Electro-spark coatings for enhanced performance of twist drills

Surface engineering approaches are being increasingly employed for enhancing the effective life of twist drills with a view to reduce machining costs. The electro-spark coating (ESC) technique provides a promising means of depositing wear resistant coatings that can potentially enhance the performance of these tools. However, it is often necessary to also optimize the machining conditions for coated tools to achieve an enhanced tool life. In the present investigation, varying spindle speeds were employed at a fixed vertical feed to evaluate the performance of WC-8Co ESC coated HSS drills in comparison to bare HSS drills. The number of holes drilled before reaching a preset average flank wear (0.5 mm), or catastrophic failure of the drill, was taken as the measure of tool life. The drill flank wear, monitored at regular intervals, as well as the cutting torque and thrust measured for all holes, were considered to be the key criteria for optimizing the cutting conditions. Results indicate that the WC-8Co coated drill tool life can be increased by a factor of more than 5, depending on the machining conditions selected. Furthermore, flank wear of the drill was found to increase rapidly at the end of drill life. Cutting torque data was also found to provide a useful indicator for predicting the end of tool life.     

Drilling of long fiber reinforced thermoplastics—Influence of the cutting edge on the machining results

The cutting edge has a large impact on the performance of a cutting tool when drilling fiber reinforced plastics (frp). Delamination, burrs and defects at hole entry and exit pose a challenge when drilling frp. Within the presented work the influence of the cutting edge on drilled hole quality when machining long fiber reinforced thermoplastics is investigated. Major influencing determinants on the machining results when drilling long fiber reinforced thermoplastics are feed force and fiber separation. The interdependencies between cutting edge radius, feed forces and fiber separation are described in a phenomenological model.     

A study of the diamond tool wear suppression mechanism in vibration-assisted machining of steel

Inability of machining steel strongly inhibits the application of diamond machining in manufacturing industry, especially in the fields of ultra-precision and micro machining. In recent years, vibration-assisted machining (VAM) has been proved to be capable of efficiently suppressing the diamond tool wear in cutting steel. Currently, the prevailing speculation claimed by most researchers for such suppression is that the tool–workpiece flash temperature was reduced in VAM, which would slow the chemical reaction between iron on steel and carbon on diamond. However, the correctness of this speculation has not been proved by any experimental or theoretical research. In this paper, in order to understand the true wear suppression mechanism of diamond tools in VAM of steel, a study is conducted by measuring the workpiece temperatures and modeling the cutting energy consumption in both VAM and conventional cutting (CC). Based on the comparison results, it is concluded that the cutting temperature and energy consumption in VAM are not smaller than in CC, and hence the reduced diamond tool wear in VAM should not be caused by the claimed reduced temperature, especially when the material removal rate is very small. Finally, based on the EDS analysis and the comparison of experimental results under different air pressure, two probable reasons are proposed for the significantly reduced diamond tool wear in VAM of steel: (i) increase of gas pressure at the tool–workpiece interface and (ii) generation of an oxide layer on the freshly machined surface.     

高速立式加工中心在轮毂加工单元中的应用

本文介绍了自主研发的轮毂加工自动生产线,此立式加工中心在整个轮毂加工单元中完成钻削加工。选用的是西门子840D数控系统,该系统可以满足各种复杂的加工任务,并且有着优于其他系统的动态品质和控制精度,尤其是其开放性的系统理念可以最大化的协助实现整个加工单元的系统化、智能化以及网络化。     

Feasibility study of the rotary ultrasonic elliptical machining of carbon fiber reinforced plastics (CFRP)

Carbon fiber reinforced plastics (CFRP) are used for various aircraft structural components because of their superior mechanical and physical properties such as high specific strength, high specific stiffness, etc. However, when CFRP are machined, rapid tool wear and delamination are troublesome. Therefore, cost effective and excellent quality machining of CFRP remains a challenge. In this paper, the rotary ultrasonic elliptical machining (RUEM) using core drill is proposed for drilling of holes on CFRP panels. This method combines advantages of core-drill and elliptical tool vibration towards achieving better quality, delamination free holes. The cutting force model and chip-removal phenomenon in ultrasonic elliptical vibration cutting are introduced and analyzed. The feasibility to machine CFRP for RUEM is verified experimentally. The results demonstrate that compared to conventional drilling (CD), the chip-removal rate has been improved, tool wear is reduced, precision and surface quality around holes is enhanced, delamination at hole exits has been prevented and significant reduction in cutting force has been achieved.     

