position of the tool cutting edge by considering the geometry of the path of the cutting edge and relates this with tangential cutting force. A greater proportion of the helix face of the cutter participating in the cutting process differs the cutting force profile in micro end milling operations a bit from that in conventional end milling operations. This is because of the reason that the depth-of-cut to tool diameter ratio is much higher in micro end milling than the conventional one. The analytical cutting force expressions developed in this model have been simulated for a set of cutting conditions and are found to be well in harmony with experimental results.     

Simplified and efficient calibration of a mechanistic cutting force model for ball-end milling

Accurate evaluation of the empirical coefficients of a mechanistic cutting force model is critical to the reliability of the predicted cutting forces. This paper presents a simplified and efficient method to determine the cutting force coefficients of a ball-end milling model. The unique feature of this new method is that only a single half-slot cut is to be performed to calibrate the empirical force coefficients that are valid over a wide range of cutting conditions. The instantaneous cutting forces are used with the established helical cutting edge profile on the ball-end mill. The half-slot calibration cut enables successive determination of the lumped discrete values of the varying cutting mechanics parameters along the cutter axis whereas the size effect parameters are determined from the known variation of undeformed chip thickness with cutter rotation. The effectiveness of the present method in determining the cutting force coefficients has been demonstrated experimentally with a series of verification test cuts.     

A unified instantaneous cutting force model for flat end mills with variable geometries

A new and unified instantaneous cutting force model is developed to predict cutting forces for flat end mills with variable geometries. This model can routinely and efficiently determine the cutting properties such as shear stress, shear and normal friction angles (SSSNFAs) involved in the cutting force coefficients by means of only a few milling tests rather than existing abundant orthogonal turning tests. Novel algorithms are developed to characterize these properties using following steps: transformation of cutting forces measured in Cartesian coordinate system into a local system on the normal plane, establishment of explicit equations to bridge SSSNFAs and the transformed cutting forces, determination of SSSNFAs by solving the equations and fitting SSSNFAs as functions of process geometries. Results definitely show that shear stress can be treated as a constant whereas shear and normal friction angles should be characterized by Weibull functions of instantaneous uncut chip thickness. Experiments verify that the proposed unified model is effective to predict the cutting forces in flat end milling in spite of cutter geometries and cutting conditions.     

A comprehensive dynamic cutting force model for chatter prediction in turning

This paper presents a model of the dynamic cutting force process for the three-dimensional or oblique turning operation. To obtain dynamic force predictions, the mechanistic force model is linked to a tool–workpiece vibration model. Particular attention was paid to the inclusion of the cross-coupling between radial and axial vibrations in the force model. The inclusion of this cross-coupling facilitates prediction of the unstable–stable chatter phenomenon which usually occurs in certain cases of finish turning due to process non-linearity. The dynamic force model developed was incorporated into a computer program to obtain time-saving chatter predictions. Experimental tests were performed on AISI 4140 steel workpieces to justify the chatter predictions of the dynamic cutting process model in both the finishing and roughing regimes. Experimental results corroborate the unstable–stable chatter predictions of the model for different cases of finish machining. In addition, experimental results also confirmed the accuracy of chatter predictions for various cases of rough turning.     

金刚石线切割单晶碳化硅锯切力的实验研究

从锯切力的角度对金刚石线锯锯切单晶SiC材料的加工过程进行了研究。得出了线速度、进给速度、线锯张紧力对锯切力的影响规律。从单位长度线锯材料去除量、锯切比能的角度讨论了锯切工艺对锯切力的影响机理。在金刚石线锯锯切单晶SiC过程中,锯切力随着线速度的增大而减小,随着进给速度的增大而增大,线速度与进给速度对锯切力的综合影响表现为:单位长度线锯材料去除量的增加会增大锯切力。单位长度线锯材料去除量对于金刚石线锯锯切单晶SiC材料的锯切比能具有显著的影响。     

金刚石框架锯锯切花岗岩的锯切力实验研究

本实验对金刚石框架锯锯切花岗岩过程当中的刀具轨迹进行了分析,通过单因素法和正交试验法对锯切力进行了跟踪监测,研究了锯切力随飞轮转速、进给速度和锯切长度的变化趋势。实验结果表明:金刚石锯条按弧线运动轨迹进行锯切,且在一个锯切往复周期内刀具只有一半时间参与锯切,锯切力Fh和Fc随着飞轮转速的增大而减小,随着进给速度和锯切长度的增大而增加。通过回归分析建立了锯切力数学模型,得出进给速度对Fh和Fc影响最明显,锯切长度次之,飞轮转速影响最小,并可以通过该模型在实际生产中预测锯切力的大小。     

