A new methodology for designing a curve-edged twist drill with an arbitrarily given distribution of the cutting angles along the tool cutting edge

The present study aims at the development of a new methodology for designing a curve-edged twist drill with an arbitrarily given distribution of the cutting angles along the tool cutting edge. The new methodology consists of 81 major mathematical equations and is developed using a method of mapping relevant planes and straight lines of a cutting tool (such as the cutting plane and the cutting edge) as corresponding image points and image lines on a projection plane. The developed methodology is used to intuitively and graphically analyze and determine the relationship between the orientation of the cutting edge and the cutting angles at each point on the cutting edge. A set of image points and image lines is established to calculate the cutting angles on the cutting edge of a twist drill, including the working tool rake angle, the working tool inclination angle, the working cutting edge angle, and the working normal rake angle. Three computer case studies are provided to show curved cutting edges that correspond, respectively, to a linear distribution of the working tool rake angle, a combined linear and uniform distribution of the working tool rake angle, and a linear distribution of the working tool inclination angle along the tool cutting edge. Finally, a set of metal drilling experiments is performed to compare the drilling torque and the thrust force between a conventional straight-edged twist drill and a new curve-edged twist drill that has a combined linear and uniform distribution of the working tool rake angle along the tool cutting edge. The experimental results show that the new curve-edged drill reduces the drilling torque by 28.5% and the thrust force by 24.6% on average.     

不同斧型钻齿切削刃角下的破岩方式

为进一步理解斧型 PDC钻齿破岩机理,建立PDC钻齿破岩的3D有限元模型,对3种不同切削刃夹角的斧型PDC钻齿破岩方式开展对比研究。结果表明:与150°和165°的钻齿相比,135°的斧型钻齿受到的剪切力和切削力更小,从而具有更高的破岩效率。在相同的后倾角、相同的切削深度和相同的切削力下,165°斧型钻齿切削力波动较小,稳定性更高。与立式车床上的实验数据相比,仿真结果与实验结果总体趋势一致,误差在可接受范围内。      

Chisel edge and cutting lip shape optimization for improved twist drill point design

This paper investigates the optimization of twist drill point geometries in order to minimize thrust and torque in drilling. A point geometry parameterization based on the drill grinding parameters is used to ensure manufacturability of the optimized geometry. Three commonly used drill point geometries, namely, conical, Racon^® and helical, are optimized for drilling forces while maintaining the inherent characteristics of each of the profiles. A significant reduction is shown in the drilling forces for the optimized drills. Drills with the optimized conical point profile are produced and tests run to validate the reduction in thrust and torque.     

Toroidal grinding method for curved cutting edge twist drills

In this paper, a new grinding procedure for the curved cutting edge twist drills is presented, i.e., the toroidal grinding procedure. Within this procedure, the clearance surface of the twist drill is a cylindrical helicoid surface with a constant pitch. Based on the principle of distance minimization and envelope theory, a numerical method of calculating the grinding wheel profile is developed. This grinding method allows the profile of the main cutting edge to be continuous and obtained directly during the grinding procedure. The feasibility of the toroidal grinding method is verified by drill grinding experiment and drilling measurements.     

A practical method of modelling and simulation for drill fluting

A grinding wheel profile for drill fluting is usually designed by the indirect method, defining the wheel profile by the desired drill flute. This paper presents an adaptive and intuitive direct method for drill flute modelling. It is summarized as follows: the grinding wheel, with analytically defined profile, is assumed to be moving helically around the stationary drill; the flute is generated by the overlapping part between the wheel locus and the workpiece. Its validity is verified by good agreement between the results computed and the data measured on the samples manufactured.     

A method of using turning process excitation to determine dynamic cutting coefficients

Identification of the dynamic cutting force coefficients is an essential work in cutting process modeling. The excitation equipment employed to produce dynamic cutting process is usually sophisticated and may lead to potential error. An alternative method of turning process excitation is proposed to simplify the procedure of cutting dynamics measurement. A cantilever workpiece used in cylindrical turning process has been modeled with a double degree-of-freedom system that supports variable dynamic parameters. The structural dynamics of the equivalent system are analyzed with the theoretical derivation and the finite element simulations. The influence of structural dynamic variation on the chatter frequency is investigated, based on which the self-excited chatter is considered as a method of the turning process excitation. This method is applied in the cutting dynamics tests. The dynamic cutting force coefficients could be measured through a single chattering turning process. Stability analysis is conducted for verification of the measured dynamic cutting coefficients.     