Specific machining forces and resultant force vectors for machining of reinforced plastics

When machining fiber reinforced plastics, the machining forces may induce workpiece damage if they exceed the workpiece's anisotropic strength values. Knowledge of the resultant force vectors is therefore important to allow optimization of tool geometry and machining strategy. This article deals with experimentally obtained machining forces on short glass fiber reinforced polyester. Specific cutting, passive and axial forces have been determined for varied parameters of cutting velocity, cutting depth, cutting edge rounding and tool inclination. Generic multivariate regression models have been calculated, which, implemented in a kinematic simulation, allow calculation of machining forces (and direction) for arbitrary milling operations.     

Rotary ultrasonic machining of ceramic matrix composites: feasibility study and designed experiments

Ceramic matrix composites (CMC) are enabling materials for a number of high-temperature and demanding applications in aerospace, power generation, ground transportation, nuclear, environmental, and chemical industries. Tremendous progress has been made in technology development, manufacturing, commercialization, and applications of CMC over the last few years. However, significant challenges (such as the lack of specifications, databases, and in-service repair methodology, and high machining cost) still remain for their widespread applications. In this paper, rotary ultrasonic machining (RUM) is introduced into drilling holes on CMC panels for the first time. The feasibility to machine CMC using RUM is investigated. Cutting forces and material removal rates (MRR) are compared for machining of CMC with and without ultrasonic vibration and for two types of CMC materials and one typical advanced ceramic material (alumina). Chippings at the hole exit are also observed under a microscope. Furthermore, the paper presents the results of a designed experimental investigation into RUM of CMC. A three-variable two-level full factorial design is employed to reveal main effects as well as interaction effects of three RUM process parameters (spindle speed, feedrate, and ultrasonic power). The process outputs studied include cutting force, MRR, and hole quality (in terms of chipping dimensions).     

不锈钢表面的电化学机械复合抛光

介绍了一台由立式铣床改装的电化学机械复合抛光装置。讨论了加工电压、磨轮压力与加工效率的关系以及加工电压对表面粗糙度的影响。     

Ductile shear failure damage modelling and predicting built-up edge in steel machining

This paper reports an improved ductile shear failure model for steels and its application, through finite element simulations, to predicting the conditions for built-up edge formation in steel machining. The model has two parts, a standard damage accumulation law and (the improved part) how damage affects the steel's flow stress after failure. The accumulation law includes a strain to failure with inverse exponential dependence on hydrostatic pressure and reducing in a blue-brittle temperature range. The flow stress after failure remains finite in compressive hydrostatic conditions, to create a friction resistance to shear across the failure surface. Predictions of built-up edge formation depend strongly on strain hardening behaviour. This affects the hydrostatic stress field in the chip formation region. Simulations show the general features of built-up edge formation (a finite cutting speed range with an upper limit determined by increased ductility with temperature and a lower limit determined, depending on conditions, by insufficient heating for blue-brittleness, lower chip/tool friction or a change to unsteady chip formation). The simulations are tested against previously published observations of built-up edge formation in orthogonal cutting of a Russian steel equivalent to AISI 5130. To extend the work to a wider range of steels requires more data to be gathered on individual steels’ damage accumulation law coefficients. Also, at this stage, the simulations only predict the conditions (cutting speed, uncut chip thickness) in which built-up edge forms. They are not able to follow the growth of the built-up edge to its final shape.     

Sequential laser and mechanical micro-drilling of Ni superalloy for aerospace application

Laser percussion drilling is inherently associated with poor geometry and thermal defects. While mechanical micro-drilling produces good quality holes, premature drill breakage often occurs and it is difficult to drill holes at acute angles. This paper presents the feasibility and basic characteristics of a new approach for micro-drilling In718 alloy sheets at an acute angle, using sequential laser and mechanical drilling. The results demonstrate that sequential laser-mechanical micro-drilling alleviates the defects associated with laser-drilled holes, reduces burr size and machining time and increases the tool life compared with mechanical drilling.     

不锈钢平面的半固着磨粒加工

以马氏体不锈钢SUS 440C为加工对象,使用#3000碳化硅磨粒进行半固着磨粒和游离磨粒加工.半固着磨具与工件的接触采用面-面接触方式,半固着磨具使用SSB结合剂,磨粒重量浓度为60%,孔隙率为70%.游离磨粒加工中研具材料为球墨铸铁.两种加工方法中,加工开始10 min后工件表面粗糙度迅速由Ra 0.2 μm左右降低至Ra 0.07 μm以下,加工30 min后工件表面质量趋于稳定.工件表面质量主要取决于磨粒粒度与加工时间,加工载荷与磨具/研具转速的影响较小.半固着磨粒加工可获得比游离磨粒加工更高的表面质量.     