Prediction of chatter in NC machining based on a dynamic cutting force model for ball end milling

Ball end milling is one of the most widely used cutting processes in the automotive, aerospace, die/mold, and machine parts industries, and the chatter generated under unsuitable cutting conditions is an extremely serious problem as it causes excessive tool wear, noise, tool breakage, and deterioration of the surface quality. Due to the critical nature of detecting and preventing chatter, we propose a dynamic cutting force model for ball end milling that can precisely predict the cutting force for both stable and unstable cutting states because our uncut chip thickness model considers the back-side cutting effect in unstable cutting states. Furthermore, the dynamic cutting force model considers both tool runout and the penetration effect to improve the accuracy of its predictions. We developed software for calculating the cutting configuration and predicting the dynamic cutting force in general NC machining as well as single-path cutting. The chatter in ball end milling can be detected from the calculated cutting forces and their frequency spectra. A comparison of the predicted and measured cutting forces demonstrated that the proposed method provides accurate results.     

加工过程的切削力模拟

给出了加工过程的切削力模型,并引入ＭＡＴＬＡＢ语言对加工过程的切削力进行了仿真分析。用ＭＡＴＬＡＢ程序可方便有效地实现非线性加工过程的切削力模拟,这对于加工系统的动态设计和教学具有重要的实用价值。     

An examination of the fundamental mechanics of cutting force coefficients

In metal cutting, the cutting force is the key factor affecting the machined surface, and is also important in determining reasonable cutting parameters. The research and construction of cutting force prediction models therefore has a great practical value. The accuracy of cutting force prediction largely depends on the cutting force coefficients of the material. In the average cutting force model, cutting force coefficients are considered to be constant. This study makes use of experiments to investigate the cutting force coefficients in the average cutting force model, with a view to accurately identifying cutting force coefficients and verifying that they are related only to the tool–workpiece material couple and the tool geometrical parameters, and are not affected by milling parameters. To this end, the paper first examines the theory behind identifying cutting force coefficients in the average cutting force model. Based on this theory, a series of slot-milling experiments are performed to measure the milling forces, fixing spindle speeds and radial/axial depths of cutting, and linearly varying the feed per tooth. The tangential milling force coefficient and the radial milling force coefficient are then calculated by linearly fitting the experimental data. The obtained results show that altering the milling parameters does not change the milling force coefficients for the selected tool/workpiece material combination.     

A model for thread milling cutting forces

This paper presents a mechanistic model for prediction of the thread milling forces. The mechanics of cutting for thread milling is analyzed similar to the end milling process but with modified cutting edge geometry. The chip thickness and cutting force models are developed considering the unique geometry of the tool. The model has been calibrated for 6061 Aluminum and validated. The effects of tool and thread geometry have been studied using the model.     

Accurate 3-D cutting force prediction using cutting condition independent coefficients in end milling

The instantaneous uncut chip thickness and specific cutting forces have a significant effect on predictions of cutting force. This paper presents a systematic method for determining the coefficients in a three-dimensional mechanistic cutting force model—the cutting force coefficients (two specific cutting forces, chip flow angle) and runout parameters. Some existing models have taken the approach that the cutting force coefficients vary as a function of cutting conditions or cutter rotation angle. This paper, however, considers that the coefficients are affected only by the uncut chip thickness. The instantaneous uncut chip thickness is estimated by following the movement of the position of the center of a cutter. To consider the size effect, the present method derives the relationship between the re-scaled uncut chip thickness and the normal specific cutting force, K_n with respect to the cutter rotation angle, while the other two coefficients—frictional specific cutting force, K_f and chip flow angle, θ_c—remain constant. Subsequently, all the coefficients can be obtained, irrespective of cutting conditions. The proposed method was verified experimentally for a wide range of cutting conditions, and gave significantly better predictions of cutting forces.     

