Some aspects of twist drill design

A mathematical approach to the flute disposal capacity based on the diameter of the circle which could be inscribed in the flute space is presented. It is important to know what order of drill rigidity is required for good performance when drilling various work materials. The main features of the cross-section profile which could affect the stiffness of a twist drill are the cross-sectional area and the second moment of area. The relationship between the various drill parameters and these features is one aspect to be investigated in this paper. Empirical equations based on the results obtained from this investigation are presented.     

Simulation-based twist drill design and geometry optimization

Designing a high-performance twist drill is difficult due to the complex relationship between drill geometry and numerous and conflicting design goals. Earlier approaches of computer-aided twist drill design are limited to only few design aspects. This article presents a new holistic method of using computing power for twist drill design and optimization. A complete drill geometry model is used to obtain drill performance characteristics and to ensure functional capability. Numerical simulation models calculate structural stiffness and strength, torque and thrust force, coolant flow resistance, chip evacuation capability and chip flute grindability. A multi-objective geometry optimization is realized by implementing metaheuristic optimization algorithms. As a result, a numerical overall optimization of twist drill performance is possible.     

A five axis computer controlled twist drill grinder

A new type of drill grinding machine controlled by a microprocessor has been designed. This machine has five computer controlled axes, each axis is driven by a DC servo motor. Three of the axes are rotary allowing the drill to take up any orientation in space. Two are translations allowing the grinding wheel to approach the drill point no matter where it is. Contouring software makes it possible to produce the necessary features on the drill point utilizing this positional flexability. For example, a racon point which has a round flank, a helical point which has a raised tip or web thinning and point splitting can be produced. Drills in the range of 0.375 in. (9.5 mm) to 1.5 in. (38.1 mm) dia. and in the length range of 7 to 15 in. (180 to 375 mm) can be ground. A sensor finds the location of the drill flute so the microcomputer can automatically orient the flute and cutting edge.     

Effect of groove-type chip breakers on twist drill performance

This paper proposes the use of grooves placed on the rake face of a twist drill to facilitate chip breaking and reduce drilling forces and chip clogging. A procedure to design grooves including groove geometry and orientation is discussed. Two sets of experiments are presented that determine the effect of grooves on the forces, chip morphology, and critical depth, and compare the life of the grooved and ungrooved drills. The grooves are found to be very effective in breaking chips and preventing chip clogging. Experiments show the positive effects of the grooves including lower drilling torque and thrust, lower chip evacuation forces, lower cutting forces, increased critical depth and increased drill life.     

Effect of eccentricity of twist drill and candle stick drill on delamination in drilling composite materials

Drilling is the most frequently employed operation of secondary machining for fiber-reinforced materials owing to the need for structure joining. Delamination is one of the serious concerns during drilling. Practical experience shows that an eccentric twist drill or an eccentric candle stick drill can degrade the quality of the fiber reinforced material. Comprehensive delamination models for the delamination induced by an eccentric twist drill and an eccentric candle stick drill in the drilling of composite materials have been constructed in the present study. For an eccentric twist drill and an eccentric candle stick drill, the critical thrust force that will produce delamination decreases with increasing point eccentricity ξ. The results agree with industrial experience. The need for control of drill eccentricity during drill regrinding has been proved analytically by the proposed models.     

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.     

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.     

Abrasive points for drill grinding of carbon fibre reinforced thermoset

In this study, an approach for using diamond grinding tools to machine holes in epoxy carbon laminates is described. The development of a suitable tool design and the influence of the cutting parameters are presented. With these tools, large total drilling lengths can be achieved without significant grain wear. Analysis of the results shows that the coolant supply can be reduced without exceeding the resin's glass transition temperature. In addition to the experimental results, a process simulation is applied to improve the tool layout and hence to avoid material clogging at the grinding layer.     

A practical method to determine rake angles of twist drill by measuring the cutting edge

Rake angle and its distribution on the cutting edge of a twist drill are of vital importance to its performance. This paper presents a practical method to determine the cutting edge and rake angles. Firstly, 3D coordinates of the points on the cutting edge are inspected by using 2D measurement apparatus. Secondly, the flute profile is deduced from the data measured, and the rake angles are evaluated by numerical computation. Conventionally, rake angle calculation is based on a series of plane definitions and laborious work in plane projection is inevitable. To facilitate the process, a vector based procedure is presented. As an example, cutting edge of a standard drill is measured by using tool microscope and image-based instrument. In each case, the normal rake angle distribution is determined. Numerical results exhibit that average error and mean square error of the latter deviated from the former are 0.95^o and 0.33^o, respectively. It verifies the validity of the proposed procedure and the measurement device.     

W6Mo5Cr4V2Al高速钢麻花钻断裂原因分析

利用化学成分分析、光学显微镜、扫描电镜以及能谱分析等手段研究了W6Mo5Cr4V2Al高速钢麻花钻的断裂原因.结果表明,麻花钻在热处理过程中发生过热、过烧,导致局部晶界熔化,基体内形成共晶莱氏体和大量网状碳化物,冷却时在表面形成较高的拉应力,当应力大于材料的断裂强度时产生沿晶裂纹,在随后的校正过程中,在外力作用下发生了...     