Modelling of the combined microstructural and cutting edge effects in ultraprecision machining

The mechanics of ultraprecision machining (UPM) is known to be affected by materials microstructures and cutting tool geometries when cutting magnitudes are reduced to micron-scale. To model the combined effects, a flow stress model that correlates the grain size and chip thickness to the relative tool sharpness is first proposed. Subsequently a novel behavioural chip formation model is developed to distinguish the transitions in chip formation regimes due to the microstructural and cutting edge effects. This led to the discovery of a unique finishing regime where surface roughness is improved by 61.7%, 63.9% and 86.4% for Al-alloy, Mg-alloy and Cu-alloy respectively.     

Effect of MQL on the tool life of small twist drills in deep-hole drilling

Drilling of deep and small boreholes using twist drills has to be considered as one of the most difficult metal cutting operations. There are many reasons for this, one of them being that the cutting fluid has to be supplied externally. This research work investigates in how far the manner of supplying and the type of minimum quantity lubricant have an effect on the tool life of coated and uncoated high-speed steel twist drills of 1.5 mm diameter. Deep-hole drilling is performed as the holes, drilled into plain carbon steel, had a depth of 10 times the diameter. The feasibility of dry machining as an appropriate alternative to MQL in deep-hole drilling has also been investigated. This work shows that, compared to a continuous supply of the minimum quantity lubricant, a discontinuous supply brings about a significant reduction in tool life, especially in the case of heat-sensitive drills. With respect to the type of minimum quantity lubricant, a low-viscous type with a high cooling-capability gave rise to a notably prolonged tool life. It is also shown that dry drilling is associated with strongly accelerated tool wear for most of the twist drills tested, resulting in a significant reduction in tool life.     

Chip geometries during high-speed machining for orthogonal cutting conditions

The originality of this work consists in taking photographs of chips during the cutting process for a large range of speeds. Contrary to methods usually used such as the quick stop in which root chips are analyzed after an abrupt interruption of the cutting, the proposed process photographs the chip geometry during its elaboration. An original device reproducing perfectly orthogonal cutting conditions is used because it allows a good accessibility to the zone of machining and reduces considerably the vibrations found in conventional machining tests. A large range of cutting velocities is investigated (from 17 to 60 m/s) for a middle hard steel (French Standards XC18). The experimental measures of the root chip geometry, more specifically the tool-chip contact length and the shear angle, are obtained from an analysis of the pictures obtained with a numerical high-speed camera. These geometrical characteristics of chips are studied for various cutting speeds, at the three rake angles −5, 0, +5° and for different depths of cut reaching 0.65 mm.     

高速加工中心的核心部件及其关键技术

本文介绍了高速加工中心所必需的核心部件和一些必不可少的关键技术，例如高速主轴、功能强大的计算机数控系统、运动控制卡、待加工轨迹监控技术（Ｌｏｏｋ Ａｈｅｄ）、高速加工的编程技术和计算机数控系统网络化（Ｄｉｒｅｃｔ ＣＮＣ Ｎｅｔｗｏｒｋｉｎｇ）的必要性等等。     

Influence of cutting edge radius on cutting forces in machining titanium

The performance of machining titanium can be enhanced by using cutting tools with rounded cutting edges. In order to better understand the influence of rounded cutting edges and to improve the modelling of the machining process, their impact on active force components including ploughing forces and tool face friction is analysed. This paper presents experimental results of orthogonal turning tests conducted on Ti-6Al-4V with different cutting edge radii and changing cutting speeds and feeds. As an accurate characterisation method for the determination of the cutting edge radius is prerequisite for this analysis, a new algorithm is described which reduces uncertainties of existing methods.     

The application of high-speed CNC machining to prototype production

This paper describes the application of high-speed milling to the production of monolithic, metallic, functional prototypes, with special emphasis placed on the applicable process times. An example component is selected and the relevant process times are presented. Fundamental requirements for the use of high-speed milling to produce prototypes in a timely manner are identified. These requirements include: 1) high speed/high power spindles, 2) proper spindle speed selection based on the system dynamics, 3) machining parameter definition based on tool wear, 4) high feed/high acceleration machine drives, 5) intelligent path generation, and 6) pre-process verification of arbitrary three-dimensional CNC part paths. The implementation of the Simultaneous Trilateration Laser Ball Bar (STLBB) system to measure the CNC part paths is described and the device verification procedure is outlined. Example two and three-dimensional path measurements are also shown.     

Modelling of high velocity, loose abrasive machining processes

In the recent years the interest in loose abrasive machining processes as efficient, flexible processes is rising. This paper describes the development of a ‘coherent set of models’ for a category of these processes, namely those which use high velocity of the particles to obtain the necessary energy to machine a workpiece surface. The usability of this ‘coherent set of models’ will be explained with its application in the field of high-pressure abrasive waterjet cutting. At the end of this paper a forecast to the application of this modelling technique to other loose abrasive machining processes as Micro-Abrasive Air Jet Machining is given.