Development of a dynamometer for measuring individual cutting edge forces in face milling

Cutting force information may be used for several tasks, such as tool design and trajectory optimization, tool condition monitoring, machinability testing and many others. Accordingly, cutting force measuring has become a crucial activity aimed at enhancing process performance. In this work, the development of an innovative rotating dynamometer for cutting force measurement in milling is illustrated. The device is capable of providing independent triaxial cutting force information from each cutting edge with a good dynamic response. Static and dynamic behavior of a simplified single-edge device was first investigated through the static calibration procedure, pulse tests and preliminary cutting tests. Afterwards, the dynamic properties of the final prototype clamped on the spindle of a high speed milling machine were assessed by means of standard and rotating pulse tests – i.e. pulse tests performed during spindle rotation. Eventually, cutting tests were performed on a benchmark workpiece. The experimental tests highlighted the superior features of the new device.     

Fast evaluation of cutting forces in milling, applying no approximate models

A new method for fast evaluation of cutting forces in milling is introduced and tested experimentally. Unlike all existing procedures, which include the use of cutting models and approximate assumptions, in this method, the elementary functions of the cutting force are obtained from measured values only.The basic force functions for the whole feed range are acquired from one experiment using a single-tooth full-diameter (slot) milling, applying a specially developed procedure. The milling experiment is conducted under low-impact conditions, enabling accurate measurement and convenient signal processing. The basic force functions are then integrated and superimposed, using known procedures, to combine the total force in any multitooth milling combination. In this work the method is explained and tested experimentally.The suggested method enables a reliable evaluation of the cutting forces, while demanding minimal experimental work, the method applies to cutters having complicated edge geometry, and to high speed milling.Nomenclature a radial depth of cut 0<a<D - feed per tooth ratio 0<1 - d axial depth of cut - D cutter diameter - a/D radial depth ratio - cutter rotation angle - cutter rotation angle [6] - F _x,y,z() instantaneous edge cutting forces in fixture coordinates - F _t,r,z() instantaneous edge cutting forces in tool coordinates - F _x,y,z ^* F_t,r,z tool cutting force components on a multitooth cutter - h instantaneous chip thickness [6] - h* equivalent edge coefficient [6] - r ₁,r ₂ tangential radial ratio coefficient [6] - K _T tangential specific cutting force [4] - K _R radial specific cutting force [4] - N number of teeth - R _r resolution reduction factor - t instantaneous chip thickness - S ₁,S feed per tooth     

Evaluation of static cutting forces and tool wear in HSM process applied to pocket milling

One of the main operations in the manufacturing of molds and dies is the opening of the initial pocket, from which more complex geometries are machined, in order to obtain the negative shape of the final product. Since this is a rough operation, high cutting forces and significant tool wear are observed. Aiming to reduce such parameters, several strategies of tool entry and internal cut of the pocket have been proposed. In this context, this work aims to evaluate the cutting forces in the different parts of a pocket milling, using three different strategies, which are composed by the tool, cutting conditions, tool entry, and tool trajectory (I: ramp entry with spiral internal cut, II: helical entry with zigzag internal cut, and III: plunge entry). The results obtained for strategies I and II showed an increase in the forces in the direction perpendicular to the face in which flank wear occurred and a sharp increase in force at points where the tool changes trajectory. In strategy III, the occurrence of tool fracture due to chip recut led to very high force values.     

Prediction of cutting forces in helical milling process

The prediction of cutting forces is important for the planning and optimization of machining process in order to reduce machining damage. Helical milling is a kind of hole-machining technique with a milling tool feeding on a helical path into the workpiece, and thus, both the periphery cutting edges and the bottom cutting edges all participated in the machining process. In order to investigate the characteristics of discontinuous milling resulting in the time varying undeformed chip thickness and cutting forces direction, this paper establishes a novel analytic cutting force model of the helical milling based on the helical milling principle. Dynamic cutting forces are measured and analyzed under different cutting parameters for the titanium alloy (Ti–6Al–4V). Cutting force coefficients are identified and discussed based on the experimental test. Analytical model prediction is compared with experiment testing. It is noted that the analytical results are in good agreement with the experimental data; thus, the established cutting force model can be utilized as an effective tool to predict the change of cutting forces in helical milling process under different cutting conditions.     