A force model for nose radius worn tools with a chamfered main cutting edge

The three-dimensional cutting forces for nose radius tools with a chamfered main cutting edge incorporated with a tool-worn factor are presented in this paper. The variations in shear plane areas occurring in the tool-worn situation are used. The results obtained from the proposed model shows good agreement with the experimental data on both chip formation as well as cutting forces. In the experimental work the throwaway tips are locked onto the pocket of the tool holder. The holders for special tools are designed first. Next, the tool holders are manufactured by using medium carbon-steel bars and the mounting tips are designed based on various specifications. Finally, the nose radius tips mounting in the tool holder are ground to a wear depth, and the worn tool dimensions are measured by using a profile projector. The shear area and the friction area are calculated accordingly. Then the three-dimensional cutting forces will be obtained from those data.     

硬脆材料的电镀金刚石线锯超声切割锯切力研究

基于冲量理论和振动加工理论,采用叠加原理建立了电镀金刚石线锯超声切割锯切力数学模型.从理论上分析了电镀金刚石线锯施加超声振动后锯切力与普通锯切力的区别,并进行了超声振动与普通锯切力对比试验研究.结果表明:锯切力的大小随线锯往复频率的提高而降低,随侧向压力的增加而增大.通过比较发现,超声振动锯切力比普通锯切力减小20%～30%.同时,对超声振动锯切过程中单颗金刚石磨粒切削运动轨迹进行了仿真分析,进一步解释了施加超声振动后锯切力减小的原因.     

Mechanistic modeling of bone-drilling process with experimental validation

In this paper, an improved mechanistic model is developed to predict the thrust force and torque for bone-drilling operation. The cutting action at the drill point is divided into three regions: the cutting lips, outer portion of the chisel edge (the secondary cutting edges), and inner portion of the chisel edge (the indentation zone). Models that account for the unique mechanics of the cutting process for each of the three regions are formulated. The models are calibrated to bovine cortical bone material using specific cutting pressure equations with modification to take advantage of the characteristics of the drill point geometry. The models are validated for the cutting lips, the chisel edge, and entire drill point for a wide range of spindle speed and feed rate. The predicted results agree well with experimental results. Only the predictions for the drilling torque on the chisel edge are lower than the experimental results under some drilling conditions. The model can assist in the selection of favorable drilling conditions and drill-bit geometries for bone-drilling operations.     

曲面精加工过程切削负载自适应新策略研究

分析了曲面积、精加工过程的不同特点,指出传统的切削负载自适应方法应用到曲面精加工过程时的缺陷,提出新的简单、易行的曲面精加工负载自适应策略－等切削力余量模型方法,论述了模型的构造算法及其关键技术。     

An in-depth analysis of the synchronization between the measured and predicted cutting forces for developing instantaneous milling force model

This paper proposes an analytical approach to synchronize the measured and predicted cutting forces for calibrating instantaneous cutting force coefficients that vary with the instantaneous uncut chip thickness in general end milling. Essential issues such as the synchronization criterion, phase determination of measured cutting forces, specification of calibration experiments and related cutting parameters are highlighted both theoretically and numerically to ensure the calibration accuracy. A closed-form criterion is established to select cutting parameters ensuring the single tooth engagement. Numerical cutting simulations and experimental test results are compared to validate the proposed approach.     

A mechanistic force model for combined axial–radial contour turning

In this paper, a mechanistic force model for combined axial–radial contour turning is presented. Analytical expressions are derived for the computation of the mechanistic parameters as a function of the axial and radial contour variations. The force model is experimentally validated for axial and radial contour turning processes. The effects of the combined axial–radial contour variations and the tool geometry parameters on the cutting forces are analyzed via additional simulations for combined contour turning.     

烧结金刚石串珠绳锯切花岗石的锯切力研究

本文对烧结金刚石串珠绳在锯切花岗石过程中,锯切力及锯切后工件表面的轮廓进行了跟踪检测,研究了锯切过程中,锯切力随锯切参数的变化,以及锯切力与工件表面轮廓的相互关系。实验结果表明：锯切过程中,工件上所承受的锯切力Fh和Fv随着线速度Vs的提高而减低,随着进给速度吩的提高而增加。垂直力与水平力之间存在着良好的对应关系,垂直力与水平力比约为4．18。加工后工件轮廓偏差量随着工件所承受的垂直力的增加而增加,两者之间呈指数关系。