A new method for analysing and calculating angles on cutting tools

A new method for analysing and calculating angles on cutting tools by means of projective geometry, vector algebra and matrix algebra is suggested. This method makes it possible to turn the solid geometry problem into a plane geometry one, and to deduce the relationship between the various angles of cutting tools more readily, promptly and intuitively. Moreover, all the working angles and dynamic angles during cutting can be calculated.     

A method for measuring cutting forces in boring operations

In boring operations, two methods of measuring cutting forces are possible: measurement of forces exerted on the tool, by means of a dynamometric boring bar, or measurement of forces exerted on the workpiece, by means of a dynamometric table.In the second method, it is difficult to read the three components of the cutting force (tangential, radial and axial force), because the tool is rotating with respect to the workpiece. A three-component dynamometer on which the workpiece is clamped gives the axial (feed) force directly. The other two outputs, instead, are projections on two fixed axes of a force that is the sum of the radial and tangential components, and that rotates at spindle speed.This paper describes a simple, reliable method for solving the problem of obtaining the single components of the rotating force. Tangential and radial forces are measured continuously by means of an electrical resolver and lowcost electronic equipment.     

Development of freeform grinding methods for complex drill flank surfaces and cutting edge contours

This paper details the development of an innovative freeform grinding method that enables the generation of complex drill flank surfaces and cutting edge contours that are non-quadratic model based. This method allows a direct and independent design of drill cutting angle distributions—normal rake angle (γ_n) and relief angle (α_f). Mathematical formulations were first developed for γ_n and α_f in terms of drill geometric parameters such as helix angle, flute contour, and cutting edge contour. The developed freeform grinding methods enhance the flexibility of the grinding process by enabling the production of drills with convex and concave flank surfaces and complex cutting edge contours with standard wheel sets, eliminating the need to manufacture specially designed form grinding wheels.     

基于正交切削模型的铣削加工残余应力预测方法

提出了一种基于正交切削模型的铣削加工残余应力预测方法.针对直齿圆柱铣刀建立了铣削加工的平面应变有限元模型,并通过分段曲线限定不同温度下应力与应变间的关系,详细表明材料的加工硬化规律.有限元模型采用相关的实验数据进行了验证.在铣削用量确定的前提下,通过对航空铝合金70507451进行加工模拟,研究了直齿圆柱铣刀前角对已加工表面残余应力的影响.     

Investigation of the effect of rake angle on main cutting force

This paper presents a study of comparison of empirical and experimental results for main cutting force during machining rotational parts by unworn cutting tools. A dynamometer was designed and produced for measuring the forces. Two strain gauges were placed at the correct position on the machine tool and cutting tool at the design stage. Correct gauge positioning sensed displacements of the tool caused by cutting forces. AISI 1040 was used as the workpiece material. Main cutting force (F_c) was measured for eight different rake angles changing from negative to positive values at five different cutting speeds. The depth of cut and feed rate were kept throughout the experiments. Empirical results according to Kienzle approach were compared with experimental results. Main cutting force was observed to have a decreasing trend as the rake angle increased from negative to positive values. The deviation between empirical approach and experiments was in the order of 10–15%.     

A study of high-performance plane rake faced twist drills. Part II: Predictive force models

Predictive cutting models for the thrust, torque and power in drilling operations using modified plane rake faced twist drills are presented and discussed. The models are based on the mechanics of cutting approach incorporating the many tool and cutting process variables and have been assessed by numerically analysing the predicted trends and by comparing with the experimental data. It is shown that the model predictions are in excellent agreement with the experimental results with an average deviation of about 5%. Simpler “empirical-type” thrust, torque and power equations are also established for use as an accurate alternative to the complex predictive models to facilitate practical applications.     

Influence of cutting edge geometry and cutting edge radius on the stability of micromilling processes

The occurrence of tool vibrations in the micromilling process is undesirable because of its negative influence on the quality of microstructures. Due to the small dimensions of the undeformed chip parameter, the influence of the cutting edge on the chip formation and on the regenerative effect seems to be larger than in macrodimensions. Within this paper the results of an experimental investigation with micro end-milling cutters (d = 1 mm) are presented. Additionally, the influences of the cutting edge radius, the corner radius, and the feed per tooth on the tool vibration trajectories, the process forces, and chatter and its causes are discussed.     