Model-based identification of tool runout in end milling and estimation of surface roughness from measured cutting forces

This paper presents a model-based approach for the identification of tool runout and the estimation of surface roughness from measured cutting forces. In the first part of the paper, the effect of tool runout on variations in the cutting forces and the effect on surface roughness generation are studied. Thereby, several influencing parameters are identified and examined systematically. Based on theoretical considerations, systematic relationships between tool runout, resultant process force variations, and surface roughness characteristics are deduced. The sensitivity of process force variation is investigated for varying runout parameters by experimental tests. In the next part, the model-based runout identification method is developed, which identifies runout parameters accurately from the measured process forces. The approach has been tested extensively and was verified by measured runout parameters and the correlation of surface roughness characteristics of the machined workpiece. The performance of the developed approach is demonstrated in the final part by comparing the result of the model-based surface reconstruction with the measured surface topography.     

On modeling of cutting forces in micro-end milling operation

Micro-end milling is used for manufacturing of complex miniaturized components precisely in wide range of materials. It is important to predict cutting forces accurately as it plays vital role in controlling tool and workpiece deflections as well as tool wear and breakage. The present study attempts to incorporate process characteristics such as edge radius of cutting tool, effective rake and clearance angles, minimum chip thickness, and elastic recovery of work material collectively while predicting cutting forces using mechanistic model. To incorporate these process characteristics effectively, it is proposed to divide cutting zone into two regions: shearing- and ploughing-dominant regions. The methodology estimates cutting forces in each partitioned zone separately and then combines the same to obtain total cutting force at a given cutter rotation angle. The results of proposed model are validated by performing machining experiments over a wide range of cutting conditions. The paper also highlights the importance of incorporating elastic recovery of work material and effective rake and clearance angle while predicting cutting forces. It has been observed that the proposed methodology predicts the magnitude and profile of cutting forces accurately for micro-end milling operation.     

数控铣削加工曲面时刀具轨迹的研究

数控铣削加工曲面过程中,刀具的运动轨迹是影响加工质量的一个重要因素.研究了数控铣削加工过程中刀具轨迹的生成,以及不同轨迹形式对加工质量有何影响等内容.     

Modeling of cutting forces in helical milling by analysis of tool contact angle and respective depths of cut

Knowledge of the behavior and magnitude of cutting forces is very important for correctly calculating cutting power and for obtaining tight tolerances and low levels of tool wear. In this way, the appropriate prediction of the force components collaborates with the correct choice of the cutting parameters and strategies. High oscillation of force values in helical milling increase the relevance of the analysis. In this context, present work describes an approach for modeling cutting forces in helical milling based on the analysis of tool contact angle and the respective depths of cut. From the model, it is possible to predict the behavior and magnitude of the force acting on the insert, which contributes to better process planning. The results indicated a good fit of the experimental values with the models, despite the observation of some errors, which occurred mainly due to the dynamics of the machine and the used approximations.     

Calculations of chip thickness and cutting forces in flexible end milling

In the end milling process of a flexible workpiece, it is well recognized that the precise determination of the instantaneous uncut chip thickness (IUCT) is essential for the cutting force calculation. This paper will present a general method that incorporates simultaneously the cutter/workpiece deflections and the immersion angle variation into the calculation of the IUCT and cutting forces. Contributions are twofold. Firstly, considering the regeneration model, a new scheme for the IUCT calculation is determined based on the relative positions between two adjacent tooth path centers. Secondly, a general approach is established to perform numerical validations. On one hand, the engagement/separation of the cutter from the workpiece is instantaneously identified. On the other hand, the calculation of the IUCT is iteratively performed. To demonstrate the validity of the method, several examples are used to show the convergence history of the cutting force and the IUCT during the flexible end milling process. Both theoretical analyses and numerical results show that the regeneration mechanism is short lived and will disappear after several tooth periods in flexible static end milling process .     