Drill flank measurement and flank/flute intersection determination

Twist drill is a cutting tool of large-batch and diversified varieties. Geometric measurement is indispensable to drill design, manufacture, and regrinding. To meet the demand of advance in manufacturing technology, a three-dimensional (3-D) drill measurement instrument was developed. Method of drill flank and flute measurement by using this device is presented in this work. Cutting angles evaluation is essential to cutting performance appraisal. But, there is no suitable instrument yet to inspect them directly. If the flank/flute intersection is determined, cutting angles calculation would be a routine work of numerical computation. Considering the peculiarity of the drill point configuration, a straightforward method for flank/flute intersection is derived. Procedure of cutting angles calculation is also detailed. The procedure is illustrated by an example of flank and flute inspection, flank/flute intersection, and cutting angles calculation for a standard twist drill. The measurement precision is appraised by using a tool-room microscopy. The maximum error is in the third decimal place. It verifies the validity of the developed 3-D drill meter and the proposed measurement methods.     

New method for determination of the pose of the grinding wheel for thinning drill points

Traditionally, twist drills are reconditioned by thinning the web so the correct chisel edge length is restored. Recently, thinning has been included in the original design of drills so as to reduce torque and tool force. Because the International Standards Organization (ISO) has a system which can comprehensively model conventional twist drills but cannot model thinning specifications, this paper presents a system for precise mathematical modeling and CNC control of a 6-axis grinding workstation for drill thinning. The presented method determines the position and orientation of the grinding wheel based on the evaluated rake and clearance angles of ISO standards for 2-flute twist drills. The mathematical model and background are discussed. For verification and demonstration, two experimental drills are produced to the identical ISO standard except that one is thinned. The modeling herein is of value to industry and research if incorporated into computer software for drill design and manufacture. It is suitable for linear notch-type cutting with controlled variable rake angle along the secondary cutting edge for purposes of thinning, notching, dubbing and advanced drill research.     

On the determination of thermal phenomena during drilling—Part II. Comparison of experimental and analytical twist drill temperature distributions

The analytical models, developed in Part I of this paper, for estimating the temperature distributions along the cutting edge and on the clearance face of a twist drill are evaluated using an experimental technique that measures average drill flank temperatures. While the transient model tends to overestimate the values of the average flank temperatures, especially during drilling to a one diameter hole depth, the temperatures predicted from the steady state model agree reasonably well with the experimental results. The difference between the analytical and experimental results varied with the physical and thermal properties of the powder metallurgy work materials used in this experiment. The analytical drill temperature distribution models are also compared with others found in the literature.     

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.     

Simulation of flank milling processes

The paper presents prediction of cutting forces when flank milling ruled surfaces with tapered, helical, ball end mills. The geometric model of the workpiece is imported from standard CAD systems, and the tapered helical ball end mill is modeled as the combination of sphere and cone primitives in ACIS^© solid modeling environment. The intersection of cutter and part with a ruled surface is evaluated, and the cutter entry into and exit angles from the work material are modeled, and stored as a function of tool center coordinates along the path. The cutter entry and exit angles, the immersion angles, are used as boundary conditions in predicting the cutting forces along the path. The methodology allows prediction of cutting load distribution on the tool and part, as well optimization of machining cycle times by scheduling the feedrate in such a way that torque, power and static deflections can be maintained at safe levels.     

Topography of the flank wear surface

In many applications, topography represents the main external features of a surface. This paper describes the topography of the flank wear surface and also presents the relationship between the maximum flank wear and the topography parameters (roughness parameters) of the flank wear surface during the turning operation. A modern CNC lathe machine (Okuma LH35-N) was used for the machine turning operation. Three-dimensional surface roughness parameters of the flank wear surface were measured by a surface texture instrument (from Talysurf series) using surface topography software (Talymap). Based on the resulting experimental data, it is found that as the flank wear increases, the roughness parameters (sR_a, sR_q, and sR_t) on the flank surface increase significantly. The greater the roughness value of the flank wear surface, the higher the friction of the tool on the workpiece and the greater the heat generation that will occur, thus ultimately causing tool failure. On the other hand, positive skewness (sR_sk) indicates the presence of a small number of spikes on the flank surface of the cutting tool, which could quickly wear off during the machining process.     

圆锥滚子裂纹分析

采用金相显微镜和扫描电镜及能谱分析法对3种不同型号的圆锥轴承滚子沿柱面纵向出现的裂纹进行了分析。结果表明，裂纹是由原材料缺陷所致．并为解决生产中出现类似的问题提供了依据。     

Surface hardening of twist drills

The present review analyzes virtually all existing methods for surface hardening of twist drills and provides a brief characterization of each method and an evaluation of its efficiency. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 6, pp. 23–30, June, 1998.