A numerical model to determine temperature distribution in orthogonal metal cutting

In this study, a thermal analysis model is developed to determine temperature distribution in orthogonal metal cutting using finite elements method. The model calculates the temperature distribution as a function of heat generation. The heat generation was introduced in the primary deformation zone, the secondary deformation zone and along the sliding frictional zone at the tool–chip interface, as well. The location and shapes of these zones was determined based on the literature work done so far and the model results. The temperature dependency of material properties was included in the model. A series of thermal simulations have been performed, and the value and location of maximum temperature have been determined for various cutting conditions. The comparison of the simulations with earlier works gave promising trend for the presented model. The thermal aspects of metal cutting as a result of the model findings were discussed.     

A simple inverse procedure to determine heat flux on the tool in orthogonal cutting

The applications of numerical simulation to machining processes have been more and more increasing in the last decade: today, a quite effective predictive capability has been reached, at least as far as global cutting variables (for instance cutting forces) are concerned. On the other hand, the capability to predict local cutting variables (i.e. stresses acting on the tool, temperature distribution, residual stresses in the machined surface) has to be furtherly improved, as well as effective experimental procedures to validate numerical results have to be developed.The aim of this paper is the proposition of an innovative approach, based on an simple inverse procedure, in order to identify both the heat flux flowing into the tool through the rake face and the heat transfer coefficient between the tool and the environment during a typical orthogonal cutting process. It is worth pointing out that the effective determination of such quantities is necessary in order to carry out a reliable prediction of the temperature distribution in the tool during the process.The procedure is based on the integration of numerical simulations, inverse approach algorithms and experimental tests.     

Prediction of the cutting forces for chamfered main cutting edge tools

A new cutting model of various tool geometries for tools with a chamfered main cutting edge has been built. Theoretical values of cutting forces were calculated and compared with the experimental results; the forces predicted by this model were consistent with the experimental values. Special tool holders were designed and manufactured to obtain various tool geometries. Cutting experiments were conducted on a carbon steel to examine the mechanism of secondary chip formation; the relationship between the shapes of secondary chips and tool geometries was observed.     

Performance of cryogenically treated WC drill using tool wear measurements on the cutting edge and hole surface topography when drilling CFRP

Drilling CFRP poses major challenges from the perspective of rapid tool wear and poor hole quality, with the development of higher strength fibers further accentuating these problems. Cryogenic treatment is one way of increasing tool hardness thereby improving tool life and hole quality through longer retention of cutting edge sharpness. In this study, tool wear is monitored by measuring flank wear, cutting edge flatting (CEF), peak flatting (PF) and cutting edge surface roughness (CESR). While flank wear is unable to distinguish the better performance of the cryo-treated drill from the untreated drill, the other wear parameters are able to account for the better hole quality (exit delamination) produced by this drill. CEF and PF are direct measures of the extent of cutting edge blunting unlike flank wear which measures wear along the flank due to rubbing. Fiber pullout is the primary reason for deterioration in surface finish and Rz and Rv are better measures than Ra in estimating surface quality.     

A practical method to evaluate radiographic unsharpness

A simple method for evaluation of total unsharpness of radiographs using wires of different diameters and plaque type penetrameters instead of knife edge method has been suggested. The theoretical basis of the method and experimental details are explained in this paper.     

Active chatter suppression by on-line variation of the rake and clearance angles in turning— principles and experimental investigations

In this paper both the principles and experimental results of active chatter suppression by on-line variation of the rake and clearance angles are presented. A non-linear theoretical model was established to discuss the effects of the changes of the rake and clearance angles on dynamic stability. Based on the theoretical analysis, a strategy for chatter suppression was developed and an experimental device constructed and tested on a lathe. The results indicated that suppression of chatter by on-line variations of the rake and clearance angles was feasible and that a good correlation between the theoretical analysis and experimental results existed.     

A new procedure to determine instantaneous cutting force coefficients for machining force prediction

This paper presents a new procedure to determine instantaneous cutting force coefficients which are required for process simulation by mechanistic modeling. This new procedure drastically reduces the number of experiments for calibration and improves the accuracy of dynamic cutting forces and force signatures by considering the size effects. Comparisons are shown to illustrate the effectiveness of the proposed method in determining the chip flow angle and those predicted by various existing analytical models. The importance of using instantaneous cutting force coefficients instead of conventional average coefficients is demonstrated through simulation based on the mechanistic models.