数控铣削加工中刀具半径补偿问题研究

刀具半径补偿是数控铣削加工中的常用功能，就数控铣削加工中刀具半径补偿的建立和取消、刀具半径补偿量的指定和计算方法、刀具半径补偿功能的应用进行了研究。     

Tool path generation and modification for constant cutting forces in direction parallel milling

This paper presents an optimized path generation algorithm for direction parallel milling, which is commonly used in the roughing and finishing stages. First, a geometrically efficient tool path generation algorithm using an intersection points graph is introduced. Second, the generated tool path is modified as an optimized tool path that maintains a constant material removal rate to achieve a constant cutting force and avoid chatter vibration, and the results are verified. Additional tool path segments are appended to the basic tool path through a pixel-based simulation technique. The algorithm is implemented for two-dimensional contiguous end milling operations with flat end mills, and cutting tests are conducted by measuring the spindle current, which reflects the changing machining situations, to verify the performance of the proposed method.     

八角环电阻式车削测力仪在车床三向力静刚度测定中的应用

阐述测定机床刚度的基本方法,并在以往测定机床刚度方法的基础上,采用八角环形电阻式三向车削测力仪测定机床刚度的方法,一方面可以不对测力圈进行标定,另一方面可以直接测量出FX、FY、FZ,从而减少几何运算,提高机床刚度的测量和计算精度.     

An improved cutting force model for micro milling considering machining dynamics

Micro milling, as a versatile micro machining process, is kinematically similar to conventional milling; however, it is significantly different from conventional milling with respect to chip formation mechanisms and uncut chip thickness modelling, due to the comparable size of the edge radius to the chip thickness, and the small per-tooth feeding. Considering tool runout and dynamic displacement between the tool and the workpiece, the contour of the workpiece left by previous tool paths is typically in a wavy form, and the wavy surface provides a feedback mechanism to cutting force generation because the instantaneous uncut chip thickness changes with both the vibration during the current tool path and the surface left by the previous tool paths. In this study, a more accurate uncut chip thickness model was established including the precise trochoidal trajectory of the cutting edge, tool runout and dynamic modulation caused by the machine tool system vibration. The dynamic regenerative effect is taken into account by considering the influence of all the previous cutting trajectories using numerical iteration; thus, the multiple time delays (MTD) are considered in this model. It is found that transient separation of the tool-workpiece occurring at a low feed per tooth, caused by MTD and the existing cutting force models, is no longer applicable when transient tool-workpiece separation occurs. Based on the proposed uncut chip thickness model, an improved cutting force model of micro milling is developed by full consideration of the ploughing effect and elastic recovery of the workpiece material. The proposed cutting force model is verified by micro end milling experiments, and the results show that the proposed model is capable of producing more accurate cutting force prediction than other existing models, particularly at small feed per tooth.     

Development of an innovative plate dynamometer for advanced milling and drilling applications

Tool geometry optimization, workpiece material characterization, process monitoring and optimization are based on the measurement of cutting forces by using machining dynamometers. Commercial dynamometers cover a wide range of machining applications, nevertheless there is a lack of measuring devices suitable for investigating milling and drilling applications with relatively small cutters and high spindle speeds. In this work, the development and testing of an innovative plate dynamometer designed for this purpose is discussed. The new measuring system was based on three high-sensitive triaxial piezoelectric force sensors arranged in a novel triangular configuration. Component design was optimized by using FE numerical approaches, according to the general guidelines derived from mathematical modeling of sensor dynamics. The prototype of the proposed device was manufactured and experimentally tested against two high-end commercial plate dynamometers by performing static calibration, modal analysis and cutting tests. Experimental results proved the excellent characteristics of the new device and its effectiveness for investigating advanced machining applications.